Plasma atrial natriuretic peptide and haemodynamics in conscious normotensive and spontaneously hypertensive rats after acute blood volume expansion.

The atrial natriuretic peptides (ANP) are a family of newly discovered peptides which are released from atrial tissue and have potent diuretic/natriuretic, vasodilating and aldosterone inhibitory properties. Plasma concentration of ANP was measured and related to haemodynamic changes after acute blood volume expansion (10 and 20%) in normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). Acute blood volume expansion resulted in an increase in central (CBV) and peripheral blood volume (PBV), central venous pressure (CVP), stroke volume (SV) and cardiac output (CO), while total peripheral resistance (TPR) and heart rate (HR) were decreased. Mean arterial pressure (MAP) was unchanged. There were larger increases in CBV, CVP and CO in SHR than in WKY rats. In contrast, the increase in PBV and the decrease in HR were more marked in the WKY rats. Basal plasma ANP concentrations were similar in both groups. Blood volume expansion caused a linear increase in plasma ANP in the WKY rats, while the increase in plasma ANP concentration was attenuated in the SHR. It is concluded that acute blood volume expansion is more centralized in the SHR than in the WKY rats. Interestingly, the ANP release in response to blood volume expansion seems to be attenuated in SHR compared with WKY rats, as maximal plasma ANP concentrations were found at 10% volume load.