Factors contributing to pressure overload-induced immediate early gene expression in adult rat hearts in vivo.

We determined the contributions of angiotensin II type 1 receptor (AT1) stimulation, adrenergic stimulation, and autonomic activation to pressure overload-induced c- fos expression in the adult rat heart in vivo. c- fos expression was increased in pressure-overloaded hearts created by aortic banding compared with sham-operated rats (458 ± 100% vs. sham, P < 0.05). GR-138950, a selective AT1 antagonist, did not blunt this expression (banding vs. banding + GR-138950: 458 ± 100% vs. 500 ± 125%, not significant). Atropine and hexamethonium partially decreased c- fos expression (banding vs. banding + atropine/hexamethonium: 700 ± 67% vs. 400 ± 67%, P < 0.05). Phentolamine had no significant effect on c- fosexpression; however, propranolol inhibited the expression (banding vs. banding + propranolol: 492 ± 108% vs. 154 ± 15%, P < 0.05). The inhibition by propranolol was independent of the decreases in heart rate. Thus factors contributing to pressure overload-induced c- fos expression in adult rat hearts in vivo are different from those in neonatal myocytes in vitro undergoing stretch.