Abstract
cGMP generation has been associated with many of the vascular and endocrine actions of atrial natriuretic factor (ANF) in vitro. To examine the role of cGMP as a second messenger for the renal hemodynamic action of ANF in vivo, we measured glomerular filtration rate (GFR) and cGMP concentration in systemic artery, renal vein, and urine as well as in Bowman's space and end-proximal tubule (by free-flow micropuncture) after administration of ANF. ANF increased GFR by 45% and simultaneously induced a greater than 5-fold increase of cGMP concentration in glomerular ultrafiltrate (Bowman's space) when compared to controls. There was no significant increase in either systemic artery or renal vein cGMP concentration. Thus, the source of increased Bowman's space cGMP is not from the blood via filtration but rather from either glomerular mesangial or epithelial cells, which are not in direct contact with the circulation. Although a small amount of tubular handling of cGMP occurred along the length of the nephron, the augmented cGMP production from the glomerulus accounted for most of the 10- to 12-fold higher urinary cGMP excretion observed after ANF administration. Intrarenal arterial infusion of dibutyryl cGMP, but not dibutyryl cAMP, increased GFR in a dose-dependent fashion (from 10 to 1000 microM) by a mechanism similar to that of ANF--an increase in glomerular hydraulic pressure. Thus, ANF markedly stimulated glomerular production of cGMP, which coincided with a marked increase in GFR. Since dibutyryl cGMP itself was capable of increasing GFR, cGMP is the likely second messenger for ANF in vivo.