Association between stimulated plasma C-peptide and age: the Wadena City Health Study

Urinary total T3 levels as a method to monitor metabolic changes in relation to variation in caloric intake in captive bonobos (Pan paniscus)

Monitoring metabolic activity in wild living animals has become of particular interest in the field of ecological research. Methods for the repeated non-invasive sampling of individuals are needed. Thyroid hormones (TH) are involved in the regulation of metabolic activity, and their measurement can be used as a proxy to monitor metabolic changes. During periods of low energy intake, serum TH levels are reduced, leading to a decrease in metabolic activity. Using urine samples collected during a food restriction experiment in captive bonobos we validated a total triiodthyronin (TT3) enzyme immunoassay (EIA) for the monitoring of metabolic changes. We found that the majority of immune reactivity of the assay in the urine samples could be explained through immunoreactivity to T3. Furthermore, urinary T3 was stable through repeated freeze-thaw cycles but prolonged exposure to room temperature lead to degradation. Most importantly, we found that for all animals urinary total T3 levels were higher when more digestible energy was consumed. We concluded that urinary total T3 measurements are a suitable method for monitoring metabolic changes in bonobos and potentially in a wide range of animal species.

Urinary C-peptide is not an accurate bioindicator of energy balance in humans

The apprehension of the factors that affect long term regulation of energy balance is indispensable to understand the rise in obesity prevalence as well as to delineate levers to prevent it. Accurate measurements of energy balance are however challenging during free-living conditions. Recent studies proposed urinary C-peptide, a metabolic byproduct of insulin synthesis, as reliable noninvasive assessment of energy balance. These studies were in fact essentially based on correlations between urinary C-peptide and energy intake and only focused on nonhuman primates. During a bed-rest study conducted in 16 healthy women in a controlled environment, we tested the existence of a relationship between 24 h-urinary C-peptide and energy balance in humans. Daily energy intake and body mass, body composition (dual-energy X-ray absorptiometry (DXA)) and total energy expenditure (doubly labeled water (DLW) method) was measured and energy balance was calculated as the difference between energy intake and expenditure. Urinary C-peptide was positively correlated with bed-rest-induced changes in fat mass (r(2) = 0.285; P = 0.03) and energy balance assessed at the end of the bed-rest (r(2) = 0.302; P = 0.027). However, in this tightly controlled environment, urinary C-peptide only accounted for 30% of variations in energy balance. No relationship was noted between urinary C-peptide and body or fat mass both at baseline and at the end of the bed-rest. These results indicate that urinary C-peptide cannot be used as an accurate biomarker of energy balance in the general human population in free-living conditions.

The role of obesity in the association of cardiovascular risk factors and glucose intolerance in small Japanese and North American communities

To investigate whether the influence of obesity on cardiovascular risk factors and glucose intolerance differs between Japan and the US, we conducted cross-sectional surveys in those with elevated plasma glucose in Tanushimaru, Japan, and a stratified random population sample, in Wadena, MN. Subjects numbered 204 in Tanushimaru and 334 in Wadena. Body mass index (BMI), blood pressure, blood lipids, fasting plasma levels of glucose, glycosylated hemoglobin A(1c,) insulin, and free fatty acids were assessed. Overweight was defined as BMI of 27.5-29.9 kg/m(2) and obesity as BMI> or =30 kg/m(2). Gradual increases in risk factors were seen as BMI increased in both studies. Most risk factors were associated with glucose intolerance, except for BMI in Tanushimaru. In Wadena, glucose intolerance increased sharply among the obese. Adjustment for BMI attenuated the associations of cardiovascular risk factors with glucose intolerance in Wadena, but not in Tanushimaru. Obesity has an exaggerated influence on risk factors, compared with being overweight. The associations of glucose intolerance with cardiovascular risk factors are more affected by adjustment for BMI in Wadena than in Tanushimaru, not because of a different influence of body weight on risk factors between the two cities, but because obesity is rare in Japan.

Are specific serum insulin levels low in impaired glucose tolerance and type II diabetes?: measurement with a radioimmunoassay blind to proinsulin, in the population of Wadena, Minnesota

It has been suggested that serum insulin levels in subjects with recently diagnosed type II diabetes have been overestimated, and that after correction for proinsulin, true insulin levels are depressed rather than elevated. We tested this possibility in a cross-sectional study of a population-based sample of 328 adults living in Wadena, a Minnesota community in which residents are of northern European background. Specificity of insulin measurements was provided by an antibody blind to proinsulin and its major metabolite. Oral glucose tolerance and liquid mixed-meal (Ensure-Plus) tests were performed on separate days. Mean insulin levels before and 90 minutes after the mixed meal were as follows. Among 302 randomly ascertained adults not previously known to have diabetes, both fasting and postmeal levels in subjects with impaired glucose tolerance (IGT) and newly identified type II diabetes were equal to or greater than levels in subjects with normal glucose tolerance (fasting: normal 52 pmol/L, IGT 78, new type II 87; postmeal: 317, 565, and 406, respectively). The fasting insulin to glucose ratio was significantly increased in IGT and new type II diabetes subjects. Among 26 established (previously known) type II diabetic subjects not taking insulin, fasting levels were elevated and postmeal levels were normal in absolute terms (75 and 328), but were normal or low with respect to plasma glucose. Relationships among the groups were not materially changed by adjustment for body mass index (BMI), sex, age, or blood pressure. There was marked overlap of individual insulin levels from group to group. In summary, randomly selected adults in Wadena with IGT or asymptomatic diabetes showed, on average, elevated insulin levels, but physician-diagnosed diabetes was associated with relative diminution of serum insulin. In this population, the current view of insulin resistance in "early" diabetes was supported by insulin-specific measurements.