CONTROVERSIES ON GLOMERULAR-FILTRATION FROM LUDWIG TO THE PRESENT

Since Ludwig's theory of filtration in the glomerulus is generally acc epted, current research interest has focussed on the regulation of thi s process. The main determinants of glomerular filtration rate are glo merular capillary pressure and glomerular blood flow, which are adjust ed via resistance changes in the pre- and postglomerular vasculature. Overall pre- and postglomerular resistances were first determined by m icropuncture in superficial glomeruli. While the predominant source of postglomerular resistance is the efferent arteriole, several results indicate that preglomerular resistance might be rather uniformly distr ibuted among all preglomerular vessels (interlobar, arcuate and interl obular arteries and afferent arterioles). Over the last decade, severa l techniques have been used to visualize renal vessels and to study th e action of various vasoactive hormones thereon. Results obtained with the split hydronephrotic kidney model, which permits in vivo microsco py of all renal vessels, provide evidence for a differential regulatio n of the various preglomerular vessels by vasoactive hormones. In part icular, mediators of inflammation almost selectively constrict interlo bar and arcuate arteries. We conclude that, given the renal vascular a rchitecture, differential regulation of preglomerular vessels can alte r haemodynamic parameters specifically for different nephron populatio ns.