GALANIN ANTAGONIST EFFECTS ON CARDIAC VAGAL INHIBITORY ACTIONS OF SYMPATHETIC-STIMULATION IN ANESTHETIZED CATS AND DOGS

1. Galantide, a putative galanin antagonist composed of twenty amino a cids, caused a significant reduction in the vagal attenuating action o f galanin injection (20 mug/kg; 6-2 nmol/kg) in anaesthetized cats at both ten times (137 mug/kg; 62 nmol/kg) and twenty-five times (343 mug /kg: 156 nmol/kg) the molar dose of galanin. Galantide did not block t he depressor action of galanin in these animals. 2. Galantide, at both doses, also significantly reduced the vagal attenuating action of a 5 min period of cardiac sympathetic stimulation at 16 Hz in anaesthetiz ed cats. 3. In anaesthetized dogs, galantide, at the same dose used in cats (137 mug/kg; 62 nmol/kg) had no significant effect on the vagal attenuation evoked by cardiac sympathetic stimulation or injection of neuropeptide Y (35 mug/kg; 8-2 nmol/kg). 4. This study therefore demon strates antagonist properties of galantide on the vagal inhibitory act ion of galanin. It supports the hypothesis that the vagal inhibitory f actor released by cardiac sympathetic nerve stimulation in the cat, bu t not the dog, is galanin, although it does not exclude the possibilit y of other factors playing a more minor role. Because galantide was no t shown to block the depressor action of galanin, this study also sugg ests that there may be more than one galanin receptor subtype.