Abstract: The action of prostaglandins on the vascular smooth muscle but not on the blood itself is well established. The present study evaluates possible effects of the prostaglandins (PGs) D2, E1, E2, F1α, F2α and of the I2 analogue Iloprost®on blood flow properties. To get insight mto the mode of action of the compounds their effects on different hemorheological parameters were measured under physiological conditions. In no case an effect on plasma viscosity could be seen; in the presence of PG D2, F1α and F2α no effect at all was observerd. With PG E2, however, the erythrocyte filtrability and the elastic component of the visco-elasticity decreased, while the erythrocyte aggregation increased. The opposite was seen as well in whole blood, run with PG E1, as in platelet- and leucocyte-depleted blood, run with Iloprost®. A similar or identic side of action is assumed for the effective compounds. Noteworthly these agents did not show typical sigmoid shaped dose-efficacy dependencies. They rather exerted their hemorheological actions with the extraordinary low doses of 10−11 resp. 10−9 mol/l and were effective over a concentration range of 2 - 3 decimal places only. The over all subtle effects utmostly were deviations of the controls about 5 - 10 %. These features are suggestive of semaphores without any therepeutic actions on the erythrocyte fluidity.
