A comparison of micro- and macrocirculation of the isolated rat mesentery preparation

To allow a comparison of microcirculatory perfusion and whole organ blood flow, pressure-flow curves were established in the isolated rat mesentery preparation at two different hematocrit values (5%; 35 +/- 4%). Besides whole organ volume flow, red blood cell (RBC) flow velocity in capillaries of the mesentery membrane, and RBC-flux in fat tissue along the mesentery arteries as well as in small intestine were simultaneously measured. The arterio-venous pressure difference over the tissue was varied from 20-100 mmHg (2.7-13.3 kPa). It could be shown, that the pressure-flow curves in the mesentery membrane as well as in fat demonstrate autoregulation over a pressure range of 30-70 mmHg (4-9.3 kPa), whereas flow through the small intestine and whole organ responded passively to pressure changes. At constant pressure differences an increase in hematocrit value from about 5% to 35 +/- 4% reduced whole organ blood flow as well as flow velocity in capillaries of the mesentery membrane by 50% over the pressure range applied. It is concluded that in a heterogeneous tissue like the isolated rat mesentery preparation the pressure-flow-relationship in tissue components with a low flow fraction might be disparate from that of the whole organ volume flow. Furthermore, despite differences in the pressure flow relationship for the whole and microcirculation, a changed blood viscosity can be quantified in both circulations.