Repeatability and reproducibility of the hyperinsulinemic-euglycemic clamp and the tracer dilution technique in a controlled inpatient setting.

The objective of the study was to evaluate the reproducibility and repeatability of the combined use of the hyperinsulinemic-euglycemic (H-E) clamp and tracer dilution techniques. Ten nondiabetic men underwent a low-dose (40 mU/[m(2) min]) H-E clamp that was repeated within 3 to 4 days using porcine or human insulin in a double-blinded, randomized, crossover design. Coefficients of variation (CVs) for intraindividual differences and repeatability coefficient were calculated to evaluate reproducibility and repeatability. The Bland and Altman method was used to quantify repeatability. The CVs for intraindividual differences were 5.7% +/- 3.5% for steady-state (SS) insulin; 6.7% +/- 6.2% and 54.2 +/- 38.3% for basal and SS endogenous glucose product (EGP), respectively; and 10.3% +/- 8.5% for total insulin-stimulated glucose disposal (M) values. Basal EGP, SS EGP, and SS glucose and insulin concentrations were similar for the 2 clamps; but glucose infusion rate (P = .02) and M (borderline significant, P = .06) were higher in the first clamp than the second clamp. No significant correlations between mean of differences and average of basal and SS EGP, SS insulin concentration, and M between the 2 clamps were observed. We also found that the different values were less than the repeatability coefficients of these parameters and that the 95% limits of agreement and the interval of repeatability coefficient of these parameters were similar. There were no differences in metabolic responses between clamps when compared by the type of insulin (porcine vs human) infused. Our findings indicate that, although SS EGP has a high CV, the clamp, which measures insulin action (ie, SS insulin, M), and the tracer dilution technique for assessing basal EGP are repeatable and reproducible. Decreased glucose infusion rate and M over a short period in the second clamp may reflect an accumulative effect of continued physical inactivity.

Physiological evidence for the involvement of peptide YY in the regulation of energy homeostasis in humans.

OBJECTIVE: To explore the potential role of the endogenous peptide YY (PYY) in the long-term regulation of body weight and energy homeostasis. RESEARCH METHODS AND PROCEDURES: Fasting and postprandial plasma PYY concentrations were measured after an overnight fast and 30 to 180 minutes after a standardized meal in 29 (21 men/8 women) non-diabetic subjects, 16 of whom had a follow-up visit 10.8 +/- 1.4 months later. Ratings of hunger and satiety were collected using visual analog scales. Resting metabolic rate (RMR) (15-hour RMR) and respiratory quotient (RQ) were assessed using a respiratory chamber. RESULTS: Fasting PYY concentrations were negatively correlated with various markers of adiposity and negatively associated with 15-hour RMR (r = -0.46, p = 0.01). Postprandial changes in PYY (area under the curve) were positively associated with postprandial changes in ratings of satiety (r = 0.47, p = 0.01). The maximal PYY concentrations achieved after the meal (peak PYY) were negatively associated with 24-hour RQ (r = -0.41, p = 0.03). Prospectively, the peak PYY concentrations were negatively associated with changes in body weight (r = -0.58, p = 0.01). DISCUSSION: Our data indicate that the endogenous PYY may be involved in the long-term regulation of body weight. It seems that this long-term effect was not exclusively driven by the modulation of food intake but also by the control of energy expenditure and lipid metabolism.

The intra- and inter-instrument reliability of DXA based on ex vivo soft tissue measurements.

OBJECTIVE: Comparison of ex-vivo soft tissue measurements using the GE/Lunar pencil (DPX-L; GE/Lunar Co., Madison, WI) and fan beam (Prodigy dual-energy X-ray absorptiometers (DXA) GE/Lunar Co.). RESEARCH METHODS AND PROCEDURES: Intra-instrument reliability was assessed by repeatedly scanning soft tissue phantoms for lean tissue (water) and fat tissue (methanol) using one DPX-L and two identical Prodigy DXAs at fast, medium, and slow scan modes. For each machine, 10 scans of each phantom were performed at each scan speed. The number of scans per instrument totaled 60. Data were analyzed using ANOVA to ascertain whether scan speed affected the intra-instrument reliability and to test whether soft tissue measurements differed among instruments. Percentage fat (phantom density) was the outcome variable. RESULTS: Intra-instrument reliability, expressed as coefficient of variation, ranged between 0.7% and 5.2% for the DPX-L and 0.4% and 4.5% for the Prodigy, with the lowest coefficients of variation observed when scanning the fat tissue phantom. Scan speed also affected the intra-instrument reliability (p < 0.01). Furthermore, differences in the measurement of percentage body fat for both the lean and fat tissue phantoms were observed among all three absorptiometers (all p < 0.01). After adjusting for scan speed, differences persisted for all three instruments. DISCUSSION: Intra- and inter-instrument reliability of DXA machines, even those from the same manufacturer, remains unpredictable. Thus, when measuring body composition using DXA, it is important to consider that even in the absence of measurement bias, the use of different DXA machines, particularly when using a variety of speed settings, will increase the residual error around the true value.