Modulation by estradiol of rabbit atrial chronotropic response to histamine

The chronotropic response (delta rate) to histamine of atria from estradiol 17-beta (E2; 0.1 mg/kg)-treated (14 days) rabbit was significantly greater compared to those from control rabbits. However, the maximum response of atria from rabbits treated with a higher dose of E2 (1.0 mg/kg) was not significantly different from control. Cimetidine (2.8 X 10(-7) M) inhibited the theoretical maximum income in rate to histamine in all 3 groups, control 25%, E2 (0.1 mg) 42% and E2 (1.0 mg) 35%.