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 (AT(1)) s timulation, adrenergic stimulation, and autonomic activation to pressure ov erload-induced c-ibs expression in the adult rat heart in vivo. c-fos expre ssion was increased in pressure-overloaded hearts created by aortic banding compared with sham-operated rats (458 +/- 100% vs. sham, P < 0.05). GR-138 950, a selective AT(1) antagonist, did not blunt this expression (banding v s. banding + GR-138950: 458 +/- 100% vs. 500 +/- 125%, not significant). At ropine 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-fos expression; however, propra nolol inhibited the expression (banding vs, banding + propranolol: 492 +/- 108% vs. 154 +/- 15%, P < 0.05). The inhibition by propranolol was independ ent of the decreases in heart rate. Thus factors contributing to pressure o verload-induced c-fos expression in adult rat hearts in vivo are different from those in neonatal myocytes in vitro undergoing stretch.