Effects Of Prenatal 5-HTP Injection On Calcium Metabolism And Casein Synthesis In Dairy Goats

Due to the growth of fetus and the need of postpartum lactation,the metabolic level of dairy goat changes dramatically,which easily leads to hypocalcemia,ketosis,fatty liver and other metabolic diseases,causing great loss to dairy goat industry.5-hydroxytryptamine(5-HT)is a biological amine and tryptophan derivative,synthesis in animal central nervous system and intestinal tract,breast,bone,pancreatic islet and other peripheral tissues,is an important molecule regulating the life activities of the body.As a hormone,5-HT synthesized in peripheral tissues can regulate calcium metabolism,bone metabolism and energy metabolism of mammary gland through autocrine or paracrine pathway.Therefore,increasing the concentration of 5-HT in the blood circulation of perinatal dairy goats may be helpful to improve the metabolic homeostasis of dairy goats.In this study,5-hydroxytryptophan(5-HTP),a precursor of 5-HT,was injected into perinatal dairy goats,the concentrations of 5-HT,Parathyroid hormone-related Protein(PTHr P)and Ca in serum and colostrum before and after delivery as well as the composition of milk were measured.Meanwhile,Goat Mammary gland Epithelial Cells(GMECs)were taken as the research object.By adding 5-HTP,5-HTR7 antagonist(SB269970)and 5-HT rate-limiting enzyme TPH1 inhibitor(PCPA)to GMECs,the effect and regulatory mechanism of 5-HTP on β-casein biosynthesis and cell apoptosis was investigated.The main results are as follows:1.Injecting 1.0 mg/kg 5-HTP 7 days before parturition increased 5-HT and PTHr P concentrations in serum and colostrum before and after parturition,and increased Ca concentration in blood after parturition;reduced casein content in colostrum on the day of parturition,but had no significant effect on the content of lactose,milk fat and milk protein in colostrum.2.In vitro,cell experiments showed that 200 μM 5-HTP inhibited the expression ofβ-Casein in GMECs by inhibiting the JAK2/ STAT5 a signaling pathway through 5-HTR7.3.200 μM 5-HTP promoted the apoptosis of GMECs through 5-HTR7.In conclusion,5-HT can regulate calcium metabolism and casein synthesis in colostrum of perinatal dairy goats.Prenatal injection of 5-HTP can increase the concentrations of 5-HT,PTHr P and Ca in the circulation before and after delivery.In GMECs,5-HTP can inhibit the synthesis of β-casein by inhibiting JAK2/STAT5 a signaling pathway through 5-HTR7,and promote GMECs apoptosis.The aim of this study was to reveal the effects of 5-HT on calcium metabolism and casein synthesis in periparturient dairy goats and its possible molecular mechanism,this study provides a theoretical reference for improving hypocalcemia and the nutritional value of colostrum in dairy goats.