Pharmacological Research Of Novel Anti-Freezing Drugs

When the cold environment exceeds the limit of human’s physiology tolerance,the work ability of human body reduces and the frostbite occurs, which evenendangers people’s life. In times of peace，frostbite mainly occurs in outdoor sports inwinter, outdoor work, polar exploration, the case of getting drunk or lost and othermainly spontaneous accidents. In the wartime, the occurrence of frostbite causesseverely injuries, which is one of the main factors of non-battle retrenchment. Thecold area in China is vast, and different regions in cold area are facing the tensesituation and insTability in recent years. In order to guarantee and improve theeffective strength and military operation efficiency in our military forces under the thecold conditions, it is of great value to research oral anti-freezing drugs for a largeforce under the emergency situations.The main characteristics of frozen pathophysiology include the dysfunctions ofvasoconstriction and relaxation, microcirculation and blood coagulation systeminduced by the process of partial freezing-thawing. Cold causes the heat dissipation ofacra being aggravated, and the thermotaxic center decreases blood flow by shrinkingthe small vessels to reduce the acra temperature rapidly, finally reaching the goal ofreducing the heat to maintain body temperature. But the acral skin and tissue willsuffer from freezing because of low temperature. It will make the diameter of microand small vessels uneven thickness, smooth muscle layer swelling and fracture andvasomotor function disorder. Blood vessels continue to shrink and even be closed.The visible components in blood gather and stack and cause blood flow slow after thelocal tissue freezes. At the same time, vascular endothelial cell will be necrosis anddrop off after being frozen. The regulative effects of endothelium on bloodcoagulation system, fibrinolytic system and platelet function will be disorder, whichwill induce the coagulation hyperfunction and the increase of blood coagulation. Then,the disorder of microcirculation is further aggravated. Pathological changes of theabove mentioned two aspects interact as both cause and effect to form vicious circle,resulting in thrombosis, tissue necrosis because of ischemic and hypoxic. Therefore, anti-freezing drugs should possess the following functions such as regulatingvasomotor, improving microcirculation and blood coagulation system, and increasingthe acral skin temperature, and so on.Oral anti-freezing compound No.45is mainly consisted of tolazoline andanisodamine. Wherein, tolazoline can dilate blood vessels, and anisodamine canimprove endings blood circulation and increase the acral skin temperature, making theacral tissue free from or put off cold injury. Because of tolazoline’s nonselectivity onα receptors, it will block presynaptic membrane α2receptors and cause tachycardia,orthostatic hypotension and other adverse effects. α1receptor blocker can selectivelyblock vascular smooth muscle postsynaptic membrane α1receptors, but does notaffect the α2receptors.Based on this, this paper is studying on the pharmacological effects of drugcombination of α1receptor blocker and anisodamin in isolated rat tail artery vascularcircle model, carrageenan induced mice tail thrombosis model and the rat tail skintemperature model in cold environment, for the development of late-model oralfrostbite prevention medicine to provide experimental basis.Results1. The regulation of α1receptor blocker on vasomotor functionThree kinds of α1receptor blocker, prazosin, terazosin and doxazosin, all candilate the rat tail artery and acral arteriolar at the concentrations of0.01～10μmol/L ina concentration-dependent manner. Among them, the vasodilatory effects of prazosinon tail artery and acral arteriolar is strongest. The maximum relaxation rate of tailartery and acral arteriolar is (82.6±8.9)%and (82.7±11.1)%in10μmol/Lconcentration respectively, and the EC50of prazosin obtained through the Blissmethod is (0.44±0.15) μ mol/Land (0.56±0.18) μ mol/Lrespectively.Anisodamine have dilation effect on tail artery and acral arteriolar, and themaximal expansion rate is (29.7±7.3)%and (20.2±5.6)%in10μ mol/Lrespectively.The vasodilator function of Prazosin basically remain unchanged when theconcentration of anisodamine increased with preincubation anisodamine (0.10~10) μmol/L, and the maximal diastolic rate only changed from (82.6±8.9)%to (92.3±4.0)%, suggesting there is no synergistic or antagonistic effect when anisodamine is combined with prazosin.2. The preventive effect and its mechanism of anisodamine combined with prazosinon thrombosis.Tail thrombosis in mice was induced by carrageenan. The tip of the tail of micewith intraperitoneal injection of2.5mg/kg carrageenan began to appear dark redthrombosis area during4~8h, and thrombus area near the tip of the tail turned purpleafter48h. According to statistics, after48hours, the tail of26mice in the total30mice formed thrombus. The rate is86.6%, and the average length of thrombosis is24.6±4.6mm.The combination of anisodamine and prazosin has significant antithromboticeffects. Compared with the model group, the combination of the two drugs shorten thethrombus length of each dose group significantly, and the thrombosis rate of high dosegroup decreased significantly. Meanwhile, anisodamine0.8~2.5mg/kg and prazosin0.07~0.6mg/kg all can shorten the length of thrombus in a dose dependent manner.The antithrombotic effect of anisodamine2.0plus prazosin0.6mg/kg is best, thethrombus length is reduced to6.9±2.7mm, and the formation of thrombus rate dropsto50%.As the result of coagulation system function shows, the combination ofanisodamine and prazosin can rectify the increase of blood coagulability induced bycarrageenan by the affecting the exogenous way of blood coagulation, while there isno effects on endogenous clotting way.The detection results of platelet activation marker and antiplatelet activitysubstances showed that the combination of anisodamine and prazosin could inhibit thereleasing of thromboxane A2(TXA2) from platelets, and promote endothelial cells tosecrete prostacyclin (PGI2), which might be involved in the mechanisms against theformation of thrombus.The results of fibrinolytic system function showed that the combination ofanisodamine and prazosin could inhibit the releasing of tissue plasminogen activatorinhibitor combined (PAI-1) significantly, which indirectly enhance the fibrinolyticactivity against thrombus.3. Effects of combination of anisodamine and prazosin in rat tail skin temperatureunder cold conditions Combination of anisodamine and prazosin can increase the temperature in rat tailskin in cold exposure after120min、240min, protect the issue from suffering anddelaying freeze.Conclusions:1. Prazosin can enhance the regulation of acral easily frozen parts of micro, smallvasodilatation function, and improve blood flow;2. Combination of anisodamine and prazosin can Fight against thrombosis andimprove microcirculation.3. The functions of the combination of anisodamine and prazosin is achieved throughimproving blood coagulation system function, inhibiting the activation of platelet,promoting vascular endothelial to release active antithrombotic substances, andimproving the activation of fibrinolytic system and other means.4. Combination of anisodamine and prazosin can increase the temperature of acralskin and delay freeze.In summary, it has solid pharmacological properties to combine anisodaminewith prazosin as oral anti-freezing drug combinations. For the further research, thisstudy provide necessary reference basis to develop new oral anti-freezing drugs.