The role of cytokines in bone metabolism of rats with induced hyperthyroidism

We have investigated the regulatory role of cytokines (interleukin 1, interleukin 6 and tumour necrosis factor alpha) in bone metabolism in experimental hyperthyroidism. The study was performed on 14 adult male Wistar albino rats of 280-300 g body weight. Hyperthyroidism was induced by administration of L-thyroxine at a dose of 0.4 mg/100 g food for 5 weeks. Blood samples from tail vein of rats were taken at the beginning of the experiment and at the end of the 5th week. Samples were analysed for triiodothyronine (T-3) and thyroid stimulating hormone (TSH) by radio immunoassay; calcium (Ca) and phosphorous (P) by autoanalyser; parathyroid hormone (PTH) by immune radiometric assay; alkaline phosphatase (ALP) and bone alkaline phosphatase (B-ALP) activities by a kinetic-enzymatic method, and interleukin 1 (IL-1), interleukin 6 (IL-6) and tumour necrosis factor alpha (TNF alpha) by microelisa. Additionally differential leucocyte counts were made. Significantly increased T-4 and decreased TSH values confirmed the establishment of experimental hyperthyroidism. Although serum Ca and P levels did not differ significantly as compared to initial values, PTH levels declined while ALP and B-ALP activities along with IL-1, IL-6 and TNF-alpha levels rose significantly. A lymphocyte predominance was observed in the hyperthyroid state. These findings suggest that cytokines may be mediators of the increased osteoclastic activity encountered in hyperthyroidism