Changes in Hypophysial and Plasma LH Levels During the Laying Cycle of the Hen

Abstract

Plasma and pituitary glands were obtained from 80 laying hens at various times in the cycle leading to ovulation of the 3rd follicle of clutch sequence. The OAAD (Ovarian ascorbic acid depletion) method was found adequate to measure LH (luteinizing hormone) in peripheral blood and in adenohypophyses of chickens. Three significant LH peaks were detected in the plasma. Two occur 13 and 8 hr. prior to ovulation and are thought to be essential for ovualtion. Both were previously reported to occur at the stated times in trials using hypophysectomy, hypothalamic lesions, and injection of a neurogenic blocking agent (Dibenamine). The 1st of the 3 peaks occurs 21 hr prior to ovualtion. Its relation to ovulation is unknown, but it occurs immediately after the ovum passes from the oviduct into the uterus. Significant peaks in hypophysial LH concentration occur 21 and 11 hr. prior to ovulation. The latter peak precedes the plasma peak by 1 hr. Hypophysial and plasma LH contents are significantly correlated through the 20-hr. period. The striking resemblance between the LH curves and the pituitary wet weight curve remains to be investigated further.