| Abstract: | A peculiar laboratory strain W1 of Wistar rats has 5 day cycles and can be made precociously receptive to a male by an injection of estradiol 10 mcg sc at 1500 of Cycle Day 2 (Diestrus III). In the course of repeating previous work the authors noted that receptivity increased from 25 to 63%, and they investigated the mechanism by checking ovaries of estrogen treated females histologically for ovulation, in comparison with ovaries of females exposed to males during the night of Diestrus III. In this experiment 56% of estrogen treated rats ovulated. 41 out of 60 (68%) of the paired rats accepted a male (verified by sperm in vaginal smear), and 93% of these ovulated. Of the 19 who were unreceptive, 1 (5.3%) ovulated (p.001). Thus estrogen treatment is much more effective than previously observed; 5 day cycling rats have a related precocity of sexual receptivity and capacity to ovulate under this stimulus. |
