MESO-Rx
Anabolic Steroids
Can your androgen receptors be saturated?
- Thread starter Paperclip
- Start date
Saturation has a pharmacological meaning: it means that almost all the receptors are occupied.
How could you guarantee that nearly all your receptors are occupied at 1 gram per week?
I'd agree it's a large percentage, almost surely way past the majority.
It is only on almost all the receptors being occupied.
Once steady-state is reached, rate of excretion equals rate of administration.
So far as I can tell any objection makes no sense at all. The closest I can come to making sense out of the objection is from people thinking that effect is defined by RATE of gain.
They see a slower rate of gain and call this less effect, and then blame the receptors.
So far as I can tell, that's all there is to that theory, and it isn't sound thinking.
The only further thoughts I have are with regard to elimination, as I have been considering this as an issue lately that is not really given merit, both exogenously and endogenously... My point would be that just because receptors are fully involved would not effect elimination, in that if you add more, and past the point of saturation, the body has to get rid of it. So I am wondering your thoughts there? But as I write this, i think pehaps you are referring as a technical and what is measured as a technical derivative in excretion. But what about what does not get metabolized and is passes unchanged. Perahps I am splitting hairs and dont meant to. But I just wanted to clarify or get clarified....
My point would be the potential interaction of a drug that is not checked for because it was not looked for. The coincidence unqualified so to speak, and the potential implications there of...
My point would be the potential interaction of a drug that is not checked for because it was not looked for. The coincidence unqualified so to speak, and the potential implications there of...
Sworder
Member
Just because the ARs don't downregulate doesn't mean the body will respond the same way. ARs are one piece of the puzzle. Does opiate receptors downregulate? I don't think so but the effect and tolerance will change even though at the receptor there is no change... ???
Do you have any idea of what you are talking about?
At least try to talk in complete sentences. WTF does "Just because the ARs don't downregulate doesn't mean the body will respond the same way" mean?
And yes, all the opiate receptors D/R. There are several of them. Receptors arent interchangable.
Ya might wanna bone up on you basics before you take on the challenging stuff.
Gawd, I hate to be such an asshole but I cant help it.
benchingover500
New Member
I'll try to find the article I referred to in the European journal of pharmacology or an online version of the Kenikan book... I think that the whole idea you get desensitization is because the cell needs to be receptive to other changes in its milieu including changes that converge at some point on the same signaling pathway or genes. Moreover, there is a difference in short term versus long term stimulation of receptors. Short term often leads to up regulation of spare receptors or changes in allosteric proteins associated with receptors. Short term stimulation can also result in increased receptor recycling versus degradation. This is not the case in long term stimulation.
Lastly, Bill, thanks for recommending I read your paper. I'll read it over the weekend.
Lastly, Bill, thanks for recommending I read your paper. I'll read it over the weekend.
Sworder
Member
Sorry about the sentences I was writing from my phone at work. "Just because androgen receptors don't downregulate doesn't mean the body will respond the same way" means that if your receptors are at 80% activity your muscle development may stagnate although diet is the same. Does that make more sense? It was just a brain fart I had and I like discussion and sharing ideas. I did not do my homework as I was at work and I was planning on checking studies when I got home. I have found many different studies on various receptors e.g. dopamine, opioid, and insulin. They are all subject to downregulation so now my brainfart is blowing the other way.
If you look at my post again there are four sentences and two of them contain question marks. I wasn't making many statements as I was seeking answers.
On the part about being an asshole I have found that generosity is the highest tier of egoism/selfishness. Being rude to others is maiming your own paths, no matter how trivial they may seem I don't think this is good for anybody.
OK, let me step back in for some MR NICE GUY STUFF
Really, Perhaps we should DEFINE some terms. Up regulate, down regulate, and I used the term saturate. So perhaps there is a difference or misunderstanding. Perhaps for me.
I do think I understand what Sworder was trying to get across. Bad ZKT, Bad...[)]
So lets see then. I think Bill clarified me as to the term saturation meaning the occupation of ALL receptors system wide. I hope I am not incorrectly recalling. So I guess the term must still be used RELATIVE to the PRINCIPLE. Which I am assuming would be either muscle tissue, a human male as a whole, or even just a part there of. But lets say all andfrogen receptors for this case is I think what its about.
So then there are theories that receptors may "regulate up or down" depending on a particular exposure to a hormone. So by "up regulate" we mean that the receptor becomes more sensitive and responsive to the stimulus hormone, and down regulate meaning the receptor becomes more "deafened" or less responsive? OR DO I HAVE THAT BACKWARDS.??
Regardless, where I was is not quite in sync as but it acutally. So TECHNICALLY, receptors are either occupied or not occupied I am assuming is a given here.. You know me. I wonder??
But then so then we are basing the notion of up or down regulation dependent upon the stimulus right? The duration of action/interaction. The STRENGTH of the interaction as well. Which I am assuming gets into the difference in action of different anabolic steroids. For example. tamox involves with estrogen receptors because it resembles estrogen molecules. Deca, Tren, etc. Must also involve with androgen and estrogen receptors via similar features. But I think some do vary in there mode of action. My knowledge lessens beyond testosterone, if even not just walking and chewing bubble gum. LOL
I often like a layman buffoon speculate that there is competition among androgen and estrogen receptors between the two hormones acting with either/or. Or that there are a certain set of receptors that are designed to respond to both. SO A GOOD QUESTION I WOULD HAVE IS THIS...: Tamox and Clomid for example are touted as having both estrogenic AND anti-estrogenic properties. Meaning they may simply block E receptors by inert occupation, or that they may involve themselves with some estrogen receptors in a way that triggers the estrogen response intended by natty estrogens. BUT DOES TAMOX TRIGGER ANDROGEN RECEPTORS? OR POSSIBLY OCCUPY AND INVOLVE WITH ANY AS A BLOCKADE?? REALLY?? I am asking? So the point is where is the line drawn in the physical model of all these interactions, and are there clear lines. IS IT A MATTER OR "REGULATION" or more truely, "INTERFERENCE".
Again, everyone focuses on the notion of "regulation", when it does not look like a sound hypothesis. But you have to wonder:
1 Do tissue receptors become more accustomed to hormones and how to use them?
2. IS there a LEARNING, where they will start to cling on to a hormone for longer periods when the body has been under physical stress for extended periods??
3. If there is variation in time a particular hormone molecule occupies a cell, does the hormore start to complete the link less effectively.
4. Does it become damaged and partially effective and blockading new hormones to site?
5. Is the sole pupose of the hormone to deliver the fuel to the tissue?
6. If so, what would any changes in available population mean?
7. Or is the lifespan of a hormone simply the length of time it takes to deliver the SHBG???? After all, with no new cellular proliferation, the only need for fuel is to run, which requires LESS, which also means size/potential energy is now maxed for given set of muscle cells short of new growth... This is a WALL, isnt it?? Or at least a REAL ONE...
Still I propose that if hormones are indeed important in delivering the fuel to tissue for growth or action, and blood protien is limited by occupation or clearance, then the culmonation of hormones in the blood may or may not service dependin on which hormones are amassing with propernsity of presence.
I would also like to know more about cellular biology and how hormones interact with the various tissues and there receptors. Because if muscle requires BOTH androgens and estrogens to operate/proliferate, then there must be some competition/hinderance depending on these factors. While I always state the body is a demand based enviroment, I am not ruling out that demand can be influenced by prevalence or availabiltiy.
But I just dont see how one can go off focusing on androgen receptors alone as a culpret when estrogen is so critcal as well.
Sorry, I went off nutty again...
Really, Perhaps we should DEFINE some terms. Up regulate, down regulate, and I used the term saturate. So perhaps there is a difference or misunderstanding. Perhaps for me.
I do think I understand what Sworder was trying to get across. Bad ZKT, Bad...[
)]So lets see then. I think Bill clarified me as to the term saturation meaning the occupation of ALL receptors system wide. I hope I am not incorrectly recalling. So I guess the term must still be used RELATIVE to the PRINCIPLE. Which I am assuming would be either muscle tissue, a human male as a whole, or even just a part there of. But lets say all andfrogen receptors for this case is I think what its about.
So then there are theories that receptors may "regulate up or down" depending on a particular exposure to a hormone. So by "up regulate" we mean that the receptor becomes more sensitive and responsive to the stimulus hormone, and down regulate meaning the receptor becomes more "deafened" or less responsive? OR DO I HAVE THAT BACKWARDS.??
Regardless, where I was is not quite in sync as but it acutally. So TECHNICALLY, receptors are either occupied or not occupied I am assuming is a given here.. You know me. I wonder??
But then so then we are basing the notion of up or down regulation dependent upon the stimulus right? The duration of action/interaction. The STRENGTH of the interaction as well. Which I am assuming gets into the difference in action of different anabolic steroids. For example. tamox involves with estrogen receptors because it resembles estrogen molecules. Deca, Tren, etc. Must also involve with androgen and estrogen receptors via similar features. But I think some do vary in there mode of action. My knowledge lessens beyond testosterone, if even not just walking and chewing bubble gum. LOL
I often like a layman buffoon speculate that there is competition among androgen and estrogen receptors between the two hormones acting with either/or. Or that there are a certain set of receptors that are designed to respond to both. SO A GOOD QUESTION I WOULD HAVE IS THIS...: Tamox and Clomid for example are touted as having both estrogenic AND anti-estrogenic properties. Meaning they may simply block E receptors by inert occupation, or that they may involve themselves with some estrogen receptors in a way that triggers the estrogen response intended by natty estrogens. BUT DOES TAMOX TRIGGER ANDROGEN RECEPTORS? OR POSSIBLY OCCUPY AND INVOLVE WITH ANY AS A BLOCKADE?? REALLY?? I am asking? So the point is where is the line drawn in the physical model of all these interactions, and are there clear lines. IS IT A MATTER OR "REGULATION" or more truely, "INTERFERENCE".
Again, everyone focuses on the notion of "regulation", when it does not look like a sound hypothesis. But you have to wonder:
1 Do tissue receptors become more accustomed to hormones and how to use them?
2. IS there a LEARNING, where they will start to cling on to a hormone for longer periods when the body has been under physical stress for extended periods??
3. If there is variation in time a particular hormone molecule occupies a cell, does the hormore start to complete the link less effectively.
4. Does it become damaged and partially effective and blockading new hormones to site?
5. Is the sole pupose of the hormone to deliver the fuel to the tissue?
6. If so, what would any changes in available population mean?
7. Or is the lifespan of a hormone simply the length of time it takes to deliver the SHBG???? After all, with no new cellular proliferation, the only need for fuel is to run, which requires LESS, which also means size/potential energy is now maxed for given set of muscle cells short of new growth... This is a WALL, isnt it?? Or at least a REAL ONE...
Still I propose that if hormones are indeed important in delivering the fuel to tissue for growth or action, and blood protien is limited by occupation or clearance, then the culmonation of hormones in the blood may or may not service dependin on which hormones are amassing with propernsity of presence.
I would also like to know more about cellular biology and how hormones interact with the various tissues and there receptors. Because if muscle requires BOTH androgens and estrogens to operate/proliferate, then there must be some competition/hinderance depending on these factors. While I always state the body is a demand based enviroment, I am not ruling out that demand can be influenced by prevalence or availabiltiy.
But I just dont see how one can go off focusing on androgen receptors alone as a culpret when estrogen is so critcal as well.
Sorry, I went off nutty again...
Exemestane is a suicide inhibitor of the estrogen receptor which actually destroys the receptor, but eventually new receptors replace what was lost. I believe normally the receptor "internalizes" and just will no longer be able to bind to anything until things normalize or it is given a reason to do otherwise. I don't believe any natural process even causes destruction of receptors, yet the body can still recreate new ones.
Ugggh. Just when I try to step down. THEY KEEP CALLING ME BACK...
OK, you have the basic premise right but you typoed a critical. And I dont know about "DESTROY". And I am not sure where AI's came in as I omitted a few responses.
Exemistane or "I forget" is a suicide inhibitor. But what ist does is render the ENZYMES APPLICABLE non functional for their effective lifespans. NOT the receptors. So - if ADEX temporarily renders enzymes unable to convert estrogens, then EXEM PERMANENTLY RENDERS THEM unable to convert estrogens.
The difference MAY be neglible in many senses as ENZYMES that make this conversion are READILY PRODUCED by the body. The application of EXEMISTANE IS THE PROOF.
THIS IS ALSO THE PROOF THAT THE BODY WILL QUICKLY ADJUST TO ANY AI ATTEMPTED TO USE AS A LONG TERM SOLUTION....
The real negligible difference is the Exem renders a 98% reduction in estrogen factors whereas ADEX will only ellicit about 75%. What this means IN REALITY is SQUAT and the TRANSFER RATE IS NOT CACULABLE AND NO ONE KNOWS HOW MUCH ESTROGEN REMAINS EFFECTIVELY PRODUCED AND EFFECTED AT THE POINT OF THE RECEPTOR.
Sure the initial effects can be acknowledged PHYSICALLY. But I THINK the diminishment thereof is also within a brief period of weeks to months.
ITS Scary to think they base cancer treatments on these drugs measured in SERUM...
OK, you have the basic premise right but you typoed a critical. And I dont know about "DESTROY". And I am not sure where AI's came in as I omitted a few responses.
Exemistane or "I forget" is a suicide inhibitor. But what ist does is render the ENZYMES APPLICABLE non functional for their effective lifespans. NOT the receptors. So - if ADEX temporarily renders enzymes unable to convert estrogens, then EXEM PERMANENTLY RENDERS THEM unable to convert estrogens.
The difference MAY be neglible in many senses as ENZYMES that make this conversion are READILY PRODUCED by the body. The application of EXEMISTANE IS THE PROOF.
THIS IS ALSO THE PROOF THAT THE BODY WILL QUICKLY ADJUST TO ANY AI ATTEMPTED TO USE AS A LONG TERM SOLUTION....
The real negligible difference is the Exem renders a 98% reduction in estrogen factors whereas ADEX will only ellicit about 75%. What this means IN REALITY is SQUAT and the TRANSFER RATE IS NOT CACULABLE AND NO ONE KNOWS HOW MUCH ESTROGEN REMAINS EFFECTIVELY PRODUCED AND EFFECTED AT THE POINT OF THE RECEPTOR.
Sure the initial effects can be acknowledged PHYSICALLY. But I THINK the diminishment thereof is also within a brief period of weeks to months.
ITS Scary to think they base cancer treatments on these drugs measured in SERUM...
Sworder
Member
I have been thinking and asking myself the same questions that BBC3 posed.
The most interesting is the learning of it and how it is expressed chemically. I come to think of tolerance as it isn't really mentioned at all in the AAS community. Can you develop a tolerance for AAS and will that lead to down-regulation of the ARs or poorer binding efficiency? Are receptors like Sega Genesis where they have a reset button or only an on/off switch?
Up-regulation and down-regulation is a funny concept. The idea implies a "command center" that controls the up/down regulation of ALL androgen receptors as a whole. Strength would increase the activity/intensity of individual ARs depending on the compound being attached to the AR. Tren being a lot "stronger" would contain more "fuel(?)" to keep the AR containing ligand pulsating gene expression.
It is generally said that using nolva/adex on cycle will tether gains from reaching their full potential. Estrogen is needed for muscle growth. I think the mechanism is a "Erm do I have any estrogen or is it cool that I use this testosterone for muscle growth?". That mechanism taking place before it even binds to the AR.
Basically I am wondering the same as BBC. Also want to note that any/all statements are not based on any research just my wild imagination of how things work. Break it down, agree, or present own thoughts.
The most interesting is the learning of it and how it is expressed chemically. I come to think of tolerance as it isn't really mentioned at all in the AAS community. Can you develop a tolerance for AAS and will that lead to down-regulation of the ARs or poorer binding efficiency? Are receptors like Sega Genesis where they have a reset button or only an on/off switch?
Up-regulation and down-regulation is a funny concept. The idea implies a "command center" that controls the up/down regulation of ALL androgen receptors as a whole. Strength would increase the activity/intensity of individual ARs depending on the compound being attached to the AR. Tren being a lot "stronger" would contain more "fuel(?)" to keep the AR containing ligand pulsating gene expression.
It is generally said that using nolva/adex on cycle will tether gains from reaching their full potential. Estrogen is needed for muscle growth. I think the mechanism is a "Erm do I have any estrogen or is it cool that I use this testosterone for muscle growth?". That mechanism taking place before it even binds to the AR.
Basically I am wondering the same as BBC. Also want to note that any/all statements are not based on any research just my wild imagination of how things work. Break it down, agree, or present own thoughts.
As far as tolerance goes I dont think if you use AAS for real long periods of time like 3 months or greater and use very high doses you dont build up a tolerance for them and you will respond to them very well. have done over 30 cycles in the past 30 years,the first 4 years i did 2 or 3 cycles a year,8 weeks on and 8 weeks off. Mostly Decca and test. I never saw much gains in muscle mass after 8 weeks so i cycled them 8 on and 8 off or some times longer that 8 weeks off. 3 years ago i started cycling again 8 on and 8 off with 1 cycle of 12 weeks to see if i could make more gains after 8 weeks.I dont use extremely high doses like 1gm a week of test but i use a substantial amount.A typical cycle is 600mg Test E a week,600mg EQ a week and 150mg Tren A EOD. I still respond to the steroids like i did when when i was younger.I dont see where i have built up a tolerance for steroids even after the 3 years i have been using them recently. Extremely high doses or long cycles might make you tolerant but i havnt seen any tolerance in my case.
I think there is a lot of confusion about what tolerance and down-regulation mean with regard to AAS use.
Take a hypothetical 200lb bodybuilder whose goal is to gain as much lean muscle mass as possible. Assume optimal training and nutrition throughout.
Place him on a continuous 1000mg test cyp/week cycle.
He will most likely make considerable gains during the first 3 months.
He may weigh 230lb at 3 months.
His gains slow. He weighs only 240lbs at 12 months
At 18 months, he weighs only 245 lbs.
At 24 months, he weighs the same.
Does this mean he has developed a tolerance for the 1000mg/wk test or that his AR have downrepulated?
No. It just means that 1000mg total androgens per week will likely only support a lean bodyweight of 245lbs.
So, he doubles his weekly androgen intake to 2000 mg/week.
He starts gaining weight again.
After 3 months of 2000mg/wk, he is at 260.
At 12 months, he's 270
This doesn't prove that 1000mg/wk stopped working.
1000mg/wk continued to work perfectly fine --- if he wanted to remain 245
For down-regulation to occur, then the bodybuilder would need to increase the dosage to maintain the same results. Otherwise, he would start losing weight.
In our hypothetical scenario, once he reached 245 on 1000mg/wk, he would have to continue to increase the androgen load simply to maintain 245.
If we were to believe in AR downregulation, then after 10 years of continuous 1000mg/wk use, the AAS user would either:
(a) gradually shrink in size over time from 245 downward
(b) gradually escalate use to 2000, 3000, 4000 mg/wk simply to maintain same size of 245lbs after 10 years of continuous use.
This doesn't reflect reality of steroid use.
Take a hypothetical 200lb bodybuilder whose goal is to gain as much lean muscle mass as possible. Assume optimal training and nutrition throughout.
Place him on a continuous 1000mg test cyp/week cycle.
He will most likely make considerable gains during the first 3 months.
He may weigh 230lb at 3 months.
His gains slow. He weighs only 240lbs at 12 months
At 18 months, he weighs only 245 lbs.
At 24 months, he weighs the same.
Does this mean he has developed a tolerance for the 1000mg/wk test or that his AR have downrepulated?
No. It just means that 1000mg total androgens per week will likely only support a lean bodyweight of 245lbs.
So, he doubles his weekly androgen intake to 2000 mg/week.
He starts gaining weight again.
After 3 months of 2000mg/wk, he is at 260.
At 12 months, he's 270
This doesn't prove that 1000mg/wk stopped working.
1000mg/wk continued to work perfectly fine --- if he wanted to remain 245
For down-regulation to occur, then the bodybuilder would need to increase the dosage to maintain the same results. Otherwise, he would start losing weight.
In our hypothetical scenario, once he reached 245 on 1000mg/wk, he would have to continue to increase the androgen load simply to maintain 245.
If we were to believe in AR downregulation, then after 10 years of continuous 1000mg/wk use, the AAS user would either:
(a) gradually shrink in size over time from 245 downward
(b) gradually escalate use to 2000, 3000, 4000 mg/wk simply to maintain same size of 245lbs after 10 years of continuous use.
This doesn't reflect reality of steroid use.
Sworder
Member
Wouldn't this be a result of tolerance and the down-regulation that follows?
Great example Millard and to clarify you are saying there is no down-regulation and that the anecdotal experiences of muscle gains becoming stagnant after 8 weeks is a result of accummulating more muscle mass and the body's demand for more androgens to maintain that muscle has increased so there are less androgens available for growth. OK that was a long sentence..
It could be but wouldnt you have to increase your doses substancialy to see further improvment.Also how long can your body tolerate high intensity training without some time to recouperate.Maby you can make more gains by doing longer cycles and increasing dosages,but can your body perform good enough to make it worth while.I believe you have to cycle your training to continue to make gains.I just feel like 8 weeks is about the longest i can train with very high intensity without burning out,so the steroids might be effective for more than 8 weeks but can your body handle the intense training.I know a lot of people stay on steroids for long periods of time just so they can look buff longer,but i use them them to gain mass.To eachhis own i guess,i believe in shorter very intense cycles vs long cycles.
Myostatin (a growth inhibitor) peaks at about 8 weeks in men administering Testosterone. Therefore growth inhibition is a likely cause of stalled gains at the 2 month mark.
Androgen Receptor Polyglutamine Repeat Length Androgen Receptor Function In Skeletal Muscle
Though the mechanisms behind the effects of T on skeletal muscle are still poorly understood, it is believed that the majority of the anabolic effects are mediated via its interaction with the androgen receptor (AR). The AR is a ligand-activated nuclear hormone receptor that upon ligand binding dissociates from binding proteins, moves into the nucleus, and acts as a transcription factor to regulate expression of androgen responsive genes. Structurally, the AR consists of three functional domains: an amino-terminal transactivation domain (NTD), a central DNA binding domain, and a carboxy-terminal ligand binding domain (LBD). The NTD harbors binding sites for a variety of additional cofactors, and mutational deletions demonstrate that the region is required for full receptor transcriptional activation, hence its designation as the transactivation domain.
The NTD also harbors a polyglutamine repeat polymorphism that has been demonstrated to affect AR transcriptional activity in a variety of cell types. This repeat has also been associated with a number of androgen-related maladies including prostate cancer, prostate hypertrophy, and spinal bulbar muscular atrophy. Though well characterized in respect to prostate, the effect of AR polyglutamine length on skeletal muscle physiology is less clear. Results from genetic association studies examining AR polyglutamine repeat length in relation to skeletal muscle have been conflicting, with both longer repeat length and shorter repeat length being correlated with greater fat-free mass. If we consider AR activity to exert an anabolic effect on muscle, then based on data from previous studies where AR activity is inversely correlated with repeat length in nonmuscle tissue one would hypothesize that AR repeat length would be inversely related to fat-free mass. Given these conflicting data further clarification on the role of the AR polyglutamine repeat polymorphism in skeletal muscle physiology is warranted.
The aim of the current study was to determine if AR polyglutamine repeat length affects AR transcriptional activity and skeletal muscle cell development in vitro. Researchers hypothesized that AR transcriptional activity would decrease with increasing repeat length. Contrary to their hypothesis, the results clearly demonstrate that AR polyglutamine repeat length is directly related to transcriptional activity in skeletal muscle and alters the development of C2C12 cells.
This is the first study to examine the relationship of AR glutamine repeat length and transcriptional activity in skeletal muscle cells, and they find strong evidence of a relationship between AR repeat length and transcriptional activity in these skeletal muscle cells. The difference in total activation between AR14 and AR33 was also quite remarkable; the nearly ninefold difference being far greater than that demonstrated by other studies using a similar spread in AR repeat length. In addition to its far greater transcriptional activity, the AR33 construct demonstrated a much greater ligand-dependent activation ratio compared with the AR14 and AR24 constructs, indicating that longer AR repeat lengths affect responsiveness to T treatment in C2C12 cells. However, both the AR24 and AR33 vectors demonstrated considerable transcriptional activity even in the absence of T, suggesting the presence of basal activity that they did not detect in the AR14 vector. Despite consistent evidence for higher transcriptional activity with longer repeat lengths, their data also show that extremes in AR activity, whether high or low, seem to have negative effects on C2C12 cell development.
Sheppard RL, Spangenburg EE, Chin ER, Roth SM. Androgen receptor polyglutamine repeat length affects receptor activity and C2C12 cell development. Physiological Genomics 2011;43(20):1135-43. http://physiolgenomics.physiology.org/content/43/20/1135.abstract (Androgen receptor polyglutamine repeat length affects receptor activity and C2C12 cell development)
Testosterone (T) has an anabolic effect on skeletal muscle and is believed to exert its local effects via the androgen receptor (AR). The AR harbors a polymorphic stretch of glutamine repeats demonstrated to inversely affect receptor transcriptional activity in prostate and kidney cells. The effects of AR glutamine repeat length on skeletal muscle are unknown.
In this study, we examined the effect of AR CAG repeat length on AR function in C2C12 cells. AR expression vectors harboring 14, 24, and 33 CAG repeats were used to assess AR transcriptional activity. C2C12 cell proliferation, differentiation, gene expression, myotube formation, and myonuclear fusion index were assessed.
Transcriptional activity increased with increasing repeat length and in response to testosterone (AR14 = 3.91 ± 0.26, AR24 = 25.21 ± 1.72, AR33 = 36.08 ± 3.22 relative light units; P < 0.001). Ligand activation was increased for AR33 (2.10 ± 0.04) compared with AR14 (1.54 ± 0.09) and AR24 (1.57 ± 0.05, P < 0.001). AR mRNA expression was elevated in each stably transfected line. AR33 cell proliferation (20,512.3 ± 1,024.0) was decreased vs. AR14 (27,604.17 ± 1,425.3; P < 0.001) after 72 h. Decreased CK activity in AR14 cells (54.9 ± 2.9 units/?g protein) in comparison to AR33 (70.8 ± 8.1) (P < 0.05) was noted. The myonuclear fusion index was lower for AR14 (15.21 ± 3.24%) and AR33 (9.97 ± 3.14%) in comparison to WT (35.07 ± 5.60%, P < 0.001). AR14 and AR33 cells also displayed atypical myotube morphology. RT-PCR revealed genotype differences in myostatin and myogenin expression.
We conclude that AR polyglutamine repeat length is directly associated with transcriptional activity and alters the growth and development of C2C12 cells. This polymorphism may contribute to the heritability of muscle mass in humans.
Though the mechanisms behind the effects of T on skeletal muscle are still poorly understood, it is believed that the majority of the anabolic effects are mediated via its interaction with the androgen receptor (AR). The AR is a ligand-activated nuclear hormone receptor that upon ligand binding dissociates from binding proteins, moves into the nucleus, and acts as a transcription factor to regulate expression of androgen responsive genes. Structurally, the AR consists of three functional domains: an amino-terminal transactivation domain (NTD), a central DNA binding domain, and a carboxy-terminal ligand binding domain (LBD). The NTD harbors binding sites for a variety of additional cofactors, and mutational deletions demonstrate that the region is required for full receptor transcriptional activation, hence its designation as the transactivation domain.
The NTD also harbors a polyglutamine repeat polymorphism that has been demonstrated to affect AR transcriptional activity in a variety of cell types. This repeat has also been associated with a number of androgen-related maladies including prostate cancer, prostate hypertrophy, and spinal bulbar muscular atrophy. Though well characterized in respect to prostate, the effect of AR polyglutamine length on skeletal muscle physiology is less clear. Results from genetic association studies examining AR polyglutamine repeat length in relation to skeletal muscle have been conflicting, with both longer repeat length and shorter repeat length being correlated with greater fat-free mass. If we consider AR activity to exert an anabolic effect on muscle, then based on data from previous studies where AR activity is inversely correlated with repeat length in nonmuscle tissue one would hypothesize that AR repeat length would be inversely related to fat-free mass. Given these conflicting data further clarification on the role of the AR polyglutamine repeat polymorphism in skeletal muscle physiology is warranted.
The aim of the current study was to determine if AR polyglutamine repeat length affects AR transcriptional activity and skeletal muscle cell development in vitro. Researchers hypothesized that AR transcriptional activity would decrease with increasing repeat length. Contrary to their hypothesis, the results clearly demonstrate that AR polyglutamine repeat length is directly related to transcriptional activity in skeletal muscle and alters the development of C2C12 cells.
This is the first study to examine the relationship of AR glutamine repeat length and transcriptional activity in skeletal muscle cells, and they find strong evidence of a relationship between AR repeat length and transcriptional activity in these skeletal muscle cells. The difference in total activation between AR14 and AR33 was also quite remarkable; the nearly ninefold difference being far greater than that demonstrated by other studies using a similar spread in AR repeat length. In addition to its far greater transcriptional activity, the AR33 construct demonstrated a much greater ligand-dependent activation ratio compared with the AR14 and AR24 constructs, indicating that longer AR repeat lengths affect responsiveness to T treatment in C2C12 cells. However, both the AR24 and AR33 vectors demonstrated considerable transcriptional activity even in the absence of T, suggesting the presence of basal activity that they did not detect in the AR14 vector. Despite consistent evidence for higher transcriptional activity with longer repeat lengths, their data also show that extremes in AR activity, whether high or low, seem to have negative effects on C2C12 cell development.
Sheppard RL, Spangenburg EE, Chin ER, Roth SM. Androgen receptor polyglutamine repeat length affects receptor activity and C2C12 cell development. Physiological Genomics 2011;43(20):1135-43. http://physiolgenomics.physiology.org/content/43/20/1135.abstract (Androgen receptor polyglutamine repeat length affects receptor activity and C2C12 cell development)
Testosterone (T) has an anabolic effect on skeletal muscle and is believed to exert its local effects via the androgen receptor (AR). The AR harbors a polymorphic stretch of glutamine repeats demonstrated to inversely affect receptor transcriptional activity in prostate and kidney cells. The effects of AR glutamine repeat length on skeletal muscle are unknown.
In this study, we examined the effect of AR CAG repeat length on AR function in C2C12 cells. AR expression vectors harboring 14, 24, and 33 CAG repeats were used to assess AR transcriptional activity. C2C12 cell proliferation, differentiation, gene expression, myotube formation, and myonuclear fusion index were assessed.
Transcriptional activity increased with increasing repeat length and in response to testosterone (AR14 = 3.91 ± 0.26, AR24 = 25.21 ± 1.72, AR33 = 36.08 ± 3.22 relative light units; P < 0.001). Ligand activation was increased for AR33 (2.10 ± 0.04) compared with AR14 (1.54 ± 0.09) and AR24 (1.57 ± 0.05, P < 0.001). AR mRNA expression was elevated in each stably transfected line. AR33 cell proliferation (20,512.3 ± 1,024.0) was decreased vs. AR14 (27,604.17 ± 1,425.3; P < 0.001) after 72 h. Decreased CK activity in AR14 cells (54.9 ± 2.9 units/?g protein) in comparison to AR33 (70.8 ± 8.1) (P < 0.05) was noted. The myonuclear fusion index was lower for AR14 (15.21 ± 3.24%) and AR33 (9.97 ± 3.14%) in comparison to WT (35.07 ± 5.60%, P < 0.001). AR14 and AR33 cells also displayed atypical myotube morphology. RT-PCR revealed genotype differences in myostatin and myogenin expression.
We conclude that AR polyglutamine repeat length is directly associated with transcriptional activity and alters the growth and development of C2C12 cells. This polymorphism may contribute to the heritability of muscle mass in humans.
benchingover500
New Member
To try to understand the effects of receptor saturation by agonists whether full agonist, partial agonist, or inverse antagonist requires a through reading in pharmacology and medicinal chemistry. Once aquired, I think its important to understand that in drug development some of the effects whether good or bad result of off target effects where the drug binds to an alternative receptor to mediate other effects.
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