ADRENERGIC CONTROL MECHANISMS OF BLOOD-FLOW IN A VASCULARIZED CANINE TIBIAL ALLOGRAFT

A vascularized canine tibial allograft was used to study the alpha-adr enoreceptor subtypes of the microcirculation of bone. Bone transplanta tion was performed on six dogs, and the bone blood flow was estimated with the use of serial injections of radiolabeled 15 mum microspheres. After microvascular anastomosis, the mean cortical blood flow in the allografted tibia was 3.6 +/- 2.1 ml/100 g/min. Alpha1-adrenoreceptor blockade, with prazosin, caused an increase in normalized blood flow i n five allografts and a slight decrease in one allograft. The mean inc rease was 32 +/- 48%, but this was not statistically significant (p < 0.2). The addition of an alpha2-adrenoreceptor blockade, with rauwolsz in, resulted in a significant increase (132 +/- 88%) in normalized blo od flow in all allografts (p < 0.02). This ex vivo experiment confirms that both alpha1 and alpha2 adrenergic mechanisms play a role in cont rolling bone blood flow in centrally denervated allografts.