Willis K. Samson - US grants

The goal of this proposal is to define the role of a new class of hypothalamic peptides in reproductive endocrinology. These peptides, called atrial natriuretic factors (ANF), exert potent effects on gonadotropin secretion and the studies detailed here will characterize the physiologic consequences of these actions, identify the site of their action and describe the interaction of these peptides with established neuropeptidergic and catecholaminergic systems which regulate the hypothalamo- pituitary-gonadal axis. This information will further our knowledge of the physiological aspects of reproductive function and provide insight into the possible mechanisms responsible for pathologic endocrine states. This proposal deals with the definition of at least one of the hypothalamic factors which can inhibit the endocrinology of reproduction. Specific aims are to: 1) identify the exact hypothalamic site of action of ANF to inhibit gonadotropin secretion by microinjecting the peptide into specific brain sites and measuring plasma gonadotropins (luteinizing hormone-LH) by radioimmunoassay, 2) identify the class of opiate receptor involved in this action of ANF by using specific opiate antagonists to block its action, 3) investigate the ability of ANF to interact with neurotransmitter systems within the brain which are known to control the secretion of LH-releasing hormone, by using a combination of in vivo and in vitro manipulations which examine the ability of ANF to block catecholamine stimulated LH release or to alter catecholamine synthesis and secretion, 4) correlate in vivo changes in hypothalamic release of ANF with established patterns of LH secretion, and 5) examine the effect of removal of locally produced ANF, by passive immunoneutralization, on LH secretory dynamics. In addition to characterizing the role these peptides play in the hypothalamic control of reporductive endocrinology, these studies will provide valuable insight into other brain actions of ANF and will establish model systems for the further definition of the neural control of reproductive function.

[unreadable] DESCRIPTION (provided by applicant): This is a rerevised, competitive renewal application (HL66023) that continues our examination of the physiologic relevance of recently described neuropeptides which we have demonstrated to act at least pharmacologically to stimulate stress hormone secretion (prolactin, PRL, and adrenocorticotropin, ACTH) by a brain site of action. Additionally, these peptides stimulate stress-related behavioral responses (activity) and at least one acts in brain to stimulate sympathetic activity resulting in increased blood pressure. These peptides (prolactin releasing peptide, PrRP; neuropeptide W, NPW; and neuropeptide B, NPB) are produced in separate populations of neurons in brain, many of which innervate the hypothalamic paraventricular nucleus (PVN), arcuate nucleus (ARC) and ventromedial and dorsomedial hypothalamic nuclei (VMH/DMH). All three peptides are contained in neurons that innervate autonomic centers in hypothalamus and brain stem. It is our goal to understand the roles these peptides play in the hypothalamic and extrahypothalamic responses to stress. We address multiple specific aims all related to the founding hypothesis that one or more of these peptides is essential for the endocrine and/or cardiovascular response to stress, under certain paradigms of stress. Our approach will be to demonstrate direct effects of these peptides on identified fore- and hindbrain neurons [e.g. in PVN, ARC, VMH/DMH, nucleus tractus solitarius (NTS), rostral lateral medulla (RVLM), and dorsal motor nucleus of the Vagus] using electrophysiologic, pharmacologic and single cell RT- PCR approaches. We will then attempt compromise of peptide production and examine hormone secretion in response to physical stress and the cardiovascular response to hypertensive and hypotensive challenge (i.e. baroreflex sensitivity). Understanding the normal mechanisms controlling the response to stress will reveal potential strategies for the management of stress in the human population and the cardiovascular and metabolic consequences of that stress. These studies may also provide insight into the central mechanisms contributing to development of the metabolic syndrome (Syndrome X), which is characterized by obesity, poor glycemic control, altered metabolic and autonomic function and a propensity for adverse cardiovascular outcomes. Additionally, these studies will provide further insight into the coordinated hormonal and autonomic responses to stress. [unreadable] [unreadable] [unreadable]

DESCRIPTION (provided by applicant): The hypocretins/orexins (Hcrts/ORXs) act within brain to stimulate autonomic function and have been demonstrated to be physiologic regulators of arousal state. Neuroendocrine and metabolic effects of these peptides, some related to sleep/wakefulness and arousal state, are just now being discovered. Indeed, these peptides exert a combination of autonomic (sympathoexcitation), behavioral (arousal), and neuroendocrine (ACTH release) effects in brain that suggests important roles for them in the CNS response to stress. However, little is known of the exact sites of action of these peptides in brain, or their mechanisms of action. We have identified neurons in hypothalamus and brain stem cardiovascular centers that are excited by orexin, suggesting a cellular basis for our reported actions of the peptide on autonomic function and stress hormone (ACTH) release (vide infra). We also have identified a pituitary action of the peptides to affect CRH-induced ACTH release. We seek to elucidate: 1) the cellular events and signal transduction pathways underlying the pituitary actions of Hcrt/ORX on ACTH release, 2) the integrated autonomic (neuroendocrine and cardiovascular) actions, underlying cellular mechanisms, and specific neuronal circuitry through which Hcrt/ORX exerts physiological actions in the hypothalamic paraventricular nucleus (PVN), 3) the integrated cardiovascular actions, underlying cellular mechanisms, and specific neuronal circuitry, through which Hcrt/ORX exerts physiological actions in the nucleus tractus solitarius (NTS), and 4) the membrane properties of Hcrt/ORX producing neurons in the lateral hypothalamic/perifornical area (LH/PFA), extrinsic factors controlling their excitability, and functional connectivity with critical autonomic nuclei in other regions of the brain. We propose to identify the exact sites of action of these peptides, provide insight into the receptor specificity of their pharmacologic effects and establish model systems for the study of the physiologic relevance of the interactions of the Hcrts/ORXs with brain and pituitary systems activated during stress. Long-term goals are to identify the physiologic relevance of these peptides in the central control of autonomic function and in the neuroendocrine regulation of anterior pituitary function, and to relate those functions to the cardiovascular responses to, and consequences of, stress.

DESCRIPTION (provided by applicant): Angiotensin II (Ang II) plays a key role in fluid homeostasis and blood pressure (BP). We have recently found that a seven amino acid peptide (PEP7) encoded within a short open reading frame in exon 2 of the 5' leader sequence of the angiotensin type 1a receptor (AT1aR) mRNA inhibits Ang II activation of extracellular signal-regulated protein kinases 1 and 2 (Erk1/2) and regulates AT1aR trafficking in cells. PEP7 also markedly reduced Ang II-mediated sodium intake without having any effect on Ang II-mediated water intake and it antagonized Ang II- induced increases in BP. Aim 1 will determine the signaling mechanism by which PEP7 inhibits Erk1/2 activation. We will test the hypothesis that PEP7 inhibition of Erk1/2 activation is Ang II dependent and mediated via the AT1aR-G protein-independent ß-arrestin signaling pathway. We will also investigate PEP7 regulation of AT1aR vesicular trafficking by inhibiting AT1aR coupling to the ß-arrestin pathway using both pharmacological and molecular approaches, and confocal microscopy. Aim 2 will elucidate the mechanism by which PEP7 regulates fluid and electrolyte homeostasis. We will investigate PEP7 effects in vivo in pathophysiological models of elevated sodium intake including hyponatremic hypovolemia and isotonic hypovolemia as well as conditions that modulate central oxytocin and vasopressin pathways and those that selectively inhibit G protein-mediated protein kinase C and G protein-independent Erk1/2 signaling cascades. Aim 3 will determine if the antihypertensive effects of PEP7 are Ang II-dependent by investigating PEP7 effects on arterial pressure in models of Ang II- and catecholamine- dependent hypertension. We will also determine if PEP7 is effective at lowering BP in two models of salt-sensitivity and what role reduced sodium intake plays in these effects. By achieving these aims, we will gain insight into PEP7 biology that could be leveraged toward developing novel interventions for diseases that are worsened by dietary sodium, like salt- sensitive hypertension.