Differential Sensitivity of Pancreatic β-cells to Phorbol Ester TPA and C-Kinase Inhibitor H-7 in Nonpregnant and Pregnant Rats

Abstract

In order to elucidate the possible role of C-kinase in exaggerated insulin release in pregnancy, the effects of phorbol ester TPA and a C-kinase inhibitor H-7 were investigated using the isolated perfused pancreas from nonpregnant and pregnant rats. At the termination of perfusion, the insulin content of the perfused pancreas was determined to estimate insulin biosynthesis. Insulin release from the perfused pancreas was markedly augmented by 20nM TPA in the presence of 4.4mM glucose in pregnant rats, but not in nonpregnant rats. When glucose concentrations in the perfusate were raised to 16.7mM, insulin release from the perfused pancreas was profoundly enhanced in pregnant rats. TPA further augmented insulin release, but the insulin content was not affected by TPA. In contrast to the considerable effect of TPA in the presence of 4.4mM glucose, the potentiating effect of TPA on insulin release was rather weaker in pregnant than in nonpregnant rats in the presence of 16.7mM glucose. The release of insulin induced by 16.7mM glucose was inhibited by the addition of 100μM H-7 in nonpregnant rats, whereas insulin release from pregnant rat pancreases was not altered. Thus, the effect of TPA and H-7 on insulin release can be more clearly observed in the β-cells of nonpregnant rats than those of pregnant ones when maximal concentrations of glucose are used as a stimulant. Exaggerated insulin release caused by glucose in pregnancy may be due to already fully activated C-kinase in the β-cells.