Biomedical subjects

J O Thompson

Publications and source records attributed to J O Thompson.

5 recordsLinked to original sources

PubMed1998

"Reagentless" flow injection determination of ammonia and urea using membrane separation and solid phase basification.

Flow injection analysis instrumentation and methodology for the determination of ammonia and ammonium ions in an aqueous solution are described. Using in-line solid phase basification beds containing crystalline media. the speciation of ammoniacal nitrogen is shifted toward the un-ionized form. which diffuses in the gas phase across a hydrophobic microporous hollow fiber membrane into a pure-water-containing analytical stream. The two streams flow in a countercurrent configuration on opposite sides of the membrane. The neutral pH of the analytical stream promotes the formation of ammonium cations, which are detected using specific conductance. The methodology provides a lower limit of detection of 10 microgram/L and a dynamic concentration range spanning three orders of magnitude using a 315-microliters sample injection volume. Using immobilized urease to enzymatically promote the hydrolysis of urea to produce ammonia and carbon dioxide, the technique has been extended to the determination of urea.

Ammonia↗

PubMed1995

Catalytically Active Regenerative Sorbent beds (CARS) for airborne contaminants.

The Pd on Al2O3 catalyst used in the projected Space Station's Trace Contaminant Control System (TCCS) catalytic oxidizer can be poisoned by volatile halogen-, sulfur-, and nitrogen-containing organic species. Catalytically Active Regenerable Sorbents (CARS) eliminate these problematic contaminants and the large carbon bed used for their elimination in a three-step process. Contaminants are conventionally adsorbed by the CARS bed. After saturation, the bed is connected to an off-line recirculation loop, filled with hydrogen, and then heated. At temperature, contaminants are hydrogenated on catalytic sites within the bed, forming simple alkanes and acid gases that are efficiently converted to innocuous salts in an in-line alkaline bed. The CARS bed is regenerated by this cycle and alkane gases are released to be safely oxidized in the catalytic oxidizer. A challenge mixture containing Freon-113, thiophene, trichloroethylene, Halon-1301, and dichloromethane at 1670, 75, 81, 68, and 83 mg/m3 was successfully treated using this technology, demonstrating the CARS feasibility.

Adsorption↗

PubMed1995

Calmodulin inhibitors and calcium channel blockers influence dideoxycytidine renal excretion.

Renal handling of 2',3'-dideoxycytidine (ddC), a new anti-HIV dideoxynucleoside which undergoes renal and non-renal clearance, was determined in CF-1 male mice. Since calmodulin inhibitors (CIs) and calcium channel blockers (CCBs) have been shown to influence the flux of pyrimidine nucleosides across mammalian membranes and since the plasma concentration (and hence the efficacy) of therapeutic nucleosides is usually affected by the rate of renal elimination, we decided to determine the impact of the CIs loperamide (LOP) and trifluoperazine (TFP) as well as the CCB verapamil (VER) on the renal excretion of ddC. The ratio of ddC clearance to inulin clearance suggests that ddC undergoes secretion into renal tubules. Pre-exposure of mice to the calmodulin inhibitors loperamide (LOP) and trifluoperazine (TFP) resulted in a decrease in ddC renal secretion while pre-treatment with the calcium channel blocker verapamil increased ddC secretion.

Animals↗

PubMed1994

Characterization of and the influence of calcium channel blockers on the renal excretion of pyrimidine anticancer agents.

The renal handling of two anticancer (a-Ca) pyrimidines 5-fluorodeoxyuridine (FUdR) and 5-fluorouracil (5-FU) was investigated in clearance experiments in CF-1 mice using specific inhibitors of classical renal transport systems. The 5-FU was derived from the metabolism of FUdR. Based on the FUdR:inulin clearance ratio and 5-FU:inulin clearance ratio, it was determined that FUdR was secreted into renal tubules while 5-FU underwent reabsorption. The secretion of FUdR was inhibited by cimetidine and dipyridamole but not by probenecid or phloridzin. While the clearance ratio of 5-FU:inulin was significantly reduced by phloridzin, it (i.e., the ratio) was not affected by cimetidine, dipyridamole, or probenecid. The impact of two calcium channel blockers, diltiazem (DZM) and verapamil (VER), on the renal handling of FUdR and 5-FU was also examined. VER increased the secretion of FUdR without affecting the reabsorption of 5-FU while DZM slightly decreased the secretion of FUdR and prevented the reabsorption of 5-FU. These data suggest that the organic cation carrier and a dipyridamole-sensitive nucleoside transporter are involved in the renal excretion of FUdR; that the renal transport of both FUdR and 5-FU is associated with the calcium channel; and that 5-FU utilizes, at least in part, the glucose transporter for its reabsorption.

Absorption↗

PubMedDate not supplied

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Career Choice↗