title: The longitudinal intraluminal concentration gradient in the perfused rat jejunum and the appropriate mean concentration for calculation of the absorption rate.
abstract: In anaesthetized rats, jejunal segments 30 cm in length were perfused (rates:0.1, 0.2,0.5 ml/min) with solutions containing antipyrine, salicylic acid, urea, L-lysine, L- and D-phenylalanine. The intraluminal concentration was determined approx. 10, 20, and 30 cm from the inflow cannula. The intraluminal concentration gradients were almost exponential and corresponded to the gradient predicted for a laminar flow through a solute-permeable circular tube. This gradient has a slightly greater curvature than the exponential one. Theoretical considerations showed that the logarithmic mean (Co-Cz)/ln(Co/Cz) of the in- and outflow concentration is the best average value for application in non-integrated absorption equations. This is also valid for the temporal concentration gradient after single administration of a substance into an intestinal segment.
mesh_terms: D000818:Animals; D000983:Antipyrine / Q000378:metabolism; D001699:Biometry; D066298:In Vitro Techniques; D007408:Intestinal Absorption; D007583:Jejunum / Q000378:metabolism*; D007700:Kinetics; D008239:Lysine / Q000378:metabolism; D008297:Male; D008954:Models, Biological; D009994:Osmolar Concentration; D010649:Phenylalanine / Q000378:metabolism; D051381:Rats; D012459:Salicylates / Q000378:metabolism; D014508:Urea / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D012459:Salicylates; D014867:Water; D010649:Phenylalanine; D014508:Urea; D008239:Lysine; D000983:Antipyrine