Effect of prazosin on microvascular perfusion during middle cerebral artery ligation in the rat

The purpose of this study was to evaluate the effects of prazosin, an α₁-adrenoceptor antagonist, on morphometric indexes of the total and perfused cerebral microvascular bed 1 hour after middle cerebral artery (MCA) ligation in pentobarbital-anesthetized rats. We hypothesized that this agent would prevent catecholamine-induced vasoconstriction in the ischemic brain. Cerebral blood flow (CBF) was determined with ¹⁴C-iodoantipyrine, and the perfused microvascular bed was visualized using fluorescein isothiocyanate-dextran. MCA occlusion did not alter systemic hemodynamic or blood gas parameters. CBF averaged 29 ± 15 (mean ± SD) ml/min/100 g in the MCA-ligated cortex and 49 ± 18 in the other examined brain regions. Prazosin did not significantly alter these CBF values, averaging 26 ± 14 and 48 ± 10, respectively. There were no significant regional differences in total capillaries/mm² in either group. The percent of the capillaries/mm² perfused (51 ± 6%) was similar in the two groups in all examined regions except the ischemic cortex. In the MCA-ligated cortex, 22 ± 8% of the capillary volume was perfused in comparison with 49 ± 8% in the prazosin-treated group. Prazosin-treated rats had an increased percentage of their microvasculature perfused despite a similarly reduced CBF. Prazosin appeared to reduce diffusion distances in the ischemic cortex. This might be due to its α₁-adrenoceptor blocking activity.