Abstract:
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 LHβ-subunit mRNA was suppressed 60% (P < 0.001) and LH 95% (P < 0.001), whereas FSHβ-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, FSHβ-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 LHβ-subunit mRNA expression without any significant effect on FSHβ-subunit mRNA. As LH and FSH contents were suppressed to a greater degree than their β-subunit mRNAs, it would appear that treatment with a GnRH agonist might influence gonadotrophin biosynthesis by a post-transcriptional mechanism(s). For LHβ-subunit mRNA, this would appear not to be reduced export of message from the nucleus.