Sexual Differentiation of the External Genitalia and the Timing of Puberty in the Presence of an Antiandrogen in Sheep

Abstract

Testicular steroids during midgestation sexually differentiate the steroid feedback mechanisms controlling GnRH secretion in sheep. To date, the actions of the estrogenic metabolites in programming neuroendocrine function have been difficult to study because exogenous estrogens disrupt maternal uterine function. We developed an approach to study the prenatal actions of estrogens by coadministering testosterone (T) and the androgen receptor antagonist flutamide, and tested the hypothesis that prenatal androgens program estradiol inhibitory feedback control of GnRH secretion to defeminize (advance) the timing of the pubertal increase in LH. Pregnant sheep were either untreated or treated with T, dihydrotestosterone (DHT) (a nonaromatizable androgen), or T plus flutamide from d 30-90 of gestation. To study the postnatal response to steroid negative feedback, lambs were gonadectomized and estradiol-replaced, and concentrations of LH were monitored in twice-weekly blood samples. Although T and DHT produced penile and scrotal development in females, the external genitalia of T plus flutamide offspring remained phenotypically female, regardless of genetic sex. Untreated females and females and males treated with T plus flutamide exhibited a pubertal increase in circulating LH at 26.4+/-0.5, 26.0+/-0.7, and 22.4+/-1.6 wk of age, respectively. In females exposed to prenatal androgens, the LH increase was advanced (T: 12.0+/-2.6 wk; DHT: 15.0+/-2.6 wk). These results demonstrate the usefulness of combining T and antiandrogen treatments as an approach to increasing prenatal exposure to estradiol. Importantly, the findings support our hypothesis that prenatal androgens program sensitivity to the negative feedback actions of estradiol and the timing of neuroendocrine puberty.

Developmental Programming: Impact of Excess Prenatal Testosterone on Intrauterine Fetal Endocrine Milieu and Growth in Sheep1

“…The adult reproductive and metabolic phenotype of prenatal testosterone-treated sheep, similar to prenatal testosterone-treated monkeys [3,7], recapitulates the phenotype seen in women with polycystic ovary syndrome (PCOS) [8][9][10]. Parallel studies in sheep with prenatal dihydrotestosterone (DHT; nonaromatizable) [11][12][13] or prenatal exposure to testosterone plus an androgen antagonist (flutamide) [14] have found that some adult reproductive defects may stem from aromatization of testosterone to estrogen. As such, while the adult consequences of exposure to prenatal testosterone excess have been investigated in depth, it remains to be established whether the fetus is exposed to both increased androgens and estrogens following gestational testosterone treatment, and, if so, at what site conversion to estrogen occurs.…”

Finding genes for economically important traits: Brahman cattle puberty

“…In pigs, the AR is considered a candidate gene for reproduction and performance traits (Trakooljul et al 2004). Manipulation of fetal androgen exposure alters the timing of puberty in sheep (Jackson et al 2008). The genes TAF1 and TAF9B encode transcription factors that form the TFIID complex, a regulator of cell cycle and differentiation.…”

Steroidogenic versus Metabolic Programming of Reproductive Neuroendocrine, Ovarian and Metabolic Dysfunctions

“…The defects in steroid negative feedback and augmented pituitary responsiveness to GnRH together contribute to the luteinizing hormone (LH) excess and consequent functional hyperandrogenism seen in prenatal T-treated females (Figure 2). Further studies investigating the effects of prenatal treatment with T, dihydrotestosterone (DHT), a non-aromatizable androgen, or co-administration of the androgen antagonist, flutamide, with T have pointed to disruptions of E 2 negative feedback being programmed by androgenic action of T, with both T and DHT and not T + flutamide reducing sensitivity to E 2 [17, 45, 50]. On the other hand, disruptions in E 2 positive feedback were found in T- but not DHT-treated females suggesting that this defect is likely programmed via estrogenic actions of prenatal T [17, 45].…”