Skeletal responsiveness to thyroid hormone is not altered at menopause

Hyperthyroidism is characterized by increased bone turnover and resorptive activity. Similar changes in remodeling are seen after menopause. To study the role of thyroid hormone in the menopause-related changes in bone metabolism, we investigated thyroid status and the sensitivity of bone to thyroid hormone in 14 premenopausal and 15 early post-menopausal women. Triiodothyronine (T3) was administered to the two groups as 20 μg doses three times daily for 7 days. The skeletal response was assessed by monitoring bone alkaline phosphatase (BAP), osteocalcin (BGP), pyridinium crosslinked telopeptide domain of type I collagen (ICTP) in serum and urinary excretion of hydroxyproline (OHP), pyridinoline (PYR), and deoxypyridinoline (DPR) at days 0, 8,15, and 57. The early postmenopausal women had increased bone turnover as reflected in sBAP (p< 0.05), sBGP (p< 0.05), and uOHP (p< 0.01) when compared with premenopausal controls. T3 stimulation of early postmenopausal and premenopausal women significantly increased the markers of bone resorption: sICTP (56% vs. 44%), uOHP (45% in both groups), and UPYR (83% vs. 17%) without any significant differences between groups. Of the formative markers, only sBGP increased significantly after stimulation (34% vs. 41%), but both sBGP and sBAP displayed significant increases from days 15 to 57. Thus, stimulation with thyroid hormone results in an immediate stimulation of ongoing bone formation and bone resorption, but also initiation of new remodeling which, after 8 weeks, reached the formative phase. PTH decreased (p< 0.01) in both groups but serum calcium and serum phosphate were unaltered. In conclusion, menopause is not characterized by altered levels of thyroid hormones or altered skeletal responsiveness to thyroid hormones.