Zeitler P, Argente J, Chowen-Breed J A, Clifton D K, Steiner R A
Department of Obstetrics and Gynecology, University of Washington, Seattle 98195.
Endocrinology. 1990 Sep;127(3):1362-8. doi: 10.1210/endo-127-3-1362.
Since intact adult male rats have higher GH pulse amplitude than do castrated animals and since GH-releasing hormone (GHRH) secretion is predominantly responsible for the production of these GH pulses, we hypothesized that testosterone stimulates GHRH synthesis in neurons of the hypothalamus. To test this hypothesis, we compared GHRH mRNA content in individual neurons of the arcuate (ARC) and ventromedial (VMH) nuclei among groups of intact (n = 3), castrated (n = 5), and castrated testosterone-replaced (n = 5) adult male rats. Cellular GHRH mRNA content was measured by using semiquantitative in situ hybridization with an 35S-labeled cRNA probe complementary to the coding sequence of rat GHRH mRNA. Castration resulted in an approximately 35% decline in GHRH mRNA signal relative to that in intact animals in both the ARC (P less than 0.005) and VMH (P less than 0.005). Replacement with testosterone at the time of castration completely prevented the decline in both areas. Testosterone can exert effects either through activation of the androgen receptor directly or through aromatization to estradiol; therefore, we also examined the effects on GHRH mRNA of replacement with 17 beta-estradiol (n = 5) or dihydrotestosterone (DHT), a nonaromatizable androgen (n = 4). Estradiol had no effect on the castration-induced decline in GHRH mRNA in either the ARC or VMH. In contrast, DHT partially prevented the postcastration decline in GHRH in the ARC (P less than 0.005), while having no statistically significant effect on GHRH mRNA in the VMH. These results clearly indicate that testosterone stimulates expression of GHRH mRNA in neurons of the hypothalamus. Furthermore, the failure of estradiol to substitute for testosterone and the ability of DHT to substantially support GHRH mRNA suggest that testosterone exerts its effects on GHRH gene expression predominantly through direct activation of the androgen receptor.
由于成年雄性大鼠完整时的生长激素脉冲幅度高于去势动物，且生长激素释放激素（GHRH）的分泌是这些生长激素脉冲产生的主要原因，我们推测睾酮会刺激下丘脑神经元中GHRH的合成。为了验证这一假设，我们比较了完整成年雄性大鼠组（n = 3）、去势成年雄性大鼠组（n = 5）和去势后补充睾酮的成年雄性大鼠组（n = 5）的弓状核（ARC）和腹内侧核（VMH）单个神经元中的GHRH mRNA含量。通过使用与大鼠GHRH mRNA编码序列互补的35S标记cRNA探针进行半定量原位杂交来测量细胞内GHRH mRNA含量。去势导致ARC（P < 0.005）和VMH（P < 0.005）中GHRH mRNA信号相对于完整动物下降约35%。去势时补充睾酮可完全防止这两个区域的下降。睾酮可通过直接激活雄激素受体或通过芳香化转化为雌二醇发挥作用；因此，我们还研究了用17β-雌二醇（n = 5）或双氢睾酮（DHT，一种不可芳香化的雄激素，n = 4）替代对GHRH mRNA的影响。雌二醇对ARC或VMH中去势诱导的GHRH mRNA下降没有影响。相比之下，DHT部分阻止了ARC中去势后GHRH的下降（P < 0.005），而对VMH中的GHRH mRNA没有统计学上的显著影响。这些结果清楚地表明，睾酮刺激下丘脑神经元中GHRH mRNA的表达。此外，雌二醇不能替代睾酮以及DHT能够显著支持GHRH mRNA，这表明睾酮主要通过直接激活雄激素受体对GHRH基因表达发挥作用。
