448
C. B. COWEY AND J. R. SAROENT
already referred to (p. 431) and (3) desaturation of fatty acids (Holloway
and Wakil, 1970). In all cases both reduced pyridine nucleotides
(either NADH* or NADPH) and molecular oxygen are involved.
While little detailed information is available concerning electron
transfer reactions in the liver microsomes from fish, it is known that
the plaice and Scyliorhinm contain the usual NADH- and NADPHcytochrome C oxidoreductase activities normally associated with liver
microsomes from mammals, although the activities and especially that
associated with NADH are reduced in the fish (Sargent, unpublished
observations). Furthermore, it is known that the trout has only a
limited ability to detoxify foreign compounds (Buhler and Rasmusson,
1968; Chan et al., 1967; Dewaide and Henderson, 1970). The drug
detoxification system in Scyliorhinm appears to be highly resistant to
induction with phenobarbitone, a compound known to cause striking
increases in the drug detoxification activity of mammalian liver
(Sargent, unpublished observations).
Fish contain high levels of polyunsaturated fatty acids that feature
in two of the reaction systems listed above, viz. fatty acid desaturation
reactions associated with chain elongation and lipid peroxidation.
Consequently it is pertinent to ask to what extent the microsomal
electron transfer reactions are competitive in fish in view of their
reacting with common substrates (reduced pyridine nucleotides and
oxygen) at a common subcellular site. Should competitions occur
between the reactions then complex interactions may well occur
between dietary cholesterol, polyenoic acids and foreign compounds,
and the biosynthetic and metabolic transformations of these compounds within the fish. While these thoughts are speculative the
consequences for fish nutrition could be profound. The effects of
polyunsaturated fatty acids in reducing cholesterol levels in mammals
are now well substantiated (Nestel, 1970), a situation which serves to
stress the importance of a correctly balanced lipid diet in iish culture.
v. VrraMINS
The sequence of events leading to present day knowledge of vitamin
structure, function and requirement probably began three t o four
hundred years ago when it was recognized that certain clinical symptoms
(night blindness, rickets, and beri beri for example) could be overcome empirically by dietary means. It is commonly known that by
the end of the eighteenth century, fresh fruit or fruit juice was
routinely administered to sailors for the prevention or cure of scurvy.
* Reduoed niootinamide adenine dinuoleotide.
C. B. COWEY AND J. R. SAROENT
already referred to (p. 431) and (3) desaturation of fatty acids (Holloway
and Wakil, 1970). In all cases both reduced pyridine nucleotides
(either NADH* or NADPH) and molecular oxygen are involved.
While little detailed information is available concerning electron
transfer reactions in the liver microsomes from fish, it is known that
the plaice and Scyliorhinm contain the usual NADH- and NADPHcytochrome C oxidoreductase activities normally associated with liver
microsomes from mammals, although the activities and especially that
associated with NADH are reduced in the fish (Sargent, unpublished
observations). Furthermore, it is known that the trout has only a
limited ability to detoxify foreign compounds (Buhler and Rasmusson,
1968; Chan et al., 1967; Dewaide and Henderson, 1970). The drug
detoxification system in Scyliorhinm appears to be highly resistant to
induction with phenobarbitone, a compound known to cause striking
increases in the drug detoxification activity of mammalian liver
(Sargent, unpublished observations).
Fish contain high levels of polyunsaturated fatty acids that feature
in two of the reaction systems listed above, viz. fatty acid desaturation
reactions associated with chain elongation and lipid peroxidation.
Consequently it is pertinent to ask to what extent the microsomal
electron transfer reactions are competitive in fish in view of their
reacting with common substrates (reduced pyridine nucleotides and
oxygen) at a common subcellular site. Should competitions occur
between the reactions then complex interactions may well occur
between dietary cholesterol, polyenoic acids and foreign compounds,
and the biosynthetic and metabolic transformations of these compounds within the fish. While these thoughts are speculative the
consequences for fish nutrition could be profound. The effects of
polyunsaturated fatty acids in reducing cholesterol levels in mammals
are now well substantiated (Nestel, 1970), a situation which serves to
stress the importance of a correctly balanced lipid diet in iish culture.
v. VrraMINS
The sequence of events leading to present day knowledge of vitamin
structure, function and requirement probably began three t o four
hundred years ago when it was recognized that certain clinical symptoms
(night blindness, rickets, and beri beri for example) could be overcome empirically by dietary means. It is commonly known that by
the end of the eighteenth century, fresh fruit or fruit juice was
routinely administered to sailors for the prevention or cure of scurvy.
* Reduoed niootinamide adenine dinuoleotide.