title: Circulating metabolic hormones during the peripubertal period and their association with testicular development in bulls.
abstract: The objective of the present study was to characterize changes in serum metabolic hormones concentrations from 20 weeks before to 20 weeks post-puberty in bulls and to investigate the associations of metabolic hormones concentrations with testicular development. Leptin concentrations increased from 16 weeks before puberty to 8 weeks post-puberty and insulin concentrations increased from puberty to 8 weeks post-puberty. Growth hormone concentrations decreased after 4 weeks post-puberty, whereas IGF-I concentrations increased from 8 weeks before puberty to 8 weeks post-puberty. During this period, testicular growth was accelerated and testosterone secretion increased substantially, without any significant changes in gonadotropin secretion. Monthly circulating concentrations of leptin, IGF-I and insulin accounted for 63% of the variation in scrotal circumference and 59% of the variation in paired testes volume. In conclusion, the secretion of metabolic hormones was not associated with changes in gonadotropins concentrations. Furthermore, the associations of leptin, IGF-I and insulin concentrations with testes size indicated that these hormones might be involved in a gonadotropin-independent mechanism regulating the testicular development in peripubertal bulls.
authors.affiliation: Western College of Veterinary Medicine, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
authors.forename: Lfc
authors.initials: L
authors.lastname: Brito
authors.forename: Ad
authors.initials: A
authors.lastname: Barth
authors.forename: Nc
authors.initials: N
authors.lastname: Rawlings
authors.forename: Re
authors.initials: R
authors.lastname: Wilde
authors.forename: Dh
authors.initials: D
authors.lastname: Crews
authors.forename: Ps
authors.initials: P
authors.lastname: Mir
authors.forename: Jp
authors.initials: J
authors.lastname: Kastelic
mesh_terms: D000375:Aging / Q000097:blood / Q000502:physiology; D000818:Animals; D002417:Cattle / Q000097:blood / Q000254:growth & development / Q000502:physiology*; D005640:Follicle Stimulating Hormone / Q000097:blood; D006062:Gonadotropins / Q000097:blood; D013006:Growth Hormone / Q000097:blood; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D020738:Leptin / Q000097:blood; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D012611:Scrotum / Q000033:anatomy & histology / Q000502:physiology; D046468:Sexual Development / Q000502:physiology*; D012741:Sexual Maturation / Q000502:physiology*; D013737:Testis / Q000033:anatomy & histology / Q000254:growth & development* / Q000502:physiology; D013739:Testosterone / Q000378:metabolism*
chemical_list: D006062:Gonadotropins; D007328:Insulin; D020738:Leptin; D013739:Testosterone; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D013006:Growth Hormone