Calcitonin reduced corticosterone-induced muscle proteolysis

Two-experiments were conducted to clarify the effect of calcitonin (CT) on growth, muscle protein breakdown, plasma corticosterone (CTC) concentration and urinary calcium excretion in young growing rats treated with CTC. Rats received hormonal treatments for 6 days (Experiment 1) or 24 h (Experiment 2). Dose levels of CTC were 10 mg and 5 mg/100 g body weight/day in experiment 1 and 2, respectively, and that of CT was 100 m unit/100 g body weight/day in both experiments. Muscle protein degradation was evaluated by urinary N tau-methylhistidine excretion. CT increased 24-h urinary calcium excretion but not 6-day calcium excretion. CTC markedly inhibited growth, accelerated muscle protein degradation and increased calcium excretion in both experiments. However, very interestingly, CT minimized CTC-induced muscle proteolysis, and normalized the CTC-induced decrease in urinary calcium excretion. Furthermore, CT decreased the CTC-induced increase in the plasma CTC concentration. The present observations indicate that CT reduces CTC-induced muscle protein breakdown by reducing the plasma CTC concentration and that increased urinary calcium excretion due to CT treatment may also play a role in reducing CTC-induced muscle protein breakdown.