Allen Camryn D, McKinnon Allan J, Lisle Allan T, D'Occhio Michael J, Johnston Stephen D
School of Animal Studies, The University of Queensland, Gatton, Queensland, Australia.
J Androl. 2006 Nov-Dec;27(6):720-4. doi: 10.2164/jandrol.106.000117. Epub 2006 Jun 2.
Testosterone secretion in mammals typically occurs in random pulses such that a single blood sample provides limited information on reproductive endocrine status. However, it has been shown in several species that an index of the prevailing testosterone biosynthetic capacity of the testes can be obtained by measuring the increase in circulating testosterone after injection of a GnRH agonist or human chorionic gonadotrophin (hCG). Hence, the aims of the present study were to examine fluctuations in testosterone secretion in the koala (n = 6) over a 24-hour period and then characterise testosterone secretion after injection of the GnRH agonist buserelin (4 micro g) or hCG (1000 IU). The latter was used to establish an index of the prevailing testosterone biosynthetic capacity of the koala testis. Individual koalas showed major changes in blood testosterone concentrations over 24 hours, but there was no apparent diurnal pattern of testosterone secretion (P > .05). Injection of buserelin and hCG resulted in an increase (P < .05) in blood testosterone concentration. After injection of exogenous hormone, near maximal concentrations of testosterone occurred at around 60 minutes. There was a tendency for plasma testosterone to decline after 90 minutes with buserelin, but concentrations remained close to the upper limit for 240 minutes with hCG. There were strong positive correlations between the average testosterone concentration over 24 hours and the maximum observed testosterone concentration after stimulation with GnRH and hCG (GnRH, r = .772; P = .07 and hCG, r = 1.0; P < .01). The findings in the present study confirmed that individual male koalas can show large fluctuations in blood testosterone concentrations over time and that a GnRH agonist and hCG can be used in the koala to obtain an index of the prevailing steroidogenic capacity of the testes.
在哺乳动物中，睾酮分泌通常以随机脉冲的形式发生，因此单次血液样本提供的关于生殖内分泌状态的信息有限。然而，在几个物种中已经表明，通过测量注射促性腺激素释放激素（GnRH）激动剂或人绒毛膜促性腺激素（hCG）后循环睾酮的增加，可以获得睾丸主要的睾酮生物合成能力指标。因此，本研究的目的是检查考拉（n = 6）在24小时内睾酮分泌的波动情况，然后在注射GnRH激动剂布舍瑞林（4微克）或hCG（1000国际单位）后对睾酮分泌进行特征描述。后者用于建立考拉睾丸主要的睾酮生物合成能力指标。个体考拉在24小时内血液睾酮浓度有重大变化，但睾酮分泌没有明显的昼夜模式（P > 0.05）。注射布舍瑞林和hCG导致血液睾酮浓度增加（P < 0.05）。注射外源激素后，睾酮浓度在大约60分钟时接近最大值。注射布舍瑞林后90分钟血浆睾酮有下降趋势，但注射hCG后240分钟浓度仍接近上限。24小时内平均睾酮浓度与GnRH和hCG刺激后观察到的最大睾酮浓度之间存在强正相关（GnRH，r = 0.772；P = 0.07；hCG，r = 1.0；P < 0.01）。本研究结果证实，个体雄性考拉随着时间推移血液睾酮浓度会有很大波动，并且GnRH激动剂和hCG可用于考拉以获得睾丸主要的类固醇生成能力指标。
