Effects of testosterone implants in pregnant ewes on their female offspring
Clarke, I.J.; Scaramuzzi, R.J.; Short, R.V.
Journal of Embryology and Experimental Morphology 36(1): 87-99
1976
ISSN/ISBN: 0022-0752 PMID: 988109 Document Number: 431039
Pregnant ewes were implanted with 1 g testosterone between days 30-80, 50-100, 70-120 or 90-140 of gestation. Ewes treated between days 30-80 and 50-100 showed increased aggressive behaviour and clitoral enlargement, whereas this was not seen in the groups treated between days 70-120 or 90-140. Although the implants released similar amounts of testosterone at all stages of gestation, plasma testosterone concentrations were lower in the groups treated between days 70-170 or 90-140. The increased testosterone clearance in late gestation could be a result of increased placental aromatization. Masculinization of the genital tubercle was complete in female lambs in the group treated at 30-80 days, partial in that treated at 50-100 or 70-120 days, and absent in that treated at 90-140 days. These results therefore suggest that the 'critical period' for masculinization of the external genitalia is between days 40 and 50 of foetal life. In contrast to this anatomical masculinization, one aspect of behavioural masculinization had a later critical period, since female lambs of the groups treated at 30-80, 50-100 or 70-120 days adopted male-like urination postures, whereas those from the group treated at 90-140 days showed the normal female pattern.