The effect of galanin and galanin fragments on blood pressure in the Cane toad, Bufo marinus

Galanin has previously been shown to have a slight vasodepressor or no effect on blood pressure in placental mammals, but causes potent increases in blood pressure in several other vertebrate species. In this paper, the part of the galanin molecule responsible for the pressor activity was investigated in the Cane toad, Bufo marinus by administration of fragments of galanin into anaesthetised toads and isolated arterial segments in an organ bath. In anaesthetised toads, the order of efficacy was human galanin > porcine galanin > Gal 1-16 > Gal 1-15 > Gal 3-15 > Gal 21-29 = 0. In isolated vessels, the first three peptides were equally effective. When four fragments of human galanin were tested in anaesthetised toads, the order of efficacy was human galanin > Gal 1-15 > Gal 5-20 > Gal 10-25 > Gal 15-30. The substitution of alanine for tryptophan at position 2 or for tyrosine at position 9 abolished the pressor response to the human galanin fragment 1-18 in anaesthetised toads. These results suggest that vascular activity in the toad is retained within the N-terminus and that positions 2 (tryptophan) and 9 (tyrosine) are key amino acids in retention of the vascular activity of galanin.