Hannan M A, Fukami Y, Kawate N, Sakase M, Fukushima M, Pathirana I N, Büllesbach E E, Inaba T, Tamada H
Department of Advanced Pathobiology, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Izumisano, Osaka, Japan.
Department of Advanced Pathobiology, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Izumisano, Osaka, Japan.
Theriogenology. 2015 Dec;84(9):1530-5. doi: 10.1016/j.theriogenology.2015.07.039. Epub 2015 Aug 4.
Insulin-like peptide 3 (INSL3) is a major secretory product of testicular Leydig cells. The mechanism of acute regulation of INSL3 secretion is still unknown. The present study was undertaken in pubertal beef bulls to (1) determine the temporal relationship of pulsatile secretion among LH, INSL3, and testosterone and (2) monitor acute regulation of INSL3 secretion by LH using GnRH analogue and hCG. Blood samples were collected from Japanese Black beef bulls (N = 6) at 15-minute intervals for 8 hours. Moreover, blood samples were collected at -0.5, 0, 1, 2, 3, 4, 5, and 6 hours after GnRH treatment and -0.5, 0, 2, 4, and 8 hours on the day of treatment (Day 0), and Days 1, 2, 4, 8, and 12 after hCG treatment. Concentrations of LH, INSL3, and testosterone determined by EIAs indicated that secretion in the general circulation was pulsatile. The frequency of LH, INSL3, and testosterone pulses was 4.7 ± 0.9, 3.8 ± 0.2, and 1.0 ± 0.0, respectively, during the 8-hour period. Seventy percent of these INSL3 pulses peaked within 1 hour after a peak of an LH pulse had occurred. The mean increase (peak per basal concentration) of testosterone pulses was higher (P < 0.001) than that of INSL3 pulses. After GnRH treatment, LH concentrations increased (P < 0.01) dramatically 1 hour after treatment and remained high (P < 0.05) until the end of sampling, whereas an elevated (P < 0.05) INSL3 concentration occurred at 1, 2, 5, and 6 hours after treatment. Testosterone concentrations increased (P < 0.01) 1 hour after the treatment and remained high until the end of sampling. After hCG treatment, an increase of INSL3 concentration occurred at 2 and 4 hours, and Days 2, 4, and 8 after treatment (P < 0.05), whereas in case of testosterone, concentrations remained high (P < 0.01) until Day 8 after treatment. The increase (maximum per pretreatment concentration) of INSL3 concentrations after injecting GnRH or hCG was much lower (P < 0.001) than that of testosterone. In conclusion, secretion of INSL3 in blood of bulls occurred in a pulsatile manner. We inferred an acute regulation of INSL3 by LH in bulls because INSL3 concentrations increased immediately after endogenous and exogenous LH stimulation. The increase of INSL3 concentrations by LH was much lower than that of testosterone in bulls.
胰岛素样肽3（INSL3）是睾丸间质细胞的主要分泌产物。INSL3分泌的急性调节机制尚不清楚。本研究以青春期肉用公牛为对象，（1）确定促黄体生成素（LH）、INSL3和睾酮脉冲分泌的时间关系，（2）使用促性腺激素释放激素（GnRH）类似物和人绒毛膜促性腺激素（hCG）监测LH对INSL3分泌的急性调节。以15分钟的间隔从日本黑毛肉用公牛（N = 6）采集血样，持续8小时。此外，在GnRH处理后-0.5、0、1、2、3、4、5和6小时以及处理当天（第0天）的-0.5、0、2、4和8小时以及hCG处理后的第1、2、4、8和12天采集血样。通过酶免疫分析（EIA）测定的LH、INSL3和睾酮浓度表明，全身循环中的分泌是脉冲式的。在8小时期间，LH、INSL3和睾酮脉冲的频率分别为4.7±0.9、3.8±0.2和1.0±0.0。这些INSL3脉冲中有70%在LH脉冲峰值出现后1小时内达到峰值。睾酮脉冲的平均增加幅度（峰值相对于基础浓度）高于INSL3脉冲（P<0.001）。GnRH处理后，LH浓度在处理后1小时显著升高（P<0.01），并在采样结束前一直保持在较高水平（P<0.05），而INSL3浓度在处理后1、2、5和6小时升高（P<0.05）。睾酮浓度在处理后1小时升高（P<0.01），并在采样结束前一直保持在较高水平。hCG处理后，INSL3浓度在处理后2和4小时以及处理后第2、4和8天升高（P<0.05），而睾酮浓度在处理后第8天前一直保持在较高水平（P<0.01）。注射GnRH或hCG后INSL3浓度的增加幅度（相对于预处理浓度的最大值）远低于睾酮（P<0.001）。总之，公牛血液中INSL3的分泌呈脉冲式。我们推断LH对公牛的INSL3有急性调节作用，因为内源性和外源性LH刺激后INSL3浓度立即升高。在公牛中，LH引起的INSL3浓度增加远低于睾酮。
