CHARACTERIZATION OF PLASMA AND TISSUE ATRIAL-NATRIURETIC-FACTOR DURING DEVELOPMENT OF MODERATE HIGH OUTPUT HEART-FAILURE IN THE RAT

Objective: The aims were (1) to characterise plasma and tissue atrial natriuretic factor (ANF) levels, haemodynamic variables, and renal function at different stages of moderate chronic high output heart failure in the rat; and (2) to assess the contribution of the atria and ventricles to plasma ANF levels. Methods: Plasma and tissue ANF levels, haemodynamics, and renal function were evaluated at 1, 2, 4, 8, and 16 weeks after the development of aorto-caval shunts. Sham operated animals served as controls at identical time points. Male Sprague-Dawley rats weighing 225-275 g were used in all experiments. Results: Mean arterial blood pressure was lower and right atrial pressure was higer in the aorto-caval shunt groups than in sham operated controls at all time periods. Left ventricular end diastolic pressure was increased significantly in aorto-caval shunt rats at 1, 2, and 4 weeks when compared with their control counterparts. Plasma COOH terminal and NH2 terminal ANF concentrations were increased significantly in aorto-caval shunt animals. Plasma ANF was positively correlated with right atrial pressure and left ventricular end diastolic pressure in aorto-caval shunt rats but not in sham operated controls. Aorto-caval shunt animals also developed marked cardiac hypertrophy with decreased atrial ANF concentration, but not content, and increased ventricular ANF concentration and content. Despite high plasma ANF concentrations, aorto-caval shunt rats had a lower packed cell volume at all observed periods and reduced urinary sodium excretion and urinary volume at 1 and 2 weeks, with trends to a reduction at 4, 8, and 16 weeks. Body weight was higher in aorto-caval shunt animals at 16 weeks than in sham operated controls. Conclusions: (1) Chronically increased cardiac filling pressure stimulated not only ANF release but also ANF synthesis in each cardiac chamber, which in turn contributed to raised plasma ANF concentrations in aorto-caval shunt rats; (2) an attenuated renal response to endogenous ANF and sodium and water retention were apparent in A-C shunt rats. Activation of neurohormonal vasoconstrictor systems and gradually decreased plasma ANF concentrations may contribute to sodium and water retention at different stages of this experimental model of heart failure.