224
G. A. D. HASLEWOOD
It is an interesting possibility that biochemical "recapitulation" may
be taking place when bile salts are formed from cholesterol in modern
animals.
C. MICROBIAL ARTIFACTS IN THE BILE
During the enterohepatic circulation, products formed by microbial
action in the intestinal tract (including the cecum) are absorbed and
excreted in the bile. Such products in the gall bladder will reflect
imperfectly the actions of the liver enzymes which presumably make
the bile salts from sterols. Their value as species characters is uncertain
and must be assessed in every individual case. Much valuable work
has been done, mainly by S. Bergström and his colleagues at Lund and
Stockholm, on studies of the action of intestinal microorganisms during
the enterohepatic circulation. A chief method of the Swedish workers
has been to establish a fistula and then to compare fistula bile with
that taken from the gall bladder. Then, C
14 - or IP-labeled steroids can
be administered and the labeled products identified in the bile. Bergström et al. (48) have reviewed their work and that of others. Some of
the main conclusions are as follows:
(a) Deoxycholic acid has been shown in all species studied (rat,
rabbit, man, two species of Boidae) to be made from cholic acid by
microbial action in the intestine. Man and the rabbit re-excrete deoxy cholic acid, which is found in the gall bladder (in the rabbit in much
the greatest concentration of the bile acids); the rat hydroxylates the
deoxycholic acid to re-form cholic acid and the Boidae put in a 16ahydroxyl group to give pythocholic acid. Thus, part of the cholic acid in
rat bile is of "secondary" origin, like pythocholic acid. The specific
character of the Boidae is the possession of liver enzymes which effect
16a-hydroxylation of deoxycholic acid, and would presumably not be
manifest if this substance was not made by intestinal microorganisms.
It does, however, look as if the rat and the Boidae have evolved
mechanisms (7a- and 16a-hydroxylation, respectively) for converting
deoxycholic acid to a trihydroxycholanic acid, and presumably such
evolution has taken place as a result of selection pressure. Man and the
rabbit have no such rehydroxylation mechanisms. It would be interesting
to know if other snakes, having cholic and not pythocholic acid, can
carry out, like the rat, 7a-hydroxylation of deoxycholic acid.
(b) The characteristic bile acids of the pig are derived from hyocholic acid. Hyodeoxycholic acid is formed from this in the intestine, as
are 3a-hydroxy-6-oxocholanic acid and probably Saßß- and Sß,6adihydroxycholanic acids.
(c) All the keto acids investigated, as well as ursodeoxycholic acid,
G. A. D. HASLEWOOD
It is an interesting possibility that biochemical "recapitulation" may
be taking place when bile salts are formed from cholesterol in modern
animals.
C. MICROBIAL ARTIFACTS IN THE BILE
During the enterohepatic circulation, products formed by microbial
action in the intestinal tract (including the cecum) are absorbed and
excreted in the bile. Such products in the gall bladder will reflect
imperfectly the actions of the liver enzymes which presumably make
the bile salts from sterols. Their value as species characters is uncertain
and must be assessed in every individual case. Much valuable work
has been done, mainly by S. Bergström and his colleagues at Lund and
Stockholm, on studies of the action of intestinal microorganisms during
the enterohepatic circulation. A chief method of the Swedish workers
has been to establish a fistula and then to compare fistula bile with
that taken from the gall bladder. Then, C
14 - or IP-labeled steroids can
be administered and the labeled products identified in the bile. Bergström et al. (48) have reviewed their work and that of others. Some of
the main conclusions are as follows:
(a) Deoxycholic acid has been shown in all species studied (rat,
rabbit, man, two species of Boidae) to be made from cholic acid by
microbial action in the intestine. Man and the rabbit re-excrete deoxy cholic acid, which is found in the gall bladder (in the rabbit in much
the greatest concentration of the bile acids); the rat hydroxylates the
deoxycholic acid to re-form cholic acid and the Boidae put in a 16ahydroxyl group to give pythocholic acid. Thus, part of the cholic acid in
rat bile is of "secondary" origin, like pythocholic acid. The specific
character of the Boidae is the possession of liver enzymes which effect
16a-hydroxylation of deoxycholic acid, and would presumably not be
manifest if this substance was not made by intestinal microorganisms.
It does, however, look as if the rat and the Boidae have evolved
mechanisms (7a- and 16a-hydroxylation, respectively) for converting
deoxycholic acid to a trihydroxycholanic acid, and presumably such
evolution has taken place as a result of selection pressure. Man and the
rabbit have no such rehydroxylation mechanisms. It would be interesting
to know if other snakes, having cholic and not pythocholic acid, can
carry out, like the rat, 7a-hydroxylation of deoxycholic acid.
(b) The characteristic bile acids of the pig are derived from hyocholic acid. Hyodeoxycholic acid is formed from this in the intestine, as
are 3a-hydroxy-6-oxocholanic acid and probably Saßß- and Sß,6adihydroxycholanic acids.
(c) All the keto acids investigated, as well as ursodeoxycholic acid,