Effects of sustained lymph drainage on cardiovascular function and thoracic duct lymph in sheep

We studied the effect of lowering the plasma protein concentration on the cardiovascular function and thoracic duct lymph in awake adult sheep. Hypoproteinemia was induced in seven nonpregnant, splenectomized sheep by drainage of the thoracic duct lymph over a 5-day period. The plasma protein went from a mean of 6.4 ± 0.2 (SE) to 4.9 ± 0.2 g/dl on day 5, and the lymph-to-plasma protein concentration ratio decreased from 0.74 ± 0.01 on day 1 to 0.48 ± 0.04 on day 5. The percentage composition of the protein fractions in plasma and lymph remained unchanged. Lymph flow was 1.79 ± 0.37 and 1.28 ± 0.10 ml/min for days 1 and 5, respectively. Renin concentration in plasma increased 50-fold by day 5. Arterial pressure fell from 102.9 ± 5.4 to 72.7 ± 4.4 mmHg by day 5. Mean hematocrit was 28.9 ± 1.7 at day 1, which was not significantly different than 24.6 ± 2.9 at day 5 and indicated that the plasma volume did not decrease. Body weight also did not change significantly. There was a decrease in the transcapillary protein escape rate, determined as the thoracic lymph flow rate multiplied the lymph protein concentration, that suggests adaptations in the microcirculation to decrease vascular-to-interstitial protein transfer during hypoproteinemia. Hypoproteinemic animals also demonstrated greater vascular retention of a fluid volume challenge. In conclusion, the sheep adaptations to sustained hypoproteinemia produced by lymph drainage were a significant decrease in arterial pressure, large increases in vascular compliance and renin concentration, and reduced transcapillary escape rate of protein. These adaptations may act together to maintain circulatory volume during a reduced plasma colloid osmotic pressure.