There have been many studies showing a relationship between E2 and Libido. The experimental paradigm is difficult to explore, but following are some abstracts.
[P3-206] Hypogonadism with Estrogen Removal (HER): Effects of Androgens and Estrogens on Sexual Desire in Young Adult Men
BZ Leder, H Lee, EW Yu, S-AM Burnett-Bowie, JC Pallais, ML Webb, KE Wulczyn, AB Servais, JS Finkelstein. Massachusetts General Hospital, Boston, MA; Massachusetts General Hospital, Boston, MA.
Testosterone (T) is thought to be the primary hormonal regulator of libido/sexual desire (SD) in men.
Methods: To determine if SD is also regulated by estrogen (E), we recruited 2 cohorts of healthy men aged 20-50. All men received goserelin acetate (Zoladex?, AstraZeneca LP, 3.6 mg q4wk) to suppress endogenous T and E. Men in Cohort 1 (T/E+, n=198) were randomized to treatment with 1 of 5 doses of a T gel (AndroGel?, Abbott) daily for 16 weeks (G1-placebo; G2-1.25g; G3-2.5g; G4-5g; G5-10g). Men in Cohort 2 (T/E-, n=200) were randomized to the same T doses plus all men received anastrozole (Arimidex?, AstraZeneca LP, 1 mg/d) to block conversion of T to E. SD was assessed using both the International Index of Erectile Function (SD-M1) and a previously-validated question asking subjects to compare their sex drive now with baseline levels (-2=much less, -1=somewhat less, 0=the same, +1=somewhat more, +2=much more) (SD-M2).
Changes were assessed within the T/E- cohort to assess T effects and between cohorts to assess E effects. Specifically, if T has an independent effect on SD, subjects in the T/E- cohort who receive no or little testosterone replacement should experience decreased SD compared to those receiving higher doses (as E levels will be the same). Conversely, if E has an independent effect on SD, differences between the T/E+ and T/E- cohorts should be observed in Groups 2-5 but not G1 (because E levels should be similarly low in subjects in G1 of both cohorts but higher in G2-5 in the T/E+ cohort).
Results: Mean serum T levels in G1-5 were 43, 173, 346, 477, and 882 ng/dL in the T/E+ cohort and 34, 199, 329, 475, and 857 ng/dL in the T/E- cohort (P=NS at each dose between cohorts). SD declined more in men receiving placebo T than in the other T dose groups in both the T/E+ (P<0.005 vs G2, 3, 4 and 5 by SD-M1 and SD-M2) and the T/E- (P<0.02 vs G4 and G5 by SD-M1 and P<0.01 vs G3, 4, and 5 by SD-M2) cohorts. Aromatase inhibition further reduced SD in men receiving T gel (G2-5, P<0.0001 by both SD-M1 and SD-M2) but had no effect on SD in men receiving placebo T gel (G1, P=0.72 by SD-M1 and P=0.53 by SD-M2).
Conclusions: As expected, lowering T levels reduces SD in men. Surprisingly, S[exual]D[esire] is further reduced in men treated with an aromatase inhibitor to reduce E production. These results suggest that non-aromatizable androgens may be less effective than aromatizable androgens for hypogonadal men with low sexual desire.
Wibowo E, Schellhammer P, Wassersug RJ. Role of estrogen in normal male function: clinical implications for patients with prostate cancer on androgen deprivation therapy. J Urol 2011;185(1):17-23. Elsevier
PURPOSE: Patients with prostate cancer on androgen deprivation therapy with luteinizing hormone-releasing hormone agonists experience deleterious side effects, including sexual dysfunction, hot flashes and osteoporosis.
Estrogen may relieve or reduce some of these side effects. We explore the role of estrogen in normal male function, emphasizing sexual interest and performance.
MATERIALS AND METHODS: We reviewed the literature on androgen deprivation therapy, estrogen and sexual function in males using PubMed(R) and other sources.
RESULTS: Estrogen receptors are present in tissues involved in sexual behavior including several brain centers and pelvic floor muscles. Exogenous estrogens can restore some sexual interest to greater than castrate level in castrated animals. This has also been reported for certain androgen deprived patients (eg voluntarily castrated men, male-to-female transsexuals) who take exogenous estrogens and others who are on high dose antiandrogens which increase endogenous estradiol levels. Estrogen also helps prevent hot flashes and bone mineral loss, which commonly occur with luteinizing hormone-releasing hormone agonist treatment. However, estrogen may cause gynecomastia and increases the risk of breast cancer. Thus, patients with prostate cancer should be informed about the pros and cons of estrogen therapy before starting androgen deprivation therapy. Based on these data estrogen is likely to have maximal benefits in men if initiated simultaneously with androgen deprivation therapy. Because estrogen autoregulates its own receptors, a constant dose of estrogen will not likely produce a constant serum concentration, suggesting that its effectiveness could be optimized if administered cyclically.
CONCLUSIONS: Prospective studies on the ability of parenteral estrogen to preserve sexual interest at greater than castrate level in patients with prostate cancer are warranted.
Simpson ER, Davis SR. Another role highlighted for estrogens in the male: Sexual behavior. Proceedings of the National Academy of Sciences 2000;97(26):14038-40. Another role highlighted for estrogens in the male: Sexual behavior
Models of lack of estrogen representation, whether they be failure of synthesis or insensitivity of response, have provided new, and in some respects counterintuitive, insights into the roles of estrogens in both males and females. Among the natural mutations, there is currently 1 man identified with a mutation of the estrogen receptor ? (ER?) and up to 10 individuals with mutations of the gene encoding aromatase, the enzyme responsible for estrogen biosynthesis. Of these, 2 are men. In addition, there are various mouse models involving targeted gene disruption. These include knock-outs of the ER? (?ERKO; ref. 1) and ER? (?ERKO; ref. 2) genes as well as the double ER? and ER? (??ERKO; ref. 3) knockout, in addition to the aromatase knockout (ArKO; refs. 4–6) mice. Analysis of the phenotypes resulting from these mutations has revealed various degrees and types of infertility in both male and female, depending on the mutation involved. Lipid and carbohydrate phenotypes involving increased adiposity with insulin resistance, hyperlipidemia and hyperleptinemia as well as disturbances in behavior patterns, both social and sexual, have also been described (6–8). These studies reveal that estrogens have more extensive roles in physiology than was previously thought, and moreover these are frequently of a non-sexually dimorphic nature. Indeed the traditional concepts of the terms estrogen and androgen are now challenged because the role of estradiol in the regulation of spermatogenesis (3, 9) is one that would more properly be classified as androgenic.
Ogawa S, Chester AE, Hewitt SC, et al. Abolition of male sexual behaviors in mice lacking estrogen receptors ? and ? (??ERKO). Proceedings of the National Academy of Sciences 2000;97(26):14737-41. Abolition of male sexual behaviors in mice lacking estrogen receptors ? and ? (??ERKO)
Male mice with a knockout of the estrogen receptor (ER)-? gene, a ligand-activated transcription factor, showed reduced levels of intromissions and no ejaculations whereas simple mounting behavior was not affected. In contrast, all components of sexual behaviors were intact in male mice lacking the novel ER-? gene. Here we measure the extent of phenotype in mice that lack both ER-? and ER-? genes (??ERKO). ??ERKO male mice did not show any components of sexual behaviors, including simple mounting behavior. Nor did they show ultrasonic vocalizations during behavioral tests with receptive female mice. On the other hand, reduced aggressive behaviors of ??ERKO mice mimicked those of single knockout mice of ER-? gene (?ERKO). They showed reduced levels of lunge and bite aggression, but rarely showed offensive attacks. Thus, either one of the ERs is sufficient for the expression of simple mounting in male mice, indicating a redundancy in function. Offensive attacks, on the other hand, depend specifically on the ER-? gene. Different patterns of natural behaviors require different patterns of functions by ER genes.
Carani C, Rochira V, Faustini-Fustini M, Balestrieri A, Granata AR. Role of oestrogen in male sexual behaviour: insights from the natural model of aromatase deficiency. Clin Endocrinol (Oxf) 1999;51(4):517-24. Role of oestrogen in male sexual behaviour: insights from the natural model of aromatase deficiency - Carani - 2001 - Clinical Endocrinology - Wiley Online Library
OBJECTIVE: In order to evaluate the role of oestrogens on human male sexual behaviour, the gender-identity, psychosexual orientation and sexual activity of a man with a congenital lack of oestradiol resulting from an inactivating mutation of the aromatase P450 gene was investigated. The psychosexual and sexual behavioural evaluations were performed before and during testosterone treatment and before oestradiol treatment, during three phases of different dosages of oestradiol treatment.
DESIGN: The study was performed before (phase A) and during (phase B) testosterone enanthate treatment (250 mg i.m. every 10 days, for 6 months), during testosterone withdrawal (phase C), and during each of the following transdermal oestradiol treatments: 50 microg twice a week for 6 months (phase D); 25 microg twice a week for 9 months (phase E), and 12.5 microg twice a week for 9 months (phase F).
MEASUREMENTS: Sexual behaviour was investigated by a sexological interview and by a 2-month self-reported daily diary performed during each phase of the protocol study. Furthermore, during each oestradiol treatment (phase C, D, E and F), a study of depression, anxiety trait and sexual behaviour was performed by the Beck Depression Inventory (BDI), the Spielberger Trait Anxiety Inventory (STAI) and the Golombok-Rust Inventory of Sexual Satisfaction (GRISS), respectively. Sexual orientation and gender-identity were evaluated by the BEM Sex Role Inventory (BSRI). Serum testosterone and oestradiol were measured during each phase of the study.
RESULTS: Before oestradiol treatment (phase C), serum oestradiol was undetectable, while it rose to 356.1, 88.1 and 55.1 pmol/l during phases D, E and F, respectively. Before any oestradiol treatment, during phase D, phase E and phase F serum testosterone was 18.13, 0.72, 14.3 and 18.51 nmol/l, respectively. The patient's gender-identity as assessed by BSRI and by the sexological interview was clearly male. The psychosexual orientation evaluated by BSRI, by the sexological interview and by the analysis of the self-filled diary was heterosexual. Relevant modification of the patient's sexual behaviour occurred only during oestrogen treatment. This was more evident during both phase E and phase F, and concerned the behavioural parameters with an increase of libido, frequency of sexual intercourse, masturbation and erotic fantasies. A reduction of BDI and STAI scores was detected during the oestrogen phases.
CONCLUSIONS: The study of the sexual behaviour in this man with aromatase deficiency suggests that oestrogens in humans do not affect gender-identity and sexual orientation but could have a role in male sexual activity.