Changes in ornithine decarboxylase activity in ovarian follicles of the laying hen (Gallus domesticus) during the ovulatory cycle.

Fowl ovarian ornithine decarboxylase activity was measured at 20, 10 and 3 h before an expected ovulation in granulosa and thecal tissues from follicles at various stages of development. An increase in the enzyme activity between 10 and 3 h before an expected ovulation was assumed to be caused by preovulatory increase in plasma LH concentration. The activity in granulosa tissue increased with increasing size of the follicle. In the largest (F1) follicle there was an 11-fold increase in granulosa ornithine decarboxylase specific activity between 10 and 3 h before ovulation. In the third (F3) and fifth (F5) largest follicles there was a 1.9- and 2-fold increase respectively. The enzyme activity in thecal tissue from the follicular hierarchy decreased with increasing size of the follicle and the F3 thecal preparation was the only tissue to respond to the preovulatory LH surge. In contrast, ornithine decarboxylase activity in thecal tissue from small (less than 5 mm) non-atretic follicles increased by two- to threefold after the preovulatory LH surge. The activity in atretic follicles of the same size was low and remained unchanged throughout the ovulatory cycle.