Rat aorta and mesenteric artery respond differently to serotonin

The sensitivity (EC50) of the ring segment of the mesenteric artery to serotonin (4.84 +/- 0.53 x 10(-7) mol.l-1) was 17x greater than that of the aortic ring segment (5.29 +/- 0.46 x 10(-6) mol.l-1). Incubation of the ring segments in physiological salt solution (PSS) containing methylene blue greatly potentiated the sensitivity of both the aorta and mesenteric artery to serotonin. The degree of potentiation was higher in the aorta than mesenteric artery. L-NAME also increased the sensitivity of both the aorta and mesenteric artery to serotonin and there was no difference in the degree of potentiation of the responses between the aorta and the mesenteric artery. Indomethacin inhibited the contractile responses of the aorta and the mesenteric artery to serotonin. Phenoxybenzamine reduced the contractile responses of both the aorta and the mesenteric artery by the same magnitude. Captopril (10(-4) mol.l-1) significantly attenuated the responses of the mesenteric artery more than the aorta, while methysergide (10(-8) mol.l-1) completely abolished the difference in the responses (EC50 for aorta = 3.50 +/- 0.55 x 10(-5) mol.l-1 vs 5.00 +/- 0.49 x 10(-5) mol.l-1 for mesenteric artery). This study demonstrates that rat aorta and mesenteric artery respond differently to serotonin and the differential response is due to a methylene blue sensitive factor and differences in either the receptor population or sensitivity.