In vivo effects of prostacyclin on segmental vascular resistances, on myogenic reactivity, and on capillary fluid exchange in cat skeletal muscle

Abstract

To analyze the local circulatory effects of prostacyclin in skeletal muscle.

A prospective experimental study.

A university laboratory.

Twelve adult cats.

The study was performed on autoperfused, sympathectomized gastrocnemius muscle.

Arterial blood flow, total and segmental vascular resistances (arterial vessels of >25 micro meter, arterioles of <25 micro meter, and veins), hydrostatic capillary pressure, tissue volume, myogenic reactivity, and the capillary filtration coefficient were followed. The capillary filtration coefficient reflects the functional capillary fluid exchange area. Myogenic reactivity was evaluated as the arteriolar resistance increase after a standardized decrease in extravascular pressure. Arterial infusion of prostacyclin decreased vascular resistance by approximate 50% at the highest dose given (500 ng/kg/min). This effect was more pronounced on the arterial side, especially in arterial vessels of >25 micro meter. Hydrostatic capillary pressure increased by 1.9 +/- 0.3 mm Hg, causing fluid filtration. The relative fluid filtration was less than that value shown for some other vasodilator drugs (isoprenaline, calcium-channel blockers, thiopental) in this muscle preparation. Capillary filtration coefficient decreased by 25%. Myogenic reactivity was depressed but to a lesser extent than previously observed for other vasodilator mechanisms (muscle exercise, beta-adrenergic receptor stimulation, thiopental infusion, nifedipine infusion).

Prostacyclin is a vasodilator, both on the arterial and venous side, that restricts the increase in hydrostatic capillary pressure. The decrease in capillary filtration coefficient most likely reflects a decrease in capillary permeability, explaining the smaller relative filtration rate. The relatively well-preserved myogenic reactivity may imply a better preserved microvascular flow distribution and peripheral oxygen uptake.