Arterial and intestinal venous blood were sampled every hour for measurement of thromboxane B2 (TXB2) and 6-keto-PGF1 alpha, stable metabolites of thromboxane A2 and prostacyclin, respectively, in dogs subjected to hemorrhagic hypotension at 32.8 +/- 1.4 mm Hg for 3 h, followed by reinfusion of the remaining shed blood. Control dogs were treated alike without hypotension. Arterial and intestinal venous TXB2 significantly increased during hypotensive and post-transfusion periods, the venous concentration being significantly higher than the corresponding arterial. The arterial and venous 6-keto-PGF1 alpha increased during hypotension but decreased during post-transfusion periods. Furthermore, arterial and venous TXB2 to 6-keto-PGF1 alpha concentration ratio increased. Intestinal TXB2 release (blood flow X arteriovenous concentration difference) increased progressively, whereas 6-keto-PGF1 alpha release decreased. No significant changes occurred in the control dogs. This study shows an imbalance in intestinal production and release of TXA2 and PGI2, in favor of TXA2 during severe hemorrhagic hypotension and after blood transfusion. The imbalance may contribute to the development of irreversible hemorrhagic shock and reperfusion injury.