MYOCARDIAL TISSUE HEMATOCRIT - EXISTENCE OF A TRANSMURAL GRADIENT ANDALTERATIONS AFTER FIBRINOGEN INFUSIONS

Tissue hematocrit was determined in left ventricular myocardium slices in in situ frozen rat hearts and the influence of experimental plasma fibrinogen increments was investigated. Hematocrit values in 100 mu m thick myocardial slices were estimated by measuring the activity of t wo different radionuclides labelling plasma (I-125-Albumin) and red bl ood cells (Tc-99m). In the control group with physiological levels of fibrinogen, myocardial tissue hematocrit was highest at the layer adja cent to epicardium. It decreased linearly through the depth of myocard ium, approaching a minimum at the myocardial layer closest to the endo cardium. In the group with about two folds higher plasma fibrinogen co ncentration, plasma viscosity and red blood cell aggregation were abou t 50% higher. In this group, tissue hematocrit difference between epic ardial and endocardial layers existed, however this difference was mor e likely due to a step change, rather than a linear gradient. These fi ndings confirm those physiological mechanisms underlying the hematocri t reduction in small blood vessels might be affected by hemorheologica l alterations.