Effects of metformin on plasma insulin, glucose metabolism and protein synthesis in the common carp (Cyprinus carpio L.)

A heterologous radioimmunoassay was developed to measure insulin levels in common carp plasma, using Bonito insulin components. The specificity of the antibodies was demonstrated by using an immunocytochemical technique and by dose-response curves of plasma dilutions from carp which were paralleled to the Bonito insulin standard curve. Plasma insulin levels of fasted carp were 5.4 ng/ml and nearly doubled in fed fish. The incorporation of ³H leucine into white muscle proteins of fed fish doubled as compared to the fasting group. Treatment with metformin increased the disposal of glucose during glucose tolerance tests and the incorporation of ³H leucine into white muscle proteins, inhibited gluconeogenesis from ¹⁴C alanine, but had no effect on plasma insulin or basal glucose levels. The mode of action of metformin is probably similar in fish and mammals.