Pure linoleate deficiency in the rat: influence on growth, accumulation

Essential fatty acid deficiency has been widely studied but the extent to which its effects are attributable specifically to deficiency of linoleate as opposed to deficiency of all unsaturated fatty acids is unknown. Our objective was to evaluate the effect of pure linoleate deficiency on growth as well as changes in the metabolism and oxidation of n-6 polyunsaturates. The diets contained 20 energy % fat blended from 3 energy % pure oleate, 2 energy % linoleate (0.01 energy % in the linoleatedeficient group), 0.3 energy % pure a-linolenate, and the balance as palmitate and stearate from fully hydrogenated soybean oil. Thirty-fiveday-old rats consumed the two diets for 84 days, after which the linoleatedeficient rats weighed 15% less than the controls ( P < 0.05), had mild scaling on the paws, and visible hair loss (in a few rats). Compared with the controls, the ratio of eicosatrienoate to arachidonate after 84 days was elevated in liver (170-fold) and serum (520fold) phospholipids of the linoleatedeficient group. In total, linoleatedeficient rats consumed 122 mg of linoleate and had a net whole body loss of 470 mg n-6 polyunsaturates compared with an intake of 24,130 mg and a net whole body gain of 7206 mg n-6 polyunsaturates in the control group. Linoleatedeficient rats oxidized 11 % of an oral bolus of [ 1-14C] linoleate over 8 h compared with 34% in the control rats ( P < 0.05) .I We conclude that pure linoleate deficiency has marked effects on accumulation of n-6 polyunsaturates but induces milder gross symptoms, particularly growth retardation, than classical essential fatty acid deficiency. a-Linolenate and possibly oleate may have a sparing effect on linoleate oxidation from body stores during linoleate deficiency.-Gunm e , S. C., and M. J. Anderson. Pure linoleate deficiency in the rat: influence on growth, accumulation of n-6 polyunsaturates, and [ 1-'4C]linoleate oxidation. J. Lipid Res. 1997. 38: 805-812, Supplementary key words arachidonate essential fatty acid eicw satrienoate Mammals consuming a diet that is either fat-free or that contains dietary fat derived exclusively from saturated fatty acids become deficient in n-6 and n-3 polyunsaturated fatty acids (PUFA) . Depending on the experimental conditions, they exhibit to varying degrees the now classical symptoms of essential fatty acid (EFA) deficiency, including growth retardation, scaliness of the skin, impaired water retention, impaired reproduction, and raised ratio of eicosatrienoate-arachidonate (20: 3n-9/20:4n-6) in tissue lipids. These symptoms are mostly attributable to the dietary absence of linoleate (18:2n-6) and to the subsequent loss of linoleate and arachidonate (20: 4n-6) from membrane lipids (1 -5). Despite numerous studies of EFA deficiency, there do not appear to be any reports in which the experimental diets have been made exclusively deficient in linoleate while providing an adequate amount of a linolenate (18:3n-3) as well as a source of monounsaturates, especially oleate (18: ln-9). Oleate can be synthesized by mammals but it is also a regular component of the mammalian diet. The only diets from which it is absent are those that are EFAdeficient. Hence, it is unclear which symptoms of EFA deficiency are dependent exclusively on the dietary absence of linoleate alone compared with those symptoms elicited or exacerbated by other dietary changes, including the absence of dietary a-linolenate or oleate, effects of added cholesterol, very high saturated fat intake, fasting, etc. (1). In the case of dietary deficiency of n-3 PUFA, it is possible to provide a diet containing a natural oil such as sunflower or safflower oil that has a range of saturated and unsaturated fatty acids but minimal levels of n-3 PUFA. In fact, the presence of high amounts of linoleate in dietary fat sources used to induce deficiency of n-3 PUFA probably helps exacerbate this condition (4, 6, 7). However, in the case of linoleate deficiency, no natural plant oils or animal fats contain a-linolenate and oleate without also containing linoleate. To reduce Abbreviations: EFA, essential fatty acid; LC, long chain; PUFA, poly'To whom correspondence should be addressed. unsaturated fatty acids. Journal of Lipid Research Volume 38, 1997 805 by gest, on A uust 4, 2017 w w w .j.org D ow nladed fom dietary linoleate to a clearly inadequate level (< 0.1 enTABLE 1 . Fdtw acid components and composition of the diets ergy %) while providing adequate a-linolenate as well as a source of oleate and saturates therefore reauires ( ,on trol Imole,itr-Dcf icieiii reconstituting the dietary fat source from a combination of virtually pure saturated fat, oleate, and a-linolenate. An extensive search of the literature has revealed no published research describing studies with such a diet or the effects of pure linoleate deficiency. Hence, surprisingly, the extent to which symptoms of EFA deficiency are attributable specifically to the deficiency of linoleate is apparently unknown. Our main objective was to determine the extent to which linoleate is conserved from oxidation during linoleate deficiency, i.e., to determine how effectively linoleate is conserved during linoleate deficiency. This objective arose from our previous study showing that when linoleate is consumed at the minimum recommended intake level of 2 energy %, 76% is oxidized (8). This led us to design this study to determine whether linoleate is better conserved at a lower, deficient intake. Measurement of [ l-'4C]linoleate oxidation during a 2day linoleate refeeding period at the end of the 84day depletion period was used to determine whether supplemental linoleate may be better conserved by linoleate-deficient rats compared with controls. Linoleate oxidation was assessed by the following two methods: recovery of I4CO2 after oral dosing with [ 1-"C] linoleate (9), and whole body fatty acid balance analysis in which the disappearance or apparent oxidation of linoleate is measured as the difference between linoleate intake and accumulation, conversion to n-6 long-chain (LC) PUFA, or excretion (10). In the apparent absence of previous studies of pure linoleate deficiency, our secondary objective was to describe the effects of pure linoleate deficiency on weight gain and on whole body accumulation of LC fatty acids.