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.
Bucher
B
B
Université Louis Pasteur, Strasbourg, Laboratoire de Pharmacologie Cellulaire et Moléculaire, C.N.R.S. URA 600, Illkirch, France.
Corriu
C
C
Stoclet
J C
JC
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