Alpha- and beta-adrenergic receptors of noradrenergic innervation modulate the lower limits of cerebral and cerebellar blood flow autoregulation in spontaneously hypertensive rats.

The effects of alpha- and beta-adrenergic receptors on the lower limits of cerebral (CBF) and cerebellar blood flow (CeBF) autoregulation were examined in spontaneously hypertensive rats. CBF and CeBF were measured during hemorrhagic hypotension in rats treated with adrenergic blockers, phenoxybenzamine (PBZ) or propranolol (PPL), using a hydrogen clearance method. The lower limits for CBF beyond which blood flow was decreased steeply were 72% of resting values in the control, 44 in the PBZ and 80 in the PPL group. Similar tendency was also observed for CeBF. In the control group, the reducing rates of mean arterial pressure (MAP) to decrease CBF by 15 and 30% of the resting values were 33% (58 mm Hg) of the resting MAP and 46% (80 mm Hg), respectively, and those to reduce CeBF to the same extent were 35% (61 mm Hg) and 52% (92 mm Hg), respectively. In the PBZ group, the respective reducing rates of MAP were 52% (71 mm Hg) and 65% (88 mm Hg), respectively, for CBF and 50% (68 mm Hg) and 65% (88 mm Hg), respectively, for CeBF. In contrast, in the PPL group, those rates were 22% (39 mm Hg) and 32% (56 mm Hg), respectively, for CBF, and 23% (40 mm Hg) and 30% (52 mm Hg), respectively, for CeBF, being significantly smaller than those in the control and the PBZ groups (p less than 0.01, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)