The effect of met-enkephalin and the opiate antagonist, naloxone, on somatostatin and insulin secretion from the isolated, perfused rat pancreas has been studied during perfusion with 300 mg/dl glucose. In response to a gradient of met-enkephalin from 0 to 10−5 M, release of somatostatin was inhibited at low concentrations and stimulated at high concentrations. However, both low and high concentrations of metenkephalin stimulated insulin secretion. A gradient of met-enkephalin from 0 to 10−6 M caused only an inhibition of somatostatin release, whereas insulin release was stimulated.

The effects of met-enkephalin on somatostatin release were antagonized by naloxone (106 M). The metenkephalin-induced insulin secretion was partially, but not completely, blocked by naloxone. Naloxone (10−6 M) alone changed the endocrine secretions by decreasing somatostatin release and by stimulating insulin release. Met-enkephalin may, therefore, be a physiologic regulator of pancreatic endocrine secretion.

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