Morphology and metabolism of adult rat hepatocytes in primary culture

Influence of hormones and growth factors on viability, DNA, and protein content of adult hepatocytes in primary culture

The survival of adult rat hepatocytes in monolayer culture was studied in the presence of different hormones (neurotensin, oxytocin, thyrotropin releasing hormone, luteinizing hormone releasing hormone, cholecalciferol, bradykinin, substance P, aldosterone, melanocyte stimulating hormone, 3,3',5-triiodo-1-thyronine, corticosterone, human growth hormone, glucagon, insulin, progesterone, testosterone, estradiol, and dexamethasone phosphate) or growth factors (fetal bovine serum). For this purpose trypan blue exclusion, lactate dehydrogenase, and DNA and protein content were measured at 24 and 72 h of culture. 10(-7) M Dexamethasone, a mixture of eight hormones, 10% fetal bovine serum, and a combination of the latter two supplements caused a more than 64% higher DNA content at 72 h when compared to control cultures. A striking agreement of these results with changes of lactate dehydrogenase leakage was observed, whereas trypan blue exclusion gave erratic results. Considerable changes of cell arrangement apparently specific for each supplement were observed by low magnification microscopy. It is concluded that glucocorticoids and fetal bovine serum have an outstanding effect on cell viability and that DNA or protein content or both are reliable indicators of cell viability in amitotic cultures.

Toxicity of D-galactosamine for rat hepatocytes in monolayer culture

Hepatocellular injury was induced by exposure of primary cultures of rat hepatocytes to 4 mM D-galactosamine. The cell damage was very similar to that seen in vivo and in the isolated perfused rat liver, both in biochemical and in structural terms. The severity of the lesions caused by D-galactosamine was dependent on the age of the culture being treated. Less severe damage was found with older cultures. Since the primary metabolic effects of D-galactosamine were age-independent, the reduction in cell damage seems to be due to progressive cell dedifferentiation. Dexamethasone (1 microM) suppressed the full development of the injury, while 1 microM triiodo-L-thyronine enhanced it. A protection of hepatocytes by alpha 2-macroglobulin against the effects of D-galactosamine could be observed neither in vivo nor in vitro. Direct cytotoxic effects of endotoxin from Salmonella minnesota R 595 could be demonstrated only on hepatocytes in the early phases of primary culture using rather high doses of the purified lipopolysaccharide. It is unlikely that they play a major role in the hepatocellular injury seen following endotoxinemia in vivo. Lowering of extracellular Ca2+ concentration and additions of calcium/calmodulin inhibitors did not prevent cell injury after treatment with D-galactosamine. The results suggest that cell death is not due to an increased influx of Ca2+ into the cells.

Characteristics of taurine transport in rat hepatocytes in primary culture

Characteristics of taurine transport in rat hepatocytes maintained in primary culture for 24 h (cultured hepatocytes) have been investigated. The uptake of [3H] taurine by cultured hepatocytes at 2 degrees C was unsaturable, whereas that at 37 degrees C consisted of unsaturable and saturable processes. The saturable transport system was sodium-dependent and consisted of two processes with low and with high affinities. The latter process (Km, 76.9 microM; Vmax, 0.256 nmole/mg protein/min; activation energy (EA), 37.8 kcal mol-1) was competitively inhibited by 2,4-dinitrophenol and ouabain, as well as by taurine analogues such as hypotaurine and guanidinoethyl sulphonate. The Vmax and EA values found in cultured hepatocytes at 37 degrees C were 6.0 and 6.8 times higher than those found in freshly isolated hepatocytes. These results indicate that taurine transport in hepatocytes in primary culture consisted of unsaturable, and saturable, sodium and energy-dependent carrier-mediated transport processes, respectively. The facilitation of the latter transport system by primary culture of hepatocytes is also suggested.

Regulation and interaction of cholesterol, bile salt and lipoprotein synthesis in liver

The liver is the junction of several inter-organ metabolic cycles which are essential for the homeostasis of mammalian metabolism. Two of these are described in greater detail and their role in control of lipid metabolism will be presented. The fatty acid-triglyceride cycle is of particular importance for our understanding of the mechanisms governing serum lipid levels. This is due to the fact that the lipoprotein secreted by the liver in the course of this metabolic cycle - very low density lipoprotein - has a relatively long half-life in the plasma compartment. Data have been collected from the literature to show that different nutritional and pharmacological stimuli affecting serum lipid levels do so by interfering with the rate of very low density lipoprotein input into the plasma compartment. The enterohepatic circulation of steroids is another cycle which contributes to control of lipid metabolism. Data are presented which show that bile acids, the major steroids circulating in this cycle, exert direct feedback control of hepatic cholesterol synthesis. This characteristic of bile acids may explain why certain bile acids, when given orally, reduce serum cholesterol levels. Several clinical and experimental observations suggest a close relation between bile acid and triglyceride metabolism. It is characterized by an inverse relation between bile acid pool size and serum triglyceride levels. Moreover, a reduction of the bile acid pool size is accompanied by an enhanced hepatic fatty acid and triglyceride synthesis and secretion into blood. The molecular basis and physiological significance of these observations have still to be explored.(ABSTRACT TRUNCATED AT 250 WORDS)

Transcellular transport of fluorescein in hepatocyte monolayers: evidence for functional polarity of cells in culture

The rat liver in vivo transfers bile salts, proteins, and dyes from blood into bile. It is the purpose of this communication to demonstrate the maintenance of this transcellular transport in cultured adult rat hepatocytes. Two minutes after adding fluorescein (20 microgram/ml) to the culture medium, maximal cellular fluorescence was observed through the fluorescence microscope. Subsequently, intercellular clefts showed a steadily increasing fluorescence with a maximum between 5 and 20 min, resulting in a brightly fluorescent network of intercellular gaps. The following observations are taken as evidence that these findings reflect cellular uptake and canalicular secretion of the dye. First, the same sequence of observations was made upon addition of fluorescein diacetate (a nonfluorescent precursor of fluorescein), proving that the compound had been taken up and metabolized in the cells to fluorescein before secretion into intercellular clefts. Second, preincubation of the monolayers with the cholestatic bile salt taurolithocholate (100 mumol/liter) suppressed almost completely intercellular but not cellular fluorescence. It is concluded that hepatocytes in culture show a functional polarity permitting the transcellular transport of substances bound for biliary secretion.