Plasma atrial natriuretic factor and atrial wall stress in hypertensive and normotensive rabbits after pacing and volume expansion.

Atrial natriuretic factor (ANF) is present in high concentration in atria but in very low concentration in the ventricles. Under conditions of haemodynamic overload ventricular gene expression may become activated, but it is not clear if ventricular ANF can be released through a regulated or constitutive pathway. The purpose of this study was to determine whether basal and stimulated release of ANF are increased in perinephritic rabbits with mild hypertension. Six rabbits were rendered hypertensive by wrapping both kidneys in cellophane, and six sham-operated rabbits were used as controls. Eight weeks after renal wrapping, mean arterial pressure was approximately 20 mmHg higher in the experimental group. After anaesthesia, the renal-wrapped group had a higher vascular resistance. Right and left atrial wall stress was measured using sonomicrometry. Volume expansion by 30% of blood volume, using donor blood, caused a small increase in right and left atrial diastolic and systolic wall stress but did not significantly increase plasma ANF. Pacing the heart at 6 Hz caused increases in systolic but not diastolic wall stress and caused a significant increase in plasma ANF; the increase was larger after volume expansion. There were no significant differences between the responses of the experimental and control groups. It is concluded that mild hypertension, in the rabbit, does not lead to changes in atrial wall stress or either basal or stimulated release of ANF.