The effect of propylthiouracil (PTU) on the growth activity of intact liver and liver regenerating after partial (65-70 %) hepatectomy (PH) was studied in rats. FEU (Propycil, Kali-Chcmie, FRG) was dissolved in drinking water (1 g PTU per litre) and this was given to the rats, as their sole source of fluids, three days before PI I and then up to the end of the experiment. In rats given FPU, marked inhibition of liver DNA synthesis and the mitotic activity of hepatocytes was found after PH. This effect was potentiated to some extent by partial inanition of the experimental animals given FITJ, as demonstrated in a paired feeding test in control rats. PTU inhibition of DNA synthesis in intact and regenerating liver also took effect in thyroidectomized rats, even with substitution (thyroid hormone) therapy. The experiments demonstrated that the effect of propylthiouracil on DNA synthesis in the liver is mediated primarily by way of its direct effect on the liver.
During 48 hours after application sublethal doses of hepatotoxic agent thiacetamide decrease cytochrome c oxidase activity of rat liver homogenate and isolated mitochondria to 46 % and 32 % of original values, respectively. This decrease may be prevented by simultaneous application of lipid emulsion (mixture of Lipofundin and Mygliol)
twice a day.
Glucagon-like peptide-1 (GLP-1) is an incretin known for proliferative and antiapoptotic effects on various tissues. Exenatide and Liraglutide are GLP-1 analogues used in clinical practice as antidiabetic drugs. Since GLP-1 and its analogues exert significant effect on liver metabolism and since changes in intermediary metabolism play an important role in the process of liver regeneration, we decided to determine the effect of Exenatide and Liraglutide on the early phase of liver regeneration and selected metabolic parameters in a model of 2/3 partial hepatectomy (PHx) in rats. Animals were submitted either to PHx or laparotomy and received 3 doses of either GLP-1 analogues (Exenatide – 42 μg/kg b.w., Liraglutide – 0.75 mg/kg b.w.) or saline intraperitoneally. We analyzed body and liver weight, liver bromodeoxyuridine incorporation, liver content of DNA, triacylglycerols and cholesterol and biochemical serum parameters. Bromodeoxyuridine labeling was significantly lower in hepatectomized rats receiving either type of GLP-1 analogues when compared to hepatectomized controls. This effect was more pronounced in the Liraglutide group compared to Exenatide (p<0.001). In addition, liver DNA content was lower in
hepatectomized rats receiving Liraglutide than in hepatectomized control rats (p<0.001). In conclusion, GLP-1 analogues Exenatide and Liraglutide significantly inhibited an early phase of liver
regeneration after PHx in rats. This inhibitory effect was more pronounced in rats receiving Liraglutide.
We studied the extent to which hormonally-induced mitochondrial glycerophosphate dehydrogenase (mGPDH) activity contributes to the supply of reducing equivalents to the mitochondrial respiratory chain in the rat liver. The activity of glycerophosphate oxidase was compared with those of NADH oxidase and/or succinate oxidase. It was found that triiodothyronine-activated mGPDH represents almost the same capacity for the saturation of the respiratory chain as Complex II. Furthermore, the increase of mGPDH activity induced by triiodothyronine correlated with an increase of capacity for glycerophosphate-dependent hydrogen peroxide production. As a result of hormonal treatment, a 3-fold increase in glycerophosphate-dependent hydrogen peroxide production by liver mitochondria was detected by polarographic and luminometric measurements.
By determining the calcium retention capacity (CRC) of rat liver
mitochondria, we confirmed and extended previous observations
describing the activation of mitochondrial swelling by phosphate
and tert-butyl hydroperoxide (t-BHP). Using CRC measurements,
we showed that both phosphate and t-BHP decrease the extent
of calcium accumulation required for the full mitochondrial
permeability transition pore (MPTP) opening to 35 % of control
values and to only 15 % when both phosphate and t-BHP are
present in the medium. When changes in fluorescence were
evaluated at higher resolution, we observed that in the presence
of cyclosporine A fluorescence values return after each
Ca2+ addition to basal values obtained before the Ca2+ addition.
This indicates that the MPTP remains closed. However, in the
absence of cyclosporine A, the basal fluorescence after each
Ca2+ addition continuously increased. This increase was
potentiated both by phosphate and t-BHP until the moment when
the concentration of intramitochondrial calcium required for the
full opening of the MPTP was reached. We conclude that in the
absence of cyclosporine A, the MPTP is slowly opened after each
Ca2+ addition and that this rate of opening can be modified by
various factors such as the composition of the media and the
experimental protocol used.
The protective effect of S-adenosylmethionine (SAMe) on D-galactosamine (GalN)-induced damage to rat hepatocytes was tested in primary cultures. SAMe at concentrations of 50 and 1000 mg/l significantly reduced lactate dehydrogenase release from cells injured by 40 mM GalN after 24 h of incubation. There were no significant changes in urea production after 24 h among tested groups, including control hepatocytes. Exposure of hepatocytes to GalN leads to 3.5-fold decrease in urea synthesis after 48 h in comparison with control cell cultures. Addition of the highest dose of SAMe (1000 mg/l) into the culture media attenuated this decrease by 180 %. None of the tested doses of SAMe (5, 25, 50 and 1000 mg/l) affected considerably the reduced activity of mitochondrial dehydrogenases. The content of reduced and oxidized glutathione in GalN-exposed cells was diminished to 1.5 % and 16 %, respectively, of the control values after 24 h. Using only the highest concentration SAMe increased significantly these contents. SAMe had no effect on dramatically decreased albumin synthesis. These findings indicate beneficial effect of SAMe, especially of the highest concentration, on GalN-induced toxicity to rat hepatocytes in primary culture. This action of SAMe seems to be associated with reduction of plasma membrane damage and increased synthesis of glutathione.
Mitochondria were isolated from regenerating rat liver 12, 24 and 48 h after partial hepatectomy. The "State 3" and "State 4" respiration were measured in the presence of succinate. The P/O quotient and respiratory control index (RCI) were calculated. The experimental data showed that the partial uncoupling of oxidative phosphorylation in regenerating liver mitochondria occurring in the early period of regeneration is partly due to free fatty acids.
Sensitivity of various mitochondrial enzymes to oxidative damage was tested on isolated rat liver hepatocytes
permeabilized by digitonin. In permeabilized hepatocytes
normal respiratory control
values were obtained and
mitochondrial membranes remained intact. Respiratory rate
s of NADH-dependent (glutamate+malate, palmitylcarnitine
+ malate) and flavoprotein-dependent (succinate) substrates were determined in hepatocytes exposed for 5 min to
0.5-3 mM
tert
-butyl hydroperoxide before addition of digitonin.
Our data showed that oxidation of NADH-dependent
substrates is much more sensitive to oxidative stress than ox
idation of flavoprotein-dependent ones, evidently due to the
modification of iron-sulfur clusters or SH groups in the NADH dehydrogenase enzyme complex (Complex I).
The recovery of total DNA content and recovery of total cytochrome c oxidase activity in the rat liver after partial hepatectomy is accelerated by triiodothyronine applied in three doses, two before and one immediately after liver resection. Triiodothyronine-treated animals already have higher cytochrome c oxidase activity before resection. The recovery of the tissue oxidative capacity after partial hepatectomy is more rapid in triiodothyronine-treated animals. These data indicate that hormonal activation of the liver regeneration process is involved.