The effect of isoproterenol on fluid and electrolyte transport in the inner medullary collecting duct.
In the late distal and cortical collecting tubule, which is the principal regulatory site for potassium (K) excretion, vasopressin stimulates, and epinephrine via beta-adrenergic action, inhibits K secretion. In the inner medullary collecting duct (IMCD) we have shown that vasopressin also stimulates K secretion. The present experiments were designed to determine whether the beta-adrenergic agonist, isoproterenol, would induce K reabsorption in the IMCD, and (or) prevent a secretory response to acute KCl infusion. Two groups of rats, with or without isoproterenol administration (3 micrograms/h), were subjected to retrograde microcatheterization of the IMCD before and during infusion of 0.83 mol/h KCl. Isoproterenol reduced plasma K concentration and urinary K excretion, but the response to acute KCl infusion was qualitatively similar to control. Isoproterenol decreased delivery of potassium, chloride, and fluid to the IMCD, there was no net transport of K along the duct in either group, and KCl infusion did not result in K secretion in either group. The results indicate that isoproterenol may inhibit K secretion in the late distal or cortical collecting tubule. However, there was no statistically significant difference in K transport along the IMCD between isoproterenol and control groups. Reduced sodium excretion, which was found during isoproterenol administration both before and after KCl infusion, was associated with no change in sodium delivery but with increased sodium reabsorption in the IMCD. This increased sodium reabsorption may be a direct effect of isoproterenol, or may be due to reflex cardiovascular adjustments associated with systemic actions of the drug.
Honrath
U
U
Department of Physiology, University of Toronto, Ont., Canada.
Wilson
D R
DR
Sonnenberg
H
H
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001826:Body Fluids / Q000187:drug effects*; D004573:Electrolytes / Q000097:blood / Q000378:metabolism* / Q000652:urine; D005919:Glomerular Filtration Rate; D006400:Hematocrit; D007545:Isoproterenol / Q000494:pharmacology*; D007679:Kidney Medulla / Q000187:drug effects / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D011188:Potassium / Q000378:metabolism; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains
D004573:Electrolytes; D011189:Potassium Chloride; D007545:Isoproterenol; D011188:Potassium