Submitted to: Comparative Biochemistry and Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 2003
Publication Date: February 13, 2004
Citation: Kuenzel, W.J., Abdel-Maksoud, M.M., Elsasser, T.H., Proudman, J.A. 2004. Sulfamethazine advances puberty in male chicks by effecting a rapid increase in gonadotropins. Comparative Biochemistry and Physiology. Part A137:349-355.
Interpretive Summary: Many systems within the body interact to initiate reproduction in the maturing animal. It is of great scientific, as well as practical, interest to understand how the onset of sexual maturation is initiated. In poultry, genetic selection for body size and growth rate has had many effects on the reproductive fitness of the bird, including the timing of sexual maturation. The studies reported here look at the mechanism(s) by which scientists have been able to experimentally advance the timing of gonadal development in male birds. Feeding the chemical sulfamethazine to very immature broiler chicks has been reported to markedly advance the growth of the testes and production of semen. Sulfamethazine is an antibiotic used as a treatment and a preventative to control coccidiosis. Our results indicate that the drug transiently lowers thyroid hormone levels and markedly elevates blood levels of luteinizing hormone and follicle stimulating hormone. These findings suggest that the drug is effecting early sexual maturation by acting at the level of the brain or pituitary to stimulate early gonadal development, possible by activating the same brain pathways through which day length normally stimulates reproduction in the sexually mature individual. This information will be used by scientists to further our understanding of how the systems of the body interact to control reproduction.
Four experiments were completed to obtain data suggesting a possible mechanism of action for the progonadal effects of a sulfonamide, sulfamethazine (SMZ). Chicks exposed to a continuous photoperiod and fed a diet containing 0.2% SMZ showed an exponential increase in testes size. When six weeks of age (five weeks on the SMZ diet), experimentals had testes weight nine times heavier than controls. Profiles for thyroid and gonadotropin plasma hormones suggested that T3 was transiently lower in experimentals solely during the first week on treatment while thyroxine levels were not different from controls. In contrast, luteinizing hormone (LH) and follicle stimulating hormone (FSH) were significantly elevated at the initial one-week sampling point and remained elevated throughout the entire experiment. In a follow up study, LH was found significantly higher than controls by 48hr. after initially consuming the compound. When T3 was added to the SMZ diet at 0.5ppm, the progonadal effect of SMZ was attenuated. Importantly, chronic intake of T3 delayed but did not block the stimulatory effect of SMZ for increasing plasma LH. We conclude that since one of the primary effects of SMZ is to increase rapidly plasma gonadotropins, data suggest the compound is acting at the level of the brain or pituitary to stimulate early gonadal development in chicks.