Luteinizing hormone activity of the hen's pituitary during the egg-laying cycle

Abstract

Anterior pituitaries of hens in a regular laying cycle with 1-day pause between clutches were removed at various times in the period from ovulation of the terminal ovum (C t) of the clutch to 8 hours after ovulation of the second ovum (C 2). They were assayed for LH activity using the rat ovarian ascorbic acid depletion method. Two peaks of LH activity were found during the period between any ovulations. In the period from ovulation of the initial ovum (C 1) of the clutch to the C 2 ovulation, the first peak appeared 6 hours after the C 1 ovulation (20 hours before the C 2 ovulation) and the second peak 18 hours after the C 1 ovulation (8 hours before the C 2 ovulation). In the period between the C t and C 1 ovulations, the first peak appeared 2 hours after the C t ovulation (38 hours before the C 1 ovulation) and the second peak 18 hours after the C t ovulation (22 hours before the C 1 ovulation). This second peak was maintained at a fairly uniform level until 10 hours before the C 1 ovulation. The decrease in the LH level from the second peak may be closely related to ovulation. The delay of the decrease from the second peak may cause an inhibition of ovulation after the C t oviposition which results in a pause in the egg-laying cycle.