FIBRONECTIN IN THE TENDON-SYNOVIAL COMPLEX - QUANTITATION IN-VIVO ANDIN-VITRO BY ELISA AND RELATIVE MESSENGER-RNA LEVELS BY POLYMERASE CHAIN-REACTION AND NORTHERN BLOT

An enzyme-linked immunosorbent assay was used to quantitate fibronecti n (Fn) levels in the outer synovia (epitenon) and internal fibrous por tion (endotenon) of chicken flexor tendon and sheath. Primary cell cul tures from these tissues and their secretions also were assayed for Fn levels. The polymerase chain reaction (PCR) was used to determine rel ative steady-state levels of Fn mRNA in primary cultures of synovial a nd internal fibroblasts from chicken tendon, and Northern blot analysi s was performed to verify relative levels of the Fn message. The epite non contained 3.8-fold more Fn than did the endotenon, and the sheath synovium contained 21-fold more Fn than did the internal fibrous porti on of sheath. Cells cultured from the epitenon produced 9.3 and 13-fol d more cell-associated and secreted Fn, respectively, than did culture d endotenon fibroblasts. Sheath synovial cells produced 17 and 3.2-fol d more cell-associated and secreted Fn, respectively, than did sheath internal fibroblasts. Levels of Fn mRNA, as measured by PCR and Northe rn blot, were 1.6 and 1.8-fold greater, respectively, in tendon synovi al cells compared with tendon internal fibroblasts. The biologic reaso n for increased Fn in tendon synovium is not known. We theorize that F n may stabilize tendon synovium to shear stress and may play a role in the modulation of synovial rheology in the normal tendon. In the inju red tendon, Fn may be involved in the organization of collagen deposit ion or may act through association with growth factors to aid healing.