Prejunctional opioid mu-receptors and adenosine A1-receptors on the sympathetic nerve endings of the rat tail artery interact with the alpha 2-adrenoceptors

Naunyn Schmiedebergs Arch Pharmacol. 1992 Jan;345(1):37-43. doi: 10.1007/BF00175467.


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.

MeSH terms

  • Adenosine / metabolism
  • Adrenergic alpha-Agonists / pharmacology
  • Animals
  • Arteries / drug effects
  • Arteries / innervation
  • Autonomic Fibers, Postganglionic / drug effects*
  • Autonomic Fibers, Postganglionic / metabolism
  • Electric Stimulation
  • Enkephalins / pharmacology
  • Male
  • Norepinephrine / metabolism
  • Rats
  • Rats, Inbred Strains
  • Receptors, Adrenergic, alpha / metabolism*
  • Receptors, Opioid / metabolism*
  • Receptors, Opioid, mu
  • Receptors, Purinergic / metabolism*
  • Tail / drug effects
  • Tail / innervation
  • Vasodilator Agents / pharmacology


  • Adrenergic alpha-Agonists
  • Enkephalins
  • Receptors, Adrenergic, alpha
  • Receptors, Opioid
  • Receptors, Opioid, mu
  • Receptors, Purinergic
  • Vasodilator Agents
  • Adenosine
  • Norepinephrine