title: Gonadotrophin-releasing hormone and human chorionic gonadotrophin tests reveal that both hypothalamic and testicular endocrine functions are suppressed during acute prolonged physical exercise.
abstract: The mechanism of suppression of gonadotrophins and testosterone during prolonged exercise was studied. Fourteen healthy males were injected immediately before an exhaustive bicycle run for 4 h, and before a control period without exercise, with one of the following substances: (1) 1 ml of saline, (2) 100 micrograms of a GnRH agonist (buserelin), and (3) 50 IU/kg of hCG. Each test was repeated for each subject 2 weeks apart, in a randomized single-blind fashion. Blood samples were taken before the injections (sample A), 6 h after the injections (sample B), and the following morning (sample C). During placebo treatment testosterone concentration decreased from A samples to B samples more in the exercise trial than in rest trial (31 vs 8%, P = 0.02). This exercise-associated decrease was reversed by both the GnRH agonist and hCG treatments. Serum gonadotrophin concentrations responded identically to GnRH agonist injections during exercise and rest trials. hCG resulted in a greater increase of serum testosterone from A to C samples at rest than during the exercise trial (52 vs 33%, P = 0.04). In conclusion, the exercise-induced suppression of serum testosterone is associated with two effects: suppressed endogenous GnRH stimulation of gonadotrophin release during exercise, and decreased testicular capacity to secrete testosterone during recovery period.
authors.affiliation: Department of Physiology, University of Turku, Finland.
authors.forename: U M
authors.initials: UM
authors.lastname: Kujala
authors.forename: M
authors.initials: M
authors.lastname: Alen
authors.forename: I T
authors.initials: IT
authors.lastname: Huhtaniemi
mesh_terms: D000328:Adult; D002064:Buserelin; D006063:Chorionic Gonadotropin; D015444:Exercise / Q000502:physiology*; D005640:Follicle Stimulating Hormone / Q000097:blood; D006062:Gonadotropins / Q000097:blood*; D006801:Humans; D007031:Hypothalamus / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D016037:Single-Blind Method; D013737:Testis / Q000502:physiology*; D013739:Testosterone / Q000097:blood*
chemical_list: D006063:Chorionic Gonadotropin; D006062:Gonadotropins; D013739:Testosterone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D002064:Buserelin