Testicular heat exposure enhances the suppression of spermatogenesis by testosterone in rats: The "two-hit" approach to male contraceptive development
Testicular heat exposure enhances the suppression of spermatogenesis by testosterone in rats: The "two-hit" approach to male contraceptive development
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DOI：
10.1210/en.141.4.1414
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发表时间：
2000-04-01
期刊：
影响因子：
4.8
通讯作者：
Swerdloff, RS
中科院分区：
文献类型：
--
作者：
Lue, YH;Hikim, APS;Swerdloff, RS
本研究的目的是确定单独给予外源性睾酮(T)诱导的生殖细胞凋亡动力学的阶段性变化，以及增加一个睾丸热暴露是否会增强T诱导生殖细胞凋亡和抑制精子生成的作用。成年雄性大鼠被植入3厘米长的硅橡胶胶囊(Dow Coming Corp.)。含有T的时间长达6周。睾丸内T水平在给药后1周降至对照组的2.9%，在给药后2周、3周和6周仍受到抑制。对照组大鼠生殖细胞凋亡率(以每100个支持细胞数表示)很低(0-9.52)。经T治疗后，VII-VIII期细胞凋亡率较治疗前显著增加(21.43+/-3.33)，6周后进一步增加(56.30+/-7.47)，早期(I-VI)和晚期(XII-XIV)细胞凋亡率仍较低。为了测试T与单次睾丸热暴露联合作用是否比单独处理更能完全抑制精子发生，四组成年大鼠接受了以下处理之一：1)皮下空聚二甲基硅氧烷植入，2)第14天施加单一睾丸加热(43℃，15分钟)，3)3 cm T植入，或4)3 cm T植入和单次睾丸热暴露(第14天)。6周后处死动物。热处理组小鼠睾丸重量和精子数分别降至对照组的65.4%和28.9%。T处理组的相应数值分别为对照水平的49.7%和24.9%。值得注意的是，向T添加热量进一步将睾丸重量降低到对照水平的31.1%，睾丸精子计数几乎为零。组织形态计量学分析显示，所有处理均使曲细精管直径、上皮腔体积和管腔体积减小，其中T和热处理联合处理的减小幅度最大。热暴露于T细胞后，粗线型精母细胞和圆形精母细胞的数量明显减少，导致小管中没有成熟的精细胞。精原细胞和细线期前精母细胞未受影响。这些结果清楚地表明，II外源T在1-6周内降低了精巢内的T并诱导细胞凋亡，主要发生在VII-VIII期；2)T和热的联合处理显著抑制精子发生，导致6周内接近无精子症；3)减数分裂和精子发生是T+热作用下最脆弱的生精发生阶段。这些发现表明，激素治疗，如T和物理制剂(热暴露)的组合，在抑制精子发生方面比单独使用任何一种治疗方法都更有效。我们假设，在精子发生周期的不同阶段联合使用两种抗精子药(两种抗精子药)将导致更好的男性避孕效果。
The objectives of the study were to determine stage-specific changes in the kinetics of germ cell apoptosis induced by administration of exogenous testosterone (T) alone and to examine whether addition of a single testicular heat exposure would enhance the induction of germ cell apoptosis and the suppression of spermatogenesis by T. Adult male rats were implanted with 3-cm SILASTIC brand capsules (Dow Coming Corp.) containing T for up to 6 weeks. Intratesticular T levels declined to 2.9% of control values by 1 week and remained suppressed at 2, 3, and 6 weeks after T administration. The incidence of germ cell apoptosis (expressed as numbers per 100 Sertoli cells) was low in control rats (0-9.52). After T treatment, the mean incidence of apoptosis at stages VII-VIII increased significantly by 1 week (21.43 +/- 3.33) and showed further increases by 6 weeks (56.30 +/- 7.47); apoptotic rates remained low at early (I-VI) and later (XII-XIV) stages. To test whether the combination of T with a single testicular heat exposure resulted in more complete suppression of spermatogenesis than either treatment alone, four groups of adult rats received one of the following treatments: 1) a subdermal empty polydimethylsilozane implant, 2) exposure to a single testicular heating (43 C for 15 min) applied on day 14, 3) 3-cm T implant, or 4) 3-cm T implant and a single testicular heat exposure (applied on day 14). All animals were killed at the end of 6 weeks. In the heat-treated group, testis weight and testicular sperm counts were decreased to 65.4% and 28.9% of control levels, respectively. The corresponding values in the T-treated group were 49.7% and 24.9% of control levels, respectively. Notably, addition of heat to T further reduced testis weight to 31.1% of control levels and testicular sperm counts to near zero. Histomorphometric analysis showed that all treatments reduced seminiferous tubular diameter and epithelial and luminal volume, with the greatest decrease after combined T and heat treatment. Heat exposure in animals bearing T implants markedly reduced the number of pachytene spermatocytes and round spermatids through apoptosis, resulting in tubules devoid of mature spermatids. Spermatogonia and preleptotene spermatocytes remained unaffected. These results clearly demonstrate that II exogenous T reduces intratesticular T and induces apoptosis mainly at stages VII-VIII within 1- 6 weeks; 2) the combined treatment of T and heat markedly inhibits spermatogenesis, resulting in near azoospermia within 6 weeks; and 3) meiosis and spermiogenesis are the most vulnerable phases of spermatogenesis in response to T plus heat treatment. These findings suggest that a combination of hormonal treatment such as T and a physical agent (heat exposure) is more effective in suppressing spermatogenesis than either treatment alone. We hypothesize that combination of two antispermatogenic agents ("two hit") working at separate stages of the spermatogenic cycle will lead to greater male contraceptive efficacy.