Cerebral autoregulation in young spontaneously hypertensive rats. Effect of sympathetic denervation.

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Abstract
Autoregulation of cerebral blood flow was studied with the hydrogen clearance method during development of hypertension in young spontaneously hypertensive rats. To examine the influence of sympathetic nerves on autoregulatory range, the unilateral superior cervical ganglion was removed 2 h or 2 or 5 wk before the study. Wall-to-lumen ratio of cerebral arteries was determined with freeze substitution technique. Basal blood pressure were 87 .+-. 1 mm Hg (mean .+-. SEM [standard error of the mean]) at 4 wk of age, 105 .+-. 2 at 6 wk, and 126 .+-. 3 at 9 wk, although resting cerebral blood flow was unchanged. Initially, cerebral blood flow remained relatively constant when the blood pressure was raised by i.v. infusion of phenylephrine. The upper limits of cerebral blood flow autoregulation in these groups were 110 .+-. 4 mm Hg, 126 .+-. 7, and 159 .+-. 6, respectively. Acute ganglionectomy significantly lowered the upper limits (P < 0.05), but chronic denervation did not affect the autoregulatory range. The wall-to-lumen ratios of cerebral arteries were 0.136 .+-. 0.007 at 4 wk and 0.130 .+-. 0.005 at 9 wk. These differences were not significant, nor did sympathetic denervation alter the ratio. The upward shift of the autoregulation is closely related to a rise in the basal blood pressure, acute interruption of sympathetic nerves modulates the autoregulatory range and adaptation of cerebral blood flow autoregulation to early developmental hypertension may be attributed to factors other than vascular smooth muscle hypertrophy.