Adrenergic control mechanisms of blood flow in a vascularized canine tibial allograft

A vascularized canine tibial allograft was used to study the alpha-adrenoreceptor subtypes of the microcirculation of bone. Bone transplantation was performed on six dogs, and the bone blood flow was estimated with the use of serial injections of radiolabeled 15 microns microspheres. After microvascular anastomosis, the mean cortical blood flow in the allografted tibia was 3.6 +/- 2.1 ml/100 g/min. Alpha 1-adrenoreceptor blockade, with prazosin, caused an increase in normalized blood flow in five allografts and a slight decrease in one allograft. The mean increase was 32 +/- 48%, but this was not statistically significant (p < 0.2). The addition of an alpha 2-adrenoreceptor blockade, with rauwolszin, resulted in a significant increase (132 +/- 88%) in normalized blood flow in all allografts (p < 0.02). This ex vivo experiment confirms that both alpha 1 and alpha 2 adrenergic mechanisms play a role in controlling bone blood flow in centrally denervated allografts.