Introduction. Reconstructive plastic surgery is the gold standard in the treatment of primary urethral strictures, but the effectiveness of these methods does not reach 100%. In cases of recurrent urethral strictures, the effectiveness of standard operations is lower than with primary strictures, which requires a search for methods to improve the results of surgical treatment.
Purpose of the study. To evaluate the structure of the intercellular matrix, the cellular composition and regenerative potential of a plasma enriched in platelets after performing urethroplasty on a biological model.
Materials and methods. Experiment was carried out on male rabbits («Burgundy» breed) weighting 3.0–4.5 kg (18 individuals). 18 animals were divided into two groups: an experimental one (contained 9 individuals) and a control one (contained 9 individuals). All animals in each group were subjected to end-to-end plastic surgery of the urethral bulbous region using standard procedures. In the control group 4 ml of 0.9% NaCl isotonic solution was injected along the perimeter of the suture into anastomotic zone of the spongy body. Autologous plasma was injected to the animals from the experimental group.
Histopathological examination was made by using routine pathological assessment with hematoxylin-eosin staining. The study also assessed the distribution and orientation of collagen fibers with Van Gieson stain. In order to objectively detail inflammatory and regenerative changes an additional immunohistochemical analysis was performed for the following antibodie groups: CD79a, CD43, CD31 (PECAM1), MMP1, MMP9. Quantitative analysis of structural changes was carried out by counting B- and T-lymphocytes having a positive membrane reaction with CD79a and CD43, respectively, in 10 representative sites in view (HPF) with a lens aperture of 0.65 in the highest concentration areas (“hot spots”). The expression level of MMP1, MMP9 was estimated by counting positive cells in 10 representative sites in view with a lens aperture of 0.65 in the submucosal and muscle layers. The level of angiogenesis in micropreparations was evaluated by counting the number of vessels in 10 sites in view (objective aperture of 0.65), reliable endothelial visualization was performed using CD31 expression (PECAM1).
Results. In the analysis of histological material use of platelet-rich plasma in the suture zone helps to reduce the area of necrotic changes and the inflammation severity, accelerated migration of macrophage-histiocytic cells to the alteration site and increased blood supply due to enhanced angiogenesis. In experimental samples a higher expression of metalloproteinases (collagenases) types 1 and 9, decreased collagen production and the correct orientation of collagen fibers during repair processes were noticed.
Conclusions. The use of platelet-rich plasma helps to accelerate the reparative processes in the spongy body after urethroplasty. Another important positive effect of platelet-rich plasma is an increase in the expression of metalloproteinases, which leads to a decrease in collagen production and the correct orientation of collagen fibers. This allows to reduce the amount of pathological fibro-scar tissue in the
operation area.

Keywords: recurrence of urethral stricture, urethral stenosis, spongy body, urethral stricture, urethroplasty, platelet-rich plasma