Nutritional implications of cephalic phase thermogenic responses

The sensory stimulation of feeding produces a cephalic thermogenic response which coincides with an increase of plasma insulin, catecholamines and glucagon. These responses also take place with sham feeding but not with tube feeding. Vagal denervation of the pancreas as well as atropine administration, block the initial release of insulin and reduce by 50% the thermogenic response and norepinephrine release. An adrenergic blocker also reduces this response by 50%. However, with the simultaneous administration of both atropine and an adrenergic beta-blocker, this reduction is not observed. Indirect evidence suggests that this paradox is possibly explained by an enhanced secretion of glucagon.