Effect of menhaden oil and various seedoils on serum lipids and lipoproteins in rabbits

Abstract

Four groups of New Zealand White rabbits (n=8) were fed semi-synthetic diets containing 7.6% fat (w/w) for 20 weeks. The fats were: 1. hydrogenated soybean oil (HSBO), 80% stearic acid, with 2% safflower oil (SO), 2. safflower oil, 78% linoleic acid, 3. linseed oil (LO), 54% linolenic acid, and 4. menhaden oil (MO), 21% palmitic acid, 13% eicosapentaenoic acid (EPA), and 8% docosahexaenoic acid (DHA). The diets contained 20% of calories from protein, 56% from carbohydrate, and 24% from fat. The MO diet also contained 0.06% cholesterol while the other diets were cholesterol free. Before assignment to experimental diets, the animals had serum cholesterol values of 62.1±20.3 mg/dl and triglyceride concentration of 40.3±14.3 mg/dl (mean±S.D.). After 4 weeks on the diets, the cholesterol values in the four groups were: HSBO, 70.9±21.2 mg/dl; SO, 59.1±15.9 mg/dl; LO, 65.1±50.7 mg/dl; and MO, 141.7±67.2 mg/dl. Only the MO value differed significantly from the pre-diet value (P<0.01). For the remainder of the study serum cholesterol value in the MO group did not change significantly while in the HSBO group the cholesterol and triglyceride concentrations rose significantly to 127.8±82.2 mg/dl, and 130.6±60.3 mg/dl, respectively, at the end of the study (P<0.05). The MO group's serum triglycerides trended higher but the change did not reach statistical significance. Low density lipoproteins (LDL) were significantly elevated (P<0.01) in the HSBO and MO groups but not in the SO and LO groups. It remains to be determined if the twenty and twenty-two carbon n-3 fatty acids (EPA and DHA) in menhaden oil will elevate serum cholesterol in rabbits in the absence of dietary cholesterol.