INVIVO EFFECTS OF ESCHERICHIA-COLI ENDOTOXEMIA ON DIAPHRAGMATIC MICROCIRCULATION IN RATS

We investigated the effects of Escherichia coli endotoxin administration on diaphragmatic microcirculation in rats by in vivo videomicroscopy. Rats were allocated into three groups: 1) intravenous inoculation of 10 mg/kg of E. coli endotoxin (group E, n = 25), 2) intravenous inoculation of sterile 0.9% NaCl (group C, n = 20), and 3) induction of a controlled hemorrhage by reducing the vascular volume via an arterial catheter (group H, n 15). Mean blood pressure (BP) and arteriolar diameters were measured at 15-min intervals and capillary perfusion pattern at 30-min intervals for 1 h. BP decreased similarly in groups E and H, whereas it was maintained in group C. Arterioles were classified as second (A2, n = 46), third (A3, n - 22), and fourth (A4, n = 21) order, according to their relative localization in the network. Basal diameters were the same in the three groups: 38.16, 17.33, and 6.80-mu-m in group C; 38.17, 17.41, and 7.04-mu-m in group E; and 37.82,19.19, and 6.99-mu-m in group H for A2, A3, and A4, respectively. During the observation period, a significant and similar vasoconstriction of A2 arterioles was observed in groups E and H but not in group C. By contrast, in the three groups, no significant changes in diameter were found for the A3 and A4 arterioles. Capillary perfusion was markedly impaired in group E: at 60 min the percentage of non-perfused capillaries was 40.92 +/- 6.65% in group E compared with 21.17 +/- 5.45% in group C (P < 0.05) and 18.18 +/- 8. 11% in group H (P < 0.05). We conclude that E. coli endotoxemia produces a marked in vivo effect on diaphragmatic microcirculation that is characterized by 1) a constriction of A2 diaphragmatic arterioles, which could be related to arterial hypotension, and 2) an impaired diaphragmatic capillary perfusion.