Effect of chronic stress and exogenous glucocorticoids on regional fat distribution and metabolism.

It has been proposed that increased glucocorticoid hormones and decreased sex hormones affect regional fat metabolism and distribution. In the present work, it was hypothesized that chronic, uncontrollable stress, known to affect the pituitary-adrenal and pituitary-gonadal axes might, therefore, lead to differences in regional fat accumulation. In comparison with controls, male Sprague-Dawley rats stressed for 28 days, had significantly larger adipocytes. In addition, a tendency for a heavier fat pad and an increased lipoprotein lipase activity in the mesenteric depot was suggested. No significant changes were seen in epididymal, retroperitoneal, and inguinal regions. In order to study if the effects observed could be attributed to increased glucocorticoids, the response to a direct administration of supraphysiological doses of corticosterone, given either in the drinking water or via subcutaneous implantation of corticosterone pellets, was studied. Increased fat accumulation was shown in all fat depots in a dose-response fashion, but was significantly more pronounced in the mesenteric region. It was concluded that mesenteric fat tissue may respond to stress in a different manner from other fat depots. Glucocorticoids seem to be partly, but not solely, responsible for the changes observed in adipose tissue metabolism and distribution following exposure to uncontrollable stress.

Medial hypothalamic serotonin: role in circadian patterns of feeding and macronutrient selection.

Hypothalamic serotonin (5-HT) is believed to have an inhibitory effect on food intake in a variety of species. To define more precisely the nature of this effect, this study investigated the effects of medial hypothalamic 5-HT injection on natural patterns of macronutrient intake in freely feeding rats. Serotonin (5-20 nmol) was injected directly into the paraventricular nucleus (PVN) of brain-cannulated rats maintained ad libitum on pure macronutrient diets, protein, carbohydrate and fat, and measurements of nutrient intake were taken one hour later. To assess whether the action of 5-HT on macronutrient intake varies across the light-dark cycle, these tests were conducted at 3 different times in the nocturnal feeding period, during hours 1, 6 and 11 after lights out. The results demonstrate that the suppressive effect of PVN 5-HT on food intake is dose dependent, nutrient selective, as well as time dependent. Specifically, PVN injection of 5-HT, at all doses tested, was effective at only one time of the nocturnal cycle, namely, at the onset of the active, dark period. While no behavioral effect of 5-HT was detected in the middle and late phases of the dark, a strong, dose-dependent reduction of nutrient intake was revealed immediately after lights out. This suppressive effect was characterized by a highly selective decrease in carbohydrate intake, along with a significant enhancement in preference for protein, as well as for fat, and little change in total caloric intake.(ABSTRACT TRUNCATED AT 250 WORDS)