Elevating serotonin pre-partum alters the Holstein dairy cow hepatic adaptation to lactation

<div><p>Serotonin is known to regulate energy and calcium homeostasis in several mammalian species. The objective of this study was to determine if pre-partum infusions of 5-hydroxytryptophan (5-HTP), the immediate precursor to serotonin synthesis, could modulate energy homeostasis at the level of the hepatocyte in post-partum Holstein and Jersey dairy cows. Twelve multiparous Holstein cows and twelve multiparous Jersey cows were intravenously infused daily for approximately 7 d pre-partum with either saline or 1 mg/kg bodyweight of 5-HTP. Blood was collected for 14 d post-partum and on d30 post-partum. Liver biopsies were taken on d1 and d7 post-partum. There were no changes in the circulating concentrations of glucose, insulin, glucagon, non-esterified fatty acids, or urea nitrogen in response to treatment, although there were decreased beta-hydroxybutyrate concentrations with 5-HTP treatment around d6 to d10 post-partum, particularly in Jersey cows. Cows infused with 5-HTP had increased hepatic serotonin content and increased mRNA expression of the serotonin 2B receptor on d1 and d7 post-partum. Minimal changes were seen in the hepatic mRNA expression of various gluconeogenic enzymes. There were no changes in the mRNA expression profile of cell-cycle progression marker cyclin-dependent kinase 4 or apoptotic marker caspase 3, although proliferating cell nuclear antigen expression tended to be increased in Holstein cows infused with 5-HTP on d1 post-partum. Immunofluorescence assays showed an increased number of CASP3- and Ki67-positive cells in Holstein cows infused with 5-HTP on d1 post-partum. Given the elevated hepatic serotonin content and increased mRNA abundance of <i>5HTR2B</i>, 5-HTP infusions may be stimulating an autocrine-paracrine adaptation to lactation in the Holstein cow liver.</p></div

Hepatic serotonin content and <i>TPH1</i> and <i>SERT</i> mRNA abundance of multiparous Holstein cows and multiparous Jersey cows administered pre-partum daily I.V. infusions of 1 liter of saline or 1 liter of 1.0 mg/kg bodyweight of 5-hyroxy-L-tryptophan (5-HTP) reconstituted in saline.

<p>Final treatment groups were saline-infused Holsteins (<i>n</i> = 6), 5-HTP infused Holsteins (<i>n</i> = 6), saline-infused Jerseys (<i>n</i> = 6), and 5-HTP infused Jerseys (<i>n</i> = 6). (A) Liver serotonin content corrected to ug of protein (B) mRNA abundance of tryptophan hydroxylase 1 (<i>TPH1</i>) and (C) mRNA abundance of serotonin reuptake transporter (<i>SERT</i>). Stars indicate statistical difference between group means (* = 0.05<<i>P</i><0.01). All values are reported as LS means ± SEM.</p

Primer sequences for genes quantified by real-time PCR.

<p>Primer sequences for genes quantified by real-time PCR.</p

Immunofluorescent images and counts of cells positive for Ki67 and CASP3 in multiparous Holstein cows and multiparous Jersey cows administered pre-partum daily I.V. infusions of 1 liter of saline or 1 liter of 1.0 mg/kg bodyweight of 5-hyroxy-L-tryptophan (5-HTP) reconstituted in saline.

<p>Final treatment groups were saline-infused Holsteins (<i>n</i> = 6), 5-HTP infused Holsteins (<i>n</i> = 6), saline-infused Jerseys (<i>n</i> = 6), and 5-HTP infused Jerseys (<i>n</i> = 6). (A) Percent of cells positive for Ki67 stain of all counted cells in representative images (<i>n</i> = 3) from each treatment group. (B) Immunofluorescent images of Ki67-positive cells. The scale bar indicates 15 microns. The arrow indicates an example of a cell considered positive for Ki67. d1 and d7 are days 1 and 7 post-partum, respectively. CON and 5-HTP represent saline-infused and 5-HTP infused groups, respectively. (C) Immunofluorescent images of CASP3-positive cells. The scale bar indicates 15 microns. The arrow indicates an example of a cell considered positive for CASP3. (D) Count of cells positive for CASP3 in representative images (<i>n</i> = 3) from each treatment group. Stars indicate statistical difference between group means (* = 0.05<<i>P</i><0.01; *** = 0.001<<i>P</i><0.0001). All values are reported as LS means ± SEM.</p

Hepatic mRNA abundance of <i>CCND1</i>, <i>CDK4</i>, <i>PCNA</i>, and <i>CASP3</i> in multiparous Holstein cows and multiparous Jersey cows administered pre-partum daily I.V. infusions of 1 liter of saline or 1 liter of 1.0 mg/kg bodyweight of 5-hyroxy-L-tryptophan (5-HTP) reconstituted in saline.

<p>Final treatment groups were saline-infused Holsteins (<i>n</i> = 6), 5-HTP infused Holsteins (<i>n</i> = 6), saline-infused Jerseys (<i>n</i> = 6), and 5-HTP infused Jerseys (<i>n</i> = 6). mRNA abundance of (A) cyclin D1 (<i>CCND1</i>) (B) cyclin-dependent kinase 4 (<i>CDK4</i>) (C) proliferating cell nuclear antigen (<i>PCNA</i>) and (D) caspase-3 (<i>CASP3</i>). All values are reported as LS means ± SEM.</p