Differences in pancreatic enzyme release from ventral and dorsal areas of the rat pancreas

The exocrine secretory function of the ventral and dorsal areas of the rat pancreas was investigated separately. In the isolated perfused rat pancreas, caerulein (10 -12, 10 -11, and 10 -10 M) and carbachol (10 -7 and 10 -6 M) caused a greaterfold increase in pancreatic secretion from the dorsal than the ventral area. Caerulein (10 -9 M) and carbachol (10 -5 M) were supramaximal concentrations with respect to secretion from the dorsal area, but this was not the case in the ventral area. Similar findings were also observed when ventral and dorsal secretions were studied in vivo in anesthetized animals. By contrast, in dispersed acini the sensitivity and responsiveness of tissue from the dorsal and ventral areas were similar to both secretagogues. The possible influence of the endocrine pancreas via the insuloacinar portal system was studied in the perfused pancreas of diabetic rats treated with insulin in vivo. Carbachol (10 -6 M)-stimulated secretion from the ventral area was similar (except for amylase) to that of controls, while a significantly reduced (P < 0.001) output was measured from the dorsal pancreas. These results demonstrate that in the intact pancreas differences of exocrine secretion exist between the ventral and dorsal areas and suggest that insulin may contribute, at least in part, to the expression of such differences.link_to_subscribed_fulltex

Glucose-insulin interactions on exocrine secretion from the perfused rat pancreas

The effects of glucose and insulin on pancreatic enzyme release have been investigated using the isolated perfused rat pancreas. Basal and caerulein-stimulated secretion was significantly less in the presence of 15 mM glucose than with 5 mM glucose, except at a supramaximal concentration of caerulein (10 -9 M) where secretion was similar in both groups. Addition of exogenous insulin also caused a reduction in enzyme secretion, but the time of onset of the inhibitory action was delayed compared to that observed with glucose. Furthermore, it was found that the effects of 15 mM glucose and exogenous insulin were not additive at the concentration used in these experiments, and that the inhibitory action of insulin was glucose-dependent. Such glucose-insulin interactions must play an important role in the modulation of pancreatic enzyme secretion.link_to_subscribed_fulltex

Activity of the insulo-acinar axis in the isolated perfused rat pancreas

The object of the present investigation was to determine whether insulin secreted by the endocrine pancreas and carried in the insulo-acinar portal system has a direct effect on pancreatic enzyme secretion. For this purpose, the isolated rat pancreas was perfused in a nonrecirculating system. The perfusate contained 3 mM glucose, and either caerulein or vasoactive intestinal polypeptide was used to stimulate exocrine secretion. The amount of insulin reaching the exocrine pancreas was reduced by two different experimental procedures. In the first, use was made of streptozotocin-diabetic rats treated with insulin in vivo. Treatment was such that the contents of amylase and lipase, vastly altered in the untreated diabetic state, were normalized before the perfusion studies. In the second procedure, insulin reaching the exocrine pancreas was reduced by antiinsulin serum in the perfusate. In these procedures, the reduced insulin bioavailability was associated with a reduction in caerulein- and vasoactive intestinal polypeptide-stimulated enzyme release, which was shown as a reduction of maximum responsiveness to caerulein without alteration of sensitivity. By contrast, in dispersed pancreatic acini where the insulo-acinar axis was completely disrupted, amylase secretion from diabetic and nondiabetic tissue was identical over a wide range of caerulein concentrations, showing that the secretory defect seen in the perfusion studies was not inherent to the exocrine tissue. The results show that basal insulin secretion has a direct effect on pancreatic enzyme output and that the insulo-acinar axis may play an important role in the regulation of acinar cell function.link_to_subscribed_fulltex