Effect of three galanin antagonists on the pressor response to galanin in the Cane toad, Bufo marinus

Galanin is a neuropeptide that causes a marked pressor response in several non-mammalian vertebrate species, and some marsupials. In this study, the effect of three galanin antagonists were tested on the pressor response to an intravenous dose (6.3 nmol/kg) of porcine galanin in anaesthetised Cane toads, Bufo marinus. Antagonists were injected at either 20 or 50 times the molar dose (x MD) of galanin. The antagonist, C7 (Galanin 1-13-spantide) reduced the pressor effect of galanin by 32.2 ± 6.0% when delivered at 20 x MD (n = 4) and by 42.9 ± 15.7% when delivered at 50 x MD (n = 4) of galanin, the response recovering within 30 min. A second antagonist, M32a (Galanin 1-13-NPY 24-36) had no effect on the pressor response to galanin at 20 x MD (n = 4), but significantly reduced the pressor effect by 54.8 ± 6.4% at 50 x MD (n = 5), which also recovered within 30 min. Administration of a third antagonist, galantide or M15 (Galanin 1-13-Substance P 5-11), resulted in a profound drop in blood pressure, and did not affect the response to galanin at either dose. In conclusion, C7 and M32a are effective, short-term antagonists of the blood pressure effects of galanin in the toad.