Ciprofibrate and triiodothyronine do not suppress in vivo induction of placental glutathione S-transferase expression in rat hepatocytes

Mechanism of 1,3-dichloropropene-induced rat liver carcinogenesis

1,3-Dichloropropene (1,3-D) is a soil fumigant used primarily for preplanting control of parasitic nematodes. In a previous chronic dietary exposure study, 1,3-D induced an increased incidence of hepatocellular adenomas in male rats at a dose of 25 mg/kg/day. Although the mechanism for tumor induction in the rat liver by 1,3-D has not been specifically elucidated, available data suggested that the observed liver tumorigenesis was through a nongenotoxic mode of action at the tumor promotion stage. Fischer 344 rats containing preneoplastic lesions were treated (via gavage) with 25 mg/kg/day 1,3-D or 80 mg/kg/day phenobarbital (PB) for 30 days and 60 days, or for 30 days followed by a 30-day recovery period (no compound exposure). Following treatment, placental form glutathione S-transferase (GSTP) positive and GSTP-negative liver focal lesions were quantitated as to size and number. 1,3-D treatment had no effect on GSTP-positive foci number or relative size but significantly increased the number, labeling index, and relative size of GSTP-negative focal lesions (identified by H and E staining) after 30 and 60 days of treatment. Following the 30-day recovery period, the number, labeling index, and relative size of the GSTP-negative lesions in 1,3-D-treated animals returned to control levels. As expected, PB treatment produced an increase in number and relative size of the GSTP-positive lesions. The results of this study are consistent with 1,3-D inducing liver carcinogenesis through a nongenotoxic mode of action by functioning as a tumor promoter specifically through induction of a non-GSTP staining focal hepatocyte population.

Exogenous thyroid hormone induces liver enlargement, whilst maintaining regenerative potential--a study relevant to donor preconditioning

We have investigated thyroid hormone- (T3) induced liver cell hyperplasia in rats to explore the potential utility of primary mitogens within the clinical context of donor conditioning prior to living-related transplantation. A single injection of T3 induced a semi-synchronized proliferative response in hepatocytes, resulting at 10 days in a peak increase in liver mass, liver/body mass ratio, total DNA and total protein. Importantly, the hyperplastic liver induced by T3 exhibits a commensurate increase in metabolic capacity, as assessed by enhanced galactose elimination capacity. Furthermore, when the liver mass had been increased by an injection of T3 given 10 days previously and 70% partial hepatectomy performed, there was a larger remnant liver mass, liver/body mass ratio, total DNA and total protein content 24 h after surgery, compared with animals given a control injection. Interestingly, the regenerative response to surgery was the same in both groups, indicating that prior T3 conditioning did not impair the regenerative response of the liver. Using more stringent conditions to test hepatic functional reserve, following 90% hepatectomy, there was a greater (57%) survival in animals pre-treated with T3 compared to 14% in controls.