Increased insulin sensitivity in iron-deficient rats

Iron deficient (ID) and control (C) rats were studied to determine if severe iron deficiency alters insulin-stimulated glucose disposal. Euglycemic hyperinsulinemic glucose clamps were conducted by infusing insulin (2 m mu.kg-1.min-1, constant rate) for 120 min while maintaining euglycemia. In a 12-h fasted state, ID rats were hyperglycemic (109.4 +/- 4.0 mg.dL-1 arterial plasma glucose, x +/- SEM) when compared with C rats (86.9 +/- 3.4 mg.dL-1) (P less than 0.05). Even though insulin was infused identically on a per kilogram body weight basis for both groups, the resulting hyperinsulinemia was higher in ID rats (3.1 +/- 0.27 ng.mL-1) compared with C rats (2.3 +/- 0.4 ng.mL-1) at the end of the clamp. Glucose infusion rates required to maintain euglycemia were twofold higher in ID rats (27.0 +/- 5.4 mg.kg-1.min-1) versus C rats (13.1 +/- 3.3 mg.kg-1.min-1) (P less than 0.05). Circulating lactic acid increased in both groups, and the concentrations in ID rats (3.2 +/- 0.4 mmol.L-1) were significantly higher than those in C rats (1.8 +/- 0.5 mmol.L-1) at the end of the clamp. When the efficiency of insulin to dispose glucose was evaluated by calculating the glucose disposal divided by the prevailing insulinemia, ID rats could dispose of almost twice the glucose per unit of insulin [9.0 +/- 0.6 (mg.kg-1.min-1)/(ng.mL-1)] when compared with C rats [5.6 +/- 0.9 (mg.kg-1.min-1)/(ng.mL-1)] (P less than 0.05). The data indicate that insulin sensitivity is increased in ID rats and that ID rats cannot metabolize exogenous insulin as well as C rats.

Exercise intensity, dietary intake, and high-density lipoprotein cholesterol in young female competitive swimmers

Plasma high-density and low-density lipoprotein cholesterol (HDL-C and LDL-C) and dietary intake were compared in female competitive swimmers (CS, n = 7), synchronized swimmers (SS, n = 11), and sedentary controls (C, n = 6). CS tended to be taller, heavier, and leaner than C; SS were intermediate. The caloric intake of CS was 21.5% greater than C (2468 +/- 534 versus 2030 +/- 668, p less than 0.001). Dietary composition for all groups was 49% carbohydrate, 35% fat, and 15% protein. Total plasma cholesterol (TC) and LDL-C were not significantly different among groups. HDL-C, and HDL-C/TC were increased in CS compared with SS and C. HDL-C was 17 and 22% higher for CS than SS or C (82.0 +/- 14.6 versus 70.0 +/- 10.9 versus 67.2 +/- 14.0 mg/dl, p less than 0.05, respectively). The results of the current study indicate that plasma HDL-C is significantly elevated in young women who participate in an intensive, but not moderate, exercise regimen.

A practical and reliable method for determination of urinary 3-methylhistidine

A practical and reliable semiautomated method for analysis of urinary 3-methylhistidine (3-MH) was designed combining the isolation of 3-MH by ion-exchange chromatography with the color reaction given by ninhydrin-orthopthalaldehyde (ninhydrin-OPT) reagent after alkalinization. 2 ml of urine were passed through disposable columns packed with an ion-exchange resin (Dowex 50-X8, 200-400 mesh) and the acidic and neutral amino acids were eluted with 10 ml of 0.2 M pyridine solution. Then, the 3-MH was quantitatively eluted and separated from histidine with a volume of 9 ml of a 1.5 M pyridine solution. Standard Autoanalyzer equipment was used for the automation of spectrophotometry. The method permits the analysis of 40 samples in duplicate per day. The 3-MH color reaction was linear for concentrations from 0.015 to 0.24 mu mol/ml. The mean recoveries of 3-MH from standards and urine were 98.6 +/- 1.3 and 99.0 +/- 1.3%, respectively. Duplicate determinations of urine samples showed a variation coefficient of 1.8%. An excellent agreement was obtained between urine samples analyzed by the present method and by an amino acid analyzer. The need for the elimination of the interfering amino acids was clearly demonstrated.