NONUNIFORM SYMPATHETIC-NERVE RESPONSES AFTER SUSTAINED ELEVATION IN ARTERIAL-PRESSURE

We tested the hypothesis that sustained increases in mean arterial pre ssure (MAP) produce nonuniform changes in regional sympathetic nerve d ischarges (SND) after the return of MAP to control levels. Renal, adre nal, splanchnic, and lumbar SND were recorded before, during, and afte r a 30-min elevation in MAP produced by phenylephrine (PE) infusion in alpha-chloralose-anesthetized spontaneously hypertensive (SH) rats. S ND remained reduced from control values after PE infusion, despite the return of MAP to control levels. Importantly, the duration of poststi mulus sympathoinhibition was significantly less in adrenal and splanch nic SND compared with renal and lumbar SND. In sinoaortic-denervated S H rats, SND remained at control levels during and after PE infusion. S imultaneous recordings of aortic depressor nerve (ADN) activity and SN D demonstrated that prolonged renal and lumbar sympathoinhibition occu rred even when ADN activity fell below control levels after PE infusio n. We conclude that poststimulus responses of efferent SND in SH rats are regionally nonuniform and that renal and lumbar sympathoinhibitory responses are not mediated solely by prolonged increases in afferent baroreceptor nerve activity.