Marlies Elger – författare

Original work on the renal structures in three classes of lower vertebrates is presented. By the application of light and electronmicroscopy, histochemistry and the compilation of available information on renal physiology and morphology, further evidence for the homology of nephron segments is forwarded. The results have been correlated with the habitat and evolutionary kinship of the lower vertebrates. A general evolutionary line can be drawn from early vertebrates (e.g. Petromyzontia) via archaic fresh-water fish (e.g. Polyteridae) and lungfish to the amphibian nephron. Renal structures of Elasmobranchs are very complex, but can be compared with the more primitive nephron of the Polyteridae. The morphological basis for the unique ability of the marine Elasmobranchs to build up a high urea concentration in the blood is given by the description of the renal countercurrent system in the lateral bundle zone. The intercalated cells which are prominent in the distal nephron of the mammalian kidney have been traced back via the lungfish and the polypterids to the Petromyzontia. The teleost kidneys appear highly specialized and supply a host of animal models for the study of renal secretion. The morphological information with the compilation of literature on renal physiology in fish is relevant for the understanding of the evolution of the vertebrate kidney and serves as a presentation of animal models for the study of basic renal mechanisms.

Glomerular flltration represents one of the basic mechanisms in the function of an organism. Our understanding of this process is still quite fragmentary. Regulation of blood flow and pressure, together with regulation of the ultraflltration coefficient (which is an attribute of the flltration barrier), are the two fundamental mechanisms accounting for maintenance and adaptability of glomerular flltration. Regulation of glomerular blood flow is generally considered to result from an interplay between afferent and efferent glomerular arterioles, and much progress has been made recently in understanding this interplay (Navar et al. 1996). The present study provides a detailed structural description of the glomerular vascular pole of rat. The results of this study appear to be relevant for several open questions of glomerular function. First, the interaction between afferent and efferent arterioles in regulating glomerular blood is generally understood to occur between the preglomerular and the postglomerular portions of these vessels. As shown in the present study, the structural elaborations of these arterioles and the spatial relationships between them within the glomerular hilum strongly suggest an interplay also at this site. Moreover, the current understanding of glomerular blood flow regulation by tuning the interplay between afferent and efferent arterioles is exclusively based on signals whose regulatory loops are established in follow-up events outside the glomerulus (tubuloglomerular balance, tubuloglomerular feedback).