Modulation by noradrenaline and yohimbine of noradrenergic transmission in the guinea-pig mesenteric artery.
In the guinea-pig mesenteric artery, transmitter release modulated by noradrenaline (NA) or yohimbine was estimated from changes in amplitude of the excitatory junction potential (e.j.p.) recorded from smooth muscle cells. NA decreased the amplitude of the e.j.p. with no change in the facilitation. Yohimbine antagonized the effect of NA on the e.j.p. amplitude and enhanced the facilitation of e.j.p.; the latter action was not antagonized by NA. TTX-resistant e.j.p.s evoked by stronger intensity of stimuli were not affected by NA or yohimbine. It is concluded that NA inhibits and yohimbine enhances the release of transmitter, and that the latter event involves prejunctional alpha-adrenoceptor-dependent and -independent processes.
D000818:Animals; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D008638:Mesenteric Arteries / Q000187:drug effects / Q000294:innervation* / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects / Q000502:physiology; D018377:Neurotransmitter Agents / Q000378:metabolism; D009638:Norepinephrine / Q000494:pharmacology*; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects*; D013779:Tetrodotoxin / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology*
D018377:Neurotransmitter Agents; D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D013779:Tetrodotoxin; D009638:Norepinephrine