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Somatostatin and dihydrosomatostatin (H2somatostatin) are equipotent in inhibiting insulin and glucagon release induced by arginine in the rat. The ID50 of H2somatostatin on insulin and glucagon secretion induced by arginine are 14 +/- 6 and 6 +/- 10 mug/100 g BW respectively, similar to the ID50 of H2somatostatin (18 +/- 10 mug/100 g BW) on inhibition of insulin release induced by glucose. Thyrotropin releasing factor, luteinizing hormone releasing factor, alpha-MSH, and the N-terminus decapeptide of the beta-chain of porcine hemoglobin did not alter the secretion of insulin and glucagon induced by arginine. With the exception of Ala2[-somatostatin and [Ala5-somatostatin, alanine substituted analogs of somatostatin were less potent than somatostatin. D-Trp8-somatostatin is 6-8 times as potent as somatostatin in inhibiting insulin and glucagon release induced by arginine. The relative potencies of these analogs to inhibit the secretion of the pancreatic hormones are in good agreement with our previously reported values based on the inhibition of GH secretion in vitro.
Brown et al. (Sun,) studied this question.