Glycerol permeability coefficient

Fig. 10. Calculated intramembrane diffusion coefficients across membranes of (A) Nil 8 hamster fibroblasts and (B) the HTC rat hepatoma cell line, as a function of molecular weight of the permeant. Ordinate logarithm of membrane thickness, taken as 50-10 cm, multiplied by the permeability coefficient (in cm/sec) and divided by the octanol/water partition coefficient. Abscissa logarithm of molecular weight. Data taken from Giorgi and Stein [19]. Permeants indicated as follows large circle, mean value for all the steroids of Fig. 8 Ur, urea Thw, thiourea Gly, glycerol Ap, antipyrine. Regression lines through the points have slopes of —3.9 for the Nil 8 cells and —3.7 for the HTC cells.

The feasibility ofthetopical/transdermal deUvery of resveratrol was examined [35]. Effects of vehicles on the in vitro permeation and skin deposition from saturated solution such as aqueous buffers and soybean oil were investigated. The general trend for the deUvery from solution was pH 6 bufFer=pH 8 bufFer> 10% glycerol formal in pH 6 buffer > pH 9.9 buffer > pH 10.8 buffer > soybean oil. A linear relationship was estabhshed between the permeability coefficient (kp) and drug accumulation in the skin reservoir. 

Note Data represent the mean S.E. (n = 3). MW, molecular weight P0/w, octanol-to-water partition coefficient CLapp, apparent membrane permeability clearance SI, midgut area of the small intestine NA, not available or applicable. Absorption was evaluated in our laboratory using the closed loop of the rat intestine in situ (urethane anesthesia, 1.125 g/4.5 ml/kg, i.p.) in 60 min for riboflavin and L-camitine and 30 min for the others. For those that are transported by carriers in part (riboflavin and glycerol in both colon and SI, and L-carnitine, 5-fluorouracil, and cephradine in SI), absorption was evaluated at higher concentrations where the contribution of carrier-mediated transport is negligible. Values of P0/w were obtained from a report by Leo et al. [30] except for that of D-xylose, which was determined in our laboratory. a Data by single-pass perfusion experiments. b Unpublished data from our laboratory. 

Available data on the permeability of cell membranes are consistent with the view that the vast majority of substances find the major barrier to their trans-membrane movement to be the tightly packed proximal chains of the phospholipid hydrocarbons, together with the cholesterol moieties and the glycerol backbone. This region has solvent properties well modelled by the less non-polar organic solvents (ether and even w-octanol). The data reveal a steep mass selectivity (three to six power inverse dependence of intramembrane diffusion coefficient on molecular... 

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