Bone Histomorphology in Tibial Diaphysis of Growing Chicks Administered Excessive Vitamin A.

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The effect of hypervitaminosis A on bone histomorphology was studied in the tibiae of young growing chicks. Male White Leghorn chicks were orally administered excessive vitamin A (300 or 600IU per g body weight per day) for 10 consecutive days. For histological examination, middle diaphyses were excised and cross sections were stained with toluidine blue. Morphological differences were examined by a computerlized histomorphometry. Radiographic and histological observations indicated the hypervitaminotic chicks to have short tibial length, narrow diaphyseal width and abnormal bone morphology characterized by flattened spindle-shaped osteoblasts. Histomorphometric analysis indicated excessive vitamin A intake to cause severe retardation of bone formation. Cortical bone thickness, measured at middle diaphysis, was less in hypervitaminotic than control chicks receiving the vehicle alone. Osteoblast area and number significantly decreased in the hypervitaminotic chicks. Changes in these osteoblast parameters are associated with marked decrease in bone volume, expressed as percentage of mineralized bone matrix area. Excessive vitamin A intake did not affect all histomorphometric indices of bone resorption. Hypervitaminosis A would thus appear to decrease osteoblastic activity and inhibit bone formation in chick tibia.
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