Correlation between juxtaglomerular index, kidney renin content and plasma renin concentration in the rat

The correlation between juxtaglomerular index, kidney renin content, and plasma renin concentration has been investigated in rats. The results indicate that renin exists in two forms. When determining the renin content of the kidney, the renin actually present in the modified smooth muscle cells of the juxtaglomerular apparatus is measured; this is called bound renin. The amount of bound renin is derived from the total of granular and subgranular renin in the modified smooth muscle cells. Since JGI and KRCont show a significant positive correlation in untreated adult rats, it is assumed that in such animals the ratio of granular and subgranular renin is constant. Since no correlation could be demonstrated between kidney renin content and PRC in untreated adult rats, and JGI and KRCont did not change parallel with the increase of PRC in numerous experimental conditions, it is assumed that part of the renin synthetized in the JG cells is secreted directly, without passing the process of condensation into membrane bound granules. This mobile renin does not significantly affect the renin content and the JGI of the kidney. Under physiological circumstances, most of the produced renin seems to mature to granules in the modified smooth muscle cells before being secreted. When renin production and release increased, maturation to granules may be inhibited, a significant part of the produced renin released by direct secretion, and the subgranular, immature renin may also be secreted.