KIDNEYS OF THE KILLERWHALE AND SIGNIFICANCE OF RENICULISM

Background: The kidneys of all Cetacea are composed of many small rela tively independent kidneys (renicules) containing considerable interre nicular tissue. Although reniculism is not entirely confined to the Ce tacea, it is desirable to consider the possible advantage of reniculis m to mammals of gigantic size, The kidneys of the killerwhale, Orcinus orca, are compared from this standpoint to the kidneys of diverse mam mals, Methods: The specific renal parenchymal mass, glomerular counts, glomerular size, and specific glomerular mass of the killerwhale are measured and compared quantitatively (statistically) with similar data from numerous diverse mammals, Simultaneously, a method is described for enumerating the renicules of a cetacean kidney, Results: Specific parenchymal mass of a killerwhale adult's two kidneys (0.33%) is close to the expected value for mammals of its adult body mass (2,087 kg), The diameter of the adult's glomerular capsules (153 mu m) is striking ly less than that expected fi om its body mass (regression equation an d graph for mammals in general), However, the number of glomeruli per kidney (similar to 100 x 10(6)) is markedly greater than that for mamm als of its body mass (regression equation and graph for mammals in gen eral) and is the first such count for a cetacean, The total glomerular mass relative to parenchymal renal mass of the O., orca infant and ad ult is, nevertheless, 5.5% and 6.0%, respectively, and is thus close t o the general mammalian value of similar to 5%., Conclusions: Organiza tion of a cetacean kidney into numerous renicules does not increase sp ecific renal parenchymal mass or specific glomerular mass, The apparen t advantage of numerous independent renicules is the Limit that is aff orded for length of tubules in the necessarily large kidneys of gigant ic mammals, (C) 1998 Wiley-Liss, Inc.