650
16 Sterols and Steroids
Neoceratodus; 5a-chimaerol and 26-deoxy-5achimaerol are restricted to Neoceratodus. The
large proportion of 5a-bufol in Lepidosirenis an
indication of the relationship between the Dipnoi
and the amphibians. The primitive bony fish,
such as Acipenser, Polyodon, Amia, Lepisosteus,
Polypterus and Calamoichthys, contain predominantly taurocholic acids and only traces of bile
alcohols. In contrast, their derived evolutionary
descendants, the teleosts, exhibit all possible
variations of the bile salt spectrum from the most
primitive, which consists mainly of 5a-cyprinol
(Cyprinidae, several Catastomidae) or 5achimaerol (several Catastomidae) and only traces
of taurine-conjugated C24 bile acids, to those
which consist almost exclusively of such bile acid
conjugates, e.g. the catastomid Carpoides carpio
and the gymnotid Electrophorus electricus. The
giant Amazonian fish Arapaima gigas (Osteoglossidae) is unique in possessing arapaimol A and B
in addition to taurocholate [46].
The amphibians also possess characteristic bile
salts. For example, the gymnophion Dermophis
mexican us has 5~-dermophol, the urodelans have
5a-dermophol, 5a-bufol or 5a-cyprinol and, in the
genus Salamandra, 5a-ranol is also present. To
date, a total of 14 different bile alcohols has been
identified in the anurans; these include the particularly common 5a- and 5~-ranol and 5~-bufol.
Non-conjugated C28 bile acids have been identified
in the American bullfrog Rana catesbeiana and the
toad Bufo bufo formosa. No bile alcohols are
found from the reptiles onwards, only C27 or
G4 bile acids; however, the alcohols may appear
under pathological conditions, even in man. The
bile acids of the reptiles are all taurine conjugated.
The gall bladder of the crocodile has mainly
3a,7a,12a-trihydroxycoprostanic acid, which is an
intermediate in the synthesis of cholic acid. Thus,
the crocodile lacks the ability to shorten the
side-chain. The turtles have a C27 bile acid,
tetrahydroxy-sterocholanic acid, which carries a
unique 22-hydroxyl group, but they apparently
also have the capacity to produce C24 bile acids.
The lizards normally synthesize cholic acid or allocholic acid; only the Varanidae are unusual in having a C27 bile acid, varanic acid [1]. The snakes, of
which more than 80 species have been investigated, also contain mainly 5~-G4 bile acids. The
pythocholic acid of the boas and pythons is a secondary bile acid. This arises by conversion of the
cholic acid, secreted from the liver, to deoxycholic
acid by gut bacteria; this is further 16ahydroxylated to pythocholic acid by the liver following reabsorption. The capacity for 16ahydroxylation is found only in this group of primitive snakes, and the 23-hydroxylation of bile acids,
which occurs in some species of the Viperidae and
Colubridae, is also highly characteristic [46].
Chenodeoxycholic acid was for a long time
regarded as the typical bile acid of the birds but,
in fact, cholic acid and ursodeoxycholic acid
are also found. ~-Phocaecholic acid, previously
known from only the seal, has additionally been
found in large quantities in the duck Anas platyrhynchos [55]. The mammals have almost exclusively 5~-C24 bile acids which are conjugated with
taurine or glycine. Taurine-conjugated trihydroxy
acids, in particular cholic acid, normally predominate in carnivorous mammals, and glycineconjugated dihydroxy acids, especially chenodeoxycholic acid and deoxycholic acid, predominate
in the herbivorous mammals, although some trihydroxy acids are also found in the herbivores.
Glycine-conjugated bile acids are found only in
the higher mammals (Eutheria); in the cloacal
(monotremes) and pouched (marsupial) mammals, the usual three bile acids are conjugated
with taurine. Whereas in the primates the three
bile acids are bound partly to glycine and partly
to taurine, the rabbit has almost exclusively
glycine-conjugated deoxycholic acid. Amongst
the rodents, the beaver Castor canadensis has the
typical herbivorous spectrum with glycineconjugated chenodeoxycholic acid as the main
component. However, the rat and the mouse have
cholic acid and also' the typical a- and ~muricholic acid, all mainly conjugated with taurine. In addition, the mouse has w-muricholic
acid, a secondary bile acid of unknown origin.
The three typical bile acids of the Carnivora are
found predominantly in the taurine-conjugated
form. In contrast to the meat-eating bears, the
vegetarian bears have glycine-conjugated dihydroxy acids such as chenodeoxycholic acid or ursodeoxycholic acid. In addition to the usual taurineconjugated bile acids, the marine mammals (Pinnipedia) have a characteristic acid, phocaecholic
acid [47]. The Artiodactyala have both glycineconjugated chenodeoxycholic acid and hyodeoxycholic acid, which may be either primary or secondary bile acids. Thus, chenodeoxycholic acid is
converted to hyocholic acid by 6a-hydroxylation
in the pig liver, and hyodeoxycholic acid is then
produced by cleavage of the 7a-hydroxyl group
by gut bacteria; 6a-hydroxylation is a speciality of
the pig (Suinae). The usual three bile acids predominate in the ruminants but, in contrast to those
found in other herbivorous mammals, they are
partly taurine conjugated [46].
16 Sterols and Steroids
Neoceratodus; 5a-chimaerol and 26-deoxy-5achimaerol are restricted to Neoceratodus. The
large proportion of 5a-bufol in Lepidosirenis an
indication of the relationship between the Dipnoi
and the amphibians. The primitive bony fish,
such as Acipenser, Polyodon, Amia, Lepisosteus,
Polypterus and Calamoichthys, contain predominantly taurocholic acids and only traces of bile
alcohols. In contrast, their derived evolutionary
descendants, the teleosts, exhibit all possible
variations of the bile salt spectrum from the most
primitive, which consists mainly of 5a-cyprinol
(Cyprinidae, several Catastomidae) or 5achimaerol (several Catastomidae) and only traces
of taurine-conjugated C24 bile acids, to those
which consist almost exclusively of such bile acid
conjugates, e.g. the catastomid Carpoides carpio
and the gymnotid Electrophorus electricus. The
giant Amazonian fish Arapaima gigas (Osteoglossidae) is unique in possessing arapaimol A and B
in addition to taurocholate [46].
The amphibians also possess characteristic bile
salts. For example, the gymnophion Dermophis
mexican us has 5~-dermophol, the urodelans have
5a-dermophol, 5a-bufol or 5a-cyprinol and, in the
genus Salamandra, 5a-ranol is also present. To
date, a total of 14 different bile alcohols has been
identified in the anurans; these include the particularly common 5a- and 5~-ranol and 5~-bufol.
Non-conjugated C28 bile acids have been identified
in the American bullfrog Rana catesbeiana and the
toad Bufo bufo formosa. No bile alcohols are
found from the reptiles onwards, only C27 or
G4 bile acids; however, the alcohols may appear
under pathological conditions, even in man. The
bile acids of the reptiles are all taurine conjugated.
The gall bladder of the crocodile has mainly
3a,7a,12a-trihydroxycoprostanic acid, which is an
intermediate in the synthesis of cholic acid. Thus,
the crocodile lacks the ability to shorten the
side-chain. The turtles have a C27 bile acid,
tetrahydroxy-sterocholanic acid, which carries a
unique 22-hydroxyl group, but they apparently
also have the capacity to produce C24 bile acids.
The lizards normally synthesize cholic acid or allocholic acid; only the Varanidae are unusual in having a C27 bile acid, varanic acid [1]. The snakes, of
which more than 80 species have been investigated, also contain mainly 5~-G4 bile acids. The
pythocholic acid of the boas and pythons is a secondary bile acid. This arises by conversion of the
cholic acid, secreted from the liver, to deoxycholic
acid by gut bacteria; this is further 16ahydroxylated to pythocholic acid by the liver following reabsorption. The capacity for 16ahydroxylation is found only in this group of primitive snakes, and the 23-hydroxylation of bile acids,
which occurs in some species of the Viperidae and
Colubridae, is also highly characteristic [46].
Chenodeoxycholic acid was for a long time
regarded as the typical bile acid of the birds but,
in fact, cholic acid and ursodeoxycholic acid
are also found. ~-Phocaecholic acid, previously
known from only the seal, has additionally been
found in large quantities in the duck Anas platyrhynchos [55]. The mammals have almost exclusively 5~-C24 bile acids which are conjugated with
taurine or glycine. Taurine-conjugated trihydroxy
acids, in particular cholic acid, normally predominate in carnivorous mammals, and glycineconjugated dihydroxy acids, especially chenodeoxycholic acid and deoxycholic acid, predominate
in the herbivorous mammals, although some trihydroxy acids are also found in the herbivores.
Glycine-conjugated bile acids are found only in
the higher mammals (Eutheria); in the cloacal
(monotremes) and pouched (marsupial) mammals, the usual three bile acids are conjugated
with taurine. Whereas in the primates the three
bile acids are bound partly to glycine and partly
to taurine, the rabbit has almost exclusively
glycine-conjugated deoxycholic acid. Amongst
the rodents, the beaver Castor canadensis has the
typical herbivorous spectrum with glycineconjugated chenodeoxycholic acid as the main
component. However, the rat and the mouse have
cholic acid and also' the typical a- and ~muricholic acid, all mainly conjugated with taurine. In addition, the mouse has w-muricholic
acid, a secondary bile acid of unknown origin.
The three typical bile acids of the Carnivora are
found predominantly in the taurine-conjugated
form. In contrast to the meat-eating bears, the
vegetarian bears have glycine-conjugated dihydroxy acids such as chenodeoxycholic acid or ursodeoxycholic acid. In addition to the usual taurineconjugated bile acids, the marine mammals (Pinnipedia) have a characteristic acid, phocaecholic
acid [47]. The Artiodactyala have both glycineconjugated chenodeoxycholic acid and hyodeoxycholic acid, which may be either primary or secondary bile acids. Thus, chenodeoxycholic acid is
converted to hyocholic acid by 6a-hydroxylation
in the pig liver, and hyodeoxycholic acid is then
produced by cleavage of the 7a-hydroxyl group
by gut bacteria; 6a-hydroxylation is a speciality of
the pig (Suinae). The usual three bile acids predominate in the ruminants but, in contrast to those
found in other herbivorous mammals, they are
partly taurine conjugated [46].