Binding of furosemide to albumin isolated from human fetal and adult serum.
Albumin was isolated from pooled fetal serum from 58 placentas obtained at normal delivery at term and from pooled adult plasma from 8 individuals. Albumin isolation was carried out by means of PEG precipitation followed by ion-exchange chromatography on DEAE-Sephadex A 50 and then on SP-Sephadex C 50. The electrophoresis on SDS-polyacrylamide gels showed only one spot that comigrated with commercial human albumin. Binding to albumin was measured by equilibrium dialysis of an aliquot of albumin solution (0.7 ml) against the same volume of 0.13 M sodium orthophosphate buffer (pH 7.4). At a total concentration of 2 micrograms/ml (therapeutic range), the unbound fraction of furosemide was 2.71% (fetal albumin) and 2.51% (adult albumin). Two classes of binding sites for furosemide were observed in fetal and adult albumin. The number of binding sites (moles of furosemide per mole of albumin) was 1.22 (fetal albumin) and 1.58 (adult albumin) for the high-affinity site and 2.97 (fetal albumin) and 3.25 (adult albumin) for the low-affinity site. The association constants (M-1) were 3.1 X 10(4) (fetal albumin) and 2.6 X 10(4) (adult albumin) for the high-affinity set of sites and 0.83 X 10(4) (fetal albumin) and 1.0 X 10(4) (adult albumin) low-affinity site. The displacement of furosemide from albumin was studied with therapeutic concentrations of several drugs. Valproic acid, salicylic acid, azapropazone and tolbutamide had the highest displacing effects which were significantly higher with fetal than with adult albumin.
Viani
A
A
Department of Experimental Biomedicine, Medical School, University of Pisa, Italy.
Cappiello
M
M
Silvestri
D
D
Pacifici
G M
GM
D000328:Adult; D000375:Aging / Q000378:metabolism; D001665:Binding Sites; D004347:Drug Interactions; D004591:Electrophoresis, Polyacrylamide Gel; D005312:Fetal Blood; D005665:Furosemide / Q000378:metabolism*; D006801:Humans; D012709:Serum Albumin / Q000302:isolation & purification / Q000378:metabolism*
D012709:Serum Albumin; D005665:Furosemide