AbstractTransforming growth factor-β1 (TGF-β1 and recombinant platelet-derived growth factor-BB (rPDGF-BB) promoted an extensive, dose-dependent development of fibrous connective tissue when continuously delivered for 8 days by mini-osmotic pumps implanted subcutaneously in adult guinea pigs. Biochemical analyses demonstrated that TGF-β1 and rPDGF-BB stimulated dose-dependent increases in the dry weight, and protein, DNA, collagen, and glycosaminoglycan (GAG) contents of the fibrous connective tissue capsule that enveloped the pumps. The GAG/DNA mass ratio was markedly elevated by TGF-β1, but the collagen/DNA, protein/DNA, and collagen/protein ratios were not significantly increased. In contrast, rPDGF-BB generally decreased these mass ratios. Histological analyses suggested that this was due to the fact that rPDGF-BB induced a very cellular response with a marked influx of neutrophils and fibroblasts. TGF-β1 induced significantly less cellular response, which consisted primarily fibroblasts and macrophages. These results indicated that rPDGF-BB and TGF-β1 induced connective tissue depositionin vivoin a dose-dependent fashion, although the cellular nature of the responses as well as the structural composition of the extracellular matrices were clearly distinguishable between the two growth factors.