Hyperoxia-Exposed Lung Injury Upregulates DVL-1 Protein Expression And Activates Wnt/β-Catenin Signaling Pathway in Newborn Rat Lung

Background: Bronchopulmonary dysplasia (BPD) is a serious and lifelong pulmonary disease in premature neonates, which has an influence on a quarter of premature newborns. Wingless/integrated(Wnt)/β-catenin signaling pathway affects lung cell differentiation and lung tissue structure, and is abnormal activation in the lungs of rats with pulmonary fibrosis. Method: Newborn rats were subjected to hyperoxia-exposure, histopathological changes in lung tissues were evaluated through Immunohistochemistry (IHC), Dishevelled (DVL-1) and signaling pathways were detected through western blotting and real-time PCR. Results: Contrasting with the normoxic lungs, hyperoxia-exposed lungs demonstrated larger alveoli, less alveoli and thicker alveolar septa, and the number of alveoli reduced obviously, alveoli enlarged seriously in hyperoxia group. SOD activity was decreased (7 th day: P < 0.05; 14 th day: P < 0.01), and MDA was increased (7 th day: P < 0.05; 14 th day: P < 0.01) after hyperoxia exposure. Protein and mRNA expression levels of β-catenin, DVL-1, Ctnnbl1 and Cyclin D1 were upregulated by hyperoxia exposure on 7 th day( P < 0.01) and 14 th day( P < 0.01). Conclusion: We confirmed the positive role of DVL-1 and Wnt/β-catenin signaling pathway in promoting BPD under hyperoxia conditions, and provided promising therapeutic targets in the future.

Calcium Imaging Analysis of Cellular Responses to Hypercapnia and Hypoxia in the NTS of Newborn Rat Brainstem Preparation

It is supposed that the nucleus of the solitary tract (NTS) in the dorsal medulla includes gas sensor cells responsive to hypercapnia or hypoxia in the central nervous system. In the present study, we analyzed cellular responses to hypercapnia and hypoxia in the NTS region of newborn rat in vitro preparation. The brainstem and spinal cord were isolated from newborn rat (P0-P4) and were transversely cut at the level of the rostral area postrema. To detect cellular responses, calcium indicator Oregon Green was pressure-injected into the NTS just beneath the cut surface of either the caudal or rostral block of the medulla, and the preparation was superfused with artificial cerebrospinal fluid (25–26°C). We examined cellular responses initially to hypercapnic stimulation (to 8% CO2 from 2% CO2) and then to hypoxic stimulation (to 0% O2 from 95% O2 at 5% CO2). We tested these responses in standard solution and in two different synapse blockade solutions: (1) cocktail blockers solution including bicuculline, strychnine, NBQX and MK-801 or (2) TTX solution. At the end of the experiments, the superfusate potassium concentration was lowered to 0.2 from 3 mM to classify recorded cells into neurons and astrocytes. Excitation of cells was detected as changes of fluorescence intensity with a confocal calcium imaging system. In the synaptic blockade solutions (cocktail or TTX solution), 7.6 and 8% of the NTS cells responded to hypercapnic and hypoxic stimulation, respectively, and approximately 2% of them responded to both stimulations. Some of these cells responded to low K+, and they were classified into astrocytes comprising 43% hypercapnia-sensitive cells, 56% hypoxia-sensitive cells and 54% of both stimulation-sensitive cells. Of note, 49% of the putative astrocytes identified by low K+ stimulation were sensitive to hypercapnia, hypoxia or both. In the presence of a glia preferential blocker, 5 mM fluoroacetate (plus 0.5 μM TTX), the percentage of hypoxia-sensitive cells was significantly reduced compared to those of all other conditions. This is the first study to reveal that the NTS includes hypercapnia and hypoxia dual-sensitive cells. These results suggest that astrocytes in the NTS region could act as a central gas sensor.

ALPHA(1)-ADRENOCEPTORS ACTIVATION DECREASES MYOCARDIAL CONTRACTILITY IN NEWBORN RATS

Alpha(1)-adrenergic receptors (α1-AR) are found in cardiomyocytes, endothelial cells, and smooth muscle cells of humans and animals. Despite the fact that α1-AR make up 10% of the total number of adrenergic receptors, these receptors also involved in the regulation of inotropic and chronotropic functions of the heart. According to some scientists, the effects of α1-AR activation are not required for the basal contractile function of the heart while other group of researchers believe that α1-AR can be considered as cardioprotective targets; in particular, it is postulated that the α1A-subtype of adrenergic receptors can provide significant inotropic support in cardiac pathologies. This study was carried out on 6-7-day-old outbred newborn rat pups to evaluate the effect of alpha(1)-adrenoceptors activation on the myocardial contractility in newborn rats. For this, Alpha1-adrenergic receptors were stimulated by the pharmacological drug methoxamine at concentrations of 10-9-10-6 mol and the reaction of the contractile force of the strips of myocardium ventricles and heart atria in response to the agonist was investigated. Results of study revealed that stimulation of alpha1-adrenergic receptors, regardless of the methoxamine concentration, led to a negative inotropic reaction of the myocardium of atria and ventricles of newborn rat pups. This study showed unidirectional inotropic responses on rat atrial and ventricular myocardium in response to α1-adrenergic receptors stimulation. Methoxamine smoothly reduces the contractile force of the strips of myocardium atria and ventricles. At the same time, the concentration dependence on the inotropic reaction of the myocardium was observed. Results of study suggested that probably α1-adrenergic receptors along with the main regulators β-adrenergic receptors carry out fine tuning of the heart activity.