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 incr eases in blood pressure in several other vertebrate species. In this p aper, the part of the galanin molecule responsible for the presser act ivity was investigated in the Cane toad, Bufo marinus by administratio n of fragments of galanin into anaesthetised toads and isolated arteri al segments in an organ bath. In anaesthetised toads, the order of eff icacy 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 we re 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 t he presser response to the human galanin fragment 1-18 in anaesthetise d toads. These results suggest that vascular activity in the toad is r etained within the N-terminus and that positions 2 (tryptophan) and 9 (tyrosine) are key amino acids in retention of the vascular activity o f galanin.