Action of Oestrin on the Vagina During Lactation

Abstract

The injection of oestrin during lactation has resulted in contradictory opinions regarding the vaginal reaction. Previous experiments on the ovarian hormonal antagonism 1 have shown that the injection of 18, 10, 6, 4, and 2 rat units of oestrin, in oily solution, daily during the first 5 days of lactation always provoked typical oestrus as indicated by vaginal smears. Doses of less than one rat unit have demonstrated the existence of different thresholds of anti-luteinic action of oestrin, the vaginal reaction of oestrus being the first to appear.

Recently, Selye and co-workers have observed that doses of thirty micrograms of Oestrone, in oily solution, daily from the fifth to the tenth day of lactation have failed to provoke vaginal oestrus. 2 , 3 They also reported that 100 or 500 micrograms of Oestrone, injected daily from the fourth to the fourteenth day, had no influence on the vaginal smear which remained typical of dioestrus. “The vaginal epithelium showed a high degree of mucification, a condition regularly seen in pregnancy but not in lactation.” It seems difficult to accept this hypothesis of complete antagonism of corpora lutea to the vaginal reaction due to oestrin since a decidual reaction is not maintained under conditions of follicular dominance.

Further experiments with the injection of oestrin during lactation confirm earlier work. 1 The typical vaginal histology of oestrus has been obtained with 0.2 rat unit of oestrin injected daily during the first 4 days of lactation, and the animal sacrificed on the fifth day, even though the vaginal smear remained falsely negative.