Natriuretic hormones: comparison of renal effects

The natriuretic properties of two small molecular weight endogenous compounds are reviewed. One may originate from the hypothalamus (natriuretic factor-NF) and the other from the cardiac atria (atrial natriuretic peptide-ANP). Differences in the intrarenal mechanisms of action of NF and ANP should be anticipated in view of the fundamentally different cellular effects of NF and ANP. NF is an inhibitor of (NaK) ATPase and inhibits active sodium transport across the isolated frog skin or toad bladder while ANP has no effect on NaK ATPase and sodium transport in vitro across the isolated anuran membrane. NF may have vasoconstrictive properties. In contrast ANP has vasorelaxing properties in some vascular beds and decreases blood pressure. Both compounds are diuretic, natriuretic and phosphaturic in intact kidneys and in kidneys with a decreased functional mass. Effects on potassium excretion are variable. For both, the increases in water and solute excretion are associated with several sites of action within the nephron. Whereas NF has little effect on glomerular filtration rate (GFR) and filtration fraction, ANP may induce impressive changes in kidney and in superficial nephron GFR, increasing the filtered load of water and solutes. ANP also increases filtration fraction changing, thereby, the peritubular physical forces of filtrate reabsorption. Both NF and ANP inhibit water and solute reabsorption in the proximal tubule. With NF, a direct tubular effect has been demonstrated in recollection micropuncture studies. In contrast, a direct epithelial effect has not been elicited with ANP in the proximal tubule.(ABSTRACT TRUNCATED AT 250 WORDS)