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

Studies with nitrogen-containing steroids and freshly isolated rat hepatocytes: role of cytochrome P-450 in detoxication

Several nitrogen-containing steroids produced concentration- and time-dependent decreases in the viability of freshly isolated F-344 rat hepatocytes. N,N-Diethyl-4-methyl-3-oxo-4-aza-5 alpha-androst-1-ene-17 beta-carboxamide (I) was not cytotoxic at or below 0.3 mM but produced decreases in cell viability at higher concentrations. In contrast, the desmethyl analog of I was essentially nontoxic, demonstrating that relatively small structural changes result in substantial differences in cytotoxicity. Testosterone and other steroids specifically potentiated the cytotoxicity of I in a concentration-dependent manner, while having no effect upon the toxicity of other chemical agents. Pargyline and methimazole had no effect upon the cytotoxicity of I, suggesting that monoamine oxidase and flavin-containing monooxygenase are not involved. The cytochrome P-450 inhibitors octylamine and metyrapone potentiated the cytotoxicity of I. Induction of cytochrome P-450 isozymes by phenobarbital and beta-naphthoflavone treatment protected the cells against the cytotoxicity of I, while acetone or dexamethasone treatment had no effect. The initial rates of hepatocyte metabolism of the six nitrogen-containing steroids investigated did not correlate with cytotoxicity. Dithiothreitol and other thiol compounds had no effect upon the cytotoxicity of I, suggesting that sulfhydryl oxidation is not involved. Galactosamine and sulfate-free media had no effect upon the cytotoxicity of I. These results suggest that cytochrome P-450 is involved in the detoxication of I by rat hepatocytes while conjugative metabolism does not play a significant role.

Investigation into the effects of the photodecomposition of norethisterone by UV-B light on Salmonella typhimurium TA98 and the rat

In view of the light-induced side-effects of the oral contraceptive pill and the development of injectable and subdermal contraceptive devices, the effects of norethisterone irradiated with UV-B light (280-320 nm) on the microorganism Salmonella typhimurium TA98 and male Wistar rats have been investigated. The observed cytotoxic effect of the photo-products on Salmonella typhimurium TA98 may in part be caused by the irreversible binding of steroid to protein from this bacterium, of which binding is in line with previous experiments. However, after intraperitoneal or percutaneous administration of 4-14C-norethisterone to rats, followed by irradiation with UV-B light, no significantly higher level of radioactivity was observed in blood, organ material of the skin, kidney or liver, on extraction or dialysis of the samples.