Effect of canrenone on the digitalis site of Na+/K(+)-ATPase in human placental membranes and in erythrocytes.
It has been reported that canrenone, which is used in hypertensive therapy as an antialdosteronic drug, may also act as a blocker of ouabain effects. Several studies suggest that human plasma contains an endogenous ouabain-like factor similar to ouabain, which may be increased in hypertension, in pregnancy, and in the neonatal state. This study evaluated (1) the effect of canrenone on Na+/K(+)-ATPase in relation to ouabain in human placental membranes and erythrocytes by 3H-ouabain binding assay; (2) the capacity of canrenone (10 microM) to reverse the inhibition of Na+/K(+)-ATPase by ouabain and by ouabain-like factor (from umbilical cord plasma) in human erythrocytes employing a 86Rb uptake assay. Increasing concentrations of canrenone (0-350 microM) partially competed with 3H-ouabain binding in placental membrane (40%) and erythrocytes (60%). Scatchard plot from radioreceptor assay in placental membrane showed that ouabain and canrenone compete for the same binding site. In erythrocytes, canrenone completely reversed the inhibition caused by ouabain (5 x 10(-9) M) and ouabain-like factor (2 x 10(-9) M ouabain equivalents). A reduction of inhibition of about 50% was observed with ouabain and ouabain-like factor respectively at a concentration of 5 x 10(-8) M and 2 x 10(-8) M (ouabain equivalents). Our results thus provide evidence that canrenone, at therapeutical concentrations, is a partial competitive agonist of ouabain and of ouabain-like factor in human placental membranes and erythrocytes.
Balzan
S
S
CNR Institute of Clinical Physiology, Pisa, Italy. Balzan@ifc.pi.cnr.it
Nicolini
G
G
Bellitto
L
L
Ghione
S
S
Biver
P
P
Montali
U
U
D001665:Binding Sites; D001667:Binding, Competitive; D002192:Canrenone / Q000494:pharmacology*; D002298:Cardenolides; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D004077:Digoxin / Q000302:isolation & purification / Q000378:metabolism*; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D005312:Fetal Blood / Q000737:chemistry; D006801:Humans; D066298:In Vitro Techniques; D000451:Mineralocorticoid Receptor Antagonists / Q000494:pharmacology*; D010920:Placenta / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D011869:Radioligand Assay; D012414:Rubidium Radioisotopes; D012503:Saponins / Q000302:isolation & purification / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D002298:Cardenolides; D000451:Mineralocorticoid Receptor Antagonists; D012414:Rubidium Radioisotopes; D012503:Saponins; C034504:digoxin-like factors; D004077:Digoxin; D002192:Canrenone; D000254:Sodium-Potassium-Exchanging ATPase