Background: Although recent studies using experimental models of ischemic brain injury indicate that systemically-administered β1-blockers have potential protective effects on the cerebrovascular system, the precise mechanisms remain unclear. In addition to their cardiovascular effects, water-soluble β1-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 β1-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 β1-blocker landiolol were administered into the cranial window to evaluate the dose-response. In the second experiment, the effect of β1-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 β1-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 β1-adrenergic receptors than normal microvessels.
Keywords: Cerebral microvasculature; Ischemia/reperfusion injury; Vasodilation; β1-adrenergic receptor blockade.