Contrast medium induced renal vasoconstriction, role of alpha receptors

Standard imaging techniques for evaluation of renal and renovascular disease require the application of radiocontrast medium. The use of high osmolar, ionic radio contrast medium is however associated with adverse effects including acute renal insufficiency. Renal vasoconstriction seems to play an important role in the pathomechanism of this side effect. The cellular mechanisms however remain unsolved. Alpha 1-adrenoceptors and their subtypes are the crucial link between sympathetic stimulation and renal vasoconstriction. We investigated the role of alpha 1-receptors and the alpha 1A and alpha 1B subtypes in the renal artery and in sodium/meglumine diatrizoate induced renal artery smooth muscle contraction. Alpha 1-receptor induced rabbit renal artery contraction was produced by stimulation with the specific agonist phenylephrine which was antagonized dose-dependently and reversibly by the alpha 1-blockers prazosin, terazosin and YM 617. The alpha 1A-receptor was the prevalent receptor subtype in rabbit renal artery. This was identified by applying the specific alpha 1A-receptor antagonist 5-methylurapidil and the irreversible alpha 1B-receptor antagonist chloroethyllonidine. These two inhibited the PE induced contraction by 96% and 66%, respectively. Sodium/meglumine diatrizoate elicited renal artery contraction at 25% of the phenylephrine control. This contraction was not influenced by alpha 1-blockers indicating the absence of an alpha 1-receptor mediated process.