Protective effects of ethynylestradiol on the hemodynamic changes induced by lipopolysaccharide in anesthetized rats

Estrogen pretreatment has been reported to protect rats from death induced by endotoxin. We investigated the effects of posttreatment with a synthetic estrogen, ethynylestradiol, on arterial pressure and hemodynamics in thiobutabarbitone-anesthetized rats challenged with Escherichia coli lipopolysaccharide. Rats were i.v. injected with lipopolysaccharide (1 mg/kg) followed by vehicle or a single dose of ethynylestradiol (0.25, 0.5, or 1 mg/kg) 1 h later. Another group (time-matched control) was given the vehicle. In the time-control group, there was a slight decrease in mean arterial pressure (-10 +/- 3 mm Hg) but no significant changes in cardiac output, total peripheral resistance, or heart rate over the 6-h study period. Lipopolysaccharide progressively reduced mean arterial pressure and cardiac output (-27 +/- 8 mm Hg and -52 +/- 6 ml/min, after 6 h) and increased total peripheral resistance and heart rate (+0.33 +/- 0.10 mm Hg/min/ml and +21 +/- 13 beats/min, after 6 h). None of the time-control rats died, but 36% of the rats treated with lipopolysaccharide died between 3 and 6 h after endotoxin challenge. Ethynylestradiol, at 0.25 and 0.5 completely, and at 1 mg/kg partially, restored mean arterial pressure and cardiac output at 6 h after injection of lipopolysaccharide. Ethynylestradiol at 0.5 and 1 mg/kg, but not 0.25 mg/kg, completely reversed the increase in total peripheral resistance at 6 h after injection of lipopolysaccharide. Mortality was 14% in each of the three groups of rats given ethynylestradiol 1 h after lipopolysaccharide. Therefore posttreatment with ethynylestradiol attenuated hemodynamic changes in endotoxic shock.