Effects of extreme hyperinsulinaemia on serum levels of trace metals, trace metal binding proteins, and electrolytes in normal females

Abstract

Abstract. In order to assess the possible effects of insulin on serum concentrations of trace metals (iron, copper, zinc) and trace metal binding proteins (ferritin, transferrin, coeruloplasmin), five normal females were studied with the hyperinsulinaemic-euglycaemic clamp technique. A 0.1 U/kg insulin bolus was administered, followed by an insulin infusion at a rate of 10 mU/kg/min for 12–16 h. Insulin levels of 1500–2000 μU/ml (9.21– 12.28 nmol/l) were attained. When iron levels in serum were assayed colorimetrically, there appeared to be a progressive rise in the mean concentration during the course of the insulin infusion. Direct analysis of serum samples by atomic absorption spectrophotometry also showed that the level of non-haeme iron increased 3-fold in the serum of the subject with the lowest concentration of this metal at the start of the study. In contrast with the results for serum iron, the levels of ferritin, total iron binding capacity (transferrin), zinc, copper and coeruloplasmin were not altered in any subject during the insulin infusion or at 24 h following discontinuation of the infusion. Within 4 h of institution of the hyperinsulinaemic clamp significant reductions in serum levels of potassium, phosphorus, cholesterol, total protein and albumin were noted. As the insulin infusion progressed, the urea nitrogen, uric acid and bicarbonate levels fell as well. These observations suggest that supraphysiologic hyperinsulinaemia of 12–16 h duration may alter serum levels of iron, but not serum levels of zinc, copper or trace metal binding proteins in some individuals. The mechanism(s) responsible for the rise in mean serum iron, the reductions in serum total protein and albumin, and for the development of a non-anion gap acidosis remain unclear.