MICROPUNCTURE STUDIES OF THE RENAL EFFECTS OF ATRIAL NATRIURETIC SUBSTANCE

Injection of atrial extract produced by homogenization, boiling and centrifugation of atrial tissue from 1 heart caused a 10-fold increase in urine flow rate and a 30-fold increase in Na excretion [in rats]. Similarly prepared extracts of ventricle were without effect. To identify the site of action of atrial natriuretic substance, extract was infused i.v. at rates corresponding to 3 or 6 atria/h. During infusion at a rate of 3 atria/h. During infusion at a rate of 3 atria/h mean urine flow increased from 9.5 .+-. 2.8 to 17.2 .+-. 1.2 .mu.l/min and Na excretion from 0.14 .+-. 0.06 to 1.78 .+-. 0.14 .mu.mol/min. Glomerular filtration rate (GFR), single nephron filtration rate (SNGFR) and proximal and loop of Henle fluid absorption did not change significantly. During infusion of 6 atria/h, paralleling a greater rise in urine flow rate (from 6.4 .+-. 2.09 to 40.3 .+-. 7.5 .mu.l/min) and in Na excretion (from 0.18 .+-. 0.0008 to 5.97 .+-. 0.93 .mu.mol/min), filtration rate, measured for either the single nephron or the whole kidney, rose. As a consequence of the rise in GFR, delivery of fluid and Cl into the distal tubule increased significantly. Apparently, to a major extent the natriuresis is caused by transport inhibition along collecting tubules and collecting ducts. At high doses a rise in filtration rate contributes to the natriuretic effect of atrial extracts.