- O Ylikorkala: Department of Obstetrics and Gynecology, Helsinki University Central Hospital, Finland.
Hormone replacement therapy (HRT) protects against cardiovascular disorders, but the mechanisms of this action are poorly understood. We assessed the plasma levels of vasoconstrictive endothelin-1 (ET-1) in 26 healthy postmenopausal women before and during HRT. The women were randomized to receive either continuous transdermal (estradiol 50 ug/24 hrs) complemented with periodic 12 days' courses with medroxyprogesterone (10.0 mg/day)(n = 13) or continuous oral estradiol (2.0 mg/day) and continuous norethisterone acetate (1.0 mg/day)(n = 13). ET-1 was measured with specific radioimmunoassay after concentrating the sample with solid phase extraction. Pretreatment plasma ET-1 (1.28 +/- 0.36 pmol/ml, mean +/- SD) in the whole study group decreased (p < 0.01) to 1.05 +/- 0.26 pmol/ml at 6 months and to 1.10 +/- 0.32 pmol/ml at 12 months of treatment. A subgroup analysis between the two HRT regimens revealed no significant differences in the response of plasma ET-1 to HRT. These first data on HRT-induced reduction in plasma ET-1 may provide a new explanation for the cardiovascular protection by HRT.