Evidence for spare alpha 1-adrenoceptors for the accumulation of inositol phosphates in smooth muscle.
The accumulation of inositol phosphates (IP) in smooth muscle from rat vas deferens and caudal artery was maximally increased 3- to 4-fold in response to exposure of the tissues to 100 microM noradrenaline. Clonidine (up to 3 mM) was a partial agonist. Pretreatment of the tissues with the irreversible alpha-adrenoceptor antagonist phenoxybenzamine (0.3-10 microM) shifted the noradrenaline concentration-response curve to the right before depressing the maximum. The maximum of the clonidine concentration-response curve was depressed without significant change in the EC50 by the same treatment. These data, which are most easily interpreted as demonstrating the presence of a receptor reserve for IP accumulation, are discussed.
D000818:Animals; D003000:Clonidine / Q000494:pharmacology; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism*; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology; D010643:Phenoxybenzamine / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000378:metabolism*; D013403:Sugar Phosphates / Q000378:metabolism*
D007295:Inositol Phosphates; D011942:Receptors, Adrenergic, alpha; D013403:Sugar Phosphates; D010643:Phenoxybenzamine; D003000:Clonidine; D009638:Norepinephrine