NON-SELECTIVE INHIBITION OF BASAL GLUCAGON RELEASE BY [d-CYS14]-ANALOGUES OF SOMATOSTATIN IN THE RAT

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Abstract
The effects of two [d-Cys14]-analogues of somatostatin on basal plasma levels of glucagon, insulin and glucose were determined in unanaesthetized rats to re-examine a glucagon-selective action of these peptides which has been claimed by others. Somatostatin, [d-Cys14]-somatostatin and [d-Trp8, d-Cys14]-somatostatin caused a short-lasting, dose-dependent decrease of plasma glucagon and insulin but they had no significant influence on plasma glucose. Glucagon and insulin reached the nadir 2 min after intravenous injection of the peptides (dose range 1–10 μg/kg) or 5 min after subcutaneous administration (30 and 300 μg/kg). At the nadir, insulin was decreased to a greater extent than glucagon and the effects of all three peptides were equipotent. However, in the period after the nadir and at high doses, the time-course of some effects of the analogues on either glucagon or insulin differed from that of somatostatin. Thus, these [d-Cys14]-analogues may show partial kinetic dissociation of effects on glucagon and insulin but they are not truly selective inhibitors of glucagon release.