Supplementation of L-arginine prevents glucocorticoid-induced reduction of bone growth and bone turnover abnormalities in a growing rat model

The present study was designed to evaluate the effects of glucocorticoid (GC) treatment on bone turnover and bone mineral density in the growing rat. Because of the recent evidence that nitric oxide (NO) can counteract prednisolone-induced bone loss in mature rats, we examined the effect on bone of the NO donor l-arginine in young male rats, in which bone mass is increased by the same biological mechanism as in children and adolescents. Thirty-six 10-week-old Sprague-Dawley male rats were assigned to six groups of six animals each, and treated for 4 weeks with either vehicle (once a week subcutaneous injection of 100 µl of sesame oil); prednisolone sodium succinate, 5 mg/kg, 5 days per week by intramuscular injection (i.m.); l-arginine, 10 mg/kg intraperitoneally (i.p.) once a day; NG-nitro-l-arginine methylester (l-NAME), 50 mg/kg subcutaneously once a day; prednisolone sodium succinate 5 mg/kg, 5 days per week i.m. +l-arginine 10 mg/kg i.p. once a day; or prednisolone sodium succinate, 5 mg/kg, 5 days per week i.m. +l-NAME 50 mg/kg subcutaneously once a day. Serum calcium, alkaline phosphatase (ALP), osteocalcin, and the C-terminal telopeptides of type I collagen (RatLaps) were measured at baseline conditions and after 2 and 4 weeks. Prior to treatment, and after 2 and 4 weeks, the whole body, vertebral, pelvic, and femoral bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DXA) scanning. Prednisolone and prednisolone + l-NAME treated rats had significantly lower ALP and osteocalcin levels than controls at 2 and 4 weeks, and significantly higher levels of Rat-Laps than controls at 4 weeks. Prednisolone, l-NAME, and prednisolone + l-NAME produced a significant inhibition of bone accumulation and bone growth at all sites measured. Supplementation with l-arginine appeared to prevent the inhibition of bone growth and increase in bone resorption induced by prednisolone. These data would suggest, for the first time, that supplementation with an NO donor could be considered as a treatment for steroid-induced osteoporosis in the developing skeleton.