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Incubation of tritium labeled dopamine (3HDA) with a preparation of rat heart or bovine serum albumin in vitro, or the intravenous injection of 3HDA to rats, gives acid insoluble, tritium labeled material that is slowly converted to soluble labeled material (SLM) by heating in dilute perchloric acid. Determination of SLM may be useful in investigations of DA-tissue adducts formed when the catecholamine is delivered by intravenous infusion.

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The adenylyl cyclase activity of homogenates of striatal tissue from rat brain has been used as a model to test the hypothesis that the products of the reaction of polyphenols with ferric iron compounds are toxic. Dopamine (DA), at levels that stimulate adenylyl cyclase, inhibited the activity in the presence of 2 mol of potassium ferricyanide (FC), methemoglobin or ferricytochrome c per mol of DA. Combinations of potassium ferrocyanide and DA were not inhibitory. Neither pyrocatechol nor hydroquinone stimulated the activity, but these polyphenols were inhibitory in the presence of FC. Tyramine, phosphorylated DA or phosphorylated pyrocatechol had no effect on the activity of the enzyme in the presence or absence of FC. Forskolin was unable to stimulate the adenylyl cyclase once the latter was inhibited by DA plus FC, and dithiothreitol could not reverse inhibition by DA plus FC. Incubation of DA with FC, in the absence of the homogenate, resulted in substances that were not inhibitory. These findings suggest that the polyphenols plus FC react to yield substances that inhibit the adenylyl cyclase by affecting the catalytic unit of the enzyme complex.

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Methods were developed for the chemical phosphorylation of dopamine and for the isolation of phosphorylated dopamine from acidic extracts of rat brain. The developed methods were applied to provide evidence that striatal tissue from rat brain can phosphorylate dopamine to yield dopamine-3-monophosphate ester and dopamine-4-monophosphate ester.

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The 3 or 4 phosphate ester of dopamine (PD) was hydrolyzed by homogenates of rat tissues to give inorganic phosphate (Pi) and dopamine. The rate of hydrolysis of PD by kidney homogenates was increased by exogenous MgCl2 but not CaCl2 or KCl. The activity of brain, heart or liver homogenates was insensitive to the added salts. Several lines of evidence indicate that alkaline phosphatase activity contributes to the high rate of PD hydrolysis by the kidney but not brain homogenate. The intravenous infusion of PD at 12 mumole/kg in one hr to anesthetized rats increased the dopamine content of the plasma, kidney and heart without altering brain or liver dopamine. The results suggest that PD may be more effective than dopamine for increasing dopamine levels of the kidney. In addition, the hydrolysis of PD by brain homogenates, which is independent of alkaline phosphatase activity, suggests that specific enzymes exist for the metabolism of PD.

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We have synthesized and characterized p-azidoclonidine (AZC) as a putative alpha 2-adrenoceptor photoaffinity label. [3H]AZC demonstrated high affinity (KD = 11.8 +/- 2.5 nM), saturability (Bmax = 171 +/- 21 fmol/mg protein), stereo-specificity, and rank order of potency expected of a specific alpha 2-receptor label when used as a reversible ligand in the rat cerebral cortex. The pharmacologic profile of AZC was similar to p-aminoclonidine (PAC), an established alpha 2-adrenoceptor partial agonist. Membranes covalently prelabeled with nonradioactive AZC showed a dose dependent decrease in the number of alpha 2-receptor sites subsequently detected by [3H]PAC and [3H]yohimbine. Specific covalent [3H]AZC binding to rat cerebral cortical alpha 2-receptors represented 35 +/- 7% of the total [3H]AZC bound. These data indicate that AZC is a selective alpha 2-adrenoceptor photoaffinity label which may be useful in the identification and purification of the alpha 2-Adrenoceptor.

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The biochemical retroaldol-like fragmentation of beta-hydroxynitrosamines has been investigated further. The extent of fragmentation of 2-hydroxy-2-methylpropyl-methylnitrosamine (HMPMN) to N-nitrosodimethylamine and acetone induced by metabolic activation increases as the NADPH level is decreased. 2-Hydroxy-2-phenylethyl-methylnitrosamine (HPhEMN) undergoes competitive oxidation to 2-oxy-2-phenylethyl-methylnitrosamine (OPhEMN) and fragmentation to benzaldehyde and N-nitroso-dimethylamine in the presence of a metabolic activation system from rat liver. The extent of the oxidation was increased by preinduction of the rats with phenobarbital, or separate addition of NADPH and NAD, but was decreased by addition of dimethyl sulfoxide. The fragmentation was observed most readily when oxidation was inhibited or was not induced by cofactors. When HPhEMN was administered to a rat intraperitoneally, benzaldehyde (fragmentation) was found in the urine with OPhEMN and the substrate, but only the last two substances were found in liver and blood. These experiments provide evidence for retroaldol-like fragmentation of beta-hydroxynitrosamines both in vitro and in vivo. In a related investigation, it was found that N-nitroso-N-4-chlorophenyl-2-aminoethanal (NCAE) is extremely reactive and induces spontaneous generation of 4-chlorobenzenediazonium ion in chloroform, as trapped by 2-naphthol. NCAE reacts with dimethylamine in chloroform, benzene or methanol to give N-nitrosodimethylamine and 4-chloroaniline, among other products. This suggests that beta-nitrosaminoaldehydes produced by the biooxidation of their corresponding alcohols could produce cell alteration through alkylation, deamination or transnitrosation.

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The binding of Warfarin by human serum albumin (HSA) and subcellular fractions from rat liver was investigated to evaluate the roles of such interactions in the pharmacokinetic properties of the anticoagulant. In vitro intracellular distribution studies showed that Warfarin was bound primarily by the soluble fraction of rat liver. Equilibrium dialysis studies were carried out to test the hypothesis that the hepatic extraction of Warfarin and drug interactions between Warfarin and other drugs involved competition between albumin and the soluble fraction of liver. A three compartment dialysis cell was designed and constructed for such studies. Three types of competitive binding interactions were identified. Iopanoic acid displaced Warfarin from HSA resulting in increased Warfarin in the protein-free compartment and in the compartment containing the soluble fraction. On the other hand, tolbutamide displaced Warfarin from HSA to the liver soluble fraction with relatively little effect on unbound anticoagulant. Sulfinpyrazone produced a third type of interaction characterized by displacement of Warfarin from HSA with an increase in the concentration of unbound drug. It was concluded that competitive binding between albumin and soluble liver proteins, is important in the hepatic uptake of Warfarin. The three compartment dialysis cells may be useful to simulate the distribution of drugs and drug combinations between non-dialyzable macromolecules.

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Various studies were carried out on the uptake of 14C-labeled warfarin and dicumarol by isolated rat hepatocytes. The uptake was rapid, reaching a steady-state level in the isolated cells in about one-half minute. Concentration studies showed that the uptake of warfarin by the cells approached saturation at about 4.5 nmoles per million cells, whereas the uptake of dicumarol did not approach saturation over the range studied. The effects of the anticoagulants on respiration were complex, having little or no effect on respiration at the lowest concentrations, stimulating respiration at the intermediate levels, and reducing respiration at the highest levels. Metabolic inhibitors such as 2,4-dinitrophenol and antimycin reduced the uptake of warfarin but not that of dicumarol. Serum albumin reduced the uptake of anticoagulants by the hepatocytes and the uptake was reciprocally related to the concentration of serum albumin. Computations showed that most of the binding of the drugs would be at the high-affinity sites on the albumin. The cells metabolized warfarin progressively for at least two hours, and serum albumin reduced the rate of metabolism of the drug. The rate of metabolism was relatively slow compared with the uptake; about 1% of the warfarin taken up by the cells was metabolized per minute.

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Ligandin binds several classes of compounds, has glutathione-S-transferase activity and is postulated to function in the intracellular transport of substances which bind to it and/or are substrates for its enzymatic activity. The effects of a group of organometals reported to inhibit the enzymatic activity of ligandin on the biliary excretion of sulfobromophthalein have been investigated to determine what role the enzymatic activity of ligandin has with respect to the biliary excretion of the dye. Triethyllead reduced the rate of dye excretion into the bile without affecting blood pressure, blood or liver sulfhydryl compounds or the volume of bile flow. The organometal had no effect on the initial rate of plasma dye clearance. Inhibited biliary sulfobromophthalein excretion by triethylead-treated rats correlated with relative increases in liver and bile unconjugated dye, decreases in liver and bile conjugated dye and reduced glutathione-S-aryltransferase activity in supernatant fractions isolated from the liver. The results clearly demonstrated that the tested organometals can inhibit the enzymatic activity of ligandin in vivo and suggested that, if ligandin has a role in the translocation of the dye from the blood to the liver, the enzymatic activity of the protein may not be involved.

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