Use of the gonadotrophin-releasing hormone antagonist azaline B to control the oestrous cycle in the koala (Phascolarctos cinereus).
The present study examined the effectiveness of the gonadotrophin-releasing hormone (GnRH) antagonist azaline B to suppress plasma LH and 17ß-oestradiol concentrations in koalas and its potential application for oestrous synchronisation. In Experiment 1, single subcutaneous injections of azaline B successfully blocked the LH response to exogenous mammalian (m) GnRH in a dose-dependent manner; specifically, 0 mg (n = 4) did not suppress the LH response, 1 mg azaline B (n = 6) suppressed the LH response for 24 h (P < 0.05), 3.3 mg azaline B (n = 8) suppressed the LH response significantly in all animals only for 3 h (P < 0.05), although in half the animals LH remained suppressed for up to 3 days, and 10 mg azaline B (n = 4) suppressed the LH response for 7 days (P < 0.05). In Experiment 2, daily 1 mg, s.c., injections of azaline B over a 10-day period during seasonal anoestrus (June-July; n = 6) suppressed (P < 0.01) the LH response to mGnRH consecutively over the 10-day treatment period and, 4 days after cessation of treatment, the LH response had not recovered. Experiment 3 was designed to test the efficacy of daily 1 mg, s.c., azaline B over 10 days to suppress plasma LH and 17ß-oestradiol concentrations and ultimately synchronise timed return to oestrus during the breeding season. Although azaline B treatment did not suppress basal LH or 17ß-oestradiol, oestrus was delayed in all treated females by 24.2 days, but with high variability (range 9-39 days). Overall, the present study demonstrates that the GnRH antagonist azaline B is able to inhibit the LH response in koalas to exogenous mGnRH and successfully delay the return to oestrus. However, although azaline B clearly disrupts folliculogenesis, it has not been able to effectively synchronise return to oestrus in the koala.
School of Agriculture and Food Science, University of Queensland, Gatton, Qld 4343, Australia.|Corresponding author. Email: kate_068@msn.com.
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Ballantyne
School of Biomedical Sciences, University of Queensland, St Lucia, Qld 4072, Australia.
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Anderson
Currumbin Wildlife Sanctuary, 28 Tomewin Street, Currumbin, Qld 4223, Australia.
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Pyne
Dreamworld, Dreamworld Parkway, Coomera, Qld 4209, Australia.
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Nicolson
Dreamworld, Dreamworld Parkway, Coomera, Qld 4209, Australia.
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Mucci
School of Agriculture and Food Science, University of Queensland, Gatton, Qld 4343, Australia.
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Lisle
School of Agriculture and Food Science, University of Queensland, Gatton, Qld 4343, Australia.
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Johnston
17ß-oestradiol; FSH; LH; oestrous synchronisation