Renal sympathetic nerve activity and renal responses during head-up tilt in conscious dogs

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Abstract
Renal sympathetic nerve activity (RSNA) was measured in conjunction with functional responses of the kidney during head-up tilt in eight conscious female dogs. A 40.degree. head-up tilt resulted in a sustained increase in RSNA by 53 .+-. 10% (P < 0.05) relative to control level. Urine flow and osmolal and sodium excretion decreased significantly to a nadir of -55 .+-. 4, -42 .+-. 7, and -59 .+-. 10%, respectively, whereas free water clearance and creatinine clearance did not change significantly during head-up tilt. The systemic arterial pressure (at kidney level) increased significantly from 110 .+-. 4 to 129 .+-. 6 mmHg, and central venous pressure decreased significantly from -0.7 .+-. 0.5 to -7.6 .+-. 0.6 mmHg. The chronic bilateral renal denervation, which was performed 2-4 wk before the experiment, abolished both the antidiuretic and antinatriuretic responses to head-up tilt. These results indicate that an increase in RSNA plays a significant role in the decrease in urine flow and sodium excretion induced by 40.degree. head-up tilt in conscious dogs.