Cytokines and Sympathetic Activation in Heart Failure

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DESCRIPTION (provided by applicant): In patients with heart failure, the presence of circulating pro-inflammatory cytokines like tumor necrosis factor-alpha (TNF-a) and interleukin-1 beta (IL-lb) correlates directly with the severity of the disease and predicts a poor prognosis. The pro-inflammatory cytokines have been shown to activate the hypothalamicpituitary- adrenal (HPA) axis and stimulate the sympathetic nervous system. Corticotropin-releasing factor (CRF) in the paraventdcular nucleus of the hypothalamus (PVN) is the principal mediator of the humoral limb of this response (i.e., cortisol release); the mediator of the sympathetic limb is not known. Cytokine activation of the HPA axis is indirect: TNF-a and IL-lb stimulate receptors on the vascular endothelium to release prostaglandins E2 (PGE2), which crosses blood brain barrier to excite the norepinephrine (NE) containing neurons in rostral ventrolateral medulla that ascend to stimulate CRF production in PVN. This model has been derived from acute studies in normal rats. The overall hypothesis of this project is that chronic stimulation by pro-inflammatory cytokines contributes to the augmented sympathetic drive in heart failure. We will seek to determine: 1) which neurotransmitter substances (leading candidates being CRF, NE, PGE2) stimulate parvocellular PVN neurons that descend to activate centers of sympathetic drive in brain stem - leading candidates are CRF itself, exciting CRF-R1 receptors that are upregulated in PVN by stress, NE, which can excite PVN neurons via an alpha-1 adrenergic mechanism, and PGE2, which we have recently shown to elicit a response similar to blood-borne TNF-a when injected directly into PVN; 2) whether these presympathetic parvocellular PVN neurons are activated in heart failure over the classical pathway for acute cytokine stimulation of the HPA axis, described above, or by alternate mechanisms such as the local hypothalamic production of cytokines that we have recently observed in our ischemic heart failure model; in the latter case, presence of pro-inflammatory cytokines within the PVN might drive local production of PGE2 and CRF and release of NE from nerve terminals. These studies will be undertaken in a model of chronic ischemia-induced heart failure in rats, using electrophysiological, immunohistochemical and molecular techniques. These studies will provide new insights into the role of the pro-imflammatory cytokines in heart failure, perhaps leading to new therapeutic strategies.