Increases of guanosine 3',5'-monophosphate-related enzymes in kidneys of developing rats

Guanylate cyclase, cGMP phosphodiesterase and protein kinase activities were determined in kidneys of developing and adult rats. Guanylate cyclase activities of crude kidney homogenates, 100,000 x g supernatant and pellet of 7- and 21-day-old and adult rats were determined (Table I). In the kidneys of 7-day-old rats activity was 162% of adult controls in the homogenates (P less than .001), 144% in the soluble (P less than .005) and 308% in the particulate fraction (P less than .001). In 3-week-old rats activity was still significantly higher at 144% in the homogenate (P less than 0.02) and at 225% in the particulate (P less than .001). Phosphodiesterase activity for cGMP was 7488 +/- 831 pmol cGMP/mg protein . min in 1-week-old and 7674 +/- 1120 in 3-week-old rats vs. 4042 +/- 122 in the adults (P less than .025) (Table II). Chromatography on Sephadex G-200 showed two peaks of cGMP-stimulatable protein kinase in both the adult and newborn kidney and in addition a minor peak of cGMP-stimulatable kinase in the newborn kidny only (Fig. 2).