Role of renal nerves in volume expansion in chronic hypoxic rats

This work was designed to study the significance of the renal nerves in chronic hypoxic (high-altitude; HA) rats after saline loading. Female Wistar rats (200-290 g) under sodium pentobarbital (40 mg/kg i.p.) anesthesia were used in these experiments. Hypoxia was induced by placing the rats in an altitude chamber (5,500 m) for 4 weeks. Both the renal efferent nervous activity (RENA) and the renal afferent nervous activity (RANA) were recorded simultaneously throughout the experimental period. It was found that the responses of RENA and RANA to an intravenous saline infusion (10 ml, 10 min) were significantly different between the sea level (SL) control and HA rats. In SL rats, a depression of RENA was found; the depressed RENA had not recovered 80 min after cessation of the saline infusion. In HA rats, an initially depressed RENA was also found; however, it returned to the control level within 10 min following the cessation of saline infusion. In HA enhanced twice a few minutes after saline loading in SL rats; however, the changes of RANA in HA rats were not significant. In both groups of rats, whether renally denervated or intact, the amount of excretory urine and sodium after saline loading was unchanged. The renal norepinephrine levels were also measured by a high-pressure liquid chromatography system in both groups of rats, and it was found that the renal norepinephrine content of the HA rats was significantly higher than in the SL rats. From these results, it was concluded that the renal nervous response to volume expansion is different in anesthetized chronic hypoxic rats; however, in spite of the impaired renal nervous activity, other regulatory systems still work successfully to maintain the renal function at a steady state.