Improved insulin response and action by chronic magnesium administration in aged NIDDM subjects

Evidence for peripheral impaired glucose handling in patients with connective tissue diseases

Sixteen patients suffering from rheumatoid arthritis (RA) (n = 8), systemic lupus erythematosus (SLE) (n = 5), and systemic sclerosis (SSc) (n = 3), and 10 healthy subjects matched for age, sex, and body mass index, were submitted to an intravenous (IV) glucose tolerance test (GTT) (0.33 g/kg of body weight in 3 minutes) and to a euglycemic hyperinsulinemic glucose clamp to study insulin response and action. In the euglycemic clamp, along with the two insulin infusion rates (0.5 mU/kg.min from 0 to 120 minutes and 1 mU/kg.min from 121 to 240 minutes), a primed (20 microCi) continuous (0.2 microCi/min) infusion of 3H-glucose allowed determination of glucose kinetics. Our data show that patients versus controls have (1) a significant increase in basal plasma insulin levels (87.2 +/- 14.8 v 41.3 +/- 6.0 pmol/L, P less than .05); (2) similar glucose-induced acute insulin response; and (3) a lower glucose disappearance rate (Rd), glucose metabolic clearance rate (gMCR), and glucose infusion rate (GIR) when the lowest insulin infusion rate was delivered. These differences disappeared when the insulin infusion rate was doubled. Furthermore, basal plasma insulin levels and glucose disappearance rate significantly correlated with the main inflammatory indices of each disease studied. We conclude that in our patients impaired glucose handling is mainly due to peripheral insulin resistance.

Magnesium and glucose homeostasis

Magnesium is an important ion in all living cells being a cofactor of many enzymes, especially those utilising high energy phosphate bounds. The relationship between insulin and magnesium has been recently studied. In particular it has been shown that magnesium plays the role of a second messenger for insulin action; on the other hand, insulin itself has been demonstrated to be an important regulatory factor of intracellular magnesium accumulation. Conditions associated with insulin resistance, such as hypertension or aging, are also associated with low intracellular magnesium contents. In diabetes mellitus, it is suggested that low intracellular magnesium levels result from both increased urinary losses and insulin resistance. The extent to which such a low intracellular magnesium content contributes to the development of macro- and microangiopathy remains to be established. A reduced intracellular magnesium content might contribute to the impaired insulin response and action which occurs in Type 2 (non-insulin-dependent) diabetes mellitus. Chronic magnesium supplementation can contribute to an improvement in both islet Beta-cell response and insulin action in non-insulin-dependent diabetic subjects.