Mesenteric lymphatic vasomotion following hemorrhage and retransfusion in the rat

The effect of hemorrhage and retransfusion on the rhythmic contraction of mesenteric lymphatic vessels was studied in 24 rats, anesthetized with pentobarbital. The rats were divided into four groups according to the amount of blood withdrawn: 0.5ml/100g body weight (BW), 1ml/100g, 2ml/100g, and 2.5ml/100g. Immediately following hemorrhage at the rate of 0.5ml/100g/min, lymphatic contraction frequencies were decreased to 67 +/- 12.5, 45 +/- 24.7, 43 +/- 33.1, and 31 +/- 17.8% of the prehemorrhage values in each of the above four groups, respectively (p less than 0.01). Twenty minutes after hemorrhage, lymphatic contraction frequencies were decreased to 70 +/- 17.2, 46 +/- 36.8, and 34 +/- 41.3% in the 0.5ml/100g, 2ml/100g, and 2.5ml/100g, respectively (p less than 0.05). Immediately following hemorrhage, the lymphatic contracted diameters were also reduced to 77 +/- 9.7 and 61 +/- 9.0% of the prehemorrhage values in the 1ml/100g and 2.5ml/100g groups, respectively (p less than 0.01). Twenty minutes after hemorrhage, all withdrawn blood was reinfused. Lymphatic contraction frequency and contracted diameter recovered after retransfusion in each group but 20 minutes after retransfusion, the lymphatic contraction frequency in the 2ml/100g group was still decreased to 42 +/- 30.3% (p less than 0.01). Lymphatic contraction frequency not only decreased proportionately with hypotension during hemorrhage but after retransfusion contraction frequency correlated directly with the mean arterial pressure 20 min after hemorrhage. These data suggest that mean arterial pressure and by inference capillary blood flow and tissue oxygenation are major factors regulating lymphatic vasomotion.