The influence of low dietary doses (0.1 and 0.8% w/w) Oi a commercial
fish oil preparation on peroxisomes in normal mice was studied and com
pared to the known strong inductive effects of high (10%) fish oil die
ts. Low fish oil doses were chosen to supply the mice with a concentra
tion of docosahexaenoic acid, which was beneficial to patients with a
peroxisomal disease. Peroxisomes were evaluated by cytochemical, morph
ometric, and enzymological techniques. The 0.1% fish oil diet had no e
ffect on peroxisomes in liver, heart, and kidney even after prolonged
treatment. The 0.8% diet did not change the peroxisomal number nor the
catalase (EC 1.11.1.6) activity in the liver. Hepatic peroxisomal bet
a-oxidation, however, was increased by 50% after 14 d. This was accomp
anied by reduced peroxisomal size. The 0.8% diet also caused a small i
ncrease (+25%) in myocardial catalase activity. No effect was observed
in kidneys. Our results indicate that in mice a low (<0.8%) dietary f
ish oil dose has no or only a slight effect on hepatic per oxisomal be
ta-oxidation. This may be of particular interest to patients with a pe
roxisomal fatty acid beta-oxidation defect and who display a severe de
ficiency of docosahexaenoic acid-diets supplemented with low fish oil
doses will improve the docosahexaenoic acid level without adding a str
ong load to the disturbed fatty acid metabolism.