Decrease in arterial blood pressure in spontaneously hypertensive rats by the TXA2 receptor antagonist BM 13177 and...

The effects of the selective TXA2 receptor antagonist BM 13177 and of the cyclooxygenase inhibitor acetylsalicylic acid on blood pressure and heart rate were investigated in anaesthetized spontaneously hypertensive rats (SHR). After intravenous injection of BM 13177 (60 mg/kg) there was a strong short-lasting decrease in arterial blood pressure (BP) with a maximum reduction of 21.6% in the third minute after injection. The heart rate was only slightly decreased. The formation of TXB2 and 6-keto-PGF1 alpha in serum, aorta thoracica, renal medulla, and renal cortex, which was determined by radioimmunoassay, was not altered by BM 13177. Pretreatment with acetylsalicylic acid (100 mg/kg) attenuated the BM 13177 induced reduction of blood pressure and heart rate in male, but not in female SHR. An intravenous application of acetylsalicylic acid (ASA) (100 mg/kg) resulted in a decrease of blood pressure and heart rate only in male rats. The extent of these effects was similar to that induced by BM 13177. A possible explanation for the different reactions of male and female animals might be sex differences in the sensitivity of cyclooxygenase in the aorta thoracica to ASA and/or in the balance of prohypertensive and antihypertensive prostanoids. TXA2 and other prostanoids seems to participate in the short-time regulation of BP in SHR.