Effect of salbutamol on regional cerebral oxygen consumption, flow and capillary and arteriolar perfusion

This study quantitatively determined the effect of salbutamol (1 microgram kg-1), a beta 2-adrenoceptor agonist, on the perfusion of the brain microvasculature, cerebral O2 consumption, O2 extraction and cerebral blood flow (CBF) in conscious rat. Indices of arteriolar and capillary structure and the percentage of the total cerebral microvascular volume/mm3 (% Vv) and number/mm2 (% Na) perfused were determined. These parameters were obtained from the perfused microvessels, identified by the presence of fluorescein isothiocyanate (FITC) - dextran, and compared with the entire microvascular bed, identified by alkaline phosphatase stain. Cerebral O2 extraction was determined microspectrophotometrically and CBF was determined using 14[C]iodoantipyrine in another group of salbutamol-treated rats. The acute administration of salbutamol did not alter systemic arterial blood pressure. Significant tachycardia was noted in the salbutamol-treated rats. Salbutamol resulted in a significant increase in the percentage of arterioles perfused. Average percentage perfused capillary Na increased significantly from 46 +/- 2 to 88 +/- 1%; %Vv increased significantly and similarly in the arteriolar and capillary beds in all brain regions examined. Average cerebral O2 consumption increased significantly from 3.0 +/- 0.2 to 7.4 +/- 0.7 ml O2 min-1 100 g-1 with salbutamol, while cerebral O2 extraction was unchanged. Average CBF increased from 50 +/- 2 to 142 +/- 9 ml min-1 100 g-1 with salbutamol. Salbutamol may increase the perfusion of the regional microvasculature by increasing cerebral O2 consumption (metabolic vasodilation) and CBF and microvascular perfusion secondarily, although a direct effect of salbutamol on cerebral microvessels cannot be ruled out.