Effect of induced hypertension on experimentally-induced cerebral arterial spasm.

Ten adult cats were anesthetized and ventilated by respirator. After the basilar artery was exposed transclivally and visualized with an operative microscope, mean arterial blood pressure (MABP) was raised gradually by intravenous drip infusion of norepinephrine (5-20 micrograms/kg) or angiotensin-II-amide (0.3-1.0 micrograms/kg). At various blood pressures, microphotographs were taken. There was no appreciable change in vessel diameter at a MABP ranging from 78 to 191 mmHg. The blood pressure was allowed to return to the initial baseline level. Arterial spasm was produced by the topical application of 0.2 M calcium gluconate, which decreased the arterial diameter by 13 to 58 percent for more than 60 min. Blood pressure was increased again after the production of the arterial spasm. Significant increases in the diameter of the arteries were produced by the drug-induced hypertension at levels of MABP ranging from 82 to 192 mmHg. The maximum arterial dilations ranged from 123 to 208 percent of the untreated control. The degree of dilation of the arteries almost paralleled the rise in MABP. Norepinephrine and angiotensin-II had a similar effect on both the blood pressure and the arterial diameter. Induced hypertension would be expected to improve blood flow parameters in the case of spastic cerebral arteries.