Search

Copyright of Proceedings of the International Scientific Conference of Daugavpils University / Daugavpils Universitates Starptautiskas Zinatniskas Konferences Materiali is the property of Daugavpils University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Neonatal hyperoxia increases contraction and decreases the relaxation of airway smooth muscle (ASM), and the balance between these processes in airways is critical for normal flow of air. Thus, it is important to search for an effective treatment that targets this balance to prevent the airway hyperreactivity. The non-adrenergic-noncholinergic inhibitory system mediators such as vasoactive intestinal peptide (VIP) play an important role in ASM tone. Therefore, we tested the hypothesis that exogenous VIP will attenuate the contraction and promote relaxation of tracheal smooth muscle exposed to neonatal hyperoxia. Tracheal cylinders were obtained from Wistar rat pups (P10) exposed to hyperoxia (= 95% O2) or room air for seven days. These cylinders were used to study contractile responses evoked by carbachol (10-8 - 10-4 M) and relaxant responses of ASM evoked by electrical field relaxation (EFS) in precontracted tissue (carbachol, 10µM) in absence or presence of a single dose of VIP (50 nM). In addition, the dose-response relaxant effect of VIP (1nM - 1µM) was tested in absence or presence of a VPAC receptor antagonist; a protein kinase A (PKA) inhibitor (Rp- 8-CPT-cAMPS); a phosphodiesterase 4 (PDE4) inhibitor (rolipram); or a large-conductance calcium-activated potassium channel blocker (charybdotoxin). The relaxation is expressed as a percentage of pre-constricted state, and the data are presented as mean/s.e.m. Hyperoxic exposure significantly decreased the relaxant responses of ASM towards EFS, as compared to those obtained from control animals exposed to room air, and these reduced relaxant responses in hyperoxic tissues were significantly reversed in presence of VIP (p<0.01). VIP induced dosedependent relaxation and the relaxant responses were overcompensated in hyperoxic animals. VPAC antagonist; PKA or PDE4 inhibition significantly reduced VIP-induced relaxation (p<0.05), while blockade of calcium-activated potassium channel did not have a significant effect. The results of this study revealed that VIP attenuates airway hyperreactivity and reverses the impaired relaxation of airway smooth muscle induced by hyperoxic exposure via cAMP/PKA signaling pathway. We speculate that the use of VIP might be an effective therapeutic approach to prevent the airway hyperreactivity induced by hyperoxia. [ABSTRACT FROM AUTHOR]

Physiological studies in small animals can be complicated, but the complexity is increased dramatically when performing live-animal synchrotron X-ray imaging studies. Our group has extensive experience in high-resolution live-animal imaging at the Japanese SPring-8 synchrotron, primarily examining airways in two-dimensions. These experiments normally image an area of 1.8 mm×1.2 mm at a pixel resolution of 0.45 μm and are performed with live, intact, anaesthetized mice. There are unique challenges in this experimental setting. Importantly, experiments must be performed in an isolated imaging hutch not specifically designed for small-animal imaging. This requires equipment adapted to remotely monitor animals, maintain their anesthesia, and deliver test substances while collecting images. The horizontal synchrotron X-ray beam has a fixed location and orientation that limits experimental flexibility. The extremely high resolution makes locating anatomical regions-of-interest slow and can result in a high radiation dose, and at this level of magnification small animal movements produce motion-artifacts that can render acquired images unusable. Here we describe our experimental techniques and how we have overcome several challenges involved in performing live mouse synchrotron imaging. Experiments have tested different mouse strains, with hairless strains minimizing overlying skin and hair artifacts. Different anesthetics have also be trialed due to the limited choices available at SPring-8. Tracheal-intubation methods have been refined and controlled-ventilation is now possible using a specialized small-animal ventilator. With appropriate animal restraint and respiratory-gating, motion-artifacts have been minimized. The animal orientation (supine vs. head-high) also appears to affect animal physiology, and can alter image quality. Our techniques and image quality at SPring-8 have dramatically improved and in the near future we plan to translate this experience to the Imaging and Medical Beamline at the Australian Synchrotron. Overcoming these challenges has permitted increasingly sophisticated imaging of animals with synchrotron X-rays, and we expect a bright future for these techniques. [ABSTRACT FROM AUTHOR]