Abstract
The influence of food restriction on the prolactin surges and circadian adrenocortical rhythms was investigated in pseudopregnant rats. Two groups (G-1 and G-2) of rats were maintained under 14L:10D (G-1: lights on 0500-1900 h, G-2: lights on 1700-0700 h), and allowed to feed ad libitum or to feed restrictedly only between 0900 and 1100 h every day for 4 weeks. Pseudopregnancy was induced 23 days after the initiation of the food restriction by uterine cervical stimulation performed on the proestrous day. Under ad libitum feeding, nocturnal and diurnal surges occurred at 0300 and 1800 h (G-1), and at 1500 h and 0600 h (G-2) respectively, suggesting that these prolactin surges are adjusted to lighting conditions. Restriction of food availability to 2 hr did not affect the nocturnal surge (G-1, 2). In contrast, the diurnal surge in individual rats occurred either irregularly or disapperared, and no significant diurnal surge was detected from the pooled data. The circadian adrenocortical rhythm adjusted to altered feeding time progressively, with the peak level immediately before the feeding time. These results are discussed in relation to the hypothesis that multiple neural oscillators may control the bimodal prolactin surges in pseudopregnant rats.
