If you go to LactaPedia.com, created by the lactation crew at the University of Western Australia, and look up "feedback inhibitor of lactation" it will say "see also serotonin" and if you look up "serotonin" it says "see also feedback inhibitor of lactation."  The old belief that FIL was a whey protein was never proven, while there are multiple studies showing such a relationship between serotonin and milk synthesis. No one has yet written the definitive paper that you're looking for, but here is some of the supporting research that authors who say FIL is serotonin base their statements on.



~Lisa Marasco



Chiba, T., Maeda, T., & Kudo, K. (2018). [Endogenous Serotonin and Milk Production Regulation in the Mammary Gland]. Yakugaku Zasshi, 138(6), 829-836. doi:10.1248/yakushi.18-00003

Collier, R. J., Hernandez, L. L., & Horseman, N. D. (2012). Serotonin as a homeostatic regulator of lactation. Domest Anim Endocrinol, 43(2), 161-170. doi:10.1016/j.domaniend.2012.03.006

Hernandez, L. L., Collier, J. L., Vomachka, A. J., Collier, R. J., & Horseman, N. D. (2011). Suppression of lactation and acceleration of involution in the bovine mammary gland by a selective serotonin reuptake inhibitor. J Endocrinol, 209(1), 45-54. doi:10.1530/JOE-10-0452

Hernandez, L. L., Stiening, C. M., Wheelock, J. B., Baumgard, L. H., Parkhurst, A. M., & Collier, R. J. (2008). Evaluation of serotonin as a feedback inhibitor of lactation in the bovine. J Dairy Sci, 91(5), 1834-1844. doi:10.3168/jds.2007-0766

Horseman, N. D., & Collier, R. J. (2014). Serotonin: a local regulator in the mammary gland epithelium. Annu Rev Anim Biosci, 2, 353-374. doi:10.1146/annurev-animal-022513-114227

Kessler, E. C., Wall, S., Hernandez, L., Bruckmaier, R., & Gross, J. J. (2018). Circulating serotonin is related to the metabolic status and lactational performance at the onset of lactation in dairy cows. Journal of dairy science, 101(12), 11455-11460. 

Marshall, A. M., Hernandez, L. L., & Horseman, N. D. (2014). Serotonin and serotonin transport in the regulation of lactation. J Mammary Gland Biol Neoplasia, 19(1), 139-146. doi:10.1007/s10911-013-9304-6

Marshall, A. M., Nommsen-Rivers, L. A., Hernandez, L. L., Dewey, K. G., Chantry, C. J., Gregerson, K. A., & Horseman, N. D. (2010). Serotonin transport and metabolism in the mammary gland modulates secretory activation and involution. J Clin Endocrinol Metab, 95(2), 837-846. doi:jc.2009-1575 [pii]

10.1210/jc.2009-1575



             ***********************************************



Archives: http://community.lsoft.com/archives/LACTNET.html

To reach list owners: [log in to unmask]

Mail all list management commands to: [log in to unmask]

COMMANDS:

1. To temporarily stop your subscription write in the body of an email: set lactnet nomail

2. To start it again: set lactnet mail

3. To unsubscribe: unsubscribe lactnet

4. To get a comprehensive list of rules and directions: get lactnet welcome