Effects of dimethoate on bone maturation of young rats during the suckling period

We have investigated thyroid function and bone growth of suckling rats whose mothers were treated by dimethoate, administered in their drinking water (0.2 g/L), equivalent to 40 mg/kg of body weight/day from day 0 until day 10 after delivery. We have obtained in treated pups a decrease in body weight and a reduction in plasma-free T4 and T3 levels by 56 and 39%, respectively. Hypothyroidism, induced by dimethoate, delayed bone growth in 10-day-old rats, which was reflected by a sharp decrease in femur length (−14%) and weight (−34%). Exposure of the mothers to dimethoate altered bone mineral composition in their pups, especially calcium and phosphorus levels of bone, which were decreased by 25 and 24%, respectively. The calcium concentration in plasma increased by 23% and the phosphorus concentration decreased by 17%. While, urinary levels of calcium decreased by 34%, those of phosphate increased by 32%. These results suggest that dimethoate accelerated bone resorption activity. In fact, in treated pups total tartrate-resistant acid phosphatase, which reflected bone resorption, was enhanced by 60% while total alkaline phosphatase, which reflected bone formation, was slightly reduced. Disorders in bone turnover were accompanied by histological changes in bones of treated pups. Growth plates in dimethoate-treated pups were grossly disorganized compared to those of control pups. Proliferating chondrocytes failed to form discreet columns, the hypertrophic zone was markedly diminished and morphologically indistinct. In addition, treated pups displayed in the primary spongium a fragmented and a more thin trabeculae relative to controls.