Differential haemodynamic effects of atrial natriuretic peptide (ANP) in normotensive and spontaneously hypertensive rats

Central haemodynamic parameters and cardiac performance were measured in conscious spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto (WKY) control rats after a 10-min infusion of rat ANP (103-125), 1 micrograms kg-1 min-1. Mean Arterial blood pressure (MAP) decreased by approximately 10% in both groups of rats. Heart rate (HR) increased slightly in both strains during the infusion. In the normotensive group the fall in MAP was due to a reduction in cardiac output (CO) while in the SHR there was a decrease in CO as well as in total peripheral resistance (TPR). The ANP infusion also reduced central blood volume (CBV) and stroke volume (SV) in both groups of rats. The reduction in CBV and CO was significantly more pronounced in the WKY strain. Left ventricular end diastolic pressure (LVEDP) and cardiac contractility (dP/dt) did not change while central venous pressure (CVP) was slightly decreased in the WKY group as a result of the ANP infusion. We conclude that ANP reduces MAP in normotensive animals by a reduction in CO. In the SHR a reduction in TPR also contributes to the fall in MAP. Atrial natriuretic peptide did not exert any negative inotropic effects, but the reduction of CO was due to an increased venous compliance.