Pituitary expression of LHβ- and FSHβ-subunit mRNA, cellular distribution of LHβ-subunit mRNA and LH and FSH synthesis during and after treatment with a gonadotrophin-releasing hormone agonist in heifers

The aim was to examine transcriptional and post-transcriptional regulation of LH and FSH biosynthesis. Female cattle were allocated to three groups: (i) Group 1, control (n = 6), synchronized to be at around Day 11 of the oestrous cycle on Day 31; (ii) Group 2 (n = 6), treated with gonadotrophin-releasing hormone ( GnRH) agonist ( deslorelin) for 31 days; and ( iii) Group 3 ( n = 6), treated with deslorelin for 28 days. All animals were slaughtered on Day 31. For animals in Group 2, pituitary content of LHbeta-subunit mRNA was suppressed 60% (P < 0.001) and LH 95% ( P < 0.001), whereas FSHbeta-subunit mRNA was suppressed 25% ( P > 0.05) and FSH 90% ( P < 0.001). Three days after treatment with deslorelin ( Group 3) LHβ-subunit mRNA and LH remained suppressed (50% and 95%, respectively; P < 0.001). At the same time, FSHbeta-subunit mRNA did not differ from controls ( P > 0.05) whereas FSH remained reduced by 80%( P < 0.001). The ratio of LHβ-subunit mRNA present in the nucleus versus cytoplasm of gonadotroph cells was reduced ( P < 0.05) in heifers during treatment with deslorelin (0.59 +/- 0.05) compared with the ratio in control heifers (1.31 +/- 0.22) and heifers 3 days after discontinuation of treatment (1.01 +/- 0.05). The findings indicated that treatment with GnRH agonist can suppress LHbeta-subunit mRNA expression without any significant effect on FSHbeta-subunit mRNA. As LH and FSH contents were suppressed to a greater degree than their beta-subunit mRNAs, it would appear that treatment with a GnRH agonist might influence gonadotrophin biosynthesis by a post-transcriptional mechanism(s). For LHbeta-subunit mRNA, this would appear not to be reduced export of message from the nucleus.