Inhibitory effect of epinephrine on phosphatidate activity in isolated rat hepatocytes.

The variations in phosphatidate phosphohydrolase activity were investigated in the post-mitochondrial fraction of isolated rat hepatocytes incubated for short periods with epinephrine, dibutyryl cyclic AMP or oleate. Epinephrine decreased the enzyme activity by 42% at 1 microM concentration. The inhibitory effect was abolished in the presence of a beta-adrenoceptor antagonist, propranolol, but was not affected by the alpha-adrenoceptor agonist, phenylephrine, or the agonist, phentolamine. Dibutyryl-cAMP inhibited the enzyme activity by 49%. The presence of the cyclic-AMP phosphodiesterase inhibitor, aminophyline, together with epinephrine slightly increased the enzyme inhibition. Oleate stimulated the enzyme activity (100%) and its effect was antagonized by dibutyryl-cyclic AMP (24%) and by epinephrine (15%). The results indicate that epinephrine acts on rat hepatocytes via beta-adrenoceptor activation and cAMP may be involved in the mechanism by which phosphatidate phosphohydrolase is regulated.

Effects of substituted 2-nitroimidazoles and related compounds on unscheduled DNA synthesis in rat hepatocytes and in non-transformed (BL8) and transformed (JB1) rat liver epithelial derived cell lines.

1. Using unscheduled DNA synthesis as an index, the possible interaction of a number of substituted nitroimidazoles, e.g. misonidazole, with cellular DNA has been investigated. Transformed (JB1), non-transformed (BL8) rat liver epithelial derived cell lines and freshly prepared rat hepatocytes have been used. 2. Under anaerobic or aerobic conditions, relative to cells exposed to a nitroquinoline-N-oxide standard, misonidazole and related nitroimidazoles were very poor at stimulating unscheduled DNA synthesis in JB1 or BL8 cells or in hepatocytes, even at the highest concentrations tested (10 mM). Under anaerobic conditions, metabolic activation did occur as judged from the time-dependent depletion of cellular reduced glutathione in all three cell types. 3. It was concluded that in hypoxic cells an important mode of action of such nitroimidazoles as chemotherapeutic sensitisers may be by their interaction with cellular thiols rather from their interaction with DNA. 4. Functionalisation of the nitroimidazole ring with a side chain containing an aziridine function, e.g. RSU-1069 (1-(2-nitro-1-imidazolyl)-3-(1-aziridinyl)-2-propanol), results in the induction of unscheduled DNA synthesis in cells exposed under both aerobic and anaerobic conditions. On a molar basis, however, this induction was not so great as that caused by the simple monofunctional alkylating agent 1-aziridineethanol itself. Methyl-substitution of the aziridine ring in RSU-1069 reduced the extent of unscheduled DNA synthesis. 5. With all the compounds tested, unscheduled DNA synthesis was greater in JB1 cells than in BL8s or in hepatocytes.

A genetic variant of human erythrocyte glucose 6-phosphate dehydrogenase.

Human erythrocyte G6PD activity was measured in more than 500 subjects in Isfahan, Iran, and the percent of enzyme deficiency for males and females are reported. Some properties of the abnormal enzyme is compared with its normal counterpart. Apparent Km values of glucose 6-phosphate for the variant and normal enzymes were 37 and 101 microM, respectively. The variant enzyme was less resistant to inhibition by 40 microM NADPH (72% inhibition) than the normal enzyme (48% inhibition). The mode of inhibition for both enzymes was competitive with NADP+. ATP at 1.5 mM concentration also inhibited normal and variant enzymes at 17% and 10%, respectively. The inhibition was competitive with glucose 6-phosphate. Polyacrylamide gel electrophores showed that normal enzyme has one major and another weak active bands, while the variant enzyme under identical conditions shows only one active band corresponding to the major band of the normal enzyme. Thermostability of variant G6PD was slightly lower that normal but no significant differences observed in their energy of activation. The activity pH profile of the variant enzyme was truncate.

Cytotoxic effects of norethindrone-4 beta,5 beta-epoxide to Walker cells in culture and to rat liver in vivo.

1. Norethindrone-4 beta,5 beta-epoxide was toxic to Walker cells in culture. The concentration required to produce a 50% reduction in the increase in cell numbers 72 h after exposure (ID50) was 0.05 mM. In this assay, the parent contraceptive steroid, norethindrone, was at least four times less toxic than the epoxide. 2. Norethandrolone-4 beta,5 beta-epoxide and norethynodrel-5 beta,10 beta-epoxide were as toxic as norethindrone epoxide to the Walker cells. 3. The cytotoxicity of norethindrome epoxide was dependent on the time of exposure of the cells to this compound if excess unreacted epoxide was removed by washing the cells with cysteine. The results are consistant with norethindrone epoxide causing cell death by reacting with sulphydryl groups of cellular proteins. 4. No metabolites toxic to Walker cells could be detected when the cells were incubated with norethindrone, rat liver microsomes and a NADPH generating system. 5. Cells treated with an ID50 of norethindrone epoxide for 1 h showed marked cytoplasmic vacuolation 3 hr after exposure. This vacuolation was much less marked in cells treated with an ID50 of norethindrone or in the controls. Neither group showed any nuclear abnormalities. 6. Norethindrone epoxide when given to rats in large doses (50 mg/kg) by lateral tail vein injection also caused cytoplasmic vacuolar degeneration of the liver hepatocytes, especially in the perilobular areas 3 days after dosing. When this compound was administered at a similar dose level via the hepatic portal vein massive haemorrhagic necrosis of the liver resulted. No damage to either lungs or kidneys was evident, irrespective of the route of administration.

Urinary excretion of aflatoxin M1 after administration of aflatoxin B1 in sucrose- or starch-rich diets.

1. Male Sprague--Dawley rats were given 630 g/kg sucrose or starch with 2 mg/kg aflatoxin b1 for periods of 75, 145 and 200 d, and the 24 h urinary excretion of aflatoxin M1 was measured. 2. Less aflatoxin M1 was excreted by the rats fed on the sucrose-rich diet compared to those fed on the starch-rich diet. This difference was especially marked when expressed per g metabolizing tissue. 3. It is concluded that sucrose probably decreases the activity of aflatoxin B1 metabolism in a similar way to its previously found effect on the drug-metabolizing enzyme.

[Contamination of cotton seeds and of cotton seed cake by aflatoxin]. / La contamination des graines du cotonnier et des tourteaux de ces grains par l'aflatoxine.

Following the discovery of aflatoxin M in cow's milk in the previous study, the contamination with aflatoxin of cotton-seed and cotton-seed cake which constitute the principal feed of local animals was measured. The samples were taken from 2 factories. The grain from the 1st factory was grown in the centre of the country in dry climate, and those from the 2nd source originated from the humid region of the north of Iran. The grain and cotton-seed cake from the 1st factory did not contain aflatoxin before storage. During storage the sample contamination amount and percent increased with time in both regions, with the dry less than the humid. In conclusion, Iranian cotton-seed and cotton-seed cake appear to be contaminated with aflatoxin B in 2 processes. The 1st is aflatoxin contamination before harvest, in the humid region of Iran; the 2nd is general storage aflatoxin contamination in both regions in which humidity and length of storage appear to be the principal factors.