α-Melanocyte-stimulating hormone directly increases the plasma calcitonin level and involves calcium metabolism in goldfish

The effects of α-melanocyte-stimulating hormone (α-MSH) on calcium metabolism were examined with goldfish. The scales on the left side of goldfish bodies were removed to allow the regeneration of scales under anesthesia. Thereafter, the influences of α-MSH injection (low dose: 0.1 μg/g body weight; high dose: 1 μg/g body weight) on plasma calcitonin (calcium-regulating hormone) and the calcium content of the scales were investigated. Ten days after removing the scales, we measured the plasma calcitonin and calcium content of both regenerating scales on the left side and ontogenic scales on the right side. At both doses of α-MSH injection, plasma calcitonin concentrations in the α-MSH-treated group were significantly higher than those in the control group. The mRNA expressions of α-MSH-receptors were detected in the ultimobranchial glands (secretory organ of calcitonin), indicating that α-MSH directly functions in ultimobranchial glands and promotes calcitonin secretion. Furthermore, we found that the calcium content of regenerating scales in α-MSH-treated goldfish was higher than that in control goldfish, while the calcium content of ontogenic scales on the right side was significantly decreased by α-MSH injection. There was a significant co-relationship between plasma calcitonin and the calcium content of regenerating scales. The mRNA expression of calcitonin receptors in regenerating scales was remarkably higher than that in ontogenic scales. These results imply that calcitonin functions to promote scale regeneration resulting from the inhibition of bone resorption because calcitonin suppresses osteoclastic activity. Thus, we are the first to demonstrate the interaction between α-MSH and calcitonin in teleosts.