Presynaptic inhibitory effects of catecholamines on cholinergic transmission in the smooth muscle of the chick stomach.
In the vagus nerve--smooth muscle preparation isolated from the chick proventriculus, adrenaline, clonidine (10(-8) - 2.5 x 10(-7) M), noradrenaline (10(-7) - 2.5 x 10(-6) M) and dopamine (10(-5) - 10(-4) M) inhibited the contraction induced by low frequency (0.5 Hz) stimulation of the vagus nerve, but they did not inhibit the contraction elicited by acetylcholine (5 x 10(-8) - 5 x 10(-7) M). The concentration producing 50% inhibition was 10(-7) M for adrenaline and clonidine, 10(-6) M for noradrenaline, and 5 x 10(-5) M for dopamine. Isoproterenol (5 x 10(-8) - 5 x 10(-7) M) inhibited the responses induced by both stimulation of the vagus nerve and acetylcholine. The inhibitory effects of the catecholamine and clonidine were blocked by phentolamine (2.7 x 10(-6) M) but not by 5-(3-tert-Butylamino-2-hydroxy)-propoxy-3, 4-dihydrocarbostyril hydrochloride (OPC 1085) which blocked the effect of isoproterenol. It is suggested that presynaptic alpha-receptors are present in the myenteric plexus of the chick proventriculus, and that the catecholamines and clonidine exert their inhibitory effects on cholinergic transmission via these receptors.
D000818:Animals; D002395:Catecholamines / Q000494:pharmacology*; D002645:Chickens; D003000:Clonidine / Q000494:pharmacology; D004298:Dopamine / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D066298:In Vitro Techniques; D007545:Isoproterenol / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects*; D009638:Norepinephrine / Q000494:pharmacology; D010275:Parasympathetic Nervous System / Q000187:drug effects*; D010656:Phenylephrine / Q000494:pharmacology; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D013270:Stomach / Q000187:drug effects / Q000294:innervation; D013569:Synapses / Q000187:drug effects*; D009435:Synaptic Transmission / Q000187:drug effects*; D014630:Vagus Nerve / Q000502:physiology
D002395:Catecholamines; D011942:Receptors, Adrenergic, alpha; D010656:Phenylephrine; D007545:Isoproterenol; D003000:Clonidine; D004298:Dopamine; D009638:Norepinephrine; D004837:Epinephrine