Comparison of Bone Changes between Hypophysectomized Rats and Mini Rats

Abstract

Growth hormone (GH) plays an important role in longitudinal bone growth, and hypophysectomized rats have generally been used as a model for GH deficiency in humans. Recently, researchers have bred Mini rats, a Wistar-derived transgenic rat strain harboring a rat GH antisense gene and showing lower plasma GH levels than Wistar rats. In a previous study, Mini rats showed a smaller femur size with lower mineral density and a reduction of the metaphyseal and diaphyseal bone mass. In the present study, Wistar rats were hypophysectomized (HX) and treated with GH, and then their bones were examined and compared with vehicle-treated intact age-matched Wistar rats and Mini rats. GH-treated (HX+GH) rats exhibited an increase in the mineral density of the tibia and increases in the length and mineral content of the femur and tibia. These changes in the HX+GH rats were attributable to an increase in the longitudinal growth and periosteal bone formation of the femur and tibia. When Mini rats and HX rats were compared with Wistar rats, both animals showed similar reductions in the bone length, mineral content, and mineral density of the femur, but the Mini rats showed a greater longitudinal growth rate, cancellous bone mass, and mineralizing surface than the HX rats, as well as less remarkable changes in body weight, relative organ weights, and hematological and blood chemical parameters. Therefore, Mini rats are considered to be a useful model for clarifying features of GH deficiency and examining effects of various treatments on the bone without any specific surgery or drug-administration.