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H M Bolt

Publications and source records attributed to H M Bolt.

At least 217 records · Page 12Linked to original sources
PubMed1977

Structural modifications in contraceptive steroids altering their metabolism and toxicity.

Norethisterone and, to a lesser extent, d-norgestrel are metabolically activated by rat liver microsomal enzymes to intermediates which are capable of irreversibly binding to proteins. This microsomal activation in vitro depends on presence of NADPH and is inhibited by glutathione. Irreversible binding of metabolites of progesterone, nortestosterone acetate and cyproterone acetate is very low, compared to that of norethisterone metabolites. Phenol as a reference compound shows quantitatively a similar binding behaviour as norethisterone. Norethisterone-4beta,5beta-epoxide, a microsomal metabolite of norethisterone, binds non-enzymatically to albumin, at a rate of 380 pmol/mg albumin per hour (at 37 degrees). The corresponding rate for norgestrel-4beta,5beta-epoxide, 42 pmol/mg albumin per hour, indicates a considerably lower reactivity of norgestrel-epoxide. The non-SH-proteins concanavalin A and bovine gamma-globulin do not react with either norethisterone-epoxide or norgestrel-epoxide. Also, DNA and RNA show no binding reaction. Thus, the requirements for irreversible protein binding of the 19-nortestosterone progestagens norethisterone and norgestrel are similar to those found for oestrogens which, when activated by rat liver microsomes, only bind to proteins with SH-groups, not to DNA or RNA.

Animals↗
PubMed1977

The significance of covalent binding of catechols to proteins in vivo.

When rats were dosed with 14 microgram/kg 3H-isoproterenol, 3H-radioactivity was measurable in the liver until 48 h. This amount was not different in livers of animals which have been pretreated with diethyl maleate. After exhaustive extraction, a significant amount of 3H-radioactivity from isoproterenol could be detected in the proteins of total liver (homogenate), of cytosol and of microsomes. In the cytosol fraction of diethyl maleate pretreated animals twice the amount of isoproterenol-radioactivity was found in the extracted proteins compared to controls. In the microsomal fraction there was no difference between diethyl maleate pretreated and control animals in the amount of radioactivity incorporated into proteins. In all fractions the radioactivity measurable in the extracted proteins declined with a half life time of about 24 h. The in vivo results on covalent binding of isoproterenol are compared to the irreversible protein binding of ethinyloestradiol in vivo. Quantitatively, these in vivo data are compared to the results on irreversible protein binding obtained during incubations of isoproterenol or ethinyloestradiol with rat liver microsomes.

Animals↗
PubMed1977

Alkylation of RNA by vinyl chloride metabolites in vitro and in vivo: formation of 1-N(6)-etheno-adenosine.

Rat liver microsomes were incubated with NADPH, 1,2-[(14)C] vinyl chloride and poly-adenosine. The latter was reisolated from the incubations and hydrolyzed. The radioactivity, originating from [(14)C] vinyl chloride, which was irreversibly attached to the poly-adenosine was confined to 1-N(6)-etheno-adenosine (3beta-ribofuranosyl-imidazo [2,1,i] purine). When rats were exposed to 1,2-[(14)C] vinyl chloride, part of the radioactivity was incorporated into RNA of liver. This radioactive labelling exhibited a first maximum, 14 h, and a second maximum, 72 h after ending the exposure. Analysis of hydrolysate of liver RNA showed that all natural nucleosides of RNA were labelled. Besides, small amounts of radioactivity could be detected which were confined to 1-N(6)-etheno-adenosine. The experiments support the theory that vinyl chloride metabolites react with adenosine moieties of nucleic acid under formation of 1-N(6)-etheno-adenosine. Furthermore, the results show that measurement of incorporation of radioactivity into nucleic acids after exposure of animals to radioactive vinyl chloride is not applicable as a means of determining the alkylating potency of vinyl chloride metabolites towards nucleic acids in vivo.

Adenine Nucleotides↗
PubMed1977

Pharmacokinetics of vinyl chloride in the rat.

When rats are exposed to [14C]vinyl chloride in a closed system, the vinyl chloride present in the atmosphere equilibrates with the animals' organism within 15 min. The course of equilibration could be determined using rats which had been given 6-nitro-1,2,3-benzothiadiazole. This compound completely blocks metabolism of vinyl chloride. The enzymes responsible for metabolism of vinyl chloride are saturated at an atmospheric concentration of vinyl chloride of 250 ppm. Pharmacokinetic analysis shows that no significant cumulation of vinyl chloride or its major metabolites is to be expected on repeated administration of vinyl chlorides. This may be consistent with the theory that a reactive, shortly living, metabolite which occurs in low concentration only, may be responsible for the toxic effects of vinyl chloride.

Animals↗
PubMed1977

Irreversible binding of chlorinated ethylenes to macromolecules.

Rats have been exposed in a closed system to the chlorinated ethylenes vinyl chloride and trichloroethylene and to carbon tetrachloride as a reference compound. Data of uptake of the compounds, of urinary excretion of metabolites, and of exhalation after exposure show that the chlorinated ethylenes are metabolized much faster than carbon tetrachloride, probably due to their common ethylene structure. To eliminate differences in uptake, calculation of metabolites of the three compounds in tissues was based on the amount actually taken up by the animals. Vinyl chloride, trichloroethylene, and carbon tetrachloride showed irreversible binding of metabolites to tissue proteins, mainly of the liver. Irreversible protein binding of either of these compounds ranged within the same order of magnitude, if related to the amount of compound which had been taken up. Also, no differences in the relative portion of irreversibly bound metabolites were found after exposure to different atmospheric concentrations of the three compounds. As already shown for vinyl chloride, trichloroethylene is metabolized in vitro by rat liver microsomes in presence of NADPH-regenerating system to intermediates that irreversibly bind to proteins. Albumin (bovine and rabbit) was a preferred target for binding. In contrast to vinyl chloride, significant irreversible binding of trichloroethylene metabolites also occurred to non-SH-proteins (gamma-globulin, concanavalin A) and to polylysine. Hence it should be inferred that, unlike vinyl chloride, trichloroethylene metabolites not only bind to sulfhydryl groups but also, to a lesser extent, to free amino groups of proteins.

Animals↗
PubMed1977

Interaction of rifampicin treatment with pharmacokinetics and metabolism of ethinyloestradiol in man.

[6,7-3H]Ethinyloestradiol (50 microng) was administered intravenously to volunteers and the free extractable ethinyloestradiol in the plasma was measured. The compound showed a biphasic plasma decline. The half-life of the second phase was 7.5+/-1.7 (SD) hours. Administration of rifampicin (600 mg for 6 days) shifted the half-life of ethinyloestradiol to 3.3+/-0.9 h while the apparent volume of distribution for the second phase of elimination was not changed. When [2,4,6,7-3H]ethinyloestradiol (100 microng) was administered orally, some of the tritium was released by oxidative metabolism from the steroid and transformed to tritiated water (HTO) which equilibrated with whole body water. This portion, normally 7.17+/-1.66% of the tritium dose, was increased by previous administration of rifampicin to 10.62+/-2.27%. The initial rate of oxication of [2,4,6,7-3H]ethinyloestradiol was increased more than twofold by rifampicin treatment. The results are consistent with previous findings that rifampicin induces the oestrogen-2-hydroxylase in the endoplasmic reticulum of human liver, and explain the reduced effectiveness of ethinyloestradiol in oral contraceptives, if the patients are treated with rifampicin.

Administration, Oral↗
PubMed1977

Effects of hepatotoxic agents on hepatic microsomal metabolism of estrogens in the rat.

Different kinds of experimental liver damage in rats are evaluated as to associated changes in breakdown of natural estrogens. Acute or chronic treatment of rats with ethanol does not influence aromatic hydroxylation of estradiol, as indicated by liver microsomal replacement of tritium from 2,4,6,7-3H-estradiol. More severe liver damage by CCl4 or thioacetamide, which lowers hepatic cytochrome P-450, causes impairment of estrogen degradation: CCl4 dosage leads to a marked decrease in aromatic hydroxylation of estradiol. Whereas thioacetamide in a chronic application schedule has been previously reported to a decrease microsomal aromatic estrogen hydroxylation, a single dose of 300 mg/kg thioacetamide in rats causes increased microsomal formation of estrone from estradiol, which is regarded to be a better (i.e., more lipophilic) substrate for the microsomal estrogen 2-hydroxylase than is estradiol. The data show that hepatotoxic agents may act differentially on hepatic metabolism of endogenous steroids.

Acetamides↗
PubMed1976

[Effect of liver damage by thioacetamide on microsomal aromatization of testosterone in rats (author's transl)].

Rat liver microsomes, NADPH-regenerating system, and 1beta, 2beta-3H-testosterone have been incubated in vitro. The loss of tritium from the steroid, associated with aromatization of testosterone, was linear with time for 20 min and required NADPH. Pre-treatment of the rats with thioacetamide raised the liberation of tritium from 1beta, 2beta-3H-testosterone. The results suggest that liver damage by thioacetamide in rats may give rise to increased aromatization of testosterone.

Acetamides↗
PubMed1976

Irreversible protein binding of norethisterone (norethindrone) epoxide.

14,15-3H-Norethisterone-4 beta, 5 beta-epoxide, a metabolite of norethisterone, was incubated with several proteins and nucleic acids. After 30 min incubation 0.19 nmol of the epoxide were irreversibly bound per mg albumin which contains free sulfhydryl groups; proteins without SH-groups, such as concanavalin A, gamma-globulin, DNA and RNA, did not irreversibly bind norethisterone epoxide. A superoxide (O2) generating enzyme system comprised of xanthine oxidase and hypoxanthine was capable of catalyzing the irreversible binding of the parent compound, norethisterone, to albumin, indicating that an oxidation product was formed which reacted with the protein. When norethisterone epoxide was incubated for 60 min with hepatic microsomes of rats in absence of NADPH, about 2.0 nmol of the epoxide were irreversibly incorporated per mg microsomal protein. This binding was increased to 5.2 nmol by addition of a NADPH regenerating system. Addition of glutathione and cytosol decreased only the NADPH-dependent protein binding; phenobarbital pretreatment of rats induced this NADPH-dependent binding of norethisterone epoxide to microsomal protein by a factor of 2. In presence of NADPH, binding of the epoxide to microsomal protein depended on substrate concentration used. The results indicate that norethisterone epoxide is able to chemically react with proteins. In addition, hepatic microsomal enzymes convert the epoxide to another metabolite which also can react with proteins.

Animals↗
PubMed1976

Implication of rifampicin-quinone in the irreversible binding of rifampicin to macromolecules.

1. When [3H]rifampicin is incubated with rat liver microsomes or rat liver homogenate, minor amounts are bound irreversibly to protein. This effect does not depend on the presence of NAD, NADH, NADP or NADPH. 2. Rifampicin is autoxidized at physiological pH. The product of autoxidation, rifampicin-quinone, if incubated with albumin, shows a much greater irreversible binding to the protein than the parent compound rifampicin. Hence it is concluded that rifampicin may bind irreversibly to proteins in a non-enzymic reaction after autoxidation to rifampicin-quinone. 3. Rifampicin-quinone also binds irreversibly to RNA and poly-L-lysine, if incubated with these compounds. This suggests that free amino groups of protein or RNA are involved in the binding. 4. 48 h after dosage of [3H]rifampicin (33 mg/kg) to rats, 29-2 +/- 4-1 (S.D.) pmol are bound irreversibly to 1 mg liver RNA, 15.8 +/- 8-1 pmol to 1 mg liver protein and 5-0 +/- 0-47 pmol to 1 mg protein in brain tissue. 5. Microsomal NADPH-cytochromcin-quinone to rifampicin. The KM of this reaction is 10(-4) M. Induction of the NADPH-cytochrome c reductase by pre-treatment of rats with 20 mg/kg rifampicin over 5 days results in a corresponding increase of increase of rifampicin-quinone reduction. 6. These results suggest that microsomal NADPH-cytochrome c reductase prevents accumulation of higher amounts of possibly toxic rifampicin-quinone by reduction to rifampicin.

Animals↗
PubMed1976

Effects of insecticide synergists on microsomal oxidation of estradiol and ethynylestradiol and on microsomal drug metabolism.

1. Oxidation of estradiol and ethynylestradiol at ring A and ring B by rat liver microsomes and NADPH-regenerating system in vitro is inhibited by the two arylimidazole insecticide synergists, 3-bromophenyl-4(5)-imidazole and 1-naphthyl-4(5)-imidazole, but not by the benzothiadiazole insectide synergists 6-nitro-1,2,3-benzothiadiazole and 5,6-dimethyl-1,2,3-benzothiadiazole. The Ki of the most potent inhibitor, 1-naphthyl-4(5)-imidazole, was 3 X 10(-6) M. 2. 6-Nitro-1,2,3-benzothiadiazole (10(-6) M), which did not inhibit hydroxylation of the estrogens, inhibited oxidation of aniline and demethylation of ethylmorphine, p-nitroanisole, and aminopyrine by 30-70%. 5,6-Dimethyl-1,2,3-benzothiadiazole inhibited only demethylation of p-nitroanisole and aminopyrine. From these results the presence of different hepatic microsomal mixed function oxidases may be inferred. 3. 1-Naphthyl-4(5)-imidazole, the most potent inhibitor of hydroxylation of drugs and estrogen rings A and B, also inhibited microsomal estrogen-16alpha-hydroxylation. 4. These data show that insecticide synergists may effect the breakdown of estrogenic hormones in the organism.

Animals↗