Non-selective inhibition of basal glucagon release by [D-Cys14]-analogues of somatostatin in the rat

Multiple subcutaneous injections of somatostatin induce tachyphylaxis of the suppression of plasma insulin, but not glucagon, in the rat

The time course of pancreatic effects of somatostatin was studied over a period of 2 h in unanesthetized unrestrained rats after administration of the peptide by intravenous infusion and by single and multiple subcutaneous injections. During infusion of 10 and 30 micrograms/kg per min, somatostatin continuously suppressed plasma insulin and plasma glucagon. Plasma glucose was significantly increased at the lower dose, but not affected at the higher dose. Single subcutaneous injections of 0.3 and 3 mg/kg decreased plasma insulin and glucagon dose-dependently for 20-60 min without affecting plasma glucose. Multiple subcutaneous injections of somatostatin (one to four doses of 3 mg/kg, administered at intervals of 30 min) caused an initial decrease of plasma insulin (at 30 min), a rebound-increase at 60 and 90 min, and a final return to control values by 120 min. Plasma glucagon remained continuously suppressed. Plasma glucose increased significantly at 60 and 90 min and tended to return towards control values thereafter. In conclusion, pancreatic B cells - but not A cells - of the rat develop tachyphylaxis to somatostatin within 2 h after multiple subcutaneous injections of the peptide. By this mode of administration, 'selective' suppression of plasma glucagon can be achieved with somatostatin in the rat.

Effect of somatostatin and two of its analogues on basal and arginine-stimulated insulin and glucagon secretion in the dog

Two analogues of somatostatin (D-Trp8,D-Cys14-somatostatin, and the octapeptide DesAA1,2,3,4,13,14,D-Trp8,GABA12-somatostatin) were compared with somatostatin using infusions of 0.1 and 0.5 microgram . kg-1 . min-1 in conscious dogs. Basal concentrations of insulin and glucagon were markedly and similarly lowered by all three somatostatin (SRIF) compounds at either dose. Arginine stimulation of insulin and glucagon secretion was entirely abolished by SRIF and by the octapeptide during infusion at 0.1 microgram . kg-1 . min-1 but both hormones were only partly inhibited by D-Trp8,D-Cys14-SRIF. The higher dose (0.5 microgram . kg-1 . min-1) of all three SRIF peptides lowered plasma insulin and glucagon before and during arginine stimulation. The recovery of plasma insulin and glucagon was delayed after discontinuation of the D-Trp8,D-Cys14-SRIF, and particularly after the octapeptide when compared with SRIF suggesting a longer duration of action of the analogues. The results did not confirm the previously suggested selective suppression of glucagon by D-Trp8,D-Cys14-SRIF. The new octapeptide appears to be promising for future clinical studies due to its potent inhibitory effect on insulin and glucagon, and its prolonged duration of action.