Contrasting cardiovascular effects following central and peripheral injections of trout galanin in trout

Abstract

Little is known about the role of galanin (Gal) in fish. In the present study, cardiovascular effects of central and peripheral administrations 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 equivalent increase in mean dorsal aortic blood pressure (PDA) without changing 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 output compared with that produced by intracerebroventricular injection of vehicle only. In contrast, intra-arterial injections of 0.1, 0.5, and 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 of 0.5 nmol/kg. None of the doses tested changed HR. At a dose of 1 nmol/kg, a significant decrease in R s( P < 0.001) was the factor responsible for the fall in PDA. Intra-arterial injection of porcine Gal (1 nmol/kg) produced a change in PDA similar to that of the same dose of tGal, but HR increased slightly. Pretreatments of trout with the cyclooxygenase inhibitors indomethacin and meclofenamate did not inhibit the vasodepressor effects of tGal. However, after intra-arterial injection of N G-nitro-l-arginine methyl ester, an inhibitor of nitric oxide synthase, 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 trout depending on whether its site of action is the brain or the peripheral circulation.