The adrenergic responses of isolated saline-perfused prebranchial arteries and gills of the elasmobranch Squalus acanthias

Cardiovascular and vasoconstrictive actions of skate bradykinin in the little skate, Leucoraja erinacea (Elasmobranchii)

The vasoconstrictive and cardiovascular actions of a recently identified bradykinin (BK)-related peptide (Gly-Ile-Thr-Ser-Trp-Leu-Pro-Phe) from the little skate, Leucoraja erinacea were examined in the unanesthetised little skate. Intra-arterial administration of a skate BK (0.1-1 nmolkg(-1)) produced a hypertensive response with a rise in blood pressure reaching a maximum elevation of 28.7±4.8% over baseline (P<0.05, n=8) that was sustained for at least 12 min following administration of a 1 and 0.3 nmolkg(-1) dose of skate BK. Further, in vivo administration of 1 nmolkg(-1) skate BK induced a significant delayed increase in stroke volume (reaching a maximum of 54.4±14.7% above baseline) without significant effect on either cardiac output or heart rate. In vitro, skate BK constricted the 1st branchial, mesenteric (EC(50) 2.7×10(-9)M) and coeliac (EC(50) 3.1×10(-9)M) arterial preparations of the skate. In contrast, skate [Arg(9)]BK, the mammalian B(1) receptor agonist des-[Arg(9)]BK, and the mammalian B(2) receptor antagonist HOE-140 failed to induce vasoconstriction in these isolated arterial preparations. The vasoconstrictor actions of skate BK in the isolated mesenteric, coeliac and branchial arterial preparations were significantly inhibited when co-administrated with esculetin and phentolamine. Indomethacin also inhibited the vasoconstrictor actions of skate BK in the isolated branchial artery. We conclude that, as in mammals and teleost fish, multiple pathways involving at least the alpha adrenergic and leukotriene synthesis pathway are involved in mediating the vasoconstrictive actions of BK in vascular smooth muscle of the little skate.

Adrenoceptor types in the respiratory vasculature of the salamander gill

Adrenoreceptor types were determined in the branchial respiratory vasculature of the neotenic tiger salamander, Ambystoma tigrinum. Phenoxybenzamine antagonized increases in branchial vascular resistance caused by both epinephrine and norepinephrine. Propranolol antagonized both epinephrine- and norepinephrine-induced dilation of this vascular bed. Isoproterenol produced solely vasodilation, phenylephrine had no effect, and methoxamine caused constriction only at a very high dose. It is concluded that alpha-adrenoceptors mediate the catecholamine-induced vasoconstriction, and beta-adrenoceptors the catecholamine-induced vasodilation in the respiratory circulation of the gill.