Endogenous Rhythms of Luteal and Adrenal Cholesterol Ester Hydrolase and Serum PRL, LH and Progesterone in Mature Pseudopregnant Rats

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Abstract
Luteal and adrenal cholesterol ester hydrolase (CEH) activity and serum PRL [prolactin], LH [lutropin] and progesterone were measured at 3 h intervals throughout day 6 of pseudopregnancy in mature rats. The nocturnal PRL surge which peaked at 0600 h was correlated (correlation coefficient] = 0.95; P < 0.01) with a significant increase in total luteal CEH activity which began between 0600 and 0900 h and attained its highest activity at 1200 h. Serum progesterone concentrations and total adrenal CEH activity did not change significantly at time intervals measured. A transient, but significant, increase in serum LH was observed at 1200 h. The nocturnal PRL surge apparently initiates the subsequent increase in luteal CEH activity. Although the LH spurt could not initiate the increased CEH activity, it could have a modulatory role.