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α-Adrenoceptor-mediated prejunctional effects of chloroethylclonidine in the canine saphenous vein
  • Faculty of Medicine
  • Universidade Estadual Paulista (UNESP)
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.
Issue Date: 
Journal of Pharmacology and Experimental Therapeutics, v. 282, n. 3, p. 1326-1330, 1997.
Time Duration: 
  • 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
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Appears in Collections:Artigos, TCCs, Teses e Dissertações da Unesp

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