[Nitric oxide modulates biphasic changes of isolated lymphatic contraction in hemorrhagic shock rats]

The aim of the present study was to investigate the changes of lymphatic contraction after hemorrhagic shock in vitro and the underlying role of nitric oxide (NO). Rat thoracic duct segments were isolated at 0, 0.5, 1, 2 and 3 h after hemorrhagic shock. Using Pressure Myograph System, we determined contraction frequency (CF), end systolic diameter (ESD), end diastolic diameter (EDD) and passive diameter (PD) of isolated rat lymphatics under different transmural pressures (1, 3, 5, 7 and 9 cmH(2)O), then calculated contraction amplitude (CA), tonic index (TI) and fractional pump flow (FPF) of lymphatics. The results showed that in several transmural pressures, lymphatic CF, TI and FPF were significantly higher in shock 0 h and shock 0.5 h groups than those in control group (sham operation group). With the development of shock, lymphatic CF, TI and FPF decreased significantly in shock 2 h and shock 3 h groups compared with those in control group. We further discovered the role of NO in the changes of lymphatic contraction after hemorrhagic shock. Under 3 cmH(2)O transmural pressure, the changes of lymphatic contraction in shock 0.5 h and shock 2 h groups were analyzed following the incubation with several NO-related drugs alone or in combination. And the results showed that NO donor L-Arg reduced CF, TI and FPF in shock 0.5 h group to the control levels, while soluble guanylate cyclase inhibitor ODQ suppressed the effect of L-Arg. Moreover, NOS inhibitor L-NAME elevated the CF, TI and FPF of 2 h shock lymphatics to the control levels, while phosphodiesterase inhibitor aminophylline (AP) suppressed the effect of L-NAME. These results suggest that the lymphatic contractile activity exhibits a biphasic change during hemorrhagic shock, increasing in early phase and declining in later stage. And NO plays a major regulating role in the biphasic change of lymphatic contraction in hemorrhagic shock rats via cGMP pathway.