title: Prejunctionally mediated inhibition of neurotransmission by isoprenaline in rat vas deferens.
abstract: Effects of isoprenaline on monophasic contractions evoked by electric field stimulation were studied in rat isolated prostatic vas deferens. Isoprenaline reduced electrically evoked contractions (EC50: 0.27 +/- 0.05 microM), and propranolol concentration-dependently antagonized the effect of isoprenaline. In contrast, isoprenaline (0.3-3 microM) did not affect the contractile response induced by exogenous noradrenaline or ATP, while forskolin (100 nM) attenuated agonist-induced contraction. In some tissues, adrenergic and purinergic components of the electrically evoked contraction were isolated by exposure to alpha,beta-methylene ATP (3 microM) and prazosin (3 microM), respectively. Isoprenaline induced a greater inhibition of purinergic than adrenergic component of the electrically evoked contraction. Iberiotoxin (50 nM), glibenclamide (3 microM), 4-aminopyridine (0.3 mM) and tetraethylammonium ions (1 mM) attenuated the effect of isoprenaline. These results indicate that isoprenaline-induced inhibition of the electrically evoked (both purinergic and adrenergic) contraction was mediated primarily through activation of prejunctional beta-adrenoceptors, which probably inhibited release of contractile transmitters from sympathetic nerves supplying vas deferens. Lack of effect of isoprenaline on agonist-induced contraction does not favour a functional role of beta-adrenoceptors in vas smooth muscle.
authors.affiliation: Department of Anatomy, Faculty of Medicine, Chinese University of Hong Kong, Shatin. yu-huang@cuhk.edu.hk
authors.forename: Y
authors.initials: Y
authors.lastname: Huang
authors.forename: C W
authors.initials: CW
authors.lastname: Lau
authors.forename: N W
authors.initials: NW
authors.lastname: Chan
authors.forename: X Q
authors.initials: XQ
authors.lastname: Yao
authors.forename: F L
authors.initials: FL
authors.lastname: Chan
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D004558:Electric Stimulation; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000187:drug effects* / Q000294:innervation / Q000502:physiology; D026902:Potassium Channel Blockers; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000187:drug effects*; D014649:Vas Deferens / Q000187:drug effects* / Q000294:innervation / Q000502:physiology
chemical_list: D000318:Adrenergic beta-Agonists; D026902:Potassium Channel Blockers; D007545:Isoproterenol