Long-term effects of superior cervical ganglionectomy on cortical blood flow of non-anesthetized rabbits in resting and hypertensive conditions.

The long-term effects of sympathectomy on cerebral cortical blood flow (CBF) were studied in the conscious rabbit. The quantitative, repeated measurements of blood flow were made by determination of helium clearance by mass spectrometry and were obtained simultaneously with measurements of local tissue pO2 and pCO2. Eight to 10 weeks after unilateral sympathectomy, resting blood flow in the homolateral cortex was decreased by a mean of 17% compared to the heterolateral cortex. In two animals in which blood flow was recorded both before and after the sympathectomy, the same phenomenon was observed from 8 to 30 days after the operation. The response to i.v. infusion of noradrenaline was identical in both hemispheres: doses inducing a 40% rise in blood pressure did not significantly modify CBF. The responses to angiotensin II-induced hypertension were also identical. Histochemical verifications demonstrated the effectiveness of the denervation in the pial arteries and the intraparenchymal arteries in the region studied. Thus the decrease in CBF induced by chronic sympathectomy cannot be attributed to the development of hypersensitivity to catecholamines. This decrease remained stable whatever the value of resting flow and was maintained under anesthesia. It is concluded that, as in the peripheral circulation, chronic sympathectomy affects the equilibrium of the vascular smooth muscle fibers, but that circulating amines play no compensatory role in the cerebral circulation because of the blood-brain barrier.