Vascular effects of neuropeptides and UDP-β-S and alterations after stroke

Sammanfattning: The aim of this thesis is to investigate the changes in vasoactive intestinal peptide (VIP) and calcitonin gene-related peptide(CGRP) and P2Y6-mediated signaling following experimental subarachnoid hemorrhage (SAH) and transient middle cerebral artery occlusion (tMCAO). VIP and CGRP are among the most powerful vasodilators known to man while P2Y6 mediates strong vasoconstriction in cerebral blood vessels. By describing the potential changes in these receptor/agonist systems, we hope to better describe the balance between vasoconstriction and vasodilation following stroke.Stroke is a common and severe disorder of the central nervous system, where disturbances in blood supply induce ischemic injury. Ischemia and the following cascade of inflammation cause not only neuronal death but also induce changes in blood vessels and surrounding tissue. We have previously demonstrated an increase in the expression of several vasoconstrictive receptor systems following both ischemic and hemorrhagic stroke. These changes are hypothesized to induce a more vasoconstrictive state, which reduce blood flow and may enhance ischemic damage in the near-ischemic zone surrounding the ischemic core. Most previous studies have focused on traditional vasoconstrictors such as endothelin, angiotensin and serotonin, while less focus has been put on more locally acting vasoconstrictors such as purines. Even less effort has been applied to the investigation of vasodilatory receptor systems and their plasticity following ischemia. The first two papers making up the basis for this thesis investigate the physiological function of CGRP, VIP and the closely related pituitary adenylate cyclase-activating polypeptide (PACAP) in rat middle cerebral arteries (MCAs). Wire myography and pressurized arteriography evaluate changes in wall tension and vessel diameter along with measurements of intracellular calcium. Immunohistochemistry is used to determine receptor localization. Based on these experiments we conclude that CGRP and VIP receptors are located on the smooth muscle cells and not on the entothelial cells of the rat MCA. VIP and CGRP both induce a sustained vasorelaxation which correlates with a decrease in intracellular calcium. It was also demonstrated that VPAC1 and VPAC2 receptors are predominant over PAC1 receptors.The last two papers of this thesis investigate changes in receptor expression and agonist effect in rat MCAs following either experimental SAH or transient MCA occlusion. Wire myography was used to determine changes in wall tension and western blot and/or flow cytometry was used to evaluate alterations in receptor expression. We demonstrate an enhanced vasodilatory response to VIP following tMCAO but not after SAH. CRGP-mediated vasodilation is completely unaffected by SAH or tMCAO. An enhanced expression of the P2Y6 receptor following both types of stroke was demonstrated, however contraction was only enhanced after tMCAO.