Cholecystographic agents and sulfobromophthalein inhibit the binding of L-thyroxine to plasma membranes of rat hepatocytes.
Cholecystographic agents and sulfobromophthalein (BSP) cause a major discharge of labeled T4 from the liver in man in vivo. In the present study we sought to determine if this discharge is partially due to inhibition of T4 binding to plasma membrane sites. Plasma membranes were isolated from hepatocytes of female Sprague-Dawley rats, and 5'-nucleotidase levels were measured to demonstrate plasma membrane viability. Specific binding of T4 (Ka, 1.01 X 10(8) M) was confirmed by displacement of labeled T4 by unlabeled hormone (10(-10)-10(-5) M). Displacement of labeled hormone was also produced by addition of tyropanoate, iopanoate, ipodate, or BSP. At 5-mM concentrations of inhibitor, the Ka for T4 declined to 4.00 X 10(7) M with BSP, 5.07 X 10(7) M with ipodate, 5.62 X 10(7) M with tyropanoate, and 7.43 X 10(7) M with iopanoate. Thus, a portion of the discharge of hepatic T4 after administration of these agents may be due to competitive inhibition of binding to plasma membrane sites.
Felicetta
J V
JV
Czanko
R
R
Huber-Smith
M J
MJ
McCann
D S
DS
D000818:Animals; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D002765:Cholecystography; D003287:Contrast Media / Q000494:pharmacology*; D005260:Female; D007480:Iopanoic Acid / Q000494:pharmacology; D007487:Ipodate / Q000494:pharmacology; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013448:Sulfobromophthalein / Q000494:pharmacology*; D013974:Thyroxine / Q000037:antagonists & inhibitors* / Q000378:metabolism; D014441:Tyropanoate / Q000494:pharmacology
D003287:Contrast Media; D013448:Sulfobromophthalein; D014441:Tyropanoate; D007487:Ipodate; D007480:Iopanoic Acid; D013974:Thyroxine