In vivo and in vitro microdialysis sampling of free fatty acids.
Microdialysis is a technique that allows continuous sampling of compounds from the interstitial fluid of different tissues with minimal influence on surrounding tissues and/or whole body function. In the present study, the feasibility of using microdialysis as a technique to sample free fatty acids (FFA) was investigated both in vitro and in vivo, by use of a high molecular weight (MW) cut-off membrane (3 MDa) and a push-pull system to avoid loss of perfusion fluid through the dialysis membrane. The relative recovery was examined in vitro for three different concentrations of radiolabelled oleic acid-BSA solutions (oleic acid:BSA molar ratio 1:1) and for various temperatures and flow rates. The recovery of oleic acid was found to be dependent on the concentration of analyte in the medium surrounding the membrane (17.3%, 29.0% and 30.6% for 50, 100 and 200 microM oleic acid-BSA solutions, respectively). Addition of 0.25% BSA to the perfusion fluid resulted, however, in a concentration-independent recovery of 31.4%, 28.1% and 28.1% for the 50, 100 and 200 microM solutions, respectively. The capability of the method to measure FFA together with glycerol was investigated in vivo in visceral adipose tissue of rats, before and after lipolytic treatment with the beta3-adrenergic agent, BRL37344. BRL37344 caused an increase in both dialysate FFA and glycerol, although the increase was markedly higher for glycerol, amounting to 24.5% and 329.2% increase from baseline, respectively. Subsequent in vitro test of probe performance revealed a decrease in the dialysing properties with regard to FFA, but not glycerol. This suggests that clogging of the membrane pores after 110 min prevented the measurement of the full FFA response in vivo.
Jensen
Signe Mølhøj
SM
Diabetes Pharmacology, Novo Nordisk A/S, Novo Nordisk Park, DK-2760 Måløv, Denmark. simj@novonordisk.com
Hansen
Harald S
HS
Johansen
Thue
T
Malmlöf
Kjell
K
D000273:Adipose Tissue / Q000187:drug effects / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D000911:Antibodies, Monoclonal / Q000378:metabolism; D001783:Blood Flow Velocity / Q000187:drug effects; D002417:Cattle; D004983:Ethanolamines / Q000008:administration & dosage / Q000494:pharmacology; D005230:Fatty Acids, Nonesterified / Q000032:analysis* / Q000096:biosynthesis / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics*; D005240:Feasibility Studies; D005260:Female; D005990:Glycerol / Q000378:metabolism; D066298:In Vitro Techniques; D007274:Injections, Intraperitoneal; D007552:Isotonic Solutions / Q000737:chemistry; D008066:Lipolysis / Q000187:drug effects; D008643:Mesentery / Q000187:drug effects / Q000378:metabolism; D017551:Microdialysis / Q000295:instrumentation* / Q000379:methods*; D019301:Oleic Acid / Q000032:analysis / Q000096:biosynthesis / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics; D010477:Perfusion; D020959:Polyethylene / Q000737:chemistry; D051381:Rats; D017208:Rats, Wistar; D000077331:Ringer's Solution; D012710:Serum Albumin, Bovine / Q000737:chemistry; D012996:Solutions / Q000737:chemistry; D013696:Temperature; D014781:Viscera / Q000187:drug effects / Q000378:metabolism
D000318:Adrenergic beta-Agonists; D000911:Antibodies, Monoclonal; D004983:Ethanolamines; D005230:Fatty Acids, Nonesterified; D007552:Isotonic Solutions; D012996:Solutions; D012710:Serum Albumin, Bovine; D019301:Oleic Acid; C057368:BRL 37344; D000077331:Ringer's Solution; D020959:Polyethylene; D005990:Glycerol