Secretion of glucagon, GLP-1 and GIP may be affected by circadian rhythm in healthy males.

BACKGROUND: Glucagon is secreted from pancreatic alpha cells in response to low blood glucose and increases hepatic glucose production. Furthermore, glucagon enhances hepatic protein and lipid metabolism during a mixed meal. Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) are secreted from gut endocrine cells during meals and control glucose homeostasis by potentiating insulin secretion and inhibiting food intake. Both glucose homeostasis and food intake have been reported to be affected by circadian rhythms and vice versa. In this study, we investigated whether the secretion of glucagon, GLP-1 and GIP was affected by circadian rhythms. METHODS: A total of 24 healthy men with regular sleep schedules were examined for 24 h at the hospital ward with 15 h of wakefulness and 9 h of sleep. Food intake was standardized, and blood samples were obtained every third hour. Plasma concentrations of glucagon, GLP-1 and GIP were measured, and data were analyzed by rhythmometric statistical methods. Available data on plasma glucose and plasma C-peptide were also included. RESULTS: Plasma concentrations of glucagon, GLP-1, GIP, C-peptide and glucose fluctuated with a diurnal 24-h rhythm, with the highest levels during the day and the lowest levels during the night: glucagon (p < 0.0001, peak time 18:26 h), GLP-1 (p < 0.0001, peak time 17:28 h), GIP (p < 0.0001, peak time 18:01 h), C-peptide (p < 0.0001, peak time 17.59 h), and glucose (p < 0.0001, peak time 23:26 h). As expected, we found significant correlations between plasma concentrations of C-peptide and GLP-1 and GIP but did not find correlations between glucose concentrations and concentrations of glucagon, GLP-1 and GIP. CONCLUSIONS: Our results demonstrate that under meal conditions that are similar to that of many free-living individuals, plasma concentrations of glucagon, GLP-1 and GIP were observed to be higher during daytime and evening than overnight. These findings underpin disturbed circadian rhythm as a potential risk factor for diabetes and obesity. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT06166368. Registered 12 December 2023.

Evaluation of Serum Insulin-like Factor 3 Quantification by LC-MS/MS as a Biomarker of Leydig Cell Function.

BACKGROUND: The peptide hormone insulin-like factor 3 (INSL3) is a marker for Leydig cell function and the clinical use of serum INSL3 measurements has been suggested by several groups. AIM: (1) To establish a reference range for liquid chromatography-tandem mass spectrometry (LC-MS/MS) of serum INSL3 in healthy boys and men; and (2) to compare the associations of serum INSL3 and testosterone (T) to pubertal stage, lifestyle factors, diurnal variation, body composition, and human chorionic gonadotropin (hCG) stimulation. RESULTS: In a reference range based on LC-MS/MS analysis of serum from 1073 boys and men, INSL3 increased from levels close to the detection limit (0.03 µg/L) in prepubertal boys to a maximum mean level of 1.3 µg/L (95% CI, 0.9-2.7) in young men (19-40 years of age) and decreased slightly in older men (0.1 µg/L per decade). Serum T, but not INSL3, was associated with body mass index or body fat percentage and with alcohol consumption. Smoking was positively associated with serum T, but negatively associated with INSL3. There were significant diurnal variations in both INSL3 and T in men (P < 0.001), but serum INSL3 varied substantially less, compared with serum T (± 11% vs ± 26%). Mean serum INSL3 increased after hCG stimulation, but less than T (+ 17% vs + 53%). In both healthy men and in patients suspected of testicular failure, baseline serum INSL3 was more closely associated to the hCG-induced increase in serum T than baseline T itself. CONCLUSION: Measurement of serum INSL3 by LC-MS/MS has promise as a marker of testicular disorders.

Diurnal variation of hematology parameters in healthy young males: the Bispebjerg study of diurnal variations.

PURPOSE: To evaluate the influence of time of day on the circulating concentrations of 21 hematology parameters. MATERIALS AND METHODS: Venous blood samples were obtained under standardized circumstances from 24 healthy young men every third hour through 24 hours, nine time points in total. At each time point, the level of melatonin, iron, transferrin, transferrin saturation, ferritin, cobalamin, folate, red blood cells and white blood cells was measured. The data were analysed by rhythmometric statistical methods. The biological variations were calculated. RESULTS: Significant oscillation of melatonin (p < 0.0001) with an amplitude (amp) of 19.84 pg/ml and a peak level at 03:34 h confirmed the normal 24-hour rhythms of the participants. Erythrocytes (p < 0.0001, amp = 0.15 × 10(12)/L), hemoglobin (p < 0.0001, amp = 0.29 mmol/L), hematocrit (p < 0.0001, amp = 0.01), iron (p < 0.0001, amp = 4.00µmol/L), transferrin (p = 0.03, amp = 1.41µmol/L), transferrin saturation (p < 0.0001, amp = 6.37%) and folate (p < 0.0001, amp = 1.55nmol/L) oscillated significantly, with gradually falling mean levels through the day to nadir around midnight. Leukocyte count (p < 0.0001, amp = 0.78 × 10(9)/L), neutrophils (p = 0.001, 0.31 × 10(9)/L), eosinophils (p < 0.0001, amp = 0.04 × 10(9)/L), monocytes (p = 0.0009, amp = 0.06 × 10(9)/L), lymphocytes (p < 0.0001, amp = 0.49 × 10(9)/L) oscillated significantly with gradually increasing mean levels through the day peaking at midnight. Iron, leukocytes and hemoglobin had the highest 24 hour oscillations in proportion to the reference intervals of the parameters for healthy young men. CONCLUSIONS: Biochemical screenings are biased by diurnal variations, which must be considered when blood concentrations of these parameters are interpreted in the clinical setting.

Biological variation of free ß chorionic gonadotropin and pregnancy-associated plasma protein A in first trimester pregnancies.

BACKGROUND: Trisomy 21 risk estimation in first trimester pregnancies can be performed by a combined test based on ultrasound measurement of fetal nuchal translucency thickness and maternal plasma concentrations of free ß human chorionic gonadotropin (hCGß) and pregnancy-associated plasma protein A (PAPP-A). However, little knowledge exists regarding the biological variation of hCGß and PAPP-A when the time interval between sampling increases. METHODS: We estimated these variations from double measurements of hCGß and PAPP-A in first trimester pregnancies in 167 women. Data were divided into three groups based on the number of days between sampling. The correlation coefficients and biological variation were estimated for each group. RESULTS: The correlation coefficient between the first and second samples was 0.841 for hCGß, and 0.706 for PAPP-A. The ranges for biological variation were 11.9%-48.5% for hCGß and 31.6%-63.3% for PAPP-A, increasing with time between sampling. The average overall biological variation for hCGß was 29%, and 49.7% for PAPP-A. CONCLUSIONS: We found high biological variation for plasma concentrations of hCGß and PAPP-A, increasing with longer time intervals between sampling. From our data that showed high correlation of hCGß and PAPP-A in the first and second sample, we found no reason to recommend retesting. However, new studies should clarify whether PAPP-A should be collected early, and hCGß late, in the first trimester of pregnancy.