Bone-anabolic effect of salmon calcitonin on glucocorticoid-induced osteopenia in rats

The anabolic effect of salmon calcitonin (SCT) on skeletal tissue was exami ned on glucocorticoid-induced osteopenia in female rats (12 weeks old). By the administration of methylprednisolone acetate (MPA: 0.1 mg/kg, s.c., 3 t imes/week) for 8 weeks, histomorphometrically detectable osteopenia with th e characteristics of decreased bone formation and increased bone resorption developed in proximal tibia metaphysis, Serum osteocalcin level was also d ecreased by MPA treatment. Subsequent treatment with SCT (10 U/kg, s.c., 5 times/week) was found to reverse once developed osteopenia with the return of the osteocalcin level, though rats were still on MPA. Histomorphometry r evealed that SCT decelerated bone resorption but augmented bone formation i n this osteopenic model. After a single injection of SCT (2.5 U/kg-40 U/kg, s.c.), the serum level of parathyroid hormone (PTH) which had a potent ana bolic on bone formation increased in a dose-dependent manner. These results indicate that SCT has a stimulating effect on osteoblastic bone formation and this anabolic effect may at least in part be due to its indirect effect to increase endogenous PTH secretion.