Leslie Zieve

Pathogenesis of Hepatic Encephalopathy

METABOLIC ALTERATIONS IN HEPATIC FAILURE A multitude of changes in metabolic processes occurs with hepatic failure. It is therefore particularly important to distinguish between correlations and causes when considering the pathogenesis of hepatic coma. The etiology appears to be multifactorial. First, to be considered a causative factor, an abnormality must be consistently present when hepatic encephalopathy is present. Second, creation of the abnormality in experimental animals should cause coma, and correction of the abnormality in animals and humans should reverse the process of encephalopathy and coma. Unfortunately hypotheses have been promoted in the absence of data which fulfill the latter criteria. Of the many abnormalities that occur with hepatic failure, the only ones that have been shown unequivocally to cause coma in experimental animals or patients are an ,xcess of ammonia, methanethiol (or its derivative dimethylsulfide), fatty acids, phenols, and the development of hypoxia, hypoglycemia, hypovolemia, hypotension, or electrolyte depletion. A summary of the metabolic abnormalities that may be present during hepatic encephalopathy (HE) is given in Table I and the following. (1) Acid-base and electrolyte abnormalities are usually present before HE develops. They probably play an auxiliary role in the progression and outcome of the HE. The patient may have respiratory alkalosis, metabolic alkalosis, a mixed respiratory and metabolic alkalosis, or metabolic acidosis, depending upon the extent and duration of respiratory or electrolyte abnormalities (Zieve, 1962). The most common variant is the mixed respiratory and metabolic alkalosis. The root causes are central respiratory center stimulation and coexistent hypokalemia. It is unlikely that enhanced movement of NH[ into cells during alkalosis has any practical significance in the progression of HE (Zieve, 1982).

Influence of magnesium deficiency on the utilization of thiamine.

The observation1 of thiamine deficiency in malnourished patients who failed to respond to parenteral injections of thiamine, was the stimulus for the experiments to be reported. An attempt has been made to evaluate the effect of magnesium deficiency on the response of thiamine-deficient rats to repletion with thiamine. Nine groups of Holtzman female rats, eight to nine rats per group, were studied in the first experiment to be presented. Their average initial weight was 105 grams. The plan of the experiment is shown in FIGURE 1. Group 1 was a control group (C), which was observed for 31 days, as indicated by the horizontal line. Group 2 received the same diet as the controls except for the absence of thiamine. These thiamine-deficient (Td) rats were sacrificed on the 31st day when they were preterminal. Group 3 (Td4-T) were similar Td animals that received intraperitoneal injections of thiamine (as the hydrochloride) in five divided doses daily for one week before they were sacrificed. Group 4 (TdMd) received a diet deficient in both thiamine and magnesium for 31 days. Group 5 (TdMdi-T) were thiamineand magnesium-deficient rats that received thiamine as indicated before sacrifice. Group 6 (TdMd +TM) were thiamineand magnesium-deficient rats that received both thiamine and magnesium (as MgS04) before sacrifice. Group 7 (Md33) were animals on the magnesium-deficient diet for 33 days. Group 8 (Md59) were on the magnesiumdeficient diet for 59 days. Group 9 (S) were rats that received the control diet for 20 days, whereafter all food was taken away. They were sacrificed after seven days of starvation. A second set of rats that received 10% alcohol in the daily drinking water was studied similarly. This normally provides approximately 20% of calories as alcohol. The average initial weight of these animals was 136 grams. The diet of the magnesium-deficient animals contained 32 p g of magnesium per gram of diet, as compared to 950 pg per gram for the control and thiaminedeficient diets. The therapeutic doses of both thiamige and MgS04 were very large. Thiamine undoubtedly moved into the cell rapidly. Magnesium, by contrast, is known to penetrate the cell membrane slowly, and most of the magnesium given was probably excreted, only a small unknown fraction being available to the cell. The variables measured were growth, liver and whole blood transketolase activity, liver and whole blood thiamine and magnesium concentrations, liver nitrogen content and liver transaminase activity, both GOT and GPT. Transketolase is an enzyme of the pentose shunt which requires thiamine pyrophosphate and Mg2+ as cofactors. Its activity was measured as the amount of sedoheptulose formed per hour per ml of blood or per half-hour per gram dry weight of liver from a substrate mixture containing ribose-5-phosphate.2

Quantitative Estimation of Some Phosphatides and Their Hydrolysis Products by Thin Layer Chromatography.

Summary The use of thin layer chromatography for analyzing phosphatides and their hydrolysis products quantitatively is described and applied to the analysis of serum phosphatides. The results are similar to those obtained with silicic acid impregnated paper chromatography and column techniques, though the time for the analysis is markedly shortened.

Post-heparin phospholipase and post-heparin lipase have different tissue origins

Abstract Post-heparin phospholipase activity is reduced by 80% in the hepatectomized rat. In contrast, post-heparin lipase activity is unaffected by hepatectomy. Since the phospholipase originates mainly in the liver and the lipase originates entirely in extrahepatic tissues, these two activities must be different enzymes.

Secretion of pancreatic enzymes

SummaryPancreatic function in patients with portal cirrhosis was evaluated by measurement of the amount of amylase, lipase, phospholipase A, carboxypeptidase, trypsin, and chymotrypsin secreted into the duodenum during the 30-min. period after the onset of a simultaneous infusion of secretin and pancreozymin. The volume and bicarbonate concentration of the fluid were also measured. Enzyme secretion varied greatly. Approximately 40% of patients had abnormally low enzyme values and bicarbonate concentration. Those with severe cirrhosis had significantly poorer pancreatic function as reflected in secretion of enzymes. Intercorrelations among the several enzymes measured were significantly positive but not high, similar in all respects to those previously observed in patients without cirrhosis. In two-thirds of the patients with cirrhotic livers, the volume of duodenal aspirate obtained after infusion of secretin and pancreozymin exceeded the highest volume previously recorded in a sample of normal men. A low volume was observed in only 2 of 34 patients.

Action of methanethiol on membrane (Na+, K+)-ATPase of rat brain

Abstract The action of methanethiol (CH3SH) on rat brain (Na+, K+)-ATPase was examined. The results show that CH3SH acts at several sites on the enzyme system. The effects are characterized by an inhibition of the ATPase activity, but a concurrent stimulation of the associated K+-dependent phosphatase. The inhibitory effect of CH3SH was of an apparently mixed type with respect to the activation of the ATPase by Na+ or by ATP suggesting that CH3SH may inhibit the formation of phosphoenzyme intermediate in the ATPase reaction, and the inhibition may not be fully reversed by increasing Na+. Methanethiol inhibited the activation of the ATPase by K+ in an apparently uncompetitive manner, whereas it produced a competitive stimulation of the K+ activation of the K+-dependent phosphatase activity by increasing the affinity of K+ for the enzyme. There was no significant change in the apparent Km for the substrate p-nitrophenyl phosphate for the phosphatase activity. These effects of CH3SH may be relevant to its toxicity, and offer a possible molecular site of its action with implications for the encephalopathy of hepatic failure.

A benzodiazepine antagonist does not alter the course of hepatic encephalopathy or neural gamma-aminobutyric acid (GABA) binding.

The progressive course of hepatic encephalopathy developing in rats after massive hepatic ischemia due to hepatic artery ligation within 48 hr of a portacaval shunt was not altered by the injection of a benzodiazepine antagonist, CGS 8216, in a dose that was sufficient to reverse diazepam-induced coma quickly. The onset of hepatic coma was shortened 20 to 25% by the antagonist, rather than being delayed, as would be expected if hepatic coma were due to a γ-aminobutyric acid (GABA)-ergic effect. The neural binding of GABA by brains from rats in deep hepatic coma was unaffected by the injection of the benzodiazepine antagonist.

Ammonia toxicity: comparative protective effect of various arginine and ornithine derivatives, aspartate, benzoate, and carbamyl glutamate.

Ornithine and arginine compounds were highly effective in preventing an increase in blood ammonia and in preventing or minimizing encephalopathy after acute subcoma, comainducing, or lethal doses of NH4+. Similar protection was seen after subacute loading with glycine. Ornithine ketoacid derivatives were no more effective than ornithine alone or ornithine glutamate. Ornithine appeared to be a little more effective than arginine, but the differences were slight. Aspartate and glutamate alone were ineffective. Carbamyl glutamate was much less effective than either ornithine glutamate or arginine glutamate. Orotic acid excretion was markedly increased in the presence of excess NH4+. This increment was eliminated with ornithine or arginine, although the reduction with arginine was unpredictably erratic. Aspartate increased the orotic acid excretion and the amount of urea formed. Sodium benzoate was borderline in its effect on the blood ammonia and on orotic acid excretion.

Adenylate energy charge: Relation to guanylate energy charge and the adenylate kinase equilibrium constant

Abstract There is no functional cascade regulatory step between the adenylate energy charge and the guanylate energy charge in rat brain in vivo . In fact, the guanylate energy charge changes slower than the adenylate energy charge in phenobarbital, ether, ammonia, and insulin coma, in ischemia and in metrazol shock. It parallels the adenylate energy charge in fasting. The adenylate kinase equilibrium appears to be a good approximation to the normal in vivo distribution of the adenosine nucleotides and is thus useful in model studies.

Hepatic regenerative enzyme activity after pericentral and periportal lobular toxic injury

Pericentral and periportal liver injuries involving less than 50% of the parenchyma were produced with acetaminophen and allyl alcohol, respectively. Doses were selected to produce comparable peak serum malate dehydrogenase, sorbitol dehydrogenase, and SGPT activities. The regenerative response was assessed by serial measurements of hepatic thymidine kinase (TK) activity and ornithine decarboxylase (ODC) activity. The initial responses reflected in ODC activity were more or less similar. However, the ultimate regenerative response reflected by TK activity was almost three times as great after periportal injury as after pericentral injury, after allowing for differences in the extent of necrosis. Histologic examination also showed greater mitotic and tissue reparative responses after periportal injury. These results suggest that the concept of hepatocellular heterogeneity applies to the regenerative response of liver cells as well as the metabolic functions previously identified.