Follicular transformation in hen's ovary after the administration of aminoglutethimide

To investigate the relationship of follicular steroids, especially estradiol-17 beta (E2) to follicular transformation to the rapid growth phase in the domestic hem, aminoglutethimide (AG), an inhibitor of steroidogenesis, was used in the present study. Experiments were done on the day when White Leghorn hens laid an intraclutch egg (Cs) between 9 : 00 and 10 : 30. AG with 100 mg/kg b. w. was injected s. c. into hens 2 hr after the Cs oviposition (Exp. 1) or 2 hr before the predicted time of the oviposition (Exp. 2) and the hens were killed 14 hr after the oviposition. To determine the time of follicular transformation, Sudan-red and -black were alternately injected i. v. to the hens 4, 8 and 12 hr after the oviposition. In both Exps. 1 and 2, blood was collected from the hens at the time of AG or vehicle injection, and 4, 8, 12 and 14 hr after the oviposition. Plasma E2 concentrations were measured by EIA. When AG was administered 2 hr after Cs oviposition (Exp. 1), the follicular transformation was found in only 50 % of the hens. Plasma E2 levels from the AG treated hens without follicular transformation tended to be lower than those from the hens with transformation during 8 to 14 hr after the oviposition. In contrast to the results obtained in Exp. 1, the occurrence of follicular transformation was found at the same frequencies (83 %) in the hens treated with AG and vehicle 2 hr before the predicted Cs oviposition time (Exp. 2). In comparison of the results in Exps. 1 and 2, it was considered that AG displayed the suppressive effect on E2 synthesis shortly before and during the period when follicular transformation was frequently performed in Exp. 1, whilst the hens were already released from the inhibitory effect by AG in Exp. 2. According to the results obtained in the present work, follicular E2 plays a principal role in the transformation to the rapid growth phase of the small follicle in hen's ovary