PVN steroid implants: effect on feeding patterns and macronutrient selection.

The glucocorticoid corticosterone (CORT) plays a major role in feeding behavior, body weight regulation and metabolism. Recent work has demonstrated an interaction between circulating CORT and the alpha 2-noradrenergic feeding system of the hypothalamic paraventricular nucleus (PVN) and the existence of two different subtypes of glucocorticoid receptors in this nucleus. To examine the function of these specific PVN receptors, crystalline CORT and other steroid hormones were implanted directly into the PVN, and feeding patterns and macronutrient selection, of freely feeding adrenalectomized (ADX) and sham rats, were monitored at the beginning and end of the nocturnal feeding cycle. Results indicate that PVN CORT implants stimulate carbohydrate intake in ADX rats, at the onset of the dark cycle when the feeding-suppressive effects of ADX are strongest. Corticosterone was ineffective in sham rats and was also ineffective in potentiating food intake in ADX rats at the end of the dark phase. In contrast, implants of the mineralocorticoid aldosterone (ALDO) stimulated the ingestion of the fat diet, in both sham and ADX rats and during both the early and the late dark periods. Implants of ALDO also enhanced carbohydrate intake, but only in ADX rats and at dark onset. While the synthetic glucocorticoid, dexamethasone, had a small carbohydrate stimulatory effect similar to CORT, other steroids (deoxycorticosterone, progesterone and estrogen) were without effect. These results indicate a central site of action for the adrenal hormones in modulating nutrient intake. Based on a variety of evidence, it is suggested that the stimulatory effects of ALDO and CORT on macronutrient intake may be differentially mediated by Type 1 and Type 2 steroid receptor subtypes within the brain.