Bl. Stewart et Jf. Roser, EFFECTS OF AGE, SEASON, AND FERTILITY STATUS ON PLASMA AND INTRATESTICULAR IMMUNOREACTIVE (IR) INHIBIN CONCENTRATIONS IN STALLIONS, Domestic animal endocrinology, 15(2), 1998, pp. 129-139
The nature of the relationship between inhibin and reproductive functi
on in the stallion is yet to be elucidated. Blood and testes from 51 l
ight horse stallions ranging in age from 2 mo to 25 years were collect
ed during the breeding and nonbreeding seasons to study the effects of
testicular maturation, aging, season, and fertility status on periphe
ral and intratesticular concentrations of Ir inhibin and other reprodu
ctive hormones. Of the 51 stallions, 12 age-matched stallions (6 ferti
le, 3 subfertile, and 3 infertile) were used in the fertility study. B
lood samples were taken before castration and plasma stored at -20 deg
rees C for analysis of Ir inhibin, luteinizing hormone (LH), follicle
stimulating hormone (FSH), testosterone (T), estradiol (E-2), and estr
ogen conjugates (EC) by radioimmunoassay (RIA). Testes were homogenize
d and testicular extracts prepared and frozen at -70 degrees C for ana
lysis of Ir inhibin, T, E-2, and EC by RIA. Plasma concentrations of I
r inhibin, LH, FSH, T, E-2, and EC and intratesticular concentrations
of Ir inhibin, T, E-2, and EC increased with age (P < 0.01). The most
dramatic effect appeared to be during testicular maturation. An aging
effect was not observed in adult stallions. A seasonal effect was not
detected for any of the plasma hormones, whereas for the intratesticul
ar hormones the only change noted was an increase in T in the nonbreed
ing season (P < 0.05). Plasma Ir inhibin, E-2, and EC were lower (P <
0.01) and gonadotropins higher (P < 0.05) in infertile stallions. Plas
ma T levels did not change. Intratesticular Ir inhibin concentrations
tended to be lower (P < 0.1) in subfertile stallions and significantly
lower (P < 0.01) in infertile stallions, whereas intratesticular ster
oid levels were not different among the three groups. In conclusion, p
lasma and intratesticular Ir inhibin concentrations seem to be affecte
d by testicular maturation and fertility status. (C) Elsevier Science
Inc. 1998.