A magnesium-deficient high fructose diet augments bone-sparing action of exogenous oestrogen in ovariectomized rats

To investigate interactions between circulating oestrogen, high dietary fructose, and low dietary magnesium on bone mineral density and numbers of trabeculae, 10 week old ovariectomized (OVX) and sham-ovariectomized (SOVX) rats were studied. The OVX animals were divided into three groups: one-third of the animals were injected with beta-oestradiol-3-benzoate dissolved in sesame oil twice a week; another one-third were injected with testosterone cypionate; and the remaining OVX and all of the SOVX animals were injected with sesame oil only. One-half of the animals in each group were fed cornstarch without magnesium and the other half, fructose without magnesium. After a 14 week experimental period, a 24 h urine sample was collected for measurements of Ca, Mg, P and cAMP. Blood was collected for determination of Ca, Mg, P, 25-hydroxy- and 1,25-dihydroxy-cholecalciferol. Femurs were used for determination of bone density, and tibiae for numbers of trabeculae. Testosterone-treated and OVX control animals fed cornstarch diets had the lowest bone density, whereas oestrogen-treated and SOVX control rats fed fructose had the greatest bone density. Oestrogen-treated animals fed fructose without magnesium had the highest serum and urinary Ca, whereas testosterone-treated animals fed cornstarch without magnesium had the lowest serum and urinary Ca. Serum alkaline phosphatase was higher in OVX- and testosterone-treated and starch-fed animals as compared to their respective counterparts. High urinary cAMP in OVX- and testosterone-treated animals may reflect the action of increased circulating concentrations of PTH, which could be responsible for bone resorption. The results show that high dietary fructose without magnesium interacts with endogenous or exogenous oestrogen to decrease bone mineral loss significantly in ovariectomized rats.