Effects of Long‐Term Flutamide Treatment During Development on Sexual Behaviour and Hormone Responsiveness in Rams

Abstract

Testosterone (T) exposure during midgestation differentiates neural circuits controlling sex-specific behaviors and patterns of gonadotropin secretion in male sheep. T acts through androgen receptors (AR) and/or after aromatization to estradiol and binding to estrogen receptors. The current study assessed the role of AR activation in male sexual differentiation. We compared rams that were exposed to the AR antagonist flutamide (Flu) throughout the critical period (i.e. day 30 – 90 of gestation) to control rams and ewes that received no prenatal treatments. The external genitalia of all Flu rams were phenotypically female. Testes were positioned subcutaneously in the inguinal region of the abdomen, exhibited seasonally impaired androgen secretion and were azospermic. Flu rams displayed male-typical precopulatory and mounting behaviors, but could not intromit or ejaculate because they lacked a penis. Flu rams exhibited greater mounting behavior than control rams, and like controls, showed sexual partner preferences for estrous ewes. Neither control nor Flu rams responded to estradiol treatments with displays of female-typical receptive behavior or LH surge responses; whereas all control ewes responded as expected. The ovine sexually dimorphic nucleus in Flu rams was intermediate in volume between control rams and ewes and significantly different from both. . These results indicate that prenatal antiandrogen exposure is not able to block male sexual differentiation in sheep and suggest that compensatory mechanisms intervene to maintain sufficient androgen stimulation during development.

Early prenatal androgen exposure reduces testes size and sperm concentration in sheep without altering neuroendocrine differentiation and masculine sexual behavior

“…The test consisted of pairing each ram individually with 2 estrous ewes for 20 min. and recording the frequencies of precopulatory behaviors, mounting and ejaculation as described previously [35]. Two weeks later rams were given a series of sexual partner preference tests, each testing session separated by at least one week.…”

Female bisexuality

“…For example, treating rhesus macaques with flutamide (a nonsteroidal anti-androgen that blocks androgen receptors) late in gestation paradoxically hypermasculinized males' behavior despite preventing full genital masculinization (Wallen, 2005). This finding suggests that estrogen masculinizes brains also in primates: estrogen receptors, after all, would not be blocked by flutamide (which only blocks androgen receptors), while the testes will still produce testosterone that is aromatized to estrogen (Roselli, Meaker, Stormshak, & Estill, 2016;Wallen, 2005). When androgen receptors have been blocked, there is an increased bioavailability of testosterone to be aromatized to estrogen, leading some behaviors to become more masculinized.…”

“…When androgen receptors have been blocked, there is an increased bioavailability of testosterone to be aromatized to estrogen, leading some behaviors to become more masculinized. As with rhesus macaques, flutamide hypermasculinizes behaviors in rams, even if elimination of androgenic actions of testosterone by flutamide causes the development of female genitalia in rams (Roselli et al, 2016). In addition, giving 1,4,6-androstatriene-3,17-dione (ATD), an aromatase inhibitor, to sheep during gestation partially disrupts masculinization of adult copulatory behavior (Roselli, Schrunk, Stadelman, Resko, & Stormshak, 2006).…”