Comparative pharmacokinetics of vinblastine after a 96-hour continuous infusion in wild-type mice and mice lacking mdr1a P-glycoprotein.
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To determine the tissue-specific impact of P-glycoprotein on the accumulation of a substrate drug, we have studied the tissue distribution of vinblastine in mdr1a(-/-) and wild-type mice at approximately similar, relatively low plasma levels. Vinblastine was administered as a 96-h continuous infusion at dose rates of 1 to 10 microgram/h, which were delivered by a s.c.-implanted osmotic pump. Drug concentrations were determined in plasma and tissues by HPLC. In comparison to wild-type mice, 4.4- to 9.6-fold higher drug concentrations were observed in the brains of mdr1a(-/-) mice (p +info)
The stability, polyadenylic acid content and ribonucleoprotein form of nulcear ribonucleic acid in artichoke.
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A nuclear preparation, containing 60-80% of the total tissue DNA and less than 0.5% of the total rRNA, was used to characterize the nuclear RNA species synthesized in cultured artichoke explants. The half-lives of the nuclear RNA species were estimated from first-order-decay analyses to be: hnRNA (heterogeneous nuclear RNA) containing poly(A), 38 min; hnRNA lacking poly(A), 37 min; 2.5 X 10(6)-mol. wt. precursor rRNA, 24 min; 1.4 X 10(6)-mol.wt. precursor rRNA, 58 min; 1.0 X 10(6)-mol.wt. precursor rRNA, 52 min. The shorter half-lives are probably overestimates, owing to the time required for equilibration of the nucleotide-precursor pools. The pathway of rRNA synthesis is considered in terms of these kinetic measurements. The rate of accumulation of cytoplasmic polydisperse RNA suggested that as much as 40% of the hnRNA may be transported to the cytoplasm. The 14-25% of the hnRNA that contained a poly(A) tract had an average molecular size of 0.7 X 10(6) daltons. The poly(A) segment was 40-200 nucleotides long, consisted of at least 95% AMP and accounted for 8-10% of the [32P]orthophosphate incorporated into the poly(A)-containing hnRNA. Ribonucleoprotein particles released from nuclei by sonication, lysis in EDTA or incubation in buffer were analysed by sedimentation through sucrose gradients and by isopycnic centrifugation in gradients of metrizamide and CsCl. More than 50% of the hnRNA remained bound to the chromatin after each treatment. The hnRNA was always associated with protein but the densities of isolated particles suggested that the ratio of protein to RNA was lower than that reported for mammalian cells, The particles separated from chromatin were not enriched for poly(A)-containing hnRNA. (+info)
Synthesis and turnover of cerebrosides and phosphatidylserine of myelin and microsomal fractions of adult and developing rat brain.
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The synthesis and turnover of cerebrosides and phospholipids was followed in microsomal and myelin fractions of developing and adult rat brains after an intracerebral injection of [U-14C]serine. The kinetics of incorporation of radioactivity into microsomal and myelin cerebrosides indicate the possibility of a precursor-product relationship between cerebrosides of these membranes. The specific radioactivity of myelin cerebrosides was corrected for the deposition of newly formed cerebrosides in myelin. Multiphasic curves were obtained for the decline in specific radioactivity of myelin and microsomal cerebrosides, suggesting different cerebroside pools in these membranes. The half-life of the fast turning-over pool of cerebrosides of myelin was 7 and 22 days for the developing and adult rat brain respectively. The half-life of the slowly turning-over pool of myelin cerebrosides was about 145 days for both groups of animals. The half-life of the rapidly turning-over microsomal cerebrosides was calculated to be 20 and 40 h for the developing and adult animals respectively. The half-life of the intermediate and slowly turning-over microsomal cerebrosides was 11 and 60 days respectively, for both groups of animals. The amount of incorporation of radioactivity into microsomal cerebrosides from L-serine was greatly decreased in the adult animals, and greater amounts of the precursor were directed towards the synthesis of phosphatidylserine. In the developing animals, considerable amounts of cerebrosides were synthesized from L-serine, besides phosphatidylserine. The time-course of incorporation indicated that a precursor-product relationship exists between microsomal and myelin phosphatidylserine. The half-life of microsomal phosphatidylserine was calculated to be about 8 h for the fast turning-over pool in both groups of animals. (+info)
Uridine diphosphate xylosyltransferase activity in cartilage from manganese-deficient chicks.
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The glycosaminoglycan content of cartilage is decreased in manganese deficiency in the chick (perosis). The activity of xylosyltransferase, the first enzyme in the biosynthetic pathway of sulphated glycosaminoglycans, was studied in the epiphysial cartilage of 4-week-old chicks which had been maintained since hatching on a manganese-deficient diet. Enzymic activity was measured by the incorporation of [14C]xylose from UDP-[14C]xylose into trichloroacetic acid precipitates. Optimal conditions for the xylosyltransferase assay were established and shown to be the same for both control and manganese-deficient cartilage. Assay of the enzyme by using an exogenous xylose acceptor showed no difference in xylosyltransferase activity between control and manganese-deficient tissue. Further, the extent of xylose incorporation was greater in manganese-deficient than in control cartilage preparations, suggesting an increase in xylose-acceptor sites on the endogenous acceptor protein in the deficient cartilage. 35S turnover in the manganese-deficient cartilage was also increased. The data suggest that the decreased glycosaminoglycan content in manganese-deficient cartilage is due to decreased xylosylation of the acceptor protein plus increased degradation of glycosaminoglycan. (+info)
Radiosensitization of hypoxic tumour cells by S-nitroso-N-acetylpenicillamine implicates a bioreductive mechanism of nitric oxide generation.
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The radiosensitizing activity of S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide (NO) donor, was assessed in a model of non-metabolic hypoxia achieved in an atmosphere of 95% nitrogen-5% carbon dioxide. A 10 min preincubation of hypoxic EMT-6 cells (10 x 10(6) ml(-1)) with 0.1 and 1 mM SNAP before radiation resulted in an enhancement ratio of 1.6 and 1.7 respectively. The level of spontaneous NO release, measured by a NO specific microsensor, correlated directly with the concentration of SNAP and was enhanced 50 times in the presence of cells. Dilution of the cell suspension from 10 to 0.1 x 10(6) ml(-1) resulted in a 16-fold decline in NO release, but only a twofold decrease in radiosensitization was observed. Preincubation of hypoxic cells with SNAP for 3 min up to 30 min caused an increasing radiosensitizing effect. Extended preincubation of 100 min led to the loss of radiosensitization although the half-life of SNAP is known to be 4-5 h. Taken together, these observations suggest that SNAP generates NO predominantly by a bioreductive mechanism and that its biological half-life is unlikely to exceed 30 min. The lack of correlation between free NO radical and radiosensitizing activity may reflect a role of intracellular NO adducts which could contribute to radiosensitization as well. (+info)
Degradation of hepatic zinc-thionein after parenteral zinc administration.
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A low-molecular-weight protein, zinc-thionein, a metallothionein, was implicated as having a regulatory function in zinc metabolism. The half-life (t 1/2) of hepatic zinc-thionein was determined by pulse-labelling with either L-[35S] cystine and/or 65Zn. In two experiments with L-[35S]cystine, the t 1/2 of zinc-thionein was 18h and 19h. Most of the soluble 35S-labelled hepatic proteins had a t 1/2 of 4 days. The t 1/2 of zinc-thionein calculated by using 65Zn was 20h. The close similarity between the calculated and measured t 1/2 values for zinc-thionein suggests that release of Zn2+ from zinc-thionein probably occurs simultaneously with degradation of the protein moiety. (+info)
Clearance of IGFs and insulin from wounds: effect of IGF-binding protein interactions.
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We have examined the role binding proteins have in regulating the clearance of exogenous growth factors from wounds. Hunt-Schilling chambers were subcutaneously implanted in rats, and the clearance of insulin-like growth factor (IGF) I from the chamber wound fluid was compared with IGF-II, LR3-IGF-I, which binds poorly to IGF-binding proteins (IGFBP), or insulin. Elimination rate constants of the slow phase of the decay curves did not differ between IGF-I and IGF-II. However, LR3-IGF-I and insulin were cleared more rapidly from wound fluid than IGF-I so that the half-lives for IGF-I, IGF-II, LR3-IGF-I, and insulin were 872, 861, 563, and 324 min, respectively. In wound fluid, minimal degradation of the IGFs occurred, whereas insulin was degraded considerably. The increased clearance of LR3-IGF-I and insulin equated with a reduced association with wound fluid IGFBPs, and increased amounts of radioactivity of these peptides were detected in the circulation and urine. These results show that this model of wound repair may be of use in examining the kinetics of growth factors and other bioactive molecules in extravascular spaces and support the hypothesis that IGFBPs can be significant regulators of IGF bioavailability in vivo. (+info)
Pharmacokinetics of intermittent intraperitoneal cefazolin in continuous ambulatory peritoneal dialysis patients.
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OBJECTIVE: To investigate the pharmacokinetic parameters of intermittent intraperitoneal (IP) cefazolin, and recommend a cefazolin dosing regimen in continuous ambulatory peritoneal dialysis (CAPD) patients. DESIGN: Prospective nonrandomized open study. SETTING: CAPD outpatient clinic in Albany, New York. PATIENTS: Seven volunteer CAPD patients without peritonitis. Three of the patients were nonanuric while 4 were anuric. INTERVENTIONS: Cefazolin (15 mg/kg total body weight) was given to each patient during the first peritoneal exchange. Blood and dialysate samples were collected at times 0, 0.5, 1,2,3,6 (end of the first antibiotic-containing dwell), 24, and 48 hours after the administration of IP cefazolin. Urine samples were collected in nonanuric patients over the study period. RESULTS: The mean+/-SD amount of cefazolin dose absorbed from the dialysate after the 6-hour dwell was 69.7%+/-8.0% of the administered dose. The cefazolin absorption rate constant from dialysate to serum was 0.21+/-0.1/hr (absorption half-life 3.5+/-0.8 hr). The mean serum concentrations reached at 24 and 48 hours were 52.4+/-3.7 mg/L and 30.3+/-5.9 mg/L, respectively. The mean dialysate cefazolin concentrations reached at 24 and 48 hours were 15.1+/-3.4 mg/L and 7.9+/-1.4 mg/L, respectively. The cefazolin serum elimination rate constant was 0.02+/-0.01/hr (elimination half-life 31.5+/-8.8 hr). The total cefazolin body clearance was 3.4+/-0.6 ml/min. In the 3 nonanuric patients the mean renal clearance of cefazolin was 0.6+/-0.4 ml/min. The peritoneal clearance of cefazolin was 1.0+/-0.3 mL/min. The systemic volume of distribution of cefazolin was 0.2+/-0.05 L/kg. No statistical difference was detected in pharmacokinetic parameters between anuric and nonanuric patients, although this may be due to the small number of patients in each group. CONCLUSION: A single daily dose of cefazolin dosed at 15 mg/kg actual body weight in CAPD patients is effective in achieving serum concentration levels greater than the minimum inhibitory concentration for sensitive organisms over 48 hours, and dialysate concentration levels over 24 hours. Caution is warranted in extrapolation of dosing recommendations to patients who maintain a significant degree of residual renal function. (+info)