DIFFERENTIAL RESPONSES OF RAT AORTA AND MESENTERIC-ARTERY TO NOREPINEPHRINE AND SEROTONIN IN-VITRO

The differences in the responses of isolated ring segments of aorta an d mesenteric artery of rat have been investigated, The aortic rings sh owed higher sensitivity to norepinephrine than the mesenteric artery r ings, On the other hand, the sensitivity of the mesenteric artery to s erotonin was 17 times greater than that of the aortic ring segments, H owever, there was no difference between the sensitivity of the aorta a nd the mesenteric artery to potassium chloride stimulation, There was also no difference in the contractile responses of the aorta and the m esenteric artery to calcium chloride either during norepinephrine stim ulation or during stimulation with serotonin. The phasic contraction o f the aorta to norepinephrine was greater than the phasic contraction of the mesenteric artery to this agonist while the magnitude of phasic contraction of the aorta to serotonin was lower than that of the mese nteric artery. These results suggest that the differences in the contr actile responses of the rat aorta and the mesenteric artery to norepin ephrine and serotonin are dependent on the ability of these agonists t o mobilise calcium from intracellular stores.