RBC and plasma distribution changes in cat mesenteric microvessels after hemorrhage and reinfusion

The mesenteries of ten cats (0.6 kg) anesthetized with Dial-urethane were exposed and studied using fluorescence television microscopy. Femoral artery pressure was determined. FITC-dextran, the plasma label, or DTAF-labeled red cells (DTAF-RBCs) were injected as a bolus (0.005 ml in 0.5 sec) into a small branch of the mesenteric artery. Animals were hemorrhaged from the left femoral artery into a reservoir. Control mean arterial pressure averaged 100 +/- 2 mmHg and decreased to 84 +/- 1 mmHg subsequent to an average bled volume of 13 ml/kg. Time-concentration curves were recorded from videotape recordings of the passage of indicator by videodensitometry. Following hemorrhage, arteriolar (N = 134) FITC-dextran mean transit time (t) was increased significantly to 194 +/- 10% of control, while t for DTAF-RBCs increased significantly to 211 +/- 10% of the control value. In the venules (N = 180) hemorrhage significantly increased FITC-dextran t to 197 +/- 9% of control while venular DTAF-RBC t was significantly increased to 182 +/- 5% of control. Arteriolar t was significantly lower for DTAF-RBC than for FITC-dextran during the control period and following reinfusion. Following hemorrhage, arteriolar t for DTAF-RBCs was not different from that for FITC-dextran. Venular values were significantly lower for DTAF-RBCs than FITC-dextran during all three periods. Dispersion was increased (reduced ta/t) by hemorrhage in arterioles and venules. The elevated t after hemorrhage would appear to be the result of increased peripheral resistance and resulting reduced flow velocity through the circuits. The absence of a difference in arteriolar t between the two indicators post-hemorrhage would indicate reduced Fahraeus effects owing to reduced blood flow velocity and perfusion pressure.