EFFECTS OF SEROTONIN, ADRENALINE AND OTHER VASOACTIVE DRUGS ON THE BRANCHIAL BLOOD-VESSELS OF THE ANTARCTIC FISH PAGOTHENIA-BORCHGREVINKI

Myography and an isolated, perfused gill arch preparation were used to investigate the actions of drugs on the gill vasculature of an Antarc tic teleost fish, Pagothenia borchgrevinki. Serotonin produced a dose- dependent vasoconstriction of the afferent branchial arteries, the gil l arch and the efferent branchial arteries, and was the most potent va soconstrictor tested. Acetylcholine, at concentrations exceeding I x 1 0(-6)M, vasoconstricted the gill arch, but had a negligible effect on the branchial arteries. The responses to adrenaline, with and without the beta-adrenergic blocking drug, sotalol and the effects of the beta -adrenergic agonist drug isoprenaline indicated the presence of both a lpha-adrenergic and beta-adrenergic receptors in the gill vasculature, with the vasoconstrictory action of the former predominating in the e fferent vasculature. Angiotensin II was without effect in either prepa ration. The results are a further demonstration of the dominance of va soconstrictory responses in the control of gill vascular resistance in P. borchgrevinki: which has been associated previously with the sub-z ero temperatures at which the animals are found.