Urea In Body Fluids Research Articles

Multiplex Chroma Response Wearable Hydrogel Patch: Visual Monitoring of Urea in Body Fluids for Health Prognosis.

Visual wearable devices can rapid intuitively monitor biomarkers in body fluids to indicate the human health status and provide valuable reference for further medical diagnosis. However, unavoidable interference factors such as skin color, natural light, and background luminescence can interfere with the visualization accuracy of flexible wearable devices, limiting their practical sensing application. Here, we designed a wearable sensing patch via an embedded upconversion optical probe in a 3D porous polyacrylamide hydrogel, exhibiting a multiplex chroma response to urea based on the inner filter effect, which overcomes the susceptibility to external conditions due to its near-infrared excited luminescence and improves the resolution and accuracy of visual sensing. Furthermore, a highly compatible portable sensing platform combined with a smartphone was designed to achieve in situ rapid quantitative analysis of urea. The limit of detection values of the upconversion optical probe and hydrogel sensor are as low as 1.4 and 30 μM respectively, exhibiting the practicality in different scenarios. The designed sensing patch provides a convenient and accurate sensing strategy for the detection of biomarkers in body fluids and has the potential to be developed into a point-of-care device to provide disease early warning and clinical diagnosis.

Active urea transport in lower vertebrates and mammals.

Some unicellular organisms can take up urea from the surrounding fluids by an uphill pumping mechanism. Several active (energy-dependent) urea transporters (AUTs) have been cloned in these organisms. Functional studies show that active urea transport also occurs in elasmobranchs, amphibians, and mammals. In the two former groups, active urea transport may serve to conserve urea in body fluids in order to balance external high ambient osmolarity or prevent desiccation. In mammals, active urea transport may be associated with the need to either store and/or reuse nitrogen in the case of low nitrogen supply, or to excrete nitrogen efficiently in the case of excess nitrogen intake. There are probably two different families of AUTs, one with a high capacity able to establish only a relatively modest transepithelial concentration difference (renal tubule of some frogs, pars recta of the mammalian kidney, early inner medullary collecting duct in some mammals eating protein-poor diets) and others with a low capacity but able to maintain a high transepithelial concentration difference that has been created by another mechanism or in another organ (elasmobranch gills, ventral skin of some toads, and maybe mammalian urinary bladder). Functional characterization of these transporters shows that some are coupled to sodium (symports or antiports) while others are sodium-independent. In humans, only one genetic anomaly, with a mild phenotype (familial azotemia), is suspected to concern one of these transporters. In spite of abundant functional evidence for such transporters in higher organisms, none have been molecularly identified yet.

Simple, selective, and sensitive measurement of urea in body fluids of mammals by reversed-phase ultra-fast liquid chromatography

Ultra-fast liquid chromatography with a photodiode array detector for simple and rapid determination of urea in body fluids of farm animals is described. Blood plasma, milk, and urine samples are treated with trichloroacetic acid and then centrifuged. Supernatants are derivatized at room temperature using p-dimethylaminobenzaldehyde. Samples are separated using a ternary gradient of methanol in buffer and water. Derivatized urea in standards and biological samples is analyzed using a Phenomenex C<sub>18</sub>-column (Synergi 2.5 µm, Hydro-RP, 100Å, 100 × 2 mm). The photodiode detector is set to 370 and/or 254 nm for detection. Temperature is maintained at 27°C by a column heater. Clear separation of derivatized urea from the endogenous species present in assayed biological samples was achieved in less than 6 min. The urea adduct peak eluted at 4.36 ± 0.05 min. Average recoveries of the urea standards added to assayed biological materials were satisfactory (i.e. 100.2 ± 4.1%). Our chromatographic method with photodiode detection at 370 nm and at 254 nm, in particular, offers low detection (L<sub>D</sub>) and quantification limits (L<sub>Q</sub>) (<sup>370nm</sup>L<sub>D</sub> = 0.47 ng, <sup>254nm</sup>L<sub>D</sub> = 0.027 ng and <sup>370nm</sup>L<sub>Q</sub> = 1.41 ng, <sup>254nm</sup>L<sub>Q</sub> = 0.080 ng, respectively). Our liquid chromato-graphy based on detection at 370 nm is the most versatile analytical tool that assures sensitive, accurate, and precise analysis of urea in urine, milk, and plasma samples, and selected diets for mammals. The presented chromatographic procedure is especially suitable for preparation of reference sample sets, very accurate and precise research purposes or rapid clinical diagnostic with smaller sample sets. Urea in urine can be also determined using our liquid chromatography with detection at 254 nm. Detection of urine urea at 254 nm is more sensitive and precise compared with monitoring at 370 nm. Our chromatographic method based on photodiode detection at 370 nm and especially at 254 nm is suitable for the non-invasive analysis of urea in only urine of humans and animals.    

Growth of embryonic softshell turtles is unaffected by uremia

We injected eggs of softshell turtles (Trionyx spiniferus) with solutions of urea at the midpoint of incubation to induce different levels of uremia in developing embryos. The experiment was undertaken as a test of the hypothesis that urea inhibits intermediary metabolism of embryos and thereby causes a reduction in their rates of growth. The injection protocol elicited a physiologically realistic range of uremias, but we found no evidence that metabolism or growth of embryos was impaired even at the highest levels of uremia. The most likely explanation for our results is that the uremias commonly encountered during natural incubation by embryos of this and other species of turtle are insufficient to inhibit intermediary metabolism. Thus, the influence of the hydric environment on metabolism and growth of embryonic turtles apparently is not mediated by differential rates of increase in the concentration of urea in body fluids.

Spectrophotometric flow-injection determination of urea in body fluids by using an immobilized urease reactor

A flow system involving a packed-bed enzyme reactor (volume 180 μl) with urease immobilized covalently on poly(glycidyl methacrylate)-coated porous glass is used for determining urea in blood serum and urine. Enzymatically produced ammonia is converted to an indophenolate dye (by oxidative coupling with hypochlorite and sodium salicylate), which is detected spectrophotometrically at 700 nm. The calibration graph is rectilinear for 25–500 μM urea when injecting samples (75 μl) diluted 1:50 for serum or 1:1000 for urine at a frequency of 60 h −1; the relative standard deviation is 1.1% for ten injections of 300 μM urea. The immobilized urease is stabilized by the addition of disodium EDTA, sodium azide and 2-mercaptoethanol to a 0.2 M phosphate buffer (pH 6.9) used as the carrier stream, which serves also as a preservative for longterm storage of the urease reactor packing at 4°C.

BLOOD UREA DETERMINATIONS IN 211 CASES

Increased urea in the blood was first demonstrated in 1823 by Prevost and Dumas,1while working with nephrectomized animals. Bostock,2in 1829, noticed an increase in the blood urea of certain albuminuries. Richard Bright3with his co-workers—Prout, Babbington, and Christison (1836)—confirmed this observation and recognized it to be of clinical importance in nephritis. Babbington and Christison also made estimations of urea in body fluids. Following the qualitative demonstration of blood urea, quantitative determinations were attempted by both French and German clinicians. Picard4(1856) was the first to determine that the amount of blood urea varies with the nitrogen intake. Interest in the subject abated about this time, and for a period of forty years the references in the literature were infrequent. Schondorf5(1899) revived the subject by an examination of the previous work, adding to it his own more accurate results, which confirmed the