Morphological Characteristics of Bone in Dwarf Rats Derived from Wistar Hannover GALAS Rats

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We found spontaneous dwarfs in Wistar Hannover GALAS rats, which were caused primarily by hypothyroidism (Doi et al. 2004, J Toxicol Pathol). It is known that juvenile hypothyroidism causes growth arrest, delay of bone age and epiphyseal dysgenesis. In this study, we morphologically investigated the bone, particularly the growth plate using 8- and 45-week-old dwarf (D) rats and compared the results with those from age-matched and younger juvenile (1-, 3-, 4- and 5-week old) normal Wistar Hannover GALAS (N) rats. At necropsy, 8- and 45-week-old D rats showed a small body size, low length of tibia and brachygnathia, which suggested dwarfism resulting from hypothyroidism. Histologically, 8-week-old D rats showed a small epiphysis ossification center, hypertrophy of osteoblasts, and a reduction of the vascular/bone cell invasion in the growth plate. Although the hypertrophied osteoblasts resembled those of 3-week-old N rats, the number of proliferating and hypertrophied chondrocytes in D rats were fewer than those of 3-week-old N rats. At 45 weeks old, the chondrocyte column structure in the growth plate of the D rats remained, suggesting a delay of epiphysial fusion. A small ossification center, hypertrophy of the osteoblasts and a delay of epiphysial fusion in D rats suggested a delay of bone age. Although low thyroid hormone and/or growth hormone might be responsible for these changes in the growth plate, these changes differed from thyroidectomized 6-week-old rats, suggesting a difference in the effect of thyroid hormone and/or growth hormone depending on the age of the animal.
日本毒性病理学会の論文
2007-09-30

Morphological Characteristics of Bone in Dwarf Rats Derived from Wistar Hannover GALAS Rats

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