The Effect of Stress and in Vivo Vasoactive Intestinal Peptide (VIP) Treatment on the Response of Isolated Rat Aorta to Norepinephrine, Angiotensin II and Vasopressin, and Adventitial Mast Cells

The effects of cold-restraint stress, repeated over 3 days, and treatment of rats with vasoactive intestinal peptide (VIP) on the contractile responses of isolated aorta to vasoconstrictors, and on aortic adventitial mast cells were investigated. Stress significantly reduced the contractile response of rat aorta smooth muscle to norepinephrine (NE), angiotensin II (Ang II) and vasopressin (VP). Decreased sensitivity to NE, Ang II and VP may result from decreased receptor density, and affinity or reduced effector efficacy. Stress induced degranulation, decreased the number and changed the granular content of mast cells; all degranulated mast cells were stained with alcian blue, and the percentage of safranin staining cells was decreased. Given prior to stress, VIP reversed the reduced contractile responses and sensitivity of aorta to NE and Ang II but had no effect on VP subsensitivity. VIP also inhibited stress-induced degranulation of mast cells, and after VIP only alcian blue-stained mast cells were seen. When VIP was given to non-stressed rats, the contractile response of the aorta to NE, but not Ang II or VP, was increased compared with control. Mast cell count was decreased in the adventitia of non-stressed VIP treated rats. The results indicate that stress decreases the heparin content of mast cells and VIP has an additive effect. In conclusion, VIP modulates both stress-induced mast cell activity and reduced sensitivity of aorta smooth muscle to NE and Ang II. It can be suggested that VIP may moderate some effects of stress on vascular pathophysiology.