ROLE OF RENAL NERVES IN VOLUME EXPANSION IN CHRONIC HYPOXIC RATS

This work was designed to study the significance of the renal nerves i n chronic hypoxic (high-altitude; HA) rats after saline loading. Femal e Wistar rats (200-290 g) under sodium pentobarbital (40 mg/kg i.p.) a nesthesia were used in these experiments. Hypoxia was induced by placi ng the rats in an altitude chamber (5,500 m) for 4 weeks. Both the ren al efferent nervous activity (RENA) and the renal afferent nervous act ivity (RANA) were recorded simultaneously throughout the experimental period. It was found that the responses of RENA and RANA to an intrave nous saline infusion (10 ml, 10 min) were significantly different betw een the sea level (SL) control and HA rats. In SL rats, a depression o f RENA was found; the depressed RENA had not recovered 80 min after ce ssation of the saline infusion. In HA rats, an initially depressed REN A was also found; however, it returned to the control level within 10 min following the cessation of saline infusion. RANA enhanced twice a few minutes after saline loading in SL rats; however, the changes of R ANA in HA rats were not significant. In both groups of rats, whether r enally denervated or intact, the amount of excretory urine and sodium after saline loading was unchanged. The renal norepinephrine levels we re also measured by a high-pressure liquid chromatography system in bo th groups of rats, and it was found that the renal norepinephrine cont ent of the HA rats was significantly higher than in the SL rats. From these results, it was concluded that the renal nervous response to vol ume expansion is different in anesthetized chronic hypoxic rats; howev er, in spite of the impaired renal nervous activity, other regulatory systems still work successfully to maintain the renal function at a st eady state.