Comparative cardiovascular effects of different progestins in menopause.

Progesterone receptors are present in the arterial wall and it is, therefore, likely that the arterial effects of progestins are mediated through progesterone receptors as well as through down-regulation of the estradiol receptor. Progestin therapy affects arterial function, as it can stabilize arteries in a state of vasomotor instability, but may also induce vasoconstriction of estrogenized vessels. Thus, the cardiovascular effects of progestins may influence the cardioprotective effect of estrogens. There has been some concern that a combined estrogen-progestogen therapy may attenuate some of estrogen's beneficial effects on cardiovascular health. This is a reflection of the past epidemiologic studies which have used primarily unopposed estrogen. The PEPI trial is the only large-scale, long-term study to compare directly the effects of different combined hormone replacement therapy regimens upon plasma lipids in healthy women. This study has shown that the adjunctive clinical impact of different progestogens on the beneficial effect of estrogen replacement therapy is trivial. It has never been proved that in normocholesterolemic women, e.g., those included in the PEPI trial, the increase in HDL reduces cardiovascular mortality or morbidity. Based on the results of PEPI, hormone replacement therapy has positive effects on key heart disease risk factors and endometrial tissue, and the magnitude of those effects does not differ significantly across the hormone replacement therapy regimens used. At present there are only few and inconclusive data available on the vascular effect of progestins in menopausal women. Some studies found that progestins reduced the beneficial effect of estrogens, while others did not. Our group has recently shown that different estrogen-progestin treatments have different effects upon vascular reactivity and that a careful selection of the progestin to be added to estrogen is of capital importance to preserve, or even enhance the positive vascular effects of estrogens. Few epidemiological studies have investigated the effect of adding a progestin to estrogen therapy upon cardiovascular mortality and morbidity, and all have suggested that hormone replacement therapy may be more effective than estrogen replacement alone in reducing cardiovascular events in primary prevention. The results of the recently published Heart and Estrogen/progestin Replacement Study (HERS) have added some critical data on the effect of hormone replacement therapy for secondary prevention in women with coronary artery disease. The study, however, is affected by several important methodological and statistical problems, which make its interpretation difficult and its conclusions useless for clinical practice. The results of the study should be evaluated with caution by physicians who give advice on hormone replacement therapy, and no woman should be taken off hormone replacement therapy because of HERS. Of importance, the results of HERS should not be used to suggest alternative forms of treatment, especially the selective estrogen receptor modulators (SERMs), for cardiovascular protection in postmenopausal women.