A retrospective cohort study evaluating pregnancy outcomes in women with MIDD

AIMS

The most common pathogenic mitochondrial mutation associated with mitochondrial disease is m.3243A>G. Increased obstetric complications, such as spontaneous abortion, gestational diabetes (GDM), preterm delivery, and preeclampsia, have been reported in women carrying this mutation. We aimed to determine the fetal and maternal outcomes in pregnant women with mitochondrial disease.

METHODS

We retrospectively studied the obstetric and perinatal outcomes in 88 pregnancies of 26 women with genetically confirmed mitochondrial disease (m.3243A>G in the MTTL1 gene (n = 25); m.12258C>A in the MT-TS2 gene (n = 1)). Outcomes included pregnancy related complications, mode of delivery, gestational age at delivery and birthweight.

RESULTS

Mean heteroplasmy rate was 18%. The miscarriage rate was higher than background at 25%. 21 pregnancies (24%) were complicated by GDM; 9 pregnancies (13.6%) had a preterm delivery and 2 of them (3%) an extreme premature delivery < 32 weeks. One woman had preeclampsia and one had a postpartum hemorrhage. The caesarean section (CS) rate was 20%. For every unit increase in maternal heteroplasmy levels there was a 26% increased risk of undergoing an assisted operative vaginal delivery (OR 1.26, 95% CI 1.04-1.53, P = 0.002, Bonferroni corrected P = 0.005) and an 18% increased risk of undergoing a CS (OR 1.18, 95% CI 1.01-1.39, P = 0.01, Bonferroni corrected P = 0.03) compared to a spontaneous vaginal delivery. There was a statistical significant correlation between maternal and offspring heteroplasmy levels. Spearman correlation rho = 0.96, 95% CI 0.78-0.99, P = 0.0002.

CONCLUSION

Women with mitochondrial disease appear to have more frequent obstetric complications including miscarriage and GDM. Pre-pregnancy diagnosis of m.3243A>G will enable the counseling of women and increase awareness of possible obstetric complications.

tRNA-derived fragments are altered in diabetes

AIMS

Maternally inherited diabetes and deafness (MIDD) is a rare form of adult-onset diabetes that can be difficult to diagnose due to its variable clinical phenotype. Transfer RNA-derived small fragments are a novel, emerging class of small non-coding RNAs (sncRNAs) that have significant potential as serum biomarkers due to their stress-induced generation, abundance, stability and ease of detection.

METHODS

We investigated the levels of tiRNA 5'ValCAC (alone and in combination with miR-23b-3p) identified from small RNA sequencing studies in serum samples from healthy controls, type 1 diabetes, type 2 diabetes and MIDD subjects.

RESULTS

Serum levels of 5'ValCAC were reduced in MIDD and type 2 diabetes subjects compared to controls. Type 2 diabetes subjects had higher serum levels of miR-23b-3p compared to all other subjects. Receiver Operating Characteristic analysis showed the potential of 5'ValCAC and miR-23b-3p as MIDD biomarkers, with the combination showing excellent separation from type 2 diabetes subjects.

CONCLUSIONS

This is the first report showing altered serum levels of tiRNAs in diabetes subjects. The combined use of 5'ValCAC and miR-23b-3p as serum biomarkers could potentially differentiate between MIDD subjects and type 2 diabetes subjects.

Phenotype, genotype and glycaemic variability in people with activating mutations in the ABCC8 gene: response to appropriate therapy

AIMS

To examine the phenotypic features of people identified with ABCC8-maturity-onset diabetes of the young (MODY) who were included in the adult 'Mater MODY' cohort and to establish their response to sulfonylurea therapy.

METHODS

Ten participants with activating ABCC8 mutations were phenotyped in detail. A 2-hour oral glucose tolerance test was performed to establish glycaemic tolerance, with glucose, insulin and C-peptide measurements taken at baseline and 30-min intervals. Insulin was discontinued and sulfonylurea therapy initiated after genetic diagnosis of ABCC8-MODY. A blinded continuous glucose monitoring sensor was used to establish glycaemic control on insulin vs a sulfonylurea.

RESULTS

The mean age at diagnosis of diabetes was 33.8 ± 11.1 years, with fasting glucose of 18.9 ± 11.5 mmol/l and a mean (range) HbA_1c of 86 (51,126) mmol/mol [10.0 (6.8,13.7)%]. Following a genetic diagnosis of ABCC8-MODY three out of four participants discontinued insulin (mean duration 10.6 ± 1.69 years) and started sulfonylurea treatment. The mean (range) HbA_1c prior to genetic diagnosis was 52 (43,74) mmol/mol (6.9%) and the post-treatment change was 44 (30,57) mmol/mol (6.2%; P=0.16). Retinopathy was the most common microvascular complication in this cohort, occurring in five out of 10 participants.

CONCLUSIONS

Low-dose sulfonylurea therapy resulted in stable glycaemic control and the elimination of hypoglycaemic episodes attributable to insulin therapy. The use of appropriate therapy at the early stages of diabetes may decrease the incidence of complications and reduce the risks of hypoglycaemia associated with insulin therapy.

Prolonged episodes of hypoglycaemia in HNF4A-MODY mutation carriers with IGT. Evidence of persistent hyperinsulinism into early adulthood

AIMS

HNF4A is an established cause of maturity onset diabetes of the young (MODY). Congenital hyperinsulinism can also be associated with mutations in the HNF4A gene. A dual phenotype is observed in HNF4A-MODY with hyperinsulinaemic hypoglycaemia in the neonatal period progressing to diabetes in adulthood. The nature and timing of the transition remain poorly defined. We performed an observational study to establish changes in glycaemia and insulin secretion over a 6-year period. We investigated glycaemic variability and hypoglycaemia in HNF4A-MODY using a continuous glucose monitoring system (CGMS).

METHODS

An OGTT with measurement of glucose, insulin and C-peptide was performed in HNF4A participants with diabetes mellitus (DM) (n = 14), HNF4A-IGT (n = 7) and age- and BMI-matched MODY negative family members (n = 10). Serial assessment was performed in the HNF4A-IGT cohort. In a subset of HNF4A-MODY mutation carriers (n = 10), CGMS was applied over a 72-h period.

RESULTS

There was no deterioration in glycaemic control in the HNF4A-IGT cohort. The fasting glucose-to-insulin ratio was significantly lower in the HNF4A-IGT cohort when compared to the normal control group (0.13 vs. 0.24, p = 0.03). CGMS profiling demonstrated prolonged periods of hypoglycaemia in the HNF4A-IGT group when compared to the HNF4A-DM group (432 vs. 138 min p = 0.04).

CONCLUSIONS

In a young adult HNF4A-IGT cohort, we demonstrate preserved glucose, insulin and C-peptide secretory responses to oral glucose. Utilising CGMS, prolonged periods of hypoglycaemia are evident despite a median age of 21 years. We propose a prolonged hyperinsulinaemic phase into adulthood is responsible for the notable hypoglycaemic episodes.

Successful maintenance on sulphonylurea therapy and low diabetes complication rates in a HNF1A-MODY cohort

AIMS

HNF1A gene mutations are the most common cause of maturity-onset diabetes of the young (MODY) in the UK. Persons with HNF1A-MODY display sensitivity to sulphonylurea therapy; however, the long-term efficacy is not established. There is limited literature as to the prevalence of micro- and macrovascular complications in this unique cohort. The aim of this study was to determine the natural progression and clinical management of HNF1A-MODY diabetes in a dedicated MODY clinic.

METHODS

Sixty patients with HNF1A-MODY and a cohort of 60 BMI-, age-, ethnicity- and diabetes duration-matched patients with Type 1 diabetes mellitus participated in the study. All patients were phenotyped in detail. Clinical follow-up of the HNF1A-MODY cohort occurred on a bi-annual basis.

RESULTS

Following a genetic diagnosis of MODY, the majority of the cohort treated with sulphonylurea therapy remained insulin independent at 84-month follow-up (80%). The HbA1c in the HNF1A-MODY group treated with sulphonylurea therapy alone improved significantly over the study period [from 49 (44-63) mmol/mol, 6.6 (6.2-7.9)% to 41 (31-50) mmol/mol, 5.9 (5-6.7)%; P = 0.003]. The rate of retinopathy was significantly lower than that noted in the Type 1 diabetes mellitus group (13.6 vs. 50%; P = 0.0001).There was also a lower rate of microalbuminuria and cardiovascular disease in the HNF1A-MODY group compared with the Type 1 diabetes mellitus group.

CONCLUSIONS

This study demonstrates that the majority of patients with HNF1A-MODY can be maintained successfully on sulphonylurea therapy with good glycaemic control. We note a significantly lower rate of micro- and macrovascular complications than reported previously. The use of appropriate therapy at early stages of the disorder may decrease the incidence of complications.

Identification of circulating microRNAs in HNF1A-MODY carriers

AIMS/HYPOTHESIS

HNF1A-MODY is a monogenic form of diabetes caused by mutations in the HNF1A gene. Here we identify, for the first time, HNF1A-MODY-associated microRNAs (miRNAs) that can be detected in the serum of HNF1A-MODY carriers.

METHODS

An miRNA array was carried out in rat INS-1 insulinoma cells inducibly expressing the common human Pro291fsinsC-HNF1A frame shift mutation. Differentially expressed miRNAs were validated by quantitative real-time PCR. Expression of miRNAs in the serum of HNF1A-MODY carriers (n = 31), MODY-negative family members (n = 10) and individuals with type 2 diabetes mellitus (n = 17) was quantified by absolute real-time PCR analysis.

RESULTS

Inducible expression of Pro291fsinsC-HNF1A in INS-1 cells caused a significant upregulation of three miRNAs (miR-103, miR-224, miR-292-3p). The differential expression of two miRNAs (miR-103 and miR-224) was validated in vitro. Strongly elevated levels of miR-103 and miR-224 could be detected in the serum of HNF1A-MODY carriers compared with MODY-negative family controls. Serum levels of miR-103 distinguished HNF1A-MODY carriers from HbA1c-matched individuals with type 2 diabetes mellitus.

CONCLUSIONS/INTERPRETATION

Our study demonstrates that the pathophysiology of HNF1A-MODY is associated with the overexpression of miR-103 and miR-224. Furthermore, our study demonstrates that these miRNAs can be readily detected in the serum of HNF1A-MODY carriers.

Early loss of mammalian target of rapamycin complex 1 (mTORC1) signalling and reduction in cell size during dominant-negative suppression of hepatic nuclear factor 1-alpha (HNF1A) function in INS-1 insulinoma cells

AIMS/HYPOTHESIS

Mutations in the HNF1A (previously known as TCF1) gene encoding hepatocyte nuclear factor-1alpha (HNF1A) lead to the development of maturity-onset diabetes of the young, type 3 (HNF1A-MODY), characterised by impaired insulin secretion and a reduction in beta cell mass. HNF1A plays an important role in pancreatic beta cell differentiation and survival. The mammalian target of rapamycin (mTOR) is a central growth factor- and nutrient-activated protein kinase controlling cell metabolism, growth and survival. We investigated the role of mTOR inactivation in the decline in beta cell mass in a cellular model of HNF1A-MODY.

METHODS

Previously we showed that suppression of HNF1A function via expression of a dominant-negative mutant (DN-HNF1A) decreases insulin gene transcription in insulinoma (INS-1) cells. We investigated the signalling of two distinct mTOR protein complexes, mTORC1 and mTORC2, in response to DN-HNF1A induction.

RESULTS

We observed delayed inactivation of mTORC2 48 h after DN-HNF1A induction, evidenced by a reduction in serine 473 phosphorylation of thymoma viral proto-oncogene 1 (AKT1). We also observed an early inactivation of mTORC1 24 h after DN-HNF1A induction, which was detected by decreases in threonine 389 phosphorylation of p70 ribosomal protein S6 kinase (S6K1) and serine 65 phosphorylation of translational inhibitor eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1). Flow cytometry and gene expression analysis demonstrated a pre-apoptotic decrease in INS-1 cell size in response to DN-HNF1A induction, and an increase in the level of the mTORC1-regulated cell-cycle inhibitor, cyclin-dependent kinase inhibitor 1B p27.

CONCLUSIONS/INTERPRETATION

Our data suggest that mTOR kinase and signalling through mTORC1 are highly sensitive to suppression of HNF1A function, and may contribute to disturbance of cell-size regulation and cell-cycle progression in HNF1A-MODY.

Clinical trial: alvimopan for the management of post-operative ileus after abdominal surgery: results of an international randomized, double-blind, multicentre, placebo-controlled clinical study

BACKGROUND

Post-operative ileus (POI) affects most patients undergoing abdominal surgery.

AIM

To evaluate the effect of alvimopan, a peripherally acting mu-opioid receptor antagonist, on POI by negating the impact of opioids on gastrointestinal (GI) motility without affecting analgesia in patients outside North America.

METHODS

Adult subjects undergoing open abdominal surgery (n = 911) randomly received oral alvimopan 6 or 12 mg, or placebo, 2 h before, and twice daily following surgery. Opioids were administered as intravenous patient-controlled analgesia (PCA) or bolus injection. Time to recovery of GI function was assessed principally using composite endpoints in subjects undergoing bowel resection (n = 738).

RESULTS

A nonsignificant reduction in mean time to tolerate solid food and either first flatus or bowel movement (primary endpoint) was observed for both alvimopan 6 and 12 mg; 8.5 h (95% CI: 0.9, 16.0) and 4.8 h (95% CI: -3.2, 12.8), respectively. However, an exploratory post hoc analysis showed that alvimopan was more effective in the PCA (n = 317) group than in the non-PCA (n = 318) group. Alvimopan was well tolerated and did not reverse analgesia.

CONCLUSION

Although the significant clinical effect of alvimopan on reducing POI observed in previous trials was not reproduced, this trial suggests potential benefit in bowel resection patients who received PCA.

Downregulation of protein kinase B/Akt-1 mediates INS-1 insulinoma cell apoptosis induced by dominant-negative suppression of hepatocyte nuclear factor-1alpha function

AIMS/HYPOTHESIS

Inactivating mutations in Tcf1, which encodes the transcription factor hepatocyte nuclear factor (HNF)-1alpha, cause maturity-onset diabetes of the young-3. We have previously shown that a dominant-negative mutant (DN-HNF-1alpha) renders INS-1 insulinoma cells sensitive to the mitochondrial apoptosis pathway, but the underlying alterations in signal transduction remain unknown.

MATERIALS AND METHODS

Using a reverse tetracycline-dependent transactivator system, DN-HNF-1alpha-induced apoptosis was assessed by immunoblotting and caspase assays. Alterations in AKT1 kinase/protein kinase B (AKT1) survival signalling during DN-HNF-1alpha-induced apoptosis were investigated by phospho-specific immunodetection and transient transfection experiments.

RESULTS

Induction of DN-HNF-1alpha caused significant changes in the activation-specific phosphorylation status of AKT1 that were preceded by a downregulation of Ins1 gene transcription. Phosphorylation of AKT1 at Ser473 was dramatically reduced after 36 to 48 h of DN-HNF-1alpha induction and coincided with maximal apoptosis activation. Overexpression of a constitutively active mutant of Akt1 rescued INS-1 cells from DN-HNF-1alpha-induced apoptosis, while ectopic expression of a dominant-negative mutant mimicked the effect of DN-HNF-1alpha on apoptosis activation. Pharmacological suppression of growth factor survival signalling through administration of the phosphatidylinositol-3 kinase (PI-3K) inhibitor wortmannin accelerated the induction of apoptosis by DN-HNF-1alpha.

CONCLUSIONS/INTERPRETATION

These data suggest that a decrease in PI-3K/AKT1 survival signalling mediates DN-HNF-1alpha-induced apoptosis in insulin-secreting cells.

Glucagon-like peptide-1 reduces the pulsatile component of testosterone secretion in healthy males

BACKGROUND

Glucagon-like-peptide-1 (7-36) amide (GLP-1), a potent regulator of glucose homeostasis, has been implicated in the control of hypothalamic-pituitary function. In vivo it is a relevant neuroendocrine modulator of gonadotropin-releasing hormone release, suggesting its possible role as a metabolic signal to the reproductive system. The present study was undertaken to establish its effect on luteinizing hormone (LH) and testosterone secretion in nine healthy male volunteers.

MATERIALS AND METHODS

Each subject underwent an oral glucose tolerance test to establish LH, testosterone, and GLP-1 responses to glucose. Euglycaemic clamp experiments (6 h) were performed on two occasions with saline or with a constant infusion of GLP-1 (0.4 pmol kg(-1) min (-1)). Blood samples were drawn at 10-min intervals to measure the pulsatile pattern of LH and testosterone secretion.

RESULTS

Ingestion of oral glucose resulted in a reduction in plasma testosterone levels at 30 min compared with baseline (P < 0.004) despite unaltered LH levels (P = 0.5). Constant GLP-1 infusion resulted in no change in LH (P = 0.83), testosterone (P = 0.96), follicle stimulating hormone (FSH) (P = 0.86) and leptin levels (P = 0.3). Pulse analysis revealed no significant difference in the number (P = 0.1) or median absolute amplitude (P = 0.3) of the LH pulses. However, there was a significant decrease in the number (3.0 +/- 0.6 vs. 1.3 +/- 0.4; P < 0.05) and a tendency for increased duration of testosterone pulses (97.4 +/- 16.7 vs. 170 +/- 27.1 min; P = 0.06).

CONCLUSION

Oral glucose ingestion and intravenous GLP-1 infusion reduce the pulsatile component of testosterone secretion by a mechanism independent of LH release.

Maternal recall bias, obstetric history and schizophrenia

BACKGROUND

This study sought to clarify the role of obstetric complications (OCs) and maternal recall bias for patients with first episodes of schizophrenia and those at increased risk of the disorder.

METHOD

Subjects at high risk of schizophrenia were compared with people with first-episode schizophrenia and with healthy volunteers. Consenting mothers of subjects were interviewed using a standardised questionnaire for the recall of OCs, and OCs were also measured from records collected at the time of pregnancy and delivery.

RESULTS

High-risk subjects and first-episode patients had higher rates of OCs recalled by their mother than controls, but hospital records showed no differences in OCs between groups. The number of OCs recalled by mothers of the high-risk group was not related to whether the mother had schizophrenia or not, but was related to the maternally rated abnormal childhood behaviour as measured by the Child Behaviour Checklist.

CONCLUSIONS

These results suggest that studies that rely on maternal recall alone are susceptible to bias. The excess of OCs recalled by the mother could be related to abnormal behaviour in their child rather than maternal illness, family history or psychotic symptoms.

Screening and preventable illness

If an agent does not discount the future at a constant rate, as in some forms of myopia, her optimal strategy is unattainable without some commitment device. We apply this familiar idea to a model of screening and disease prevention, and explore how financial incentives can correct suboptimal health choices. In general, myopia need not imply under-screening. While the optimal intervention for prevention effort is a state-invariant subsidy, the optimal intervention for screening may involve a tax or a subsidy. When screening and prevention are coincident, a simple and practical subsidy equal to one minus the discount factor to both screening and intervention is indicated.

A psychometric analysis of the measurement level of the rating scale, time trade-off, and standard gamble

A fundamental assumption of utility-based analyses is that patient utilities for health states can be measured on an equal-interval scale. This assumption, however, has not been widely examined. The objective of this study was to assess whether the rating scale (RS), standard gamble (SG), and time trade-off (TTO) utility elicitation methods function as equal-interval level scales. We wrote descriptions of eight prostate-cancer-related health states. In interviews with patients who had newly diagnosed, advanced prostate cancer, utilities for the health states were elicited using the RS, SG, and TTO methods. At the time of the study, 77 initial and 73 follow-up interviews had. been conducted with a consecutive sample of 77 participants. Using a Rasch model, the boundaries (Thurstone Thresholds) between four equal score sub-ranges of the raw utilities were mapped onto an equal-interval logit scale. The distance between adjacent thresholds in logit units was calculated to determine whether the raw utilities were equal-interval. None of the utility scales functioned as interval-level scales in our sample. Therefore, since interval-level estimates are assumed in utility-based analyses, doubt is raised regarding the validity of findings from previous analyses based on these scales. Our findings need to be replicated in other contexts, and the practical impact of non-interval measurement on utility-based analyses should be explored. If cost-effectiveness analyses are not found to be robust to violations of the assumption that utilities are interval, serious doubt will be cast upon findings from utility-based analyses and upon the wisdom of expending millions in research dollars on utility-based studies.

Uncovering racial bias in nursing fundamentals textbooks

This article describes research that sought to identify and critique selected content areas from three nursing fundamentals textbooks for the presence or absence of racial bias embedded in the portrayal of African Americans. The analyzed content areas were the history of nursing, cultural content, and physical assessment/hygiene parameters. A researcher-developed guide was used for data collection and analysis of textual language, illustrations, linguistics, and references. A thematic analysis resulted in I I themes reflecting the portrayal of African Americans in these sampled textbooks. An interpretive analysis with a lens of Sadker and Sadker's categories of bias, along with other literary and theoretical contexts, were used to explore for the presence or absence of racial bias. Recommendations for nursing education are provided.

GLP-1-induced alterations in the glucose-stimulated insulin secretory dose-response curve

The present study was undertaken to establish in normal volunteers the alterations in beta-cell responsiveness to glucose associated with a constant infusion of glucagon-like peptide-1 (GLP-1) or a pretreatment infusion for 60 min. A high-dose graded glucose infusion protocol was used to explore the dose-response relationship between glucose and insulin secretion. Studies were performed in 10 normal volunteers, and insulin secretion rates (ISR) were calculated by deconvolution of peripheral C-peptide levels by use of a two-compartmental model that utilized mean kinetic parameters. During the saline study, from 5 to 15 mM glucose, the relationship between glucose and ISR was linear. Constant GLP-1 infusion (0.4 pmol x kg(-1) x min(-1)) shifted the dose-response curve to the left, with an increase in the slope of this curve from 5 to 9 mM glucose from 71.0 +/- 12.4 pmol x min(-1) x mM(-1) during the saline study to 241.7 +/- 36.6 pmol x min(-1) x mM(-1) during the constant GLP-1 infusion (P < 0.0001). GLP-1 consistently stimulated a >200% increase in ISR at each 1 mM glucose interval, maintaining plasma glucose at <10 mM (P < 0.0007). Pretreatment with GLP-1 for 60 min resulted in no significant priming of the beta-cell response to glucose (P = 0.2). Insulin clearance rates were similar in all three studies at corresponding insulin levels. These studies demonstrate that physiological levels of GLP-1 stimulate glucose-induced insulin secretion in a linear manner, with a consistent increase in ISR at each 1 mM glucose interval, and that they have no independent effect on insulin clearance and no priming effect on subsequent insulin secretory response to glucose.

Intestinal proliferation and delayed intestinal transit in a patient with a GLP-1-, GLP-2- and PYY-producing neuroendocrine carcinoma

Glucagon-like peptides (GLP) 1 and 2 are hormones derived from the post-translational processing of proglucagon in the intestinal L cells that influence intestinal motility and small bowel growth, respectively. We describe a patient with a neuroendocrine tumor of unknown primary origin with peritoneal carcinomatosis and diffuse liver metastases, who presented with constipation and nocturnal itching for over 3 years. Small bowel follow-through showed decreased small intestinal motility and marked intestinal hypertrophy. Biopsies from mesenterial lymph nodes showed, histologically, a well-differentiated neuroendocrine tumor (G1), with positive immunostaining for chromogranin A, GLP-1, GLP-2 and polypeptide YY (PYY). Jejunal biopsy demonstrated marked intestinal mucosal hypertrophy. HPLC analysis combined with RIA of tumor and serum extracts revealed that the tumor was producing and releasing fasting levels of GLP-1 of 738+/-20.7 pg/ml (normal levels (nl) <100 pg/ml), GLP-2 of 3,150+/-9 pg/ml (nl <100 pg/ml) as well as PYY 550 pg/ml (nl <100 pg/ml). Octreotide administration decreased levels of GLP-1 and GLP-2 and reduced small intestinal transit time from 150 to 50 min. However, tumor growth was not inhibited by octreotide, interferon or dacarbazine therapy and the patient died 8 months later. This is the first case report demonstrating the overproduction of GLP-1, GLP-2 and PYY from an neuroendocrine tumor, in a patient with intestinal hypertrophy and delayed intestinal transit time.

Evaluating the findings of qualitative research

This article provides an overview of strategies used to support and evaluate qualitative research. Research consumers should critique qualitative research to see how the concepts of credibility, transferability, and confirmability are met in a study. Further, as qualitative research evolves and transforms the understanding of phenomena, the strategies for evaluating credibility may evolve and change, as well. Qualitative research just as personal knowing, is a dynamic process.

A positive analysis of financial incentives for cadaveric organ donation

Financial incentives of various kinds have been suggested to alleviate the chronic shortage of transplantable organs in the United States. This paper analyzes the possible consequences of financial incentives on organ supply. We show that under current practice and current law (which are not the same), inducements to donate organs or to register as an organ donor may lead to a decline in the supply of organs. Furthermore, some financial incentives that have been proposed lead to time inconsistent choices.

A trial for comparing methods for eliciting treatment preferences from men with advanced prostate cancer: results from the initial visit

OBJECTIVE

The objective of this study was to evaluate the convergent validity of 3 types of utility measures: standard gamble, time tradeoff, and rating scale.

RESEARCH DESIGN

A prospective cohort of 120 men with advanced prostate cancer were first asked to rank order 8 health states, and then utility values were obtained from each participant for each of the 8 health states through 2 of the 3 techniques evaluated (standard gamble, time tradeoff and rating scale). Participants were randomly assigned to 1 of 3 possible pairs of techniques. The validity of the 3 methods, as measured by the convergence and raw score differences of the techniques, was assessed with ANOVA. The ability of the techniques to differentiate health states was determined. The inconsistencies between rankings and utility values were also measured. Proportions of illogical utility responses were assessed as the percent of times when states with more symptoms were given higher or equal utility values than states with fewer symptoms.

RESULTS

There were significant differences in raw scores between techniques, but the values were correlated across health states. Utility values were often inconsistent with the rank order of health states. In addition, utility assessment did not differentiate the health states as well as the rank order. Furthermore, utility values were often illogical in that states with more symptoms received equal or higher utility values than states with fewer symptoms.

CONCLUSIONS

Use of the utility techniques in cost-effectiveness analysis and decision making has been widely recommended. The results of this study raise serious questions as to the validity and usefulness of the measures.

Assessing the performance of utility techniques in the absence of a gold standard

BACKGROUND

Utility techniques are the most commonly used means to assess patient preferences for health outcomes. However, whether utility techniques produce valid measures of preference has been difficult to determine in the absence of a gold standard.

OBJECTIVE

To introduce and demonstrate two methods that can be used to evaluate how well utility techniques measure patients' preferences.

SUBJECTS AND DESIGN

Patients treated for advanced prostate cancer (n = 57) first ranked eight health states in order of preference. Four utility techniques were then used to elicit patients' utilities for each health state.

MEASURES

The rating scale, standard gamble, time trade-off, and a modified version of willingness-to-pay techniques were used to elicit patients' utilities. Technique performance was assessed by computing a differentiation and inconsistency score for each technique.

RESULTS

Differentiation scores indicated the rating scale permitted respondents to assign unique utility values to about 70% of the health states that should have received unique values. When the other techniques were used, about 40% or less of the health states that should have received unique utility scores actually did receive unique utility scores. Inconsistency scores, which indicate how often participants assign utility scores that contradict how they value health states, indicated that the willingness-to-pay technique produced the lowest rate of inconsistency (10%). However, this technique did not differ significantly from the rating scale or standard gamble on this dimension.

CONCLUSIONS

Differentiation and inconsistency offer a means to evaluate the performance of utility techniques, thereby allowing investigators to determine the extent to which utilities they have elicited for a given decision problem are valid. In the current investigation, the differentiation and inconsistency methods indicated that all four techniques performed at sub-optimal levels, though the rating scale out-performed the standard gamble, time trade-off, and willingness-to-pay techniques.

Incentives for vertical integration in healthcare: the effect of reimbursement systems

In the United States, many healthcare organizations are being transformed into large integrated delivery systems, even though currently available empirical evidence does not provide strong or unequivocal support for or against vertical integration. Unfortunately, the manager cannot delay organizational changes until further research has been completed, especially when further research is not likely to reveal a single, correct solution for the diverse healthcare systems in existence. Managers must therefore carefully evaluate the expected effects of integration on their individual organizations. Vertical integration may be appropriate if conditions facing the healthcare organization provide opportunities for efficiency gains through reorganization strategies. Managers must consider (1) how changes in the healthcare market have affected the dynamics of production efficiency and transaction costs; (2) the likelihood that integration strategies will achieve increases in efficiency or reductions in transaction costs; and (3) how vertical integration will affect other costs, and whether the benefits gained will outweigh additional costs and efficiency losses. This article presents reimbursement systems as an example of how recent changes in the industry may have changed the dynamics and efficiency of production. Evaluation of the effects of vertical integration should allow for reasonable adjustment time, but obviously unsuccessful strategies should not be followed or maintained.

Glucagon-like peptide 1 improves the ability of the beta-cell to sense and respond to glucose in subjects with impaired glucose tolerance

Impaired glucose tolerance (IGT) and NIDDM are both associated with an impaired ability of the beta-cell to sense and respond to small changes in plasma glucose concentrations. The aim of this study was to establish if glucagon-like peptide 1 (GLP-1), a natural enteric peptide and potent insulin secretagogue, improves this defect. Two weight-matched groups, one with eight subjects having IGT (2-h glucose, 10.1 +/- 0.3 mmol/l) and another with seven subjects with diet-treated NIDDM (2-h glucose, 14.5 +/- 0.9 mmol/l), were studied on two occasions during a 12-h oscillatory glucose infusion, a sensitive test of the ability of the beta-cell to sense and respond to glucose. Glucose was infused with a mean rate of 4 mg x kg(-1) x min(-1), amplitude 33% above and below the mean rate, and periodicity of 144 min, with infusion of saline or GLP-1 at 0.4 pmol x kg(-1) x min(-1) for 12 h. Mean glucose levels were significantly lower in both groups during the GLP-1 infusion compared with during saline infusion: 9.2 +/- 0.4 vs. 6.4 +/- 0.1 mmol/l in the IGT subjects (P < 0.0004) and 14.6 +/- 1.0 vs. 9.3 +/- 0.7 mmol/l in NIDDM subjects (P < 0.0002). Despite this significant reduction in plasma glucose concentration, insulin secretion rates (ISRs) increased significantly in IGT subjects (513.3 +/- 77.6 vs. 583.1 +/- 100.7 pmol/min; P < 0.03), with a trend toward increasing in NIDDM subjects (561.7 +/- 122.16 vs. 642.8 +/- 128 pmol/min; P = 0.1). These results were compatible with enhanced insulin secretion in the presence of GLP-1. Spectral power was used as a measure of the ability of the beta-cell to secrete insulin in response to small changes in the plasma glucose concentration during the oscillatory infusion. Spectral power for ISR increased from 2.1 +/- 0.9 during saline infusion to 7.4 +/- 1.3 during GLP-1 infusion in IGT subjects (P < 0.004), but was unchanged in NIDDM subjects (1.0 +/- 0.4 to 1.5 +/- 0.6; P = 0.3). We concluded that low dosage GLP-1 improves the ability of the beta-cell to secrete insulin in both IGT and NIDDM subjects, but that the ability to sense and respond to subtle changes in plasma glucose is improved in IGT subjects, with only a variable response in NIDDM subjects. Beta-cell dysfunction was improved by GLP-1 infusion, suggesting that early GLP-1 therapy may preserve beta-cell function in subjects with IGT or mild NIDDM.

Inhibitory effects of hyperglycaemia on fed jejunal motility: potential role of hyperinsulinaemia

BACKGROUND

Acute hyperglycaemia is known to inhibit jejunal interdigestive motility. This study was undertaken to establish the effects of hyperglycaemia on fed jejunal motility and small intestinal transit time, and to establish if the effects of hyperglycaemia are mediated in part by hyperinsulinaemia.

METHODS

Nine healthy male volunteers were studied in random order using three experimental conditions: (a) euglycaemic clamp [glucose 5 mmol L(-1)]; (b) hyperglycaemic clamp [glucose 15 mmol L(-1)]; and (c) euglycaemic hyperinsulinaemic clamp [glucose 5 mmol L(-l)]. Fed jejunal motility was induced by an intrajejunal perfusion of lipid (Lipofundin medium-chained triglyceride 10%) at 1.5 mL min(-1) [1.5 kcal min(-1)] for 180 min through the most proximal port of a manometry catheter (eight ports spaced at 2-cm intervals) located just distal to the ligament of Treitz. One minute after starting the lipid perfusion, 15 g of lactulose dissolved in 20 mL of tap water was infused. Small intestinal transit time was measured by the hydrogen breath test.

RESULTS

Acute hyperglycaemia reduced the total number of jejunal contractions and progradely propagated contractions, the motility index (P < 0.05) and the mean amplitude of contractions and delayed intestinal transit time. Hyperinsulinaemia reduced the total number of jejunal contractions, motility index (P < 0.05) and intestinal transit time.

CONCLUSIONS

Thus, hyperinsulinaemia may contribute to the inhibitory effects of hyperglycaemia on jejunal motility. In addition, this study demonstrated that intrajejunal infusion of lipid stimulates sustained glucagon-like peptide-1 release. In contrast to fat-induced gastric inhibitory polypeptide release, this glucagon-like peptide-1 release is not inhibited by exogenous or endogenous hyperinsulinaemia (P = 0.59).

Treatment with the oral antidiabetic agent troglitazone improves beta cell responses to glucose in subjects with impaired glucose tolerance

Impaired glucose tolerance (IGT) is associated with defects in both insulin secretion and action and carries a high risk for conversion to non-insulin-dependent diabetes mellitus (NIDDM). Troglitazone, an insulin sensitizing agent, reduces glucose concentrations in subjects with NIDDM and IGT but is not known to affect insulin secretion. We sought to determine the role of beta cell function in mediating improved glucose tolerance. Obese subjects with IGT received 12 wk of either 400 mg daily of troglitazone (n = 14) or placebo (n = 7) in a randomized, double-blind design. Study measures at baseline and after treatment were glucose and insulin responses to a 75-g oral glucose tolerance test, insulin sensitivity index (SI) assessed by a frequently sampled intravenous glucose tolerance test, insulin secretion rates during a graded glucose infusion, and beta cell glucose-sensing ability during an oscillatory glucose infusion. Troglitazone reduced integrated glucose and insulin responses to oral glucose by 10% (P = 0.03) and 39% (P = 0.003), respectively. SI increased from 1.3+/-0.3 to 2.6+/-0.4 x 10(-)5min-1pM-1 (P = 0.005). Average insulin secretion rates adjusted for SI over the glucose interval 5-11 mmol/liter were increased by 52% (P = 0.02), and the ability of the beta cell to entrain to an exogenous oscillatory glucose infusion, as evaluated by analysis of spectral power, was improved by 49% (P = 0.04). No significant changes in these parameters were demonstrated in the placebo group. In addition to increasing insulin sensitivity, we demonstrate that troglitazone improves the reduced beta cell response to glucose characteristic of subjects with IGT. This appears to be an important factor in the observed improvement in glucose tolerance.

Sleepiness, performance, and neuroendocrine function during sleep deprivation: effects of exposure to bright light or exercise

The temporal profiles of subjective fatigue (as assessed by the Stanford Sleepiness Scale), of cognitive performance (on a digit symbol substitution test and a symbol copying task), of body temperature, and of the peripheral concentrations of melatonin, thyroid-stimulating hormone (TSH), and cortisol were obtained simultaneously at frequent intervals in 17 normal young subjects submitted to a 43-h period of constant routine conditions involving continuous wakefulness at bed rest in dim indoor light. The subjects had knowledge of time of day. Caloric intake was exclusively in the form of an intravenous glucose infusion, and plasma glucose levels were monitored continuously in 8 of the 17 subjects. Under these conditions, fluctuations in plasma glucose reflect primarily changes in glucose use because endogenous glucose production is suppressed by the exogenous infusion. Following the completion of a baseline constant routine study, the volunteers participated in two subsequent studies using the same protocol to determine the immediate psychophysiological effects of exposure to a 3-h pulse of bright light or to a 3-h pulse of physical exercise. Sleepiness and performance varied in a mirror image, with significant negative correlations. Sleepiness scores were minimal around noon and then increased at a modest rate throughout the rest of the normal waking period. Staying awake during usual bedtime hours was associated with an acceleration in the rate of increase in sleepiness, which coincided with decreasing body temperature, rapidly rising cortisol concentrations, and maximal levels of melatonin and TSH. When body temperature reached its nadir, a further major increase in sleepiness occurred in parallel with a pronounced decrease in plasma glucose (reflecting increased glucose use). Recovery from maximal sleepiness started when blood glucose levels stopped falling and when significant decreases in cortisol and melatonin concentrations were initiated. Lower levels of subjective sleepiness resumed when glucose concentrations and body temperature had returned to levels similar to those observed prior to sleep deprivation and when melatonin and TSH concentrations had returned to daytime levels. The synchrony of behavioral, neuroendocrine, and metabolic changes suggests that circulating hormonal levels could exert modulatory influences on sleepiness and that metabolic alterations may underlie the sudden increase in fatigue consistently occurring at the end of a night of sleep deprivation. Effects of bright light or exercise exposure on subjective sleepiness appeared to be critically dependent on the timing of exposure.

Altered insulin secretory responses to glucose in diabetic and nondiabetic subjects with mutations in the diabetes susceptibility gene MODY3 on chromosome 12

One form of maturity-onset diabetes of the young (MODY) results from mutations in a gene, designated MODY3, located on chromosome 12 in band q24. The present study was undertaken to define the interactions between glucose and insulin secretion rate (ISR) in subjects with mutations in MODY3. Of the 13 MODY3 subjects, six subjects with normal fasting glucose and glycosylated hemoglobin and seven overtly diabetic subjects were studied as were six nondiabetic control subjects. Each subject received graded intravenous glucose infusions on two occasions separated by a 42-h continuous intravenous glucose infusion designed to prime the beta-cell to secrete more insulin in response to glucose. ISRs were derived by deconvolution of peripheral C-peptide levels. Basal glucose levels were higher and insulin levels were lower in MODY3 subjects with diabetes compared with nondiabetic subjects or with normal healthy control subjects. In response to the graded glucose infusion, ISRs were significantly lower in the diabetic subjects over a broad range of glucose concentrations. ISRs in the nondiabetic MODY3 subjects were not significantly different from those of the control subjects at plasma glucose levels <8 mmol/l. As glucose rose above this level, however, the increase in insulin secretion in these subjects was significantly reduced. Administration of glucose by intravenous infusion for 42 h resulted in a significant increase in the amount of insulin secreted over the 5-9 mmol/l glucose concentration range in the control subjects and nondiabetic MODY3 subjects (by 38 and 35%, respectively), but no significant change was observed in the diabetic MODY3 subjects. In conclusion, in nondiabetic MODY3 subjects insulin secretion demonstrates a diminished ability to respond when blood glucose exceeds 8 mmol/l. The priming effect of glucose on insulin secretion is preserved. Thus, beta-cell dysfunction is present before the onset of overt hyperglycemia in this form of MODY. The defect in insulin secretion in the nondiabetic MODY3 subjects differs from that reported previously in nondiabetic MODY1 or mildly diabetic MODY2 subjects.

Human studies with glucagon-like-peptide-1: potential of the gut hormone for clinical use

So far, a wealth of data originating from in vitro or animal experiments has been collected supporting the concept that the gut hormone, glucagon-like peptide-1 (GLP-1) may serve as a model molecule for the design of a new drug for the treatment of diabetes mellitus. This is supported by observations that GLP-1 has potent insulinotropic action in patients with non-insulin-dependent diabetes mellitus (NIDDM). It enhances beta-cell sensitivity to glucose stimulated insulin secretion. GLP-1 may also have a role in the treatment of impaired glucose tolerance, where the beta-cell is already insensitive to changes in plasma glucose concentrations. It may, as has previously been shown in animal models of 'prediabetes', delay the progressive decline in glucose tolerance to NIDDM. The glucose-dependent action of this peptide is an important feature in the treatment of NIDDM as it will protect against hypoglycaemic reactions, the most serious acute side-effect of antidiabetic therapy. Glucose utilization may be enhanced which would improve metabolic control in both NIDDM and IDDM. A glucagon lowering effect will further enhance metabolic control. This article reviews current experiences of the effects of GLP-1 in human studies. It points out the outcomes and limitations of previous trials and discusses future directions for the investigation of its potential use as a new agent in diabetes treatment.

A new family with hyperthyroxinemia caused by transthyretin Val109 misdiagnosed as thyrotoxicosis and resistance to thyroid hormone--a clinical research center study

Serum transthyretin (TTR) is a protein of liver origin that under normal conditions transports approximately 20% T4. Missense mutations of the TTR gene produce familial amyloidotic polyneuropathy and rarely, euthyroid hyperthyroxinemia (EHT). Of the 3 TTR variants so far identified with increased affinity for T4, Ser6, Thr109, and Met119, only TTR-Thr109 has high enough affinity for T4 to produce consistent hyperthyroxinemia in the heterozygous individuals. Because the mutation GCC-->ACC in codon 109 results in the loss of one Bso FI site in exon 4 of the TTR gene, the use of this enzyme was suggested to screen for TR-Thr109 in subjects with EHT. We investigated a family with dominantly inherited EHT, in which two of eight affected members received ablative thyroid treatment for presumed thyrotoxicosis, and one was misdiagnosed as having resistance to thyroid hormone. All affected individuals had serum reverse T3 concentrations above normal and average T4 50% above the mean of unaffected relatives. Total T3 and TSH levels were within the normal range. Although loss of the Bso FI site in one allele of the two TTR suggested the presence of Thr109, gene sequencing revealed a different mutation in the same codon (GCC-->GTC) producing TTR-Val109. T4-binding to TTR-Val109 was compared to that of the normal TTR-Ala109 and the formerly identified variant TTR-Thr109. Association constants were 1.3, 9.5, and 13.6 X 10(7) M-1 for TTR-Ala109, Val109, and Thr109, respectively. Thus, for equally expressed mutant and normal allele and 20% of serum T4 bound to TTR, the calculated mean serum T4 concentration of heterozygotes for TTR-Val109 should be 50% above the normal mean; the observed value being 55%. These results are in agreement with the observations based on the crystallographic structure of TTR-Thr109 indicating that the extra atoms in Val as in Thr, which are absent in the Ala of the wild type TTR, widen the ligand binding site.

Relationships between sleep quality and glucose regulation in normal humans

To define the effects of sleep on glucose regulation, we analyzed plasma glucose levels, insulin secretion rates (ISR), and plasma growth hormone and cortisol levels in normal subjects receiving a constant glucose infusion during nocturnal sleep, nocturnal sleep deprivation, and daytime recovery sleep. Plasma glucose and ISR markedly increased during early nocturnal sleep and returned to presleep levels during late sleep. These changes in glucose and ISR appeared to reflect the predominance of slow-wave (SW) stages in early sleep and of rapid-eye-movement and wake stages in late sleep. Major differences in glucose and ISR profiles were observed during sleep deprivation as glucose and ISR remained essentially stable during the first part of the night and then decreased significantly, despite the persistence of bed rest and constant glucose infusion. During daytime recovery sleep, SW stages were increased, glucose levels peaked earlier than during nocturnal sleep, and the decreases of glucose and ISR in late sleep were reduced by one-half. Thus sleep has important effects on brain and tissue glucose utilization, suggesting that sleep disturbances may adversely affect glucose tolerance.

Advice for beginning nurse researchers

Heideggerian hermeneutics was used to illuminate the advice of six nurse researchers who were interviewed by the authors. The advice given to us as beginning researchers included identifying a planned program of research with a topic that we "love" and conducting research that is meaningful. Additional advice included keeping an idea log, networking, mentoring, and developing collegial relationships. The words of these researchers are intended for future investigators, yet much wisdom exists for all nurses.

Clinical phenotypes, insulin secretion, and insulin sensitivity in kindreds with maternally inherited diabetes and deafness due to mitochondrial tRNALeu(UUR) gene mutation

An A-to-G transition in the mitochondrial tRNALeu(UUR) gene at base pair 3243 has been shown to be associated with the maternally transmitted clinical phenotype of NIDDM and sensorineural hearing loss in white and Japanese pedigrees. We have detected this mutation in 25 of 50 tested members of five white French pedigrees. Affected (mutation-positive) family members presented variable clinical features, ranging from normal glucose tolerance (NGT) to insulin-requiring diabetes. The present report describes the clinical phenotypes of affected members and detailed evaluations of insulin secretion and insulin sensitivity in seven mutation-positive individuals who have a range of glucose tolerance from normal (n = 3) to impaired (n = 1) to NIDDM (n = 3). Insulin secretion was evaluated during two experimental protocols: the first involved the measurement of insulin secretory responses during intravenous glucose tolerance test, hyperglycemic clamp, and intravenous injection of arginine. The second consisted of the administration of graded and oscillatory infusions of glucose and studies to define C-peptide kinetics. This protocol was aimed at assessing two sensitive measures of beta-cell dysfunction: the priming effect of glucose on the glucose-insulin secretion rate (ISR) dose-response curve and the ability of oscillatory glucose infusion to entrain insulin secretory oscillations. Insulin sensitivity was assessed by euglycemic-hyperinsulinemic clamp. Evaluation of insulin secretion demonstrated a large degree of between- and within-subject variability. However, all subjects, including those with NGT, demonstrated abnormal insulin secretion on at least one of the tests. In the four subjects with normal or impaired glucose tolerance, glucose failed to prime the ISR response, entrainment of ultradian insulin secretory oscillations was abnormal, or both defects were present. The response to arginine was always preserved, including in subjects with NIDDM. Insulin resistance was observed only in the subjects with overt diabetes. In conclusion, the pathophysiological mechanisms responsible for the development of NIDDM and insulin-requiring diabetes in this syndrome are complex and might include defects in insulin production, glucose toxicity, and insulin resistance. However, our data suggest that a defect of glucose-regulated insulin secretion is an early possible primary abnormality in carriers of the mutation. This defect might result from the progressive reduction of oxidative phosphorylation and implicate the glucose-sensing mechanism of beta-cells.

Elevated plasma glucose 2 h postchallenge predicts defects in beta-cell function

Studies were performed in subjects with no known family history of diabetes, normoglycemic subjects who have first-degree relatives with non-insulin-dependent diabetes mellitus (NIDDM), and subjects with nondiagnostic oral glucose tolerance tests (NDX) or impaired glucose tolerance (IGT). Insulin sensitivity index (SI) was similar in all four groups. However, a number of defects in insulin secretion were seen in the NDX and IGT groups, including reduced first-phase insulin secretory responses in intravenous glucose in relation to the degree of insulin resistance, and reduced normalized spectral power of insulin secretion during oscillatory glucose infusion. The latter finding demonstrates a decreased ability of the beta-cell to detect and respond to the successive increases and decreases in glucose and therefore to be entrained by the exogenous glucose infusion. The ability of a low-dose glucose infusion to prime the insulin secretory response to a subsequent glucose stimulus was normal in subjects with IGT but reduced or absent in subjects with overt NIDDM. These studies demonstrate that a number of alterations in beta-cell function are detectable in nondiabetic first-degree relatives of subjects with NIDDM with mild elevations in the 2-h postchallenge glucose level, and these abnormalities antedate the onset of overt hyperglycemia and clinical diabetes.

Effects of morning cortisol elevation on insulin secretion and glucose regulation in humans

The time course of the effects of an acute elevation in morning plasma cortisol on the daytime profiles of plasma glucose, serum insulin, and insulin secretion under constant glucose infusion was determined using a placebo-controlled design in two groups of eight normal men. In one group, the elevation of plasma cortisol was obtained by oral administration of 100 mg hydrocortisone. In the other group, the elevation was obtained by intravenous administration of 25 micrograms of corticotropin-releasing hormone. In both studies, the immediate effect of the increase in plasma cortisol, even when of very small amplitude, was an abrupt inhibition of insulin secretion without change in glucose concentration. Larger cortisol elevations, such as occurred after hydrocortisone administration, were additionally associated with the appearance of insulin resistance, which developed 4-6 h after the cortisol elevation and persisted for > 16 h. These observations support the concept that the 24-h cortisol rhythmicity is responsible, at least in part, for the normal diurnal variation in glucose tolerance.

Effects of aging on glucose regulation during wakefulness and sleep

Glucose intolerance, reduced sleep efficiency, and disturbed circadian rhythmicity occur in aging. In normal young subjects, glucose regulation is modulated by sleep and circadian rhythmicity. To examine age-related alterations in the temporal pattern of glucose tolerance and insulin secretion, eight modestly overweight healthy older men, eight weight-matched young men, and six young lean men were studied during constant glucose infusion for 53 h. Levels of glucose, insulin, C-peptide, and growth hormone (GH) were measured every 20 min. Rates of insulin and GH secretion were calculated by deconvolution. In older volunteers, sleep ws shallow and more fragmented than in young subjects but was nevertheless associated with robust glucose elevations. However, postsleep increases of insulin secretion were markedly dampened. During wakefulness, the normal morning-to-evening increase in glucose was preserved in the elderly, but insulin secretion failed to increase proportionately. Thus decreased glucose tolerance in aging is associated with insulin resistance and also with a relative insensitivity of the beta-cell to the modulation of glucose regulation by sleep and circadian rhythmicity.

Insulin secretion in insulin-resistant women with a history of gestational diabetes

Women with a history of gestational diabetes mellitus (GDM) tend to be insulin-resistant and hyperinsulinemic and are predisposed to the subsequent development of non-insulin-dependent diabetes mellitus (NIDDM). In the evolution of glucose intolerance, the first clinically detectable abnormality has not been defined and the relative importance of contributions of abnormal insulin secretion and insulin resistance is controversial. The present study was performed to evaluate the insulin secretory responses to oral and intravenous glucose and to mixed meals in women with a history of GDM, and to determine if the hyperinsulinemia present in these subjects is appropriate for the degree of insulin resistance. To address these questions, we studied the insulin secretory responses to oral glucose over a 3-hour period and to three mixed meals over a 24-hour period, and quantified the acute insulin response to glucose (AIRglucose) and insulin sensitivity (SI) during frequently sampled intravenous glucose tolerance tests (FSIVGTTs). Studies were performed in seven subjects with a history of GDM and in seven matched controls. Insulin secretion rates (ISRs) were derived by deconvolution of peripheral C-peptide values using a two-compartment model and standard C-peptide kinetic parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin secretory defects in polycystic ovary syndrome. Relationship to insulin sensitivity and family history of non-insulin-dependent diabetes mellitus

The increased prevalence of non-insulin-dependent diabetes mellitus (NIDDM) among women with polycystic ovary syndrome (PCOS) has been ascribed to the insulin resistance characteristic of PCOS. This study was undertaken to determine the role of defects in insulin secretion as well as familial factors to the predisposition to NIDDM seen in PCOS. We studied three groups of women: PCOS with a family history of NIDDM (PCOS FHx POS; n = 11), PCOS without a family history of NIDDM (PCOS FHx NEG; n = 13), and women without PCOS who have a family history of NIDDM (NON-PCOS FHx POS; n = 8). Beta cell function was evaluated during a frequently sampled intravenous glucose tolerance test, by a low dose graded glucose infusion, and by the ability of the beta cell to be entrained by an oscillatory glucose infusion. PCOS FHx POS women were significantly less likely to demonstrate appropriate beta cell compensation for the degree of insulin resistance. The ability of the beta cell to entrain, as judged by the spectral power for insulin secretion rate, was significantly reduced in PCOS FHx POS subjects. In conclusion, a history of NIDDM in a first-degree relative appears to define a subset of PCOS subjects with a greater prevalence of insulin secretory defects. The risk of developing NIDDM imparted by insulin resistance in PCOS may be enhanced by these defects in insulin secretion.

Altered insulin secretory responses to glucose in subjects with a mutation in the MODY1 gene on chromosome 20

This study was undertaken to test the hypothesis that the diabetes susceptibility gene on chromosome 20q12 responsible for maturity-onset diabetes of the young (MODY) in a large kindred, the RW family, results in characteristic alterations in the dose-response relationships between plasma glucose concentration and insulin secretion rate (ISR) that differentiate this form of MODY from MODY in subjects with glucokinase mutations. Ten marker-positive subjects and six matched nondiabetic marker-negative subjects from the RW family received graded intravenous glucose infusions on two occasions separated by a 42-h continuous intravenous glucose infusion designed to prime the beta-cell to secrete more insulin in response to glucose. ISR was derived by deconvolution of peripheral C-peptide levels. Basal glucose and insulin levels were similar in marker-negative and marker-positive groups (5.3 +/- 0.2 vs. 5.0 +/- 0.2 mmol/l, P > 0.2, and 86.1 +/- 3.9 vs. 63.7 +/- 12.1 pmol/l, P > 0.1, respectively). However, the marker-positive subjects had defective insulin secretory responses to an increase in plasma glucose concentrations. Thus, as the glucose concentration was raised above 7 mmol/l, the slope of the curve relating glucose and ISR was significantly blunted in the marker-positive subjects (13 +/- 4 vs. 68 +/- 8 pmol.min-1.mmol-1 x 1, P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Insulin secretion and clearance during low-dose graded glucose infusion

The present study was undertaken in normal volunteers to define the alterations in beta-cell responsiveness to glucose associated with different physiological states, including fasting and refeeding, and after prolonged intravenous glucose infusion. A low-dose graded glucose infusion protocol was used to explore the dose-response relationship between glucose and insulin secretion. Studies were performed in 10 normal volunteers, and insulin secretion rates (ISR) were calculated by deconvolution of peripheral C-peptide levels using a two-compartment model utilizing individual kinetic parameters. From 5 to 9 mmol/l glucose, the relationship between glucose and ISR was linear. After a 42-h glucose infusion at a rate of 4 mg.kg-1.min-1, the ISR increased by 53% over the same glucose concentration range (P < 0.002), resulting in a shift of the dose-response curve to the left. Insulin clearance rates decreased 27% after the 42-h glucose infusion (P < 0.001). After a 72-h fast, ISR decreased by 32% from baseline over the 5-8 mmol/l glucose range (P = 0.056), resulting in a shift of the dose-response curve to the right. This shift was reversed by a 42-h period of refeeding, after which ISR was increased by 77% compared with the fasting study (P < 0.02). Refeeding enhanced the beta-cell responsiveness, and ISR increased by 31% after refeeding compared with the baseline study (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Abnormal temporal patterns of glucose tolerance in obesity: relationship to sleep-related growth hormone secretion and circadian cortisol rhythmicity

To define the chronobiology of glucose tolerance and insulin secretion in obesity, nine obese men and nine lean men were studied during constant glucose infusion for 53 h, including 8 h of nocturnal sleep, 28 h of continuous wakefulness, and 8 h of daytime sleep. Blood samples were collected at 20-min intervals to assay glucose, insulin, C-peptide, cortisol, and GH. Sleep was polygraphically monitored. Abnormal temporal profiles of glucose regulation were observed during wakefulness and sleep in obese subjects. During daytime hours, the normal profile of glucose tolerance was reversed, as an improvement, rather than a deterioration, was observed from morning to late evening. This reversal of the daytime pattern appeared to be caused by a dual defect in glucose regulation during the previous night. Indeed, during early sleep, GH secretion was markedly reduced, and the nocturnal rises of glucose and insulin secretion were dampened. During late sleep, obese subjects failed to suppress insulin secretion and plasma glucose, resulting in high morning levels. Comparisons of metabolic and hormonal patterns during nocturnal and daytime sleep suggest that the failure to suppress insulin secretion in late sleep may reflect a relative insensitivity of the beta-cell to acute inhibitory effects of cortisol in addition to insulin resistance.

Demonstration of rapid light-induced advances and delays of the human circadian clock using hormonal phase markers

To determine the magnitude and direction of phase shifts of human circadian rhythms occurring within 1 day after a single exposure to bright light, plasma thyrotropin, melatonin, and cortisol levels and body temperature were monitored for 38 h in 17 men who were each studied two times, once during continuous dim light conditions and once with light exposure. After a period of entrainment to a fixed sleep-wake cycle, a 3-h light pulse (5,000 lux) was presented under constant routine conditions, and the resultant phase shifts were measured, also under constant routine conditions, on the 1st day after pulse presentation. The phase shifts in response to light occurred within 24 h and were in the delaying direction for most of the nocturnal period, with the crossover to phase advances occurring approximately 1 h after the temperature minimum. Phase shifts averaged 1 h, with delays being larger than advances, and were achieved without significant changes in rhythm amplitude. The immediate response of the human circadian clock to a single 3-h light pulse is thus characteristic of "type 1" resetting.

Nocturnal exercise phase delays circadian rhythms of melatonin and thyrotropin secretion in normal men

To determine whether a single episode of physical activity is capable of inducing rapid phase shifts in human circadian rhythms, 17 subjects were studied two times under constant routine conditions, once in the absence of stimulus and once with a 3-h nighttime pulse of exercise interrupting the constant routine conditions. The profiles of plasma cortisol, thyrotropin (TSH), and melatonin and of body temperature were monitored continuously to derive estimations of circadian phase position. The phase shifts were measured on the 1st day after exercise exposure. The timing of the exercise period ranged from -5 h to +4 h around the time of the minimum body temperature rhythm. Nighttime exercise was associated with 1- to 2-h phase delays of both the melatonin and TSH rhythms, with the size of the delays tending to be smaller when the exercise was presented in the latter part of the nighttime period and in the early morning. These data demonstrate that nonphotic stimuli may exert phase-shifting effects on the human circadian pacemaker.

Compensation in pancreatic beta-cell function in subjects with glucokinase mutations

The relationship between the in vivo insulin secretory responsiveness of the pancreatic beta-cell to glucose and the flux of glucose through the enzyme glucokinase was investigated in six subjects with heterozygous glucokinase mutations and in six matched control subjects. This was done by combining data published previously on the in vivo dose-response relationships between glucose and insulin secretion and on the in vitro enzymatic properties of wild-type and mutant forms of glucokinase. The flux of glucose through glucokinase (GK flux) in these subjects was estimated using a model based on the approximate Michaelis-Menten kinetics of wild-type and mutant forms of the enzyme. In two subjects with glucokinase mutations, which resulted in only a small reduction in enzymatic activity, the decrease in insulin secretion was directly proportional to the decrease in GK flux predicted using a Michaelis-Menten model for both mutant and wild-type glucokinase. However, in four subjects with glucokinase mutations, which resulted in severe reductions in enzymatic activity, insulin secretion was reduced compared with control subjects but less than predicted. This latter result implies the existence of a compensatory change in the beta-cells of such subjects, which results in a relative increase in insulin secretory response. We propose modifications to the simple model relating glucose concentration and GK flux, including glucose-induced overexpression of the normal allele and a role of glucokinase regulatory protein. The modifications take into account the possibility that the degree of compensation may be directly related to the severity of the mutation.