Inhibitory effects of rimorphin and dynorphin on insulin secretion from the isolated, perfused rat pancreas.

In order to settle the question about whether or not opioid peptides stimulate or inhibit insulin secretion, we studied effects of rimorphin and dynorphin, two members of the preproenkephalin B group, on glucose-induced insulin secretion in the isolated, perfused rat pancreas. These peptides (3.95 X 10(-8) M), like morphine (3.95 X 10(-8) M), significantly inhibited the glucose-induced insulin secretion. The inhibitory effect of rimorphin was attenuated by naloxone (1.2 X 10(-6) M) and phentolamine (10(-6) M), suggesting an involvement of adrenergic alpha receptors in the inhibition of glucose-induced insulin secretion mediated through specific opiate receptors. Rimorphin also inhibited glucose-induced insulin secretion even in the cysteamine-treated rat pancreas from which somatostatin had been depleted. Thus, somatostatin does not appear to play a major regulatory role in the insulin secretion in the pancreas.