Glucose metabolism in the common carp (Cyprinus carpio L.): the effects of cobalt and chromium

The basal glucose levels in carp plasma are in the same range as in mammals. Glucose tolerance tests in fish resulted in prolonged hyperglycemia with disposal rates resembling the diabetic state in mammals. Increasing doses of glucose and various physiological conditions had little effect on glucose disposal rates, suggesting a low sensitivity of insulin towards glucose levels. High rates of gluconeogenesis from ¹⁴C alanine were observed in starved fish and in fish fed a high-protein diet. The transformation of the amino acid to glucose via organic acid intermediates revealed a sensitive control of this pathway, probably at the substrate level. Treatment with cobalt or chromium salts improved glucose utilization and inhibited gluconeogenesis, most likely by modulating the endogenous insulin activity. In preliminary studies, cobalt also increased the incorporation of labelled amino acid into fish protein. These results might indicate a protein-sparing effect, thereby allowing a reduction in the protein levels in the fish diet while increasing the levels of these minerals in the diet.