Galanin antagonist effects on cardiac vagal inhibitory actions of sympathetic stimulation in anaesthetized cats and dogs.

1. Galantide, a putative galanin antagonist composed of twenty amino acids, caused a significant reduction in the vagal attenuating action of galanin injection (20 micrograms/kg; 6.2 nmol/kg) in anaesthetized cats at both ten times (137 micrograms/kg; 62 nmol/kg) and twenty-five times (343 micrograms/kg: 156 nmol/kg) the molar dose of galanin. Galantide did not block the 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 anaesthetized cats. 3. In anaesthetized dogs, galantide, at the same dose used in cats (137 micrograms/kg; 62 nmol/kg) had no significant effect on the vagal attenuation evoked by cardiac sympathetic stimulation or injection of neuropeptide Y (35 micrograms/kg; 8.2 nmol/kg). 4. This study therefore demonstrates antagonist properties of galantide on the vagal inhibitory action of galanin. It supports the hypothesis that the vagal inhibitory factor released by cardiac sympathetic nerve stimulation in the cat, but not the dog, is galanin, although it does not exclude the possibility of other factors playing a more minor role. Because galantide was not shown to block the depressor action of galanin, this study also suggests that there may be more than one galanin receptor subtype.