Reversal of ageing changes in the thymus of rats by chemical or surgical castration.

Differences in the thymus of young and old male CSE Wistar rats were examined by use of routine histological stains on paraffin-embedded sections. There was a highly significant loss of thymic weight and disruption of architecture with age. Both surgical castration and chemical castration induced by a luteinizing hormone-releasing hormone analogue (Goserelin) caused a significant increase in thymic weight and the reappearance of a well-defined cortex and medulla in ageing rats. Cell surface antigens were detected on cryosections after incubation with a range of monoclonal antibodies. The Pan T cell marker (detected with antibody W3/13) showed fewer positive cells in ageing rats, and an increase after chemical castration. The smaller glands of old rats had fewer positive T cells with CD4 (MRC OX35) and CD8 (MRC OX8) antigens, and more after chemical castration in both young and ageing rats, but the greatest changes were seen in the intensity of Class II major histocompatibility complex (MRC OX6) immunoreactivity. In both young and ageing chemically-castrated rats, the number of cells and the intensity of immunoreactivity were greatly increased in the medulla.