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 Q_L and the lymph/plasma L/P protein ratio to reflect transvascular fluid flux and changes in microvescular hydrostatic pressure, Pmv.

Unanesthetized sheep with prefemoral lymph fistulae were infused with PGI₂ (0.2 ug/kg/min) for two hours. Changes in Q_L and L/P were compared to animals in which P_mv was increased by volume loading. During PGI₂, Q_L was significantly increased, as was cardiac output while mean aortic pressure decreased. The UP ratio did not decrease to the degree seen with a comparable increase in Q_L, due to an increase in P_mv. The increase in Q_L was most likely due to an increase in microvescular surface area. Q_L remained significantly increased for several hours after infusion and L/P decreased to the same degree as seen with an increase in P_mv. This indicates that Pmv is increased for several hours in soft tissue after PGI₂ infusion, due to a relative increase in venous resistance probably secondary to activation of the renin-angiotensin system.