Howard G A, Bottemiller B L, Turner R T, Rader J I, Baylink D J
Proc Natl Acad Sci U S A. 1981 May;78(5):3204-8. doi: 10.1073/pnas.78.5.3204.
We have developed an in vitro system, using embryonic chicken tibiae grown in a serum-free medium, which exhibits simultaneous bone formation and resorption. Tibiae from 8-day embryos increased in mean (+/- SD) length (4.0 +/- 0.4 to 11.0 +/- 0.3 mm) and dry weight (0.30 +/- 0.04 to 0.84 +/- 0.04 mg) during 12 days in vitro. There was increased incorporation of [3H]proline into hydroxyproline (120 +/- 20 to 340 +/- 20 cpm/mg of bone per 24 hr) as a measure of collagen synthesis, as well as a 62 +/- 5% increase in total calcium and 45Ca taken up as an indication of active mineralization. A physiologic concentration (1 pM) of parathyroid hormone was found to stimulate bone resorption over control levels in this system. Parathyroid hormone stimulated the release of [3H]hydroxyproline from the bone shafts but not from the cartilage ends, indicating the specificity of the response. With 1 pM parathyroid hormone we observed an acute inhibition of bone formation, followed (after 12-16 hr) by a chronic stimulation of bone formation during the 12-day incubation. Both mineral uptake and matrix formation were enhanced at approximately the same rate during the 12-day incubation. The chronic enhancement of formation required parathyroid hormone only for the initial 8-10 hr of incubation. These results could be explained by the production or release of a factor from bone to stimulate formation in response to the acute increase in resorption--a "coupling factor." Indeed, dialyzed culture medium conditioned by actively resorbing bones stimulated bone formation over controls when added to organ cultures at a 1:20 dilution. The factor is larger than 12,000 daltons as determined by dialysis. The factor is specific for the bone shaft and did not affect the cartilage ends.
我们开发了一种体外系统，使用在无血清培养基中生长的鸡胚胫骨，该系统呈现出同时的骨形成和骨吸收。来自8日龄胚胎的胫骨在体外培养12天期间，平均（±标准差）长度从（4.0±0.4至11.0±0.3毫米）增加，干重从（0.30±0.04至0.84±0.04毫克）增加。作为胶原蛋白合成的指标，[3H]脯氨酸掺入羟脯氨酸的量增加（每24小时从120±20至340±20 cpm/毫克骨），同时总钙和摄取的45Ca增加62±5%，作为活跃矿化的指标。发现甲状旁腺激素的生理浓度（1 pM）在该系统中比对照水平刺激骨吸收。甲状旁腺激素刺激[3H]羟脯氨酸从骨干释放，但不刺激从软骨端释放，表明反应具有特异性。使用1 pM甲状旁腺激素时，我们观察到骨形成受到急性抑制，随后（12 - 16小时后）在12天的培养期间对骨形成有慢性刺激。在12天的培养期间，矿物质摄取和基质形成以大致相同的速率增强。形成的慢性增强仅在培养的最初8 - 10小时需要甲状旁腺激素。这些结果可以通过骨产生或释放一种因子来解释，该因子响应吸收的急性增加刺激形成——一种“偶联因子”。实际上，由活跃吸收骨调节的透析培养基以1:20的稀释度添加到器官培养物中时，比对照刺激骨形成。通过透析确定该因子大于12,000道尔顿。该因子对骨干具有特异性，不影响软骨端。
