150
ERNEST SCHOFFENIELS
b. Fatty Acids. As far as fatty acids are concerned, not many data
are available in the literature to clarify the nature of the forces responsible for the absorption of these organic ions from the lumen of the
intestine. It is known that in some parts of the digestive tract of different
herbivorous or phytophagous mammals, the enzymatic degradation of
cellulose by bacterial cellulase is followed by the fermentation of
hydrolytic products into carbonic anhydride and volatile fatty acids like
acetic, propionic, and butyric acids (53-56). This degradation takes
place not only in the rumen when this structure is present, but also in
the cecum and colon. Fatty acids are then absorbed: venous blood
irrigating these organs is more concentrated in fatty acids than venous
blood irrigating the small intestine. These observations have been made
not only at the level of the rumen and cecum of different ruminants, but
also in the colon of the horse and the pig and in the cecum of the
beaver, the rat, and the rabbit (54, 56a,b, 57, 57a).
More recently, experiments have been described in which transfer
of short-chain fatty acid by an in vitro intestinal preparation of rat
has been demonstrated (58). It is however, difficult, on the basis of
these experiments, to decide whether or not there is an active transport
of fatty acids, since the flux values were not correlated with the spontaneous potential difference existing across the intestinal wall. It should
indeed be remembered that conditions known to modify the potential
difference as well as the active transport of glucose and sodium, affect
also the transfer of fatty acids.
Long-chain fatty acids are continuously absorbed from the solution
bathing the mucosal side of the golden hamster intestine and appear in
the serosal solution as triglycerides with small amounts of diglycerides
and free fatty acids (59). The distribution of glyceride activity in the
intestinal wall is similar to that in the serosal solution. These results
suggest the greatest caution in interpreting results on the transfer of
long-chain fatty acids since they demonstrate that the fatty acid transported appears mainly as another chemical species in the serosal fluid.
This fact has thus to be taken into consideration, before applying to this
phenomenon the well-defined and strictly restricted concept of active
transport.
3. Organic Molecules: Sugars
There are a number of in vitro observations, using the everted intestine sac technique (20), showing that sugars may be divided into two
groups: (a) those that are transported against an apparent concentration
gradient and (6) those that are not.
The experiment begins with sugar at the same concentration on both
ERNEST SCHOFFENIELS
b. Fatty Acids. As far as fatty acids are concerned, not many data
are available in the literature to clarify the nature of the forces responsible for the absorption of these organic ions from the lumen of the
intestine. It is known that in some parts of the digestive tract of different
herbivorous or phytophagous mammals, the enzymatic degradation of
cellulose by bacterial cellulase is followed by the fermentation of
hydrolytic products into carbonic anhydride and volatile fatty acids like
acetic, propionic, and butyric acids (53-56). This degradation takes
place not only in the rumen when this structure is present, but also in
the cecum and colon. Fatty acids are then absorbed: venous blood
irrigating these organs is more concentrated in fatty acids than venous
blood irrigating the small intestine. These observations have been made
not only at the level of the rumen and cecum of different ruminants, but
also in the colon of the horse and the pig and in the cecum of the
beaver, the rat, and the rabbit (54, 56a,b, 57, 57a).
More recently, experiments have been described in which transfer
of short-chain fatty acid by an in vitro intestinal preparation of rat
has been demonstrated (58). It is however, difficult, on the basis of
these experiments, to decide whether or not there is an active transport
of fatty acids, since the flux values were not correlated with the spontaneous potential difference existing across the intestinal wall. It should
indeed be remembered that conditions known to modify the potential
difference as well as the active transport of glucose and sodium, affect
also the transfer of fatty acids.
Long-chain fatty acids are continuously absorbed from the solution
bathing the mucosal side of the golden hamster intestine and appear in
the serosal solution as triglycerides with small amounts of diglycerides
and free fatty acids (59). The distribution of glyceride activity in the
intestinal wall is similar to that in the serosal solution. These results
suggest the greatest caution in interpreting results on the transfer of
long-chain fatty acids since they demonstrate that the fatty acid transported appears mainly as another chemical species in the serosal fluid.
This fact has thus to be taken into consideration, before applying to this
phenomenon the well-defined and strictly restricted concept of active
transport.
3. Organic Molecules: Sugars
There are a number of in vitro observations, using the everted intestine sac technique (20), showing that sugars may be divided into two
groups: (a) those that are transported against an apparent concentration
gradient and (6) those that are not.
The experiment begins with sugar at the same concentration on both