Renin Status of the Afferent Arteriole and Ultrastructure of the Juxtaglomerular Apparatus in ‘Superficial’ Juxtamedullary Nephrons from Rats

The present light (LM) and transmission electron microscopic (TEM) studies were carried out to further document the anatomy of the 'superficial' juxtamedullary nephrons (SJMNs) located on the inside cortical surface of the rat kidney. TEM revealed that SJMNs possess all vascular and tubular cell types constituting the juxtaglomerular apparatus (JGA) in typical cortical and juxtamedullary nephrons (JMNs). Proximal to the glomeruli, epithelioid cells filled with secretory granules predominated in the media of afferent arterioles. The presence of renin in the granules was immunocytochemically demonstrated by the protein A-gold method. Further upstream from the glomeruli, epithelioid cells alternated with plain smooth muscle cells. The use of renin and angiotensin II antisera revealed similar arteriolar distributions of renin and angiotensin II positive cells in SJMNs as well as in typical JMNs. Numerous nerve terminals were found along afferent and efferent arterioles, suggesting a dense innervation of these vessels. The distribution of renin-containing (i.e., epithelioid) cells in the preglomerular arterioles was assessed in various nephron populations by LM using the PAP method and renin antiserum. In SJMNs, most renin-positive cells were found in the vicinity of the JGA along a mean arteriolar length of 35 +/- 3 micron (range 7-107 micron). In JMNs, renin-positive cells had a similar distribution along a mean arteriolar length of 35 +/- 1 micron. Scattered renin-positive cells were observed up to a maximal arteriolar length of 173 and 238 micron in SJMNs and JMNs, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)