Presynaptic inhibition of vascular sympathetic neurotransmission by adenosine.

Infusion of adenosine (1 mg/kg/min i.v.) to pentobarbital-anesthetized dogs resulted in a decrease in blood pressure and significant attenuation of the femoral vasoconstrictor responses to lumbar sympathetic nerve stimulation. The vasoconstrictor action of exogenous norepinephrine was unaltered during adenosine infusion. The inhibitory action of adenosine on responses to sympathetic nerve stimulation could be antagonized by theophylline (5 mg/kg i.v.), but not indomethacin (10 mg/kg i.v.). Additional experiments were performed to study the role of this sympathoinhibitory action of adenosine in the vasodilator effect of the compound. Intraarterial administration of adenosine produced dose related femoral vasodilatation. Sympathetic denervation of the femoral vascular bed did not alter the vasodilatory action of adenosine. Continuous lumbar sympathetic nerve stimulation or intraarterial norepinephrine infusion also did not change the vasodilatation produced by adenosine. The vasodilatory action of adenosine was antagonized by theophylline. These results suggest that adenosine causes inhibition of sympathetic neurotransmission to the femoral vasculature via an action on presynaptic purinergic receptors. However, this presynaptic inhibitory action of adenosine is not involved in the femoral vasodilatation produced by the compound.