Nutritional implications of the cephalic-phase reflexes: Endocrine responses

Cephalic phase hormonal release occurs through activation of vagal-efferent fibers in response to food-related sensory stimuli. Thus, tasting, chewing and expectorating food elicits hormonal release prior to nutrient absorpti on. Differential sensitivity of cell types within the islet to neural activ ation determines the profile and magnitude of hormonal release. While the m agnitude of cephalic phase insulin release is relatively small (25% above b aseline), pancreatic polypeptide, a hormone almost exclusively under vagal control increases 100% above baseline when individuals taste, chew and expe ctorate food. Thus, the cephalic phase pancreatic polypeptide response is a sensitive indicator of vagal activation to food stimuli. The physiological significance of the cephalic phase hormonal responses is demonstrated by e xperimental manipulations which inhibit or bypass cephalic phase insulin re lease. Under these circumstances hyperglycemia and hyperinsulinemia are evi dent. Conversely, supplementation of insulin during the preabsorptive time period improves glucose tolerance in certain clinical populations. These da ta suggest that cephalic phase insulin release plays a role in glucose home ostasis.