Discrepancies between the doses of cholecystokinin or caerulein-stimulating exocrine and endocrine responses in perfused isolated rat pancreas

Abstract

The effects of highly purified natural porcine cholecystokinin (CCK) and synthetic caerulein on the rate of flow of pancreatic juice, the rate of output of amylase, and the rate of release of immunoreactive insulin (IRI) and immunoreactive glucagon (IRG) were simultaneously investigated in the isolated perfused rat pancreas. The maximal flow rate of pancreatic juice was obtained with concentrations of CCK ranging from 0.5 to 10 mU/ml, whereas amylase output was maximal at CCK concentrations from 1 to 10 mU/ml. Caerulein at concentrations of 0.05-1 ng/ml induced a similar maximal flow rate and amylase secretion. Supramaximal stimulatory concentrations of these peptides resulted in lower rates of release of fluid and amylase than with the maximally effective concentrations. Stimulation of IRI and IRG release was elicited only with concentrations of peptides supramaximal for effects on the exocrine responses. The demonstration of very similar discrepancies between the doses of caerulein required to elicit maximal exocrine responses and those required to elicit endocrine responses provide strong evidence that the pattern of the effect of the porcine CCK is accounted for by CCK itself. Although caerulein had no influence on IRI response when superimposed on 100 or 150 mg/100 ml glucose stimulation, preperfusion of caerulein led to a significant enhancement of IRI response to a subsequent glucose stimulation in both phases. The augmentation effect was completely separate from the direct IRI-stimulating effect of caerulein, because the CCK-like peptide requires no glucose for insulinotropic action. Because the concentrations of the peptides necessary for stimulation of endocrine responses were inhibitory in their effects on exocrine responses, it may be inferred that it is unlikely that the endocrine effect is physiologically important, though the results of caerulein for augmenting glucose-stimulated IRI release suggests a possible role for CCK in carbohydrate metabolism.