On the nature of the galanin action on the endocrine pancreas: studies with six galanin fragments in the perfused dog pancreas

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Abstract
Galanin, a 29 amino acid peptide, inhibits insulin and somatostatin secretion from the isolated, perfused dog pancreas. To assess the nature of the influences of galanin on the endocrine pancreas, we examined the effects of porcine galanin and six different galanin analogues at the equimolar cocnentration of 1 nmol/l on the hormone release from the isolated, perfused dog pancreas. It was found that galanin2-29 (by 75 .+-. 4%), like the native galanin1-29 (by 90 .+-. 3%) potently inhibited insulin secretion (p < 0.001). In contrast, galanin3-29 did not significantly affect insulin secretion. This indicates that removal of the two N-terminal amino acids markedly reduces the potency of galanin. Also, the replacement of the amino acid number 2 (Trp) by Tyr of Phe was followed by a loss of the insulin lowering effect of galanin at this dose level. Likewise, galanin10-29 had no significant effect on insulin secretion. In cotnrast, the C-terminally deleted galanin1-15 significantly inhibited insulin secretion (by 24 .+-. 5% p < 0.01), though with a lower potency than did native galanin (p < 0.05). Consequently, the C-terminal end of galanin is also of importance for the effect. Somatostatin secretion was inhibited by galanin (p < 0.001), but not by any of the other investigated peptides. Glucagon secretion was not affected by galanin. It is concluded that the two N-terminal amino acids of galanin are essential for the inhibitory action on the insulin secretion. The removal of the N-terminal Gly residue decreases the action of galanin on insulin secretion to a much smaller extent than does the removal of, in addition, the Trp residue. However, the remainder of the molecule seems necessary for full potency. It is also concluded that the inhibition by galanin of somatostatin secretion seems to require the entire molecule.

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