STUDIES OF SEXUAL DIFFERENTIATION OF SHEEP

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Abstract
Gonadotropin releasing hormone (GnRH) (1 .mu.g/kg) was injected i.v. into pre-natally adrogenized and untreated control ram and ewe lambs and castrated pre-natally androgenized rams on each of the 6th, 14th, 22nd and 30th wk of post-natal life, and plasma samples collected at -20, -10, 0, 15, 30, 60, 90, 120 and 240 min from injection for LH [lutropin] estimation. No difference in pre-injection LH levels of responses to GnRH were observed between pre-natally androgenized and control male and female lambs. Castration resulted in significantly elevated pre-injection LH levels (P < 0.001) and responses to GnRH (P < 0.05). Forty-five week old control and pre-natally androgenized ewes were subjected to a GnRH injection and plasma sampling routine identical to that described above both before and 2 wk after ovariectomy. Significantly elevated pre-injection LH levels and LH responses to GnRH (P < 0.001) resulted from ovariectomy but there were no differences in either parameter between control and androgenized ewes either before or after ovariectomy. Since pre-natal androgenization altered neither pituitary gonadotropic activity nor pituitary or hypothalamic steroid negative feedback activity, the depressed basal LH secretion reported earlier in pre-natally androgenized lambs was probably due to impairment of hypothalamic production and/or release of endogenous GnRH rather than to modification of pituitary gland function.