Acute endothelin-receptor inhibition does not attenuate acetylcholine- induced coronary vasoconstriction in experimental hypercholesterolemia

Endothelin (ET) may mediate the enhanced coronary vasoconstriction associated with hypercholesterolemia. We hypothesized that short-term inhibition of ET receptors attenuates the coronary epicardial vasoconstrictor response to acetylcholine in experimental hypercholesterolemia. ET-1 (group I, n=5; 5 ng · kg^-1 · min^-1) and acetylcholine (group III, n=7; 10^-6 to 10^-4 mol/L) were given by intracoronary infusion in pigs. ET-1 and acetylcholine were also infused with the specific ETA-receptor blocker FR- 139317 (5 μg · kg^-1 · min^-1; group II, n=6; group IV, n=6). Acetylcholine was also infused with the combined ET-receptor blocker, bosentan (0.5 mg/kg plus 1 mg · kg^-1 · h^-1, group V, n=5). The ETB- receptor agonist sarafotoxin 6c (5 ng · kg^-1 · min^-1; n=4) was also infused. The percentage change in coronary artery diameter (%ΔCAD) to the infusions was measured at baseline and after 10 weeks of high-cholesterol diet in all animals. Sarafotoxin 6c mildly reduced %ΔCAD at baseline and 10 weeks (-10 ± 2% and -12 ± 3%, respectively). FR-139317 did not attenuate the epicardial vasoconstrictor response to ET-1 at baseline (%ΔCAD -18 ± 8% for group I versus -12 ± 6% for group II; P=NS) but did at 10 weeks (%ΔCAD -77 ± 14% for group I versus -14 ± 6% for group II; P<.05). FR-139317 did not affect the response to acetylcholine at baseline (%ΔCAD 5 ± 2% for group III versus 7 ± 3% for group IV, P=NS) or at 10 weeks (%ΔCAD -23 ± 12% for group III versus -19 ± 7% for group IV; P=NS). Bosentan did not affect the response to acetylcholine at baseline or 10 weeks. Short-term ET- receptor inhibition in experimental hypercholesterolemia attenuated the enhanced coronary epicardial vasoconstrictor effects of ET-1 but not acetylcholine-induced coronary epicardial vasoconstriction, suggesting that acetylcholine-induced coronary epicardial vasoconstriction may not be mediated by ET receptors.