Vasoactive properties of dihomo-gamma-linolenic acid and series one prostaglandins in a freshwater teleost, Channa maculata

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 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 (Rs) 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 Rs (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 NG-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.

A prostaglandin, not NO, mediates endothelium-dependent dilation in ventral aorta of shark (Squalus acanthias)

In mammals, the vascular endothelium releases a variety of paracrine factors, including the vasodilatory prostaglandin (PG)I2 and nitric oxide (NO), which is generally accepted as the major endothelium-derived relaxing factor (EDRF) in mammals. Current evidence for the vascular NO-EDRF system in fishes is contradictory. In addition, the role of PGs in the control of fish vascular tension is also unclear. We have utilized isolated rings of the ventral aorta of the spiny dogfish shark to examine the ability of various components of the NO system to dilate this vessel. Neither the NO precursor L-arginine, the NO donor sodium nitroprusside, nor NO itself dilated the rings. The Ca2+ ionophore A-23187 did produce an endothelium-dependent dilation that was not inhibited by the NO synthase inhibitor NG-nitro-L-arginine methyl ester but was inhibited by the cyclooxygenase inhibitor indomethacin, suggesting that PGs are involved. PGE1 and carbaprostacyclin, but not PGI2, produced concentration-dependent dilation, and intact aortic rings secreted five times as much PGI2 as PGE in both the unstimulated state and after stimulation with A-23187. Our data suggest strongly that a PG, most probably PGI2, is the EDRF in the ventral aorta of this shark species.