Xanthine oxidase activity in regenerating liver

The xanthine oxidase activity of mouse regenerating liver has been shown to be elevated during the period of rapid liver growth and proliferation. This increase is evident when the enzyme activity is expressed per unit wet tissue weight, per unit nitrogen, or per cell. The adrenal cortex probably plays only a minor role in implementing this phenomenon. Further augmentation of the xanthine oxidase level of regenerating liver is not induced by the administration of large quantities of the substrate, xanthine, to the animal.     

Sialyltransferase activity in regenerating rat liver

Liver microsomal fractions catalyse the transfer of sialic acid from CMP-N-acetyl-neuraminic acid to various exogenous acceptors such as desialylated fetuin, desialylated human Tamm–Horsfall glycoprotein and desialylated bovine submaxillary-gland mucin. An increase in the rate of incorporation of sialic acid into desialylated glycoproteins was found after a lag period (7h) in regenerating liver. The increase was maximum 24h after partial hepatectomy for all acceptors tested. At later times after operation the sialyltransferase activity remained high only for desialylated fetuin. No soluble factors from liver or serum of partially hepatectomized animals influenced the activity of the sialyltransferases bound to the microsomal fraction. The sensitivity of sialyltransferases to activation by Triton X-100, added to the incubation medium, was unchanged in the microsomal preparation from animals 24h after sham operation or partial hepatectomy. The full activity of sialyltransferases towards the various desialylated acceptors showed some differences. Human Tamm–Horsfall glycoprotein was a good acceptor of sialic acid only when desialylated by mild acid hydrolysis. After this treatment, but not after enzymic hydrolysis, a decrease in molecular weight of human Tamm–Horsfall glycoprotein was observed. Further, the sialyltransferase activity as a function of incubation temperature gave different curves according to the acceptor used. The relationship between the biosynthesis of glycoproteins by regenerating liver and the sialyltransferase activity of microsomal fraction after partial hepatectomy is discussed.     

Disulfide reductase activity in mouse regenerating liver

Fourteen hours after partial hepatectomy there was a decrease in basal disulfide reductase and glutathione reductase activity in cytosole fraction of proliferating hepatocytes. In nuclear fraction, the activation effect of cAMP and cGMP on the disulfide recovery was replaced by inhibition. Meanwhile the activity of glutathione reductase noticeably increased. Forty-five hours after operation disulfide reductase activity of cytosole appreciably rose during maximal mitotic activity of the regenerating liver. The data obtained provide evidence in favor of the involvement of disulfide reductase enzymes into reparative regeneration of the liver.     

Intralobular distribution of albumin synthetic activity in the hepatocytes of the normal and regenerating mouse liver

Immunolocalization of albumin was investigated in normal and regenerating adult mouse liver after perfusion fixation with saponin. Light and electron microscopy have demonstrated that in normal liver the intralobular activity of albumin synthesis was distributed along the gradient decreasing from the portal tract to central vein. The uniform intensive staining of all hepatocytes was observed in regenerating liver. In addition, albumin synthesis was expressed in the epithelial cells of portal bile ducts.     

Diamine oxidase activity induction in regenerating rat liver

The synthesis and turnover of diamine oxidase (EC 1.4.3.6) activity was studied in regenerating rat liver after partial hepatectomy using inhibitors of protein and RNA syntheses. The administration to animals of cycloheximide or actinomycin D prevented the increase in diamine oxidase activity normally observed during the first hours after hepatectomy. The study of the turnover rate of diamine oxidase with cycloheximide demonstrated that the half-life of this enzyme was about 15 h in normal and regenerating liver. These results suggest that the rise in diamine oxidase activity in regenerating rat liver was due to the synthesis of new enzyme rather than to a lengthening of its turnover.     

The activity of gamma-glutamyltranspeptidase in regenerating rat liver

gamma-Glutamyltranspeptidase is expressed at low levels in the liver of the male Fischer 344 rat where it exhibits 15-fold purification and 33% recovery in isolated plasma membranes. While the activity of the enzyme is unaltered in regenerating liver 24 h after partial hepatectomy, it increases steadily thereafter over a period of one week. Seven days after partial hepatectomy the enzyme is maximally activated: 5.6-fold in liver homogenates and 5.3-fold in isolated liver plasma membranes. The enzyme declines in activity over the next fourteen days and is expressed at normal levels three weeks after partial hepatectomy. These results demonstrate that the activity of gamma-glutamyltranspeptidase increases in regenerating liver but that the increase is out of phase with the proliferative response.     

Thymidine triphosphate dephosphorylating activity in regenerating rat liver

The enzyme activity of dephosphorylation of thymidine triphosphate was found in microsomal fraction of rat liver. The enzyme activity decreased at the time when [³H]thymidine incorporation into DNA of regenerating liver increased. When the [³H]thymidine incorporation was suppressed by 1,3-diaminopropane, the enzyme activity remained elevated. These results suggest that the enzyme activity appears to be closely linked to DNA synthesis.     

Adenosine aminohydrolase activity in the regenerating rat liver

The specific activity of adenosine aminohydrolase in the regenerating rat liver is significantly increased 12 h after partial hepatectomy. There is a twofold increase in enzyme activity at 48 h, after which the activity begins to decline. However, increased values still persist 7 days postsurgery. The enzyme is located mainly in the soluble supernatant (90-95%) of the cell. The purified enzyme from 48-h regenerating liver and control liver has similar kinetic properties (Km 54-58 microM for adenosine), similar molecular weights (30,000-35,000), and are equally inhibited by an irreversible transition-state analog and a reversible competitive inhibitor. It is concluded that adenosine aminohydrolase in regenerating liver is an integral component of a salvage pathway designed for the reutilization of nucleotides, and thus helps maintain a "growth state" for the regenerating liver.     

Inhibition of ornithine decarboxylase activity and spermidine accumulation in regenerating rat liver.

Injections of 1,3-diaminopropane, a close structural analogue of putrescine (1,4-diaminobutane), into partially hepatectomized rats powerfully inhibited ornithine decarboxylase (EC 4.1.1.17) activity in the regenerating liver in vivo. The compound did not have any effect on the enzyme activity in vitro (under assay conditions employed) but appeared to exert an inhibitory influence on the synthesis of ornithine decarboxylase itself.Repeated injections of diaminopropane into rats after partial hepatectomy, starting at the time of the operation and continued until 33 h postoperatively, markedly diminished the stimulation of ornithine decarboxylase activity in the regenerating liver remnant, and completely prevented the increases in hepatic spermidine concentration normally occurring in response to partial hepatectomy.Treatment of the rats with diaminopropane did not depress the activity of adenosylmethionine decarboxylase (EC 4.1.1.50) in the regenerating liver. Nor did the compound have any effect, whatsoever, on the activity of spermidine synthase (EC 2.5.1.16) in vitro, thus obiviously proving that the increased accumulation of liver spermidine after partial hepatectomy primarily depends upon a stimulation of ornithine decarboxylase activity and a concomitant accumulation of putrescine. The results also showed that 1,3-diamino-propane could not replace putrescine in the synthesis of higher polyamines in rat liver. The inhibition of ornithine decarboxylase by diaminopropane thus appears to represent “gratuitous” repression of polyamine biosynthesis and might conceivably be used for studies devoted to the elucidation of the physiological functions of natural polyamines.     

Length-tension relationships are altered in regenerating muscles of the rat after bupivacaine injection.

Intramuscular injection of bupivacaine causes complete degeneration of fibers in extensor digitorum longus (EDL) muscles of rats, followed by complete regeneration within 60 days. Previous studies have shown that regenerated EDL muscles are protected from contraction-induced injury 60 days after bupivacaine injection. It is possible that these regenerated muscles have altered length-tension relations because of fiber remodeling. We tested the hypothesis that length-tension relations are different in bupivacaine-injected and noninjected control muscles. EDL and soleus muscles of the right hindlimb of deeply anesthetized rats were injected with bupivacaine and then allowed to recover for 7, 14, 21, or 60 days (7D, 14D, 21D, 60D), and isometric contractile properties were assessed. Muscles of the contralateral limb were not injected and served as control. EDL muscles recovered from bupivacaine injection more rapidly than soleus muscles, with mass restored to control levels at 21D, and isometric tetanic force (P(o)) restored to control at 60D. In contrast, mass and P(o) of injected soleus muscles was not restored to control even at 60D. In 7D EDL muscles, length-tension curves were shifted leftward compared with control, but in 21D and 60D EDL muscles length-tension curves were right shifted significantly (treatment x muscle length: P < 0.001). Although no clear shift in the position of the length-tension curve was observed in regenerating soleus muscles, force production was enhanced on the descending limb of the curve in 60D soleus muscles (treatment x relative muscle length: P < 0.01). The rightward shift in the length-tension curve of EDL muscles 60 days after bupivacaine injection is likely to contribute to the mechanism for their previously observed protection from contraction-induced injury.     

Changes in the activity of matrix metalloproteinases in regenerating rat liver after CCl4-induced injury

Molecular mechanisms involved in mediating alteration in cell matrix interaction have been examined by studying the changes in the activity of matrix metalloproteinases (MMPs) in CCl4-induced regenerating liver, using zymography and ELISA. Activity of MMPs (72 kD, 92 kD and 130 kD gelatinases) in the rat liver increased progressively during acute injury till the 4th day and then decreased to near normal level after CCl4 administration (0.5 ml/100 g body wt.) on the 6th day. Hepatocyte lysate of injured liver on the 4th day showed significantly higher levels of MMP2 and MMP9 compared to the control. In the culture medium of hepatocytes, the levels of MMP2 and MMP9 increased progressively with the duration of culture, indicating that hepatocytes are the major source of these MMPs in regenerating liver. These results suggest an involvement of MMPs in matrix degradation and remodeling during regeneration after acute liver injury induced by CCl4.     

Changes in the proliferative activity of the corneal epithelium and the regenerating liver in partial splenectomy in mice

The mitotic activity in epithelial cells of the mouse cornea was studied 4 h, 1, 2, 5, 8 and 14 days after a sham operation or partial (2/3) splenectomy. The decrease in the number of dividing cells in the corneal epithelium was observed within two days after a sham operation and within five days after partial splenectomy. On the contrary, partial hepatectomy increased the number of mitoses in the corneal epithelium. Liver regeneration against the background of a sham operation or partial splenectomy was accompanied by a lesser number of mitoses (by a factor of 2.5-4) in hepatocytes than in the animals subjected to partial hepatectomy only.