ラット膝関節と椎間円板の軟骨における膠原線維の発達

胎生18日から生後25週までの雌雄ラットを用い,膝関節の脛骨関節軟骨と胸部脊柱の椎間円板で,成長につれて膠原線維の量と分布がどのように変化するかを,光学顕微鏡(光顕)と電子顕微鏡(電顕)で調べた.胎生18日には,脛骨の近位骨端は軟骨で構成され,マッソン・ゴールドナー染色で膠原線維はほとんど認められなかった.生後0日には,膠原線維は関節軟骨の最も表層で弱く染まっただけだったが,成長とともに増加した.生後2,3週には,関節軟骨の表層の膠原線維が濃く染まり,骨端中心部の石灰化領域に近づくにつれて染色が薄くなった.生後9週には,関節軟骨全体が濃く染まった.このように,関節軟骨では,骨端の表面から中心部に向けて膠原線維が増加した.成長板は,生後2週で出現し,関節軟骨と対照的に膠原線維の増加はわずかだった.椎間円板では,胎生18日に最も周辺部の線維輪に膠原線維が認められた.膠原線維の増加は,成長とともに,周辺部の線維輪から椎間円板の中心部に,中心部では髄核に近い部位から椎体に向かって進行し,生後2週には椎間円板の膠原線維は均一に濃く染色された.生後9週以降は,椎間円板の所々に骨化が観察された.光顕で観察された線維は,電顕で膠原線維に特有な縞模様が観察されたので,膠原線維と同定した.また,光顕での染色の濃度と電顕での線維の増加とはよく相関した.このような膠原線維の増え方には,関節の運動,荷重や栄養の供給経路が関係しているものと推測される.本研究で,胎仔期の軟骨や成長板では膠原線維が乏しいことが示された.これらの軟骨は活発に増殖することが知られている.対照的に,関節軟骨や線維輪では膠原線維が豊富で,軟骨細胞はまれにしか分裂増殖しない.膠原線維の増加と軟骨細胞の増殖減少とは,関連があるのかもしれない.

Changes in the amount and distribution of collagen fibers in the developing tibial articular cartilage of theknee joint and the thoracic intervertebral disc in the rat (ranging from 18 gestational days to postnatal 25weeks) were studied by light and electron microscopy. At 18 gestational days, the proximal epiphysis of thetibia, as revealed by Masson-Goldner staining, was composed of cartilage with few collagen fibers. On day 0,collagen fibers were weakly stained in the most marginal layer but increased in amount with time. At 2 and 3weeks, the staining of collagen fibers was pronounced in the superficial zone, but decreased in intensitytoward the deeper ossified region. At 9 weeks, uniform and intense staining was found throughout thearticular cartilage. In contrast, the collagen fibers in the growth plate, which appeared at 2weeks, increasedonly a little. In the intervertebral disc, collagen fibers were recognized at the most peripheral annulus fibrosusat 18 gestational days. The increase of collagen fibers proceeded from the peripheral annulus fibrosus towardthe center of disc, and at the center, from places near the nucleus pulposus toward the vertebral bodies in avertical direction. At 2 weeks, the intervertebral discs were intensely and homogeneously stained for collagenfibers. From 9 weeks onwards, ossified regions were occasionally found in the intervertebral discs.Electron microscopy demonstrated characteristic periodic striations for collagen in fibers observed bylight microscopy. In addition, the intensities of staining in light microscopic specimens correlated well withthe amount of collagen fiber at the electron microscopic level. The progression pattern of collagen fiberaccumulation is possibly correlated with the joint movement, weight loading and route of nutrient supply.The fetal cartilage and the growth plate were shown to contain only a small amount of collagen fiber in thepresent study. It is known that the chondrocytes in these cartilages actively proliferate. In contrast, thearticular cartilage and intervertebral disc contained a great deal of collagen fiber and chondrocytes withrare cell division. Some correlation may exist between an increase in collagen fibers and a reciprocaldecrease in the proliferative activity of chondrocytes.