AJP - Gastrointestinal and Liver Physiology, Vol 239, Issue 5 363-G371, Copyright © 1980 by American Physiological Society
Effect of age on uptake of homologous series of saturated fatty acids into rabbit jejunum
A. B. Thomson
The effect of age on the rate of uptake (Jd) of a homologous series of
saturated fatty acids into rabbit jejunum was determined in suckling,
mature, and old animals. A previously validated in vitro technique was
used, and the bulk phase was stirred at different rates to vary the
effective resistance of the unstirred water layer (UWL). When UWL was high,
Jd of fatty acids was greater in old than in young animals; Jd was greatly
increased when UWL was low, and Jd was not higher in the suckling and
mature rather than the old animals. At each rate of stirring UWL was lowest
in the suckling rabbits and highest in the old animals. The values of Jd
were corrected for UWL, yielding estimates of the true passive permeability
properties of the membrane. From these values, the incremental free energy
change associated with the addition of each -CH2- group to the fatty acid
chain was 50% higher in the suckling and mature animals than in the old
animals, and the estimated surface area of the jejunal membrane was also
higher in the suckling and mature animals. Variations in UWL had a profound
effect on the Jd of passively absorbed fatty acids, and failure to account
for UWL leads to gross underestimation of the permeability properties of
the jejunal microvillus membrane. Furthermore, the difference between the
true and apparent passive permeability coefficients becomes greater as the
fatty acid chain length increases. The results suggest that discrepancies
in uptake of fatty acids in animals of different ages are explained by
differences in the passive permeability properties and functional surface
area of the membrane and by differences in the overlying UWL.
