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Biomedical subjects

N Allen

Publications and source records attributed to N Allen.

At least 19 recordsLinked to original sources
PubMed1991

Seizures in patients simultaneously receiving theophylline and imipenem or ciprofloxacin or metronidazole.

Five patients had apparently drug-induced seizures while simultaneously receiving theophylline and either imipenem (three patients), ciprofloxacin (one patient), or ciprofloxacin and metronidazole (one patient). Seizures ceased upon reduction in dosage or discontinuation of the suspected offending agents. Imaging studies failed to reveal new structural lesions in the central nervous system in any patient, and only one had a history of neurologic disease. Although the exact mechanism for seizure induction cannot be determined from these cases, potential drug interactions exist, because theophylline, imipenem, and ciprofloxacin are all believed to increase excitation of the central nervous system by inhibition of gamma-aminobutyric acid binding to receptors. In addition, ciprofloxacin decreases the clearance of theophylline from the body, predisposing the patient to elevated theophylline levels. Physicians prescribing theophylline with imipenem, ciprofloxacin, or metronidazole should carefully monitor patients for indications for drug therapy, drug dosage, organ impairment affecting drug metabolism, and signs of toxicity. Seizures may accompany oral theophylline therapy, even at "therapeutic" serum theophylline concentrations.

Aged↗
PubMed1978

Activities of enzymes of the hexose monophosphate pathway in nervous system tumors induced by ethylnitrosourea.

The activities of three enzymes of the hexose monophosphate pathway (HMP) were measured in frozen samples of rat cerebral cortex and ethylnitrosourea-induced tumors of the rat nervous system. Results show that in most tumors, adequate amounts of glucose-6-phosphate dehydrogenase (G6PDH), 6-phosphogluconate dehydrogenase (6PGDH), and transketolase (TK) were present so as not to be rate-limiting for utilization of the HMP. When enzyme activites were expressed on the basis of fresh weight, TK was increased in most tumors as compared with cerebral cortex; G6PDH and 6PGDH were more variable, showing either higher or lower activities in tumors as compared to control. Tumors in general had a lower protein content than cerebral cortex. When activities were expressed in terms of this protein content, mean values for the dehydrogenases in all groups of tumors were higher than the average value in cortex, indicating that G6PDH and 6PGDH were spared in tumors relative to other proteins. TK activities in tumors, expressed in terms of cytosol protein were lower than or in the same range as cortex. Increased activities of HMP enzymes in some tumors indicated that the potential activity of the HMP in some (but not all) tumors of the nervous system is greater than that of cerebral cortex.

Animals↗
PubMed1978

Inhibition of Na+-K+-activated ATPase activity following experimental spinal cord trauma.

The specific activity of the membrane-bound enzyme, Na+-K+-activated adenosine triphosphatase (ATPase), has been shown to be decreased following experimental impact injury (400 gm-cm) to the spinal cord in dogs. The prompt and significant (p less than 0.01) fall in activity was evident as early as 5 minutes after injury, and remained at 56% to 67% of control for the 1-hour period studied. This decrease was most prominent in the central core of the traumatized segments of spinal cord. Central core samples, excised immediately adjacent to the trauma site, gave values for the Na+-K+-activated enzyme intermediate to those of the trauma and control sites. For these same samples, the activity of the Mg+2-dependent ATPase did not change appreciably. No alterations were observed in the tissue surrounding the zone of maximum injury at these early time periods. The relationship of membrane-bound enzyme alterations to blood flow, clotting mechanisms, and abnormal free radical reactions are briefly discussed.

Adenosine Triphosphatases↗
PubMed1977

Acid hydrolase and cytochrome oxidase activities in nitrosourea induced tumors of the nervous system.

Nitrosourea induced tumors of the nervous system in rats have proven useful for biochemical studies combined with morphological approaches. The pattern of enzyme activities for acid hydrolases and cytochrome oxidase resemble those previously observed in spontaneous nervous system tumors of man. The activities of 4 acid hydrolases were generally high in the gliomas. This could not be attributed solely to zones of regression or necrosis but was a general characteristic of the neoplasms. The activities were predominantly particulate and most likely lysosomal in localization. In schwannomas a similar increase in hydrolases was found in comparison with normal neural tissues but aryl-sulfatase was not increased. Cytochrome oxidase activities were markedly reduced in all tumors studied. The proportionate reduction with respect to normal brain was comparable to that noted in man. No differences were found with respect to fairly well differentiated gliomas.

Animals↗