title: Inhibition by alpha 2-adrenoceptor agonists of the secretion of catecholamines from isolated adrenal medullary cells.
abstract: In adrenal medullary cells, carbachol evokes the secretion of catecholamines with simultaneous uptake of 45Ca. Highly selective agonists for alpha 2-adrenoceptors, clonidine, naphazoline, guanfacine, tramazoline and oxymetazoline inhibited carbachol evoked secretion of catecholamines in a dose-dependent manner. These alpha 2-agonists also inhibited the uptake of 45Ca evoked by carbachol with similar dose-response curve to inhibition of catecholamine secretion. On the contrary, highly selective agonists for alpha 1-adrenoceptors, phenylephrine and norfenefrine did not inhibit the secretion of catecholamines and cellular uptake of 45Ca. The inhibition by alpha 2-agonists was not restored either by the increase in carbachol or Ca concentrations, suggesting that the mode of inhibition was distinct from competition at cholinergic receptors or Ca-channels. It is likely that alpha 2-agonists inhibited the secretion of catecholamines via the inhibition of Ca uptake which was probably caused through the activation of alpha 2-adrenoceptors.
mesh_terms: D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002395:Catecholamines / Q000378:metabolism*; D002417:Cattle; D003000:Clonidine / Q000494:pharmacology; D004110:Diltiazem / Q000494:pharmacology; D066298:In Vitro Techniques; D014403:Tubocurarine / Q000494:pharmacology; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D000316:Adrenergic alpha-Agonists; D002395:Catecholamines; D015016:Yohimbine; D004110:Diltiazem; D003000:Clonidine; D002118:Calcium; D014403:Tubocurarine