POTENTIATION OF ANGIOTENSIN-II ACTION BY CORTICOSTEROIDS IN VASCULAR TISSUE

Objectives: Studies were performed to determine if corticosteroids act directly on the vasculature to potentiate the vasoconstrictor action of angiotensin II and to determine whether corticosteroids upregulate angiotensin II receptors by receptor redistribution or by synthesis of new receptors, Methods: Aortic rings from normal Sprague-Dawley rats were incubated ex vivo with corticosteroids in aerated Krebs-Henseleit buffer to avoid secondary systemic effects prior to stimulated contra ction, In cultured vascular smooth muscle cells, these experimental te chniques were used: colchicine (blocker of microtubule assembly), chlo roquine (inhibitor of endosomal pH gradients), measuring surface-bound I-125-Ang II internalization rate, immunoblotting of angiotensin AT(1 ) receptor protein, and incorporation of [S-35]methionine into AT(1) r eceptor protein. Results: Contractions to 100 nM angiotensin II in rin gs incubated with 1 mu M aldosterone or dexamethasone for 10 min ex vi vo were not different from contractions in control rings, However, ang iotensin II-stimulated (but not KCl-stimulated) contractions were enha nced by almost 100% if ex vivo incubation with aldosterone (or cortico sterone) lasted for 24 h. Endothelium-dependent relaxation was nor sig nificantly reduced by aldosterone pre-incubation. Incubation of cultur ed vascular smooth muscle cells with a number of corticosteroids for > 8 h resulted in concentration-dependent upregulation of angiotensin I I receptor binding and was reversible upon removal of the corticostero id. Aldosterone did not affect the rate of internalization of surface- bound angiotensin II. In addition, concomitant incubation of colchicin e or chloroquine with aldosterone did not hamper angiotensin II recept or upregulation, Incubation of cells with various concentrations of al dosterone for 24 h resulted in concentration-dependent increases in to tal cell angiotensin II receptor protein content and increases in [S-3 5]methionine incorporation into immunoprecipitated AT(1) receptor prot ein. Conclusions: At least a portion of the enhancement of angiotensin II action by corticosteroids is via direct interaction of corticoster oids with the vasculature. Corticosteroids appear to upregulate angiot ensin II receptors by synthesis of new receptor protein rather than by alterations in receptor trafficking.