Ultrastructural effects of estrogen on epiphyseal cartilage

Ten male weanling Holtzman rats, injected intraperitoneally with aqueous estradiol (Progynon, Schering), in daily doses of 1 μg. per g body weight, were sacrificed, simultaneously with controls receiving an equivalent amount of diluent, at intervals ranging from one hour to six days. Upper tibial epiphyseal cartilage plates (ECP), procesed for electron microscopy, revealed, as early as three hours after injection, appreciable enhancement of secretory activity, evidenced, in the zone of matrix secretion, by the abundance in Golgi cisternae of stippled material representing proteinpolysaccharide complexes. Disintegration of the lining membrane of individual Golgi vesicles was advanced after twenty-four hours; following three days of treatment, few vesicles remained intact, and pools of initially intravacuolar material were observable in the gound plasm. Long filaments, suggestive of primary or precursor collagen fibrils were apparent in this secretion. After six days, virtual lakes of this substance filled cells in the zone of prehypertophy, with consequent displacement of the rough endoplasmic reticulum against the cell periphery. Cytoplasmic vacuoles, containing mateerial similar to that found in the lacunar moat, and displaying finely beaded, radially arrayed filaments on the lining membrane were frequently encountered. Our observations suggest an initial acclleration of chondrocytic secretory activity, with subsequent retardation of transport. The resultant retention and intracellular polymerization of precollagenous products accelerates hypertrophy, thereby promoting early degeneration of chondrocytes. These ultrastructural alterations are apparently estrogen-specific.