||Autophagy is an important cellular process in maintenance of protein homeostasis. Emerging evidence indicates differential roles of autophagy in cellular function under different pathophysiologic conditions. In some circumstance, autophagy results in cell survival, wheras in other situations it results in cell death. Endotoxin affects neurons in the nucleus tractus solitarii (NTS), baroreceptor afferent terminal site in the brain stem, resulting in cardiovascular depression. The aim of this study was to examine whether modulation of autophagic activity in NTS and other brain regions subserving cardiovascular regulation are associated with cardiovascular depression during experimental endotoxemia.|
Adult male Sprague-Dawley rats received continuously intraperitoneal infusion via osmotic minipump of lipopolysaccharide (LPS, 2.5 mg/kg/day) or normal saline (NS). Body weight (BW) and systolic blood pressure (SBP) were recorded in animals on days 1, 2, 3, 5, 7, 10, and 14 after LPS treatment. Western bolotting was used to assess the expression of autophagic activity marker, microtubule-associated protein 1 light chain 3 (LC3). Rapamycin (0.55 mg/Kg/day), chemical reported to activate autophagy, was infused continuously into the lateral ventricle of the endotoxemic rats for 7 days via osmotic minipump.
Both BW and SBP of rats were decreased in the initial 5 days, followed by a gradual return to baseline after LPS treatment. There was a trend in the decrease in autophagic activity (using the ratio of LC3-Ⅱ/LC3-I as an experimental index) at NTS. However, there is no apparent association between the change in autophagic activity at NTS and the LPS-induced cardiovascular depression. In addition, there was no obvious change in the autophagic activity at RVLM, hypothalamus and hippocampus. Intracranial infusion of rapamycin, a mTOR inhibitor that maintains cellular autophagic activity, resulted in a further enhancement of cardiovascular depression induced by LPS.
These results suggest that continuously intraperitoneal infusion via osmotic minipump of LPS result in decreases of body weight and systolic blood pressure. However, the present study provides no direct evidence to support for a cause-and-effect role of autophage at NTS, RVLM, hypothalamus as well as hippocampus in the LPS-induced cardiovascular depression during experimental endotoxemia.