(1/127079) The bioavailability, dispostion kinetics and dosage of sulphadimethoxine in dogs.

The disposition kinetics of sulphadimethoxine were studied in six normal beagle dogs after intravenous injection of a single dose (55 mg/kg). The median (range) distribution and elimination half times of the drug were 2.36 (2.06-3.35) hours and 13.10 (9.71-16.50) hours, respectively. Total body clearance of the drug had a median value of 21.7 ml/kg/h and a mean value of 21.4 ml/kg/h. While the overall tissue to plasma level ratio (k12/k21) of the drug was 0.55 after distribution equilibrium had been attained, analogue computer simulated curves showed that at 24 hours the fractions (percentage) of the dose in the central and tissue compartments were 12 and 11%, respectively. The drug was shown, by equilibrium dialysis method, to be highly bound to plasma proteins (greater than 75%) within the usual therapeutic range (50 to 150 mug/ml) of plasma levels. The systemic availability of sulphadimethoxine from the oral suspension was 32.8% (22.5-80.0). Since the absorption half time, 1.87 (0.86-3.22) hours, was considerably shorter than the half-life, 13.10 (9.71-16.50) hours, of the drug, the rate of absorption would have little influence on the dosage regimen. Based on the experimental data obtained, a satisfactory dosage regimen might consist of a priming dose of 55 mg/kg by the intravenous route and maintenance doses of either 27.5 mg/kg of sulphadimethoxine injection given intravenously or 55 mg/kg of the oral suspension administered at 24 hour intervals. The adequacy and duration of therapy will depend upon the clinical response obtained.  (+info)

(2/127079) Serum ampicillin levels in the calf: influence of dosage, route of administration and dosage form.

Holstein bull calves received ampicillin sodium by the intravenous, intramuscular and subcutaneous routes and ampicillin trihydrate by the intramuscular route, at a dosage of 5 mg/kg. In addition ampicillin sodium and ampicillin trihydrate were given at a 12 mg/kg dosage intramuscularly. The serum ampicillin concentrations were determined at five, 30, 60, 120, 180, 240 and 300 min after drug administration and at 360 min after ampicillin trihydrate injection. Intravenous administration gave a high initial level (16.2 mug/ml) at five min that declined to below 1 mug/ml by 120 min. Subcutaneous administration produced the lowest initial levels of drug but concentrations of drug detected did not differ significantly from the intramuscular administration at any sampling interval. The 12 mg/kg intramuscular ampicillin sodium dosage produced significantly higher levels than the 5 mg/kg dosage only at five min. Ampicillin trihydrate gave higher levels than ampicillin sodium at all times except 30 min (5 mg/kg) and five min (12 mg/kg). The serum ampicillin disappearance study (5 mg/kg intravenous) gave a two component bi-exponential curve. Kinetic analysis of the first component showed a C01 (theoretical initial conc) of 44.8 mug/ml, a ke1 (rate constant of disappearance) of 0.064 mug min and a t1/21 (calculated half-life) of 10.8 min. The Co2, ke2 and t1/22 of the second component were 6.2 mug/ml, 0.0157 mug/min and 46.2 min respectively.  (+info)

(3/127079) Specific receptors for glucocorticoid in the cytoplasm of the liver of AH 130 tumor-bearing rats.

Specific receptors for dexamethasone (11beta, 17alpha, 21-trihydroxy-9alpha-fluoro-16alpha-methyl-1,4-pregnadiene-3,20-dione) in the cytoplasm of the liver from AH 130 (solid type) tumor-bearing rats markedly increased in the advanced stage of tumor growth. The cytoplasmic receptors of the livers of normal and tumor-bearing rats differed in their affinities for dexamethasone, and their apparent equilibrium (dissociation) constants (K) for dexamethasone were 4.0 and 2.6 X 10(-9) M, respectively. The rates of dissociation of dexamethasone-receptor complexes and the heat denaturations of the receptors in the livers of normal and tumor-bearing rats were similar. The glucocorticoid receptors of tumor-bearing rat liver had slightly higher affinities than did those of normal liver for all the steroids tested. Only a trace amount of receptors for dexamethasone could be detected in the cytoplasm of AH 130 ascites cells.  (+info)

(4/127079) An investigation into the binding of the carcinogen 15,16-dihydro-11-methylcyclopenta[a]phenanthren-17-one to DNA in vitro.

After metabolic activation the carcinogen 15,16-dihydro-11-[3H]methylcyclopenta[a]phenanthren-17-one binds to DNA in vitro, and this binding is prevented by 7,8-benzoflavone. Radioactivity cannot be removed from the DNA with organic solvents or by chromatography on Sephadex G-50, even after heat denaturation of the DNA. Enzymatic hydrolysis yields radioactive fractions, which elute from a column of Sephadex LH-20 immediately after the natural nucleosides. At least two species of reactive metabolites are involved in this bending, those with a half-life of a few hr and others with greater stability. After extraction from the aqueous incubation mixture, they could be detected in discrete polar fractions from separations of the complex metabolite mixture by high-pressure liquid chromatography. Their ability to bind to DNA decreased with time at ambient temperature, and they were rapidly deactivated by acid. 7,8-Benzolflavone acted by suppressing the formation of polar metabolites derived from enzymatic oxidation of the aromatic double bonds. The inhibitor had no effect on the enzymes hydroxylating saturated carbon; hence it is unlikely that metabolism of the methyl group is important in conversion of this carcinogen to its proximate form, although the presence of the 11-methyl group is essential for carcinogenic activity in this series.  (+info)

(5/127079) Action of partially thiolated polynucleotides on the DNA polymerase alpha from regenerating rat liver.

The effects of partially thiolated polynucleotides on the DNA polymerase alpha from regenerating rat liver were investigated. The enzyme was isolated from the nuclear fraction essentially according to the method of Baril et al.; it was characterized as the alpha polymerase on the basis of its response to synthetic templates and its inhibition with N-ethylmaleimide. Although polycytidylic acid had no effect on the DNA polymerase alpha either as a template or as an inhibitor, partially thiolated polycytidylic acid (MPC) was found to be a potent inhibitor, its activity being directly related to its extent of thiolation (percentage of 5-mercaptocytidylate units in the polymer). In comparison, the DNA polymerase beta which was purified from normal rat liver nuclear fraction, was much less sensitive to inhibition by MPC. Analysis of the inhibition of the alpha polymerase by the method of Lineweaver and Burk showed that the inhibitory action of MPC was competitively reversible with the DNA template, but the binding of the 7.2%-thiolated MPC to the enzyme was much stronger than that of the template (Ki/Km less than 0.03). Polyuridylic acid as such showed some inhibitory activity which increased on partial thiolation, but the 8.4%-thiolated polyuridylic acid was less active than the 7.2% MPC. When MPC was annealed with polyinosinic acid, it lost 80% of its inhibitory activity in the double-stranded configuration. However, 1 to 2%-thiolated DNA isolates were significantly more potent inhibitors than were comparable (1.2%-thiolated) MPC and showed competitive reversibility with the unmodified (but "activated") DNA template. These results indicate that the inhibitory activities of partially thiolated polynucleotides depend not only on the percentage of 5-mercapto groups but also on the configuration, base composition, and other specific structural properties.  (+info)

(6/127079) Blood thymidine level and iododeoxyuridine incorporation and reutilization in DNA in mice given long-acting thymidine pellets.

A long-acting thymidine pellet consisting of 190 mg of cholesterol and 60 mg of thymidine has been developed for the study of thymidine metabolism and reutilization in vivo. Implantation of such a pellet s.c. in adult mice will maintain the blood plasma concentration of thymidine at levels between 40 and 8 X 10(-6) M, which are from 36 to 7 times those of normal mice, for periods up to 48 hr. During this period, in vivo uptake and reutilization of [125I]iododeoxyuridine, a thymidine analog, into intestinal and tumor DNA were almost completely suppressed. While iododeoxyuridine reutilization is not large in normal proliferative tissue even in the absence of pellet implants, reutilization of over 30% was measured in large, rapidly growing ascites tumors. The inhibition of iododeoxyuridine incorporation by elevated thymidine blood levels is directly proportional to serum concentration. This appears to be due to a thymidine pool in rapid equilibrium with blood thymidine. This pool is at least 10 times larger than the 4-nmole pool of extracellular thymidine.  (+info)

(7/127079) The effects of glucocorticoids and progesterone on hormone-responsive human breast cancer in long-term tissue culture.

Glucocorticoids, at physiological concentration, inhibit cell division and thymidine incorporation in three lines of human breast cancer maintained in long-term tissue culture. At steroid concentrations sufficient to inhibit thymidine incorporation 50%, little or no effect is seen on protein synthesis 48 hr after hormone addition. All three of these lines are shown to have glucocorticoid receptors demonstrable by competitive protein binding assays. Receptors are extensively characterized in one line by sucrose density gradient analysis and binding specificity studies. Good correlation between receptor-binding specificity and biological activity is found except for progesterone, which binds to glucocorticoid receptor but is noninhibitory. Cross-competition and quantification studies demonstrate a separate receptor for progesterone. This receptor has limited binding specificities restricted largely to progestational agents, whereas the glucocorticoid receptor bound both glucocorticoids and progesterone. Two other human breast cancer lines neither contain glucocorticoid receptor nor are inhibited by glucocorticoids. It is concluded that in some cases glucocorticoids can directly limit growth in human breast cancer in vitro without requiring alterations in other trophic hormones.  (+info)

(8/127079) Effect of hepatocarcinogens on the binding of glucocorticoid-receptor complex in rat liver nuclei.

The effects of a number of carcinogens and hepatotoxins on the binding kinetics of the interactions of glucocorticoidcytosol receptor complex with nuclear acceptor sites in rat liver were investigated. Both the apparent sites in rat liver were investigated. Both the apparent concentration of nuclear binding sites and the Kd were significantly diminished following treatment of rats with sublethal doses of the carcinogens aflatoxin B1, diethylnitrosamine, dimethylnitrosamine, thioacetamide, 3'-methyl-4-dimethylaminoazobenzene, 4-dimethylaminoazobenzene, and 3-methylcholanthrene. Treatment with actinomycin D resulted in a slight reduction in the apparent concentration of nuclear acceptor sites but had no effect on the nuclear binding Kd. The hepatotoxic but noncarcinogenic analgesic, acetaminophen, as well as the weakly toxic aflatoxin B1 cognate, aflatoxin B2, were without effect on the kinetics or binding capacity of glucocorticoid-nuclear acceptor site interaction. These experiments suggest that chemically induced alteration of functional glucocorticoid binding sites on chromatin may be involved in the biochemical effects produced in liver by carcinogens of several chemical types. This experimental model may provide a useful approach for further elucidation of early events in carcinogenesis.  (+info)