Every fifth inhabitant of the earth has been diagnosed with osteoarthritis of various etiologies. Morphological studies of arthritis provide a theoretical basis for creating optimal treatments for this pathology. Given the polyetiological nature of the disease, the choice of the optimal experimental model, which would be as close as possible to the real conditions of inflammatory process reproduction, is the topical issue. The purpose of the study was to confirm the pathological reaction of the joint tissues of laboratory animals in response to intraperitoneal administration of ƛ-carrageenan. The study was performed on 50 white Wistar rats males aged 12 weeks, weighing 130-150 g. The animals were euthanized by an overdose of anaesthesia according to the terms of the study (1 - 30 days). Fragments of the distal metaepiphyses of the femur and proximal metaepiphyses of the tibia were used for histological examination. Staining of sections obtained on the microtome was performed with haematoxylin, eosin, and Van Gieson`s stain. From the first day of the experimental study, a corresponding reaction of the joint tissues was being observed. Particularly pronounced were the changes in the synovial membrane in the form of oedema of the villi accompanied by an increased filling of blood vessels with foci of thrombosis. Gradually, up to 5 days in the synovial membrane, proliferative changes took place with a clear definition of the multilineage of the integumentary layer, vascular reaction with a tendency to thrombosis, in some places necrosis of synoviocytes was observed, but relative integrity of the morphological structure was still provided by protective barriers of bone and cartilage. On the 7th day pronounced resorption of both bone and cartilage tissue occurred, tissue structure became disorganized and functional layer became thin, accompanied by massive intracellular lysis. The process of synoviocytes necrobiosis with fatty degeneration spread. The histological picture of 10 days is characterized by generalized destruction of bone beams; the destroyed cartilage was replaced by granulation tissue with the presence of cavities. Massive foci of lymphocytic infiltration were observed in the synovial membrane. On the 14th day, a fragmentation of cartilage happened, most of the bone beams (trabeculae) were destroyed. After 3 weeks the morphological picture of cartilage tissue was determined by the appearance in the lacunae of viable cells, the number of which was close to normal. Bone beams were restored, although they remained thin. In a synovial membrane, the hyperplasia of apical departments of villi, leukocytes infiltration, disorganization of connective tissue, and separate vascular disturbances remained. 30 days of the experiment were characterized by a relative recovery of structural relationships to normal. The obtained data confirm the feasibility of using carrageenan in experimental studies of osteoarthritis.
