Background Angiotensin Ⅱ （Ang Ⅱ） acting at angiotensin AT1 receptor （AT1R） has well documented effects on cardiovascular structure such as the promotion of cardiovascular hypertrophy and fibrosis, which are believed to be opposed by angiotensin AT2 receptor （AT2R） stimulation. The expressions of AT1R and AT2R are up-regulated in senescent hearts. The purpose of this study was to investigate the interaction of signal transduction between AT1R and AT2R, and to detect whether there is any difference in the interaction in rat hearts of different age.Methods In 3.5-, 12-, 18- and 24-month-old rats, the heart cell membrane activities of protein kinase C （PKC） and tyrosine kinase were measured when AT1R and AT2R were both activated by Ang Ⅱ or just the AT1R was activated by Ang Ⅱ and PD123319. The activities of cytosolic phospholipase A2 （cPLA2） and the levels of cGMP were investigated when AT1R and AT2R were both activated by Ang Ⅱ or just the AT2R was activated by Ang Ⅱ and losartan.Results When AT1R and AT2R were both activated compared to when the AT1R was activated, the activities of PKC were not different in hearts from 3.5- and 12-month-old rats, but decreased significantly in 18- and 24-month-old rats; the activities of tyrosine kinase were not different in 3.5-month-old rats but decreased significantly in 12-, 18- and 24-month-old rats. The activities of cPLA2 were all decreased significantly in rats of different age when AT1R and AT2R were both activated compared to when the AT2R was activated. Treatment with Ang Ⅱalone compared to Ang Ⅱ and Iosartan decreased the levels of cGMP （fmol/mg） in rats of different age （102.7±12.7 versus 86.0±8.0 in 3.5-month-old rats, P〈0.05; 81.0±9.4 versus 70.0±6.3 in 12-month-old rats, P〈0.05; 69.8±5.6 versus 54.2±5.3 in 18-month-old rats, P〈0.01 ; 57.7±8.0 versus 39.0±3.0 in 24-month-old rats, P〈0.01）.Conclusions The activation of AT1R inhibited the signal transduction of AT2R during the aging variation, and the activa
