title: Adrenergic and purinergic neurotransmission in arterial resistance vessels of the cat intestinal circulation.
abstract: The contribution of adrenoceptors and purine receptors in mediating neurogenic vasoconstriction was investigated in the autoperfused intestinal circulation of anaesthetised cats treated with atropine and propranolol. Prazosin (0.5 mg/kg) and yohimbine (1.5 mg/kg) reduced but did not abolish the vasoconstrictor responses to stimulation of the efferent sympathetic nerves. The inhibitory actions of the two antagonists were additive but even after alpha 1- and alpha 2-adrenoceptor blockade nerve stimulation still elicited a residual, frequency-related vasoconstriction. The initial, rapid, phase of this response was completely abolished after desensitisation of P2x-purinoceptors with a high dose (1.5 mg i.a.) of alpha,beta-methylene ATP. In the absence of alpha-adrenoceptor antagonists, alpha,beta-methylene ATP reduced neurogenic vasoconstriction particularly at low frequency (1 Hz) nerve stimulation, but also caused a short-lasting decrease in noradrenaline and methoxamine responses which indicates that the drug may have some non-specific effects on arterial smooth muscle. The results suggest that neurotransmission in arterial resistance vessels of the cat intestinal circulation is predominantly under adrenergic control mediated by postsynaptic alpha 1- and alpha 2-adrenoceptors, with a possible purine involvement in the initial rapid response of the blood vessels, particularly to low frequency nerve stimulation.
authors.affiliation: Department of Pharmacology, Smith Kline & French Research Ltd., Frythe, Welwyn, Hertfordshire, U.K.
authors.forename: E M
authors.initials: EM
authors.lastname: Taylor
authors.forename: M E
authors.initials: ME
authors.lastname: Parsons
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002415:Cats; D004558:Electric Stimulation; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D011224:Prazosin / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D011983:Receptors, Purinergic / Q000187:drug effects*; D013268:Stimulation, Chemical; D013564:Sympathetic Nervous System / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*; D013997:Time Factors; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000317:Adrenergic alpha-Antagonists; D011983:Receptors, Purinergic; D015016:Yohimbine; D001285:Atropine; D000255:Adenosine Triphosphate; D011433:Propranolol; C002630:alpha,beta-methyleneadenosine 5'-triphosphate; D011224:Prazosin