Prostacyclin production in whole blood throughout normal pregnancy.

In a longitudinal study of twelve normal pregnant women the base-line plasma values of 6-keto prostaglandin (PG)F1 alpha, the stable degradation product of prostacyclin, were determined. At the same time the capacity of their blood to produce prostacyclin was assessed using a stimulation test. When collagen is added to citrated whole blood there is a prompt rise in plasma 6-keto PGF1 alpha, which results from the synthesis of prostacyclin by leukocytes. These cells use cyclic endoperoxides in part coming from activated platelets and in part derived from endogenous substrate to produce prostacyclin. Both the base-line values and the capacity to produce prostacyclin fell significantly after 33 weeks of pregnancy. The decreased capacity to produce prostacyclin in the later stages of pregnancy may help account for the relatively diminished refractoriness to angiotensin II, characterizing the last two months of normal pregnancies.