Prenatal Programming of Reproductive Neuroendocrine Function: The Effect of Prenatal Androgens on the Development of Estrogen Positive Feedback and Ovarian Cycles in the Ewe1

Abstract

Exposure of the female ovine fetus to male hormones during a sensitive window of in utero life causes disruption to reproductive function. In some animals, androgen exposure completely abolishes reproductive cycles, but in others, cycles are progressively lost with age. The present study tested two predictions: that noncycling, androgenized animals are unable to respond to estrogen with a preovulatory-like surge of LH (estrogen positive feedback), and that the androgenized animals that exhibit a progressive loss of cycles also show a progressive loss of estrogen positive feedback. Androgenized ewes were generated by injection of their mothers with testosterone propionate twice per week from Day 30 to Day 90 of pregnancy (term, 147 days). Control ewes received no injections. Whether ewes could exhibit estrogen positive feedback was tested on five occasions before puberty (30 wk) and once during the anestrous period. All control animals had repeated reproductive cycles in both the first and second breeding season, and all showed robust LH surges during test periods. Despite the fact that 64% of androgenized animals showed reproductive cycles, estrogen positive feedback could be demonstrated in only 6.1% of trials. Subsequent experiments revealed that the lack of response to estrogen in androgenized animals was not because of pituitary insensitivity to GnRH, a requirement for higher concentrations of estrogen, or a surge that was delayed relative to the time of estrogen administration. The mechanisms by which some androgenized ewes can produce normal reproductive cycles in the apparent absence of estrogen positive feedback are currently unknown.

Disordered follicle development in ovaries of prenatally androgenized ewes

“…Previously published studies of the effects of prenatal androgenization on the hypothalamic-pituitary-ovarian axis of the ewe have shown disruption of reproductive cycles associated with disordered neuroendocrine function , Unsworth et al 2005. In this study, we show that prenatal androgenization with testosterone has a marked effect on ovarian morphology.…”

“…The administration of testosterone propionate had a virilizing effect on the external genitalia of female lambs as described previously (Barnes et al 1995, Unsworth et al 2005. Testosterone-treated lambs had genitalia that were very similar to males, with a penis and scrotal tissue, but with no testicular tissue.…”

“…Details of reproductive cycles during the first breeding season of androgenized and control sheep have been reported elsewhere , Unsworth et al 2005. Whereas all control ewes showed cyclical progesterone secretion, none of the androgenized sheep had regular cycles; eight out of nine had erratic cyclical activity with occasional peaks of progesterone production but only one had no evidence of progesterone production.…”

“…Twelve of the female sheep had been exposed to exogenous androgen prenatally; their mothers had been given i.m. injections of testosterone for 60 days between days 30 and 90 of the 147-day pregnancy, as described in previous studies (Robinson et al 1999, Unsworth et al 2005. Specifically, pregnant ewes were treated with testosterone propionate (100 mg twice weekly in 1 ml vegetable oil; Sigma-Aldrich).…”

“…Blood samples were obtained at twice weekly intervals from about 15 weeks of age and continued until the animals were 20 months of age (Unsworth et al 2005). Plasma was stored at -20 8C until preparation for progesterone immunoassay.…”