A COMPARISON OF THE ACTION OF PROGESTINS AND ESTROGEN ON THE GROWTH AND DIFFERENTIATION OF NORMAL ADULT HUMAN OSTEOBLAST-LIKE CELLS IN-VITRO

Estrogen/gestagen replacement therapy prevents excess bone loss in pos tmenopausal women. The mode of action by which these sex steroids exer t their anabolic effects on bone has not been completely clarified yet . In this study, 17 beta-estradiol (E(2)), as well as the progestins p rogesterone (P), dydrogesterone (DD), 20 alpha-dihydroxydydrogesterone (DHD), medroxyprogesterone acetate (MPA), and cyproterone acetate (CP A) were able to stimulate the mitogenesis and differentiation of norma l adult human osteoblast-like (HOB) cells harvested from female trabec ular bone explants. The different progestins exerted a more pronounced stimulatory effect on HOB proliferation than E(2) did. The combinatio n of E(2) with P, DD, or DHD did not result in a statistically signifi cant further increase of HOB proliferation, as compared with the proge stins alone. In general, E(2) showed a stronger differentiation-induci ng effect than the progestins, as measured by histochemical staining o f the HOB cells for alkaline phosphatase activity. Combining E(2) and the progestins did not result in a further increase of the number of a lkaline phosphatase positive cells, compared with E(2) alone. The diff erent progestins proved to be equally potent in stimulating HOB prolif eration and differentiation. In conclusion, progestins as well as E(2) exerted anabolic but differential effects on normal adult human osteo blasts in vitro.