Menhaden Oil Diet Research Articles

Fish Oil and Oxidative Stress by Inflammatory Leukocytes

We investigated the effects of diets with different fatty acid composition upon the oxidative stress of inflammatory leukocytes of rats. After weaning, two groups of rats were fed isoenergetic semipurified diets for five weeks containing 5% of corn oil or menhaden oil. Polymorphonuclear leukocytes from rats fed menhaden oil diet incorporated n-3 polyunsaturated fatty acids into phospholipid membranes at the expense of arachidonic acid. These cells showed diminished superoxide production and, as a consequence, the total antioxidant status in the inflammatory exudate was increased. However, nitric oxide production was not affected by diet. Free malondialdeyde concentration increased in the exudate because of lower mitochondrial activity. These results add new aspects that help clarifying the anti-inflammatory mechanisms of n-3 polyunsaturated fatty acids.

Effects of dietary lipid on the hematology of channel catfish, Ictalurus punctatus

Juvenile channel catfish were fed diets containing either soybean oil, menhaden oil, beef tallow, or a combination of these three lipid sources. After 90 days, total erythrocyte, leucocyte, and thrombocyte counts, hematocrit, mean corpuscular volume, plasma recalcification time, erythrocyte osmotic fragility, total serum iron, and iron-binding capacity were measured. Total erythrocyte counts, leucocyte counts, and mean corpuscular volume were not significantly different ( P < 0.05) among dietary groups. However, fish fed the menhaden oil diet had significantly lower ( P < 0.05) hematocrits, higher thrombocyte counts, and higher serum iron concentrations. They also had the highest concentration of n − 3 fatty acids in the pronephros tissue and their erythrocytes were the least susceptible to osmotic lysis. Catfish fed the beef tallow diet had the lowest level of n − 3 fatty acids in pronephros tissue and their erythrocytes were the most susceptible to osmotic lysis. Results suggest that dietary lipids affect several hematological factors of cultured channel catfish.

Dietary Polyunsaturated Fatty Acids Modulate Responses of Pigs to Mycoplasma hyopneumoniae Infection

Polyunsaturated fatty acids (PUFA) are immunomodulators, but few studies have examined how these dietary components influence infectious respiratory disease. Groups of nine pigs were fed casein and corn starch-based diets containing 10.5 g/100 g corn oil (CO), linseed oil (LO), menhaden oil (MO), linseed + corn oil (LC, 1:1) and menhaden + corn oil (MC, 1:1). As a methodological control, one group of pigs (n = 15) was fed a commercial ration (control diet; C). Pigs inoculated intratracheally with Mycoplasma hyopneumoniae after 4 wk of consuming the diets were killed 3 wk later. Gross lung lesions in MO-fed pigs were less (P < 0.05) than those in LC- and MC-fed pigs. Pigs fed MO had less peribronchial inflammation (P < 0.05) than all other groups. Gross lung lesions correlated negatively with basal in vitro alveolar macrophage tumor necrosis factor (TNF) production in pigs fed diets that contained negligible levels of (n-3) PUFA (C and CO). Basal macrophage TNF production did not correlate with lung lesion scores for diets containing more (n-3) PUFA than C or CO (LO, MO, LC and MC). For pigs fed the LO, MO, LC and MC diets, mean gross lung lesions increased as the mean ratio of (n-3):(n-6) PUFA in alveolar macrophage lipids decreased. Serum levels of α1 acid glycoprotein (AGP) were less (P < 0.05) in pigs fed MO, and there was a rise in mean lung lesions scores for each PUFA-fed group as mean AGP levels increased. These results indicate that dietary PUFA can affect disease pathogenesis and that the (n-3):(n-6) PUFA ratio may modulate the host response.

Effects of diet on responses to exhaustive exercise in Nile tilapia ( Oreochromis nilotica) acclimated to three different temperatures

The effects of exhaustive exercise on O 2 consumption (Ṁ O 2 ), waste nitrogen (ammonia and urea) excretion, and on lactate, ammonia and water content of white muscle and liver, were determined in tilapia fed a diet enriched either in long chain polyunsaturated fatty acids of the ω3 series (ω3 LCPUFA) as menhaden oil (menhaden oil diet; MOD) or in saturated fatty acids (SFA) as coconut oil (coconut oil diet; COD), and acclimated to three different temperatures (16°, 23° and 33°C). At all temperatures, exhaustive exercise elicited an increase in postexercise Ṁ O 2 and ammonia excretion rates, and in white muscle lactate and ammonia levels. There were no differences between the two dietary groups in the total amount of O 2 consumed and muscle lactate accumulated, but at 23°C and 33°C exhaustive exercise stimulated a significantly greater increase in ammonia excretion in COD as compared with MOD tilapia. The magnitude of the difference in postexercise ammonia excretion between COD and MOD animals increased with increases in environmental temperature, being greater at 33°C than at 23°C. The increased ammonia excretion observed in the COD group was not a result of differences in white muscle ammonia or water content following exhaustive exercise. The data indicate that diets enriched in ω3 LCPUFA are beneficial in that tilapia fed these diets exhibited reduced ammonia excretion following exhaustive exercise, compared with tilapia fed diets enriched in SFA.

Dietary menhaden oil enhances mitomycin C antitumor activity toward human mammary carcinoma MX-1.

In the present study, we investigated the effects of high levels of dietary fish oil on the growth of MX-1 human mammary carcinoma and its response to mitomycin C (MC) treatment in athymic mice. We found that high levels of dietary fish oil (20% menhaden oil + 5% corn oil, w/w) compared to a control diet (5% corn oil, w/w) not only lowered the tumor growth rate, but also increased the tumor response to MC treatment. We also found that high levels of dietary fish oil significantly increased the activities of tumor xanthine oxidase and DT-diaphorase, which are proposed to be involved in the bioreductive activation of MC. Since menhaden oil is highly unsaturated, its intake caused a significant increase in the degree of fatty acid unsaturation in tumor membrane phospholipids. This alteration in tumor membrane phospholipids made the tumor more susceptible to oxidative stress, as indicated by the increased levels of both endogenous lipid peroxidation and protein oxidation after feeding the host animals the menhaden oil diet. In addition, the tumor antioxidant enzyme activities, catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPOx), and glutathione S-transferase peroxidase (GSTPx), were all significantly enhanced by feeding a diet high in fish oil. MC treatment caused further increases in tumor lipid peroxidation and protein oxidation, as well as in the activities of CAT, SOD, GPOx, and GSTPx, suggesting that MC causes oxidative stress in this tumor model which is exacerbated by feeding a diet high in menhaden oil. Thus, feeding a diet rich in menhaden oil decreased the growth of human mammary carcinoma MX-1, increased its responsiveness to MC, and increased its susceptibility to endogenous and MC-induced oxidative stress, and increased the tumor activities of two enzymes proposed to be involved in the bioactivation of MC, that is, DT-diaphorase and xanthine oxidase. These findings support a role of these two enzymes in the bioactivating of MC and indicate that the type of dietary fat may be important in tumor response to therapy.

Influence of Fish Oils in Production Catfish Feeds on Selected Disease Resistance Factors

Healthy channel calfish, Ictalurus punctatus (mean weight: 62.5g), were fed two production feeds that were identical except for the lipid portion, which was either catfish oil or menhaden oil. Fish were held at 18 or 28°C and fed the experimental feeds for four monlhs. A subsample of fish from each of the four treatments was then used to measure scrum antibody titers to Edwardsiella ictaluri, macrophage phagocytic index, phagocytic capacity, and production of intracellular and extracellular superoxide anion. The remaining fish were vaccinated with an E. icraluri bacterin, held for 18-24 days, and the assays were repeated. Fatty acid profiles of the diets indicated catfish oil had a higher percentage of monounsaturated fatty acids and slightly higher n-6 fatty acids. The menhaden oil diet had a higher percentage of the n-3 fatty acids. At 28°C, weight gain and feed conversion were slightly higher in calfish fed the feed containing menhaden oil. Weight gains and feed conversion were similar in fish maintain...

INFLUENCE OF DIETARY MENHADEN FISH OIL ON FATTY ACID COMPOSITION OF THE EGG

ABSTRACTThe influence of menhaden fish oil and other oils on the fatty acid composition of the egg was studied. Diets containing 1.5% menhaden oil, 1.5% corn oil and no oil added were fed to 50 hens. The menhaden oil diet increased the composition of C14:0, C16:1, C18:1, C18:3w3, C20:5w3 and C22:6w3 in the eggs but decreased C18:2w6 and C20:4w6 compared with the corn oil diet. The concentration of C20:5w3 was greater than C22:6w3 in menhaden oil, but more C22:6w3 was found in eggs than C22:6w3. A significant increase in total w‐3 PUFAs (polyunsaturated fatty acids) occurred in the eggs after feeding the menhaden oil diet for 5 days and the concentration continued to increase through day 15. Dietary fats tend to produce a fatty acid pattern in eggs similar to that of the diet and varies with the oil source concentration. Most fatty acid profiles in egg yolks were altered within 15 days after hens began to consume test diets.

Dietary Menhaden Oil Influences Sensory Characteristics and Headspace Volatiles of Shell Eggs

ABSTRACTEggs from hens fed n‐3 fatty acids (n‐3FA) may provide a means for increased marketing of these healthful fatty acids. Eggs from hens fed graded levels (0, 0.5, 1.5, 3.0%) of menhaden oil (MO) were evaluated for fatty acid composition, sensory characteristics, and headspace volatiles. Eggs from hens fed 1.5% and 3.0% MO contained the greatest n‐3 FA content and were not different. A linear increase in fishy notes occurred as level of dietary MO increased from 0 to 1.5%; however, these notes were not different between 1.5% and 3.0% eggs. Changes in headspace volatile profiles were quantitative. No unique volatiles characterized eggs from hens fed MO; however, concentration differences were noted between eggs from hens fed all levels of dietary MO. Changes in volatile profiles in response to dietary MO may be responsible for perception of fishy notes in such eggs.

Dietary menhaden oil reduced resistance of channel catfish ( Ictalurus punctatus) to Edwardsiella ictaluri

Fingerling channel catfish were fed practical-type diets supplemented with 2% catfish offal oil, beef tallow, or menhaden oil for 8 or 10 weeks at 24±1°C under laboratory conditions in two separate experiments. At the end of the feeding period, fish were exposed to live Edwardsiella ictaluri by immersion and mortalities were recorded daily for 3 weeks. Growth, feed efficiency, and survival rate of channel catfish at the end of the feeding period were not significantly different among dietary treatments in either experiment. Fish fed a diet supplemented with menhaden oil had significantly higher levels of 20:5 n−3, 22:6 n−3, and total n−3 HUFA (highly unsaturated fatty acids), and lower levels of 20:4 n−6 and total n−6 HUFA in liver polar lipids than fish fed the other two diets. Average mortality of fish exposed to E. ictaluri was 21 and 15% higher for fish fed supplemental menhaden oil than for fish fed supplemental catfish offal oil in Experiments 1 and 2, respectively. Antibody titers were not different among fish regardless of diet, 3 weeks after exposure to E. ictaluri. The results of this study indicate that channel catfish fed practical diets containing 2% menhaden oil are more susceptible to E. ictaluri. These results do not preclude the use of menhaden fish oil in catfish diets, but it may be prudent to use a mixture of menhaden oil and other animal and/or plant lipids in commercial catfish feeds to provide a balance in the dietary n−3 n−6 ratio.

Effects of continuous tube feeding of dietary fat emulsions on eicosanoid production and on fatty acid composition during an acute septic shock in rats

The effects of a short-term (5 days) continuous intragastric tube feeding of diets containing n − 6 polyunsaturated fatty acids (PUFA) from safflower oil (SO) or n − 3 PUFA from menhaden oil (MO) on the production of proinflammatory mediators, and on the number of animals surviving after an intravenous injection of lipopolysaccharide (LPS) were investigated in rats. The phospholipid fatty acid composition of cell membranes from several organs and of plasma were also analyzed. No marked differences in the number of animals surviving or in the production of tumor necrosis factor-α were observed between the 2 groups of animals. However, 90 min after LPS exposure the plasma levels of prostaglandin (PG) E 2 and 6-keto-PGF 1α decreased significantly (40% and 60%, respectively) for the group of rats fed MO diet compared to those fed SO diet ( P < 0.05). Following continuous infusion of liquid MO diet, the amount of arachidonic acid (AA) detected was significantly lower in plasma (23%), spleen (43%), lungs (41%), and liver (38%), but was unchanged in the heart tissues. The percent of eicosapentaenoic acid (EPA) incorporated into phospholipids of plasma, spleen, lungs, liver, and heart were 7.6, 4.4, 2.1, 7.2, and 1.1%, respectively. These data indicate that after continuous MO feeding, a significant decrease in the production of proinflammatory eicosanoids was associated with a marked reduction in AA content. Further, these data suggest that nutritional intervention may have a therapeutic potential to ameliorate clinical symptoms due to excessive productions of eicosanoids during acute septic complications.

Effect of Dietary Lipid Sources on Production of Leukotriene B by Head Kidney of Channel Catfish Held at Different Water Temperatures

Abstract Separate and combined effects of dietary fatty acids and water temperature on the production of leukotriene B (LTB) by the head kidney of channel catfish Ictalurus punctatus were investigated. Fish were fed semipurified diets containing 7% lipid as beef tallow, corn oil, linseed oil, menhaden oil, or a mixture (1:1:1) of menhaden oil, beef tallow, and corn oil. At 28°C, fish fed corn oil produced the greatest amount of LTB, and fish fed beef tallow produced the least. At 17°C, production of LTB by fish fed the beef tallow diet was again lowest; production of LTB by fish fed the corn oil diet was highest but was not significantly different from that obtained with the mixed-oil or menhaden oil diet. Production of LTB for the other diets was intermediate. This is the first report that the head kidney of channel catfish produces LTB; this production was affected by dietary lipid sources but not by the two water temperatures tested. Production of LTB was not related to weight gain. Moreover, the patte...

Aged lymphocyte proliferation following incorporation and retention of dietary omega-3 fatty acids

T cell activation involves events at the plasma membrane; therefore, molecules such as long chain omega-3 fatty acids that alter the structure of the plasma membrane may affect the activation of aged T cells. In this project we investigated whether the incorporation of omega-3 fatty acids (from fish oil), in the presence of vitamin E, improves age-diminished T cell proliferation. Young and old mice were fed diets rich in either fish (menhaden) oil or saturated fat for various lengths of time. Splenocytes were harvested from these mice and stimulated in culture with either mitogen or the antigen keyhole limpet hemocyanin (for a secondary response); proliferation was estimated by [ 3H]thymidine incorporation. We found no discernible effect of dietary omega-3 fatty acids (with vitamin E supplementation) on lymphocyte proliferation stimulated by the mitogens concanavalin A or phytohemagglutinin. We did, however, find that the saturated fat diet and the menhaden oil diet in young mice lowered protein kinase C activities in the particulate fractions of spleen cells when compared to chow-fed mice. Middle-aged and old mice were less affected by the experimental diets than young mice, but they demonstrated decreased protein kinase C activity as well. These alterations did not affect the ability of splenocytes to respond to mitogenic stimulation. Fatty acid analysis revealed that lymphocytes from mice fed saturated fat for 8.5 months retained significant amounts of the omega-3 fatty acid docosahexaenoic acid, despite the lack of dietary omega-3 fatty acids. However, when aged (but not young) lymphocytes were clonally expanded by antigen in vivo in the presence of dietary omega-3 fatty acids, they produced a greater secondary proliferative response than old lymphocytes expanded during a saturated fat diet. Although our results suggest that omega-3 fatty acids may enhance aged lymphocyte proliferation, the tenacious retention of these fatty acids makes comparison with omega-3-depleted lymphocytes difficult.

Oxidative Stability and Sensory Quality of Stored Eggs From Hens Fed 1.5% Menhaden Oil

ABSTRACTEffects of refrigerated storage on thiobarbituric acid (TBA) values and sensory scores of shell eggs from hens fed 1.5% menhaden oil (MO) and a no‐added fat control diet were investigated. Eggs were collected weekly (0, 1, 2, 3, 4) for each of three replicates/diet and all weeks were analyzed within 24 hr of 0 week. The flavor of scrambled samples from stored shell eggs (wk 0, 2, 4) was determined by scoring difference scale administered to two consumer panels (n = 40/panel). Flavor scores for eggs from all treatments were not different. TBA values were greater (P &lt; 0.05) in MO eggs at week 0 but did not increase during storage. Storage stability of shell eggs from hens fed 1.5% dietary menhaden oil is comparable to that from hens fed a no‐added fat diet.

Dietary Menhaden Oil Contributes to Hepatic Lipidosis in Laying Hens

Clinical and epidemiological investigations have indicated that there may be substantial human cardiovascular benefits associated with increased consumption of n-3 fatty acids commonly found in fish oils. Recent studies have indicated that egg yolk n-3 fatty acid content is significantly increased when hens are fed diets enriched with selected fish oils such as menhaden oil (MO). In the present study, reproductively active females but not males exhibited increased hepatic lipidosis following 6 mo of feeding 3% MO. Hens fed 3% animal-vegetable oil (AV) did not exhibit hepatic lipid accumulation. Serum triglyceride and cholesterol concentrations were reduced (P ≤ .05) in hens fed MO. Subsequently, yolk and total egg weights of hens fed MO were decreased as compared with those of hens fed AV. A significant interaction of dietary MO and exogenous 17β-estradiol was noted among chick liver and gallbladder weights. These data suggest that dietary MO and estradiol may interact in a manner that enhances the lipogenic activity of the liver, thereby inducing hepatic lipidosis in laying hens.

Effects of dietary fish oil on fatty acids and eicosanoids in metastasizing human breast cancer cells.

We examined the relationships between the suppressive effects of dietary fish oil on growth and metastasis of MDA-MB-435 human breast cancer cells in female nude mice and the primary tumor phospholipid fatty acid concentrations, phospholipase A2 activity, and eicosanoid levels. Mice (n = 120) were fed a 23% (wt/wt) corn oil (CO) linoleic acid (LA)-rich diet for seven days before and after 10(6) tumor cells were injected into a mammary fat pad, and then the mice receive one of three isocaloric diets containing 23% total fat but different proportions of CO and menhaden oil (MO) (18% CO-5% MO, 11.5% CO-11.5% MO, 5% CO-18% MO) or a 23% fat diet containing 18% deodorized fish oil supplemented with tocopherol and tert-butylhydroquinone antioxidants (FAO). Primary tumor growth rate was significantly greater in mice fed the 18% CO diet than in the three diets containing higher levels of fish oil (all p < 0.05). The 18% MO diet, but not the 11.5% MO or the 18% FAO diet, suppressed the development of lung metastases compared with the 18% CO diet. Increasing the proportion of MO relative to CO in the diets produced corresponding increases in the primary tumor phospholipid eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) concentrations and reductions in LA and arachidonic acid. There was a significant positive correlation between the LA concentration in these tumors and the extent of lung metastasis (r = 0.504). Tumor phospholipase A2 activity was unaffected by dietary MO intake. Prostaglandin E2 concentration was inversely correlated with phospholipid EPA (r = -0.484) and DHA (r = -0.439), but there was no relationship with lung metastasis. Tumor leukotriene B4 and 5-hydroxyeicosatetraenoic acid levels were not reduced by dietary MO. The 18% FAO- and the 18% MO-fed mice showed similar relationships for the phospholipid fatty acids and prostaglandin E2, despite the lack of effect on metastasis. The strong correlation between phospholipid LA levels and metastasis and the lack of an association with tumor eicosanoids suggest that the 18% MO diet inhibited metastasis because dietary LA was replaced by other fatty acids.

Effects of dietary menhaden oil on mucosal adaptation after small bowel resection in rats

Adaptive hyperplasia of the small intestine is important in the outcome of short bowel syndrome. Previous studies have shown that long-chain fats stimulate this process. In the present study, the trophic effects of dietary menhaden oil, a highly unsaturated fat source, on mucosal adaptation following small bowel resection in rats was evaluated. Thirty weanling Sprague-Dawley rats and their controls were fed diets containing fats provided primarily as menhaden oil, safflower oil, or beef tallow. After 4 weeks, animals underwent a 70% jejunoileal resection. Mucosal mass, DNA, protein, and sucrase levels were assessed 14 days after a 70% jejunoileal resection or control feeding. Serum fatty acid composition and several gastrointestinal hormone levels were measured. Resected animals fed menhaden oil showed a marked increase in mucosal weight, DNA, and protein levels compared with rats fed the other fat sources. Enteroglucagon level was increased in all resected groups, but least increased in the menhaden-fed animals. In contrast, peptide YY concentrations were most increased in animals fed menhaden oil. Menhaden oil appears more effective in inducing intestinal adaptation than less highly unsaturated fats. Analysis of gastrointestinal hormones revealed no clear-cut explanation for this finding, other than a modest but associated increase in peptide YY levels.

Differential response of glucose utilization by three rat muscle tissues to dietary fatty acid composition.

Rats were fed a semisynthetic diet containing 14% of either beef fat, safflower oil, or menhaden oil plus 2% corn oil for 7 weeks, and three tissues, diaphragm, heart, and skeletal muscle, were examined for fatty acid composition in their phospholipids and triglycerides. In addition, the lipid concentrations in these tissues were examined. The in vitro oxidation and incorporation of glucose into lipids of these tissues were also examined. Skeletal muscle showed the greatest change in phospholipid composition with diet. All tissues were responsive to changes in diet in regards to the triglyceride fraction. Dietary alteration of tissue phospholipid composition did not alter lipid concentration in these tissues. However, in diaphragm tissue, rats fed the beef fat diet had lower phospholipid and higher triglyceride synthesis compared with those fed either menhaden oil or safflower oil. In addition, triglyceride synthesis was higher in the diaphragm of animals fed the menhaden oil diet as compared with the safflower oil diet. Therefore, dietary fatty acid composition may play a role in the triglyceride and phospholipid metabolism of rat diaphragm.

Effect of dietary menhaden oil on growth and muscle fatty acid composition of hybrid striped bass, Morone chrysops × M. saxatilis

Hybrid striped bass were fed four diets in triplicate containing 0, 4, 8 and 12% menhaden fish oil (MFO) for 18 weeks to determine uptake of n−3 fatty acids and its effect on body composition and fish health during growth to market size. Fish (X = 624 ± 26 g) were stocked in 12 circular flow-through tanks (2000 liters) with 9 ppt salinity and temperature at 22°C. Fish fed the 4 and 8% MFO diets had significantly better growth compared to fish fed the 0 or 12% MFO diets. Survival ranged from 89 to 96% and did not appear to be diet-related. Fatty acid profiles in muscle tissue reflected the diet concentrations with significant increases ( P ≤ 0.05) in eicosapentaenoic acid (EPA) in fish fed the 8 and 12% MFO diets. Other fatty acids demonstrating significant ( P ≤ 0.05) muscle concentration increases of 1% or greater in fish fed the MFO diets were: 14:0,16:1 n−7, 22:6 n−3, as well as total polyunsaturates, total n−3 fatty acids, and the n-3 n-6 ratio. Fatty acids showing significant decreases ( P ≤ 0.05) of 1% or greater were 16:0, total saturates and monounsaturates. Fish fed the 0% MFO diet had a decline in both EPA (6.1 to 5.4%) and docosahexaenoic acid (DHA) (12.5 to 8.6%). Thus, a dietary source of n−3 fatty acids is important in maintaining EPA and DHA levels during intensive culture. Fish fed the 8 and 12% MFO diets had twice as much n−3 fatty acids (1.0 g/100 g tissue) as those without MFO (0.5 g/100 g tissue). There were no significant ( P ≤ 0.05) differences in muscle composition except lipid content which increased from 3.2% in the 0% MFO, to 3.5%, 3.9% and 4.4% in the 4, 8 and 12% MFO treatments, respectively. No significant changes were observed in serum triglyceride concentration, hepato-somatic index, and hepatic structure.

Effect of varying proportions of dietary menhaden and corn oil on experimental rat mammary tumor promotion.

Dose-related effects of long-chain highly unsaturated n-3 fatty acids on the development of N-nitrosomethylurea (NMU)-induced rat mammary tumors were assessed in female F344 rats. Four test groups (36 rats/group) were fed the following high-fat (HF) diets (23% fat, w/w): Group 1, 18% menhaden oil (MO) and 5% corn oil (CO); Group 2, 11% MO and 11.8% CO; Group 3, 5% MO and 18% CO; Group 4, CO alone. A fifth group, serving as an internal control, was fed a low-fat diet containing 5% CO alone. Experimental diets were begun after initiation with NMU, and the experiment was terminated 31 wk later. Total tumor numbers in the five groups were 28, 16, 32, 26 and 11, respectively, indicating that the promotion phase of NMU-induced carcinogenesis was significantly suppressed only when equal parts of CO and MO (Group 2) were fed or when CO alone was fed at 5% (w/w). At high (Group 1) or low (Group 3) levels of MO, tumor numbers were indistinguishable from the HF CO group (Group 4). The same pattern was observed when assessed in terms of cumulative tumor incidence and multiplicity. However, when expressed in terms of final tumor incidence, dietary MO did not suppress tumor promotion in a statistically significant fashion at any concentration. Animals fed MO gained weight at the same rate as those fed CO, indicating that the presence of MO in the diet did not result in food avoidance behavior. Measurement of total serum cholesterol indicated an inverse trend with respect to the MO content of the diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Dependence of the plasma triacylglycerol-lowering effect of fish oil on insulin replacement in streptozotocin diabetic rats

Streptozotocin diabetic rats, with and without insulin replacement, and sham-injected controls were fed a high-fat (30% of energy) menhaden oil (MO) or corn oil (CO) diet for 2 weeks. After an overnight fast, plasma and livers were collected for analysis of insulin, glucose, triacylglycerol, cholesterol and glucose-6-phosphate dehydrogenase activity. Streptozotocin treatment resulted in decreased plasma insulin and elevated glucose. MO-feeding to insulin-replaced diabetic rats resulted in higher insulin and lower glucose levels compared to the respective CO-fed rats, suggesting decreased hepatic insulin extraction and greater peripheral utilization of glucose with MO. Plasma triacylglycerol and cholesterol, and hepatic glucose-6-phosphate dehydrogenase activity were reduced in MO-fed vs. CO-fed control rats. These effects of MO were prevented in the diabetic rats but were restored by insulin replacement. We conclude from our data that the presence of insulin is required to observe at least some of the effects of fish oil (FO). To explain our observations we propose that many of the effects of FO on hepatic metabolism are mediated by an inhibition of insulin action in the liver, thus providing a possible central mechanism for the regulation of hepatic lipid metabolism by dietary FO.