Inhibition of renal sympathetic nerve traffic from cardiac receptors in normotensive and spontaneously hypertensive rats

The reflex inhibition of the sympathetic outflow to the kidney was examined during volume load with horse plasma in 6 normotensive rats (NCR) and 6 spontaneously hypertensive rats (SHR). The rats were anesthetized with chloralose and urethane. The arterial baroreceptors were denervated. The renal nervous inhibition was mediated via the vagal nerves and was mainly due to activation of receptors in the left side of the heart. The average thresholds in mean left atrial pressure for renal nervous inhibition was 5.4 mmHg for NCR and 9.2 mmHg for SHR indicating a clear resetting of the reflex arch in the hypertensive animal: The reason is probably a decreased distensibility of the wall of the left atrium due to a chronic elevation of left atrial pressure. This resetting of the atrial receptors in the hypertensive animals is probably of importance to allow an adequate filling pressure of the hypertrophied left ventricle and might also be of importance for the reflex neural control of renal function in these animals.