TRAPPED BLOOD ELEMENTS WITHIN THE DECIDUA OF THE RAT PREGNANT UTERUS GENERATE A LIPOXYGENASE PRODUCT(S) WHICH INHIBITS MYOMETRIAL PROSTACYCLIN SYNTHESIS

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Abstract
1 Prostacyclin (PGI2) production by chopped segments of rat pregnant uterus was low compared with synthesis by separated myometrial tissue. Incubation of separated myometrium with decidua (2:1 by weight) led to an inhibition of myometrial PGI2 output. 2 Boiling decidual tissue abolished the inhibitory influence on myometrial PGI2 output. Preincubation of decidua with 5, 8, 11, 14-eicosatetraynoic acid (ETA) (30 m̀g/ml) also suppressed decidual inhibitory activity but indomethacin (30 m̀g/ml) was ineffective. 3 Incubation of decidual and myometrial tissue with arachidonic acid (AA) 10m̀g/ml did not increase the inhibition of myometrial PGI2 synthesis, even if the decidua were pre-incubated with indomethacin. 4 Myometrial PGI2 production was reduced if the chopped tissue was pre-incubated with soya bean lipoxidase for 10 min at 4°C. This reduction was reversed if the lipoxidase was incubated with ETA (30°g/ml) for 30 min at 37°C before addition to the myometrial tissue. 5 Perfusion of the uterus to remove blood elements removed the inhibitory action that the decidua exerted upon myometrial PGI2 production. PGI2 synthesis by separated decidual and whole uterine tissue was markedly elevated. 6 The addition of rat blood platelets (0.75 × 109/ml) to incubations of perfused decidual tissue reduced PGI2 output and restored the inhibitory action that the decidua exerted on myometrial PGI2 synthesis. 7 It is concluded that a lipoxygenase enzyme contained in blood platelets trapped within the decidual vasculature produces a hydroperoxy acid which inhibits decidual PGI2 production or myometrial PGI2 synthesis when the tissues are incubated together. It is suggested that perfusion is a pre-requisite before study of PGI2 synthesis in highly vascularised tissues. 8 The pathophysiological importance of such platelet lipoxygenase products is discussed.