The trophic influence of sympathetic nerves on rabbit ear vasculature is absent in coarctation hypertension.

We recently investigated the effect of chronic sympathetic denervation on the intact ear vasculature of normotensive rabbits and found an important long-term or trophic influence of sympathetic nerves on vascular structural properties. To determine the effect of coarctation hypertension on this relationship, we studied 12 wk old rabbits 8 wk after a unilateral superior cervical ganglionectomy and induction of coarctation hypertension. Successful denervation was demonstrated by a shift of the norepinephrine dose-response curve to the left in the denervated ears as well as a decreased threshold (p less than 0.05), an increased slope (p less than 0.02) and a decreased M50 (p less than 0.01) (the concentration of norepinephrine that produced 50% of the maximal vasoconstrictor response to norepinephrine). The flow-pressure curves of the denervated compared to the innervated ears at maximal dilation (used as a functional assessment of structural alterations) did not differ. The maximal pressor responses to vasopressin and barium chloride (used as an indication of smooth muscle mass) also did not differ. These results suggest that sympathetic innervation does not importantly influence blood vessel structure during coarctation hypertension in contrast to the changes we previously found in normotensive rabbits.