OBJECTIVE: To establish an HPLC method for the determination of the contents of the related substances in metoclopramide.METHODS: The sample was separated on C18 column with the mobile phase consisted of acetonitrile-0.02 mol?L-1 phosphonic acid solution(19∶81) at a flow rate of 1.0 mL?min-1.The detection wavelength was set at 275 nm;the column temperature was kept under room temperature and the injected volume was 20 ?L.The contents of the related substances in metoclopramide were computed by self-control method of main constituent.RESULTS: Under the above described chromatographic conditions,metoclopramide was completely separated from its impurities.A good linearity between impurities' peak area and metoclopramide(contrast solution) concentration was achieved when the concentrations of impurities were over the range of 0.05%～4.0%.The lowest detectable limit of metoclopramide was 0.3 ng,and the contents of the related substances were all less than 0.26%.CONCLUSION: The method is convenient,accurate,sensitive and,specific,and it can be used for the determination of the related substances in metoclopramide.

Objective:To discuss the effect of cold exposure on nociception in the rats and its regulatory mechanism on transient receptor potential(TRP)ion channels in the sensory neurons,and to provide the basis for clarifying the biological mechanism of cold-sensitive pain.Methods:Sixteen female SD rats were divided into control group(n=8)and cold group(n=8).The rats in control group were exposed to the environment of(24±2)℃,and the rats in cold group were exposed to low temperature(4 ℃±1 ℃)in an artificial intelligence climate chamber for 4 h daily,for one week.Von Frey filaments were used to detect the mechanical withdrawal threshold(MWT)of the rats in two groups;immunofluorescence staining was used to observe the expression levels of TRPA1,TRPM8,TRPV1,and TRPV4 in dorsal root ganglion(DRG)tissue of the rats in two groups,the expression levels of calcitonin gene-related peptide(CGRP)and substance P(SP)in DRG tissue of the rats in two groups,and the expression levels of TRPA1,TRPM8,TRPV1,and TRPV4 in synovial tissue of the rats in two groups.Results:Compared with control group,the MWT of the rats in cold group was significantly decreased(P＜0.05),the expression levels of TRPA1 and TRPM8 in DRG tissue were significantly increased(P＜0.05),the expression level of TRPV1 was significantly decreased(P＜0.05),there was no significant difference in the expression level of TRPV4(P＞0.05),and the expression levels of CGRP and SP were significantly increased(P＜0.05).Compared with control group,the expression level of TRPA1 in synovial tissue of the rats in cold group was significantly increased(P＜0.05),while the expression levels of TRPM8,TRPV1,and TRPV4 were significantly decreased(P＜0.05).Conclusion:Short-term cold exposure can induce the hyperalgesia of the rats,and its mechanism may be associated with the changes in the expression of TRP ion channels in DRG and synovial tissues.TRPA1 sensory neurons play an important role in local joint cold pain.