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Biomedical subjects

C P Lewis

Publications and source records attributed to C P Lewis.

23 records · Page 2Linked to original sources
PubMed1990

The identification and characterization of an uptake system for taurine into rat lung slices.

The objective of this study was to determine whether taurine was accumulated by rat lung slices and if so, to establish the role of this uptake as a source of pulmonary taurine. We have shown that taurine is accumulated into rat lung by an active uptake process that was both ATP and Na(+)-dependent and obeyed saturation kinetics, exhibiting an apparent Km of 186 microM and Vmax of 970 nmol/g wet wt/hr. Substrate specificity of the system was high and only compounds possessing anionic and cationic groups separated by two methylene groups were able to competitively inhibit taurine uptake. Subsequent to its uptake, taurine was not significantly metabolized, and since the apparent Km for the uptake process is similar to the known plasma concentration of taurine, it can be inferred that this system will contribute to pulmonary taurine uptake in vivo. Taurine has been suggested to possess antioxidant and antiinflammatory properties, and we suggest that this uptake system may contribute to the defence of pulmonary tissue against oxidative stress.

1-Methyl-3-isobutylxanthine↗
PubMed1990

The importance of epithelial uptake systems in lung toxicity.

The discovery that the herbicide paraquat was selectively accumulated by the lung, both in vivo and in vitro, in comparison with other tissues, provided an explanation for its selective toxicity to the lung. This uptake process is energy dependent and obeys saturation kinetics. A characterization of the process led to the identification of endogenous chemicals that are the natural substrates for the system. Among these are a series of diamines and polyamines, as well as the diaminodisulfide cystamine. It appears that paraquat, because of specific structural similarities to these endogenous polyamines, is mistakenly accumulated by the lung. This uptake process is specifically located in the alveolar Type II cell, the Clara cell, and probably the alveolar Type I cell. With the development of knowledge of the structural requirements of chemicals to be accumulated by this system, it is possible to predict which chemicals will be accumulated by the lung or design molecules that are targeted to the alveolar epithelial and Clara cells. In the wider perspective, this polyamine uptake system has been found on a number of cancerous cells or tissues. With the knowledge of the uptake system in the lung, it should be possible to design drugs that will be specifically concentrated in cells that possess this system.

Animals↗
PubMed1989

The accumulation of cystamine and its metabolism to taurine in rat lung slices.

The objective of these studies was to determine the accumulation and fate of the disulphide, cystamine by rat lung slices. Cystamine was accumulated by two active uptake systems that obeyed saturation kinetics, with apparent Km values of 12 and 503 microM, and maximal rates of 530 and 5900 nmol/g wet weight/hr respectively. The high affinity system was competitively inhibited by the diamine, putrescine and the herbicide paraquat, which are themselves accumulated. Thus, this pulmonary uptake process appears to be identical for all three compounds. In contrast, the low affinity process was not inhibited by putrescine, and this process results from the diffusion of cystamine into the cell and its subsequent metabolism. Upon accumulation, cystamine was metabolised, predominantly to the sulphonic acid, taurine, with 10-20% of the intracellular label covalently binding to protein. Conversion to taurine was unaffected by amine oxidase inhibitors, but was decreased after GSH depletion, suggesting that pulmonary cystamine metabolism is glutathione-dependent, and is not mediated by diamine oxidase. Both cystamine and taurine have been implicated as antioxidants, and we suggest that cystamine is actively accumulated by the lung as part of the process to protect pulmonary tissue against oxidative stress.

Animals↗
PubMed1988

Alprazolam in panic disorder and agoraphobia: results from a multicenter trial. III. Discontinuation effects.

Preliminary reports of discontinuation of alprazolam therapy in patients with panic disorder have revealed worsening of symptoms despite gradual withdrawal of medication. In this study, 126 patients with panic disorder and phobic avoidance received either alprazolam or placebo in doses of 2 to 10 mg daily for eight weeks. The medication was tapered over a period of four weeks, and patients were observed for another two weeks after all medication was discontinued. Sixty of the 63 alprazolam-treated patients and 49 of the 63 placebo-treated patients entered the taper and discontinuation study. After improvement in the active treatment period, the alprazolam-treated group had significant relapse between the first and last week of taper. However, during the second postdiscontinuation week, outcome scores were not significantly different from those of the placebo-treated group who did not deteriorate during taper. Twenty-seven percent of the alprazolam-treated group reported a rebound of panic attacks during taper and 13% reported a rebound of anxiety on the Hamilton Anxiety Scale. No serious or life-threatening withdrawal symptoms were reported, but distinct, transient, mild to moderate withdrawal syndrome occurred in 35% of the alprazolam-treated group and in none of the placebo-treated group. The coexistence of symptom rebound and a withdrawal syndrome occurred in 10% of the alprazolam-treated group, but both subsided by the end of the second week without alprazolam. We recommend that patients with panic disorder be treated for a longer period, at least six months, and that medication be tapered over a more prolonged period, at least eight weeks, especially where high doses are employed.

Adult↗