A recording showing the relaxant effect of 17β-estradiol on human female coronary arteries. In panel A, histamine had no effects on a denuded ring. In panel B, endothelium was preserved and histamine had a relaxant effect. In panel C, a ring was precontracted with PGF2α and exposed to the solvent (ethanol), without vasorelaxation. Adding 3 μM of 17β-estradiol to the organ bath with ethanol, the force transducer recorded the maximum decrease in force within 10 minutes. Panel D shows the dose-dependent relaxation of a precontracted ring exposed to increasing concentrations of 17β-estradiol (3–30–300–3000 nmol/l).