title: Studies on the tubular effects of atrial extract and of atriopeptin III in conscious rats.
abstract: To investigate a tubular action of atrial natriuretic peptide (ANP), in the present study the effects of rat atrial extract (AE) and of synthetic rat atriopeptin III (AP III) were assessed in conscious rats during hypotonic saline infusion. Renal plasma flow (RPF) and glomerular filtration rate (GFR) were estimated by the clearances (C) of PAH and of endogenous creatinine, respectively. CPO4 was used as a marker of proximal tubular function. Distal delivery (DD) and distal fractional absorption of chloride (DFACl), a measure of solute absorption in the diluting segments, were calculated from CH2O and CCl. AE and AP III increased RPF in all groups of animals. Low doses of AP III (40 ng/100 g B.W.) significantly increased urine flow rate and CCl, whereas GFR, CNa, CPO4, and CK remained unaltered. The marked natriuresis at high doses of ANP was associated with a rise in GFR and in absolute and fractional CPO4 as well as an increase in DD and CK. AE and AP III (1 microgram/100 g B.W.) decreased DFACl from 0.94 +/- 0.03 and 0.87 +/- 0.03 to 0.80 +/- 0.07 (p less than 0.05) and 0.54 +/- 0.07 (p less than 0.01), respectively. Some of the effects on tubular reabsorptive capacity probably result from medullary wash-out which thereby contributes to the natriuresis by potentiating the rise in the filtered load of sodium at high ANP levels. In the absence of changes in GFR and CPO4, the tubular action of ANP is more accurately reflected by CCl which may result from decreased absorption in the medullary collecting tubule.
mesh_terms: D000818:Animals; D016275:Atrial Function; D009320:Atrial Natriuretic Factor / Q000494:pharmacology*; D004231:Diuresis / Q000187:drug effects; D004573:Electrolytes / Q000652:urine; D005260:Female; D005919:Glomerular Filtration Rate / Q000187:drug effects; D007684:Kidney Tubules / Q000187:drug effects*; D008657:Metabolic Clearance Rate / Q000187:drug effects; D051381:Rats; D011919:Rats, Inbred Strains; D013997:Time Factors; D014020:Tissue Extracts / Q000494:pharmacology*
chemical_list: D004573:Electrolytes; D014020:Tissue Extracts; D009320:Atrial Natriuretic Factor