A long-term receptor stimulation is requisite for angiotensin II-dependent DNA synthesis in vascular smooth muscle cells from spontaneously hypertensive rats

Abstract

Angiotensin II stimulates DNA synthesis in aortic smooth muscle cells prepared from spontaneously hypertensive rats, with maximal levels detected 20 h after stimulation. Angiotensin II receptor antagonists inhibited the angiotensin II-induced DNA synthesis. In particular, the noncompetative antagonist 2-ethoxy-1-[[2′(1H-tetrazol-5-yl)biphenyl-4-yl]methyl-1]H-benzimidazole-7-carboxylic] acid (CV11974) was more effective than expected from its affinity for the angiotensin II receptor and its potency for inhibiting angiotensin II-induced increase in cytosolic free Ca²⁺ concentration. 2-n-Butyl-4-chloro-5-hydroxymethyl-1-[(2′-(1 H-tetrazol-5-yl)biphenyl-4-yl)methyl]imidazole, potassium salt (losartan), one of the antagonists, inhibited angiotensin II-induced DNA synthesis by 92% and 79%, even when added 2 and 4 h after angiotensin II stimulation, respectively. Angiotensin II also increases the mRNA of platelet-derived growth factor-A chain and basic fibroblast growth factor. The increase was observed within 4 h after angiotensin II stimulation. In this case, the addition of losartan at 4 h after angiotensin II stimulation hardly influenced the time course of the mRNA level of growth factors. Also, conditioned media of cells stimulated with angiotensin II did not influence DNA synthesis in the presence of CV11974. These results suggest that sustained receptor stimulation with angiotensin II is required for DNA synthesis in addition to the early intracellular signaling following phospholipase C activation in a manner independent of the induction of growth factors such as platelet-derived growth factor-AA and basic fibroblast growth factor.