Differential effects of dietary canola, soybean, and cod liver oils on arachidonic acid content of the rat adrenal glands

Abstract

We investigated the effect of canola, soybean, corn and cod liver oils, and lard fat on arachidonic acid content of the adrenal gland lipids. Adrenal gland lipids from rats fed canola oil, lard fat, and cod liver oil contained much lower levels of linoleic acid (18:2, n-6) (6.8, 3.6, and 2.9%, respectively) compared with those of the corn oil and soybean groups. The arachidonic acid (20:4, n-6) content varied slightly (13.4% to 14.5%) between different dietary groups with the exception of the cod liver oil group. Adrenals from rats receiving cod liver oil contained only 1,650 ng of arachidonic acid (20:4, n-6) compared with those from lard, corn oil, soybean oil, and canola oil groups, which contained 6,000, 9,740, 6,500, and 8,500 ng, respectively. Docosatetraenoic acid (22:4, n-6) and docosapentaenoic acid (22:5, n-6) were found only in adrenals from the corn oil group and amounted to 5.3% of the total fatty acids. On the other hand, soybean- and canola oil-fed groups contained detectable levels of α-linolenic acid (0.5% to 2%) and docosahexaenoic acid (22:6, n-3) (1.4% to 1.9%). Adrenals from the cod liver oil group contained 4.2% 20:5 (n-3), 3.3% 22:5 (n-3), and 6.7% 22:6 (n-3) fatty acids. The greater accumulation of long chain n-3 fatty acids in the cod liver oil group is likely to have resulted from the differences in the acyltransferase-mediated uptake and metabolic conversion and retroconversion of eicosapentaenoic acid (20:5, n-3). The results of this study demonstrate that soybean oil, canola oil, and cod liver oil modulate arachidonic acid as well as its precursor pools in differential manner in adrenal glands, and that these diet-induced changes may be important for the eicosanoid-mediated adrenal functions such as steroidogenesis and the release of adrenocorticotropic hormone and catecholamines.