Effect Of MCI-154 And Arginine Vasopressin On Vascular Reactivity And Its Mechanisms Following Hemorrhagic Shock In Rats

The occurrence of vascular hyporeactivity after severe trauma or shock has been shown to have important roles in the incidence, development, and the outcome of shock and interfered with the therapy of shock, but its mechanisms remain unclear. Our recent study showed that hemorrhagic shock caused calcium desensitization of blood vessels, which played important roles in vascular hyporeactivity, and Rho-kinase (Rho-associated kinase, the downstream effector molecule of Rho) can regulate the calcium sensitivity of vascular smooth muscle following hemorrhagic shock. MCI-154 is a new cardiotonic agent, which exerts its positive inotropic action by increasing Ca²⁺ sensitivity of the contractile proteins in cardiac muscles; however, its effect on vascular reactivity is still unclear. Arginine vasopressin (AVP) is a neurohypophysial hormone of 9-amino-acid peptide synthesized in the hypothalamus. Recent studies have reported that arginine vasopressin can constrict blood vessels via activation of Rho-kinase, and had beneficial effect on advanced vasodilatory shock. But whether AVP has effects on vascular reactivity following hemorrhagic shock is unknown. So we used hemorrhagic shock model of rats to investigate the effects of MCI-154 and AVP on vascular reactivity following hemorrhagic shock in rats, and explore its primary mechanism from the calcium sensitivity pathway.Methods: The experiments were conducted in three parts. In the first part, we observed the effects of MCI-154 on vascular reactivity following hemorrhagic shock in rats in vivo and in vitro. In vivo, the hemorrhagic shock (30 mmHg for 2 hours) model of rats was adopted to observe the effects of MCI-154(0.1, 0.5, 1.0, 2.0 mg/kg) on mean arterial pressure (MAP) and pressor effect of norepinephrine(NE). In vitro, superior mesenteric artery (SMA) was used to observe the effects of MCI-154( 10^-7, 10^-6, 10^-5, 10^-4 mol/L) on NE induced-vascular contraction with isolated organ perfusion system. In the second part, we observed the effects of MCI-154 on calcium sensitivity of vascular smooth muscle and its relationship with Rho-kinase, PKC and PKG, calcium sensitivity was determined byobserving the contractile response of SMA to Ca2+ under depolarizing conditions (120 mmol/L K+). In the third part, we observed the effects of AVP on vascular reactivity and calcium sensitivity and its relationship to Rho-kinase following hemorrhagic shock in rats. In vivo, the hemorrhagic shock model of rats was used to observe the effects of AVP (0.1 and 0.4 U/kg) on MAP and pressor effect of NE. In vitro, the effects of AVP (0.5 and 5.0 nmol/L) on the contractile response of SMA to NE and calcium sensitivity and its relationship with Rho-kinase were observed. Results:1. In vivo NE-induced pressor response following hemorrhagic shock was significantly decreased (PO.01), the pressor effect of NE in sham operated group was maintained at 36 mmHg, but in shock control group, the pressor effect of NE was only at 19 mmHg. In vitro, the contractile response of SMA to NE and Ca2+ following hemorrhagic shock was significantly decreased as compared with normal control group, the cumulative dose-response curve of SMA to NE and Ca2+ in shock control group was shifted to the right, the maximal contraction (Emax) of NE and Ca"+ was decreased significantly (PO.01), and pD2 of NE was decreased significantly, too.2. After pretreatment with MCI-154, the MAP and pressor response of NE was further decreased, it was significantly lower than the sham operated and shock control groups (PO.05^PO.01), and in vitro, after MCI-154 pretreatment for 30 minutes, the responsiveness of SMA to NE was further decreased as compared to shock control group (PO.01), this effect of MCI-154 was in dose-dependent manner. Similarly, MCI-154 further decreased the calcium sensitivity, MCI-154 pretreatment made the cumulative dose-response curve of Ca"+ further shift to the right as compared to shock control group (PO.Ol)o Angll and PMA, the Rho-kinase agonist and PKC agonist, increased the calcium sensitivity, made the cumulative dose-response curve of Ca2+ shift to the left. After MCI-154 (10° mol/L) pretreatment, the dose-response curve of Ca2+ was shifted to the right as compared to Angll and PMA alone group (PO.01). But, KT-5823, the PKG antagonist, antagonized MCI-154-induced right shift of the dose-response curve of Ca2+. It was suggested that MCI-154 induced the decrease of calcium sensitivity may be related to Rho-kinase, PKG and PKG.3. AVP significantly increased the MAP and pressor response of NE of hemorrhagicshock rats in vivo, in AVP (0.4 U/kg) group, the pressor effect of NE was increased to 42 mmHg at 4 hours after AVP administration. In vitro, AVP pretreatment significantly increased the contractile response of SMA to NE and Ca2+ and made the cumulative dose-response curve of NE and Ca2+ shift to the left, Emax of NE and Ca2+ was increased significantly (P<0.01). HA-1077, the Rho-kinase antagonist, antagonized AVP-induced leftward shift of the dose-response curve of NE and Ca2+. Conclusions:1. The vascular reactivity and calcium sensitivity of vascular smooth muscle following hemorrhagic shock were significantly decreased. MCI-154 can further reduce the vascular reactivity of hemorrhagic shock rats including the systemic and local vascular reactivity, and decrease the calcium sensitivity of vascular smooth muscle following hemorrhagic shock.2. MCI-154 may regulate the calcium sensitivity through Rho-kinase, PKC and PKG.3. AVP can increase the vascular reactivity and calcium sensitivity of SMA in hemorrhagic shock rats. Rho-kinase may be an important action site that AVP regulates the vascular reactivity and calcium sensitivity following hemorrhagic shock.