Vascular interactions of serotonin and norepinephrine in renal hypertensive rabbits

Vascular responses to norepinephrine (NE) are potentiated in the presence of serotonin (5-HT) and are attenuated by previous exposure to 5-HT. This study was designed to determine whether alterations in the interactions of these agonists occur in renal hypertension. Helical strips of femoral artery from two-kidney, one clip (2K1C) hypertensive and control rabbits were mounted in muscle baths for isometric force recording. Arterial strips from 2K1C rabbits were more sensitive to 5-HT than were those of control rabbits. The sensitivities of these two groups of vessels to NE were not significantly different. The 5-HT potentiation of NE was present at lower 5-HT concentrations in vessels from 2K1C rabbits than in those from control rabbits. Previous exposure to 5-HT attenuated NE responses of arteries from 2K1C less than it did those of control rabbits. Although 5-HT had little effect on loading of cellular stores of calcium in the resting muscle, previous 5-HT exposure attenuated calcium influx during an NE response, and this attenuation was not as great in vascular smooth muscle from the hypertensive animal as it was in that from the normotensive control. These results indicate that in vascular smooth muscle cells from 2K1C rabbits the potentiating action of 5-HT is increased, due to the increased sensitivity to this agonist, and the attenuating action is decreased due to a greater calcium influx during NE stimulation.