Haemostatic mechanism in the endometrium: role of cyclo-oxygenase products and coagulation factors.

1. The primary mechanism of haemostasis in the endometrium of rat was studied and results were compared to that in the mesenteric artery. 2. The bleeding time of the rat endometrium as assessed by haemoglobin output was significantly decreased after pretreatment of the animals with either indomethacin (5 mg kg-1, i.v.) or meclofenamate (3 mg kg-1, i.v.) whereas the bleeding time was significantly increased in the rat mesenteric artery. 3. The bleeding time of the rat endometrium was unchanged from control values following treatment with prostacyclin (0.5 microgram kg-1 min-1, i.v.) or 1-benzylimidazole (50 mg kg-1, i.v.) whereas the bleeding times were increased in the rat mesentric artery. 4. Administration of heparin (100 units kg-1) increased the bleeding time in the rat mesenteric artery but had no effect on the bleeding time of the endometrium. 5. Superfusion of the endometrium with 16, 16-dimethyl PGE2 (1 microgram ml-1) a vasodilator, increased the bleeding time of the endometrium but superfusion of PGE2 over the mesenteric artery did not affect the bleeding time from this site. 6. Histological studies of the mesenteric artery and the endometrium following haemostatis revealed that the haemostatic plug in the mesenteric artery was mainly composed of platelets and fibrin whereas in the endometrium it was mainly composed of fibrin. 7. These findings suggest that haemostasis in the endometrium may be mediated by the vascular tone and fibrin whereas formation of the platelet plug may be primary mechanism for haemostasis in the mesenteric artery.