CENTRAL AND PERIPHERAL VASOPRESSIN INTERACT DIFFERENTLY WITH SYMPATHETIC NERVOUS-SYSTEM AND RENIN-ANGIOTENSIN SYSTEM IN RENAL HYPERTENSIVE RABBITS

This study was designed to elucidate how central and peripheral arginine vasopressin (AVP) interacts with the sympathetic nervous system and the renin-angiotensin system to maintain blood pressure in two-kidney, one-clip hypertensive rabbits. We recorded renal sympathetic nerve activity (RSNA) in the conscious state as an index of sympathetic nervous system function. The changes in mean arterial pressure, heart rate, and RSNA were recorded continuously for 60 minutes after intravenous administrations of captopril (2.5 mg/kg) and nicardipine (3.2 mug . kg-1 . min-1) in eight identical rabbits. Despite equivalent reductions in mean arterial pressure (10+/-1 mm Hg), the increase in RSNA was significantly larger with captopril than that with nicardipine, and the plasma concentration of AVP was elevated (from 100% to 255+/-24%) with captopril. Mean arterial pressure was reduced, and RSNA was increased by intravenous infusion of AVP antagonist d(CH2)5Tyr(Me)AVP (n=8), whereas vertebral artery infusion of the antagonist (n=6) did not change RSNA. During central and peripheral infusions of AVP antagonist, RSNA was exaggerated by blood pressure reduction with nicardipine as well as with captopril. Increases in RSNA induced by captopril and nicardipine were larger by central infusion of AVP antagonist than by intravenous infusion. The decrease in mean arterial pressure by captopril (30+/-4 mm Hg) in eight sinoaortic-denervated hypertensive rabbits was larger than that in hypertensive rabbits with intact baroreflex. These data suggest that compensatory activation of RSNA was revealed by central and peripheral attenuation of AVP and that the sympathetic nervous system became the most important mechanism for blood pressure maintenance in the absence of AVP. The interaction of AVP with the sympathetic nervous system may be independent of the state of the renin-angiotensin system, since the exaggeration of RSNA by AVP antagonist was qualitatively the same with nicardipine as with captopril. In conscious renal-hypertensive rabbits, AVP in the central nervous system played a substantial role when blood pressure was reduced, although it did not contribute to blood pressure maintenance in the basal condition.