Effects of reverse triiodothyronine on bone and calcium metabolism in rats
Ohashi, H.; Shimazaki, M.; Hashimoto, R.; Kuwahara, H.; Kobayashi, A.; Shimazu, A.
Osaka City Medical Journal 34(2): 179-189
1988
ISSN/ISBN: 0030-6096 PMID: 3237403 Document Number: 324797
To study the possible role of reverse triiodothyronine (rT3) in calcium metabolism, propylthiouracil-treated, supplemented with T3 (0.1 .mu.g/100 g/day) rats were given rT3 (0.3 .mu.g/100 g/day) or vehicle intraperitoneally. The rats were fed ad libitum and after 28 days of treatment, the serum and proximal part of the tibia were measured as to their calcium and inorganic phosphate levels. In addition, the tibia and brown adipose tissue were examined histologically. The thyroid glands of both groups were hypertrophic macroscopically. The weight increase in the T3 and rT3 administered group (rT3 group) was larger than that in another group (control group). Serum calcium and phosphate levels were 11.2 mg/dl and 5.9 mg/dl respectively in the control group and 12.2 mg/dl, 6.8mg/dl in the rT3 group (p < 0.05). Calcium and phosphate measurements of proximal tibia did not reveal significant differences. Histological examination of tibiae showed that calcification in cartilage matrix of the growth plate was less advanced and bone matrix deposition in the secondary spongiosa was relatively poor in the rT3 group. The brown adipose tissue of this group consisted of larger fat cells with large lipid droplets and there PAS positive cells were scarcely observed. These findings suggest that the physiological dose of rT3 has a substantial affect on the regulation of systemic metabolism to maintain the serum calcium in a higher level and in another way to keep down the energy expenditure.