NONINVASIVE QUANTIFICATION OF ORGAN DAMAGE

Quantitative evaluation of organ damage can be achieved by non-invasiv e, direct or indirect methods. Direct methods include echography, tomo graphy, scintigraphy and magnetic resonance. The accuracy of these ima ging techniques has been demonstrated in human medicine. Most of them have not been validated in animals: however, and their use is limited by cost. Indirect methods are based on determination of the total rele ase of intracellular markers (mainly enzymes) into body fluids. Quanti fication of organ damage depends on extracellular disposition of the m arker. Thus, in the kidney, the marker is directly and totally leaked into the urine and is voided at each micturition. The amount of marker eliminated in this way allows easy quantification of organ damage occ urring during the period preceding the micturition. Muscle markers wit h molecular weights exceeding 50 kDa reach the blood via the lymph. Th is results in (a) partial inactivation, (b) delay between cell damage and increased plasma concentration and (c) accumulation in the plasma as long as delivery into the plasma exceeds clearance. In such cases, quantitative evaluation requires pharmacokinetic tools and calculation of the area under the curve (concentration vs time) and of the plasma clearance. Comparison of the intensity and chronology of markers loca ted in different cell compartments may contribute to the understanding of pathophysiological events.