Allogeneic heart transplantations were performed in rats. The animals were sectioned and samples for histopathology were taken on each consecutive day from the right ventricle, the left ventricle, the apex and the septum. The samples were analysed in respect to changes typical of heterotopic transplant rejection applying the Stanford criteria. Muscle sample from the septum, known to give high rates of acute rejection, were analysed with silver test accoding to D.Ploton. This test is useful in marking out the region of nucleolar organiser. The test revealed intensification of lymphocyte reaction beginning in the phase of moderate rejection, becoming more distinct in the advanced rejection phase. Signs of intense reaction were observed in muscle fibres. No reaction was found in the endothelium. The results suggest that detection of nuclealar organiser may be useful in the diagnosis of transplant rejection.

Keywords: nucleoral organiser, Heart Transplantation, Rejection