Mechanisms for preserved cerebrovascular autoregulation during hypertension in rats after sinoaortic denervation.

1. Cerebral blood flow (CBF) and cerebrovascular resistance (CVR) autoregulate to higher levels of arterial pressure (AP) in rats after sinoaortic denervation (SAD) than in intact rats. 2. Potential mechanisms for this phenomenon were studied by monitoring CBF by laser flowmetry while increasing AP in rats after: (i) SAD; (ii) SAD plus bilateral removal of the superior cervical ganglia; (iii) SAD plus interruption of all renal vessels and nerves (renal isolation); (iv) SAD plus sympathectomy and renal isolation; and (v) intravenous treatment with the nitric oxide synthase inhibitor L-nitroarginine (LNA). 3. Compared to intact control rats autoregulation persisted to higher absolute levels of AP in SAD rats with isolation of the kidneys and resistance did not fall significantly below that in rats with SAD alone. 4. Effects of SAD on autoregulation were not altered by combining renal isolation with an interruption of sympathetics. 5. LNA did not affect the baroreflex but blocked a breakthrough of autoregulation even at a maximal mean AP (MAP) of 189 +/- 2 mmHg. 6. Breakthrough occurred in animals pretreated with LNA plus L-arginine but not in animals given LNA plus D-arginine. 7. These data are consistent with a role of the baroreflex in the expression of breakthrough and suggest that breakthrough may result from release of nitric oxide or a nitric oxide donor.