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The Negative Feedback Effects of Testicular Steroids Are Predominantly at the Hypothalamus in the Ram*
- Source :
- Endocrinology. 129:3080-3092
- Publication Year :
- 1991
- Publisher :
- The Endocrine Society, 1991.
-
Abstract
- This study aimed to delineate the hypothalamic and/or pituitary actions of testosterone and its primary metabolites 5 alpha-dihydrotestosterone and estradiol (E) in adult castrated rams (wethers) during the breeding season. In Exp 1, wethers were treated for a week with twice daily injections (im) of peanut oil, 8, 16 or 32 mg/day testosterone propionate (TP) or dihydrotestosterone benzoate (DHTB) or an sc silastic implant containing 1 or 3 cm E. TP decreased plasma LH concentrations, increased (P less than 0.05) LH interpulse interval, did not have consistent effects on LH pulse amplitude, and had minimal effects on plasma FSH concentrations. DHTB decreased LH and FSH concentrations and increased (P less than 0.05) LH interpulse interval. E reduced (P less than 0.05) plasma LH and FSH concentrations and increased LH interpulse interval but had no effects on LH pulse amplitude. In Exp 2, hypothalamo-pituitary disconnected wethers given 125 ng GnRH every 2 h, were treated with either peanut oil, 32 mg/day TP or DHTB or 3 cm E. None of the treatments affected plasma LH or FSH concentrations or LH pulse amplitude. Exp 3 investigated the effects on GnRH of treatment of wethers either with peanut oil or TP. TP reduced GnRH concentrations (P less than 0.05) and pulse amplitude (P less than 0.01) and increased interpulse interval (P less than 0.05). These data provide evidence that, during the breeding season, the principal site of negative feedback of testicular steroids in the ram is the hypothalamus, resulting in decreased GnRH secretion; feedback effects at the pituitary are minimal.
- Subjects :
- Male
Testosterone propionate
Pituitary gland
medicine.medical_specialty
medicine.drug_class
Hypothalamus
Gonadotropin-releasing hormone
Biology
Feedback
Gonadotropin-Releasing Hormone
chemistry.chemical_compound
Endocrinology
Internal medicine
medicine
Seasonal breeder
Animals
Testosterone
Sheep
Estradiol
Dihydrotestosterone
Luteinizing Hormone
medicine.anatomical_structure
chemistry
Follicle Stimulating Hormone
Gonadotropin
Orchiectomy
medicine.drug
Subjects
Details
- ISSN :
- 19457170 and 00137227
- Volume :
- 129
- Database :
- OpenAIRE
- Journal :
- Endocrinology
- Accession number :
- edsair.doi.dedup.....c36d40f70128095fe4a426b08eb57059