EFFECT OF ESTROGEN ON BONE METABOLISM IN TISSUE-CULTURE - ENHANCEMENT OF THE STEROID EFFECT BY ZINC

The present investigation was undertaken to clarify the effect of estrogen (17-beta-estradiol) on bone metabolism in tissue culture. Calvariae were removed from weanling rats (3-week-old females) and cultured for periods up to 96 h in Dulbecco's Modified Eagle Medium (high glucose, 4500 mg/dl) supplemented with antibiotics and bovine serum albumin. The experimental cultures contained 10(-10) to 10(-8) M estrogen. All cultures were incubated at 37-degrees-C in 5% CO2/95% air. Bone calcium content was significantly increased by the presence of 10(-10) to 10(-8) M estrogen. The steroid (10(-10) to 10(-8) M) also significantly increased alkaline phosphatase activity in the bone, whereas it did not significantly alter acid phosphatase activity. No appreciable effect on bone alkaline phosphatase activity was produced with 17-alpha-estradiol (10(-9) and 10(-8) M). Tamoxifen (10(-6) M), an anti-estrogen, completely blocked the effect of estrogen (10(-9) M) of increasing bone alkaline phosphatase activity. Furthermore, bone DNA content was significantly increased by 10(-10) to 10(-8) M estrogen. Meanwhile, the presence of 10(-4) M zinc, which can stimulate bone protein synthesis, significantly enhanced the effect of 10(-9) M estrogen to increase DNA content in rat calvaria, while the metal did not enhance the steroid effect on bone calcium content and alkaline phosphatase activity. The presence of 10(-7) M cycloheximide completely prevented the stimulatory effect of estrogen (10(-9) M) on calcium content, alkaline phosphatase activity, and DNA content in rat calvaria. The present study demonstrates that estrogen has a direct stimulatory effect on bone metabolism in tissue culture and that zinc can enhance the steroid effect on bone DNA.