Effects of β1-adrenergic receptor blockade on the cerebral microcirculation in the normal state and during global brain ischemia/reperfusion injury in rabbits

Background Although recent studies using experimental models of ischemic brain injury indicate that systemically-administered beta(1)-blockers have potential protective effects on the cerebrovascular system, the precise mechanisms remain unclear. In addition to their cardiovascular effects, water-soluble beta(1)-blockers can pass the blood-brain barrier and may exert their vascular action on cerebral microvessels. The aim of this study was to investigate the direct effects of beta(1)-blockade on the cerebral microvasculature both in the normal state and ischemia/reperfusion state using the cranial window method. Methods The closed cranial window method was used to visualize the cerebral microcirculation and changes in the pial arteriole diameter in adult male rabbits. In the first experiment, various concentrations of the selective beta(1)-blocker landiolol were administered into the cranial window to evaluate the dose-response. In the second experiment, the effect of beta(1)-blockade on the brain during ischemic/reperfusion injury was investigated. Global brain ischemia/reperfusion was induced by clamping the brachiocephalic, left common carotid, and left subclavian arteries for 15 min. Either landiolol or artificial cerebrospinal fluid was infused 5 min after initiation of ischemia through 120 min after reperfusion. Pial arteriole diameter and hemodynamic and physiological parameters were recorded before ischemia, during ischemia, and 5, 10, 20, 40, 60, 80, 100, and 120 min after reperfusion. Results In the first experiment, topical administration of landiolol at higher concentrations produced slight pial arteriole dilation (10(- 8) mol/L: 4.3 +/- 3.4%, 10(- 6) mol/L: 8.0 +/- 5.8%, 10(- 4) mol/L: 7.3 +/- 4.0%). In the second experiment, the topical administration of landiolol significantly dilated the pial arteriole diameters during ischemia/reperfusion injury (ischemia: 30.6 +/- 38.6%, 5 min: 47.3 +/- 42.2%, 10 min: 47.8 +/- 34.2%, 20 min: 38.0 +/- 39.0%). There were no statistical differences in hemodynamic and physiological parameters between the landiolol and control groups. Conclusions The blockade of beta(1)-adrenergic receptors induced significant vasodilation of pial arterioles during ischemia/reperfusion injury. By contrast, only a slight dilation of the arterioles was observed in the normal state, indicating that ischemic cerebral microvessels are more susceptible to the vasodilatory effect induced by selective blockade of beta(1)-adrenergic receptors than normal microvessels.