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Elevated circulating serotonin alters calcium metabolism in mid-late lactation dairy cows.

M. K. Connelly




Elevated circulating serotonin alters calcium metabolism in mid-late lactation dairy cows.
M. K. Connelly*, H. P. Fricke, J. Kuehnl, M. Klister, L. L. Hernandez. University of Wisconsin-Madison Madison, WI.

Serotonin is an evolutionary conserved monoamine that modulates a variety of physiological functions. Of interest in the dairy cow is serotonin's action on calcium homeostasis due to the increased calcium demand that occurs during lactation. Understanding serotonin's mechanism, specifically at the level of the mammary gland, is critical to understanding the role of serotonin during lactation. Therefore, the objective of this study was to determine how intravenous infusion of 5-hydroxytryptophan (5-HTP) in mid-late lactation dairy cows altered calcium metabolism. Twelve multiparous Holstein cows were blocked by parity in a randomized complete block design. Cows were intravenously infused daily at a constant rate with (1) 1.5 mg/kg 5-HTP (n = 6) or (2) 0.9% saline (n = 6) for 3 consecutive days with sampling through 24h post termination of final infusion. Baseline mammary biopsies, blood and milk samples were taken one day before initiation of treatment. Additional mammary biopsies and blood samples were collected at 0, 8, and 24h post final intravenous treatment. Mammary tissues were analyzed via qPCR to evaluate calcium metabolism genes. Milk samples were taken each morning before infusion and the morning following final infusion. Circulating serotonin increased in 5-HTP infused cows (P = 0.03), while circulating calcium concentrations were decreased (P = 0.03) relative to control cows. Relative expression of plasma membrane calcium ATPase 2 and calcium release-activated channel protein 1 were upregulated in 5-HTP treated cows when compared with control cows (P = 0.118 and P = 0.116, respectively). Cows infused with 5-HTP had increased (P = 0.01) milk serotonin concentrations on d 4 and increased milk calcium concentration (P = 0.03) on d 3 of the experiment. Eight hours after final intravenous treatment, relative expression of parathyroid hormone-related peptide was increased (P = 0.04) and mammary gland serotonin content tended to be elevated (P = 0.08) relative to control. This supports previous rodent and cow data from our lab on serotonin's regulation of mammary gland physiology and calcium trafficking.

Keywords: serotonin, calcium.