Hyperammonaemia without portal systemic shunting does not resemble hepatic encephalopathy

Ammonia-mediated LTP inhibition: effects of NMDA receptor antagonists and L-carnitine

Because hyperammonemia is thought to contribute to the pathogenesis of hepatic encephalopathy, we examined the effects of ammonia on ATP levels, neuronal morphology, and synaptic function in rat hippocampal slices. Although ammonia did not alter ATP levels supported by 10 mM glucose, ammonia significantly depressed ATP levels in the presence of 3.3 mM glucose or 10 mM pyruvate, suggesting effects on respiratory energy metabolism. Ammonia also impaired synaptic function and neuronal integrity sustained by pyruvate. In 10 mM glucose, ammonia inhibited the induction and maintenance of long-term potentiation (LTP) in a concentration-dependent fashion. These inhibitory effects of ammonia were overcome by L-carnitine. DL-APV, an antagonist of NMDA receptors, also diminished the effects of ammonia on ATP levels and LTP induction, indicating that ammonia impairs neuronal function via altered metabolism and untimely NMDA receptor activation. These results suggest that L-carnitine and NMDA receptor antagonists have the potential to preserve neuronal function during hyperammonemia.

Diagnosis and Monitoring of Hepatic Injury. I. Performance Characteristics of Laboratory Tests

Purpose: To review information on performance characteristics for tests that are commonly used to identify acute and chronic hepatic injury.

Data Sources and Study Selection: A MEDLINE search was performed for key words related to hepatic tests, including quality specifications, aminotransferases, alkaline phosphatase, γ-glutamyltransferase, bilirubin, albumin, ammonia, and viral markers. Abstracts were reviewed, and articles discussing performance of laboratory tests were selected for review. Additional articles were selected from the references.

Guideline Preparation and Review: Drafts of the guidelines were posted on the Internet, presented at the AACC Annual Meeting in 1999, and reviewed by experts. Areas requiring further amplification or literature review were identified for further analysis. Specific recommendations were made based on analysis of published data and evaluated for strength of evidence and clinical impact. The drafts were also reviewed by the Practice Guidelines Committee of the American Association for the Study of Liver Diseases and approved by the committee and the Association’s Council.

Recommendations: Although many specific recommendations are made in the guidelines, some summary recommendations are discussed here. Alanine aminotransferase is the most important test for recognition of acute and chronic hepatic injury. Performance goals should aim for total error of <10% at the upper reference limit to meet clinical needs in monitoring patients with chronic hepatic injury. Laboratories should have age-adjusted reference limits for enzymes in children, and gender-adjusted reference limits for aminotransferases, γ-glutamyltransferase, and total bilirubin in adults. The international normalized ratio should not be the sole method for reporting results of prothrombin time in liver disease; additional research is needed to determine the reporting mechanism that best correlates with functional impairment. Harmonization is needed for alanine aminotransferase activity, and improved standardization for hepatitis C viral RNA measurements.