Cardiovascular control via angiotensin II and circulating catecholamines in the spiny dogfish, Squalus acanthias

The contributions of circulating angiotensin II (Ang II) and catecholamines to cardiovascular control in the spiny dogfish were investigated by monitoring the effects of exogenous and endogenous dogfish [Asn1, Pro3, Ile5]-Ang II (dfAng II) on plasma catecholamine levels and blood pressure regulation. Bolus intravenous injections of dfAng II (30-1200 pmol kg-1) elicited dose-dependent increases in plasma adrenaline and noradrenaline concentrations, caudal artery pressure (PCA), and systemic vascular resistance (RS), and a decrease in cardiac output (Q). Similar injections of Ang II in dogfish pre-treated with the alpha-adrenoceptor antagonist yohimbine (4 mg kg-1) also elicited dose-dependent increases in plasma catecholamine levels yet the cardiovascular effects were abolished. Dogfish treated with yohimbine were hypotensive and had elevated levels of plasma Ang II and catecholamines. Intravenous injection of the smooth muscle relaxant papaverine (10 mg kg-1) elicited a transient decrease in PCA and RS, and increases in plasma Ang II and catecholamine levels. In dogfish first treated with lisinopril (10(-4) mol kg-1), an angiotensin converting enzyme inhibitor, papaverine treatment caused a more prolonged and greater decrease in PCA and RS, an attenuated increase in plasma catecholamines, and no change in plasma Ang II. By itself, lisinopril treatment had little effect on PCA, and no effect on RS, plasma Ang II or catecholamines. In yohimbine-treated dogfish, papaverine treatment elicited marked decreases in PCA, RS, and Q, and increases in plasma Ang II and catecholamines. Among the three papaverine treatments, there was a positive linear relationship between plasma Ang II and catecholamine concentrations, and the cardiovascular and hormonal changes were most pronounced in the yohimbine + papaverine treatment. Therefore, under resting normotensive conditions, while Ang II does not appear to be involved in cardiovascular control, catecholamines play an important role. However, during a hypotensive stress elicited by vascular smooth muscle relaxation. Ang II indirectly contributes to cardiovascular control by dose-dependently stimulating catecholamine release.