The expression of thyroid hormones receptors in osteoblasts and osteoclasts has involved these cells as direct targets for triiodothyronine (T3), but thyroid hormones may also interact with other hormones or local growth factors to exert their actions on bone cells. Among these, growth hormone (GH) is recognised as participating in the acquisition and maintenance of bone mass and exerting stimulatory effects on human osteoblastic cells. The aim of this study was to investigate T3 effects on primary human adult osteoblast-like cells (HOB) as well as to test for possible interactions between T3 and GH on bone cell metabolism. Primary human bone cell cultures were obtained by outgrowth from trabecular bone fragments from the hip and knee. Dose-response studies demonstrated enhanced [3H]-thymidine incorporation for T3 at 10(-9), 10(-8), 10(-7) and 20(-7) M, with a maximal response of 162.81 +/- 12.97 % with T3 10(-8) M, compared to vehicle (p < 0.001). Time-course studies showed an increased osteoblast-like cell proliferation after 24 h, followed by a decrease of cell proliferation by 48 h and 72 h of culture, respectively, when compared to control cells, with a maximal response after 72 h (T3 10(-10) M: 45.21 +/- 6.97 %, p < 0.01). In addition, T3 markedly increased specific alkaline phosphatase (AP) activity in HOB (10(-10) M: 169.86 +/- 12.14 % vs. control, p < 0.001), but no significant influence on type I procollagen propeptide (PICP) production was observed. At 10(-9) - 10(-7) g/ml, GH significantly enhanced HOB proliferation (p < 0.001) however, GH effects were not dose-dependent. Triiodothyronine, at a high concentration (10(-7) M), stimulated GH-receptor (GHR) mRNA levels by 165.20 +/- 16.54 % after 24 h (p < 0.05). Correspondingly, a synergistic effect of T 3 with the same concentration and GH on cell proliferation in human adult osteoblast-like cells was found.

Objective: Data from cell culture experiments suggest that local growth factors (GFs) may mediate the effects of estrogens, calcitonin or fluor ions on the skeleton. To assess the in vivo relevance of the in vitro reports, the effect of fluor salts, hormone replacement therapy (HRT) and calcitonin on the concentrations of IGF-I, IGF-II and transforming growth factor (TGF)-b1 in bone matrix extracts from osteoporotic patients was evaluated. Design: Iliac crest bone biopsies were obtained from 170 patients (76 men and 94 women) with primary osteoporosis aged 55.5^0.8 years. Methods: Bone matrix extraction was performed based on a guanidine -HCl/ethylendiamine -tetraacetic acid method. Results: In comparison with age-and body mass index (BMI)-matched controls, no influence of longterm therapy with fluor ions (n ¼ 41) or calcitonin (n ¼ 16) on the bone matrix concentration of GFs was noticed. Postmenopausal women with osteoporosis on HRT (n ¼ 39) had lower skeletal IGF-I but not IGF-II levels as compared with age-and BMI-matched non-users. However, the lower rate of bone turnover in women with HRT may account for this difference, since the significance was lost after adjustment for alkaline phosphatase. Likewise, a tendency for lower TGF-b1 levels was observed in HRT users as compared with non-users but was lost after adjustment for bone turnover. None of the therapies influenced the serum levels of GFs when patients receiving continuous therapy for at least 1 year before bone biopsy were considered. Conclusions: Our data suggest no direct effect of fluor therapy on skeletal GFs levels. At the concentrations used, neither HRT nor calcitonin appeared to exert any significant influence on serum or bone matrix GF levels.European Journal of Endocrinology 150 81-91