The goal of the proposed research is to determine the Y receptor subtype stimulated in the posterior hypothalamic nucleus (PHN) by the pancreatic polypeptide neuropeptide Y (NPY) that mediates increases in mean arterial pressure (MAP) and heart rate (HR), and to explore the mechanism by which the related pancreatic polypeptide PYY, which appears to stimulate a receptor different from the one stimulated by NPY, increases MAP and decreases HR. These studies will contribute to the long-term goal of this laboratory to understand the relationship between NPY and acetylcholine in the PHN with respect to the control of the cardiovascular system. The hypothesis to be addressed is that NPY stimulates the Y1 receptor subtype within the PHN to activate the mechanisms observed as increases in MAP and HR while PYY stimulates a different receptor.
Four specific aims will be addressed. The first three specific aims will utilize conscious, freely moving rats instrumented with indwelling vascular catheters for the measurement of MAP and HR, the systemic administration of drugs, and an indwelling cannula targeted to the PHN for the microinjection of peptides. The fourth specific aim will utilize tissue slices derived from the PHN.
Specific aim 1 will involve developing a pharmacological profile of several NPY-related peptides based on the magnitude of the increase in MAP evoked by these compounds, correlating the increase in MAP to published binding affinities of these peptides for the various Y receptor subtypes, and determining if a selective Y1 receptor antagonist can block the changes evoked by these peptides.
Specific aim 2 will determine the mechanism by which PYY evokes the increase in MAP and HR for comparison to the mechanism by which NPY evokes increases in MAP and HR.
Specific aim 3 will examine the effect of PYY on regional blood flows for determining the hemodynamic changes evoked by PYY from the PHN for comparison to those evoked by NPY. The rats of specific aim 3 will be instrumented with pulsed Doppler flow probes.
Specific aim 4 will determine the effect of NPY and related peptides on the increase in cAMP evoked by forskolin in tissue slices derived from the PHN. The cAMP levels will be measured by enzyme immunoassay. The effect of NPY and related peptides on inositol (1,4,5) triphosphate (IP3) levels evoked by the cholinergic agonist carbachol (CCh) will also be examined to determine if NPY pretreatment might enhance IP3 levels similar to the previously observed NPY induced enhancement of the CCh evoked increase in MAP. The effect that PYY has on the CCh evoked response will be compared to that of NPY. IP3 levels will be measured using competitive binding between [3H]IP3 and IP3 from the tissue slices to a binding protein. These studies will increase our understanding of the physiological: 1) role of NPY in the central regulation of the cardiovascular system; 2) functions of the Y receptor subtypes; 3) differences between NPY and PYY; and 4) role of NPY and acetylcholine in arousal. These findings will serve as a foundation for future studies of NPY involvement in hypertension and arousal. ? ?
