title: Effect of thyroxine on testicular function, circulating luteinising hormone and pituitary sensitivity to luteinising hormone-releasing hormone in the cockerel (Gallus domesticus).
abstract: 1. The effect of thyroxine (T4) on reproductive function in the adult cockerel was followed for 11 weeks. Broiler cockerels aged 96 weeks were fed on diets containing either 0, 2 or 5 mg T4/kg for 4 weeks. 2. Daily sperm output (DSO) was significantly reduced (P < 0.01) in the T4-treated groups compared with that of controls at weeks 5 and 7. In the group given 5 mg T4/kg, plasma testosterone concentration was significantly reduced (P < 0.01) compared with that in controls during the T4 treatment, in spite of the fact that there was a decrease in concentration in both control and experimental birds. Plasma luteinising hormone (LH) concentration was significantly decreased (P < 0.05) in both of the groups given T4 treatments after 3 weeks. 3. Plasma testosterone concentrations and DSO had returned to control values at weeks 5 and 11 respectively, while plasma LH showed a transient but significant (P < 0.001) rebound after removal of thyroxine from the food. 4. In contrast to other variables, the pituitary responsivity to cLHRH-I injections, was not decreased during the feeding of the T4 diet but was, on the contrary, significantly increased (P < 0.05) during treatment with 5 mg T4/kg diet, and after the end of the treatment with 2 mg T4/kg diet. 5. These results provide some evidence for an inhibitory effect of large doses of T4 on the reproductive function in the adult cockerel. Although the possibility of a direct effect of T4 on the testes cannot be excluded, T4 is likely to act, at least in part, at the hypothalamo-pituitary level, and not through a reduction in the pituitary sensitivity to LHRH.
authors.affiliation: Station de Recherches Avicoles, Institut National de la Recherche Agronomique-Centre de Tours, Nouzilly, France.
authors.forename: J M
authors.initials: JM
authors.lastname: Jacquet
authors.forename: F
authors.initials: F
authors.lastname: Seigneurin
authors.forename: M
authors.initials: M
authors.lastname: De Reviers
mesh_terms: D000818:Animals; D001835:Body Weight; D002645:Chickens / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000502:physiology*; D007986:Luteinizing Hormone / Q000097:blood*; D008297:Male; D010902:Pituitary Gland / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology; D013737:Testis / Q000502:physiology*; D013739:Testosterone / Q000097:blood; D013974:Thyroxine / Q000097:blood / Q000502:physiology*
chemical_list: D007987:Gonadotropin-Releasing Hormone; D013739:Testosterone; D007986:Luteinizing Hormone; D013974:Thyroxine