Effects of high doses of manganese on carbohydrate homeostasis.

The effects of manganese (Mn) toxicity on carbohydrate homeostasis was examined in Sprague-Dawley and Osborne-Mendel rats. Mn injection was followed by increases in Mn concentration in both liver and pancreas. Concentrations of Mn in the pancreas increased more rapidly than in the liver. Plasma insulin levels decreased, plasma glucose levels increased, and a spike in glucagon concentration was observed following Mn injection. Increases in blood glucose in response to Mn injection were also observed in 24- and 48-h fasted rats, although the magnitude of the increase was less than that observed in fed rats. Both strains of rats appeared to respond similarly to Mn injection. The present studies demonstrate that acute Mn injection can affect glucose homeostasis. These effects may be mediated through altered endocrine pancreatic function.