J. Goncalves et G. Queiroz, FACILITATORY AND INHIBITORY MODULATION BY ENDOGENOUS ADENOSINE OF NORADRENALINE RELEASE IN THE EPIDIDYMAL PORTION OF RAT VAS-DEFERENS, Naunyn-Schmiedeberg's archives of pharmacology, 348(4), 1993, pp. 367-371
The present study aimed at determining the modulation by adenosine of
the release of noradrenaline in the epididymal portion of the rat vas
deferens. The tissues were treated with pargyline and perifused in the
presence of desipramine and yohimbine. Up to four periods of electric
al stimulation were applied (5 Hz, 9 min). The A1-adenosine receptor s
elective agonist R-N6-phenylisopropyladenosine (R-PIA; 100-900 nmol.l-
1) reduced, whereas the A2A-receptor selective agonist thyl)phenethyla
mino-5'-N-ethylcarboxamidoadenosine (CGS 21680; 3-30 nmol.l-1) increas
ed the electrically-evoked noradrenaline overflow in a concentration-d
ependent manner. The nonselective agonist 5'-N-ethylcarboxamidoadenosi
ne (NECA; 30 - 300 nmol.l-1) reduced noradrenaline overflow, but the e
ffect did not depend on the concentration. Adenosine deaminase at the
concentration of 0.5 mu.ml-1 decreased but at that of 2.0 mu.ml-1 incr
eased noradrenaline overflow. The inhibitors of adenosine uptake, S-(4
-nitrobenzyl)-6-thioinosine (NBTI; 50 nmol.l-1) and dipyridamole (3 mu
mol.l-1), increased the electrically-evoked noradrenaline overflow. Th
e A1-adenosine receptor antagonist 1,3-dipropyl-8-cy-clopentylxanthine
(DPCPX; 20 nmol.l-1) caused an increase whereas the A2-adenosine rece
ptor antagonist 3,7-dimethyl-1-(2-propynyl)xanthine (DMPX; 0.1 mumol.l
-1) caused a decrease. NBTI (50 nmol.l-1), partially antagonized the e
ffect of both DPCPX (20 nmol.l-1) and DMPX (0.1 mumol.l-1). It is conc
luded that, in the epididymal portion of the rat vas deferens, endogen
ous adenosine tonically modulates the release of noradrenaline evoked
by electrical stimulation, through activation of both inhibitory (A1)
and facilitatory (A2A) adenosine receptors.