Cephalic phase metabolic responses in normal weight adults

Abstract

The presence and physiologic importance of cephalic phase insulin release in humans remains controversial. The aim of these studies was to determine whether cephalic phase insulin release could be demonstrated in normal weight subjects and whether it would be associated with changes in blood glucose, free fatty acid, and pancreatic polypeptide levels. The studies were followed by a hyperglycemic clamp to determine whether cephalic responses would alter overall glucose disposal or glucose-stimulated insulin secretion. In all, 17 subjects were studied on two occasions with and without (control study) presentation of food stimuli. Tease-feeding alone (n = 6), or the administration of a sweet taste alone (aspartame, n = 5) failed to stimulate cephalic responses. However, the presentation of the combined stimuli (tease meals plus sweet taste, n = 7) resulted in a significant fall ( P < .005) in blood glucose levels and a variable rise in serum insulin (% insulin rise 38 ± 15%, P < .05) and C-peptide levels (7 ± 6%, NS) within five minutes of the food presentation when compared with control studies, with no change seen in free fatty acid or pancreatic polypeptide levels. The blood glucose fall correlated strongly ( r = .90, P < .01) with a score of the subjective response to the food and taste. There were strong negative correlations between the individual cephalic insulin responses and the initial blood glucose increment following the start of the dextrose infusion ( r = .87, P < .02) and also between the cephalic insulin responses and an index of glucose metabolism (mean blood glucose increment/mean dextrose infusion rate) during the first 30 minutes of the hyperglycemic clamp ( r = −.87, P < .02). We conclude that cephalic phase metabolic responses can be elicited in normal weight humans using a combination of food-associated stimuli. Cephalic responses include a prompt rise in insulin and a seemingly independent fall in blood glucose with the magnitude of the latter proportional to the subjective perception of the stimuli. Cephalic phase responses have a restraining effect on the early blood glucose rise induced by an intravenous glucose load and may have a role in postprandial glucoregulation.