Serotonin (5-HT) has many important functions in both central and peripheral nervous systems. Although it has been demonstrated that manipulation of serotonin metabolism is possible in many species, there is limited information about l-tryptophan (TRP), a serotonin precursor, in cattle, and these provide conflicting results. Furthermore, there is no study evaluating how different patterns of intra-abomasal infusion of TRP impact circulating 5-HT. The objective of this study was to evaluate if intra-abomasal infusion patterns of TRP can affect circulating 5-HT and other metabolites from TRP metabolism in the plasma and serum and circulating glucose and insulin in cattle. Eight ruminally cannulated Holstein steers were used in a replicated 4 × 4 Latin square design. Each received intra-abomasal water infusion (control) or intra-abomasal TRP infusion (50 mg/kg BW) in 3 different patterns: a pulse infusion once a day (pulse once), pulse infusion twice a day (pulse twice), or continuous infusion (continuous). For continuous treatment, the TRP dose was diluted in tap water and infused by a peristaltic pump (300 mL/h). To equalize conditions, the other treatments had a water infusion (300 mL/h). The steers were fed every 2 h, and blood was collected from a jugular vein catheter every 4 h for 24 h after the initial infusion. Urine produced during the 24 h period was collected. Serum and plasma TRP, 5-HT and kynurenine, plasma glucose, and serum insulin concentrations were analyzed. Urine was analyzed for concentrations of 5-hydroxyindoleacetic acid. Both serum TRP and kynurenine were increased (P < 0.05) by all TRP infusion treatments, but concentrations in pulse dose treatments were greater than those in continuous infusion. Serum 5-HT increased (P < 0.05) with both pulse TRP infusion treatments; however, the continuous TRP infusion did not increase the serum 5-HT. Plasma 5-HT, glucose, and insulin had a tendency to increase with TRP pulse infusions. The urinary 5-hydroxyindoleacetic acid excretion was highest for pulse dose treatments. An acute supply of TRP in 1 or 2 daily doses increases serum 5-HT and increases circulating glucose and insulin in cattle. The TRP and kynurenine concentrations are similar in plasma and serum. However, the serum 5-HT concentration is more responsive to TRP administration than plasma.

血清素 (5-HT) 在中枢和外周神经系统中具有许多重要功能。尽管已经证明在许多物种中可以操纵血清素代谢，但关于l 的信息有限-色氨酸 (TRP)，一种血清素前体，在牛身上，这些提供了相互矛盾的结果。此外，没有研究评估不同的腹腔内输注 TRP 对循环 5-HT 的影响。本研究的目的是评估 TRP 的腹腔内输注模式是否会影响循环 5-HT 和来自血浆和血清中 TRP 代谢的其他代谢物以及牛的循环葡萄糖和胰岛素。八头瘤胃插管荷斯坦公牛用于复制的 4 × 4 拉丁方设计。每个人都接受了 3 种不同模式的腹腔内水输注（对照）或腹腔内 TRP 输注（50 mg/kg BW）：每天一次脉冲输注（脉冲一次），每天两次脉冲输注（脉冲两次），或连续输液（连续）。对于连续治疗，将 TRP 剂量在自来水中稀释并通过蠕动泵 (300 mL/h) 注入。为了平衡条件，其他治疗进行了输注水 (300 mL/h)。每 2 小时给公牛喂食一次，在初次输注后的 24 小时内，每 4 小时从颈静脉导管收集一次血液。收集在 24 小时期间产生的尿液。分析了血清和血浆 TRP、5-HT 和犬尿氨酸、血浆葡萄糖和血清胰岛素浓度。分析尿液中的 5-羟基吲哚乙酸浓度。血清 TRP 和犬尿氨酸均升高（收集在 24 小时期间产生的尿液。分析了血清和血浆 TRP、5-HT 和犬尿氨酸、血浆葡萄糖和血清胰岛素浓度。分析尿液中的 5-羟基吲哚乙酸浓度。血清 TRP 和犬尿氨酸均升高（收集在 24 小时期间产生的尿液。分析了血清和血浆 TRP、5-HT 和犬尿氨酸、血浆葡萄糖和血清胰岛素浓度。分析尿液中的 5-羟基吲哚乙酸浓度。血清 TRP 和犬尿氨酸均升高（P < 0.05) 通过所有 TRP 输注治疗，但脉冲剂量治疗的浓度高于连续输注的浓度。两种脉冲 TRP 输注治疗后血清 5-HT 均增加（P < 0.05）；然而，连续输注 TRP 并没有增加血清 5-HT。随着 TRP 脉冲输注，血浆 5-HT、葡萄糖和胰岛素有增加的趋势。脉冲剂量治疗的尿 5-羟基吲哚乙酸排泄量最高。每天 1 或 2 次急性供应 TRP 会增加血清 5-HT 并增加牛的循环葡萄糖和胰岛素。血浆和血清中的 TRP 和犬尿氨酸浓度相似。然而，血清 5-HT 浓度对 TRP 给药比血浆更敏感。