Effect of a milk diet on rat gastric mucosa: receptor activity, histamine metabolism and ultrastructural analyses

Evaluation of in vivo insulin action and glucose metabolism in milk-fed rats

Milk diet has long been recommended in the management of gastrointestinal pathologies. Since milk feeding represents a high fat-low carbohydrate diet and it is acknowledged that insulin resistance is one of the consequences of high fat feeding, it is important to know whether or not chronic milk feeding leads to an impairment of the insulin-mediated glucose metabolism. To examine this question, adult female rats were given raw cow's milk (50% of total calories as lipids) for 18 days. They were compared to rats raised in parallel and fed the standard laboratory diet (15% of total calories as lipids). At the end of the 18 day period, body weight, daily caloric intake, basal plasma glucose and insulin levels in the milk-fed rats were similar to those in the control rats. In vivo insulin action was assessed with the euglycemichyperinsulinemic clamp technique in anesthetized animals. These studies were coupled with the 2-deoxyglucose technique allowing a measurement of glucose utilization by individual tissues. In the milk fed rats: 1) the basal rate of endogenous glucose production was significantly (p < 0.01) reduced (by 20%); 2) their hepatic glucose production was however normally suppressed by hyperinsulinemia; 3) their basal glucose utilization rate was significantly (p < 0.01) reduced (by 20%); 4) their glucose utilization rate by the whole-body mass or by individual tissues was normally increased by hyperinsulinemia. These results indicate that insulin action in adult rats is not grossly altered after chronic milk-feeding, at least under the present experimental conditions.

Membrane receptors in the gastrointestinal tract

This review focusses on the roles that membrane receptors and their transducers play in the physiology and pathology of the gastrointestinal tract. The multifactorial regulation of [correction] mucosal growth and function is discussed in relation to the heterogeneity of exocrine and endocrine populations that originate from progenitor cells in stomach and intestine.

Regulation of receptors on parietal cells on acid secretion

Four types of receptors have so far been identified on the parietal cell: receptors for gastrin, acetylcholine, and histamine, whose activation leads to stimulation of acid secretion, and receptors for prostaglandins of the E series, whose activation leads to inhibition of acid secretion. Postreceptor events following drug-receptor interaction include mobilization of calcium ions and cAMP formation. Moreover, a number of putative receptors (for somatostatin, CCK, adenosine, secretin, etc.) have been hypothesized, even though definite evidence is still lacking. Finally, other substances may influence gastric acid secretion in a positive or negative way, but no evidence for an involvement of specific receptors on the parietal cells is available so far.