Natriuretic peptides and the control of catecholamine release in two freshwater teleost and a marine elasmobranch fish

Experiments were carried out in sifts and ill vivo to investigate the relat ionship between natriuretic peptides (NPs) and humoral catecholamine secret ion in the American eel (Anguilla rostrata), rainbow trout (Oncorhynchus my kiss) and spiny dogfish (Squalus acanthias). III situ perfusion of the chro maffin tissue of A. rostrata with homologous atrial NP (ANP; 10(-9) mol 1(- 1)) or ventricular NP (VNP; 10(-9) mol 1(-1)), or O. mykiss with either rat ANP (10(-9) mol 1(-1)), eel VNP (10(-9) mol 1(-1)), or trout VNP (10(-9) m ol 1(-1)), did not significantly affect basal or carbachol-elicited (10(-5) mol kg(-1)) catecholamine release. Bolus injections of homologous ANP (10( -9) mol kg(-1)) or VNP (10(-9) mol kg(-1)) in A. rostrata in vivo elicited a rapid and prolonged reduction in arterial blood pressure and an increase in heart rate (f(H)); circulating plasma catecholamine levels were unaffect ed. In O. mykiss, bolus injections of rat ANP (10(-9) mol kg(-1)) or trout VNP (10(-9) mol kg(-1)) elicited a significant bi-phasic presser-depressor response and a marked increase in SH. Neither the acute presser or the long er-term depressor effects of NPs in O. mykiss were associated with any chan ge in circulating plasma catecholamine levels. In S. acanthias. bolus injec tions of homologous C-type natriuretic peptide (CNP; 10(-9) mol kg(-1)) eli cited a bi-phasic presser-depressor response, an increase in systemic resis tance, a decrease in cardiac output and stroke volume, but no change in f(H ) Plasma noradrenaline levels were elevated 15-fold after CNP injection whi le circulating adrenaline levels remained unchanged. These results show tha t NPs of systemic origin do not directly or indirectly affect basal or chol inergically-mediated catecholamine release in A. rostrata and O. mykiss and that the initial presser response to NP's in trout cannot be attributed to an elevation of circulating catecholamines. Conversely, CNP appears to be a potent secretagogue (direct or indirect) of noradrenaline release in S. a canthias and thus there is likely to be a significant humoral adrenergic co mponent to the cardiovascular effects of NPs in this species.