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

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 hours or 2 or 5 weeks before the study. Wall-to-lumen ratio of cerebral arteries was determined with freeze substitution technique. Basal blood pressures were 87 +/- 1 mm Hg (mean +/- SEM) at 4 weeks of age, 105 +/- 2 at 6 weeks, and 126 +/- 3 at 9 weeks, although resting cerebral blood flow was unchanged. Initially, cerebral blood flow remained relatively constant when the blood pressure was raised by intravenous 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 less than 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 weeks and 0.130 +/- 0.005 at 9 weeks. These differences were not significant, nor did sympathetic denervation alter the ratio. These results indicate that (1) the upward shift of the autoregulation is closely related to a rise in the basal blood pressure, (2) acute interruption of sympathetic nerves modulates the autoregulatory range, and (3) adaptation of cerebral blood flow autoregulation to early developmental hypertension may be attributed to factors other than vascular smooth muscle hypertrophy.