Nucleotides as Cotransmitters in Vascular Sympathetic Neuroeffector Transmission

Abstract

Postganglionic sympathetic cotransmission by noradrenaline (NA) and adenosine 5’-triphosphate (ATP) was studied in isolated arteries from rabbits using as tools α-adrenoceptor antagonists and αβ-methylene-ATP which first activates and then desensitizes purine P_2X receptors. In the pulmonary artery, NA was the only chemical signal responsible for neurogenic vasoconstriction. In sharp contrast, ATP was the only signal eliciting electric as well as mechanical postjunctional responses in small jejunal arteries. Mixed adrenergic and purinergic transmission was found in the largest ramus caecalis of the ileocolic artery. The purinergic component prevailed in short pulse trains and early in long trains, whereas the adrenergic component prevailed in the late phases of long (20 s) trains. Prejunctional α₂-adrenergic autoinhibition markedly depressed purinergic as well as adrenergic transmission as soon as a latency of about 2 s was exceeded.