CONTROL OF ARTERIOVENOUS ANASTOMOSES IN RABBIT EAR MODEL OF DIGITAL PERFUSION

The arteriovenous anastomoses (AVA) of the cutaneous microcirculation of the hands and feet are fundamental determinants of thermoregulatory blood flow and may be involved in cold intolerance. These direct micr ovascular studies are an initial characterization of adrenergic recept or subtypes participating in control of AVA in the ears of anesthetize d male New Zealand White rabbits. Adrenergic alpha(1)-stimulation with phenylephrine produced AVA constriction, whereas terazosin (an alpha( 1)-antagonist) produced dilation and attenuated the responses to pheny lephrine. Adrenergic alpha(2)-stimulation with UK-14304 produced const riction of the AVA, whereas atipamezole (an alpha(2)-antagonist) produ ced dilation and attenuated the responses to UK-14304. When equimolar concentrations of antagonists were studied, the AVA dilation produced by alpha(2)-blockade was greater than that produced by alpha(1)-blocka de. Norepinephrine (a mixed alpha(1)- and alpha(2)-agonist) also produ ced vasoconstriction, which was attenuated by both prazosin (an alpha( 1)-antagonist) and atipamezole. In summary, 1) AVA contain a heterogen eous mixture of both aland alpha(2)-receptors, and 2) alpha(2)-recepto rs may have a greater influence than alpha(1)-receptors on overall ton e in AVA.