[Effect of prostaglandins on in vitro electrolyte metabolism in human spongiosa]

Prostaglandins seem to be involved in the pathogenesis of juxtaarticular osteopenia in rheumatoid arthritis. Therefore the influence of prostaglandins on in vitro electrolyte metabolism of human trabecular bone was tested. Trabecular bone was prepared from femoral heads of patients who had undergone hip replacement surgery for coxarthrosis. 500 mg samples of trabecular bone were incubated in modified Eagle's minimal essential medium. Net electrolyte movements between bone and incubation medium were measured. PGE2 caused an increase in the release of calcium (Ca) and magnesium (Mg) from bone into incubation medium as compared to controls (PGE2 1 micrograms/ml: Ca = 0.87 +/- 0.09 mmol/l*, Mg = 0.44 +/- 0.03 mmol/l*; controls: Ca = 0.81 +/- 0.09 mmol/l, Mg = 0.41 +/- 0.05 mmol/l; n = 15, *p less than 0.001). The effect of PGE2 was dose-dependent and comparable to the effect of human parathyroid hormone 1-34 (hPTH 1-34). PGE2 turned out to be the most potent prostaglandin on human trabecular bone. PGE1 and PGF2 alpha had about 50% and PGF1 alpha about 40% of the potency of PGE2. PGA1 and PGA2 had no effect. The effect of PGE2 could be completely inhibited by human calcitonin (hCT), similar to the inhibition of the effect of hPTH 1-34 by hCT. The effect of PGE2 was not further enhanced by hPTH 1-34. Magnesium metabolism was affected in all experiments in the same way as calcium metabolism. Phosphate metabolism, release of alkaline phosphatase and hydroxyproline from bone into incubation medium were not affected by prostaglandins.