Effects of chronic paraventricular nucleus infusion of clonidine and α-methyl-para-tyrosine on macronutrient intake

Abstract

Earlier studies have demonstrated that acute injections of norepinephrine (NE) and clonidine (CLON) into the paraventricular nucleus (PVN) elicit feeding in satiated rats. This study examined the effects of chronic PVN infusion of α-methyl-para-tyrosine (α-MpT), a catecholamine synthesis inhibitor, on intake of a mixed milk-mash diet and on the ingestion of pure macronutrients, protein, carbohydrate and fat. The impact of chronic CLON administration on intake of these macronutrient preparations was also investigated. Over a 14-day period, chronic infusion of α-MpT (50 nmoles/30 sec/0.5 μl) resulted in a reduction of total daily food intake in rats maintained on a milk-mash diet. Chronic administration of CLON (3 nmoles/30 sec/0.5 μl) was observed to produce a specific increase in ingestion of the carbohydrate, along with a suppression in the intakes of the protein and fat. These results are similar to those previously demonstrated for NE. In contrast, chronic infusion of α-MpT into the PVN caused a specific reduction of carbohydrate consumption and an enhancement of protein ingestion, with fat intake unaffected. This evidence suggests that the α 2-noradrenergic system of the PVN plays an important role in the daily regulation of macronutrient intake, specifically of carbohydrate.