Prostaglandin B2-induced pulmonary hypertension is mediated by TxA2/PGH2 receptor stimulation

We investigated whether the physiological effects of prostaglandin B2 (PGB2) in the pulmonary circulation might be due to stimulation of thromboxane A2-prostaglandin H2 (TxA2/PGH2) receptors. In seven anesthetized rabbits, intravenous infusion of PGB2 (5.0 micrograms/kg) caused pulmonary hypertension as evidenced by increases in right ventricular systolic blood pressure. The magnitude of the pulmonary hypertension was comparable to that observed after infusion of the TxA2 mimetic U-46619 at a significantly lower dose (0.5 micrograms/kg), indicating that the effects of PGB2 in the intact animal are similar to TxA2 but less potent. Additionally, the TxA2/PGH2-receptor antagonist SQ-29548 blocked the pulmonary blood pressure responses elicited by PGB2. Receptor-binding studies using the TxA2 receptor ligand [3H]SQ-29548 indicated that PGB2 was a potent competitor for TxA2/PGH2 receptor binding. In agreement with the results from the intact animal, however, the efficacy of inhibition with PGB2 was significantly less than that measured for the TxA2 agonist U-46619. All of these results are consistent with the hypothesis that the physiological effects of PGB2 are mediated by stimulation of TxA2/PGH2 receptors.