The effect of atropine on plasma vasoactive intestinal polypeptide after intraduodenal infusion of fat in man

Distribution of muscarinic receptor subtypes in rat small intestine

Despite its great promise, small intestinal transplantation in some patients is complicated by difficult postoperative management. The reasons for this are complex. In a rat model of small intestinal transplantation, frequencies of migrating myoelectric complexes during fasting are reduced in ileal isografts and muscarinic receptor density is decreased. We hypothesized that the distribution of muscarinic 1 receptors localized to enteric neurons is altered after small intestinal transplantation. Distal small intestine was orthotopically transplanted in Lewis-to-Lewis donor-recipient combinations. At 3 months, transplanted and normal ileum was obtained to prepare membrane fractions. [N-methyl-3H]Scopolamine served as ligand, while scopolamine methylbromide, pirenzepine, and methoctramine were used in competitive homologous and heterologous displacement experiments. Receptor subtype models were examined by nonlinear regression analysis. In normal and transplanted ileum, heterologous displacement was consistent with three site models (P < 0.05). In normals, the muscarinic 1 receptor subtype was most abundant, with a relative distribution of 69 to 78%. There was a relative distribution of 13 to 16% for muscarinic 3 receptor subtype. After transplantation, the muscarinic 1 subtype decreased to a mean of 45% but the muscarinic 3 subtype increased to a mean of 42%. Using pirenzepine, mean pKD values were not different between the two groups. It is concluded that the decrease in muscarinic 1 receptor subtype after transplantation could be related to neuronal cell loss or to downregulation of the expression of muscarinic 1 receptors. The results did not support defective posttranslational processing of receptor proteins.

Exocrine pancreatic response to intraduodenal fatty acids and fats in rabbits

1. The exocrine pancreatic secretion in rabbits after intraduodenal perfusion of, respectively, a short-chain fatty acid (propionate), a long-chain fatty acid (oleate) and a neutral fat (intralipid) has been studied. 2. Only the neutral fat and the long-chain fatty acid stimulated the hydroelectrolyte fraction of exocrine pancreatic secretion in a dose-related fashion, but this response was not mediated by secretin release. 3. Acinar secretion was more effectively stimulated after propionate perfusion than by oleate and this was governed by different mechanisms. 4. Neutral fat, without predigestion, stimulated the pancreatic enzyme secretion in the rabbit.

Thermic effect of food: possible implication of parasympathetic nervous system

To investigate the effect of the autonomic nervous system on the thermic response to food ingestion, respiratory exchange measurements were performed on seven healthy young men for 1 h and 45 min before and 6 h after ingestion of a mixed meal, approximately 560 kcal, 53% carbohydrate, 30% fat, and 17% protein (control) and under the same conditions during infusion of either propranolol (80 micrograms/kg bolus and 1 microgram.kg-1.min-1), atropine (10 micrograms/kg and 10 micrograms.kg-1.min-1), or atropine plus propranolol. The postabsorptive resting metabolic rates were the same on each occasion and were slightly altered by drug treatment. The thermic responses to the meal were the same with the control and propranolol tests (9.3 +/- 0.9 and 9.2 +/- 0.5%, respectively) and were greater (P less than 0.001) than with atropine 3.6 +/- 0.6% and atropine plus propranolol 3.3 +/- 0.8%. Blockade of the sympathetic nervous system does not decrease the thermic response to food taken orally, whereas muscarinic receptor blockade does. Although some confounding effects of atropine might explain some of this decrease, our results suggest that the parasympathetic nervous system is involved in the thermic effect of food.

The effect of insulin-induced hypoglycemia with and without atropine on plasma vasoactive intestinal polypeptide in man

Plasma vasoactive intestinal polypeptide (VIP) was measured in six healthy male students on 2 separate days after insulin-induced hypoglycemia with and without atropine and on a 3rd day in five of the students after atropine alone. A significant increase in peripheral plasma VIP was observed when atropine was given together with insulin, whereas insulin or atropine alone had no effect on plasma VIP. It is suggested that cholinergic nicotinic receptors may be involved in the increase of VIP after insulin-induced hypoglycemia and that the lack of VIP increase seen after insulin alone may be caused by an inhibitory effect of other gastrointestinal hormones.