α-Adrenoceptor-mediated prejunctional effects of chloroethylclonidine in the canine saphenous vein
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Data
1997-09-01
Autores
Guimarães, Serafim
Paiva, Maria Q.
Pereira, Oduvaldo [UNESP]
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Resumo
The present study was undertaken to look for the effect of chloroethylclonidine (CEC) on prejunctional alpha-2 autoreceptors of the canine saphenous vein. The effect was tested on tritium overflow evoked by electrical stimulation from tissues preloaded with 0.2 μM 3H- norepinephrine. Yohimbine (3-300 nM) and CEC (1-125 μM) increased and UK- 14,304 reduced the overflow of tritium evoked by 300 pulses (1 Hz). The maximal increase of tritium overflow caused by yohimbine was much higher than that caused by CEC: 3.82 and 1.74 times, respectively. CEC (5 μM) abolished both the inhibition caused by UK-14,304 and the enhancement of tritium overflow caused by yohimbine. However, when CEC was added after yohimbine, it reduced the electrically evoked overflow of tritium, the maximal effect being a reduction of tritium overflow by 35%. Prazosin (1-100 nM) did not change either the inhibitory effect of UK-14,304 or the facilitatory effect of CEC. These results suggest that CEC acts on two different subtypes of prejunctional alpha-2 autoreceptors; on one of them it acts as an antagonist and increases the electrically evoked overflow of tritium (and inhibits both the effect of UK-14,304 and yohimbine); on the other it acts as an agonist and reduces the electrically evoked overflow of tritium. Alternatively, one can admit that CEC is able to inhibit alpha-2 autoreceptors, which causes an increase of the transmitter release, and to activate a nonadrenergic inhibitory receptor thus causing a reduction of the transmitter release.
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alpha adrenergic receptor, brimonidine, chloroethylclonidine, tritium, yohimbine, animal tissue, controlled study, dog, drug effect, drug mechanism, electrostimulation therapy, evoked response, female, male, neurotransmission, nonhuman, presynaptic nerve, priority journal, saphenous vein, Adrenergic alpha-Antagonists, Animals, Autoreceptors, Clonidine, Dogs, Dose-Response Relationship, Drug, Female, Male, Prazosin, Quinoxalines, Receptors, Adrenergic, alpha-2, Saphenous Vein, Yohimbine
Como citar
Journal of Pharmacology and Experimental Therapeutics, v. 282, n. 3, p. 1326-1330, 1997.