Feasibility study of morphine-induced rat pica model by tail vein injection to replace vomiting model

Objective： To explore the feasibility of the morphine-induced rat pica model by tail vein injection to replace the vomiting model，and the effective dose of morphine with less severe complications when the model was developed.Methods： Fifty SD rats were randomly divided into the blank control group and the M1，M2，M3 and M4 groups，each consisting of 10 animals. The rats in the blank control group were injected with 10 ml/kg normal saline（NS） via tail vein，while the animals in the M1，M2，M3 and M4 groups were injected with morphine hydrochloride injection at a dosage of 5，10，20 and 30 mg/kg via tail vein.Heart rate，blood oxygen saturation and activities of the animals were closely observed and recorded at 5，10 and 15 minutes after medication.Then，changes in the intake of kaolin，feed and water of the rats in each group were recorded and compared between the groups for 4 successive days after medication.Results： The blood oxygen saturation in the morphine treatment groups all reduced significantly，and statistical significance could be seen，when it was compared with that of the blank control group（P<0.05）.On the first day after medication，the intake of kaolin in the M3 and M4 groups increased significantly，as compared with that of the blank control group（P<0.05）.On the third day after medication，the intake of kaolin in the M1 group significantly increased，as compared with that of the blank control group（P<0.05）.Conclusion： The rat pica model was established by tail vein injection of morphine，which could be used to replace the vomiting model.The effective dose of morphine was 20 mg/kg with less severe complications.