Differences in the plasma concentrations of FSH and LH in ovariectomized Booroola FF and ++ ewes

Abstract

During 12 sampling days before ovariectomy the mean plasma FSH but no LH concentrations in FF ewes were higher (P < 0.01) than those in ++ ewes (16 ewes/genotype). After ovariectomy increases in the concentrations of FSH and LH were noted for ewes of both genotypes within 3-4 h and the rates of increase of FSH and LH were 0.18 ng ml-1 h-1 and 0.09 ng ml-1 h-1 respectively for the first 15 h. From Days 1 to 12 after ovariectomy, the overall mean ± s.e.m. concentrations for FSH in the FF and ++ ewes were 8.1 ± 0.6 and 7.1 ± 0.4 ng/ml respectively and for LH they were 2.7 ± 0.3 and 2.1 ± 0.2 ng/ml; these differences were not statistically significant (P = 0.09 for both FSH and LH; Student's t test). However, when the frequencies of high FSH and LH values after ovariectomy were compared with respect to genotype over time, significant F gene-specific differences were noted (P < 0.01 for both FSH and LH; median test). In Exp. 2 another 21 ewes/genotype were blood sampled every 2nd day from Days 2 to 60 after ovariectomy and the plasma concentrations of FSH and LH were more frequently higher in FF than in ++ ewes (P < 0.01 for FSH and LH). The F gene-specific differences in LH concentration, observed at 21-36 days after ovariectomy were due to higher mean LH amplitudes (P < 0.025) but not LH peak frequency in FF than in ++ ewes. Collectively the evidence shows that the greater frequency of high plasma gonadotrophin concentrations in FF compared to ++ Booroola ewes occurs independently of ovarian hormones and that the principal site(s) of F gene expression may not be in the gonad.