Specialization in beta-1 and beta-2 adrenoceptor distribution in veins of the rabbit face: relationship to myogenic tone and sympathetic nerve innervation

Abstract

Studies were performed on several superficial veins from the rabbit face to examine the relationship between beta adrenoceptor subtype distribution, intrinsic myogenic tone and sympathetic nerve innervation. Experiments using selective beta adrenoceptor agonists and antagonists indicate that the dorsal nasal and angularis oculi veins possess a homogeneous population of beta-2 adrenoceptors. Sympathetic nerve stimulation in these segments results only in contraction mediated through postjunctional alpha adrenoceptors. These segments are devoid of intrinsic myogenic tone. In the facial vein, of which both veins are tributaries, both beta-1 and beta-2 adrenoceptors are found. Studies with the beta-1 adrenoceptor antagonist, betaxolol, and beta-2 adrenoceptor antagonist, ICI 118,551, indicate that the prominent relaxation observed in this tissue to sympathetic nerve stimulation is mediated through postjunctional beta-1 adrenoceptors. At physiological temperatures, the facial vein possesses a marked intrinsic myogenic tone that is inhibited by this beta-1 adrenoceptor-mediated sympathetic activity. Considering the anatomical relationship between these vessels and the unique association between beta adrenoceptor subtype, intrinsic myogenic tone and sympathetic innervation, it is possible that facial blood redistribution in the rabbit can be markedly affected by sympathetic nerve stimulation. Such a process could have an important role in cranial thermoregulation.