Parasympathetic involvement in rapid meal-associated conditioned insulin secretion in the rat

Abstract

Blood glucose and plasma insulin concentrations were measured in blood sampled via a cardiac catheter in freely moving rats. To obtain a rapid conditioned cephalic phase of insulin secretion, rats were habituated to one of two feeding schedules. Clock-activated opening of doors in front of the food hopper imposed a feeding schedule of either six meals per day or two meals per day. When the doors were opened in both conditions, insulin increased rapidly during the first minute of feeding in the middle of the light phase. However, when presented an empty food hopper immediately after door opening, only rats in the two meal per day condition showed raised insulin levels and not rats in the six meal per day condition. This response was abolished following pharmacological blockade of nicotinic receptors with hexamethonium and muscarinic receptors with atropine. The present study shows that rapid conditioned insulin secretion can be evoked within one minute by a meal-associated stimulus. These results further indicate that this conditioned insulin secretion is vagally mediated and that its occurrence is dependent on the nature of the feeding schedule.

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].…”

The psychobiology of meals

“…Activity cycles (and related hormonal patterns) are in turn able to become imprinted upon both regular meals and the day/night cycle (e.g., Aschoff, 1987;Krieger, Hauser, & Krey, 1977;Strubbe, Prins, Bruggink, & Steffens, 1987). We previously found that any stimulus that reliably predicts food availability, including time of day as weIl as arbitrary stimuli, can acquire the ability to elicit meal anticipatory responses (Strubbe, 1992;Woods, 1976;Woods & Kulkosky, 1976;Woods et al, 1977) .…”

Vagotomy suppresses cephalic phase insulin release in sheep

“…1B and D), the cephalic phase insulin secretion, is well documented in non-ruminants including humans (Strubbe & Steffens, 1975;Berthoud et al 1980Berthoud et al , 1981Berthoud & Jeanrenaud, 1982;Strubbe, 1992;Teff et al 1995) and in ruminants (Bassett, 1974;Bhattacharya & Alulu, 1975;Chase et al 1977;Porter & Bassett, 1979;Vasilatos & Wangsness, 1980;Faverdin, 1986). However, the observation (Figs 1 and 2) that vagotomy suppresses the secretion of insulin that occurs immediately after the start of eating, has not been reported previously for ruminants.…”