Clinical studies have demonstrated that chloroquine and hydroxychloroquine improve glucose metabolism in patients with insulin-resistant diabetes mellitus. The mechanism of action has not been determined. We undertook a randomized double-blind placebo-controlled trial of 3 days of oral chloroquine phosphate, 250 mg four times daily, in 20 patients with non-insulin-dependent diabetes mellitus controlled by diet. Rates of glucose appearance (Ra) and disappearance (Rd) were evaluated by infusion of stable isotopically labeled D-glucose ([6,6-2H2]glucose) during hyperinsulinemic euglycemic clamps before and after treatment with chloroquine or placebo. Chloroquine significantly improved fasting plasma glucose from 199.8 +/- 8.6 to 165.6 +/- 7.6 mg/dl (P less than 0.01). Total exogenous glucose infusion required to maintain euglycemia significantly increased (1,792.6-2,040.1 mg.kg-1.330 min-1, P less than 0.05) due to an increase in Rd (2,348.0-2,618.9 mg.kg-1.330 min-1, P less than 0.01) without change in Ra. Metabolic clearance rate of insulin decreased by 39% from 14.4 +/- 1.3 to 11.0 +/- 0.6 ml.kg-1.min-1 (P less than 0.01) at plasma insulin levels of 150-200 mU/l but not at levels of 2,000-3,000 mU/l. In addition, chloroquine increased fasting C-peptide secretion by 17% and reduced feedback inhibition of C-peptide by 9.1 and 10.6% during low- and high-dose insulin infusions, respectively.

Insulin-like growth factor I (IGF-I) is thought to mediate the anabolic action of growth hormone. A glucose and amino acid clamp technique was used to investigate the effects of a 3-h intravenous infusion of either 43.7 pmol.kg-1.min-1 (20 micrograms.kg-1.h-1) IGF-I or 3.4 pmol.kg-1.min-1 (0.5 mU.kg-1.min-1) insulin on whole body leucine turnover in five normal human volunteers. During the IGF-I infusion, IGF-I levels increased (P < 0.01; 26.6 +/- 2.8 to 88.9 +/- 14.2 nmol/l) and insulin levels fell (P < 0.05; 0.096 +/- 0.018 to 0.043 +/- 0.009 nmol/l). During the insulin infusion, insulin levels increased (P < 0.01; 0.057 +/- 0.013 to 0.340 +/- 0.099 nmol/l), and there was no change in IGF-I. There was no significant change in leucine production rate (Ra; a measure of protein degradation) during the IGF-I infusion (2.23 +/- 0.17 to 2.13 +/- 0.2 mumol.kg-1.min-1), but there was an increase (P < 0.03) in nonoxidative leucine disposal rate (Rd; a measure of protein synthesis; 1.83 +/- 0.15 to 2.05 +/- 0.21 mumol.kg-1.min-1). In contrast, insulin reduced (P < 0.02) leucine Ra (1.81 +/- 0.24 to 1.47 +/- 0.24 mumol.kg-1.min-1) and had no effect on nonoxidative leucine Rd (1.44 +/- 0.25 to 1.41 +/- 0.22 mumol.kg-1.min-1). We conclude that IGF-I, under conditions of adequate substrate supply, directly increases protein synthesis in contrast to insulin, which exerts its anabolic action by reducing proteolysis.

The effect of thyroid hormone excess on hepatic glucose balances and fractional hepatic extraction of insulin and glucagon was examined in six conscious dogs with catheters in the portal vein, hepatic vein, and femoral artery and Doppler flow probes on the portal vein and hepatic artery. An oral glucose tolerance test was performed before and after the animals were made hyperthyroid by intramuscular thyroxine administration (100 micrograms.kg-1.day-1) for 10 days. In the basal state and after oral glucose, insulin and glucagon levels in the three vessels and the basal fractional hepatic extraction of insulin and glucagon were not significantly modified by thyroid hormone. These results suggest that in short-term thyrotoxicosis insulin secretion is not impaired, and the rise in fasting plasma glucose and increased hepatic glucose production could reflect hepatic insulin resistance, increased availability of precursors for gluconeogenesis, or increased glycogenolysis. Hyperthyroidism significantly increased basal flows in the portal vein (14.7 +/- 0.6 vs. 12.9 +/- 0.5 ml.kg-1.min-1), the hepatic artery (4.8 +/- 0.3 vs. 3.9 +/- 0.2 ml.kg-1.min-1) and vein (19.6 +/- 0.7 vs. 16.9 +/- 0.4 ml.kg-1.min-1), the fasting plasma glucose concentration (104 +/- 3 vs. 92 +/- 2 mg/dl), and basal hepatic glucose output (2.1 +/- 0.2 vs. 1.5 +/- 0.2 mg.kg-1.min-1). It did not alter the nonhepatic splanchnic uptake of glucose, the percent of orally administered glucose that appeared in the portal vein (47 +/- 2 vs. 45 +/- 11%), the percent of hepatic uptake of glucose (59 +/- 11 vs. 74 +/- 22%), or the shape of the glucose tolerance test.

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