Somatostatin: analogs with selected biological activities.

[D-Cys14]-Somatostatin is the first analog of somatostatin found to be more potent in inhibiting glucagon and growth hormone secretion that it is in inhibiting insulin secretion. [D-Trp8]-Somatostatin is eight to ten times more potent than somatostatin in inhibiting insulin, glucagon, and growth hormone secretion. [D-Trp8, D-Cys14]-Somatostatin is more potent than [D-Cys14]-Somatostatin, but retains its relative selectivity in being a more potent inhibitor of the secretion of glucagon and growth hormone than of insulin.