S. A. Duursma

Oestrogen binding proteins in bone cell cytosol.

SummaryAttempts were made to demonstrate the presence of specific oestrogen binding proteins (“receptors”) in bone cells. High speed cytosol preparations of bone were incubated with several concentrations of radioactive oestradiol alone and with radioactive oestradiol in the presence of a specific antioestrogen, Nafoxidine. Separation of bound and free oestradiol was carried out by dextran coated charcoal treatment and by sucrose gradient ultracentrifugation. Several types of bones likely to be oestrogen-sensitive were investigated: human femoral heads, human phalanx, rat and rabbit calvaria, humeri and femora of female rats.In all experiments we were unable to demonstrate the presence of specific oestrogen receptors in bone cell cytosol indicating that the direct effect of oestrogens on bone, if present, is not mediated by specific oestrogen receptors.

Oestrogens and bone metabolism: a hypothesis

The explanations so far proposed for the effects of oestrogens on bone metabolism in post-menopausal women have been based on the changes seen in calciotrophic hormones. However, we demonstrated in a previous study [6] that there is a decrease in the concentration of somatomedin (an insulin-like growth factor) and an increase in that of growth hormone (GH) in oestrogen-treated post-menopausal women. On the basis of those findings and the relevant data published in the literature, we advance a hypothesis to the effect that the bone-metabolism changes that occur in post-menopausal women following oestrogen replacement therapy come about via changes in serum somatomedin and growth hormone concentrations.

Biochemical Parameters of Bone Metabolism in the Pre-, Peri-, and Post-menopausal State

The suggestion of Albright et al.1 in 1941 that osteoporosis is associated with the post-menopausal state has been sufficiently confirmed2–5. Kinetic studies, using 47Ca and strontium, measuring the skeletal acretion rate of calcium, revealed normal values6, whereas bone resorption was increased7. Significant differences in plasma calcium and phosphate between pre-menopausal women and women after natural or artificial menopause were published by Young et al.8. Gallagher et al.9 showed a significant rise in the fasting plasma and urine calcium and phosphate levels after oophorectomy. The urinary hydroxyproline/creatinine ratio is higher in post-menopausal women than before menopause. Plasma alkaline phosphatase is known to be higher in women after the age of 5011,12.