Plasma catecholamines and the counterregulatory responses to hypoglycemia in infants: a critical role for epinephrine and cortisol

Environmental stress and salivary cortisol levels in preterm infants

BACKGROUND

Preterm infants are exposed to numerous environmental stressors during their Neonatal Intensive Care Unit (NICU) stay, particularly during the first week after birth. The aim of this study is to assess whether salivary cortisol levels are correlated with Neonatal Infant Stressor Scale (NISS) scores in preterm infants during the first week of life. We also quantified the changes in both NISS scores and cortisol levels in the first week, and whether cortisol levels are associated with gestational age.

METHODS

Preterm infants (n = 38, birth weight <1250 g and/or gestational age <29 weeks) were included. Saliva samples were collected on day 0-3 (early) and day 4-7 (late), and cortisol concentrations were measured by immunoassay. NISS scores were assessed retrospectively for the six hours preceding each saliva collection.

RESULTS

NISS scores were not significantly correlated with salivary cortisol levels at either time point. However, infants born at <28 weeks gestation had higher median cortisol levels than infants born at >28 weeks (p = 0.0068), and there was also a significant inverse relationship between NISS score and gestational age (p = 0.04). There was no significant difference between the early and late time points for either NISS scores or cortisol levels.

CONCLUSIONS

Cortisol levels are elevated in infants <28 weeks gestation but do not correlate with NISS scores. NISS scores are inversely related to gestational age, likely reflecting increased exposure to interventions and invasive procedures for the smallest infants.

The Role of Pro-Opiomelanocortin Derivatives in the Development of Type 2 Diabetes-Associated Myocardial Infarction: Possible Links with Prediabetes

Myocardial infarction is a major contributor to CVD-related mortality. T2DM is a risk factor for MI. Stress activates the HPA axis, SNS, and endogenous OPS. These POMC derivatives increase the blood glucose and cardiovascular response by inhibiting the PI3K/AkT insulin signaling pathway and increasing cardiac contraction. Opioids regulate the effect of the HPA axis and SNS and they are cardioprotective. The chronic activation of the stress response may lead to insulin resistance, cardiac dysfunction, and MI. Stress and T2DM, therefore, increase the risk of MI. T2DM is preceded by prediabetes. Studies have shown that prediabetes is associated with an increased risk of MI because of inflammation, hyperlipidemia, endothelial dysfunction, and hypertension. The HPA axis is reported to be dysregulated in prediabetes. However, the SNS and the OPS have not been explored during prediabetes. The effect of prediabetes on POMC derivatives has yet to be fully explored and understood. The impact of stress and prediabetes on the cardiovascular response needs to be investigated. This study sought to review the potential impact of prediabetes on the POMC derivatives and pathways that could lead to MI.

Glucagon, cyclic AMP, and hepatic glucose mobilization: A half‐century of uncertainty

For at least 50 years, the prevailing view has been that the adenylate cyclase (AC)/cyclic AMP (cAMP)/protein kinase A pathway is the predominant signal mediating the hepatic glucose‐mobilizing actions of glucagon. A wealth of evidence, however, supports the alternative, that the operative signal most of the time is the phospholipase C (PLC)/inositol‐phosphate (IP3)/calcium/calmodulin pathway. The evidence can be summarized as follows: (1) The consensus threshold glucagon concentration for activating AC ex vivo is 100 pM, but the statistical hepatic portal plasma glucagon concentration range, measured by RIA, is between 28 and 60 pM; (2) Within that physiological concentration range, glucagon stimulates the PLC/IP3 pathway and robustly increases glucose output without affecting the AC/cAMP pathway; (3) Activation of a latent, amplified AC/cAMP pathway at concentrations below 60 pM is very unlikely; and (4) Activation of the PLC/IP3 pathway at physiological concentrations produces intracellular effects that are similar to those produced by activation of the AC/cAMP pathway at concentrations above 100 pM, including elevated intracellular calcium and altered activities and expressions of key enzymes involved in glycogenolysis, gluconeogenesis, and glycogen synthesis. Under metabolically stressful conditions, as in the early neonate or exercising adult, plasma glucagon concentrations often exceed 100 pM, recruiting the AC/cAMP pathway and enhancing the activation of PLC/IP3 pathway to boost glucose output, adaptively meeting the elevated systemic glucose demand. Whether the AC/cAMP pathway is consistently activated in starvation or diabetes is not clear. Because the importance of glucagon in the pathogenesis of diabetes is becoming increasingly evident, it is even more urgent now to resolve lingering uncertainties and definitively establish glucagon’s true mechanism of glycemia regulation in health and disease.

Low Adrenomedullary Function Predicts Acute Illness in Infants With Classical Congenital Adrenal Hyperplasia

CONTEXT

Youth with classical congenital adrenal hyperplasia (CAH) exhibit abnormal adrenomedullary function with decreased epinephrine levels noted in newborns and young infants. Little is known about how this relates to morbidity during the first year of life.

OBJECTIVE

This work aimed to study plasma epinephrine levels in infants with classical CAH and examine the clinical significance of epinephrine deficiency in the first year of life.

METHODS

This prospective cohort study comprised participants recruited from a pediatric tertiary care center: 36 infants with classical CAH due to 21-hydroxylase deficiency and 27 age-matched unaffected controls with congenital hypothyroidism. Main outcome measures included plasma epinephrine levels (N = 27), CYP21A2 genotype (N = 15), and incidence of acute illnesses from birth to age 1 year (N = 28).

RESULTS

Epinephrine levels in CAH infants independently predicted illness incidence in the first year of life (β = -0.018, R = -0.45, P = .02) and were negatively correlated with 17-hydroxyprogesterone at diagnosis (R = -0.51, P = .007). Infants with salt-wasting CAH exhibited lower epinephrine levels as newborns than simple-virilizing infants (P = .02). CAH patients had lower epinephrine as newborns than did controls (P = .007) and showed decreases in epinephrine from birth to age 1 year (P = .04). Null genotype was associated with lower newborn epinephrine and more illness in the first year of life, compared to less severe mutation categories.

CONCLUSION

Lower epinephrine levels are associated with increased risk of illness among CAH infants. While not currently part of clinical standard of care, measuring epinephrine levels and assessing genotype may help predict acute illness in the first year of life.

Neonatal Hypoglycemia and Brain Vulnerability

Neonatal hypoglycemia is a common condition. A transient reduction in blood glucose values is part of a transitional metabolic adaptation following birth, which resolves within the first 48 to 72 h of life. In addition, several factors may interfere with glucose homeostasis, especially in case of limited metabolic stores or increased energy expenditure. Although the effect of mild transient asymptomatic hypoglycemia on brain development remains unclear, a correlation between severe and prolonged hypoglycemia and cerebral damage has been proven. A selective vulnerability of some brain regions to hypoglycemia including the second and the third superficial layers of the cerebral cortex, the dentate gyrus, the subiculum, the CA1 regions in the hippocampus, and the caudate-putamen nuclei has been observed. Several mechanisms contribute to neuronal damage during hypoglycemia. Neuronal depolarization induced by hypoglycemia leads to an elevated release of glutamate and aspartate, thus promoting excitotoxicity, and to an increased release of zinc to the extracellular space, causing the extensive activation of poly ADP-ribose polymerase-1 which promotes neuronal death. In this review we discuss the cerebral glucose homeostasis, the mechanisms of brain injury following neonatal hypoglycemia and the possible treatment strategies to reduce its occurrence.

Arterio-venous differences in cord levels of catecholamines, glucose, lactate and blood gases

BACKGROUND

Norepinephrine (NE) and epinephrine (EPI) levels are higher in cord arterial blood relative to venous blood, consistent with active mechanisms of placental-maternal clearance. There are no contemporary studies of cord arteriovenous blood levels of sulfated and non-sulfated catechols.

AIM

To assess the arteriovenous differences in cord blood levels of dopamine (DA), the sulfated catecholamines and their sulfated and non-sulfated metabolites. To correlate levels of oxygen, H+/CO2, and glucose with cord catecholamine levels.

METHODS

Fifty-seven term infants, delivered by elective cesarean section, were recruited. Cord arterial and venous blood was sampled; levels of glucose, lactate, blood gases, six catechols and their sulfated conjugates were measured.

RESULTS

With one exception (DOPA sulfate), mean cord arterial levels of sulfated and non-sulfated catechols were significantly higher than venous levels. Arterial lactate and glucose levels were independently associated with NE levels, but only lactate was associated with levels of EPI and DA.

CONCLUSION

This study establishes that in vivo metabolic parameters of hypoxia, respiratory and metabolic acidosis are associated with catecholamine levels, a key relationship for perinatal adaptation and homeostasis, and findings that are consistent with in vitro studies of the regulators of catecholamine secretion.

Insulin and glucagon levels of umbilical cord blood in appropriate for gestational age - preterm infants with or without postnatal hypoglycemia

PURPOSE

To determine whether serum insulin and glucagon levels of umbilical cord blood correlate with subsequent postnatal hypoglycemia in appropriate for gestational age (AGA) - preterm infants at different gestational ages (GAs).

METHODS

The serum insulin and glucagon levels of umbilical cord blood were measured using magnetic bead based multiplex immunoassay in 69 AGA - premature infants, stratified according to GA: GA 23-30 weeks, early preterm (EP, n=31); GA 31-34 weeks, late preterm (LP, n=38). Postnatal hypoglycemia was defined as a capillary glucose level <40 mg/dL within the first 60 minutes of life, regardless of GA.

RESULTS

The capillary glucose concentration in EP infants (65.5±21.2 mg/dL) was significantly higher than that of LP infants (55.9±17.3 mg/dL) (P=0.043). The serum glucagon level in EP infants (44.3±28.7 pg/mL) was significantly higher than that in LP infants (28.1±13.6 pg/mL) (P=0.006). There was not a significant difference in serum insulin level between EP and LP infants (372.7±254.2 pg/mL vs. 372.4±209.1 pg/mL, P=0.996). There was a significant difference in the serum glucagon level between infants with and without hypoglycemia (27.7±8.9 mg/dL vs. 36.8±24.6 mg/dL, P=0.036), but not in the serum insulin level (451.9±256.9 pg/mL vs. 357.4±222.2 pg/mL, P=0.211). Postnatal glucose concentration within the first 60 minutes of life had a significant positive correlation with serum glucagon levels (r=0.256, P=0.034), but not with serum insulin levels (r=-0.020, P=0.867).

CONCLUSION

Lower glucagon levels of cord blood were seen in premature infants with higher GA, which might contribute to the occurrence of postnatal hypoglycemia.

Development of glassy carbon electrode modified with ruthenium red-multiwalled carbon nanotubes for simultaneous determination of epinephrine and acetaminophen

A glassy carbon electrode modified with ruthenium red and functionalized multi-walled carbon nanotube has been developed. The electrochemical response characteristics of the modified electrode toward epinephrine (EP) and acetaminophen (AC) was investigated by differential pulse voltammetry (DPV). Linear calibration plots were obtained over the range of 0.3 - 333.3 μM for both EP and AC with sensitivities of 0.221 and 0.174 μA μM(-1) for EP and AC, respectively. The detection limits for EP and AC were 0.04 and 0.06 μM, respectively. The diffusion coefficients for the oxidation of EP and AC at the modified electrode were calculated as 2.74 ± 0.05 × 10(-5) and 1.75 ± 0.07 × 10(-5) cm(2) s(-1), respectively. The practical analytical utilities of the modified electrode were demonstrated by the determination of EP and AC in human urine and serum as well as AC tablet samples.

Lactate in cord blood and its relation to fetal gluconeogenesis in at term deliveries

BACKGROUND

In the human fetus, an increased lactate and glucose level can be anticipated when hypoxia and stress are present and is likely to be a function of both anaerobic metabolism and catecholamine-mediated glycogenolysis/glycolysis.

AIM

We assessed if measurement of lactate in cord artery blood after vaginal and cesarean delivery may predict glucose concentration.

STUDY DESIGN

Umbilical artery cord blood lactacidemia, acidemia, and glucose concentration was tested by 'mini-lab' Radiometer ABL90 FLEX analyzers (Radiometer®, Copenhagen, Denmark) after vaginal delivery (VD), spontaneous (n=493) and by vacuum extractor (n=41) or by cesarean delivery (CD), elective (n=120) and emergency (n=68) in at term, vigorous neonates delivered from March to December 2012 at the 2nd level maternity ward of Policlinico Abano Terme, Abano Terme (Italy).

RESULTS

Cord blood lactacidemia and glucose levels were significantly higher in VD by vacuum extractor than in all other groups (5.32±1.96mmol/L, p=0.050 and 103.6±30.5mg/dL, p<0.001, respectively) and significantly lower in elective CD group (1.77±0.99mmol/L, p<0.001 and 69.8±13.0mg/dL, p<0.001). The cord blood lactate concentration was significantly and positively correlated with glucose levels (r=0.434, p<0.001), but significantly and negatively correlated with pH (r=-0,662, p<0.001), NaHCO3(-) (r=-0,802, p<0.001), and base excess (BE) (r=-0,698, p<0.001). However, in multivariate linear regression analysis, only BE, PaCO2 and cord blood lactate were significant predictive variables (R(2)=0.410; p<0.001) of glucose levels at birth.

CONCLUSION

Cord blood artery lactate and glucose concentration are significantly and positively correlated at birth in healthy, at term vaginally and cesarean delivered neonates, but BE is the best indicator of activated fetal gluconeogenesis.

Instability of glucose values in very preterm babies at term postmenstrual age

OBJECTIVE

To determine if very preterm (VPT) babies are capable of maintaining glucose levels within normal ranges at or near term postmenstrual age.

STUDY DESIGN

Glucose levels were intermittently or continuously monitored during 48 hours in a cohort of 60 VPT infants near hospital discharge. Hypoglycemic (≤45 mg/dL, 2.5 mmol/L) and hyperglycemic (≥140 mg/dL or 7.8 mmol/L, severe if ≥180 mg/dL or 10 mmol/L) episodes were considered relevant if they lasted longer than 30 minutes. Feeding regimes followed current practice.

RESULTS

With intermittent capillary, 2 hypoglycemic values and another 3 that were abnormally high were detected. With continuous monitoring, 6 babies (10.0%) had isolated hypoglycemia ≤45 mg/dL (2.5 mmol/L) (3 of them reaching 40 mg/dL, 2.2 mmol/L), 14 (23.3%) had isolated hyperglycemia, and 8 (13.3%) had episodes of both. The mean duration of hypoglycemia per patient was 2.8 ± 2.9 hours and 4.68 ± 4.35 hours in the case of hyperglycemia, with 12 infants becoming severely hyperglycemic. Of the 12 severely hyperglycemic patients, 5 also developed severe hypoglycemia. No specific characteristics identified the hypoglycemic babies. A history of intrauterine growth restriction (P = .037) and female sex (P = .063) seemed to increase the risk of severe hyperglycemia.

CONCLUSIONS

VPT infants continue to have abnormal glucose values, especially hyperglycemia, by the time of hospital discharge. No specific factors identify babies at higher risk for hypoglycemia, and intrauterine growth restriction and female sex seemed to predispose to hyperglycemia.

Decreased adrenomedullary function in infants with classical congenital adrenal hyperplasia

CONTEXT

Classical congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency can cause life-threatening adrenal crises as well as severe hypoglycemia, especially in very young children. Studies of CAH patients 4 years old or older have found abnormal morphology and function of the adrenal medulla and lower levels of epinephrine and glucose in response to stress than in controls. However, it is unknown whether such adrenomedullary abnormalities develop in utero and/or exist during the clinically high-risk period of infancy and early childhood.

OBJECTIVE

The objective of the study was to characterize adrenomedullary function in infants with CAH by comparing their catecholamine levels with controls. Design/Settings: This was a prospective cross-sectional study in a pediatric tertiary care center.

MAIN OUTCOME MEASURES

Plasma epinephrine and norepinephrine levels were measured by HPLC.

RESULTS

Infants with CAH (n = 9, aged 9.6 ± 11.4 d) had significantly lower epinephrine levels than controls [n = 12, aged 7.2 ± 3.2 d: median 84 [(25th; 75th) 51; 87] vs 114.5 (86; 175.8) pg/mL, respectively (P = .02)]. Norepinephrine to epinephrine ratios were also significantly higher in CAH patients than controls (P = .01). The control infants had primary hypothyroidism, but pre- and posttreatment analyses revealed no confounding effects on catecholamine levels.

CONCLUSIONS

This study demonstrates for the first time that infants with classical CAH due to 21-hydroxylase deficiency have significantly lower plasma epinephrine levels than controls, indicating that impaired adrenomedullary function may occur during fetal development and be present from birth. A longitudinal study of adrenomedullary function in CAH patients from infancy through early childhood is warranted.

Pediatric hypoglycemia

Hypoglycemia in the pediatric population is a common finding important to recognize and manage to prevent brain injury. Recent advances in molecular genetics have provided new insight into its biochemical and physiologic basis and have led to more appropriate and specific treatment. Although a major cause of brain injury in pediatrics, the ability to predict the long-term outcome in these patients remains difficult. Identification of these at-risk individuals is important. The physiologic adaptations associated with transition from fetal to neonatal life are now better understood thus allowing for improved surveillance and management. Despite these advances, analytical limitations of point-of-care testing instruments at low glucose concentration continue to persist, This review aims to address these questions and provide an overview of pediatric hypoglycemia and the molecular pathways involved.

'Two-step' head-to-body delivery activates foetal gluconeogenesis

AIM

The 'two-step' head-to-body delivery method, which involves waiting for the next contraction to deliver the shoulders, causes a decrease in umbilical artery pH. The aim of this study was to assess whether foetal acidemia activates gluconeogenesis.

METHODS

We tested umbilical artery cord blood glucose concentration and pH after 341 spontaneous and 25 vacuum extractor 'two-step' vaginal deliveries (VD) and after 85 elective and 49 emergency caesarean sections (CS).

RESULTS

Cord blood glucose concentration was significantly higher (95.5 ± 21.4 mg/dL vs 75.6 ± 16.4, p < 0.001), and pH values significantly lower (7.31 ± 0.09 vs 7.33 ± 0.06, p = 0.003) in 'two-step' VD neonates than in CS delivered neonates. In addition, cord blood glucose concentration was significantly higher (101.4 ± 30.6 mg/dL, p = 0.004), and pH values were significantly lower (7.26 ± 0.10, p < 0.001) in VD by vacuum extractor than in all other groups. The cord blood glucose concentration is significantly and negatively correlated with pH in the study population (r = -0.094, p = 0.036) and strongly significantly and negatively correlated in VD by vacuum extractor (r = -0.594, p = 0.007).

CONCLUSION

Cord blood glucose concentrations are significantly higher and pH values significantly lower in 'two-step' VD neonates, indicating activated foetal gluconeogenesis.

Gluconeogenesis is not regulated by either glucose or insulin in extremely low birth weight infants receiving total parenteral nutrition

OBJECTIVE

To determine potential factors regulating gluconeogenesis (GNG) in extremely low birth weight infants receiving total parenteral nutrition.

STUDY DESIGN

Seven infants (birth weight, 0.824 ± 0.068 kg; gestational age, 25.4 ± 0.5 weeks; postnatal age, 3.3 ± 0.2 days) were studied for 11 hours, with parenteral lipid and amino acid therapy continued at prestudy rates. Glucose was supplied at prestudy rates for the first 5 hours (period 1) and was then reduced to 6 mg/kg·min for 1 hour and further to ~3 mg/kg·min for 5 hours (period 2). A total of 2.5 mg/kg·min of the glucose was replaced by [U-(13)C]glucose throughout the study for measurements of glucose production and GNG. Concentrations of glucose, insulin, glucagons, and cortisol were determined.

RESULTS

GNG and glucose production remained unchanged (2.12 ± 0.23 vs. 1.84 ± 0.25 mg/kg·min [P = NS] and 2.44 ± 0.27 vs. 2.51 ± 0.31 mg/kg·min [P = NS], respectively), despite a 60% reduction of the glucose infusion rate and subsequent 30% (124.7 ± 10.8 to 82.6 ± 8.9 mg/dL; P = .009) and 70% (26.9 ± 4.7 to 6.6 ± 0.4 μU/mL; P = .002) decreases in glucose and insulin concentrations, respectively. Cortisol and glucagon concentrations remained unchanged.

CONCLUSION

In extremely low birth weight infants receiving total parenteral nutrition, GNG is a continuous process that is not affected by infusion rates of glucose or concentrations of glucose or insulin.

Update on investigating hypoglycaemia in childhood

Identification and investigation of hypoglycaemia in childhood remains an important clinical emergency. Rapid recognition and appropriate management of this clinical state continues to be important in order to prevent neurological damage or even death. The purpose of this review is to provide an update on the advances made in this area since the review by Bonham in this journal in 1993. Advances in molecular science and diagnostic techniques have assisted in understanding the mechanisms involved in the homeostasis of glucose metabolism at rest and when stressed. New disorders causing hypoglycaemia are described using the classification based upon aetiologies, which was used in Bonham's original paper. The development and use of guidelines and pre-assembled packs for investigating hypoglycaemia is also discussed.

Hypoglycemia during acute illness in children with classic congenital adrenal hyperplasia

Congenital adrenal hyperplasia (CAH) describes a group of genetic, autosomal recessive conditions, where there is a block in cortisol biosynthesis. Approximately 95 percent of cases are due to 21-hydroxylase deficiency, which is discussed in this article. Patients with the severe or classic form of CAH have epinephrine deficiency in addition to cortisol deficiency. Both epinephrine and cortisol are important counterregulatory hormones and help prevent hypoglycemia during physical stress. This is the first prospective study to evaluate the incidence of hypoglycemia during acute illness in children with classic CAH. Our objective was to examine blood glucose levels and symptoms of these children during the physical stressor of a typical acute illness managed at home. Twenty patients, ages 3 to 10 years with classic CAH participated. Parents were instructed regarding management of illnesses, home blood glucose monitoring and questionnaire completion. Over 29 months, 20 patients completed questionnaires and 6 patients performed home blood glucose monitoring. A blood glucose of <60 mg/dL was documented in 3 out of 8 monitored acute illness episodes, and in 2 out of 6 of monitored children. The acute illness episodes with documented blood glucose <60 mg/dL were not associated with vomiting. Our data suggest that children with classic CAH may experience lowering of blood glucose during illnesses, and patient education regarding the management of common childhood illness should include glucose supplementation.

Chronic late-gestation hypoglycemia upregulates hepatic PEPCK associated with increased PGC1alpha mRNA and phosphorylated CREB in fetal sheep

Hepatic glucose production is normally activated at birth but has been observed in response to experimental hypoglycemia in fetal sheep. The cellular basis for this process remains unknown. We determined the impact of 2 wk of fetal hypoglycemia during late gestation on enzymes responsible for hepatic gluconeogenesis, focusing on the insulin-signaling pathway, transcription factors, and coactivators that regulate gluconeogenesis. Hepatic phosphoenolpyruvate carboxykinase and glucose-6-phosphatase mRNA increased 12-fold and 7-fold, respectively, following chronic hypoglycemia with no change in hepatic glycogen. Chronic hypoglycemia decreased fetal plasma insulin with no change in glucagon but increased plasma cortisol 3.5-fold. Peroxisome proliferator-activated receptor-gamma coactivator-1alpha mRNA and phosphorylation of cAMP response element binding protein at Ser(133) were both increased, with no change in Akt, forkhead transcription factor FoxO1, hepatocyte nuclear factor-4alpha, or CCAAT enhancer binding protein-beta. These results demonstrate that chronic fetal hypoglycemia triggers signals that can activate gluconeogenesis in the fetal liver.

Genetic variation in hepatic glucose-6-phosphatase system genes in cases of sudden infant death syndrome

Genetic deficiencies of the hepatic glucose-6-phosphatase system, either of the enzyme (G6PC1) or of the glucose-6-phosphate transporter (G6PT1), result in fasting hypoglycaemia. Low hepatic G6PC1 activities were previously reported in a few term sudden infant death syndrome (SIDS) infants and assumed to be due to G6PC1 genetic deficiencies. In preterm infants, failures of postnatal activation of G6PC1 expression suggest disordered development as a novel cause of decreased G6PC1 activity in SIDS. G6PC1 and G6PT1 functional and mutational analysis was investigated in SIDS and non-SIDS infants. G6PC1 hepatic activity was abnormally low in 98 SIDS (preterm, n=13; term, n=85), and non-SIDS preterm infants (n=35) compared to term non-SIDS infants (n=29) and adults (n=9). Mean glycogen levels were elevated, except in term non-SIDS infants. A novel G6PT1 promoter polymorphism, 259C --> T was found; the - 259*T allele frequency was greater in term SIDS infants (n=140) than in term control infants (n=119) and preterm SIDS infants (n=30). Heterozygous and homozygous prevalence of 259C --> T was 38.6% and 7.1%, respectively, in term SIDS infants. In cell-based expression systems, the presence of - 259T in the promoter decreased basal luciferase activity by 3.2-fold compared to - 259C. Glucose-6-phosphatase latency in hepatic microsomes was elevated (indicating decreased G6PT1 function) in heterozygous and homozygous - 259T states. Delayed postnatal appearance of hepatic glucose-6-phosphatase in infants makes them vulnerable to hypoglycaemic episodes and this may occur in some SIDS infants. However, SIDS may be an association of more complex phenotypes in which several genes interact with multiple environmental factors. A UK-wide DNA Biobank of samples from all infant deaths, with an accompanying epidemiological database, should be established by pathologists to allow cumulative data to be collected from multiple genetic investigations on the same large cohort of samples, with the aim of selection of the best combination of genetic markers to predict unexpected infant death.

Serum glucagon counterregulatory hormonal response to hypoglycemia is blunted in congenital hyperinsulinism

The mechanisms involved in the release of glucagon in response to hypoglycemia are unclear. Proposed mechanisms include the activation of the autonomic nervous system via glucose-sensing neurons in the central nervous system, via the regulation of glucagon secretion by intra-islet insulin and zinc concentrations, or via direct ionic control, all mechanisms that involve high-affinity sulfonylurea receptor/inwardly rectifying potassium channel-type ATP-sensitive K(+) channels. Patients with congenital hyperinsulinism provide a unique physiological model to understand glucagon regulation. In this study, we compare serum glucagon responses to hyperinsulinemic hypoglycemia versus nonhyperinsulinemic hypoglycemia. In the patient group (n = 20), the mean serum glucagon value during hyperinsulinemic hypoglycemia was 17.6 +/- 5.7 ng/l compared with 59.4 +/- 7.8 ng/l in the control group (n = 15) with nonhyperinsulinemic hypoglycemia (P < 0.01). There was no difference between the serum glucagon responses in children with diffuse, focal, and diazoxide-responsive forms of hyperinsulinism. The mean serum epinephrine and norepinephrine concentrations in the hyperinsulinemic group were 2,779 +/- 431 pmol/l and 2.9 +/- 0.7 nmol/l and appropriately rose despite the blunted glucagon response. In conclusion, the loss of ATP-sensitive K(+) channels and or elevated intraislet insulin cannot explain the blunted glucagon release in all patients with congenital hyperinsulinism. Other possible mechanisms such as the suppressive effect of prolonged hyperinsulinemia on alpha-cell secretion should be considered.

Glucose homeostasis in the newborn

Hepatic glucose production by glycogenolysis and gluconeogenesis is essential to maintain blood glucose levels, and the glucose-6-phosphatase system catalyses the terminal step of both pathways. Developmental delays in the postnatal up-regulation of hepatic glucose-6-phosphatase enzyme activity are common in preterm infants. Two groups of infants have been identified with failure of developmental regulation of glucose homeostasis. Firstly, up to 20% of preterm infants about to be discharged home are at risk of hypoglycaemia if a feed is delayed. Cortisol, corticotrophin and epinephrine levels are higher in the infants with severe and persistent hypoglycaemia, but insulin, glucagon and human growth hormone do not differ from normoglycaemic infants. Secondly, preterm infants with an inadequate glycaemic response to glucagon (30% at the time of discharge home) have relative fasting hyperglycaemia, hyperinsulinaemia, increased insulin:glucagon ratios and a lower insulin sensitivity index. Hormonal dysfunctions in preterm infants may contribute to failures in postnatal expression of hepatic enzymes.