Chowen-Breed J, Fraser H M, Vician L, Damassa D A, Clifton D K, Steiner R A
Department of Obstetrics and Gynecology, University of Washington, Seattle 98195.
Endocrinology. 1989 Apr;124(4):1697-702. doi: 10.1210/endo-124-4-1697.
GnRH regulates the secretion of LH and FSH, which stimulate the secretion of testicular hormones. Acting in a reciprocal fashion, these hormones, including testosterone and inhibin, exert a negative feedback effect on GnRH and gonadotropin secretion. Endogenous opioid peptides (EOPs) have been implicated to play a role in steroid-mediated regulation of gonadotropin secretion. In this context, certain steroid hormones (e.g. testosterone) increase EOP activity and ultimately inhibit GnRH secretion; however, the cellular mechanism by which this occurs is unknown. beta-Endorphin is one of these EOPs, and it is derived from a larger precursor molecule, POMC. We tested the hypothesis that testicular hormones and testosterone, in particular, stimulate POMC gene expression in the arcuate nucleus of the male rat brain. First, we compared POMC mRNA levels between intact and castrated male rats. Adult male rats were killed 4 days (n = 4) and 21 days (n = 5) after castration. Intact animals (sham-operated; n = 6) were used as controls. Using in situ hybridization and a computerized image analysis system, we measured the POMC mRNA content in individual cells of the arcuate nucleus. POMC mRNA signal was significantly lower (P less than 0.0003) in both 4-day (126 +/- 2 grains/cell) and 21-day (117 +/- 5 grains/cell) castrates than in controls (142 +/- 2 grains/cell). In a second experiment we tested whether testosterone would reverse the castration-induced loss of POMC message. Again, we castrated animals and immediately implanted them with either empty (sham; n = 6) or testosterone-containing Silastic implants (n = 5) of a size that would deliver physiological levels of testosterone (3.6 +/- 1.5 ng/ml). We observed that testosterone-treated animals had significantly higher levels of POMC mRNA signal (121.8 +/- 3.8 grains/cell) than sham-treated castrates (111.4 +/- 3.6 grains/cell; P less than 0.03) and that the testosterone-treated castrates had POMC mRNA signal levels indistinguishable from those of intact controls (122.0 +/- 1.1 grains/cell). These observations lend credence to the theory that one mechanism by which testosterone may regulate GnRH secretion is by increasing the synthesis of POMC in the arcuate nucleus.
促性腺激素释放激素（GnRH）调节促黄体生成素（LH）和促卵泡生成素（FSH）的分泌，而后两者又刺激睾丸激素的分泌。这些激素，包括睾酮和抑制素，以相互作用的方式对GnRH和促性腺激素的分泌产生负反馈作用。内源性阿片肽（EOPs）被认为在类固醇介导的促性腺激素分泌调节中发挥作用。在这种情况下，某些类固醇激素（如睾酮）会增加EOPs的活性并最终抑制GnRH的分泌；然而，其发生的细胞机制尚不清楚。β-内啡肽就是这些EOPs之一，它来源于一个更大的前体分子——阿片促黑激素皮质素原（POMC）。我们验证了这样一个假说，即睾丸激素，尤其是睾酮，会刺激雄性大鼠脑弓状核中POMC基因的表达。首先，我们比较了完整雄性大鼠和去势雄性大鼠之间的POMC mRNA水平。成年雄性大鼠在去势后4天（n = 4）和21天（n = 5）被处死。完整动物（假手术；n = 6）用作对照。使用原位杂交和计算机图像分析系统，我们测量了弓状核单个细胞中的POMC mRNA含量。在4天（126±2颗粒/细胞）和21天（117±5颗粒/细胞）的去势大鼠中，POMC mRNA信号均显著低于对照组（142±2颗粒/细胞；P＜0.0003）。在第二个实验中，我们测试了睾酮是否会逆转去势引起的POMC信息丢失。同样，我们对动物进行去势，并立即给它们植入空的（假手术；n = 6）或含睾酮的硅橡胶植入物（n = 5），植入物大小能释放生理水平的睾酮（3.6±1.5 ng/ml）。我们观察到，经睾酮处理的动物的POMC mRNA信号水平（121.8±3.8颗粒/细胞）显著高于经假手术处理的去势大鼠（111.4±3.6颗粒/细胞；P＜0.03），并且经睾酮处理的去势大鼠的POMC mRNA信号水平与完整对照组（122.0±1.1颗粒/细胞）无显著差异。这些观察结果支持了这样一种理论，即睾酮调节GnRH分泌的一种机制可能是通过增加弓状核中POMC的合成。
