Direct actions of the luteinizing hormone-releasing hormone agonist, deslorelin, on anterior pituitary contents of luteinizing hormone (LH) and follicle-stimulating hormone (FSH), LH and FSH subunit messenger ribonucleic acid, and plasma concentrations of LH and FSH in castrated male cattle

William J. Aspden, Alexandra Rao, Paul T. Scott, Iain J. Clarke, Timothy E. Trigg, John Walsh, Michael J. D'Occhio

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Abstract

The objective in this study was to characterize direct effects of the LHRH agonist, deslorelin, on anterior pituitary gland function in male cattle in the absence of gonadal feedback. Castrated bulls (steers), 30 mo old, were allocated to four groups: group 1, control, no treatment (n = 8); group 2, five deslorelin implants (~250 μg total deslorelin/day) for 42 days (n = 8); group 3, control + LHRH (50 μg i.m.) at weekly intervals (n = 3); group 4, five deslorelin implants + LHRH as for group 3 (n = 3). Plasma LH was similar (p > 0.05) for steers in groups 1 and 2 on Day 0 and lower (p < 0.05) for steers in group 2 on Day 4, and continued to decrease to Day 41 (group 1, 1.71 ± 0.20 ng/ml [mean ± SEM]; group 2, 0.38 ± 0.03 ng/ml [p <0.001]). Mean plasma concentrations of FSH were similar (p > 0.05) for steers in groups 1 and 2 on Day 0 and lower (p < 0.05) for steers in group 2 on Day 7, and declined to Day 41 (group 1, 43.5 ± 3.9 ng/ml; group 2, 17.5 ± 1.5 ng/ml [p < 0.001]). Steers in group 3 showed increases in plasma LH after injection of LHRH on all occasions, while steers in group 4 did not show increases in plasma LH from Day 14 onward. Mean relative pituitary contents (arbitrary units) of LHβ- and FSHβ-subunit mRNAs were reduced on Day 42 in steers treated with deslorelin (LHβ: groups 1 and 3, 1.56 ± 0.27; groups 2 and 4, 0.08 ± 0.01 [p < 0.001]; FSHβ: groups 1 and 3, 1.01 ± 0.08; groups 2 and 4, 0.34 ± 0.07 [p < 0.001]). However, α-subunit mRNA was similar for control steers and steers treated with deslorelin (groups 1 and 3, 1.00 ± 0.11; groups 2 and 4, 0.86 ± 0.12 [p > 0.1]). Pituitary content of LH, but not FSH, was reduced in steers treated with deslorelin. In summary, steers treated with deslorelin showed desensitization to natural LHRH, and this was associated with reduced pituitary contents of LH and FSH β-subunit mRNAs, a reduction in pituitary content of LH, and decreases in plasma concentrations of LH and FSH. This demonstrated, for the first time, a direct action of LHRH agonist on LH and FSH β-subunit gene expression in cattle, independent of gonadal feedback. Also, there was a differential effect of treatment with deslorelin on gonadotropin α- and β-subunit mRNA contents in the anterior pituitary.

Original languageEnglish
Pages (from-to)386-392
Number of pages7
JournalBiology of Reproduction
Volume55
Issue number2
DOIs
Publication statusPublished - 1 Jan 1996
Externally publishedYes

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