The Juxtamedullary Nephron Preparation

Major aspects of renal function such as glomerular filtration, blood flow autoregulation, tubular reabsorption, and medullary concentrating ability rely on an exquisite paracrine-autocrine control of renal microvascular resistances, and on the coordinated network behavior of the vasculature (1 ,2 ). However, vascular and microvascular networks of mammalian kidneys are mostly inaccessible to microscopic observation, which greatly limits the direct study of renal microcirculation. There have been ongoing efforts to overcome this technical difficulty. In the seventies, glomerular microcirculation was observed in adult renal tissue grafted into a chamber in the rabbit ear (3 ), and in neonatal renal tissue grafted into a chamber in the hamster cheek pouch (4 ,5 ). At the same time, micropuncture techniques were applied to the Munich-Wistar rat, which is endowed with surface glomeruli. This greatly increased our knowledge of single-nephron dynamics and filtration (6 ,7 ). By the mid-eighties, three additional techniques were implemented for real-time microscopic evaluation of single renal arteriolar dynamics (8 ). Steinhausen et al. (9 ) took advantage of the tubular destruction provoked by hydronephrosis to visualize all segments of the renal microvasculature. Using an adaptation of the tubular microperfusion techniques (10 ), Edwards (11 ) and Osgood et al. (6 ) perfused single glomerular arterioles of rabbits and dogs in vitro. Peti-Peterdi (Chapter 8 ) and Pallone (Chapter 30 ) present further refinements of this elegant technique elsewhere in this book.