Effect of androstenedione on the oestrous cycle of the rat

The implantation of Silastic capsules containing androstenedione (release rate 63.2 +/- 4.4 micrograms/24 h) into 4-day cyclic rats resulted in a prolongation of the cycle (P less than 0.001), most rats showing 5-day cycles after the first, largely unaffected cycle. There was a reduction in ovulation rate (P less than 0.01) and lower serum LH levels on the morning of oestrus (P less than 0.01) but serum FSH levels were unaffected.