title: Plasma beta-endorphin and adrenocorticotrophin in young horses in training.
abstract: A controlled period of submaximal exercise on a treadmill was used as a standardised stress test in 6 young horses to monitor the effects of training. Circulating plasma concentrations of immunoreactive beta-endorphin (IR beta-EP) were measured before, during and after the exercise period. The stress test was conducted on 3 occasions during an intensive training program lasting 14 weeks. In week 3 a marked increase in plasma IR beta-EP (P = 0.003) was demonstrated as a result of training, but by the last exercise test performed in week 9 no significant increase in plasma IR beta-EP concentrations could be detected. During the training period the basal concentrations of plasma IR beta-EP significantly decreased (P = 0.0059). Plasma adrenocorticotrophin (ACTH) did not increase during exercise, although there was a trend of decreasing basal plasma ACTH by the end of the training period. It was concluded that a standardised work test acted as a mild stress to unfit horses, but as the horses' fitness increased the hormonal response to exercise diminished. Basal plasma beta-EP concentrations were decreased with increasing fitness.
authors.affiliation: Department of Veterinary Science, University of Melbourne, Victoria.
authors.forename: R N
authors.initials: RN
authors.lastname: McCarthy
authors.forename: L B
authors.initials: LB
authors.lastname: Jeffcott
authors.forename: J W
authors.initials: JW
authors.lastname: Funder
authors.forename: M
authors.initials: M
authors.lastname: Fullerton
authors.forename: I J
authors.initials: IJ
authors.lastname: Clarke
mesh_terms: D000324:Adrenocorticotropic Hormone / Q000097:blood*; D000818:Animals; D005080:Exercise Test / Q000662:veterinary; D005260:Female; D006736:Horses / Q000097:blood*; D008297:Male; D010805:Physical Conditioning, Animal; D001615:beta-Endorphin / Q000097:blood*
chemical_list: D001615:beta-Endorphin; D000324:Adrenocorticotropic Hormone