The effects of galanin and galanin fragments on cardiac-vagal action and blood pressure in the anaesthetised cat.

Galanin (GAL), 29 amino acid peptide, has previously been shown to inhibit cardiac vagal action, and to cause a fall in systemic blood pressure in anaesthetised cats, at a dose of 6.2 nmol/kg. Here, the biological activity of exogenous GAL fragments was assessed in anaesthetised cats. GAL 1-16 at a dose equimolar with the full GAL 1-29 peptide (6.2 nmol/kg) and at a dose five times the molar dose of GAL 1-29 (31 nmol/kg), was found to be biologically active although the effects were less than that of the full peptide. GAL 1-15 at doses up to 10-times the molar dose of GAL 1-29, however, was not active, suggesting that amino acid 16, isoleucine, is critical for activity. In addition, GAL 15-29 and 21-29 showed no biological activity at doses up to 10-times the molar dose of GAL 1-29. These results suggest that the N-terminal rather than the C-terminal end of the GAL molecule is the one responsible for most of GAL's biological activity in this preparation.