The release of free prostate specific antigen into the circulation during transurethral resection of the prostate: kinetics and interaction with serum protease inhibitors

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Abstract
Objective To determine the nature and extent of the release of prostate specific antigen (PSA) and its interaction with its plasma protein‐derived inhibitors after transurethral resection of the prostate (TURP). Materials and methods Twenty‐three consecutive patients undergoing routine TURP for benign prostatic hyperplasia had blood samples taken pre‐operatively and then post‐operatively at 8‐hourly intervals for 24 h. Further samples were obtained at 48 and 72 h post‐operatively. Serum free and total PSA were determined by immunofluorometric assay. The major plasma protein inhibitors for PSA were also determined by immunoassay. Results The mean free and total PSA fractions increased significantly post‐operatively with levels greatest immediately after surgery. There was also a gradual increase in the complexed PSA fraction, reaching a peak at 48 h. The concentration of the major serum inhibitors of PSA (alpha‐1‐antichymotrypsin and alpha‐2‐macroglobulin) also declined immediately after surgery. Conclusion Increases of serum total PSA in patients after TURP are caused by increases in the free PSA fraction. The exponential decline in free PSA concentrations is consistent with the complexing of PSA with its protease inhibitors present in the plasma. The formation of this complex suggests that the free PSA released into the circulation at the time of TURP is the enzymatically active form.