STUDIES OF SEXUAL DIFFERENTIATION OF SHEEP

Abstract

ABSTRACT Gonadotrophin releasing hormone (GnRH) (1 μg/kg was injected intravenously into pre-natally androgenised and untreated control ram and ewe lambs and castrated pre-natally androgenised rams on each of the 6th, 14th, 22nd and 30th week of post-natal life, and plasma samples collected at −20, −10, 0, 15, 30, 60, 90, 120 and 240 min from injection for LH estimation. No difference in pre-injection LH levels or responses to GnRH were observed between pre-natally androgenised 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 androgenised ewes were subjected to a GnRH injection and plasma sampling routine identical to that described above both before and 2 weeks 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 androgenised ewes either before or after ovariectomy. It is concluded that since pre-natal androgenisation altered neither pituitary gonadotrophic activity nor pituitary or hypothalamic steroid negative feedback activity, the depressed basal LH secretion reported earlier in pre-natally androgenised lambs (Wilson & Tarttelin 1978) was probably due to impairment of hypothalamic production and/or release of endogenous GnRH rather than to modification of pituitary gland function.