Lymphatic hyporeactivity and calcium desensitization following hemorrhagic shock.
ABSTRACT The lymphatic circulation is an important component of the circulatory system. In preliminary studies, we found contractile activity of lymphatic vessels to be decreased during severe shock. In the present study, our aim was to observe changes in lymphatic reactivity to norepinephrine (NE) and to explore the mechanism of calcium sensitivity in rats subjected to hemorrhagic shock (HS). Thirty-two Wistar rats were randomly divided into sham and shock groups, and changes in lymphatic pressure and contractility of mesenteric lymphatics in response to NE were measured at different time points after shock. The results showed that NE-induced changes in lymphatic pressure were decreased at 1 h after shock and that hyporeactivity was maintained for 3 h after shock. The reactivity of mesenteric lymphatics to NE in the shock group at 1 to 2 h after shock was significantly lower than that of the sham group and before shock. The other 49 rats were divided into sham, shock 1 h, and shock 2 h groups for isolation thoracic duct rings. Forty-eight isolated lymphatics per group were used to assay lymphatic reactivity to NE and calcium sensitivity in an isolated vessel perfusion system. The NE concentration-response curves for postshock lymphatic rings (1 or 2 h) and calcium concentration-response curves after shock (2 h) were shifted to the right; isolated lymphatic reactivity to NE and contraction in response to calcium were markedly reduced in shock groups. Lymphatic reactivity to NE and calcium sensitivity were significantly increased in the 2-h shock group following incubation with the calcium sensitizer angiotensin II, and the lymphatic reactivity was reduced after incubation with the calcium sensitivity inhibitor insulin. In conclusion, lymphatic reactivity declines progressively during HS as a result of calcium desensitization. The results suggest that lymphatic hyporeactivity is one of the mechanisms of lymphatic hypocontraction in rats subjected to HS.
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ABSTRACT: The aim of this present study was to examine changes in RhoA protein levels and the role in RhoA in lymphatic contractility and reactivity after hemorrhagic shock. Levels of RhoA and phospho-RhoA (p-RhoA) in lymphatic tissue isolated from hemorrhagic shock rats were measured, and the contractility and reactivity to substance P (SP) of lymphatics isolated from control, 0.5 h- and 2 h-shocked rats were determined with an isolated lymphatic perfusion system at a transmural pressure of 3 cmH2O. At the same time, lymphatics isolated from 0.5 h- and 2 h-shocked rats were incubated with agonists and antagonists of RhoA/Rho kinase signaling. Contractile frequency (CF), end-diastolic and end-systolic diameter, and passive diameter were recorded and used to calculate lymphatic tonic index (TI), contractile amplitude (CA) and fractional pump flow (PFP). After stimulation with a gradient of SP, the differences between the pre- and post- administration values of CF, CA, TI and FPF were calculated to further assess lymphatic reactivity. RhoA protein levels were significantly increased at 0.5 h post-shock but decreased at 2 and 3 h post-shock; p-Rho levels were initially increased post-shock and subsequently decreased. The contractility and reactivity of 0.5 h-shocked lymphatics were significantly reduced by the RhoA antagonist C3 transferase and the Rho kinase antagonist Y-27632. The RhoA agonist U-46619 increased the contractility and reactivity of 2 h-shocked lymphatics, while Y-27632 suppressed the effect of U-46619. OA, an inhibitor of myosin light chain phosphatase (MLCP), had no effect on the contractility of 2 h-shocked lymphatics, but improved lymphatic reactivity. These results suggest that RhoA is involved in the modulation of lymphatic pump function during hemorrhagic shock and that its effects may be mediated by Rho kinase and MLCP.Shock (Augusta, Ga.) 04/2013; DOI:10.1097/SHK.0b013e31829635cf · 2.73 Impact Factor