AGE-RELATED DECREASES IN SERUM GONADOTROPIN-LEVELS AND GONADOTROPIN-RELEASING-HORMONE GENE-EXPRESSION IN THE MEDIAL PREOPTIC AREA OF THE MALE-RAT ARE DEPENDENT UPON TESTICULAR FEEDBACK
AGE-RELATED DECREASES IN SERUM GONADOTROPIN-LEVELS AND GONADOTROPIN-RELEASING-HORMONE GENE-EXPRESSION IN THE MEDIAL PREOPTIC AREA OF THE MALE-RAT ARE DEPENDENT UPON TESTICULAR FEEDBACK
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DOI：
10.1210/endo-129-5-2442
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发表时间：
1991-11-01
期刊：
影响因子：
4.8
通讯作者：
MATSUMOTO, AM
中科院分区：
文献类型：
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作者：
GRUENEWALD, DA;MATSUMOTO, AM
在雄性大鼠中，年龄相关的生殖能力下降被认为部分是由于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中GnRH mRNA和肽的含量，检验了GnRH分泌与年龄相关的减少是由于GnRH基因表达减少的假设。 由于性类固醇调节GnRH分泌，我们还通过比较完整和去睾丸的年轻和老年大鼠的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。10个20 μ m的冠状面从内侧视前区（MPOA）解剖匹配，并在完整的年轻人进行比较，（3月龄）和老龄（24月龄）雄性F344大鼠（n = 5只/组）。 在另一组年轻和年老的雄性大鼠（n = 8-12/组）中，将动物随机分配为双侧卵巢切除或假手术。 术后21天处死大鼠，取12个解剖学匹配的MPOA切片和4个匹配的Broca斜角带切片进行比较。 在这两项研究中，GnRH mRNA定量原位杂交，使用S-35标记的寡脱氧核苷酸探针互补大鼠prepro-GnRH mRNA和计算机图像分析系统。 在第三项研究中，通过RIA测定了完整的3月龄和24月龄雄性大鼠（n = 10和8，分别）的弓状核和正中隆起的显微解剖区域中的GnRH含量。 用放射免疫分析法测定各组大鼠血清LH、FSH和外周血睾酮（T）水平，结果显示，假手术组大鼠MPOA中GnRH基因阳性神经元数量明显减少（平均值+/- SEM，10.5 +/- 0.5个细胞/切片）（13.7 +/- 0.7个细胞/切片; P < 0.01），而细胞GnRH mRNA含量随年龄变化无变化（103 +/- 1 vs. 103 +/- 2粒/细胞）。 在完整的老年和年轻大鼠中获得了类似的结果。 正常老年人弓状核GnRH肽含量明显减少（0.5 +/- 0.08 ng/mg蛋白质）与幼龄动物相比（2.3 +/- 0.7 ng/mg蛋白质; P < 0.05），老年人的中位隆起有下降的趋势。（53 +/- 2 ng/mg蛋白质）与年轻大鼠（69 +/- 7 ng/mg蛋白质; P = 0.06）。 与年轻大鼠相比，假手术（完整）老年大鼠的LH、FSH和T水平较低（LH，0.9 +/- 0.2 vs. 1.7 +/- 0.2 μ g/L; FSH，2.9 +/- 0.4 vs. 7.9 +/- 0.5 μ g/L; T，1.4 +/- 0.1 vs. 4.5 +/- 0.7 nmol/L;所有P < 0.05）。 与完整大鼠相比，去卵巢老年大鼠和年轻大鼠MPOA中表达GnRH的细胞数量（11.1 +/- 0.5 vs. 11.9 +/- 0.6细胞/切片）和GnRH mRNA含量（105 +/- 2 vs. 104 +/- 2颗粒/细胞）相似。 性腺激素和T水平在老年和青年去势大鼠也相似（LH，19.5 ± 2.9对23.1 ± 1.6 μ g/L; FSH，62.0 ± 5.1对52.6 ± 3.6 μ g/L;总之，与年轻雄性大鼠相比，完整老年雄性大鼠中表达GnRH基因的MPOA神经元数量、下丘脑GnRH肽含量以及促性腺激素和T水平均降低。 与此相反，在MPOA中表达GnRH的神经元的数量和促性腺激素和T的水平在去卵巢的老年和年轻大鼠中是相似的。 我们的结论是GnRH合成能力下降，在老龄雄性Fischer 344大鼠，这可能有助于与年龄相关的促性腺激素分泌和生殖功能的下降。 此外，年龄相关的GnRH合成能力和促性腺激素水平的下降取决于睾丸反馈因素。
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-mu-m 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 S-35-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 < 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 < 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). LH, FSH, and T levels were lower in sham-operated (intact) old compared to young rats (LH, 0.9 +/- 0.2 vs. 1.7 +/- 0.2-mu-g/liter; FSH, 2.9 +/- 0.4 vs. 7.9 +/- 0.5-mu-g/liter; T, 1.4 +/- 0.1 vs. 4.5 +/- 0.7 nmol/liter; all P < 0.05). In contrast to intact rats, orchidectomized old and young rats demonstrated similar numbers of cells expressing GnRH (11.1 +/- 0.5 vs. 11.9 +/- 0.6 cells/section) and GnRH mRNA content (105 +/- 2 vs. 104 +/- 2 grains/cell) in the MPOA. Gonadotropin and T levels were also similar in old and young orchidectomized rats (LH, 19.5 +/- 2.9 vs. 23.1 +/- 1.6-mu-g/liter; FSH, 62.0 +/- 5.1 vs. 52.6 +/- 3.6-mu-g/liter; T, 0.7 +/- 0.07 vs. 0.7 +/- 0.03 nmol/liter).In summary, the number of MPOA neurons expressing the GnRH gene, hypothalamic GnRH peptide content, and levels of gonadotropins and T were decreased in intact old compared to young male rats. In contrast, the number of neurons expressing GnRH in the MPOA and levels of gonadotropins and T were similar in orchidectomized old and young rats. We conclude that GnRH synthetic capacity is decreased in the aging male Fischer 344 rat, which may contribute to the age-associated decline in gonadotropin secretion and reproductive function. Furthermore, the age-related decreases in GnRH synthetic capacity and gonadotropin levels are dependent upon testicular feedback factors.