ENDOTHELIN ET(A) RECEPTOR ANTAGONIST, BQ-123, BLOCKS THE VASOCONSTRICTION INDUCED BY SARAFOTOXIN 6B IN THE HEART BUT NOT IN OTHER VASCULAR BEDS

1. The cardiovascular effects of SRT6b in control and BQ-123, a specific ET(A) receptor antagonist, pretreated rats were determined in anesthetized rats using a radioactive microsphere technique. 2. Infusion of SRT6b produced an increase in brood pressure and total peripheral resistance, decrease in cardiac output and stroke volume, and no change in heart rate of control or BQ-123 treated rats. 3. SRT6b induced a decrease in blood flow to the heart which was completely blocked by BQ-123 pretreatment. The decrease in blood flow to other organs by SRT6b was not affected by BQ-123 pretreatment. 4. This study indicates that ET receptors in the coronary blood Vessels are of a different type (neither ET(A) nor ET(B)) to those in other vascular beds.