[Effect of exogenous progesterone on 17 beta estradiol secretion in 4-day cyclic rats]

The rate of ovarian 17 beta oestradiol was showed to be decreased on the decreased on the afternoon of dioestrus 2 in 4-day cyclic female rats with cycles prolonged to 5 days following progesterone treatment as compared to untreated 4-day cyclic females. OEstradiol values also appeared lower on dioestrus 3 and prooestrus in experimental 5-day cycles than, on prooestrus, in natural 4-day cycles.