Endothelial permeability of the afferent arteriole and its changes as the result of alteration in the activity of the renin-angiotensin system

Recent studies have demonstrated fenestrations in the juxtaglomerular part of the afferent arteriole facing the extraglomerular mesangium and the epit helioid cells in different mammals including humans. The permeability of th e endothelium in afferent arteriole may play an important role in various p hysiologic and pathophysiologic processes. This study therefore was conduct ed to examine the permeability along the length of afferent arteriole using ferritin particles as an indicator of permeability/fenestration. Assuming the presence of a relationship between the development of permeable endothe lial fenestration and renin formation, the permeability of the endothelium and renin granulation and their correlation along the wall of the afferent arteriole under control conditions and during inhibition of renin-angiotens in system by converting enzyme inhibition or AT(1) receptor blockade were e xamined. The intra-aortically administered ferritin particles appeared in t he interstitium of the distal part of the efferent arterioles. About one-th ird to half of the length of the afferent arteriole wall was ferritin-posit ive. There was a correlation between ferritin-positive and renin-positive p ortions. The density of ferritin particles was high close to the glomerulus and decreased continuously, similar to the profile of renin distribution. There was also a correlation between ferritin density in basal membrane and the renin granulation index. On the basis of these results, the afferent a rteriole, according to its endothelial permeability, can be divided into tw o distinct portions, i.e., the permeable and the nonpermeable, the length a nd ratio of which may be related to the actual renin formation. These porti ons not only are different in the presence or absence of fenestration of th e endothelium, but they also show difference in myosin and renin contents, suggesting that each portion may serve different function(s).