Increasing serotonin concentrations alter calcium and energy metabolism in dairy cows

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   Figure 1

   Schematic representation of the experimental design. Four doses (0, 0.5, 1.0, and 1.5 mg/kg) of 5-hydroxy-l-tryptophan (5-HTP) were infused intravenously (at a constant rate for 1 h) for 4 days (1–4) into four Holstein dairy cows in a 4×4 Latin square design. There were a total of four infusion periods (with a 5-day washout period in between each infusion period). Only period I is shown here as an example. Before the initiation of period I, blood, urine, and milk samples were collected daily for 5 days (baseline). Milk samples were collected daily (morning milking), urine samples were collected pre- and post-infusion, and blood samples were collected pre-infusion (at 0 min) and post-infusion (at 5, 10, 30, 60, 90, and 120 min). Animal health parameters (heart rate, respiration rate, and rectal temperature) were recorded pre-infusion, every 15 min during infusion, and 15 min post-infusion. Manure frequency and score were recorded during infusion. Liver tissue was harvested at the beginning of the baseline period and on day 2 during each of the four infusion periods. Blood, urine, and milk samples were collected daily during the washout periods as well.
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   Figure 2

   Animal health parameters and serum serotonin concentrations in response to 5-HTP infusion. (A) Heart rate (beats/min), (B) respiration rate (inhalations/min), (C) rectal temperature (°Fahrenheit, °F), (D) manure score (0=normal to 4=diarrhea) were monitored pre- (0), every 15 min (15, 30, and 45) during 1 h of continuous i.v. infusion of four doses of 5-HTP (0, 0.5, 1.0, or 1.5 mg/kg), and 15 min post-infusion (+15) into late-lactation, non-pregnant Holstein dairy cows (n=4). Defecation frequency was monitored only during 5-HTP infusion (D). (E and F) Circulating serotonin concentrations in response to (E) treatment (5-HTP dose) (E) and day of infusion (1–4) (F). (G) Hepatic concentrations of serotonin by 5-HTP dose. Different letters indicate statistical differences between group means (Tukey's P<0.05). Data are presented as LS means±s.e.m.
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   Figure 3

   Circulating glucose levels in response to the i.v. infusion of four 5-hydroxy-l-tryptophan (5-HTP) doses (0, 0.5, 1.0, and 1.5 mg/kg) for 4 consecutive days into late-lactation, non-pregnant Holstein dairy cows (n=4). (A) Main effect of treatment (5-HTP dose). (B) Interaction between day of infusion and 5-HTP dose. Different letters indicates statistical differences between group means (Tukey's P<0.05). Data are presented as means±s.e.m.
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   Figure 4

   Circulating insulin concentrations in response to the i.v. infusion of four 5-hydroxy-l-tryptophan (5-HTP) doses (0, 0.5, 1.0, and 1.5 mg/kg) for 4 consecutive days into late-lactation, non-pregnant Holstein dairy cows (n=4). (A) Main effect of treatment (5-HTP dose) and (B) time after 5-HTP infusion (0–120 min). (C) Interaction between 5-HTP dose and day of infusion, and (D) interaction between 5-HTP dose and min after infusion. Different letters indicates statistical differences between group means (Tukey's P<0.05). Data are presented as LS means±s.e.m.
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   Figure 5

   Circulating non-esterified fatty acid (NEFA) concentrations in response to the i.v. infusion of four 5-hydroxy-l-tryptophan (5-HTP) doses (0, 0.5, 1.0, and 1.5 mg/kg) for 4 consecutive days into late-lactation, non-pregnant Holstein dairy cows (n=4). (A) Main effect of treatment (5-HTP dose), (B) time after 5-HTP infusion (0–120 min), and (C) days of 5-HTP infusion (1–4). (D) Interaction between day of infusion and 5-HTP dose, and (E) interaction between 5-HTP dose and min after infusion. Different letters indicates statistical differences between group means (Tukey's P<0.05). Data are presented as LS means±s.e.m.
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   Figure 6

   Circulating beta-hydroxybutyrate (βHBA) concentrations in response to the i.v. infusion of four 5-hydroxy-l-tryptophan (5-HTP) doses (0, 0.5, 1.0, and 1.5 mg/kg) for 4 consecutive days into late-lactation, non-pregnant Holstein dairy cows (n=4). (A) Main effect of treatment (5-HTP dose), (B) time after 5-HTP infusion (0–120 min), and (C) days of 5-HTP infusion (1–4). Different letters indicates statistical differences between group means (Tukey's P<0.05). Data are presented as LS means±s.e.m.
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   Figure 7

   Serum calcium and plasma parathyroid hormone-related protein (PTHrP) concentrations in response to the i.v. infusion of four 5-hydroxy-l-tryptophan (5-HTP) doses (0, 0.5, 1.0, and 1.5 mg/kg) for 4 consecutive days into late-lactation, non-pregnant Holstein dairy cows (n=4). (A) Main effect of treatment (5-HTP dose), (B) days of 5-HTP infusion (1–4), and (C) interaction between 5-HTP dose and min after infusion for calcium concentrations. (D) Percentage change of urine calcium (uCa) calculated as: ((uCa 120 min−uCa 0 min)/(uCa 120 min))×100 by 5-HTP dose. (E and F) Milk calcium (Ca) and phosphorus (P) concentrations by 5-HTP dose. (G) Main effect of 5-HTP dose and (H) time after infusion for PTHrP concentrations. Different letters indicates statistical differences between group means (Tukey's P<.05). Data are presented as LS means±s.e.m.
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   Figure 8

   Hepatic mRNA expression of genes associated with glucose (pyruvate dehydrogenase kinase, isozyme 4, PDK4 (A); glucose-6-phosphatase, G6P (B)), ketone (3-hydroxy-3-methylglutaryl-CoA, HMG-COA (C)), and fatty acid (peroxisome proliferator-activated receptor α, PPARα (D); carnitine palmitoyltransferase 1, CPT1 (E); acyl-CoA dehydrogenase, very long chain, ACADVL (F)) synthesis after the i.v. infusion of four doses (0, 0.5, 1.0, and 1.5 mg/kg) of 5-hydroxy-l-tryptophan (5-HTP) for 4 consecutive days into late-lactation, non-pregnant Holstein dairy cows (n=4). Liver tissue was harvested before the initiation of the experiment (baseline) and after 2 days of 5-HTP infusion. Different letters indicates statistical differences between group means (Tukey's P<0.10). Data are presented as LS means±s.e.m.

• © 2015 Society for Endocrinology