Presynaptic muscarinic and alpha-adrenergic receptor blocking effect of atropine on the noradrenergic neurones of the rabbit pulmonary artery.
The effect of atropine on the electrical-field stimulation-evoked overflow of tritium from isolated rabbit pulmonary arteries preincubated with 3H-noradrenaline was studied. Atropine (10(-4) M) and phentolamine (10(-6) M) increased stimulation-induced overfoow of tritium. Clonidine (10(-6) to 10(-5) M) and acetylcholine (10(-6) M) diminished the stimulation-evoked overflow of tritium. After the overflow had been raised by either atropine (10(-4) M) or phentolamine (10(-6) M), clonidine (10(-6) M) decreased the overflow below control values. Clonidine (10(-5) M) prevented the enhancement of tritium overflow evoked by atropine (10(-4) M). A lower concentration of clonidine (10(-6) M) only caused a partial prevention. Enhancement of the overflow by phentolamine (10(-6) and 3 X 10(-5) M) was not altered by atropine (10(-4) M). Atropine (10(-7) M), in a concentration which was without any effect on the stimulation-induced tritium overflow, prevented the reduction evoked by acetylcholine (10(-6) M). It is concluded that atropine in a low concentration blocks presynaptic inhibitory muscarinic receptors; at higher concentrations it blocks in addition presynaptic alpha-adrenoceptors.
D000109:Acetylcholine / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists; D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D003000:Clonidine / Q000494:pharmacology; D004347:Drug Interactions; D004558:Electric Stimulation; D009474:Neurons / Q000187:drug effects*; D009638:Norepinephrine / Q000378:metabolism / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011651:Pulmonary Artery / Q000187:drug effects / Q000294:innervation*; D011817:Rabbits; D011950:Receptors, Cholinergic / Q000187:drug effects*; D011976:Receptors, Muscarinic / Q000187:drug effects*
D000317:Adrenergic alpha-Antagonists; D011950:Receptors, Cholinergic; D011976:Receptors, Muscarinic; D001285:Atropine; D003000:Clonidine; D000109:Acetylcholine; D009638:Norepinephrine; D010646:Phentolamine