Neuropeptide Y and vasoactive intestinal peptide in experimental subarachnoid hemorrhage: immunocytochemistry, radioimmunoassay and pharmacology

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Abstract
The involvement of noradrenaline (NA), neuropeptide Y, (NPY), 5-hydroxytryptamine (5-HT), acetylcholine (ACh) and vasoactive intestinal polypeptide (VIP) has been examined in the late phase of spasm after an experimental subarachnoid hemorrhage (SAH) in a rat model. Immunocytochemistry and radioimmunoassay of blood vessels from the circle of Willis did not show significant differences in NPY- and VIP-like immunoreactivity 2 days post SAH as compared to control vessels. The postjunctional effects of NA, NPY, 5-HT, ACh and VIP were studied two days after SAH using a sensitive in vitro system. NPY induced contractions were significantly (p < 0.01) weaker (lower Emax) in SAH as compared to control rats while the relaxant responses to ACh and VIP were slightly increased after SAH. These observations reveal that in a rat model of SAH, with an approximately 20% in vivo constriction at two days, dynamic changes occur in cerebral artery reactivity despite any obvious change in sympathetic or parasympathetic perivascular nerve networks.