Nucleotides as cotransmitters in vascular sympathetic neuroeffector transmission

Postganglionic sympathetic cotransmission by noradrenaline (NA) and adenosine 5'-triphosphate (ATP) was studied in isolated arteries from rabbits using as tools alpha-adrenoceptor antagonists and alpha, beta-methylene-ATP which first activates and then desensitizes purine P2X 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 alpha 2-adrenergic autoinhibition markedly depressed purinergic as well as adrenergic transmission as soon as a latency of about 2 s was exceeded.