Analysis of molecular mechanism on the training effects using adrenergic receptor agonists

本研究通过对骨化三醇(10 NM)和地塞米松(10 NM)诱导的小鼠骨髓破骨细胞进行逆转录-聚合酶链式反应(RT-PCR)分析，探讨了β2肾上腺素能受体激动剂克伦特罗对破骨细胞生长的纵向抑制作用。在破骨前细胞向成熟破骨细胞分化的过程中，加入克伦特罗。克伦特罗可增加破骨细胞的数量。Tulobuterol和异丙肾上腺素均能增加破骨细胞的数量。但选择性的β-2拮抗剂(丁毒胺)和H89(蛋白激酶A抑制剂)可抑制增加的破骨细胞。提示破骨细胞的增多可能与cAMP的增加有关。众所周知，前列腺素E_2促进破骨细胞的形成。盐酸克伦特罗、特罗布特罗和异丙肾上腺素处理后，PGE2合成酶COX-2mRNA的表达也增加。此外，克伦特罗还可上调骨吸收细胞因子IL-1、β和IL-6mRNA的表达，从而促进成骨细胞活化和促进骨形成.这些结果表明，克伦特罗对破骨细胞形成系统的影响较大，而对成骨细胞影响较小。这意味着这些药物对各种细胞都有激活作用，但整体作用是复杂的。因此，这些药物的使用应谨慎。我们证实，克伦特罗增加了UCP3和MyoD的mRNAs的表达，UCP3的mRNAs增加了脂解作用，MyoD是核调节因子。提示克伦特罗作为肌源性主调节因子增加了MyoD，并可能诱导肌肉肥大和由慢肌向快肌的转化。

In this study, we tried to examine the longitudinal inhibitory growth effects on bone of clenbuterol (beta-2 adrenergic receptor agonist) using reverse-transcription polymerase chain reaction (RT-PCR) analysis of the cultured osteoclast cells derived from mouse bone marrow cells with calcitriol (10 nM)and dexamethasone (10 nM). During the differentiation process from preosteoclasts into the matured osteoclasts, the clenbuterol were administered into the culture system. Clenbuterol increased the number of osteoclasts. The both of tulobuterol and isoproterenol also increased the osteoclasts. But the selective beta-2 antagonist (butoxamine) and H89 (protein kinase A inhibitor) inhibited the increased osteoclasts. It suggested the increased osteoclasts might be induced by the increased cAMP.It is well known that the PGE2 accelerate the forming of osteoclasts. The mRNA expression of COX-2 which is PGE2 synthetase also increased with the treatments of clenbuterol, turobuterol, and isoproterenol. Furthermore, the mRNA expression of bone resorptive cytokines, IL-1β and IL-6 were increased by clenbuterol, which also accelerated the bone forming by the osteoblasts activation... These results suggested that this clenbuterol affected more strongly on osteoclast forming system but a little on osteoblast. It means that these drugs have the activating action on various cells but the whole effects are complicated. Therefore, the using of these drugs should be careful.We confirmed that clenbuterol increased the expression of mRNAs of UCP3 which increases lipolysis and MyoD which is nuclear regulatory factor. They suggested that clenbuterol increased the MyoD as the myogenic master regulator and might induce the muscle hypertrophy and the transformation from slow-to fast-twitch muscle.