Rapid insulin release after ingestion of a meal in the unanesthetized rat

Abstract

Blood glucose and insulin levels were measured in undisturbed and free-moving rats. The insulin level rises already in the 1st min after the start of food ingestion, whereas the glucose level begins to increase only in the 3rd min if carbohydrate-rich food is eaten. This early rise in insulin level is observed also under conditions in which either carbohydrate-free food or even "food" without any caloric value is offered. The smell of food cannot produce this early insulin response. It is concluded that in the rat other factors besides a rise in nutrient content in the blood produce insulin release in the first minutes after food ingestion.

Early insulin release following suckling in neonatal lambs and rabbits

“…It does not seem to depend on the quantity of food consumed since it can be stimulated during sham feeding by a variety of methods [5,6,7,12] including sucking on an empty bottle as shown here and even by the mere anticipation of a meal [13,14], whereas it is generally absent when food is infused into the stomach. Total vagotomy abolishes the response in the rat [8] and the effects of atropinisation in the present study are consistent with a role for the vagus.…”

“…In man and other species the insulin responses to oral glucose and amino acid loads are significantly greater than those to similar loads given intravenously, showing that the gut amplifies these responses [1][2][3]. Furthermore in several species including man [4], dog [5], sheep [6], rat [7,8], it has been shown that insulin concentrations rise within a few minutes of eating and before any increase in systemic plasma glucose concentration which might account for this change. Both insulinogenic gastro-intestinal hormones and the autonomic nervous system have been proposed as mediators of this extra insulin response.…”

Autonomic regulation of islet hormone secretion - Implications for health and disease

“…They consist of three different pathways: first the afferent pathway activated by olfactory, visual, gustatory and oroparyngeal mechanical receptors, second the central integratory mechanism and third the efferent pathway [118]. In rats, a cephalic phase regulation of insulin secretion has been verified by insulin secretion seen during sham feeding [119,120], after food ingestion but before any significant increase in postabsorptive glycaemia is evident [121,122], and after ingestion of non-metabolisable food [123]. In humans, a cephalic phase regulating insulin secretion was first shown by an increased circulating insulin after imaginary food ingestion under hypnosis [124] and after the sight, smell and expectation of food in healthy subjects [125].…”

Reduced insulin secretion after short-term food deprivation in rats plays a key role in the adaptive interaction of glucose and free fatty acid utilization

“…Blood glucose Free fatty acids Food deprivation Insulin secretion IN vitro and in vivo studies of insulin secretion have shown that the insulin secretory response to glucose is markedly reduced in the fasted state [4,21,22,25]. The mechanism for this phenomenon has been studied in detail and there is evidence that decreased c-AMP formation from ATP is involved [4,25].…”