Previous research indicates the presence of a feedback inhibitor of lactation (FIL) in milk (Peaker and Wilde, 1996). Recently, tryptophan hydroxylase I (TPH1), the rate-limiting enzyme in serotonin (5-HT) biosynthesis, was identified in the mouse mammary gland and to be regulated by prolactin (PRL). Furthermore, 5-HT was present in rodent milk and addition of 5-HT to in vitro mammary cultures and in vivo administration of 5-HT to lactating mice reduced milk protein synthesis. Studies were conducted to determine the presence of the enzymatic machinery necessary to produce 5-HT in the bovine mammary gland, the presence of specific 5-HT receptors within the bovine mammary gland, the effects of 5-HT and non-selective and selective receptor antagonists on milk protein gene expression in cultures of primary bovine mammary epithelial cells (BMEC), and to determine the effects of intra-mammary infusions of 5-HT and a non-selective 5-HT receptor antagonist on milk production and composition in lactating dairy cows. Tryptophan hydroxylase I, aromatic amino acid decarboxylase (AADC) and the 5-HT reuptake transporter (SERT) were detected in lactating bovine mammary tissue by qRT-PCR and immunohistochemical staining. Additionally, mRNA for the 5-HT 1B, 2A, 2B, 4 and 7 receptors were detected in bovine mammary tissue as well as BMEC by qRT-PCR and in situ hybridization. Tryptophan hydroxylase I mRNA is in BMEC and up-regulated by PRL. Serotonin down-regulates milk protein gene expression but has not apparent effects on apoptosis and methysergide, ritanserin, SB-224289, and pimozide (receptor antagonists) increased milk protein gene expression in BMEC. Intra-mammary 5-HT infusions decreased overall milk yield in late-lactating dairy cows by 11.1%. Intra-mammary infusions of METH increased overall milk yield by 10.9%. In conclusion, the enzymatic machinery for 5-HT biosynthesis and uptake, as well as receptors involved 5-HT signaling are present in the bovine mammary gland. Furthermore, 5-HT appears to be a FIL in the bovine, but further research regarding its cellular mechanism of action and the location of its receptor populations should be conducted.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/196049 |
| Date | January 2007 |
| Creators | Hernandez, Laura L |
| Contributors | Collier, Robert J., Baumgard, Lance H., Collier, Robert J., Baumgard, Lance H., Horseman, Nelson D., Limesand, Kirsten H., Goll, Darrel E. |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | English |
| Detected Language | English |
| Type | text, Electronic Dissertation |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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