When the diet containing 5% ethyl ester of highly unsaturated fatty acids obtained from fish oil was given to rat, it showed quite the same good nutritive effect as the diet containing ethyl oleate.
To the contrary, the autoxidized form of the above mentioned unsaturated fatty acid esters showed an extremely toxic effect to rat. The toxicity of autoxidized fatty acid ester ran parallel to the content of peroxide.
The mixture of aqueous solution of the ovoalbumin and the ethyl ester of unsaturated fatty acid or its autoxidized product was left at 37°C, the solution to which the original ester (not oxidized) was added showed little noticeable change.
The solution to which autodized ester was added, on the otherhand, gradually turned to yellowish brown. As the time passed, the precipitate increased and became more deeply colored. Almost ovoalbumin was precipitated in about 100 hours.
The amount of precipitate in weight was the highest in the case of fibrinogen, serum γ-globulin came second, and serum albumin third.
The lipoproteins are labile and the lipid can be separated by suitable solvents. On the other hand, autoxidized fatty acid-protein complexes are not amenable to similar easy separation. The carbonyl group seemed to have a pronounced influence on complex formation.
In order to investigate the action of autoxidized fatty acid ester on amino-acids, experiments were conducted using glycine, glycylglycine and cystine. Cystine, for example, was oxidized into cysteic acid with the -S-S-bond ruptured.
Succinodehydrogenase, ptyalin and potato-amylase were affected to a greater extent by autoxidized ester also.
The polymerized fish oil obtained by heating at 250°C for 10 hours showed remarkable toxicity when rats were fed on basal diet containing 20% of it. This toxicity was found due to cyclic compounds, which was separated by the urea adduct forming method. The rat all died in three of four days, when the cyclic compound was given to them, but did not die at all with straight chain compound.
Ethyl linolenate, which was thermally polymerized at 250°C in a carben dioxide stream for 40 hours, had a toxic effect upon a rat. The origin of the toxicity of thermally polymerized ethyl linolenate was a cyclic monomer, and the main component of this cyclic monomer was a compound having a cyclohexene ring.
An adduct compound of ethyl β-eleostearate and acrolein having cyclohexene ring in its molecule was synthesized. This showed severe toxicity when rats were fed on basal diet containing 10% of it.
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