Abstract

1. The helospectins are peptides structurally related to helodermin, vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI) and secretin, which all potently stimulate glucagon secretion in the mouse. Therefore, the effects of helospectin I (0.1-0.8 nmol kg-1) on insulin and glucagon secretion under basal conditions and after stimulation with glucose (2.8 mmol kg-1) or the cholinoceptor agonist, carbachol (0.16 mumol kg-1), were examined in vivo in the mouse. 2. Helospectin I potently increased plasma levels of glucagon after its intravenous injection in mice. The increase was observed after only 2 min, and was evident also after 6 min. 3. In contrast, plasma insulin levels were not altered by helospectin I after 2 min, but slightly increased after 6 min. Plasma glucose levels were not altered by the peptide. 4. Carbachol-induced glucagon secretion was markedly potentiated by helospectin I. In contrast, glucose- or carbachol-stimulated insulin secretion was not affected by the peptide. 5. In conclusion, helospectin I markedly stimulates glucagon secretion in the mouse whereas the peptide has no direct action on insulin secretion. This pattern of effect of helospectin I is similar to that previously reported for helodermin, VIP, PHI and secretin in the mouse, i.e., for all peptides belonging to this superfamily of peptides.