Bergfeld E G, D'Occhio M J, Kinder J E
CSIRO Division of Tropical Animal Production, Rockhampton, Queensland, Australia.
Biol Reprod. 1996 Apr;54(4):769-75. doi: 10.1095/biolreprod54.4.769.
The objective in this study was to evaluate pituitary and testicular function in young bulls during and after treatment with the LHRH agonist deslorelin. The primary focus was to ascertain the period required for a return to typical LH and testosterone secretion after cessation of treatment with deslorelin, in order to establish whether desensitization was a phenomenon restricted to the pituitary or also occurred at the testes. Brahman bulls, 13.0 +/- 0.6 mo of age and 224 +/- 5 kg, were allocated to four groups and received treatment as follows: group C (n = 5), control, received no treatment; group C + LHRH (n = 5), control, received LHRH tests (50 micrograms LHRH i.m.) at the same times as group D + LHRH below; group D (n = 5), received deslorelin (approximately 200 micrograms/day) for 28 days; group D + LHRH (n = 5), received deslorelin for 28 days and were given LHRH test (50 micrograms LHRH i.m.) on Day 28 of treatment and on Days 2, 4, 8, 12, 16, and 20 after treatment. Deslorelin induced acute increases (p < 0.01) in plasma concentrations of LH and testosterone within 2 h, after which concentrations of both hormones declined by 24 h. From Day 6 to Day 28 of the treatment period, plasma LH concentrations were similar for treated and control bulls. During the same period, concentrations of plasma testosterone were greater (p < 0.01) in treated than in control bulls. Mean concentrations of both LH and testosterone were lower in treated than in control bulls for approximately one week after cessation of deslorelin treatment. Bulls treated with deslorelin did not exhibit a release of LH in response to exogenous LHRH on Day 28 of treatment. A relatively small but significant (p < 0.05) release of LH occurred on Day 4 after cessation of treatment with deslorelin (group D + LHRH, 0.49 +/- 0.11 ng/ml; group C + LHRH, 7.17 +/- 0.90 ng/ml). LH release in response to LHRH in bulls previously treated with deslorelin increased to Day 12 and then remained constant to Day 20 after cessation of treatment. However, LH release in these bulls remained significantly lower compared with that of control bulls during the 20 days after cessation of treatment with deslorelin. Bulls treated with deslorelin had a typical release of testosterone after administration of LHRH on Days 2-20 after discontinuation of treatment, even though there were relatively small releases of LH. Therefore, the pituitary in bulls remained desensitized to LHRH for at least 20 days after cessation of treatment with an LHRH agonist. In contrast, desensitization did not occur at the testes, which retained the capacity for a typical testosterone response to the LH that was released after administration of LHRH.
本研究的目的是评估年轻公牛在使用促性腺激素释放激素（LHRH）激动剂地洛瑞林治疗期间及治疗后的垂体和睾丸功能。主要重点是确定在停止使用地洛瑞林治疗后恢复典型促黄体生成素（LH）和睾酮分泌所需的时间，以便确定脱敏是否是仅限于垂体的现象，还是也发生在睾丸。将13.0±0.6月龄、体重224±5千克的婆罗门公牛分为四组，并接受如下治疗：C组（n = 5），对照组，不接受治疗；C + LHRH组（n = 5），对照组，在与以下D + LHRH组相同的时间接受LHRH试验（50微克LHRH肌肉注射）；D组（n = 5），接受地洛瑞林（约200微克/天）治疗28天；D + LHRH组（n = 5），接受地洛瑞林治疗28天，并在治疗第28天以及治疗后第2、4、8、12、16和20天接受LHRH试验（50微克LHRH肌肉注射）。地洛瑞林在2小时内可使血浆LH和睾酮浓度急剧升高（p < 0.01），之后两种激素的浓度在24小时内下降。在治疗期的第6天至第28天，治疗组和对照组公牛的血浆LH浓度相似。在同一时期，治疗组公牛的血浆睾酮浓度高于对照组（p < 0.01）。停止使用地洛瑞林治疗后约一周内，治疗组公牛的LH和睾酮平均浓度均低于对照组。接受地洛瑞林治疗的公牛在治疗第28天对外源性LHRH无LH释放反应。在停止使用地洛瑞林治疗后第4天出现相对较小但显著（p < 0.05）的LH释放（D + LHRH组，0.49±0.11纳克/毫升；C + LHRH组，7.17±0.90纳克/毫升）。先前接受地洛瑞林治疗的公牛在停止治疗后，对LHRH的LH释放反应在第12天增加，然后在第20天保持稳定。然而，在停止使用地洛瑞林治疗后的20天内，这些公牛的LH释放仍显著低于对照组公牛。在停止治疗后的第2 - 20天，接受地洛瑞林治疗的公牛在给予LHRH后有典型的睾酮释放，尽管LH释放相对较小。因此，公牛的垂体在停止使用LHRH激动剂治疗后至少20天对LHRH仍处于脱敏状态。相比之下，睾丸未发生脱敏，保留了对LHRH给药后释放的LH产生典型睾酮反应的能力。
