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.