A RE-EVALUATION OF THE IMPORTANCE OF PARTITION COEFFICIENTS IN THE GASTROINTESTINAL ABSORPTION OF ANUTRIENTS

¹ Biochemistry Department, University of Surrey, Guildford, and Medical Division, Chemical Defence Establishment, Porton Down, Wiltshire, England

The gastrointestinal absorption of a homologous series of carbamates has been investigated in the rat using both in vitro and in situ techniques. An increase in the intestinl absorption rate was observed when the chain length of the carbamate was increased from methyl to n-butyl. A further increase in the chain length resulted in a fall in the absorption rate. The absorption process appeared to be passive and no metabolism by the gut wall was detected. The concept of an optimal partition coefficient for intestinal absorption is discussed in terms of a two-compartment model where a hydrophilic barrier and a lipoidal membrane control the rate of absorption. The gastric absorption rates of the same series of compounds did not share the same optimal partiction coefficient. The absorption rates from the stomach increased regularly as the chain length of the carbamate was extended from methyl to n-hexyl.