title: Hypothyroidism in adult male rats alters posttranscriptional mechanisms of luteinizing hormone biosynthesis.
abstract: BACKGROUND
  Studies in men are not consistent regarding the effects of thyroid hormone on the production of gonadotropins. In hypothyroidism consequent to diverse causes, an increase or no change in serum luteinizing hormone (LH) have been reported. The attempt to explain the mechanisms involved in this pathology using rats as an experimental model also seems to repeat this divergence, since hypothyroidism has been shown to induce hypogonadotropic hypogonadism, a hypergonadotropic state, or not to affect the basal levels of LH. Notably, the promoter region of the gene encoding the Lh beta subunit and GnRH (gonadotropin-releasing factor) does not contain a thyroid responsive element. Therefore, we investigated the hypothesis that, in male rats, posttranscriptional mechanisms of LH synthesis are altered in hypothyroidism. We also attempted to determine if hypothyroidism directly affects testicular function in male rats.
  
  
  METHODS
  Male Wistar rats, 60 days old, were thyroidectomized or sham-operated. After 20 days, they were decapitated, and the pituitaries were collected and analyzed for Lh mRNA, LH content, poly(A) tail length, and polysome profile. The testes were collected and analyzed for Lh receptor mRNA, LH receptor content, and histology using morphometric analyses. The testis, epididymis, seminal vesicle, and ventral prostate were weighed, and serum concentrations of LH, testosterone, thyrotropin (TSH), and triiodothyronine (T3) were measured.
  
  
  RESULTS
  Hypothyroidism was associated, in the pituitary, with an increase in Lh mRNA expression, a reduction in Lh mRNA poly(A) tail length, a reduction in the number of LH transcripts associated with polysomes. Pituitary LH was decreased but serum LH was increased from 102 to 543 pg/mL. Despite this, serum testosterone concentrations were decreased from 1.8 to 0.25 ng/mL. A decreased germinative epithelium height of the testes and a reduced weight of androgen-responsive tissues were observed (ventral prostrate: 74 vs. 23 mg/100 g body weight [BW]; seminal vesicle undrained: 280 vs. 70 mg/100 g BW; and seminal vesicle drained: 190 vs. 60 mg/100 g BW).
  
  
  CONCLUSIONS
  Hypothyroidism in adult male rats has dual effects on the pituitary testicular axis. It alters posttranscriptional mechanisms of LH synthesis and probably has a direct effect on testicular function. However, these data suggest the possibility that reduced LH bioactivity may account in part for impaired testicular function.
authors.affiliation: Department of Physiology and Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo, Brazil. renataromano20@gmail.com
authors.forename: Renata Marino
authors.initials: RM
authors.lastname: Romano
authors.forename: Paula
authors.initials: P
authors.lastname: Bargi-Souza
authors.forename: Erika Lia
authors.initials: EL
authors.lastname: Brunetto
authors.forename: Francemilson
authors.initials: F
authors.lastname: Goulart-Silva
authors.forename: Maria Christina Werneck
authors.initials: MC
authors.lastname: Avellar
authors.forename: Claudio Alvarenga
authors.initials: CA
authors.lastname: Oliveira
authors.forename: Maria Tereza
authors.initials: MT
authors.lastname: Nunes
mesh_terms: D000818:Animals; D004822:Epididymis / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000235:genetics / Q000378:metabolism; D007037:Hypothyroidism / Q000235:genetics / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000096:biosynthesis* / Q000097:blood; D008297:Male; D010902:Pituitary Gland / Q000378:metabolism*; D011467:Prostate / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013737:Testis / Q000378:metabolism; D013965:Thyroidectomy
chemical_list: D012333:RNA, Messenger; D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone