Changes in plasma gonadotrophin and prolactin concentrations following castration of the pony stallion

Changes in plasma gonadotrophin and prolactin concentrations following castration of the pony stallion

Concentration of gonadotrophins and prolactin were recorded in pony stallions castrated during the early breeding season, to examine the regulatory role of the gonad at a time when testosterone has been postulated to exert positive feedback on LH secretion Further, gonadotrophin concentrations in ge...

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Bibliographic Details
Published in:Theriogenology Vol. 55; no. 5; pp. 1171 - 1180
Main Authors: Collingsworth, M.G.R., Fuller, Z., Cox, J.E., McG. Argo, C.
Format: Journal Article
Language:English
Published: United States Elsevier Inc 15-03-2001
Subjects:
Animals
castration
Follicle Stimulating Hormone - blood
gonadotrophins
Horses - blood
Luteinizing Hormone - blood
Male
Orchiectomy
prolactin
Prolactin - blood
Regression Analysis
seasonal breeding
stallions
Time Factors
stallions
gonadotrophins
prolactin
castration
seasonal breeding
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Summary:Concentration of gonadotrophins and prolactin were recorded in pony stallions castrated during the early breeding season, to examine the regulatory role of the gonad at a time when testosterone has been postulated to exert positive feedback on LH secretion Further, gonadotrophin concentrations in geldings are reported to return to values within the normal range of the entire stallion. In an attempt to characterize this species-specific reversal, the gonadotrophin concentrations of 6 male ponies castrated on 25 March were monitored for 4 months, and 4 stallions were used to generate control data. Blood samples were collected daily, from 3 d before to 10 d after castration (Day 0), and weekly thereafter until Day 122. The pituitary response to castration was immediate. Castration resulted in a previously unreported, dramatic (13-fold) but transient (3 d) surge in circulating concentrations of LH. Concentrations of LH and FSH increased in a logarithmically scaled (LH, R 2 = 0.77; FSH, R 2 = 0.93) manner over the subsequent 5 wk, during which temporal changes in concentrations of both hormones were strongly correlated (R 2 = 0.97). The ratio of plasma gonadotrophin concentrations was consistent throughout (LH:FSH, 1.43 ± 0.04). Maximal concentrations of LH (20.58 ± 1.97 ng/mL, Day 34.8 ± 3.2) were attained approximately 2 wk before the peak in FSH (16.99 ± 1.97 ng/mL, Day 49.7 ± 3.0). Plasma gonadotrophin concentrations exceeded those of entire stallions throughout the study. The equine testes inhibited LH secretion during the early breeding season, and no chronic decrease in plasma gonadotrophin concentrations was recorded. However, the LH surge evident for 3 d immediately afer castration, may be related to the dynamic seasonal interaction between gonadal steroids and the regulation of pituitary gonadotrophin release.
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ISSN:0093-691X
1879-3231
DOI:10.1016/S0093-691X(01)00475-7