Alloxan inhibits ligand binding to adrenoceptors of vascular smooth muscle microsomes.
We have examined the effects of alloxan on the binding of [3H]prazosin and [125I]monoiodocyanopindolol (ICYP) to plasma-membrane-enriched microsomes isolated from dog aortas and dog mesenteric arteries respectively. Preincubation of the vascular smooth muscle membranes with alloxan reduced the number of binding sites of the alpha- and beta-adrenoceptors in a concentration-dependent manner, whereas the affinity of the radioligands for the adrenoceptors was not affected by alloxan. Streptozotocin, which is also a diabetogenic agent like alloxan, had no effect on the radioligand binding to these adrenoceptors under similar experimental conditions. The inhibitory effects of alloxan on binding to beta-adrenoceptors were found to be highly pH-dependent. These results indicate that alloxan exerts adverse effects on cell membrane adrenoceptors in addition to those on the ion-transport function of vascular smooth muscle cell [Kwan (1988) Biochem. J. 254, 293-296], and also suggest that the primary site of action of alloxan is the plasma membrane.
Smooth Muscle Research Program, McMaster University Health Sciences Centre, Hamilton, Ontario, Canada.
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D000496:Alloxan / Q000494:pharmacology*; D000818:Animals; D001011:Aorta; D004285:Dogs; D066298:In Vitro Techniques; D020120:Iodocyanopindolol; D008024:Ligands; D008638:Mesenteric Arteries; D008861:Microsomes / Q000378:metabolism; D009131:Muscle, Smooth, Vascular / Q000502:physiology*; D010869:Pindolol / Q000031:analogs & derivatives / Q000378:metabolism; D011224:Prazosin / Q000378:metabolism; D011941:Receptors, Adrenergic / Q000187:drug effects*
D008024:Ligands; D011941:Receptors, Adrenergic; D000496:Alloxan; D020120:Iodocyanopindolol; D010869:Pindolol; D011224:Prazosin