The effect of somatostatin on the activation of adenosine 3',5'-monophosphate-dependent protein kinase in isolated rat islets of Langerhans.

Abstract

Somatostatin has been reported to inhibit the increases in cAMP levels induced by glucagon in isolated islets of Langerhans. The present study was undertaken to test whether the reported effects of somatostatin on islet cAMP levels were also reflected in changes in the cAMP-dependent protein kinase activity. Isolated islets were found to contain both isoenzymes of the cAMP-dependent protein kinase. In the presence of theophylline (2 mM), glucagon (2.9 X 10(-6) M) increased the islet protein kinase activity ratio from 0.24 +/- 0.02 to 0.55 +/- 0.02. Somatostatin (6.6 X 10(-7) M) fully inhibited both the glucagon (2.9 X 10(-7) M)- and theophylline (2 mM)-induced increases in the protein kinase activity ratio. Omission of Ca2+ from the islet incubation media did not alter the inhibitory effect of somatostatin on the glucagon-dependent activation of the cAMP-dependent protein kinase. The present study has demonstrated that in the islets of Langerhans, glucagon-dependent activation of the cAMP-dependent protein kinase can be modulated by somatostatin.