Sexual behaviour and LH secretion in spayed androgenized ewes after a single injection of testosterone or oestradiol-17β

Abstract

The behavioural and endocrine responses to single injections of 50 or 500 μg oestradiol-17β or 5 mg testosterone were recorded in spayed (control) ewes and in spayed ewes exposed to testosterone between Days 30 and 80 or Days 50 and 100 of prenatal life. The control ewes showed oestrus after injections on 17/18 occasions. The androgenized ewes showed poorer oestrous responses to each hormone although rams showed interest in the ewes. Masculine sexual and aggressive behaviour was shown by the androgenized ewes given either steroid. Both steroids caused a reduction in the plasma LH levels of all the ewes (negative feedback), followed by a preovulatory-type surge (positive feedback). The peak LH values were significantly lower (P<0.05) in the Day 50-100 androgenized ewes than in the controls. It is concluded that prenatal androgenization causes a qualitative shift in the sexual behaviour of ewes from the female type to the male type and affects the sensitivity of the brain to 'positive feedback' by steroids.