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.