Net secretion of furosemide is subject to indomethacin inhibition, as observed in Caco-2 monolayers and excised rat jejunum.
OBJECTIVE
To determine if intestinal secretion occurs for the poorly bioavailable diuretic, furosemide.


METHODS
Jejunal segments of male Sprague-Dawley rats were mounted on diffusion chambers, and the permeation of furosemide was measured across the excised tissue in both directions. Studies were repeated using cultured epithelia from adenocarcinoma cells (Caco-2) grown on filter inserts mounted in 6-well plates. Temperature-dependence and chemical inhibition by indomethacin was also tested using the cell culture model.


RESULTS
Net secretion from rat intestine of over 3-fold was observed for 20 microM furosemide. Net secretion of furosemide by Caco-2 cells was over 300% greater than for intestinal segments (10-fold vs. 3-fold). For both models, a decrease in furosemide transport in the direction of secretion was observed in the presence of indomethacin (100 microM), although only results using the Caco-2 cells showed in increase in the absorptive transport. Furosemide secretion from Caco-2 cells decreased with decrease in temperature from 37 degrees C to 4 degrees C, suggesting a carrier-mediated process.


CONCLUSIONS
Furosemide appears to be secreted in the small intestine. These preliminary results indicate that furosemide bioavailability may be limited by an intestinal transporter.
Flanagan
S D
SD
Department of Biopharmaceutical Sciences, School of Pharmacy, University of California, San Francisco 94143-0446, USA.
Benet
L Z
LZ
D000818:Animals; D000894:Anti-Inflammatory Agents, Non-Steroidal / Q000494:pharmacology; D001692:Biological Transport; D018938:Caco-2 Cells; D005665:Furosemide / Q000378:metabolism*; D006801:Humans; D007213:Indomethacin / Q000494:pharmacology*; D007408:Intestinal Absorption / Q000187:drug effects; D007583:Jejunum / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley
D000894:Anti-Inflammatory Agents, Non-Steroidal; D005665:Furosemide; D007213:Indomethacin