title: The influence of old age and poloxamer-407 on the hepatic disposition of diazepam in the isolated perfused rat liver.
abstract: OBJECTIVE
  The normal liver sinusoidal endothelium is thin and punctuated with fenestrations 50-200 nm in diameter that filter endobiotics and xenobiotics. Defenestration of the liver sinusoidal endothelium in old age and after pre-treatment with poloxamer-407 (P407) has been shown to prevent the transfer of small chylomicrons across the liver sinusoidal endothelium. The aim of this study was to investigate the impact of liver sinusoidal endothelium fenestrations on the hepatic uptake of the highly protein-bound drug diazepam. We hypothesized that defenestration will reduce the hepatic extraction of drugs which are highly bound to albumin.
  
  
  METHODS
  The isolated perfused rat liver (IPRL) model and multiple indicator dilution technique were used to investigate the effect of fenestrations in the liver sinusoidal endothelium on the hepatic disposition of diazepam in old and young rats, and in young rats treated with P407 or vehicle. A bolus dose of (14)C-diazpeam and non-extracted tracers ((3)H-sucrose and Evans blue) was injected into the portal vein. The single-pass recovery of diazepam and markers and the apparent volume of distribution were determined.
  
  
  RESULTS
  Scanning electron microscopy confirmed reduced porosity of the liver sinusoidal endothelial cells in P407-treated rats and old rats compared to young and control rats. The fractional recovery of diazepam was significantly increased in P407-treated rats compared to controls (0.20 ± 0.16, n = 12, P407; 0.08 ± 0.05, n = 8, controls; p = 0.0029), and in old rats compared to young rats (0.15 ± 0.03, n = 11, old; 0.10 ± 0.02, n = 11, young; p = 0.0004) following a single pass.
  
  
  CONCLUSIONS
  Defenestration due to age-related pseudocapillarization and treatment with P407 resulted in reduced hepatic extraction of diazepam after a single pass through the IPRL. These results highlight the importance of the liver sinusoidal endothelium in the ultrafiltration of highly protein-bound drugs, and may also provide an additional mechanism for reduced hepatic clearance of diazepam in conditions associated with defenestration.
authors.affiliation: Kolling Institute of Medical Research, Royal North Shore Hospital, Sydney, NSW, Australia. sarah.mitchell@sydney.edu.au
authors.forename: Sarah J
authors.initials: SJ
authors.lastname: Mitchell
authors.forename: Aniko
authors.initials: A
authors.lastname: Huizer-Pajkos
authors.forename: Victoria C
authors.initials: VC
authors.lastname: Cogger
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: McLachlan
authors.forename: David G
authors.initials: DG
authors.lastname: Le Couteur
authors.forename: Brett
authors.initials: B
authors.lastname: Jones
authors.forename: Rafael
authors.initials: R
authors.lastname: de Cabo
authors.forename: Sarah N
authors.initials: SN
authors.lastname: Hilmer
mesh_terms: D000375:Aging / Q000378:metabolism; D000818:Animals; D003975:Diazepam / Q000008:administration & dosage* / Q000493:pharmacokinetics; D004727:Endothelium / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D010477:Perfusion; D020442:Poloxamer / Q000008:administration & dosage*; D051381:Rats; D011916:Rats, Inbred F344; D013501:Surface-Active Agents / Q000008:administration & dosage*
chemical_list: D013501:Surface-Active Agents; D020442:Poloxamer; D003975:Diazepam