Direct augmentation by cyclosporin A of the vascular contractile response to nerve stimulation

Cyclosporin A administration is associated with an increased incidence of hypertension. To evaluate the direct effects of the drug on the contractile responses of vascular tissue to adrenergic stimuli, rat caudal artery ring segments were studied before and after the addition of cyclosporin A or its ethanol vehicle in vitro. In a dose-related manner, cyclosporin A augmented the contractile response to transmural nerve stimulation, with a highly significant (p less than 0.001 relative to that produced by the vehicle) lowering of the stimulation rate, a 50% of maximum contractile response (ED50) that elicited. The difference between pretreatment and treatment maximal responses to transmural nerve stimulation was also significantly greater (p less than 0.01) in the cyclosporin A-treated preparations than in those receiving the vehicle. In similar experiments, the responses to exogenous norepinephrine were not significantly affected. The effect of cyclosporin A on transmural nerve stimulation was demonstrated at several extracellular calcium concentrations. The results suggest that cyclosporin A enhances nerve stimulation responses by a presynaptic mechanism.