Evaluation of serotonin as a feedback inhibitor of lactation in the bovine
Evaluation of serotonin as a feedback inhibitor of lactation in the bovine
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DOI：
10.3168/jds.2007-0766
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发表时间：
2008-05-01
影响因子：
3.5
通讯作者：
Collier, R. J.
中科院分区：
文献类型：
--
作者：
Hernandez, L. L.;Stiening, C. M.;Collier, R. J.
5-羟色胺（5-HT）是一种由色氨酸合成的神经递质，被认为是泌乳的反馈抑制剂。我们确定，编码色氨酸羟化酶1，5-HT合成的限速酶的基因，在体外牛乳腺上皮细胞中表达，并通过催乳素上调。此外，5-HT在体外降低α-乳白蛋白和酪蛋白基因的表达。此外，用对氯苯丙氨酸抑制5-HT合成或用麦角新碱（METH）阻断5-HT受体可增加乳蛋白基因表达。然后，我们评估了乳房内注射5-HT或METH对6头经产荷斯坦奶牛的生产和牛奶成分的影响。奶牛被分配到一个重复的措施设计，对侧乳房内注入METH（20 mg/乳区/天）或生理盐水3天，随后是7天的洗脱期，然后给予5-HT（50 mg/乳区/天）或SAL 3天。对于每半个乳房，每天记录两次产奶量并测定一次组成。每天采集血液样本用于血浆测定葡萄糖和非酯化脂肪酸浓度。在每次挤奶后获得蒸发热损失、呼吸率、左右乳房温度和直肠温度，以评价输注可能的全身效应。在METH和盐水输注期间，产奶量增加10.9%。在5-HT和生理盐水输注期间，产奶量下降11.1%。产奶量和生理反应表明，乳房内5-HT和METH剂量足够高，引起全身效应。输注生理盐水、METH和5-HT可增加乳汁SCC。相对于生理盐水，输注5-HT倾向于降低平均乳糖浓度（4.3 vs. 4.6%）。METH和SAL使乳蛋白含量降低（2.0%），5-HT使乳蛋白含量升高（5.8%），输注后降低33%。输注METH使蒸发热损失增加11%，输注后减少11%。输注5-HT或METH不影响血浆非酯化脂肪酸或葡萄糖浓度、呼吸速率或乳脂含量。我们得出结论，5-HT输注减少牛奶的合成，而阻断5-HT受体与甲基增加牛奶的合成。本研究中使用的5-HT和METH剂量可能导致全身效应。这些数据支持的概念，5-HT是一种反馈抑制剂的泌乳牛。
Serotonin (5-HT), a neurotransmitter synthesized from tryptophan, has been proposed as a feedback inhibitor of lactation. We determined that the gene coding for tryptophan hydroxylase 1, the rate-limiting enzyme for 5-HT synthesis, is expressed in bovine mammary epithelial cells in vitro and is upregulated by prolactin. In addition, 5-HT reduced the expression of alpha-lactalbumin and casein genes in vitro. Furthermore, inhibiting 5-HT synthesis with p-chlorophenylalanine or blocking the 5-HT receptor with methysergide (METH) increased milk protein gene expression. We then evaluated effects of intramammary 5-HT or METH infusion on production and milk composition in 6 multiparous Holstein cows. Cows were assigned to a repeated measures design of contralateral intramammary infusions of METH (20 mg/quarter per d) or saline for 3 d followed by a 7-d washout period before administering 5-HT (50 mg/quarter/d) or SAL for 3 d. For each udder half, milk yield was recorded twice and composition was determined once per day. Blood samples were harvested each day for plasma to determine glucose and nonesterified fatty acid concentrations. Evaporative heat loss, respiration rate, left and right udder temperatures, and rectal temperatures were obtained after each milking to evaluate possible systemic effects of infusions. During METH and saline infusions milk yield increased 10.9%. During 5-HT and saline infusion milk yield decreased 11.1%. Milk yield and physiological responses suggested intramammary 5-HT and METH doses were high enough to cause systemic effects. Infusing saline, METH, and 5-HT increased milk SCC. Infusing 5-HT tended to reduce mean lactose concentration (4.3 vs. 4.6%) relative to saline. Milk protein content was decreased by METH and SAL (2.0%) and was increased (5.8%) by 5-HT followed by a 33% decrease postinfusion. Infusion of METH increased evaporative heat loss 11%, which decreased 11% postinfusion. Infusions of 5-HT or METH did not affect plasma nonesterified fatty acid or glucose concentrations, respiration rate, or milk fat content. We conclude 5-HT infusion reduced milk synthesis, whereas blocking the 5-HT receptor with METH increased milk synthesis. Doses of 5-HT and METH used in this study likely resulted in systemic effects. These data support the concept that 5-HT is a feedback inhibitor of lactation in the bovine.