Sustained increases in aortic depressor nerve activity after acute elevation in arterial pressure.

OBJECTIVE

Despite the return of mean arterial pressure (MAP) to control levels, aortic depressor nerve activity remains elevated from control levels after sustained phenylephrine-induced increases in MAP in spontaneously hypertensive rats (SHR) (Kenney MJ, Morgan DA, Mark AL: Am J Physiol 1990, 258:H1476-H1481). This suggests that sustained increases in arterial pressure may produce prolonged pressure-induced changes in afferent baroreceptor nerve activity in SHR. However, because phenylephrine can exert an excitatory effect on the aortic arch baroreceptors, the increase in aortic depressor nerve activity might have resulted from a persistent direct effect of phenylephrine. The aim of the current study was to determine whether elevations in MAP induced by aortic occlusion produce increases in aortic depressor nerve activity which persist after the return of MAP to control levels.

METHODS

MAP and aortic depressor nerve activity were recorded before, during and after sustained (15-30 min) periods of aortic occlusion in SHR with intact adrenal glands (n = 18) and in adrenalectomized SHR (n = 10). Control experiments were completed in which the same variables were recorded before, during and after sham aortic occlusion in intact (n = 8) and adrenalectomized (n = 8) SHR.

RESULTS

Aortic occlusion increased MAP and aortic depressor nerve activity significantly from control levels. After aortic occlusion and the return of MAP to control levels, aortic depressor nerve activity remained significantly increased in 15 experiments, whereas in three experiments aortic depressor nerve activity was reduced. Aortic depressor nerve activity was increased significantly from control levels after aortic occlusion in adrenalectomized rats. Aortic depressor nerve activity remained unchanged from control levels after sham aortic occlusion in intact and adrenalectomized SHR.

CONCLUSIONS

Sustained elevations in MAP induce increases in aortic depressor nerve activity in intact and adrenalectomized SHR, which persist after the return of MAP to control levels. These observations suggest that sustained increases in arterial pressure may produce prolonged pressure-induced changes in afferent baroreceptor nerve activity in SHR.