title: Indirect evidence that purinergic modulation of perivascular adrenergic neurotransmission in the portal vein is a physiological process.
abstract: The effects of adenine nucleotides and nucleosides on the contractile response to perivascular nerve stimulation were compared in the isolated portal vein of rabbit, rat and guinea-pig. 2-Chloroadenosine was more potent than adenosine and ATP, which were equipotent in producing inhibition of neurogenic contractions in the rabbit and rat via prejunctional P1-purinoceptors. In contrast, neurogenic contractions of the guinea-pig portal vein were not inhibited by adenosine and were potentiated by 2-chloroadenosine and, to a lesser extent, by ATP. Fluorescence histochemical localization of quinacrine, which binds to high levels of ATP, revealed a dense perivascular nerve plexus in the portal vein of rabbit and rat but not of guinea-pig. After chemical sympathectomy, quinacrine-positive nerves persisted in the rabbit (supporting other evidence for the presence of purinergic nerves) but not in the rat (supporting other evidence for ATP as a cotransmitter in adrenergic nerves). It is concluded that a prejunctional purinergic modulatory mechanism operates in adrenergic neurotransmission in the portal vein of rabbit and rat but not guinea-pig, and it is suggested that this indicates a physiological mechanism.
mesh_terms: D015762:2-Chloroadenosine; D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D001808:Blood Vessels / Q000294:innervation*; D004347:Drug Interactions; D006168:Guinea Pigs; D006651:Histocytochemistry; D066298:In Vitro Techniques; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000502:physiology; D011169:Portal Vein / Q000294:innervation; D011687:Purines / Q000502:physiology*; D011796:Quinacrine; D011817:Rabbits; D051381:Rats; D011919:Rats, Inbred Strains; D013563:Sympathectomy, Chemical; D013564:Sympathetic Nervous System / Q000502:physiology*; D009435:Synaptic Transmission; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D011687:Purines; D015762:2-Chloroadenosine; D000255:Adenosine Triphosphate; D013806:Theophylline; C028322:8-phenyltheophylline; D011796:Quinacrine; D000241:Adenosine