Summary. Ovarian regression was induced in hens by infusing 30 μg corticosterone/h, feeding diets deficient in Ca2+ or Na+ and by withdrawal of food and water. The weight of the ovary was most severely reduced by the corticosterone infusion. The total number of normal ovarian follicles weighing > 0·012 g was not altered by any of the treatments. However, the number of large yolk-filled follicles decreased while the numbers of smaller follicles and atretic follicles increased when ovarian regression was induced by dietary changes or hormone infusion as compared to normally fed or solvent-infused hens.
These experimental treatments resulted in decreases in plasma concentrations of LH, progesterone and oestradiol, and increases in the plasma levels of corticosterone. These changes were immediate except for the low sodium diet with which there was a delay of about 6 days. When fasted birds were fed oats and given water, plasma LH and oestradiol, but not progesterone, increased. The infusion of corticosterone did not affect the ability of the pituitary gland to secrete LH after an injection of LH-RH, but this response was reduced or eliminated by the other experimental treatments. It is concluded that the regression of the ovary induced by these experimental treatments is a consequence of the reduction in the secretion of LH, which may itself be caused by increased plasma levels of corticosterone. It also appears that recruitment of follicles in the maturational stage which precedes entry into the hierarchy of large yolky follicles was unaffected by all of the methods of inducing ovarian regression which were studied.