Urinary cGMP as biological marker of the renal activity of atrial natriuretic factor

Current evidence suggests guanosine 3',5'-cyclic monophosphate (cGMP) serves as the second messenger for atrial natriuretic factor (ANF) in the kidney in vivo. We examined whether extracellular cGMP accumulation quantitatively reflected the concentration of cGMP within renal cells and whether urinary excretion of cGMP correlated with the physiological action of ANF. cGMP egression was examined in renal epithelial LLC-PK1 cells. ANF augmented intracellular cGMP concentration and extracellular cGMP appearance. Extracellular cGMP was an excellent function of the time-integrated intracellular cGMP concentration. In clearance studies in awake rats, urinary cGMP was primarily of renal cellular origin and correlated with the natriuresis induced by ANF in a time-dependent and concentration-dependent fashion. Urinary cGMP excretion may be useful as a biological marker for the renal activity of ANF in vivo.