Objective: To investigate the effect of oral administration of arginine on linear growth of long bones in male pubertal rats and the underlying mechanisms, focusing on expression of genes related to the hypothalamus-pituitary growth axis and the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway.
Methods: Rats were randomly divided into control and intervention groups. In the intervention group, arginine was solved in water (0.045 g L-arginine was mixed with 1 mL water) and administered in rats (10 mL/kg) through gastric perfusion once per day, for totally 28 d. Rats in the control group received normal saline treatment. Bone histomorphometry analysis was used to measure growth plate width and mineral apposition rate of the tibia, as well as trabecular bone volume fraction, osteoblast surface and osteoclast surface of the femur. Serum growth hormone (GH) concentration was determined by radioimmunoassay. Real-time PCR was used to measure the expression of neuronal nitric oxide synthase (nNOS), soluble guanylyl cyclases (sGCα1 and sGCβ1), growth hormone-releasing hormone (Ghrh) and somatostatin (SS) in hypothalamus, as well as Gh in pituitary. Western blot was used to detect the protein levels of nNOS, sGCα1 and sGCβ1 in hypothalamus.
Results: After treatment with arginine, the growth plate width of tibia and osteoblast surface of femur were increased (P < 0.05), and serum GH concentration was elevated (P < 0.05). Besides, mRNA and protein levels of nNOS and sGCα1 (P < 0.05), as well as the expression of Gh mRNA (P < 0.01), were significantly up-regulated, while the expression of SS mRNA was down-regulated (P < 0.05).
Conclusion: Oral administration of arginine could improve linear growth of long bones by regulating mRNA expression of SS and Gh and inducing GH secretion, possibly via nNOS-NO-sGC-cGMP signal transduction pathway.
目的: 观察口服精氨酸对雄性青春期大鼠长骨线性生长的影响, 并从下丘脑-5782体生长轴及一氧化氮-环磷酸鸟苷通路相关的基因表达的角度探讨其机制。
方法: 将青春期大鼠分为对照组和干预组, 干预组大鼠每天灌胃 10 mL/kg 精氨酸水溶液 (0.045 g/mL), 共给药28 天。 对照组大鼠每天给予同剂量的生理盐水。 采用骨形态计量学方法分别测定胫骨生长板宽度和77FF化沉积率, 以及股骨骨小梁体积百分数、 成骨细胞面积及破骨细胞面积。 用放射免疫法测定血清中生长激素的浓度。 实时定量聚合酶链式反应检测下丘脑神经型一氧化氮合酶(nNOS)、 可溶性鸟苷环化酶(sGCα1/sGCβ1)、 生长激素释放激素(Ghrh)、 生长抑素(SS)及5782体Gh基因表达水平。 Western blot 法测定下丘脑nNOS、 sGCα1及sGCβ1的蛋白表达水平。
结果: 口服精氨酸后,青春期大鼠胫骨生长板宽度及股骨成骨细胞面积明显增加(P < 0.05), 血清生长激素浓度显著提高(P < 0.05)。 此外, 下丘脑nNOS和sGCα1的基因及蛋白表达水平均显著上调(P < 0.05), 而SS基因表达水平显著下调(P < 0.05)。 5782体Gh基因表达显著上调(P < 0.01)。
结 论: 口服精氨酸可能通过调控nNOS-NO-sGC-cGMP通路使得下丘脑SS的基因表达下调、 5782体Gh基因表达上调、 5782体生长激素分泌增多, 从而显著促进长骨的线性生长。