ACUTE HYPOCAPNIA BLUNTS NATRIURETIC AND DIURETIC EFFECTS OF ATRIAL-NATRIURETIC-FACTOR IN RATS

Recent studies suggest that the autonomic nervous system, when activated by respiratory alkalosis, may attenuate the renal effects of atrial natriuretic factor (ANF). We evaluated the renal responses to infusion of ANF during acute exposure to hypocapnia in the presence or absence of the renal nerves in anesthetized rats. In this study, renal function during hypocapnia was assessed and was compared with renal function during normocapnia produced by normal ventilation as well as by hyperventilation. Rats were divided into three experimental groups (n = 8): 1) a normally ventilated normocapnic (NV-N) (control) group; 2) a hyperventilated normocapnic (HV-N) group; and 3) a hyperventilated hypocapnic (HV-H) group. The innervated (Inn) right kidney served as a control for the contralateral denervated (DNX) kidney. In Inn and DNX kidneys of HV-H rats, an infusion of ANF (12 mu g . kg(-1) . h(-1)) produced a smaller increase in urine flow rate (Delta V: 9.8 +/- 3.9 and 1.3 +/- 4.2 mu l/min) and in fractional Na excretion (Delta FE(Na): 1.35 +/- 0.52 and 0.73 +/- 0.58%) compared with NV-N rats (Delta V: 37.6 +/- 4.9 and 59.9 +/- 9.7 mu l/min; Delta FE(Na): 3.24 +/- 0.37 and 3.88 +/- 0.65%). No differences were observed in Delta V and Delta FE(Na) in Inn kidney between HV-H and HV-N groups; however, the attenuated natriuretic and diuretic responses to ANF in DNX kidney of HV-H rats were also observed in comparison with HV-N rats (Delta V: 27.4 +/- 4.3 mu l/min; Delta FE(Na): 2.94 +/- 0.48%). ANF induced natriuresis in DNX kidney to the same degree in NV-N and HV-N rats. In summary, we find that 1) hyperventilation in the absence of hypocapnia results in a blunted natriuresis to ANF infusion that is restored by renal denervation; and 2) hypocapnia attenuates the natriuretic and diuretic responses to ANF in the presence and absence of the renal nerves. These data suggest that the renal sympathetic nervous system does not modulate the renal actions of ANF during hypocapnia but plays an important role during normocapnia.