Response of the soft tissue microcirculation to prostacyclin infusion

We studied the effect of prostacyclin infusion on the soft tissue microcirculation. We used lymph flow QL and the lymph/plasma L/P protein ratio to reflect transvascular fluid flux and changes in microvascular hydrostatic pressure, Pmv. Unanesthetized sheep with prefemoral lymph fistulae were infused with PGI2 (0.2 microgram/kg/min) for two hours. Changes in QL and L/P were compared to animals in which Pmv was increased by volume loading. During PGI2, QL was significantly increased, as was cardiac output while mean aortic pressure decreased. The L/P ratio did not decrease to the degree seen with a comparable increase in QL, due to an increase in Pmv. The increase in QL was most likely due to an increase in microvascular surface area. QL remained significantly increased for several hours after infusion and L/P decreased to the same degree as seen with an increase in Pmv. This indicates that Pmv is increased for several hours in soft tissue after infusion, due to a relative increase in venous resistance probably secondary to activation of the renin-angiotensin system.