Pédiatrie [Pediatrics].

Several preliminary studies suggest that prophylactic administration of probiotics reduces the incidence of necrotizing enterocolitis (NEC) in preterm infants, and several neonatology units have introduced this treatment under strict surveillance. Nonetheless, breast milk feeding remains the mainstay of NEC prevention. The beta-blocker propranolol, known for its effectiveness on cutaneous hemangiomas, is also proving useful for the treatment of subglottic or visceral hemangiomas. Following the decrease in severe bacterial infections thanks to widespread vaccinations, the McCarthy clinical score has regained importance in the prediction of the risk of bacterial infection in febrile infants. It is easy to use, economical, and has a diagnostic value comparable to laboratory tests. The new WHO growth charts have been introduced in Switzerland in 2011 to take into account the increasing regional and ethnic variations in our country. Any significant change in growth velocity should prompt an evaluation of the need of further investigations.

Effects of neuropeptide Y on intrarenal hemodynamics, plasma renin activity and urinary sodium excretion in rats.

Neuropeptide Y (NPY) is a vasoconstrictor peptide possibly involved in the regulation of renal sodium handling and renin release. This investigation was undertaken to assess in conscious normotensive rats the acute effects of a non-pressor dose of NPY on renal plasma flow, glomerular filtration rate, sodium excretion and plasma renin activity. Experiments were also performed during concomitant beta-adrenoceptor stimulation with isoproterenol. NPY per se had no effect on the studied parameters. Renal plasma flow was increased by isoproterenol and was significantly higher when the beta-adrenoceptor stimulant was infused alone (13.4 +/- 2.1 ml/min, p < 0.05, mean +/- SEM) that when administered together with NPY (7.2 +/- 2.0 ml/min). This was also true for glomerular filtration rate (3.3 +/- 0.3 vs. 1.8 +/- 0.3 ml/min, p < 0.01) and plasma renin activity (6.3 +/- 1.7 vs. 2.1 +/- 0.4 ng Ang I/ml/h, p < 0.05). Our data however do not allow to deduce whether the inhibitory effect of NPY on isoproterenol-induced renin release is mediated by changes in intrarenal hemodynamics or a direct effect on juxtaglomerular cells.

Magnetic resonance stress tagging in ischemic heart disease.

High-dose dobutamine magnetic resonance stress testing has been shown to be superior to dobutamine stress echocardiography for diagnosis of coronary artery disease (CAD). We determined the feasibility of quantitative myocardial tagging during low- and high-dose dobutamine stress and tested the ability of global systolic and diastolic quantitative parameters to identify patients with significant CAD. Twenty-five patients suspected of having significant CAD were examined with a standard high-dose dobutamine/atropine stress magnetic resonance protocol (1.5-T scanner, Philips). All patients underwent invasive coronary angiography as the standard of reference for the presence (n = 13) or absence (n = 12) of significant CAD. During low-dose dobutamine stress, systolic (circumferential shortening, systolic rotation, and systolic rotation velocity) and diastolic (velocity of circumferential lengthening and diastolic rotation velocity) parameters changed significantly in patients without CAD (all P < 0.05 vs. rest) but not in patients with CAD. Identification of patients without and with CAD during low-dose stress was possible using the diastolic parameter of "time to peak untwist." At high-dose stress, none of the global systolic or diastolic parameters showed the potential to identify the presence of significant CAD. With myocardial tagging, a quantitative analysis of systolic and diastolic function was feasible during low- and high-dose dobutamine stress. In our study, the diastolic parameter of time to peak untwist as assessed during low-dose dobutamine stress was the most promising global parameter for identification of patients with significant CAD. Thus quantitative myocardial tagging may become a tool that reduces the need for high-dose dobutamine stress.

The daily energy expenditure in stable chronic obstructive pulmonary disease.

Resting energy expenditure is frequently increased in chronic obstructive pulmonary disease (COPD), but it is unknown if this hypermetabolism holds true over 24 h. The aim of this study was to measure the actual 24-h energy expenditure (24-h EE) in patients with stable COPD. Energy expenditure was measured by indirect calorimetry, using a metabolic chamber for 24-h EE and a canopy for basal metabolic rate (BMR). Physical activity was detected in the chamber by a radar system, and its duration was quantified. Two groups matched for age and height were studied: 16 male ambulatory patients with stable COPD and 12 male normal subjects. Body weight was 92 +/- 12% of ideal body weight in the group with COPD and 108 +/- 11% in the control group (p = 0.01). BMR was 120 +/- 7% of predicted in the group with COPD and 108 +/- 12% in the control group (p < 0.01). However, 24-h EE was similar in the two groups, amounting to 1,935 +/- 259 kcal in patients with COPD and 2,046 +/- 253 kcal in the control group (NS). This corresponded to 145% and 137% of predicted BMR, and to 121% and 126% of measured BMR in patients with COPD and the control group, respectively (NS). Patients were allowed to pursue their usual treatment within the chamber, and a positive correlation existed between 24-h EE and the daily dose of inhaled beta 2-agonists (p < 0.03). During daytime, physical activity was lower in patients with COPD. This study shows that patients with stable COPD are characterized by a normal daily energy expenditure in controlled conditions in spite of an increased basal metabolic rate. They appear to save energy by reducing their spontaneous level of physical activity.

Cyclooxygenase-2 controls energy homeostasis in mice by de novo recruitment of brown adipocytes.

Obesity results from chronic energy surplus and excess lipid storage in white adipose tissue (WAT). In contrast, brown adipose tissue (BAT) efficiently burns lipids through adaptive thermogenesis. Studying mouse models, we show that cyclooxygenase (COX)-2, a rate-limiting enzyme in prostaglandin (PG) synthesis, is a downstream effector of beta-adrenergic signaling in WAT and is required for the induction of BAT in WAT depots. PG shifted the differentiation of defined mesenchymal progenitors toward a brown adipocyte phenotype. Overexpression of COX-2 in WAT induced de novo BAT recruitment in WAT, increased systemic energy expenditure, and protected mice against high-fat diet-induced obesity. Thus, COX-2 appears integral to de novo BAT recruitment, which suggests that the PG pathway regulates systemic energy homeostasis.

Comparison of thermogenic activity induced by the new sympathomimetic Ro 16-8714 between normal and obese subjects.

In a previous study, we demonstrated that the new beta-adrenoceptor agonist Ro 16-8714 possesses thermogenic property in normal male volunteers. The aim of the present study was to compare the metabolic response of lean vs obese individuals to a similar dose of this compound. Following an overnight fast, Ro 16-8714 (0.17 mg/kg fat free mass) or a placebo was given per os to six normal-weight subjects and to six moderately obese subjects. The rate of energy expenditure (EE) and the substrate utilization were determined by indirect calorimetry (hood system) before and for 6 h following the drug administration. Heart rate and blood pressure as well as plasma glucose, insulin and free fatty acid (FFA) concentrations were also measured at regular intervals throughout the study. The increment relative to base-line (mean +/- s.e.m.) in EE was similar in the two groups and averaged 4.0 +/- 1.4 per cent and 12.2 +/- 1.4 per cent with placebo and with Ro 16-8714 respectively in lean subjects, whereas the values reached 3.5 +/- 1.2 per cent and 14.4 +/- 2.0 per cent in obese subjects. Heart rate, systolic blood pressure, insulin and FFA were increased without any significant difference between the two groups. This study shows that Ro 16-8714 is a potent thermogenic agent both in normal and obese subjects.

ENaC-mediated alveolar fluid clearance and lung fluid balance depend on the channel-activating protease 1.

Sodium transport via epithelial sodium channels (ENaC) expressed in alveolar epithelial cells (AEC) provides the driving force for removal of fluid from the alveolar space. The membrane-bound channel-activating protease 1 (CAP1/Prss8) activates ENaC in vitro in various expression systems. To study the role of CAP1/Prss8 in alveolar sodium transport and lung fluid balance in vivo, we generated mice lacking CAP1/Prss8 in the alveolar epithelium using conditional Cre-loxP-mediated recombination. Deficiency of CAP1/Prss8 in AEC induced in vitro a 40% decrease in ENaC-mediated sodium currents. Sodium-driven alveolar fluid clearance (AFC) was reduced in CAP1/Prss8-deficient mice, due to a 48% decrease in amiloride-sensitive clearance, and was less sensitive to beta(2)-agonist treatment. Intra-alveolar treatment with neutrophil elastase, a soluble serine protease activating ENaC at the cell surface, fully restored basal AFC and the stimulation by beta(2)-agonists. Finally, acute volume-overload increased alveolar lining fluid volume in CAP1/Prss8-deficient mice. This study reveals that CAP1 plays a crucial role in the regulation of ENaC-mediated alveolar sodium and water transport and in mouse lung fluid balance.

S100A1 deficiency results in prolonged ventricular repolarization in response to sympathetic activation.

S100A1 is a Ca(2+)-binding protein and predominantly expressed in the heart. We have generated a mouse line of S100A1 deficiency by gene trap mutagenesis to investigate the impact of S100A1 ablation on heart function. Electrocardiogram recordings revealed that after beta-adrenergic stimulation S100A1-deficient mice had prolonged QT, QTc and ST intervals and intraventricular conduction disturbances reminiscent of 2 : 1 bundle branch block. In order to identify genes affected by the loss of S100A1, we profiled the mutant and wild type cardiac transcriptomes by gene array analysis. The expression of several genes functioning to the electrical activity of the heart were found to be significantly altered. Although the default prediction would be that mRNA and protein levels are highly correlated, comprehensive immunoblot analyses of salient up- or down-regulated candidate genes of any cellular network revealed no significant changes on protein level. Taken together, we found that S100A1 deficiency results in cardiac repolarization delay and alternating ventricular conduction defects in response to sympathetic activation accompanied by a significantly different transcriptional regulation.

Salmeterol for the prevention of high-altitude pulmonary edema.

BACKGROUND: Pulmonary edema results from a persistent imbalance between forces that drive water into the air space and the physiologic mechanisms that remove it. Among the latter, the absorption of liquid driven by active alveolar transepithelial sodium transport has an important role; a defect of this mechanism may predispose patients to pulmonary edema. Beta-adrenergic agonists up-regulate the clearance of alveolar fluid and attenuate pulmonary edema in animal models. METHODS: In a double-blind, randomized, placebo-controlled study, we assessed the effects of prophylactic inhalation of the beta-adrenergic agonist salmeterol on the incidence of pulmonary edema during exposure to high altitudes (4559 m, reached in less than 22 hours) in 37 subjects who were susceptible to high-altitude pulmonary edema. We also measured the nasal transepithelial potential difference, a marker of the transepithelial sodium and water transport in the distal airways, in 33 mountaineers who were prone to high-altitude pulmonary edema and 33 mountaineers who were resistant to this condition. RESULTS: Prophylactic inhalation of salmeterol decreased the incidence of high-altitude pulmonary edema in susceptible subjects by more than 50 percent, from 74 percent with placebo to 33 percent (P=0.02). The nasal potential-difference value under low-altitude conditions was more than 30 percent lower in the subjects who were susceptible to high-altitude pulmonary edema than in those who were not susceptible (P<0.001). CONCLUSIONS: Prophylactic inhalation of a beta-adrenergic agonist reduces the risk of high-altitude pulmonary edema. Sodium-dependent absorption of liquid from the airways may be defective in patients who are susceptible to high-altitude pulmonary edema. These findings support the concept that sodium-driven clearance of alveolar fluid may have a pathogenic role in pulmonary edema in humans and therefore represent an appropriate target for therapy.

Effects of catecholamines on volemic replacement with saline solution and the impact on heart rate variability in rabbits subjected to hemorrhage. A study by spectral analysis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Regulation of cardiac sodium-calcium exchanger by beta-adrenergic agonists.

Na+-Ca2+ exchanger and Ca2+ channel are two major sarcolemmal Ca2+-transporting proteins of cardiac myocytes. Although the Ca2+ channel is effectively regulated by protein kinase A-dependent phosphorylation, no enzymatic regulation of the exchanger protein has been identified as yet. Here we report that in frog ventricular myocytes, isoproterenol down-regulates the Na+-Ca2+ exchanger, independent of intracellular Ca2+ and membrane potential, by activation of the beta-receptor/adenylate-cyclase/cAMP-dependent cascade, resulting in suppression of transmembrane Ca2+ transport via the exchanger and providing for the well-documented contracture-suppressant effect of the hormone on frog heart. The beta-blocker propranolol blocks the isoproterenol effect, whereas forskolin, cAMP, and theophylline mimic it. In the frog heart where contractile Ca2+ is transported primarily by the Na+-Ca2+ exchanger, the beta-agonists' simultaneous enhancement of Ca2+ current, ICa, and suppression of Na+-Ca2+ exchanger current, INa-Ca would enable the myocyte to develop force rapidly at the onset of depolarization (enhancement of ICa) and to decrease Ca2+ influx (suppression of INa-Ca) later in the action potential. This unique adrenergically induced shift in the Ca2+ influx pathways may have evolved in response to paucity of the sarcoplasmic reticulum Ca2+-ATPase/phospholamban complex and absence of significant intracellular Ca2+ release pools in the frog heart.

Negative antagonists promote an inactive conformation of the beta 2-adrenergic receptor.

The beta 2-adrenergic receptor undergoes isomerization between an inactive conformation (R) and an active conformation (R*). The formation of the active conformation of the receptor molecule can be promoted by adrenergic agonists or by mutations in the third cytoplasmic domain that constitutively activate the receptor. Here we show that, of several beta-adrenergic receptor-blocking drugs tested, only two, ICI 118551 and betaxolol, inhibit the basal signaling activity of the beta 2-adrenergic receptor, thus acting as negative antagonists. We document the molecular properties of the more efficacious ICI 118551; (i) it shows higher affinity for the inactive form of the receptor and (ii) it inhibits the spontaneous formation of a beta-adrenergic receptor kinase substrate by the receptor. These properties are opposite those of adrenergic agonists, indicating that, in a fashion reciprocal to that of agonists, negative antagonists promote the formation of an inactive conformation of the receptor.

Catechol-binding serines of beta(2)-adrenergic receptors control the equilibrium between active and inactive receptor states.

The binding free energy for the interaction between serines 204 and 207 of the fifth transmembrane helix of the beta(2)-adrenergic receptor (beta(2)-AR) and catecholic hydroxyl (OH) groups of adrenergic agonists was analyzed using double mutant cycles. Binding affinities for catecholic and noncatecholic agonists were measured in wild-type and mutant receptors, carrying alanine replacement of the two serines (S204A, S207A beta(2)-AR), a constitutive activating mutation, or both. The free energy coupling between the losses of binding energy attributable to OH deletion from the ligand and from the receptor indicates a strong interaction (nonadditivity) as expected for a direct binding between the two sets of groups. However, we also measured a significant interaction between the deletion of OH groups from the receptor and the constitutive activating mutation. This suggests that a fraction of the decrease in agonist affinity caused by serine mutagenesis may involve a shift in the conformational equilibrium of the receptor toward the inactive state. Direct measurements using a transient transfection assay confirm this prediction. The constitutive activity of the (S204A, S207A) beta(2)-AR mutant is 50 to 60% lower than that of the wild-type beta(2)-AR. We conclude that S204 and S207 do not only provide a docking site for the agonist, but also control the equilibrium of the receptor between active (R*) and inactive (R) forms.

Activation of beta(2)-adrenergic receptors hastens relaxation and mediates phosphorylation of phospholamban, troponin I, and C-protein in ventricular myocardium from patients with terminal heart failure

Background-Catecholamines hasten cardiac relaxation through beta-adrenergic receptors, presumably by phosphorylation of several proteins, but it is unknown which receptor subtypes are involved in human ventricle. We assessed the role of beta(1)- and beta(2)-adrenergic receptors in phosphorylating proteins implicated in ventricular relaxation. Methods and Results-Right ventricular trabeculae, obtained from freshly explanted hearts of patients with dilated cardiomyopathy (n=5) or ischemic cardiomyopathy (n=5), were paced at 60 bpm. After measurement of the contractile and relaxant effects of epinephrine (10 mu mol/L) or zinterol (10 mu mol/L), mediated through beta(2)-adrenergic receptors, and of norepinephrine (10 mu mol/L), mediated through beta(1)-adrenergic receptors, tissues were freeze clamped. We assessed phosphorylation of phospholamban, troponin I, and C-protein, as well as specific phosphorylation of phospholamban at serine 16 and threonine 17, Data did not differ between the 2 disease groups and were therefore pooled. Epinephrine, zinterol, and norepinephrine increased contractile force to approximately the same extent, hastened the onset of relaxation by 15+/-3%, 5+/-2%, and 20+/-3%, respectively, and reduced the time to half-relaxation by 26+/-3%, 21+/-3%, and 37+/-3%. These effects of epinephrine, zinterol, and norepinephrine were associated with phosphorylation (pmol phosphate/mg protein) of phospholamban 14+/-3, 12+/-4, and 12+/-3, troponin I 40+/-7, 33+/-7, and 31+/-6; and C-protein 7.2+/-1.9, 9.3 +/- 1.4, and 7.5 +/- 2.0. Phosphorylation of phospholamban occurred at both Ser16 and Thr17 residues through both beta(1)- and beta(2)-adrenergic receptors. Conclusions-Norepinephrine and epinephrine hasten human ventricular relaxation and promote phosphorylation of implicated proteins through both beta(1)- and beta(2)-adrenergic receptors, thereby potentially improving diastolic function.