The Effect of Leukopenia and Thrombocytopenia in Polyvinyl Sponge Implanted Rabbits

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Abstract
Polyvinyl sponge implants have been used in the rabbit to produce an inflammatory proliferative response in the subcutaneous areolar tissue of the back. In addition, the sponges have served as a source of interstitial inflammatory fluid for use in cell culture to measure fibroblast growth factors. Serum and plasma can also be obtained from sponge implanted rabbits allowing for simultaneous assay of growth factor activity in serum, plasma, and inflammatory fluid. Connective tissue DNA synthesis stimulation can be measured using 3HTdR† incorporation and autoradiography of capsular connective tissue fragments. Compositional differences between serum and inflammatory fluid include a lower glucose, protein, calcium, and cholesterol level, and a higher chloride level in fluid than in serum. Fibroblast growth-promoting activity in serum, plasma, and inflammatory fluid was assayed against early passage fibroblasts. Fibroblast proliferation was most rapid in cultures during the first four days, and 15 to 20 percent concentrations of serum or plasma produced maximum growth rates. Inflammatory fluid obtained on day three contained fibroblast growth factor activity and showed increasing rates of growth at concentrations up to 40 percent. Low growth factor activity was noted in day one inflammatory fluid. Cyclophosphamide-induced neutropenia resulted in hypocellular one-day inflammatory fluid and raised growth factor activity in this fluid to the level found in three-day fluid. No evidence of an inhibitor was found in one-day fluid. A suppressive role of neutrophils on fibroblast growth factor levels on day one was suggested by these results. Deficiency of a dialyzable low molecular weight cofactor is present in one-day fluid with low growth factor activity, and this factor is not replaced by known nutrients. Thrombocytopenic rabbits showed normal cell cycle activation in connective tissue fragments as evidenced by a normal labeling index and elevated 3HTdR incorporation rates relative to zero-day tissue. Severe thrombocytopenia did not impair the ability of tissue fibroblasts to begin a proliferative cycle in vivo. Inflammatory fluid growth factors can now be measured in a wide variety of situations. This is important since this fluid is actually the aqueous phase in contact with fibroblasts in vivo.