The present proposal is a logical extension of our previous work and will focus on understanding the interactions, physiological importance and regulation of release of mediators thought to be expressed in sympathetic nerves: norepinephrine (NE), neuropeptide Y (NPY) and adenosine triphosphate (ATP), suspected mediator of nonadrenergic nerves, calcitonin gene related peptide (CGRP), and locally formed angiotensin (Ang) in the mesenteric vascular-neuroeffector junction of normotensive and hypertensive rats.
Specific Aim 1 will examine 3 hypotheses: First that NE, NPY and ATP act as co-transmitters in sympathetic nerves innervating the mesentery where they exert pre and postjunctional effects; second that there is an enhanced release of NE in young SHR while an enhancement of NPY and ATP occur in mature SHR, finally, that there are alterations in the presynaptic receptor modulation of the release of all 3 mediators in the SHR. Release of NE will be measured by HPLC-EC detection, ATP by HPLC-fluorometry and NPY by RIA. Postjunctional changes in perfusion pressure will also be monitored. Experiments have been designed to qualitatively and quantitatively distinguish between the neuronal vs non-neuronal source of these mediators and to dissect the various aspects of release in the mesenteric arterial bed (neuronal release, muscle contraction and endothelial cells).
Aim 2 will examine the hypothesis that CGRP is the NANC vasodilator neurotransmitter in the mesenteric vascular bed and that its release and function are also altered in the SHR. Strategies will include measuring the release of CGRP by RIA and its modulation. Experiments have been designed to qualitatively and quantitatively distinguish between the neuronal and non-neuronal release of CGRP, to use the rank order of agonists and antagonists to define the nature of the CGRP receptors in the vasculature as contrasted to the heart; to utilize antagonists to define the functional importance of CGRP in the mesenteric artery, to define the cardiovascular effects and mechanism of action of CGRP released from the sensory nerves in the spinal cord and to define the role of CGRP in the SHR.
In Aim 3 we will define and characterize the regulation and modulation of Ang release in the perfused mesenteric artery of normotensive and hypertensive rats. These studies will establish whether or not there is a basis for the postulated local vascular-renin-angiotensin system. Two hypotheses will be addressed, first that there is a greater enhancement of the beta- adrenoceptor mediated increase in synthesis and release of Ang II measured by RIA in the mesenteric arterial bed that explains the enhanced beta-adrenoceptor release of NE in blood vessels of SHR. Secondly that Ang II release is modulated by transmitters released from sympathetic and NANC nerves. These studies will provide useful new information on the mechanism and interactions of locally formed mediators in the vasculature. A thorough understanding of these interactions could aid in understanding the pathophysiology of hypertension in the SHR.
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