Intranuclear Changes in Rat Liver During the Early Stages of Feeding the Hepatocarcinogens Thioacetamide and 4-Dimethylaminoazobenzene

Abstract

IT has been previously shown that during the feeding to rats of thioacetamide and 4-dimethylaminoazobenzene (DAB), parenchymal liver cell nuclei show an increase in their chemical constituents (Rees and Rowland, 1961). These measurements were carried out at regular time intervals throughout the tumour induction period of approximately 6 months. In the case of thioacetamide feeding it was observed that mar-ked changes in nuclear composition were already established by 2 weeks. This would reflect the histological finding (Gupta, 1956) of enlargement of the nucleus and nucleolus after a few days of such feeding. With the development of a technique of sub-nuclear fractionation (Rees, Rowland and Varcoe, 1963) it is now possible to examine changes in composition of the nucleolus and other Farts of the nucleus during the very early stages of chemical carcinogenesis.In the present investigation subnuclear proteins have been studied at various time intervals from the livers of rats fed thioacetamide for up to 3 weeks. As a comparison, similar studies have been made on the livers of rats fed with DAB for up to 5 weeks, no histological changes being apparent before 3 weeks with this carcinogen (Rees and Rowland, 1961). In addition to the determination of chemical composition of these fractions the incorporation in vivo has been followed of 32P into ribonucleic acid (RNA) and phosphotlipid.

Liver nucleotides in acute experimental liver injury induced by dimethylnitrosamine and by thioacetamide

“…Both dimethylnitrosamine and thioacetamide likewise produce very early disturbances in the endoplasmic reticulum, as indicated, for example, by the rapid decreases in protein synthesis after administration of single doses of these toxic materials (Magee, 1958;Barker, Smuckler & Benditt, 1963). The interactions of dimethylnitrosamine and thioacetamide with the endoplasmic reticulum appear to involve conversion of each material into a more toxic derivative through the participation of the enzyme systems responsible for the metabolism of foreign compounds (see Magee, 1964;Clifford & Rees, 1966;Rees, Rowland & Varcoe, 1965). A similar 'activation' of carbon tetrachloride to a more toxic form has been suggested to occur in rat liver (Butler, 1961;Ghoshal & Recknagel, 1965;Slater, 1966).…”

The metabolism of tritiated thioacetamide in the rat

“…The extract was taken to dryness and re-dissolved in 1 ml ethanol. 0.5 ml of this solution was used for measurement of radioactivity and 0.2 ml for determination of phospholipid phosphorus as described previously (Rees et al, 1965 Separation of thioacetamide and acetamide by thin-layer chromatography A slurry of " silica gel G " (E. Merck, Darmstadt, Germany) was prepared, with 0.6 g and 12-15 ml water for every 20 cm x 20 cm plate. The slurry was spread at a thickness of 0.35 mm with an applicator designed and built in this laboratory (Godwin, 1965).…”

“…The extract was taken to dryness and re-dissolved in 1 ml ethanol. 0.5 ml of this solution was used for measurement of radioactivity and 0.2 ml for determination of phospholipid phosphorus as described previously (Rees et al, 1965).…”

“…The extracts were neutralized with N KOH, the KC10, centrifuged down and 0.5 ml of the supernatant transferred to counting phials to activity (Rees et al, 1965) of the parenchymal liver cell nuclei are apparent after only four days of feeding. It was thus decided to study the metabolic fate of thi~acetamide-~H in the first instance over a four-day feeding period.…”

“…Samples of the pooled urines from each rat were analysed by thin-layer chromatography as described under '' Materials and be mixed with thixotropic fluid. Samples of 0.2 ml were taken for determination of nucleic acid phosphorus as described previously (Rees et a[., 1965). The protein residue was digested overnight with 1.5 ml N NaOH at 37" C, then samples of 0.5 ml were transferred to counting phials and mixed with thixotropic fluid.…”