Modification by metyrapone of the “open period” for pre‐ovulatory LH release in the hen

Abstract

1. A single injection into laying hens of 60 mg metyrapone 28 h after the final ovulation of a sequence induced increases in the plasma concentrations of LH and progesterone, followed by premature ovulation. Injection of metyrapone 8 h after ovulation, however, did not affect plasma concentrations of either LH or progesterone.

2. Injection of laying hens with 60 mg metyrapone on 5 successive days reduced the effectiveness of exogenous ACTH in increasing the plasma concentration of corticosterone and abolished the system of “ open “ and “ closed periods “ for pre‐ovulatory LH release. Thus, pre‐ovulatory LH surges and ovipositions occurred throughout the 24‐h day instead of being restricted to an 8 to 10‐h period of the day.

3. These observations suggest that changes in environmental stimuli such as light act via the adrenal gland in regulating the timing of the “ open period “ for the pre‐ovulatory release of LH in the hen.