Does fasting interval affect the glucose challenge test?

Short-term sleep deprivation with nocturnal light exposure alters time-dependent glucagon-like peptide-1 and insulin secretion in male volunteers

The intestinal L cell is the principal source of glucagon-like peptide-1 (GLP-1), a major determinant of insulin release. Because GLP-1 secretion is regulated in a circadian manner in rodents, we investigated whether the activity of the human L cell is also time sensitive. Rhythmic fluctuations in the mRNA levels of canonical clock genes were found in the human NCI-H716 L cell model, which also showed a time-dependent pattern in their response to well-established secretagogues. A diurnal variation in GLP-1 responses to identical meals (850 kcal), served 12 h apart in the normal dark (2300) and light (1100) periods, was also observed in male volunteers maintained under standard sleep and light conditions. These findings suggest the existence of a daily pattern of activity in the human L cell. Moreover, we separately tested the short-term effects of sleep deprivation and nocturnal light exposure on basal and postprandial GLP-1, insulin, and glucose levels in the same volunteers. Sleep deprivation with nocturnal light exposure disrupted the melatonin and cortisol profiles and increased insulin resistance. Moreover, it also induced profound derangements in GLP-1 and insulin responses such that postprandial GLP-1 and insulin levels were markedly elevated and the normal variation in GLP-1 responses was abrogated. These alterations were not observed in sleep-deprived participants maintained under dark conditions, indicating a direct effect of light on the mechanisms that regulate glucose homeostasis. Accordingly, the metabolic abnormalities known to occur in shift workers may be related to the effects of irregular light-dark cycles on these glucoregulatory pathways.

Improved tolerance to sequential glucose loading (Staub-Traugott effect): size and mechanisms

Improved glucose tolerance to sequential glucose loading (Staub-Traugott effect) is an important determinant of day-to-day glycemic exposure. Its mechanisms have not been clearly established. We recruited 17 healthy volunteers to receive two sequential oral glucose tolerance tests (OGTTs), at time 0 min and 180 min (Study I). The protocol was repeated on a separate day (Study II) except that plasma glucose was clamped at 8.3 mmol/l between 60 and 180 min. beta-Cell function was analyzed by mathematical modeling of C-peptide concentrations. In a subgroup, glucose kinetics were measured by a triple-tracer technique (infusion of [6,6-(2)H(2)]glucose and labeling of the 2 glucose loads with [1-(2)H]glucose and [U-(13)C]glucose). In both Studies I and II, the plasma glucose response to the second OGTT equaled 84 +/- 2% (P = 0.003) of the response to the first OGTT. Absolute insulin secretion was lower (37.8 +/- 4.3 vs. 42.8 +/- 5.1 nmol/m(2), P = 0.02), but glucose potentiation (i.e., higher secretion at the same glycemia) was stronger (1.08 +/- 0.02- vs. 0.92 +/- 0.02-fold, P = 0.006), the increment being higher in Study II (+36 +/- 5%) than Study I (+19 +/- 6%, P < 0.05). In pooled data, a higher glucose area during the first OGTT was associated with a higher potentiation during the second OGTT (rho=0.60, P = 0.002). Neither insulin clearance nor glucose clearance differed between loads, and appearance of glucose over 3 h totalled 60 +/- 6 g for the first load and 52 +/- 5 g for the second load (P = not significant). Fasting endogenous glucose production [13.3 +/- 0.6 micromol x min(-1) x kg fat-free mass (FFM)(-1)] averaged 6.0 +/- 3.8 micromol x min(-1) x kg FFM(-1) between 0 and 180 min and 1.7 +/- 2.6 between 180 and 360 min (P < 0.03). Glucose potentiation and stronger suppression of endogenous glucose release are the main mechanisms underlying the Staub-Traugott effect.

Screening and testing for gestational diabetes mellitus

Gestational diabetes mellitus is defined as carbohydrate intolerance of variable severity first diagnosed during pregnancy. Although universal screening for gestational diabetes mellitus is practiced by more than 75% of obstetricians in the United States, agreement is lacking worldwide regarding the appropriateness of this approach. This article discusses the assumption that some type of screening program is desirable and considers how best to conduct screening and diagnostic testing for gestational diabetes mellitus.

Glucose intolerance as a predictor of hypertension in pregnancy

Insulin resistance is associated with and may be causal in essential hypertension, but the relation between insulin resistance and hypertension arising de novo in pregnancy is unclear. Transient hypertension of pregnancy (new-onset nonproteinuric hypertension of late pregnancy) is associated with a high risk of later essential hypertension and thus may have similar pathophysiology. To assess the association between glucose intolerance and subsequent development of proteinuric and nonproteinuric hypertension in pregnancy in women without underlying essential hypertension or overt glucose intolerance, we performed a retrospective case-control study comparing glucose levels on routine screening for gestational diabetes mellitus among women subsequently developing hypertension. Women who developed hypertension in pregnancy (n = 97) had significantly higher glucose levels on 50-g oral glucose loading test (P < .01) and a significantly higher frequency of abnormal glucose loading tests (> or = 7.8 mmol/L) (P < .01) than women who remained normotensive (n = 77). Relative glucose intolerance was particularly common in women who developed nonproteinuric hypertension. Women who developed hypertension also had greater prepregnancy body mass index (P < or = .0001) and baseline systolic and diastolic blood pressures (P < or = .0001 for both), although all subjects were normotensive at baseline by study design. However, after adjustment for these and other potential confounders, an abnormal glucose loading test remained a significant predictor of development of hypertension (P < .05) and, specifically, nonproteinuric hypertension in pregnancy (P < .01). Among a subgroup of women in whom insulin levels were also measured (n = 80), there was a nonsignificant trend toward higher insulin levels in women developing hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)