Central chemoreceptors and neural mechanisms of cardiorespiratory control

The arterial partial pressure (P CO2) of carbon dioxide is virtually constant because of the close match between the metabolic production of this gas and its excretion via breathing. Blood gas homeostasis does not rely solely on changes in lung ventilation, but also to a considerable extent on circulatory adjustments that regulate the transport of CO2 from its sites of production to the lungs. The neural mechanisms that coordinate circulatory and ventilatory changes to achieve blood gas homeostasis are the subject of this review. Emphasis will be placed on the control of sympathetic outflow by central chemoreceptors. High levels of CO2 exert an excitatory effect on sympathetic outflow that is mediated by specialized chemoreceptors such as the neurons located in the retrotrapezoid region. In addition, high CO2 causes an aversive awareness in conscious animals, activating wake-promoting pathways such as the noradrenergic neurons. These neuronal groups, which may also be directly activated by brain acidification, have projections that contribute to the CO2-induced rise in breathing and sympathetic outflow. However, since the level of activity of the retrotrapezoid nucleus is regulated by converging inputs from wake-promoting systems, behavior-specific inputs from higher centers and by chemical drive, the main focus of the present manuscript is to review the contribution of central chemoreceptors to the control of autonomic and respiratory mechanisms.

Development and validation of HPLC and UV spectrophotometric methods for the determination of lumiracoxib in tablets

In this study, two methods, based on high-performance liquid chromatography (HPLC) and UV spectrophotometry, were developed and validated for the quantitative determination of lumiracoxib in tablets. The HPLC was carried out on a column of propylsulfonic acid bonded to silica gel (250 x 4.6 mm; 5 mium), with a mobile phase of phosphate buffer (pH 7.4; 10 mM)-water-acetonitrile (10:40:50, v/v/v) fl owing at 1.0 mL/min and detection of the drug at 278 nm. The UV method was based on absorbance at 275 nm, with ethanol as solvent. Both assays were linear over the concentration range of 2–30 miug/mL (R approximate 0.999), as wellas accurate and precise, with recoveries between 98 and 100% and relative standard deviation (%RSD) smaller that 2.0%. The proposed methods are highly sensitive, precise and accurate and were successfully applied to the quantitation of lumiracoxib in the commercial formulation. The spectrophotometric method is a simple, cheap and less time-consuming method. However, the chromatographic method is selective for the determination of the degradation products of lumiracoxib.