Endogenous Rhythmsof LutealandAdrenalCholesterol EsterHydrolaseandSerumPRL, LH andProgesterone in MaturePseudopregnant Rats

Luteal and adrenal cholesterol ester hydrolase (CEH) activity and serum PRL, LH and proges terone 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 (r = 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 data suggest that the nocturnal PRL surge initiates the subsequent increase in luteal CEH activity. Although the LH spurt could not initiate the increased CEH activ