Renal alpha 2-adrenoceptors, their locations and effects on sodium excretion.
Research on alpha 2-adrenoceptors has been explosive since the first functional or pharmacologic classification of these agents in 1977. While several properties of renal alpha 2-adrenoceptors have been characterized, their possible role in the pathophysiology of hypertension remains elusive. Under normal circumstances, alpha 1-adrenoceptors appear to be located postjunctionally and alpha 2-adrenoceptors are extrajunctional. However, following chronic alpha 1-adrenoceptor blockade with prazosin, the renal alpha 2-adrenoceptor density increases and they may assume the otherwise exclusive alpha 1-adrenoceptor postjunctional domain. This assumed role of alpha 2-adrenoceptors may explain the absence of natriuresis with the clinical use of prazosin and, if a similar change occurs in vascular tissue, the temporary nature of the first-dose phenomenon (orthostatic hypotension) that occurs with the use of this drug. Finally, our description of the "postsynaptic" location of the ubiquitous plasma membrane alpha 2-adrenoceptors in the original functional or pharmacologic basis of classification of alpha-adrenoceptors should now be updated. Under normal conditions, the predominant alpha 2-adrenoceptors on effector organ plasma membranes appear to be extrajunctional and do not ordinarily mediate the effects of sympathetic neuronally released norepinephrine. Postjunctional alpha 1-adrenoceptors remain postjunctional and ordinarily mediate effects of nerve-stimulated norepinephrine release.
Pettinger
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WA
Smyth
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Umemura
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D000818:Animals; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000494:pharmacology; D001127:Arginine Vasopressin / Q000494:pharmacology; D004231:Diuresis / Q000187:drug effects; D006143:Guanabenz / Q000494:pharmacology; D007668:Kidney / Q000294:innervation / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D012964:Sodium / Q000652:urine*; D013268:Stimulation, Chemical; D015016:Yohimbine / Q000494:pharmacology
D001095:Arachidonic Acids; D011942:Receptors, Adrenergic, alpha; D001127:Arginine Vasopressin; D016718:Arachidonic Acid; D015016:Yohimbine; D012964:Sodium; D006143:Guanabenz; D009638:Norepinephrine