Effects of perfusion pressure during flushing on the viability of the procured liver using noninvasive fluorometry

The influence of perfusion pressure and flow rate on hepatic cellular viability was investigated in the procured liver using noninvasive pyridine nucleotide fluorometry, in relation to other metabolic indices such as nicotinamide adenine dinucleotide (NAD) concentration, adenine nucleotides, tissue ketone bodies, and mitochondrial phosphorylative activity. Rat liver was perfused at a controlled flow rate through the portal vein with a nonrecirculating open-end-design perfusion system driven by a roller pump using cooled oxygenized Euro-Collins' solution. The maximum pressures (mean pressure in parentheses) of experimental groups were 8 (5) mmHg, 15 (9) mmHg, 40 (25) mmHg, 80 (50) mmHg, 120 (73) mmHg, 240 (152) mmHg. The amplitude between oxidation and reduction levels (RxA) in the fluorometric trace, and the gradient or velocity of the trace curve from oxidation to reduction (RxV) were determined by the measurement of fluorescence from NAD phosphate, reduced form (NADPH) using a new fluorometric device. Other metabolic indices were measured after attainment of a fully oxygenated state. RxA decreased in accordance with the increase of pressure. Similar results were obtained in the changes of NAD concentration, total adenine nucleotides, and total tissue ketone bodies, possibly due to the wash-out of these metabolites. RxV decreased in inverse proportion to the increase of pressure. There were close positive correlations between RxV and tissue ketone body ratio (acetoacetate/3-hydroxybutyrate) (r = 0.793, less than 0.01), RxV and respiratory control ratio in isolated mitochondria (r = 0.617, P less than 0.05), RxV and state 3 respiration (r = 0.792, P less than 0.01), and RxV and phosphorylation rate (r = 0.833, P less than 0.01). These results suggest that perfusion pressure and flow rate can easily deteriorate the energy metabolism of the procured liver, and that the gravity-induced hydrostatic pressure presently used in procurement perfusion should be reevaluated on the basis of energy metabolism.