Hepatic uptake of octreotide, a long-acting somatostatin analogue, via a bile acid transport system.
The hepatic transport mechanism of octreotide (Sandostatin), a somatostatin analogue, was studied using freshly prepared rat hepatocytes. The initial uptake rate of octreotide represented exclusively a saturable transport process. The half-saturation constant, Kt, and the maximum uptake-rate, Jmax, for the uptake of octreotide were 91.1 +/- 28.4 microM and 104.6 +/- 19.7 pmol/mg protein/min, respectively. An energy requirement was demonstrated for [14C]octreotide uptake since metabolic inhibitors (DNP, rotenone, antimycin and NaCN) significantly reduced the initial uptake rate. [14C]octreotide uptake was also significantly inhibited by ouabain. [14C]octreotide uptake was reduced in the absence of Na+ in the uptake medium. [14C]octreotide uptake was significantly inhibited by bile acids, iodipamide, d-tubocurarine, whereas it was not inhibited by bilirubin, TEMA and insulin. Competitive inhibition of taurocholic acid was observed for octreotide uptake with the inhibition constant, Ki, of 82 +/- 17 microM. Moreover, a significant inhibitory effect of octreotide was observed for the Na+ dependent uptake of [14C]taurocholic acid. These results suggest that octreotide is transported into hepatocytes via a bile acid carrier-mediated system.
Terasaki
T
T
Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
Mizuguchi
H
H
Itoho
C
C
Tamai
I
I
Lemaire
M
M
Tsuji
A
A
D000595:Amino Acid Sequence; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D001667:Binding, Competitive; D001692:Biological Transport; D002250:Carbon Radioisotopes; D002478:Cells, Cultured; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D015282:Octreotide / Q000493:pharmacokinetics*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000494:pharmacology; D013656:Taurocholic Acid / Q000494:pharmacology; D013997:Time Factors
D001647:Bile Acids and Salts; D002250:Carbon Radioisotopes; D013656:Taurocholic Acid; D012964:Sodium; D015282:Octreotide