Insulin secretion from pancreatic islets: effect of growth hormone and related proteins

Insulin responses to clinical grade human growth hormone (hGH), intact hGH, naturally occurring diabetogenic substance (NDS), and subtilisin cleaved forms of hGH (S1 and S3) were studied using hypophysectomized rat pancreatic islets. While clinical grade hGH (200 microgram/ml) elicited a prompt and sustained release of insulin, purified intact hGH (200 microgram/ml) did not. Naturally occurring diabetogenic substance, isolated from clinical grade hGH preparations, stimulated insulin release at 200 ng/ml. Upon repeat stimulation with NDS, a significantly greater insulin release than with initial stimulation was observed. Although S3 (200 microgram/ml) elicited significant insulin release, S1 (200 microgram/ml) did not. Direct stimulation of insulin release with clinical grade hGH is not due to intact hGH but another proteins(s) such as NDS. Enzymic modification of intact hGH appears to enhance insulin stimulatory capacity.