The metabolism of lignocaine to monoethylglycinexylidide has been found useful as an indicator of hepatic function in association with liver transplantation. It has been postulated that this might be due to the common effect of hypoxic damage on liver function and lignocaine metabolism. The aim of this work was to establish whether hepatic lignocaine elimination was impaired by hypoxia and whether lignocaine extraction ratio and clearance could be used as an indicator of hepatic function. This was studied using the isolated pig liver perfused via the hepatic artery and portal vein. To establish whether the pig liver could be used as a possible human model for this investigation and whether lignocaine had any detrimental effects on liver function and blood flow in vivo, hepatic lignocaine elimination and the effects of lignocaine administration on hepatic function and blood flow were studied in the anaesthetized pig, surgically prepared to allow sampling across the liver and direct hepatic blood flow measurement. Hepatic lignocaine elimination was then studied in the isolated perfused liver to determine whether this was similar to that found in vivo. The definitive studies required preliminary investigations not available from the literature to determine the feasibility of comparing in vivo and ex vivo hepatic function using the same liver. In addition, by studying the decay of lignocaine after bolus dose administration the necessary pharmacokinetic parameters to achieve similar constant hepatic affluent lignocaine concentrations in vivo and in the isolated preparation could be determined. The preliminary investigations showed that a sequential experiment using the same liver to compare in vivo and ex vivo function was inappropriate as the energy state of isolated perfused livers previously studied in vivo was significantly different from that in livers perfused immediately. The decay of lignocaine after a bolus dose in vivo and ex vivo could be described by a two-compartment open model and in both preparations the derived pharmacokinetic parameters from this analysis were used to achieve similar constant hepatic affluent concentrations over the study period used to determine hepatic lignocaine elimination. Lignocaine extraction ratio by the in situ pig liver was similar to that reported in man and together with hepatic clearance and intrinsic clearance was similar to that determined in the isolated state when different livers were used for this comparison. There was no detrimental effect of lignocaine administration on hepatic function and blood flow In vivo. Lignocaine extraction ratio and clearance and monoethylglycinexylidide formation were significantly impaired in livers subjected to hypoxia. Lignocaine elimination correlated strongly with hepatic cellular ATP, energy charge and ATP/ ADP ratio as well as with hepatic potassium release but less strongly with aspartate aminotransferase release when this relationship was tested using the combined data from hypoxic and normoxic livers ex vivo. These correlations were positive for hepatic adenine nucleotide status and negative for hepatic potassium and aspartate aminotransferase release. Neither hepatic alanine aminotransferase release nor lactate utilization were significantly affected by hypoxia. Lignocaine extraction ratio, hepatic oxygen consumption, ATP content, bile flow and potassium release were shown to be equivalent, more highly sensitive, and earlier indicators of hypoxic hepatic injury than hepatic aspartate aminotransferase release in the isolated perfused pig liver.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/27152 |
| Date | January 1992 |
| Creators | Mets, Berend |
| Contributors | Folb, Peter I, Hickman, Rosemary |
| Publisher | University of Cape Town, Faculty of Health Sciences, Division of Clinical Pharmacology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Doctoral Thesis, Doctoral, PhD |
| Format | application/pdf |
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