Effects of prostaglandins E2, I2 and F2 alpha, arachidonic acid and indomethacin on pressor responses to norepinephrine in conscious rats.

The effects of prostaglandins E2 (PGE2), I2 (PGI2) and F2 alpha (PGF2 alpha), arachidonic acid and indomethacin on pressor responses to norepinephrine were examined in conscious rats. Intravenously infused PGE2, (0.3, 1.25 micrograms/kg/min), PGI2 (50, 100 ng/kg/min), PGF2 alpha (1.8, 5.4 micrograms/kg/min) and arachidonic acid (0.7, 1.4 mg/kg/min) did not change the basal blood pressure. Both PGE2 and PGI2 significantly attenuated pressor responses to norepinephrine, whereas PGF2 alpha significantly potentiated them. Arachidonic acid, a precursor of the prostaglandings (PGs), significantly attenuated pressor responses to norepinephrine. Since the attenuating effect of arachidonic acid was completely abolished by the pretreatment with indomethacin (5 mg/kg), arachidonic acid is thought to exert an effect through its conversion to PGs. On the contrary, intravenously injected indomethacin (0.2--5.0 mg/kg) facilitated pressor responses to norepinephrine in a dose-related manner without any direct effect on the basal blood pressure. These results suggest that endogenous PGs may participate in the regulation of blood pressure by modulating pressor responses to norepinephrine in conscious rats.