Prejunctional opioid mu-receptors and adenosine A1-receptors on the sympathetic nerve endings of the rat tail artery interact with the alpha 2-adrenoceptors.
Experiments were designed to study the interaction between prejunctional alpha 2-adrenoceptors and both adenosine and opioid receptors at the postganglionic sympathetic nerve endings innervating the tail artery of the rat. Segments of this vessel were preincubated with [3H]-noradrenaline and then perfused/superfused with [3H]-noradrenaline-free medium. Their perivascular nerves were field stimulated with standard stimulation parameters: 24 pulses at 0.4 Hz, 0.3 ms, 200 mA. In some experiments, the stimulation parameters were adjusted in order to obtain similar reference release values despite the presence of a first release-modulating drug. The adenosine agonist 5'-N-ethylcarboxamidoadenosine (NECA; 0.3-10 mumol/l) and [D-Ala2,MePhe4,Glyol5]enkephalin (DAGO; 0.3-10 mumol/l) depressed the stimulation-evoked overflow of tritium in a concentration dependent manner. The release-inhibiting effect of both NECA and DAGO was enhanced in the presence of the alpha 2-adrenoceptor antagonist rauwolscine (3 mumol/1) while it was attenuated in the presence of the alpha 2-adrenoceptor agonist 5-bromo-6-[2-imidazolin-2yl-amino]-quinoxaline (UK-14,304; 0.1 mumol/l). These changes occurred both at standard and adjusted stimulation parameters. These results demonstrate that the prejunctional adenosine A1- and opioid mu-receptors interact with the prejunctional alpha 2-adrenoceptors. The level at which these interactions take place (receptors themselves or transduction mechanisms) as well as the physiological significance of the phenomenon remain to be determined.
Université Louis Pasteur, Strasbourg, Laboratoire de Pharmacologie Cellulaire et Moléculaire, C.N.R.S. URA 600, Illkirch, France.
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Bucher
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Corriu
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Stoclet
D000241:Adenosine / Q000378:metabolism; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000294:innervation; D001338:Autonomic Fibers, Postganglionic / Q000187:drug effects* / Q000378:metabolism; D004558:Electric Stimulation; D004745:Enkephalins / Q000494:pharmacology; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D011957:Receptors, Opioid / Q000378:metabolism*; D017450:Receptors, Opioid, mu; D011983:Receptors, Purinergic / Q000378:metabolism*; D013623:Tail / Q000187:drug effects / Q000294:innervation; D014665:Vasodilator Agents / Q000494:pharmacology
D000316:Adrenergic alpha-Agonists; D004745:Enkephalins; D011942:Receptors, Adrenergic, alpha; D011957:Receptors, Opioid; D017450:Receptors, Opioid, mu; D011983:Receptors, Purinergic; D014665:Vasodilator Agents; D000241:Adenosine; D009638:Norepinephrine