Evaluation of a dual-function pH and PCO2 in vivo sensor.

A newly developed, dual-function pH and PCO2 sensor was evaluated in this study. The sensors were placed in the femoral arteries of dogs anesthetized with sodium pentobarbital. Comparisons were made between systemic arterial pH and PCO2 measured using the sensor and those measured from blood samples drawn at 15-min intervals over a 7-h period using a bench instrument. The mean pH of the bench instrument measurements was 7.43. The mean difference of the sensor measurements from the bench instrument measurements for 207 comparisons was 0.0003 pH +/- 0.061 SD. The mean PCO2 of the bench instrument measurements was 40 mmHg. The mean difference of the sensor measurements from those of the bench instrument for 212 comparisons was -1.43 mmHg +/- 5.17 SD. The sensors performed equally well in the presence of metabolic or respiratory acidosis and alkalosis. The dual-function sensors evaluated in this study are useful for trend monitoring of pH and PCO2 over at least a 7-h period without recalibration. With improvement in the consistency of sensor construction, these sensors will be reliable in vivo sensing devices for blood pH and PCO2 and thus valuable research and clinical instruments.     

Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering

Hydrogels that mimic the natural extracellular matrix (ECM) are used in three-dimensional cell culture, cell therapy, and tissue engineering. A semi-synthetic ECM based on cross-linked hyaluronana offers experimental control of both composition and gel stiffness. The mechanical properties of the ECM in part determine the ultimate cell phenotype. We now describe a rheological study of synthetic ECM hydrogels with storage shear moduli that span three orders of magnitude, from 11 to 3 500 Pa, a range important for engineering of soft tissues. The concentration of the chemically modified HA and the cross-linking density were the main determinants of gel stiffness. Increase in the ratio of thiol-modified gelatin reduced gel stiffness by diluting the effective concentration of the HA component.     

Purine metabolism in high- and low-uric acid lines of chickens: hypoxanthine/guanine phosphoribosyltransferase activities

The activity of hypoxanthine/guanine phosphoribosyltransferase (HGPRT) was examined in the livers and kidneys of two genetic lines of chickens selected for different plasma uric acid levels. Previous work demonstrated that the high-uric acid line (HUA) had significantly greater de novo uric acid synthesis rates in kidney tissue compared to the low-uric acid line (LUA). In addition, phosphoribosylpyrophosphate (PRPP) synthetase and xanthine dehydrogenase activities in livers and kidneys were significantly higher in the HUA compared to the LUA line. PRPP pool sizes were also significantly higher in both livers and kidneys of HUA birds. HGPRT activities in livers of HUA birds were significantly (P less than 0.05) greater than in LUA birds. The mean value of liver HGPRT was 7.36 +/- 0.25 pmole inosine-5'-monophosphate (IMP) and 6.05 +/- 0.27 pmole IMP produced/micrograms protein/hr, respectively, for the HUA and LUA lines. There were no significant differences (P greater than 0.05) in kidney HGPRT activities between the two groups. The mean value of kidney HGPRT was 52.87 +/- 1.62 pmole IMP and 50.72 +/- 1.62 pmole IMP produced/micrograms protein/hr, respectively, for the HUA and LUA line. Elevated liver HGPRT may serve to enhance the regeneration of PRPP in the HUA liver. Elevated liver PRPP synthetase and PRPP pool size suggest an increased flux through the de novo purine biosynthetic pathway in HUA birds. The resulting additional pyrophosphate from the glutamine PRPP amidotransferase reaction would stimulate recovery of PRPP and spare the system from a substantial loss of energy.