Lymphatic Hyporeactivity and Calcium Desensitization Following Hemorrhagic Shock
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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