High Concentrations Of Catecholamines Research Articles

Association of Fetal Catecholamines With Neonatal Hypoglycemia

Perinatal stress and fetal growth restriction increase the risk of neonatal hypoglycemia. The underlying pathomechanism is poorly understood. In a sheep model, elevated catecholamine concentrations were found to suppress intrauterine insulin secretion, followed by hyperresponsive insulin secretion once the adrenergic stimulus subsided. To determine whether neonates with risk factors for hypoglycemia have higher catecholamine concentrations in umbilical cord blood (UCB) and/or amniotic fluid (AF) and whether catecholamines are correlated with postnatal glycemia. In a prospective cohort study of 328 neonates at a tertiary perinatal center from September 2020 through May 2022 in which AF and UCB were collected immediately during and after delivery, catecholamines and metanephrines were analyzed using liquid chromatography with tandem mass spectrometry. Participants received postnatal blood glucose (BG) screenings. Risk factor for neonatal hypoglycemia. Comparison of catecholamine and metanephrine concentrations between at-risk neonates and control participants, and correlation of concentrations of catecholamines and metanephrines with the number and severity of postnatal hypoglycemic episodes. In this study of 328 neonates (234 in the risk group: median [IQR] gestational age, 270 [261-277] days; and 94 in the control group: median [IQR] gestational age, 273 [270-278] days), growth-restricted neonates showed increased UCB median (IQR) concentrations of norepinephrine (21.10 [9.15-42.33] vs 10.88 [5.78-18.03] nmol/L; P < .001), metanephrine (0.37 [0.13-1.36] vs 0.12 [0.08-0.28] nmol/L; P < .001), and 3-methoxytyramine (0.149 [0.098-0.208] vs 0.091 [0.063-0.149] nmol/L; P = .001). Neonates with perinatal stress had increased UCB median (IQR) concentrations of norepinephrine (22.55 [8.99-131.66] vs 10.88 [5.78-18.03] nmol/L; P = .001), normetanephrine (1.75 [1.16-4.93] vs 1.25 [0.86-2.56] nmol/L; P = .004), and 3-methoxytyramine (0.120 [0.085-0.228] vs 0.091 [0.063-0.149] nmol/L; P = .008) (P < .0083 was considered statistically significant). Concentrations of UCB norepinephrine, metanephrine, and 3-methoxytyramine were negatively correlated with AF C-peptide concentration (rs = -0.212, P = .005; rs = -0.182, P = .016; and rs = -0.183, P = .016, respectively [P < .017 was considered statistically significant]). Concentrations of UCB norepinephrine, metanephrine, and 3-methoxytyramine were positively correlated with the number of hypoglycemic episodes (BG concentration of 30-45 mg/dL) (rs = 0.146, P = .01; rs = 0.151, P = .009; and rs = 0.180, P = .002, respectively). Concentrations of UCB metanephrine and 3-methoxytyramine were negatively correlated with the lowest measured BG concentration (rs = -0.149, P = .01; and rs = -0.153, P = .008, respectively). Neonates at risk for hypoglycemia displayed increased catecholamine and metanephrine concentrations that were correlated with postnatal hypoglycemic episodes and lower BG levels; these results are consistent with findings in a sheep model that fetal catecholamines are associated with neonatal β-cell physiology and that perinatal stress or growth restriction is associated with subsequent neonatal hyperinsulinemic hypoglycemia. Improving the pathomechanistic understanding of neonatal hypoglycemia may help to guide management of newborns at risk for hypoglycemia.

Stress-Induced Down-Regulation of Nitric Oxide Synthase in the Rat Heart

beta₃-adrenoceptor (beta₃-AR) is expressed in a smaller proportion than beta₁-AR and beta2-AR in the hearts of rats and humans and is activated in the presence of high concentrations of catecholamines. In the myocardium, beta₃-ARs couple to G inhibitory protein that activates nitric oxide synthases (NOS), thus increasing nitric oxide production that reduces inotropism. Beta₂-ARs and beta₁-ARs remodeling was described in failing and senescent human and rodent hearts as well as in the heart of foot shock stressed rats.

Prevalence and Impact of Atrial Fibrillation on Prognosis in Takotsubo Cardiomyopathy Patients.

The purpose of this review is to describe the impact of atrial fibrillation (AF) on the cardiovascular outcomes and prognosis in patients with Takotsubo Cardiomyopathy (TTC). The pathophysiological basis of TTC is set on the release of catecholamines, occurring post an emotional or stressful event. The cardiovascular system of patients with TTC is affected by the high concentrations of catecholamines, creating the ideal background for the development of AF: inflammation, myocardial stress, and excessive sympathetic activity. AF is considered to be the most frequent arrhythmia in TTC patients and is associated with higher rates of cardiovascular and all-cause mortality. AF is also linked with a worse prognosis concerning the hemodynamic status, cardiac fibrosis, lethal arrhythmias, thromboembolic events, and adverse heart failure associated outcomes. The early diagnosis of AF in these patients plays significant role in the prevention of adverse events, the reversibility of left ventricular function, and the restoration of sinus rhythm.

Catecholamine-Induced Secondary Takotsubo Syndrome in Children With Severe Enterovirus 71 Infection and Acute Heart Failure: A 20-year Experience of a Single Institute.

Background: Acute heart failure (AHF) is the major cause of death in children with severe enterovirus 71 (EV71) infection. This study aimed to report our clinical experience with EV71-related AHF, as well as to discuss its pathogenesis and relationship to Takotsubo syndrome (TTS).Methods: A total 27 children with EV71-related AHF between 1998 and 2018 were studied. The TTS diagnosis was based on the International Takotsubo Diagnostic Criteria.Results: Acute heart failure-related early death occurred in 10 (37%) of the patients. Sinus tachycardia, systemic hypertension, and pulmonary edema in 100, 85, and 81% of the patients, respectively, preceded AHF. Cardiac biomarkers were significantly increased in most patients. The main echocardiographic findings included transient and reversible left ventricular (LV) regional wall motion abnormality (RWMA) with apical ballooning. High concentrations of catecholamines either preceded or coexisted with AHF. Myocardial pathology revealed no evidence of myocarditis, which was consistent with catecholamine-induced cardiotoxic damage. Patients with EV71-related AHF who had received close monitoring of their cardiac function, along with early intervention involving extracorporeal life support (ECLS), had a higher survival rate (82 vs. 30%, p = 0.013) and better neurological outcomes (59 vs. 0%, p = 0.003).Conclusion: EV 71-related AHF was preceded by brain stem encephalitis-related hypercatecholaminemia, which resulted in a high mortality rate. Careful monitoring is merited so that any life-threatening cardiogenic shock may be appropriately treated. In view of the similarities in their clinical manifestations, natural course direction, pathological findings, and possible mechanisms, TTS and EV71-related AHF may represent the same syndrome. Therefore, we suggest that EV71-related AHF could constitute a direct causal link to catecholamine-induced secondary TTS.

Augmented glucose production is not contingent on high catecholamines in fetal sheep with IUGR.

Fetuses with intrauterine growth restriction (IUGR) have high concentrations of catecholamines, which lowers the insulin secretion and glucose uptake. Here, we studied the effect of hypercatecholaminemia on glucose metabolism in sheep fetuses with placental insufficiency-induced IUGR. Norepinephrine concentrations are elevated throughout late gestation in IUGR fetuses but not in IUGR fetuses with a bilateral adrenal demedullation (IAD) at 0.65 of gestation. Euglycemic (EC) and hyperinsulinemic-euglycemic (HEC) clamps were performed in control, intact-IUGR, and IAD fetuses at 0.87 of gestation. Compared to controls, basal oxygen, glucose, and insulin concentrations were lower in IUGR groups. Norepinephrine concentrations were five-fold higher in IUGR fetuses than in IAD fetuses. During the EC, rates of glucose entry (GER, umbilical + exogenous), glucose utilization (GUR), and glucose oxidation (GOR) were greater in IUGR groups than in controls. In IUGR and IAD fetuses with euglycemia and euinsulinemia, glucose production rates (GPR) remained elevated. During the HEC, GER and GOR were not different among groups. In IUGR and IAD fetuses, GURs were 40% greater than in controls, which paralleled the sustained GPR despite hyperinsulinemia. Glucose-stimulated insulin concentrations were augmented in IAD fetuses compared to IUGR fetuses. Fetal weights were not different between IUGR groups but were less than controls. Regardless of norepinephrine concentrations, IUGR fetuses not only develop greater peripheral insulin sensitivity for glucose utilization but also develop hepatic insulin resistance because GPR was maintained and unaffected by euglycemia or hyperinsulinemia. These findings show that adaptation in glucose metabolism of IUGR fetuses are independent of catecholamines, which implicate that hypoxemia and hypoglycemia cause the metabolic responses.

Editorial Comment to Acute hypotension induced by suction of cystic fluid containing extremely high concentrations of catecholamines during resection of giant pheochromocytoma.

Editorial Comment to Acute hypotension induced by suction of cystic fluid containing extremely high concentrations of catecholamines during resection of giant pheochromocytoma.

Fetal adaptations in insulin secretion result from high catecholamines during placental insufficiency.

Placental insufficiency and intrauterine growth restriction (IUGR) of the fetus affects approximately 8% of all pregnancies and is associated with short- and long-term disturbances in metabolism. In pregnant sheep, experimental models with a small, defective placenta that restricts delivery of nutrients and oxygen to the fetus result in IUGR. Low blood oxygen concentrations increase fetal plasma catecholamine concentrations, which lower fetal insulin concentrations. All of these observations in sheep models with placental insufficiency are consistent with cases of human IUGR. We propose that sustained high catecholamine concentrations observed in the IUGR fetus produce developmental adaptations in pancreatic β-cells that impair fetal insulin secretion. Experimental evidence supporting this hypothesis shows that chronic elevation in circulating catecholamines in IUGR fetuses persistently inhibits insulin concentrations and secretion. Elevated catecholamines also allow for maintenance of a normal fetal basal metabolic rate despite low fetal insulin and glucose concentrations while suppressing fetal growth. Importantly, a compensatory augmentation in insulin secretion occurs following inhibition or cessation of catecholamine signalling in IUGR fetuses. This finding has been replicated in normally grown sheep fetuses following a 7-day noradrenaline (norepinephrine) infusion. Together, these programmed effects will potentially create an imbalance between insulin secretion and insulin-stimulated glucose utilization in the neonate which probably explains the transient hyperinsulinism and hypoglycaemia in some IUGR infants.

La importancia del temperamento en la producción de ganado de carne bovina

En las explotaciones ganaderas, los bovinos son expuestos a diferentes factores estresantes desde el crecimiento hasta el sacrificio, afectando el bienestar y temperamento de los animales. El término “temperamento” se define como la reacción producida en un animal ante la presencia del hombre y se encuentra afectado por diferentes factores como la raza, el género, la edad, el manejo y la genética. Durante la evaluación del temperamento los bovinos excitables (nerviosos) tienden a presentar resultados altos en las evaluaciones de corral (EC), brete (EB) y velocidad de salida del brete (VSB), los cuales están relacionados con concentraciones elevadas de glucocorticoides y catecolaminas. Asimismo, los animales de temperamento nervioso presentan bajas ganancias diarias de peso (crecimiento lento) y bajos resultados de calidad de la canal y de la carne en comparación con animales de temperamento calmado. Por lo que el propósito de este documento fue revisar la relación entre el temperamento y la producción de carne bovina.

Glucagon sensitivity and clearance in type 1 diabetes: insights from in vivo and in silico experiments.

Glucagon use in artificial pancreas for type 1 diabetes (T1D) is being explored for prevention and rescue from hypoglycemia. However, the relationship between glucagon stimulation of endogenous glucose production (EGP) viz., hepatic glucagon sensitivity, and prevailing glucose concentrations has not been examined. To test the hypothesis that glucagon sensitivity is increased at hypoglycemia vs. euglycemia, we studied 29 subjects with T1D randomized to a hypoglycemia or euglycemia clamp. Each subject was studied at three glucagon doses at euglycemia or hypoglycemia, with EGP measured by isotope dilution technique. The peak EGP increments and the integrated EGP response increased with increasing glucagon dose during euglycemia and hypoglycemia. However, the difference in dose response based on glycemia was not significant despite higher catecholamine concentrations in the hypoglycemia group. Knowledge of glucagon's effects on EGP was used to develop an in silico glucagon action model. The model-derived output fitted the obtained data at both euglycemia and hypoglycemia for all glucagon doses tested. Glucagon clearance did not differ between glucagon doses studied in both groups. Therefore, the glucagon controller of a dual hormone control system may not need to adjust glucagon sensitivity, and hence glucagon dosing, based on glucose concentrations during euglycemia and hypoglycemia.

Microfluorescent analysis for bioindication of ozone on unicellular plant systems

Various unicellular model plant systems, on which autofluorescence, fluorescence after histochemical treatment, and growth rates were investigated, have been proposed as bioindicators of ozone. Analysis is performed using fluorescent microscopy in different modifications, including microspectrofluorimetry and laser scanning confocal microscopy. It is found that low ozone doses (0.005 μLL−1 for 2.5-h exposure or 0.008 μLL−1 for 4-h exposure) do not affect or stimulate autofluorescence of the samples. In addition, vegetative microspores and pollen retain their ability to germinate in an artificial medium, and their growth is even enhanced. Higher ozone concentrations lead to either a decrease in the emission intensity or a shift of peaks in the fluorescence spectrum. In particular, 16-h exposure of vegetative microspores of horsetail to ozone (total dose 0.032 μLL−1) leads to occurrence of a new peak in the wavelength range of 515 to 520 nm in their autofluorescence spectrum. Exposure to high (more than 0.1 μLL−1) doses gives rise to a similar peak in the spectrum of leaf secretory hairs of Raphanus sativus. The spectrum of leaf secretory hairs of Fragaria viridis exhibits a decrease in the emission intensity at wavelengths of 520 to 550 nm. Stress metabolites have been revealed by fluorescence at wavelengths from 460 to 480 nm after specific histochemical reactions for determination of catecholamines or histamine. After exposure in ozone to a total dose of 0.012 μLL−1, a significant increase in the amount of catecholamines and the histamine content was observed for pollen of Populus balsamifera. Higher concentrations of catecholamines (in comparison with control samples) are found in vegetative microspores of Equisetum arvense and pollen of Corylus avellana and Populus balsamifera after exposure in ozone to high doses (0.032 μLL−1), whereas a decrease in the catecholamine concentration was observed for pollen of Tulipa hybridum and Dolichothele albescens after this treatment.

Abstract 92: The Protective Effect of β3-Adrenergic Signaling Occurs via Differential Phosphorylation of nNOS in Cardiac Myocytes

Objective: The aim of this study is to identify the mechanisms involved in β3-adrenoreceptor (β3-AR)-dependent cardiac protection via nNOS signaling in cardiomyocytes in the setting of hypertrophy. Background: β3-AR and its downstream signaling pathways are recognized as novel modulators of heart function. Unlike β1- and β2-ARs, β3-ARs are stimulated at high catecholamine concentrations and induce negative inotropic effects, it serves as a “brake” to protect the heart from catecholamine overstimulation. We previously showed that β3-agonism restored left ventricular function, generated nitric oxide, and suppressed reactive oxygen species in mouse myocardium after pressure overload. Interestingly, cardioprotection was lost after acute nNOS inhibition and in nNOS -/- animals. Methods: Neonatal rat ventricular cardiomyocytes (NRVMs) were isolated from 2-4 day old Sprague-Dawley pups. Cells were treated with hypertrophic agents (angiotensin II, endothelin-1, and norepinephrine), the specific β3-AR agonist (BRL-37433),and phosphometic Sindbis viruses for nNOS. Results: Forty-eight hours of ET-1 (100nM) or 72 hours of NE (100μ M) treatment increased cell size and β3-AR mRNA expression vs. untreated cells. In hypertrophied cardiomyocytes, BRL (75nM) reduced cell size and induced NOS activity, nNOS phosphorylation at stimulatory site Ser1412, dephosphorylation of deactivation site Ser847, and ROS suppression. BRL-dependent NOS activity and ROS suppression were both attenuated by the nNOS inhibitor L-VNIO. NOS activity was also attenuated by phosphomemetic mutants Ser1412A (constitutively dephosphorylated) and Ser847D (constitutively phosphorylated). In addition, G i/o and Akt inhibition suppressed BRL-induced nNOS-Ser1412 phosphorylation and NOS activity. Conclusion: Our data suggest that BRL regulates β3-specific myocardial NOS activity via alterations in nNOS phosphorylation in isolated hypertrophied myocytes and failing hearts of murine animals. This is the first study to demonstrate a role for nNOS phosphorylation as a key factor in cardiac myocyte and β3-AR signaling. These results contribute significantly to our understanding of the cardiac protection.

Cardioprotective Effect of Beta-3 Adrenergic Receptor Agonism: Role of Neuronal Nitric Oxide Synthase

The aim of this study was to determine whether activation of β3-adrenergic receptor (AR) and downstream signaling of nitric oxide synthase (NOS) isoforms protects the heart from failure and hypertrophy induced by pressure overload.β3-AR and its downstream signaling pathways are recognized as novel modulators of heart function. Unlike β1- and β2-ARs, β3-ARs are stimulated at high catecholamine concentrations and induce negative inotropic effects, serving as a "brake" to protect the heart from catecholamine overstimulation.C57BL/6J and neuronal NOS (nNOS) knockout mice were assigned to receive transverse aortic constriction (TAC), BRL37344 (β3 agonist, BRL 0.1 mg/kg/h), or both.Three weeks of BRL treatment in wild-type mice attenuated left ventricular dilation and systolic dysfunction, and partially reduced cardiac hypertrophy induced by TAC. This effect was associated with increased nitric oxide production and superoxide suppression. TAC decreased endothelial NOS (eNOS) dimerization, indicating eNOS uncoupling, which was not reversed by BRL treatment. However, nNOS protein expression was up-regulated 2-fold by BRL, and the suppressive effect of BRL on superoxide generation was abrogated by acute nNOS inhibition. Furthermore, BRL cardioprotective effects were actually detrimental in nNOS(-/-) mice.These results are the first to show in vivo cardioprotective effects of β3-AR-specific agonism in pressure overload hypertrophy and heart failure, and support nNOS as the primary downstream NOS isoform in maintaining NO and reactive oxygen species balance in the failing heart.

Reduced Vascular Smooth Muscle (VSM) Sensitivity to Contraction in ex vivo Hemorrhaged Rabbit Epigastric Artery (EA)

Compensation to hemorrhage includes vasoconstrictor‐induced VSM contraction. Severe hemorrhage can lead to reduced VSM reactivity to vasoconstrictors and decompensation. Vasoconstrictors not only cause VSM contraction, but also can activate a cellular negative feedback mechanism that causes prolonged VSM desensitization, termed VSM memory. To explore the hypothesis that VSM memory plays a role in decompensation, we studied EA reactivity ex vivo 45 min after severe hemorrhage. Compared to control rabbit EA removed before hemorrhage, EA after hemorrhage displayed depressed contractions to phenylephrine (PE) and histamine (HA). These data suggest that VSM memory participates in vascular decompensation during hemorrhagic shock. We more fully characterized VSM memory in rabbit and mouse arteries in vitro. Strong receptor stimulation (10–30 μM PE) for 30 min followed by PE washout to cause complete relaxation reduced the ability of G protein‐coupled receptor (GPCR) agonists (PE, HA, U‐46619 and vasopressin) and a non‐GPCR agonist (KCl) to subsequently contract renal, femoral, epigastric and mesenteric arteries for at least 1 hr after PE washout. These data indicate that high catecholamine concentrations can induce a generalized VSM desensitization in rabbit and mouse arteries (VSM memory) that may be responsible, in part, for vascular decompensation during hemorrhage. Funding: R01HL061320

Giant Cystic Pheochromocytoma Containing High Concentrations of Catecholamines and Metanephrines

A 27-yr-old woman, known with neurofibromatosis type 1 and generalized anxiety disorder, presented with headaches, episodic palpitations, and pallor. Atenolol, started for hypertension by her family doctor, triggered a hypertensive crisis (226/126 mm Hg). Twentyfour-hour urine analysis demonstrated elevated excretion of metanephrine [65.7 ( 1.52; upper limit of reference range) mol/d] and normetanephrine [59.27 ( 1.95) mol/d], and to a lesser extent norepinephrine [2806 ( 569) nmol/d] and epinephrine [1222 ( 149) nmol/d]. Abdominal computed tomography (CT) scan showed a large solid and cystic lesion involving the right adrenal gland (Fig. 1A). 131-I methyliodobenzylguanidine scan showed a right adrenal tumor with prominent peripheral uptake and large central defect (Fig. 1B). After medical preparation with 3 wk of phenoxybenzamine (up to 90 mg/d), propranolol, and preoperative saline loading, the patient appeared clinically adequately blocked. However, anesthetic induction (fentanyl, propofol, lidocaine, and rocuronium) caused a hypertensive crisis (280/170 mm Hg) and prevented surgery. Phenoxybenzamine dosage was increased to 60 mg three times a day, and nifedipine SR 30 mg was added. Intravenous phenylephrine (1 mg) did not affect intraarterial blood pressure, indicating adequate -blockade. The next day, during open adrenalectomy, brittle blood pressure was noted until completion of tumor dissection. A sample of the liquefied tumor center was obtained (Fig. 2). Compared with plasma reference values (1), the cystic fluid contained extremely high concentrations of norepinephrine [65,967 ( 3.4) nmol/liter], epinephrine [51,000 ( 0.8) nmol/liter], dopamine [791.5 ( 0.21) nmol/liter], metanephrine [1,150 ( 0.3) nmol/liter], and normeta-

Fat as a fuel: emerging understanding of the adipose tissue–skeletal muscle axis

The early pioneers in the field of metabolism during exercise such as Lindhard and Krogh understood the importance of fat as a fuel for muscle contraction. But they could not have understood the details of the pathways involved, as neither the metabolic role of adipose tissue nor the transport role of non-esterified fatty acids (NEFA) in the plasma was clearly understood at the time. We now recognize that the onset of muscular contraction coincides with an increase in the delivery of NEFA from adipose tissue, probably coordinated by the sympatho-adrenal system. During light exercise, adipose tissue-derived NEFA make up the majority of the oxidative fuel used by muscle. As exercise is prolonged, the importance of NEFA increases. The onset of exercise is marked by an increased proportion of NEFAs entering beta-oxidation rather than re-esterification and recycling. At moderate intensities of exercise, other sources of fat, potentially plasma- and intramyocellular-triacylglycerol, supplement the supply of plasma NEFA. The delivery of NEFA is augmented by increased adipose tissue blood flow and by other stimuli such as atrial natriuretic peptide. Only during high-intensity exercise is there a failure of adipose tissue to deliver sufficient fatty acids for muscle (which is coupled with an inability of muscle to use them, even when fatty acids are supplied artificially). This limitation of adipose tissue NEFA delivery may reflect some feedback inhibition of lipolysis, perhaps via lactate, or possibly alpha-adrenergic inhibition of lipolysis at very high catecholamine concentrations.

Polymorphism of the bovine ADRB3 gene

The β(3)-adrenergic receptor (ADRB3) is predominantly expressed in white and brown adipose tissue and mediates the lipolytic and thermogenic effects of high catecholamine concentrations. Variation in the ADRB3 gene (ADRB3) has been associated with obesity and the earlier onset of non-insulin-dependent diabetes mellitus in some ethnic groups, as well as some production traits of sheep, but to date variation of bovine ADRB3 has not been reported. In this study, variation in the promoter region of bovine ADRB3 was investigated in 737 cattle by polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP) analysis. Six PCR-SSCP patterns representing six allelic variations and containing four single nucleotide polymorphisms (SNPs) and three nucleotide deletions/insertions were observed. Allele A was the most common allele (93.83%), whereas alleles C, D, E and F were rare (0.07, 1.09, 0.41, and 0.34%, respectively). The variation identified here might have an impact on both the function and level of expression of bovine ADRB3.

Agonist Dose-dependent Phosphorylation by Protein Kinase A and G Protein-coupled Receptor Kinase Regulates β2 Adrenoceptor Coupling to Gi Proteins in Cardiomyocytes

Adrenoceptors receptors (ARs) play a pivotal role in regulating cardiovascular response to catecholamines during stress. beta(2)ARs, prototypical G protein-coupled receptors (GPCRs), expressed in animal hearts, display dual coupling to both G(s) and G(i) proteins to control the adenylyl cyclase-cAMP dependent protein kinase A (PKA) pathway to regulate contraction responses. Here, we showed that the beta(2)AR coupling to G(i) proteins was agonist dose-dependent and occurred only at high concentrations in mouse cardiac myocytes. Both the beta(2)AR-induced PKA activity, measured by fluorescence resonance energy transfer (FRET) imaging, and the increase in myocyte contraction rate displayed sensitivity to the G(i) inhibitor pertussis toxin (PTX). Further studies revealed that activated beta(2)ARs underwent PKA phosphorylation at a broad range of agonist concentrations. Disruption of the PKA phosphorylation sites on the beta(2)AR blocked receptor/G(i) coupling. However, a sufficient beta(2)AR/G(i) coupling was also dependent on the G protein-coupled receptor kinase (GRK)-mediated phosphorylation of the receptors, which only occurred at high concentrations of agonist (> or = 100 nm). Disruption of the GRK phosphorylation sites on the beta(2)AR blocked receptor internalization and coupling to G(i) proteins, probably by preventing the receptor's transportation to access G(i) proteins. Furthermore, neither PKA nor GRK site mutated receptors displayed sensitivity to the G(i)-specific inhibitor, G(i)CT. Together, our studies revealed distinct roles of PKA and GRK phosphorylation of the beta(2)AR for agonist dose-dependent coupling to G(i) proteins in cardiac myocytes, which may protect cells from overstimulation under high concentrations of catecholamines.

Role of the excessive amounts of circulating catecholamines and glucocorticoids in stress-induced heart disease

Various stressful stimuli are known to activate the sympathetic nervous system to release catecholamines and the hypothalamic-pituitary-adrenal axis to release glucocorticoids in the circulation. Although initial actions of both catecholamines and glucocorticoids are beneficial for the function of the cardiovascular system, their delayed effects on the heart are deleterious. Glucocorticoids not only increase plasma levels of catecholamines by inhibiting their extraneuronal uptake, but they have also been shown to induce supersensitivity to catecholamines in the heart by upregulating different components of the betta-adrenoceptor signal transduction system. Low concentrations of catecholamines stimulate the heart by promoting Ca2+ movements, whereas excessive amounts of catecholamines produce cardiac dysfunction by inducing intracellular Ca2+ overload in cardiomyocytes. Several studies have shown, however, that under stressful conditions high concentrations of catecholamines become oxidized to form aminolutins and generate oxyradicals. These oxidation products of catecholamines have been demonstrated to produce coronary spasm, arrhythmias, and cardiac dysfunction by inducing Ca2+-handling abnormalities in both sarcolemmal and sarcoplasmic reticulum, defects in energy production by mitochondria, and myocardial cell damage. In this article we have focused the discussion to highlight the interrelationship between catecholamines and glucocorticoids and to emphasize the role of oxidation products of catecholamines in the development of stress-induced heart disease.

Extensive Diversity of the ADRB3 Gene in Chinese Sheep Identified by PCR-SSCP

The beta(3)-adrenergic receptor (ADRB3) is the main mediator of the lipolytic and thermogenic effects of high catecholamine concentrations. Polymorphism in the ovine ADRB3 gene has been reported to be associated with birth weight, growth rate, carcass composition, and cold survival. Eight alleles have been identified in New Zealand sheep, but to date, breeds from other countries have not been studied in detail. In this study, we employed PCR-SSCP to detect ADRB3 polymorphism in the Hu, Tan, small-tailed Han, and Tibet breeds of Chinese sheep. Thirteen SSCP patterns were observed, including the eight previously reported and five new patterns. The newly identified SSCP patterns represent five novel sequences, increasing the reported number of alleles of ADRB3 from 8 to 13. In these Chinese sheep, the most common allele was the previously reported allele C (49.0%); the A allele was the next most common (22.0%). These results suggest that Chinese sheep have more diversity in ADRB3 than New Zealand sheep and therefore have possibly been selected either naturally or via breeding for different traits.

Catecholamine-storing Cells at Acupuncture Points of Rabbits

Recent studies have shown that specific sites of the skin related to the acupoints contain a high concentration of catecholamines, especially noradrenaline (NA). Considering this newly discovered property of the acupoints we assumed that heterogeneous distribution of cutaneous catecholamines could be associated with a specific location of catecholamine-storing cells in acupoint sites. In the present work we used an immunohistochemical method and confocal laser scanning microscopy to examine the presence of catecholamine-storing cells at acupoints of rabbits. Double immunofluorescence staining with antibodies against adrenaline and NA revealed only the cells storing NA in the dermal layer of rabbit skin. NA-storing cells were randomly scattered as single cells as well as existing in small clusters in a globular tissue formation surrounded by blood vessels and capillaries. Microscopic analysis of histological sections also revealed that the distribution of NA-storing cells was closely associated with the location of acupoints. Thus results from our study strongly suggest that acupoint areas of rabbit skin contain catecholamine-storing cells which can release a high level of NA during acupuncture stimulation.