GIANT RENIN SECRETORY GRANULES IN BEIGE MOUSE RENAL AFFERENT ARTERIOLES

The mutant beige mouse (C57BL/6 bg) has a disease characterised by abn ormally enlarged cytoplasmic granules in a variety of cells. With the purpose of establishing a suitable cellular model for studying renin s ecretion, the present study was undertaken to compare renin granule mo rphology in beige mice with that of control (NMRI) mice. Immunohistoch emistry with an antibody specific for renin revealed intense staining of the juxtaglomerular part of the afferent arterioles in both strains of mice. Plasma renin concentrations were higher in the controls than in the beige mice (4.4+/-0.6 vs 2.5+/-0.3 mGoldblatt units/ml). The t otal volume of renin granules per afferent arteriole was similar in th e two mice strains (1114 mu m(3) in the controls and 1507 mu m(3) in t he beige mice). The total number of renin granules per arteriole as as sessed by stereological techniques was about 1900 in controls (average granular volume 0.681 mu m(3)), whereas 1-2 large granules were prese nt per cell in beige mice. The volume of afferent arteriole that conta ined secretory granules was lower in the beige mice. We conclude that the beige mouse synthesizes, stores and releases active renin. Renin s ecretory granules in beige mice are grossly enlarged with 1-2 granules per juxtaglomerular cell. Compared with control mice, a similar amoun t of total renin granule volume per afferent arteriole is contained in a smaller part of beige mouse afferent arteriole. Granular cells from beige mice could therefore be a valuable tool in the study of renin r elease.