THE ROLE OF ENDOGENOUS ANGIOTENSIN-II IN ANTIDIURESIS AND NOREPINEPHRINE OVERFLOW INDUCED BY STIMULATION OF RENAL NERVES IN ANESTHETIZED DOGS

We examined the possible involvement of endogenous angiotensin II (ANG II) in norepinephrine (NE) overflow and antidiuresis induced by renal nerve stimulation (RNS). RNS at a frequency of 0.5-2.0 Hz, which did not influence renal hemodynamics, produced significant reductions in urine flow and urinary excretion of sodium, and elevations in NE secretion rate (NESR) and renin secretion rate (RSR). Intrarenal arterial (i.r.a.) infusion of phentolamine (10-mu-g/kg/min) abolished the RNS-induced antidiuresis. In dogs receiving captopril (15 mu-g/kg/min i.v.), RNS-induced antidiuresis and increase in NESR were significantly attenuated. The i.r.a. administration of propranolol at 5-mu-g/kg/min, a dose that inhibited completely the RNS-induced increase in RSR, did not influence the alterations in NESR and urine formation in response to RNS. During ANG II infusion (1 ng/kg/min i.r.a.), RNS produced a reduction in urine formation and an increase in NESR, at a magnitude similar to that seen without ANG II infusion. These results suggest that RNS at a low frequency increased the NESR and RSR without affecting renal hemodynamics and that the antidiuretic effect was probably produced via the activation of postsynaptic alpha-adrenoceptors, but not via the ANG II receptor, located on the renal tubules. The release of NE appears to be modulated by ANG II through the activation of a facilitatory prejunctional mechanism, which is maximally stimulated by endogenously and locally generated basal levels of ANG II.