ENDOCRINE ASPECTS OF AGEING IN THE GUPPY, LEBISTES RETICULATUS (PETERS)-II. THE INTERRENAL GLAND

The paper describes changes in the interrenal gland of a laboratory-bred population of Lebistes reticulatus (Peters) throughout life. Changes in the volume of the interrenal tissue, the height of the interrenal cells, and interrenal nuclear volume were measured; and detailed recordings of cytological characteristics were kept. Differences were found between female and male fish. In young female Lebistes the interrenal tissue was disposed in long cords of cuboidal or polygonal cells, with sparse cytoplasmic granulation. With increasing age there was a tendency for the volume of the interrenal gland to increase, whilst there was a steady fall in cell height and also a decline in the volume of the nucleus. There was a marked increase with age in cytoplasmic granulation of the interrenal cells, with nuclear changes apparent in the increased staining reaction and pycnosis of the nuclei. In young male Lebistes the arrangement of the interrenal gland, which occurred more anteriorly than in female fish, was principally in groups of polygonal cells containing pale-staining granules. With advancing age there was a marked increase in the volume of the gland, whilst the volume of the cell nucleus fell. There was no change in interrenal cell height with age, and only a slight increase in cytoplasmic granulation. Interrenal cells with pycnotic nuclei were more numerous in old male fish than in old females. Chromaffin tissue occurred as small groups of pale-staining cells surrounded or bordered by interrenal cells. There was no evidence of any marked change in the amount of chromaffin tissue with age; great individual variations were found throughout life. Chromaffin cells with an unusually large basophilic nucleus were recorded in old fish of both sexes. The general impression was one of decreasing interrenal activity with age; the increased granulation was considered to be associated with degeneration and pycnosis of cells, rather than with increased secretory activity. The appearance of the gland in old age was similar to that found in hypophysectomized fish, and it was suggested that the ageing changes in the interrenal tissue of Lebistes may reflect a gradual decrease in the secretion of adrenocorticotrophic hormone by the ageing pituitary gland.