CONTRASTING CARDIOVASCULAR EFFECTS FOLLOWING CENTRAL AND PERIPHERAL INJECTIONS OF TROUT GALANIN IN TROUT

Little is known about the role of galanin (Gal) in fish. In the presen t study, cardiovascular effects of central and peripheral administrati ons of a synthetic replicate of trout Gal (tGal) were investigated in the unanesthetized trout. Intracerebroventricular injection of 0.1, 0. 5, 1.0, and 3.0 nmol/kg body mass of the peptide demonstrated that the two highest doses tested produced a significant (P < 0.001) and equiv alent increase in mean dorsal aortic blood pressure (PDA) without chan ging heart rate (HR). At a dose of 1.0 nmol/kg, the systemic vascular resistance (R-s,) increased, but no change was detected in cardiac out put compared with that produced by intracerebroventricular injection o f vehicle only. In contrast, intra-arterial injections of 0.1, 0.5, an d 1.0 nmol/kg body mass of tGal produced a dose-dependent decrease in PDA With a threshold dose for significant effects observed at a dose o f 0.5 nmol/kg. None of the doses tested changed HR. At a dose of 1 nmo l/kg, a significant decrease in R-s (P < 0.001) was the factor respons ible for the fall in PDA Intra-arterial injection of porcine Gal(1 nmo l/kg) produced a change in P-DA similar to that of the same dose of tG al, but HR increased slightly. Pretreatments of trout with the cycloox ygenase inhibitors indomethacin and meclofenamate did not inhibit the vasodepressor effects of tGal. However, after intra-arterial injection of NG-nitro-L-arginine methyl ester, an inhibitor of nitric oxide syn thase, the hypotensive action of Gal was reduced threefold, suggesting the possible involvement of the nitric oxide system in mediating the vasodilatory effect of Gal. In conclusion, our results have shown that tGal may have contrasting cardiovascular regulatory functions in trou t depending on whether its site of action is the brain or the peripher al circulation.