Effects of norethisterone on bone related biochemical variables and forearm bone mineral in post-menopausal osteoporosis.

OBJECTIVE

Progestogens may be a useful therapeutic alternative to oestrogen in the treatment of post-menopausal osteoporosis. The purpose of this study was to determine the effects of norethisterone on forearm bone mineral content and bone related biochemical variables in patients with post-menopausal osteoporosis.

DESIGN/PATIENTS: The effects of treatment with norethisterone (5 mg/day) on bone related biochemical variables was determined in 44 women with post-menopausal osteoporosis. The effects of norethisterone on forearm bone mineral content (FMC) were evaluated by serial measurements in 39 of these women.

MEASUREMENTS

We measured forearm mineral content, forearm mineral density, forearm fat content and fat-corrected forearm mineral density. Biochemical measurements included plasma calcium and plasma calcium fractions (ionized, protein bound, complexed and ultrafiltrable), alkaline phosphatase, bicarbonate, phosphate, albumin and globulins, serum parathyroid hormone, osteocalcin and 1,25-dihydroxyvitamin D, radiocalcium (45Ca) absorption and fasting urinary calcium/creatinine, sodium/creatinine, phosphate/creatinine and hydroxyproline/creatinine molar ratios.

RESULTS

After 4 months of treatment norethisterone produced a fall in plasma calcium (mean +/- SEM from 2.40 +/- 0.14 to 2.32 +/- 0.13 mmol/l, P < 0.001), primarily in the non-ionized calcium, due to a decrease in plasma bicarbonate (from 29 +/- 0.28 to 27 +/- 0.28 mmol/l, P < 0.001). There were decreases in urinary calcium/creatinine (from 0.41 +/- 0.03 to 0.19 +/- 0.02, P < 0.01) and sodium/creatinine (from 15 +/- 1.1 to 10 +/- 0.93, P < 0.001) molar ratios and a rise in the renal tubular maximum for calcium reabsorption (TmCa) (from 2.36 +/- 0.041 to 2.55 +/- 0.059 mmol/l of glomerular filtrate, P < 0.001). Plasma phosphate, urinary phosphate/creatinine and tubular maximum for phosphate reabsorption (TMP) all fell (P < 0.01). Both the urinary hydroxyproline/creatinine (P < 0.001) and plasma alkaline phosphatase (P < 0.001) fell. Serum parathyroid hormone rose from 4.1 +/- 0.36 to 5.5 +/- 0.51 pmol/l (P < 0.02) and radiocalcium absorption increased from 0.67 +/- 0.08 to 0.81 +/- 0.10 fx/h (P < 0.01). There was no change in serum 1,25-dihydroxy vitamin D. After treatment with norethisterone for 4 months there was an increase in forearm bone mineral content (P < 0.05) and a decrease in forearm fat content (P < 0.02). After two years treatment with norethisterone fat-corrected forearm bone mineral content rose (mean change 17.0 +/- 5.5 mg/cm, P < 0.01).

CONCLUSIONS

These results suggest that norethisterone prevents bone loss in post-menopausal osteoporosis by decreasing bone turnover, has a vitamin-D independent effect on intestinal calcium absorption, and increases serum parathyroid hormone levels.