Pregnancy Alters Diurnal Variation of Plasma Glucose Concentration

Human pregnancy introduces a diurnal variation of fasting plasma glucose concentrations, with significantly lower values found after a daytime fast of eight hours compared with a night-time fast of the same duration. The diurnal variation of plasma glucose clearance, found in nonpregnant subjects, is not demonstrable during pregnancy. Insulin tolerance does not exhibit a circadian valuation but is substantially decreased during pregnancy.     

Insulin and Corticoid Response to Intravenous Fructose in Relation to Glucose Tolerance

In 12 subjects with normal glucose tolerance fructose infusion was associated with a rise in plasma insulin and plasma corticoid levels. Similar but lesser changes were seen in seven maturity onset diabetics in whom there was also a considerable rise in blood glucose. It is suggested that a catabolite of fructose is responsible for these changes.     

Further Observations on the Diurnal Variation in Oral Glucose Tolerance

Diurnal variation in oral glucose tolerance was studied in 122 male volunteers aged 40 yearsand over who participated in a screening health examination. In those with screening blood sugar levels exceeding 110 mg./100 ml. the degree of diurnal variation was least in those with the highest morning glycaemia; the latter also tended to have lower afternoon fasting bloodsugar levels.In a group of 40 control subjects, afternoon glucose tolerance tests yielded significantly higher post-glucose blood sugar levels. The degree of diurnal variation was significantly and inversely related to the degree of obesity.     

Diurnal Variation of Oral Glucose Tolerance: a Possible Pointer to the Evolution of Diabetes Mellitus

Possible diurnal variation in the blood sugar response to oral glucose was studied by comparing, in the same individuals, the results of oral glucose tolerance tests performed in the morning and the afternoon. In a group of normal individuals the blood sugar levels were significantly higher in the afternoon. In hyperglycaemic individuals the diurnal variation decreased as the blood sugar levels reached during the morning test increased, so that in a group of grossly hyperglycaemic men the mean morning and afternoon tests were almost identical. The causes of this diurnal variation are not known.     

Effects of Dietary D-Psicose on Diurnal Variation in Plasma Glucose and Insulin Concentrations of Rats

The effects of supplemental D-psicose in the diet on diurnal variation in plasma glucose and insulin concentrations were investigated in rats. Forty-eight male Wistar rats were divided into four groups. Each group except for the control group was fed a diet of 5% D-fructose, D-psicose, or psico-rare sugar (3:1 mixture of D-fructose and D-psicose) for 8 weeks. Plasma glucose levels were lower and plasma insulin levels were higher at all times of day in the psicose and psico-rare sugar groups than in the control and fructose groups. Weight gain was significantly lower in the psicose group than in the control and fructose groups. Liver glycogen content, both before and after meals was higher in the psicose group than in the control and fructose groups. These results suggest that supplemental D-psicose can lower plasma glucose levels and reduce body fat accumulation. Hence, D-psicose might be useful in preventing postprandial hyperglycemia in diabetic patients.     

Diurnal Variation in Glucose Tolerance: Associated Changes in Plasma Insulin,Growth Hormone,and Non-esterified

Oral glucose tolerance tests were performed in the morning and afternoon of separate days on 31 people derived from a normal population sample. Blood sugar levels were higher in the afternoon test from and including 60 minutes after the glucose load. The degree of diurnal variation was similar in men and women, but greater in the older half of the group. It was negatively correlated with the degree of obesity. The plasma insulin response was less at the 30 minute time point in the afternoon, but significantly exceeded the morning values at 120 and 150 minutes after the glucose load. Growth hormone levels were similar in morning and afternoon tests. Fasting non-esterified fatty acid levels were significantly higher before the afternoon test.The relatively impaired glucose tolerance in the afternoon is associated with a delayed insulin response to the glucose load. This seems unlikely to be the sole explanation, however, and increased non-esterified fatty acid metabolism with a consequent decrease in glucose disposal may also contribute.     

Diurnal Variation in Urodynamics of Rat

In humans, the storage and voiding functions of the urinary bladder have a characteristic diurnal variation, with increased voiding during the day and urine storage during the night. However, in animal models, the daily functional differences in urodynamics have not been well-studied. The goal of this study was to identify key urodynamic parameters that vary between day and night. Rats were chronically instrumented with an intravesical catheter, and bladder pressure, voided volumes, and micturition frequency were measured by continuous filling cystometry during the light (inactive) or dark (active) phases of the circadian cycle. Cage activity was recorded by video during the experiment. We hypothesized that nocturnal rats entrained to a standard 12:12 light:dark cycle would show greater ambulatory activity and more frequent, smaller volume micturitions in the dark compared to the light. Rats studied during the light phase had a bladder capacity of 1.44±0.21 mL and voided every 8.2±1.2 min. Ambulatory activity was lower in the light phase, and rats slept during the recording period, awakening only to urinate. In contrast, rats studied during the dark were more active, had a lower bladder capacities (0.65±0.18 mL), and urinated more often (every 3.7±0.9 min). Average bladder pressures were not significantly different between the light and dark (13.40±2.49 and 12.19±2.85 mmHg, respectively). These results identify a day-night difference in bladder capacity and micturition frequency in chronically-instrumented nocturnal rodents that is phase-locked to the normal circadian locomotor activity rhythm of the animal. Furthermore, since it has generally been assumed that the daily hormonal regulation of renal function is a major driver of the circadian rhythm in urination, and few studies have addressed the involvement of the lower urinary tract, these results establish the bladder itself as a target for circadian regulation.     

Individual Differences in the Diurnal Cortisol Response to Stress

The objectives of this study were to explore individual differences associated with diverse reactions in cortisol secretion under different stress levels. This study was part of a larger project concerning working hours and health. Thirty-four white-collar workers participated under two different conditions; one work week with a high stress level (H) and one with a lower stress level (L) as measured through self-rated stress during workdays. Based on the morning cortisol concentration during a workday subjects were divided into two groups. One group consisted of subjects whose morning level of cortisol increased in response to the high-stress week, compared to their morning levels in the low-stress condition (Group 1). The other group consisted of subjects whose morning cortisol response was the opposite, with a lower level under the high stress condition (Group 2). Subjects wore actiwatches, completed a sleep diary, and rated their sleepiness and stress for one work week in each condition, i.e., high and low stress. Saliva samples for measures of cortisol were collected on a Wednesday. Group 2 reported higher workload, fatigue, and exhaustion during both weeks. Since there were no differences in perceived stress, neither within nor between groups, the data indicate that there are other factors influencing morning cortisol. The results suggest that one component modulating the cortisol response might be the level of exhaustion, probably related to work overload. Higher levels of stress in exhausted individuals might suppress morning cortisol levels.     

Zinc Supplementation Does Not Affect Glucagon Response to Intravenous Glucose and Insulin Infusion in Patients with Well-Controlled Type 2 Diabetes

Glucagon dysregulation is an essential component in the pathophysiology of type 2 diabetes. Studies in vitro and in animal models have shown that zinc co-secreted with insulin suppresses glucagon secretion. Zinc supplementation improves blood glucose control in patients with type 2 diabetes, although there is little information about how zinc supplementation may affect glucagon secretion. The objective of this study was to evaluate the effect of 1-year zinc supplementation on fasting plasma glucagon concentration and in response to intravenous glucose and insulin infusion in patients with type 2 diabetes. A cross-sectional study was performed after 1-year of intervention with 30 mg/day zinc supplementation or a placebo on 28 patients with type 2 diabetes. Demographic, anthropometric, and biochemical parameters were determined. Fasting plasma glucagon and in response to intravenous glucose and insulin infusion were evaluated. Patients of both placebo and supplemented groups presented a well control of diabetes, with mean values of fasting blood glucose and glycated hemoglobin within the therapeutic goals established by ADA. No significant differences were observed in plasma glucagon concentration, glucagon/glucose ratio or glucagon/insulin ratio fasting, after glucose or after insulin infusions between placebo and supplemented groups. No significant effects of glucose or insulin infusions were observed on plasma glucagon concentration. One-year zinc supplementation did not affect fasting plasma glucagon nor response to intravenous glucose or insulin infusion in well-controlled type 2 diabetes patients with an adequate zinc status.     

Diurnal Variation in Oral Glucose Tolerance: Blood Sugar and Plasma Insulin Levels Morning,Afternoon, and Evening

Twenty-four subjects received three oral glucose tolerance tests, in the morning, afternoon, and evening of separate days. The mean blood sugar levels in the afternoon and evening tests were similar, and they were both significantly higher than those in the morning test. Plasma immunoreactive insulin levels, however, were highest in the morning test. The pattern of insulin levels during the afternoon and evening tests resembled that described as typical of maturity-onset diabetes.     

Diurnal Variation in Nutrients and Chimpanzee Foraging Behavior

Primate feeding behavior varies over long (e.g., weekly, seasonally, yearly) and short (e.g., hourly) scales of time due to changes in resource availability and the nutritional composition of foods. While the factors that affect long‐term changes in feeding behavior have received considerable attention, few data exist regarding what drives variability in feeding behavior over the course of a single day. To address this problem, we investigated diurnal variation in chimpanzee feeding on the leaves of two species of saplings, Pterygota mildbraedii and Celtis africana, at Ngogo, Kibale National Park, Uganda. Specifically, we related short‐term changes in chimpanzee feeding behavior on these leaves to diurnal variation in their nutritional composition. Results showed that chimpanzees fed on the leaves of both saplings more in the evening than they did in the morning. The nutritional quality of leaves also improved over the course of the day. Concentrations of cellulose and lignin were lower and total nonstructural carbohydrates (including sugars and starch) were higher in the evening for P. mildbraedii, and sugars were higher in the evening for C. africana. These data suggest that chimpanzees consume these resources when their quality is highest, and consequently, may track the nutrient composition of their foods over very short periods that span only a few hours. In the future, foods collected for analyses must control for time of sampling to ensure biologically meaningful assays of nutrient composition. Am. J. Primatol. 75:342‐349, 2013. © 2013 Wiley Periodicals, Inc.     

Diurnal Variation in Insulin-stimulated Systemic Glucose and Amino Acid Utilization in Pigs Fed with Identical Meals at 12-Hour Intervals.

The diurnal variation in insulin-stimulated systemic glucose and amino acid utilization was investigated in eleven pigs of approximately 40 kg. Pigs were fed isoenergetic/isoproteinic diets (366 kJ/kg BW (0.75) per meal) in two daily rations (06:00 and 18:00 h). After a 3-week habituation period, hyperinsulinemic euglycemic euaminoacidemic clamp studies (by intra-portal insulin, glucose and amino acids infusion and arterial blood sampling) were performed starting at 06:00 or 18:00 h (while skipping the meal), using a cross-over within-animal design. Basal (preclamp) plasma concentrations of insulin, glucose, lactate, individual amino acids and urea were similar in the morning compared to the evening. Insulin-stimulated ( approximately 4-fold increase over basal) systemic glucose utilization was similar (17.6+/-1.4 and 18.9+/-1.8 mg.kg (-1).min (-1)) but amino acid utilization was 19% greater in the morning VS. the evening (2.37+/-0.21 VS. 1.99+/-0.15 mg.kg (-1).min (-1), p<0.05), respectively. Insulin-stimulated plasma lactate concentrations remained constant in the morning (0.77+/-0.06 to 0.71+/-0.04 mmol.l (-1)) but declined in the evening (0.89+/-0.09 to 0.65+/-0.06 mmol.l (-1), p<0.05). By contrast, insulin-stimulated plasma urea concentrations declined in the morning (2.48+/-0.11 to 2.03+/-0.10 mmol.l (-1), p<0.005) but remained constant in the evening (2.18+/-0.14 to 2.12+/-0.12 mmol.l (-1)). In conclusion, pigs fed identical meals at 12-hour intervals follow a clear diurnal biorhythm in protein anabolism, with greater insulin-stimulated systemic amino acid utilization and lower plasma urea response in the morning compared to the evening.     

Diurnal Glucose Profiles Using Continuous Glucose Monitoring to Identify the Glucose-Lowering Characteristics of Colesevelam HCL (WELCHOL)

ObjectiveThe study's purpose was to identify the antihyperglycemic affects of colesevelam-HCl (C-HCl) by characterizing the diurnal and postprandial glucose patterns in type 2 diabetic subjects treated concomitantly with metformin, sulfonylurea, or a combination of metformin/ sulfonylurea. A secondary aim was to determine whether C-HCl significantly increased the risk of hypoglycemia.MethodsA prospective, randomized, double-blind, placebo-controlled, crossover study employing continuous glucose monitoring (CGM) with ambulatory glucose profile (AGP) analysis was undertaken. Fifteen males and 6 females, age 60 ± 8 years, treated with metformin (n = 8), sulfonylurea (n = 2), or combination (n = 11) participated.ResultsTreatment with C-HCl led to reductions in glycated hemoglobin (HbAlc) (7.5 ± 0.3 to 7.0 ± 0.4% P<.0001), LDL (90.9 ± 18.6 to 68.9 ± 15.2 mg/dL, P<.0007) and total cholesterol (169.2 ± 24.4 to 147.8 ± 21.5 mg/dL, P<.001). Significantly lower normalized diurnal (21 mg/dL/hour, P = .0006), nocturnal (19 mg/dL/hour, P = .0005), and daytime (22 mg/dL/hour, P = .0008) glucose exposure was detected immediately upon C-HCl administration. Additionally, there was a significant (P<.004) decline in postprandial glucose excursions (averaging 15% or -36 mg/dL/hour) pronounced at dinner following C-HCl administration. There was a nonsignificant increase in the incidence of hypoglycemia (0.4-1%), with no difference due to antihyperglycemic medications.ConclusionsAGP analysis of CGM visually and quantitatively showed immediate and midterm impacts of C-HCl on basal and postprandial glucose patterns. This suggests a multifactorial glucose-lowering mechanism for C-HCl affecting both meal-related and basal glucose levels. (Endocr Pract. 2013;19:275-283)     

Shoot Elongation in Scots Pine: Diurnal Variations and Response to Temperature

Kanninen, M. 1985. Shoot elongation in Scots pine: Diurnal variationsand response to temperature.—J. exp. Bot. 36: 1760–1770. Time series analysis is used to study the diurnal variationsin the rate of shoot elongation of Scots pine (Pinus sylvestrisL.) seedlings, and its response to temperature. The shoot elongation of three 5-year-old Scots pine seedlingswas measured at 2 h intervals over a 12 d period in June 1979.Ambient temperature, measured with a thermocouple, was continuouslyrecorded during the same period. The measurements were carriedout in the field. Time series analysis of the data was carried out by estimatedauto-correlation and partial auto-correlation functions. A multiplicative‘seasonal’ model was applied to both the input andoutput series to ‘prewhiten’ the data set. Serialcross-correlation analysis of the prewhitened series was usedto identify the structure of the transfer function model betweentemperature and growth rate. There was a phase shift between the air temperature and shootextension. The cross-correlation function peaked at 2 h lagvalue. The influence of temperature on the growth rate was adequatelydescribed by a first-order transfer function model. The characteristicfeature of the model was a time constant of 3.3 h and a basetemperature of 6.3 °C for the response of shoot elongationto temperature. Key words: Scots pine, Pinus sylvestris L., shoot elongation, temperature response, time-series analysis     

Diurnal Variation in the Symptoms of Colds and Influenza

The present research examined diurnal variation in the severity of symptoms of experimentally-induced colds and influenza. Nasal secretion was greatest in the morning, decreased over the day, and then showed a slight increase in the late evening. Colds did not change the average temperature, nor did they alter the temperature rhythm. Similar, negative results were found with alertness ratings.

Influenza B illnesses produced an increase in nasal secretion and systemic effects. The average temperature increased during this illness and subjects reported that they felt more drowsy. Diurnal variation in the severity of local and central symptoms was observed, with nasal secretion and the temperature increase being greatest in the early morning. These results have important implications for the assessment and treatment of the illnesses.     

Therapeutic Utilization of the Diurnal Variation in Pituitary-Adrenocortical Activity

The degree of pituitary-adrenocortical suppression resulting from exogenous corticosteroid is related to the time of day the steroid is administered. Morning administration has less effect and evening administration a greater effect than do divided doses given over the course of the day.Clinical studies have shown that in the great majority of patients with corticosteroid responsive diseases, an intermittent dosage schedule is at least as effective as is administration of an equal dose in a three or four times a day regimen. Other undesirable side effects of corticosteroid therapy may also be decreased by an intermittent schedule. It is suggested that the customary divided dosage schedule for corticosteroid administration be replaced with an intermittent regimen, the medication being given in the morning. This may be once a day, or, if therapeutic results are satisfactory, once every other day.