Gruenewald D A, Matsumoto A M
Gerontology Research, Education, and Clinical Center, Veterans Affairs Medical Center, Seattle, Washington 98108.
Endocrinology. 1991 Nov;129(5):2442-50. doi: 10.1210/endo-129-5-2442.
In the male rat, age-associated reproductive decline is thought to be due in part to diminished GnRH secretion. We tested the hypothesis that the age-related decrease in GnRH secretion is due to decreased GnRH gene expression by comparing GnRH mRNA and peptide content in the anterior forebrain of intact young and old male rats. Since sex steroids modulate GnRH secretion, we also determined hypothalamic-pituitary responsiveness to removal of testicular feedback by comparing GnRH mRNA and gonadotropin levels in intact and orchidectomized young and old rats. In an initial study, 10 20-micron coronal sections from the medial preoptic area (MPOA) were anatomically matched and compared in intact young (3-month-old) and old (24-month-old) male F344 rats (n = 5/group). In another group of young and old male rats (n = 8-12/group), animals were randomly assigned to be either orchidectomized or sham operated. Rats were killed 21 days after surgery, and comparisons were made in 12 anatomically matched sections of MPOA and 4 matched sections of diagonal band of Broca. In both studies, GnRH mRNA was quantitated by in situ hybridization, using a 35S-labeled oligodeoxynucleotide probe complementary to rat prepro-GnRH mRNA and a computerized image analysis system. In a third study, GnRH content was measured by RIA in microdissected regions of the arcuate nucleus and median eminence in intact 3- and 24-month-old male rats (n = 10 and 8, respectively). Serum LH, FSH, and testosterone (T) levels were measured by RIA in trunk blood of all animals. The number of neurons expressing the GnRH gene in the MPOA was significantly lower in sham-operated old rats (mean +/- SEM, 10.5 +/- 0.5 cells/section) than in young rats (13.7 +/- 0.7 cells/section; P less than 0.01), while cellular GnRH mRNA content was unchanged with age (103 +/- 1 vs. 103 +/- 2 grains/cell). Similar results were obtained in intact old and young rats. GnRH peptide content was significantly decreased in the arcuate nucleus of intact old (0.5 +/- 0.08 ng/mg protein) compared to young animals (2.3 +/- 0.7 ng/mg protein; P less than 0.05), with a trend toward a decrease in the median eminence of old (53 +/- 2 ng/mg protein) vs. young rats (69 +/- 7 ng/mg protein; P = 0.06).(ABSTRACT TRUNCATED AT 400 WORDS)
在雄性大鼠中，与年龄相关的生殖功能衰退被认为部分归因于促性腺激素释放激素（GnRH）分泌减少。我们通过比较完整的年轻和老年雄性大鼠前脑前部的GnRH mRNA和肽含量，来检验GnRH分泌随年龄下降是由于GnRH基因表达降低这一假设。由于性类固醇调节GnRH分泌，我们还通过比较完整和去势的年轻及老年大鼠的GnRH mRNA和促性腺激素水平，来确定下丘脑 - 垂体对去除睾丸反馈的反应性。在一项初步研究中，对来自内侧视前区（MPOA）的10个20微米冠状切片进行解剖学匹配，并在完整的年轻（3个月大）和老年（24个月大）雄性F344大鼠（每组n = 5）中进行比较。在另一组年轻和老年雄性大鼠（每组n = 8 - 12）中，动物被随机分配接受去势或假手术。术后21天处死大鼠，并对MPOA的12个解剖学匹配切片和布罗卡斜带的4个匹配切片进行比较。在两项研究中，使用与大鼠前促GnRH mRNA互补的35S标记寡脱氧核苷酸探针和计算机图像分析系统，通过原位杂交对GnRH mRNA进行定量。在第三项研究中，通过放射免疫分析（RIA）测量完整的3个月和24个月大雄性大鼠（分别为n = 10和8）弓状核和正中隆起的微切割区域中的GnRH含量。通过RIA测量所有动物躯干血中的血清促黄体生成素（LH）、促卵泡生成素（FSH）和睾酮（T）水平。假手术老年大鼠MPOA中表达GnRH基因的神经元数量（平均±标准误，10.5±0.5个细胞/切片）显著低于年轻大鼠（13.7±0.7个细胞/切片；P < 0.01），而细胞GnRH mRNA含量随年龄无变化（103±1对103±2颗粒/细胞）。在完整的老年和年轻大鼠中获得了类似结果。与年轻动物（2.3±0.7 ng/mg蛋白质）相比，完整老年大鼠弓状核中的GnRH肽含量显著降低（0.5±0.08 ng/mg蛋白质；P < 0.05），老年大鼠正中隆起中的GnRH肽含量有下降趋势（53±2 ng/mg蛋白质），而年轻大鼠为（69±7 ng/mg蛋白质；P = 0.06）。（摘要截断于400字）
