DIETARY MAGNESIUM PREVENTS FRUCTOSE-INDUCED INSULIN INSENSITIVITY IN RATS

Increased dietary fructose may produce insulin insensitivity and eleva te blood pressure in rats. It is possible that the reduced magnesium c ontent of the high-fructose commercial diet used in some studies may p lay a role in these abnormalities because it is known that magnesium d eficiency can produce insulin insensitivity and increased angiotensin II action in humans. To study this, we maintained rats for 9 weeks on either a normal control diet, a standard high-fructose diet, or the sa me high-fructose diet supplemented with magnesium. Glucose uptake was assessed using a perfused rat hindquarter preparation sequentially wit h 0, 900, and 120 000 pmol/L of added insulin. Basal serum glucose, pl asma insulin, and basal glucose uptake in the absence of insulin were similar among all three groups. However, insulin sensitivity, defined as glucose uptake in the presence of 900 pmol/L insulin minus basal, w as depressed in the high-fructose compared with the control group (1.0 2+/-0.38 to 1.77+/-0.57 mu mol/g per hour, P<.05). In contrast, the hi gh-fructose group supplemented with normal magnesium had similar insul in sensitivity as the control group (2.09+/-0.69 mu mol/g per hour). T otal serum magnesium was reduced in the high-fructose group compared w ith control or high-fructose plus magnesium-supplemented groups. Blood pressure and fasting insulin levels were also lower in the magnesium- supplemented group. These results suggest that magnesium deficiency an d not fructose ingestion per se leads to insulin insensitivity in skel etal muscle and changes in blood pressure.