Diagnostic challenges in patients with reninomas and extrarenal renin-producing tumours.

Renin-secreting tumours are rare causes of secondary hypertension and hypokalaemia. They are usually surgically curable, hence proper diagnostic work-up and tumour localisation is essential. In this paper, we present three Swedish patients recently diagnosed with renin secreting tumours, two with reninomas and one with an extrarenal renin-producing tumour, to illustrate diagnostic challenges. We also discuss the biochemical work-up, the pros and cons of different imaging techniques (computer tomography [CT], magnetic resonance imaging and [18F]fluorodeoxyglucose-positron emission tomography-CT), as well as how renal vein sampling (RVC) may contribute to localisation of the tumour.

[Hyperthyroidism - a classic disease]. / Hypertyreos är inte bara endokrinologens angelägenhet.

Hyperthyroidism presents with various forms of generalized symptoms. Primary care physicians as well as other specialists should have this in mind when meeting patients with symptoms such as palpitations, sweating, fatigue and weight loss. Thyroid-stimulating hormone (TSH) is a highly specific test and useful in ruling out hyperthyroidism. The severity of the disease determines the pace of management. Primary care is often involved in detection of hyperthyroidism but also takes part in the work of rehabilitation and the lifelong hormonal substitution that is necessary for 2/3 of all patients. Subclinical hyperthyroidism, characterized by low TSH levels but normal levels of T4 and T3, is associated with increased mortality by 24 percent and risks of cardiovascular disease, atrial fibrillation and osteoporosis. Treatment depends on age, presence of comorbidity and TSH-levels. In addition to specific endocrinological treatment, person-centered care is crucial during active disease and rehabilitation. The first Swedish care program for hyperthyroidism aims to enhance care efficiency and equity.

Mortality Not Increased in Patients With Nonfunctional Adrenal Adenomas: A Matched Cohort Study.

CONTEXT: Mild autonomous cortisol secretion (MACS) is associated with increased mortality in patients with adrenal incidentalomas, but little is known regarding the potential risk associated with nonfunctional adrenal adenomas (NFAA), which constitute the majority of adrenal incidentalomas. OBJECTIVE: Compare mortality risk in patients with NFAA, and different levels of MACS, to matched controls. METHOD: This was a retrospective matched cohort study. All patients referred to 2 endocrine centers in southern Sweden because of an adrenal incidentaloma between 2005 and 2015 were enrolled. Controls (3:1) matched for sex, age, and residency were included. Primary endpoint was all-cause mortality. Outcome data were obtained from the Cause of Death Register. Patients were grouped according to cortisol level post 1-mg dexamethasone suppression test (cortisolDST) (<50 (NFAA), 50-82, 83-137, and ≥138 nmol/L). RESULTS: 1154 patients and 3462 matched controls were included. During a median follow-up of 6.6 years, 210 patients and 505 controls died. There were no statistically significant differences in mortality between patients with NFAA and their controls (HR 1.13 [0.87-1.46]) whereas mortality was increased compared to controls in patients with cortisolDST 83-137 (HR 1.99 [1.38-2.88]) and ≥138 nmol/L (HR 4.09 [2.41-6.93]). Likewise, the mortality risk was increased in patients younger than 65 years with cortisolDST 50-82 nmol/L compared with controls (HR 2.33 [1.30-4.17]). CONCLUSION: NFAA does not seem to pose a clinically relevant risk for increased mortality in patients with adrenal incidentalomas while patients with MACS, and especially younger patients and those with cortisolDST ≥83 nmol/L, have significantly increased mortality risk compared with matched controls.

Glucose-dependent insulinotropic polypeptide and glucagon-like peptide-1 secretion in humans: Characteristics and regulation.

AIMS/INTRODUCTION: Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are important incretin hormones. They are released from the gut after meal ingestion and potentiate glucose-stimulated insulin secretion. Their release after meal ingestion and oral glucose are well established and have been characterized previously. During recent years, knowledge of other regulatory aspects that potentially may affect GIP and GLP-1 secretion after meal ingestion have also begun to emerge. Here, the results of human studies on these novel aspects of meal- and nutrient-stimulated incretin hormone secretion are reviewed. MATERIALS AND METHODS: The human literature was revisited by identifying articles in PubMed using key words GIP, GLP-1, secretion, meal, and nutrients. RESULTS: The results show that all macronutrients individually stimulate GIP and GLP-1 secretion. However, there was no synergistic action when given in combination. A pre-load 30 min before a meal augments the GIP and GLP-1 response. GIP and GLP-1 secretion have a diurnal variation with a higher response to an identical meal in the morning than in the afternoon. There is no difference in GIP and GLP-1 secretion whether a meal is ingested slowly or rapidly. GIP and GLP-1 secretion after dinner are the same whether or not breakfast and lunch have been ingested. The temperature of the food may be of importance for the incretin hormone response. CONCLUSIONS: These novel findings have increased our knowledge on the regulation of the complexity of the incretin system and are also important knowledge when designing future studies.

Increased risk of Graves´ophthalmopathy in patients with increasing TRAb after radioiodine treatment and the impact of CTLA4 on TRAb titres.

INTRODUCTION: Treatment of Graves´ disease (GD) with radioiodine increases the risk of developing Graves´ ophthalmopathy (GO), and the link between thyroid and orbital tissue may be the presence of TSH-receptors. Radioiodine increases the titers of TRAb and the aim was to investigate the relationship between GO and TRAb titers after treatment with radioiodine and to define the impact of risk genes. METHODS: GD patients without ophthalmopathy or previous treatment with radioiodine were prospectively included at treatment with radioiodine for hyperthyroidism. A follow-up was performed 1 year later for the registration of GO development. The study was performed at a University Hospital Clinic; a referral center of all patients treated with radioiodine in the south of Sweden. The main outcome measures were the development of TRAb, anti-TPO, and anti-TG after 3 months and GO after 12 months and relationship to the genetic background (HLA, CTLA-4, and CYR61). RESULTS: Three months of radioiodine TRAb titers increased in two thirds of patients (p < 0.0005) but not in the other third. Anti-TPO titers were associated with TRAb (R = 0.362, p < 0.0001) but not anti-TG. At follow-up 1 year later (n = 204) 32 patients developed GO with a proportion of 70% in the group increasing in TRAb titers and 30% in the group with unchanged or lower TRAb titers (p-value < 0.0005). Patients with GO had higher titers of TRAb than patients without GO. CTLA-4 (rs231775 SNP) was significantly (p < 0.005) associated with TRAb titers above the median three months after radioiodine. CONCLUSIONS: The increase in TRAb titers after treatment with radioiodine is associated with GO and a genetic variation in CTLA-4 is associated with higher titers of TRAb.

Association Between Mortality and Levels of Autonomous Cortisol Secretion by Adrenal Incidentalomas : A Cohort Study.

BACKGROUND: Autonomous cortisol secretion in patients with adrenal incidentalomas is associated with increased mortality, but detailed information about the risk associated with specific levels of autonomous cortisol secretion is not available. OBJECTIVE: To measure the association between mortality and levels of autonomous cortisol secretion in patients with adrenal incidentalomas. DESIGN: Retrospective cohort study. (ClinicalTrials.gov: NCT03919734). SETTING: Two hospitals in southern Sweden. PATIENTS: Consecutive patients who had adrenal incidentalomas identified between 2005 and 2015 and were followed for up to 14 years. Outcome data were collected from national registers. MEASUREMENTS: Patients were grouped according to plasma cortisol level after a 1-mg dexamethasone suppression test (cortisolDST; <50, 50 to 82, 83 to 137, or ≥138 nmol/L). RESULTS: During a median follow-up of 6.4 years, 170 of 1048 patients died. Compared with a cortisolDST less than 50 nmol/L, a cortisolDST of 50 to 82 nmol/L was not associated with increased mortality (hazard ratio [HR], 1.15 [95% CI, 0.78 to 1.70]). However, a cortisolDST of 83 to 137 nmol/L (n = 119) had an HR of 2.30 (CI, 1.52 to 3.49), and a cortisolDST of 138 nmol/L or higher (n = 82) had an HR of 3.04 (CI, 1.86 to 4.98). Analyses using restricted cubic splines indicated that the association between cortisolDST and mortality was linear up to a cortisolDST of 200 nmol/L. LIMITATION: The results are not based on verified autonomous cortisol secretion; thus, the association may be underestimated. CONCLUSION: The association between mortality and cortisolDST increased linearly until cortisolDST reached 200 nmol/L. A cortisolDST of 83 to 137 nmol/L was associated with a 2-fold increase in mortality, and a cortisolDST of 138 nmol/L or higher was associated with a 3-fold increase in mortality. Additional studies should be done, and until those studies are completed some clinicians may consider these findings when deciding which patients to recommend for surgery. PRIMARY FUNDING SOURCE: Lisa and Johan Grönberg Foundation and Gyllenstiernska Krapperup Foundation.

Pituitary Function after High-Dose 177Lu-DOTATATE Therapy and Long-Term Follow-Up.

INTRODUCTION: The pituitary gland has a high expression of somatostatin receptors and is therefore a potential organ at risk for radiation-induced toxicity after 177Lu-DOTATATE treatment. OBJECTIVE: To study changes in pituitary function in patients with neuroendocrine tumors (NETs) treated with dosimetry-based 177Lu-DOTATATE to detect possible late toxicity. METHODS: 68 patients from a phase II clinical trial of dosimetry-based, individualized 177Lu-DOTATATE therapy were included in this analysis. Patients had received a median of 5 (range 3-9) treatment cycles of 7.4 GBq/cycle. Median follow-up was 30 months (range 11-89). The GH/IGF-1 axis, gonadotropins, and adrenal and thyroid axes were analyzed at baseline and on a yearly basis thereafter. Percent changes in hormonal levels over time were analyzed statistically using a linear mixed model and described graphically using box plots. The absorbed radiation dose to the pituitary was estimated based on post-therapeutic imaging, and the results analyzed versus percent change in IGF-1 levels over time. RESULTS: A statistically significant decrease in IGF-1 levels was found (p < 0.005), which correlated with the number of treatment cycles (p = 0.008) and the absorbed radiation dose (p = 0.03). A similar decrease, although non-significant, was seen in gonadotropins in postmenopausal women, while in men there was an increase during the first years after therapy, after which the levels returned to baseline. No change was observed in the adrenal or thyroid axes. CONCLUSIONS: No signs of severe endocrine disorders were detected, although a significant decrease in the GH/IGF-1 axis was found, where dosimetric analyses indicated radiation-induced damage to the pituitary gland as a probable cause.

ACTH following overnight dexamethasone suppression can be used in the verification of autonomous cortisol secretion in patients with adrenal incidentalomas.

OBJECTIVE: During the investigation of adrenal incidentalomas, it is important to accurately diagnose autonomous cortisol secretion (ACS) but the specificity of cortisol ≥50 nmol/L after overnight dexamethasone suppression (cortisolONDST ) is low. Therefore, ACTH following overnight dexamethasone suppression (ACTHONDST ) and cortisol following a 2-day dexamethasone suppression test (cortisol2-DAYDST ) were examined as markers of HPA axis suppression during ONDST. DESIGN: This cross-sectional study examined patients with adrenal incidentalomas and basal ACTH ≥ 2.0 pmol/L who underwent ONDST. MEASUREMENTS: ACTHONDST /ACTH ratio (ACTH ratio) was calculated for all patients. To define cut-off levels for ACTHONDST and ACTH ratio as markers of HPA axis suppression, ROC curves were used to separate patients with cortisolONDST <50 and ≥50 nmol/L. RESULTS: CortisolONDST was ≥50 nmol/L in 140 out of 373 patients. In patients with cortisolONDST <50 nmol/L, ACTHONDST was 0.28 pmol/L (<0.23-2.7). DHEAS was positively correlated to ACTHONDST , demonstrating a 9% increase with a doubling in ACTHONDST , p = 0.02. The best cut-off levels for ACTHONDST and ACTH ratio to detect cortisolONDST ≥50 nmol/L were ≥0.6 pmol/L and ≥18% respectively. These cut-off levels were tested on patients with cortisolONDST <50 nmol/L, considered to have adequate suppression (n = 233), and patients with reduction of ≥50 nmol/L from cortisolONDST to cortisol2-DAYDST , who were considered to have inadequate suppression (n = 16). ACTHONDST ≥0.6 pmol/L and ACTH ratio ≥18% had a sensitivity of 75% and 81% respectively, and a specificity of 78% and 85% respectively, for detecting patients with inadequate suppression. CONCLUSIONS: ACTHONDST and ACTH ratio can be markers of HPA axis suppression in the investigation of adrenal incidentalomas. CortisolONDST ≥50 nmol/L with ACTHONDST <0.6 pmol/L or ACTH ratio <18% should lead to the suspicion of ACS.

Consequences on islet and incretin hormone responses to dinner by omission of lunch in healthy men.

BACKGROUND: Omission of breakfast results in higher glucose and lower insulin and incretin hormone levels after both lunch and dinner. Whether omission of lunch has a similar impact on the following meal is not known. AIM: This study therefore explored whether omission of lunch ingestion affects glucose, islet and incretin hormones after dinner ingestion in healthy subjects. MATERIALS & METHODS: Twelve male volunteers (mean age 22 years, BMI 22.5 kg/m2) underwent two test days in random order with standard breakfast and dinner on both days with provision or omission of standard lunch in between. RESULTS: The results showed that throughout the 300 minutes study period, glucose, insulin, glucagon and GIP levels after dinner ingestion did not differ between the two tests. In contrast, C-peptide, and GLP-1 levels were 26%-35% higher at later time points after dinner ingestion when lunch had been omitted (P < .05). CONCLUSION: We conclude that omission of lunch increases GLP-1 and insulin secretion and possibly also insulin clearance resulting in unchanged glucose and insulin levels after dinner ingestion.

High prevalence of smoking in patients with adrenal incidentalomas: causality or case selection?

OBJECTIVE: Autonomous cortisol secretion and possible autonomous cortisol secretion (ACS/pACS) are associated to an increase of cardiovascular risk factors such as hypertension, diabetes mellitus and dyslipidaemia. To our knowledge, the prevalence of smoking, another well-established risk factor for cardiovascular disease, has not been studied in detail in people with ACS/pACS or adrenal incidentalomas. METHODS: Patients with adrenal incidentalomas were examined with the 1-mg overnight dexamethasone suppression test (cortisolONDST). Information about current smoking was collected from the patient's records. RESULTS: We studied 1044 patients, of whom 370 (35%) were current smokers. Of these, 22% had bilateral AI compared to 12% of the non-smokers (P < 0.001). Among patients with unilateral adrenal incidentalomas, smokers had larger adrenal incidentalomas than non-smokers (22 mm vs 19 mm, P < 0.001). Smokers also more often had cortisolONDST ≥50 nmol/L than non-smokers, 54% vs 40% (P < 0.001), a finding independent of the size of the adrenal incidentaloma in patients with unilateral adrenal incidentalomas. CONCLUSIONS: In the present study of patients with adrenal incidentalomas, the prevalence of current smoking was higher than in the general population. Furthermore, smokers had larger unilateral adrenal incidentalomas, more often bilateral adrenal incidentalomas, and more frequently ACS/pACS. Whether smoking is a risk factor for adrenal incidentalomas and ACS/pACS or our findings are due to case selection needs to be further studied.

The Effect of Radioiodine Treatment on TRAb, Anti-TPO, and Anti-TG in Graves' Disease.

BACKGROUND: In Graves' disease (GD), immunocompetent cells infiltrate thyroid tissue with release of TSH-receptor antibodies (TRAb), and radioiodine treatment is known to elicit an immune response with an increase in TRAb. OBJECTIVES: The aim was to study if all patients treated with radioiodine respond with a release of TRAb, anti-thyroperoxidase (anti-TPO), and anti-thyroglobulin (anti-TG). METHODS: This is a prospective observational study. GD patients (n = 131) were admitted for treatment with radioiodine. Thyroid antibodies were measured before and 3 months after iodine-131 treatment. RESULTS: After 3 months, a fold change > 1.1 was found in 66% of the GD patients, while the remaining 34% did not have a change or decrease in in TRAb. Anti-TPO and anti-TG also increased; the former showed an increase in 73% and the latter of 52%, while 27 and 48% decreased/were unchanged. A significant positive correlation was found between TRAb and anti-TPO, but not between TRAb and anti-TG. In the group with an increase in TRAb, the median fold change was 5.1, but there were no additional effects of tobacco smoking. The proportion of females below the median age (51.5 years) was significantly higher in the group that increased in TRAb compared to the one that decreased/was unchanged (66 vs. 34%). CONCLUSIONS: Treatment with radioiodine elicits an increase in thyroid antibodies, but not in all GD patients. The proportion of responders varied and was affected by age, resulting in a stronger immune response at younger age. However, there were no additional effects of smoking.

Suppressed ACTH Is Frequently Unrelated to Autonomous Cortisol Secretion in Patients With Adrenal Incidentalomas.

Objective: ACTH is considered a weak marker for autonomous cortisol secretion (ACS) in patients with adrenal incidentalomas (AIs). Our aim was to investigate suppressed basal ACTH as a marker of ACS and to elucidate why this criterion is of limited value. Methods: Basal ACTH and cortisol after overnight dexamethasone suppression test (cortisolONDST) were measured in 198 patients with unilateral AI and at 2-year follow-up. Basal ACTH was measured in 100 control subjects. Results: In patients with cortisolONDST <50 nmol/L (n = 145), ACTH was <2 pmol/L in 19%, compared with 4% in control subjects (P < 0.001). ACTH and size of AI correlated negatively (P = 0.002). Among patients with cortisolONDST ≥50 nmol/L, ACTH was <2 pmol/L in 53%. The patients were grouped according to whether cortisolONDST was <50 or ≥50 nmol/L and whether ACTH was <2.0 or ≥2.0 or pmol/L. At follow-up, these four groups were still separated with statistically significant differences in ACTH and cortisolONDST. Conclusions: This study identifies a previously unrecognized group of patients defined by suppressed ACTH despite normal cortisolONDST. This suppression of ACTH by a factor other than ACS may explain the limitation of suppressed ACTH as a marker for ACS. We suggest increased cortisol secretion in response to ACTH by the AI to be an additional factor.

Incretin effect after oral amino acid ingestion in humans.

CONTEXT: The incretin effect is the augmented insulin secretion by oral vs iv glucose at matching glucose levels. We previously demonstrated an augmented insulin secretion when fat is given orally rather than iv, suggesting an incretin effect also after fat. However, whether an incretin effect is also present after amino acid ingestion is not known. OBJECTIVE: The objective of the study was to explore insulin secretion and incretin hormones after oral and iv amino acid administration at matched total amino acid concentrations in healthy subjects. DESIGN: An amino acid mixture (Vaminolac) was administered orally or iv at a rate resulting in matching total amino acid concentrations to 12 male volunteers with age 22.5 ± 1.4 years and a body mass index 22.4 ± 1.4 kg/m(2), who had no history of diabetes. MAIN OUTCOME MEASURES: Main outcome measures were area under the 120-minute curve for insulin, C-peptide, glucagon, intact and total glucagon like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP), and the insulin secretory rate and insulin clearance. RESULTS: Insulin, C-peptide, and glucagon levels increased after both oral and iv administration, but insulin secretion was 25% higher after oral than after iv amino acid challenges (P = .006), whereas there was no significant difference in the glucagon response. Intact and total GIP rose after oral but not after iv amino acid administration, whereas intact and total GLP-1 levels did not change significantly in either test. CONCLUSION: Oral amino acid mixture ingestion elicits a stronger insulin secretory response than iv amino acid at matching amino acid levels and this is associated with increased GIP level, suggesting that an incretin effect exists also after oral amino acids, possibly mediated by GIP.

Incretin hormone and insulin responses to oral versus intravenous lipid administration in humans.

CONTEXT: The incretin effect is responsible for the higher insulin response to oral glucose than to iv glucose at matching glucose levels. It is not known whether this effect is restricted to glucose only. OBJECTIVE: The aim of the study was to examine whether insulin and incretin hormone responses are higher after oral vs. iv challenge of a lipid emulsion with matching triglyceride levels in humans. DESIGN, SETTINGS, AND PARTICIPANTS: A lipid emulsion (Intralipid) was administered orally (3 ml/kg) or iv (variable infusion rates to match triglyceride levels after oral ingestion) in healthy lean males (n = 12) at a University Clinical Research Unit. Samples were collected during 300 min. MAIN OUTCOME MEASURES: We measured the suprabasal area under the curve for insulin, glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and the insulin secretory rate based on C-peptide levels by deconvolution. RESULTS: Triglyceride levels increased similarly after oral and iv lipid; also, glucose and free fatty acid levels were similar in the two tests. Oral lipid elicited a clear insulin and C-peptide response, whereas no insulin or C-peptide responses were observed during iv lipid. Total and intact GIP and GLP-1 levels both increased after oral lipid administration but were not significantly altered after iv lipid. CONCLUSIONS: At matching triglyceride levels and with no difference in glucose and free fatty acid levels, oral lipid ingestion but not iv lipid infusion elicits a clear insulin response in association with increased GIP and GLP-1 concentrations. This may suggest that the incretin hormones also contribute to the islet response to noncarbohydrate nutrients.

Secretion and dipeptidyl peptidase-4-mediated metabolism of incretin hormones after a mixed meal or glucose ingestion in obese compared to lean, nondiabetic men.

CONTEXT: Glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) are cleaved by dipeptidyl peptidase-4 (DPP-4); plasma activity of DPP-4 may be increased in obesity. The impact of this increase on incretin hormone secretion and metabolism is not known. OBJECTIVE: The aim of the study was to assess incretin hormone secretion and degradation in lean and obese nondiabetic subjects. DESIGN, SETTINGS, AND PARTICIPANTS: We studied the ingestion of a mixed meal (560 kcal) or oral glucose (2 g/kg) in healthy lean (n = 12; body mass index, 20-25 kg/m(2)) or obese (n = 13; body mass index, 30-35 kg/m(2)) males at a University Clinical Research Unit. MAIN OUTCOME MEASURES: We measured the area under the curve of plasma intact (i) and total (t) GIP and GLP-1 after meal ingestion and oral glucose. RESULTS: Plasma DPP-4 activity was higher in the obese subjects (38.5 +/- 3.0 vs. 26.7 +/- 1.6 mmol/min . microl; P = 0.002). Although GIP secretion (AUC(tGIP)) was not reduced in obese subjects after meal ingestion or oral glucose, AUC(iGIP) was lower in obese subjects (8.5 +/- 0.6 vs. 12.7 +/- 0.9 nmol/liter x 300 min; P < 0.001) after meal ingestion. GLP-1 secretion (AUC(tGLP-1)) was reduced in obese subjects after both meal ingestion (7.3 +/- 0.9 vs. 10.0 +/- 0.6 nmol/liter x 300 min; P = 0.022) and oral glucose (6.6 +/- 0.8 vs. 9.6 +/- 1.1 nmol/liter x 180 min; P = 0.035). iGLP-1 was reduced in parallel to tGLP-1. CONCLUSIONS: 1) Release and degradation of the two incretin hormones show dissociated changes in obesity: GLP-1 but not GIP secretion is lower after meal ingestion and oral glucose, whereas GIP but not GLP-1 metabolism is increased after meal ingestion. 2) Increased plasma DPP-4 activity in obesity is not associated with a generalized augmented incretin hormone metabolism.

Differential islet and incretin hormone responses in morning versus afternoon after standardized meal in healthy men.

CONTEXT: The insulin response to meal ingestion is more rapid in the morning than in the afternoon. Whether this is explained by a corresponding variation in the incretin hormones is not known. OBJECTIVE: Our objective was to assess islet and incretin hormones after meal ingestion in the morning vs. afternoon. DESIGN, SETTINGS, AND PARTICIPANTS: Ingestion at 0800 and 1700 h of a standardized meal (524 kcal) in healthy lean males (n = 12) at a University Clinical Research Unit. MAIN OUTCOME MEASURES: We assessed early (30-min) area under the curve (AUC30) of plasma levels of insulin and intact (i) and total (t) glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) after meal ingestion and made an estimation of beta-cell function by model analysis of glucose and C-peptide. RESULTS: Peak glucose was lower in the morning than in the afternoon (6.1 +/- 0.2 vs. 7.4 +/- 0.3 mmol/liter, P = 0.001). AUC30(insulin) (4.9 +/- 0.6 vs. 2.8 +/- 0.4 nmol/liter . 30 min; P = 0.012), AUC30(tGLP-1) (300 +/- 40 vs. 160 +/- 30 pmol/liter . 30 min, P = 0.002), AUC30(iGIP) (0.7 +/- 0.1 vs. 0.3 +/- 0.1 nmol/liter . 30 min, P = 0.002), and AUC30(tGIP) (1.1 +/- 0.1 vs. 0.6 +/- 0.1 nmol/liter . min, P = 0.007) were all higher in the morning. AUC30(iGLP-1) (r = 0.68; P = 0.021) and AUC30(iGIP) (r = 0.78; P = 0.001) both correlated to AUC30(insulin). Model analysis of beta-cell function showed a higher first-hour potentiation factor in the morning (P = 0.009). This correlated negatively with the 60-min glucose level (r = -0.63; P < 0.001). CONCLUSIONS: The early release of GLP-1 and GIP are more pronounced in the morning than in the afternoon. This may contribute to the more rapid early insulin response, more pronounced potentiation of beta-cell function, and lower glucose after the morning meal.

Incretin and islet hormonal responses to fat and protein ingestion in healthy men.

Glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP) regulate islet function after carbohydrate ingestion. Whether incretin hormones are of importance for islet function after ingestion of noncarbohydrate macronutrients is not known. This study therefore examined integrated incretin and islet hormone responses to ingestion of pure fat (oleic acid; 0.88 g/kg) or protein (milk and egg protein; 2 g/kg) over 5 h in healthy men, aged 20-25 yr (n=12); plain water ingestion served as control. Both intact (active) and total GLP-1 and GIP levels were determined as was plasma activity of dipeptidyl peptidase-4 (DPP-4). Following water ingestion, glucose, insulin, glucagon, GLP-1, and GIP levels and DPP-4 activity were stable during the 5-h study period. Both fat and protein ingestion increased insulin, glucagon, GIP, and GLP-1 levels without affecting glucose levels or DPP-4 activity. The GLP-1 responses were similar after protein and fat, whereas the early (30 min) GIP response was higher after protein than after fat ingestion (P<0.001). This was associated with sevenfold higher insulin and glucagon responses compared with fat ingestion (both P<0.001). After protein, the early GIP, but not GLP-1, responses correlated to insulin (r(2)=0.86; P=0.0001) but not glucagon responses. In contrast, after fat ingestion, GLP-1 and GIP did not correlate to islet hormones. We conclude that, whereas protein and fat release both incretin and islet hormones, the early GIP secretion after protein ingestion may be of primary importance to islet hormone secretion.