Effects of limiting water intake on the rat estrous cycle with observations on LH, prolactin, and corticosterone

Pituitary-gonadal function in adult male rats subjected to chronic water restriction

The effect of water restriction on the pituitary-gonadal axis has been studied in adult male rats. Water restriction did not modify FSH, LH and testosterone levels. However, both LH and testosterone responses to acute noise stress were impaired by water restriction. It was unlikely that the inhibition of the pituitary-gonadal response to stress was due to an alteration of the circadian pattern of LH since no evidence for such a daily rhythm was found in either of the two experimental groups. The effects of water restriction on the pituitary-gonadal axis appear to be at least partially a consequence of the resulting reduction in food intake, so that the pituitary-gonadal response to stress would be a more sensitive index of abnormalities induced by protein-calorie deficit than basal concentrations of LH, FSH, or T.

Bidirectional responsiveness of the pituitary-adrenal system in old and young male and female rats

Bidirectional responsiveness of the pituitary-adrenal system was examined in young adult (3-5 months) and old (24-26 months) male and female rats. In Experiment 1, an approach-avoidance conflict was created by exposing food- and water-deprived subjects to a flavored solution which had previously been paired with lithium chloride-induced illness in a conditioned taste aversion paradigm. Young and old males and young females elevated plasma corticosterone in response to deprivation; males showed a further elevation when reexposed to the solution, whereas young females did not. Old females did not exhibit a corticosterone elevation to deprivation or upon reexposure. In Experiment 2, water was restricted to a fixed period in the morning when corticosterone levels are typically low. Plasma corticosterone was measured before and after watering. Young and old males and young females reentrained their circadian corticosterone rhythm so that levels were elevated just prior to watering; consumption was followed by a drop in corticosterone. Old females failed to reentrain or to suppress corticosterone secretion upon drinking. These findings indicate that the lability of the pituitary-adrenal system is more markedly affected by senescence in females than in males.

Suprachiasmatic nuclear lesions do not abolish food-shifted circadian adrenal and temperature rhythmicity

Daytime restriction of food and water availability in nocturnal animals phase shifts the circadian periodicity of plasma corticosteroid concentrations and body temperature. These shifted rhythms persist in animals with lesions of the suprachiasmatic nuclei who are arrhythmic under normal conditions. These findings suggest the existence of an additional "clock" that may be involved in the generation of the rhythm.