Regulation of vascular smooth muscle growth by α1-adrenoreceptor subtypes in vitro and in situ

Abstract

Rat aorta smooth muscle cells which express all three α1- adrenoreceptors (α(1A), α(1B) and α(1D)) were used to determine the effect of stimulation of α1-adrenergic receptor subtypes on cell growth. 'Combined' α1-adrenoreceptor subtype stimulation with norepinephrine alone caused a concentration-dependent, prazosin-sensitive increase in protein content and synthesis: 48 h of stimulation at 1 μM increased cell protein to 216 ± 40% of time-matched controls (p = 0.008) and RNA to 140 ± 13% (p = 0.03); protein synthesis increased to 167 ± 13% (p < 0.01) after 24 h. Stimulation with norepinephrine plus the selective α(1A)/α(1D) antagonist 5-methylurapidil produced greater increases in α-actin mRNA (270 ± 40% at 8 h; p = 0.007), total cell protein (220 ± 45% at 24 h; p = 0.004 h and RNA (135 ± 8% at 24 h; p = 0.01). These effects were prevented by pretreatment with the selective α(1B) antagonist chloroethylclonidine. Comparable results were obtained for intact aortae. Stimulation with norepinephrine plus 5- methylurapidil increased (p < 0.05) tissue protein, RNA, dry weight, and α- actin mRNA; and as in cultured cells, combined stimulation with norepinephrine alone attenuated these responses. By comparison, adventitia (fibroblasts) was unaffected. Removal of endothelial cells had no effect. α(1B) mRNA decreased by 42 ± 12% (p = 0.01) in cultured cells during combined α1-adrenoreceptor stimulation and by 23 ± 8% (p = 0.03) for intact aorta. α(1D) and β-actin mRNA were unchanged in cultured cells, aorta media, and adventitia. These findings suggest that prolonged stimulation of chloroethylclonidine-sensitive, possibly α(1B)- adrenoreceptors induces hypertrophy of arterial smooth muscle cells and that stimulation of 5-methylurapidil-sensitive, non-α(1B)-adrenoreceptors attenuates this growth response.