Post-infarct sympathetic hyperactivity differentially stimulates expression of tyrosine hydroxylase and norepinephrine transporter

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Item Type:	Article
Title:	Post-infarct sympathetic hyperactivity differentially stimulates expression of tyrosine hydroxylase and norepinephrine transporter
Creators Name:	Parrish, D.C., Gritman, K., Van Winkle, D.M., Woodward, W.R., Bader, M. and Habecker, B.A.
Abstract:	The balance between norepinephrine (NE) synthesis, release, and reuptake is disrupted after acute myocardial infarction resulting in elevated extracellular NE. Stimulation of sympathetic neurons in vitro increases NE synthesis and the synthetic enzyme tyrosine hydroxylase (TH) to a greater extent than it increases NE reuptake and the NE transporter (NET) which removes NE from the extracellular space. We used TGR(ASrAOGEN) transgenic rats, which lack post-infarct sympathetic hyperactivity, to test the hypothesis that increased cardiac sympathetic nerve activity accounts for the imbalance in TH and NET expression in these neurons after myocardial infarction. TH and NET mRNA levels were identical in the stellate ganglia of unoperated TGR(ASrAOGEN) rats compared to Sprague Dawley (SD) controls, but the 3-fold increase in TH and 2-fold increase in NET mRNA seen in the stellate ganglia of SD rats one week after ischemia-reperfusion was absent in TGR(ASrAOGEN) rats. Similarly, the increase in TH and NET protein observed in the base of the SD ventricle was absent in the base of the TGR(ASrAOGEN) ventricle. Neuronal TH content was depleted in the left ventricle of both genotypes while NET was unchanged. Basal heart rate and cardiac function were similar in both genotypes, but TGR(ASrAOGEN) hearts were more sensitive to the beta agonist dobutamine. Tyramine-induced release of endogenous NE generated similar changes in ventricular pressure and contractility in both genotypes, but post-infarct relaxation was enhanced in TGR(ASrAOGEN) hearts. These data support the hypothesis that post-infarct sympathetic hyperactivity is the major stimulus increasing TH and NET expression in cardiac neurons.
Keywords:	Ischemia-reperfusion, Sympathetic hyperactivity, Autonomic, Animals, Rats
Source:	American Journal of Physiology Heart and Circulatory Physiology
ISSN:	0363-6135
Publisher:	American Physiological Society
Volume:	294
Number:	1
Page Range:	H99-H106
Date:	1 January 2008
Official Publication:	https://doi.org/10.1152/ajpheart.00533.2007
PubMed:	View item in PubMed

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