Head-up tilt in the nonhuman primate. Effects of renal denervation.

Experiments were performed to determine the role of the renal nerves in mediating the antinatriuresis of head-up tilt in the nonhuman primate. Male Macaca fascicularis monkeys underwent chronic bilateral renal denervation or sham surgery and were allowed a 1- to 2-week recovery period. After that time, each animal was anesthetized with sodium pentobarbital and subjected to 40 min of 35 degrees head-up tilt. Renal perfusion pressure was maintained constant throughout the experiment. Tilt caused significant decreases in urine flow, sodium excretion and osmolar clearance and increases in urine osmolality in both groups. Creatinine and para-aminohippurate clearances decreased in the sham-operated animals but were unchanged in the denervated animals. Although the pattern of the renal excretory responses showed some group differences in that a significant antidiuresis and antinatriuresis occurred after 10 min of tilt in the sham-operated group but not until 20 min in the denervated group, the magnitudes of these excretory responses were similar in both groups throughout the entire tilt procedure. These results suggest that, in this species, the renal nerves are not necessary for eliciting the overall antinatriuretic response to orthostasis but may have some minor involvement in the onset of the response.