Meal-induced increases in parasympathetic and sympathetic activity elicit simultaneous rises in plasma insulin and free fatty acids

Abstract

The aim of this study was to investigate sympathetic and parasympathetic activity during food intake in rats by measuring plasma norepinephrine (NE), epinephrine (E), insulin, free fatty acids (FFA), glycerol and blood glucose. Therefore male Wistar rats were implanted with silastic jugular vein cannulas so that blood could be withdrawn from freely moving animals. Blood samples were frequently taken before, during and after intake of a test meal. The effects of the blood sampling procedure on above mentioned blood compounds was also determined. Insulin increased considerably within the first minutes of food intake before a rise in blood glucose which is mediated by a vagal mechanism. An increase in plasma NE could be observed during the whole period of ingestive behavior whereas E increased considerably only in the first minute. Plasma FFA level was augmented sharply during food intake and a few minutes afterwards, whereas plasma glycerol levels did not changes. After termination of food intake sympathetic activation disappeared and both plasma FFA and glycerol levels declined significantly below levels as observed in control rats. In contrast, plasma insulin and blood glucose increased considerably. It is concluded that food intake in rats causes a simultaneous increase in both sympathetic and parasympathetic activity and because of that a rise in plasma FFA and insulin respectively. It is argued that augmented sympathetic activity elicits a rise in plasma FFA levels, which is not mediated by increased lipolysis but by either decreased FFA utilization or reduced reesterification.