Comparative studies on the effects of semipurified and commercial diet on longevity and spontaneous and induced lesions in the Syrian golden hamster

Syrian golden hamsters were fed a semipurified or commercial diet from weaning throughout life. Bis(2‐oxopropyl)nitrosamine (BOP) was administered at 8 weeks of age (10 mg/kg body wt, sc). Longevity was improved by 26% and 36% increases in the mean life‐spans of male and female hamsters, respectively, fed the semipurified diets. Carcinogen treatment did not alter survival. The age‐adjusted occurrence rates of pancreatic ductular proliferation, carcinomas, adenomas, and common duct polyps were higher in hamsters fed commercial diet; this indicates an earlier onset of these BOP‐induced lesions in hamsters fed this diet. However, their overall incidences were generally similar when the two diet groups were compared. Acinar cell nodules were observed only in hamsters fed semipurified diets and were elevated in BOP‐treated females. The onset of pancreatic ductular proliferation and adenomas, bile duct proliferation, parathyroid hyperplasia, and common duct papillary hyperplasia was earlier in females than in male hamsters, especially in groups fed commercial ration. Generalized vascular calcification was observed at an elevated rate and reached a higher overall incidence in hamsters fed commercial ration. The age‐adjusted rate of amyloidosis was high in female hamsters and elevated in groups that consumed the commercial ration. In addition, colitis and islet cell hyperplasia occurred more often and earlier in hamsters fed commercial ration, but gallbladder stones occurred most in animals fed semipurified diet. This paper discusses the possible association between these and other observed lesions and survival.     

Enhancement of BOP-induced pancreatic carcinogenesis in selenium-fed Syrian golden hamsters under specific dietary conditions

We measured the effects of dietary selenium (Se) on pancreatic cancer induced in Syrian golden hamsters by N-nitrosobis(2-oxopropyl)amine (BOP). The animals were fed six experimental diets that contained different combinations of the following: 0.1, 2.5, or 5.0 ppm Se from sodium selenite or 2.5 ppm Se from D,L-selenomethionine in either a low (6.0%)- or high (24.4%)-fat diet. Se treatment was begun four weeks before BOP treatment, and the high-fat diet was fed from one week after the last BOP treatment. No evidence for inhibition of pancreatic cancer by Se was observed; in fact, with some experimental conditions, high-Se diets increased the pancreatic carcinoma yield. However, the dietary conditions needed for enhancement differed between the sexes. The male hamsters that received the high-fat diet containing 2.5 ppm Se had more carcinomas than did males given the 0.1 ppm Se level. Carcinoma yields in females did not differ between these diets. Females that received 2.5 ppm Se from D,L-selenomethionine had a greater pancreatic carcinoma yield that did those given 0.1 ppm Se diet. However, carcinoma yields did not differ in males fed these diets. Acinar cell nodule yields were generally reduced in hamsters given the high-Se diets, especially when Se levels in the high-fat diets were compared. Prefeeding 0.1 or 2.5 ppm Se did not influence the elution constants of pancreatic DNA from ductal cells, indicating no effect of Se on the repair of BOP-induced, single-strand breaks in DNA from these cells. Measurements in acinar cells suggested a more rapid repair of single-strand breaks in hamsters prefed 2.5 ppm Se than in those prefed 0.1 ppm Se.     

Effects of dietary fat on virus-induced pancreatic carcinogenesis in guinea fowl

The present study was performed to assess the effects of diets supplemented with low (5%) and high (20%) corn oil on a Pts 56 retrovirus-induced model of pancreatic carcinogenesis in guinea fowl. The early microscopic lesions appear after 3 mo after virus treatment and progress over time. Eight to 10 mo after initiation, up to 100% of virus-inoculated birds develop multiple hyperplastic and neoplastic pancreatic lesions of duct/ductular phenotype. Short-term (1-4 mo) feeding of low- or high-fat diets, beginning at Month 3, had no significant effects on body and pancreatic weight. However, the incidence, multiplicity, and areas of the pancreatic tissue occupied by intra- and interlobular aggregates of hyperplastic ducts with mucinous metaplasia of the lining cells were significantly increased compared with the birds fed the common diet. At the same time, development of ductular neoplasms, particularly carcinomas, was retarded compared with the common diet-fed controls. Long-term (5-7 mo) fat intake resulted in an increase in body weight gain, while absolute pancreatic weights remained relatively constant. Furthermore, the high- and low-fat diets caused a significant increase in areas of retrovirus-induced pancreatic lesions, as well as an increase in multiplicity of ductular neoplasms compared with short-term fat feeding. It is concluded that short-term feeding of diets supplemented with 5% or 20% corn oil delayed the development of the common virus-induced ductular neoplasms, particularly carcinomas, and had an enhancing effect on development of hyperplastic inter- and intralobular aggregates of ducts. This finding was not observed, however, during the long-term feeding period of the study.     

Body weights of C3H/HeN mice fed semipurified or commercial diets of different fat content

Oncology studies often require specially formulated diets to be fed to laboratory animals. To determine the effect of dietary fat on body weight, C3H/HeN mice were carefully assigned by weight into three groups. The first group was fed a high-fat semipurified diet (23% fat by weight) from 21 to 73 days of age then returned to a low-fat semipurified diet (5% fat by weight). A second group was fed the low-fat diet from 21 to 73 days of age, then the high-fat diet until 129 days of age, then returned to the low-fat diet. A final group was fed a 4.5% fat commercial diet for the entire 193-day study. The results showed that the mice fed the semipurified diets did not differ significantly from each other in weight over the course of the study but did differ significantly between 21 and 73 days of age, possibly from a taste preference for the high-fat diet. Mice fed the commercial diet always weighed significantly less. It was estimated that mice fed the commercial diet consumed more food and were less efficient in their food utilization. Mice should be carefully assigned, by weight, into experimental groups, and all groups, including untreated controls, should be fed the same type of diet.     

Effect of soy products on methotrexate toxicity in rats.

Several experiments were conducted to determine the effect of various soy products on methotrexate (MTX) toxicity. Products tested included soybean meal, soybean concentrate, soybean isolate and soybean fiber, which were provided as replacements for casein or cornstarch in a semipurified diet. Soybean meal and soybean concentrate offered the greatest protection, completely alleviating MTX-induced anorexia and diarrhea when included as the sole protein source and fed 14 d prior to and 7 d following intraperitoneal MTX injection at 20 mg/kg body weight. Positive responses also were observed with soybean isolate and soybean fiber. Histological examination of the small intestine of MTX-injected animals revealed that soybean concentrate and soybean isolate prevented the necrosis observed in animals fed the casein-based semipurified diet. Methotrexate levels in plasma were similar for animals fed semipurified diets in which protein was supplied by casein, soybean concentrate or soybean isolate. Thus, altered plasma MTX levels did not explain the differences among protein sources in ameliorating MTX-induced anorexia and gut toxicity. White blood cell counts were depressed by MTX in animals fed all diets.     

Increased susceptibility to lead toxicity in rats fed semipurified diets

Rats fed stock diets, like Purina Chow, are known to be relatively insensitive to the toxic effects of lead. The addition of lead acetate (1000 ppm of Pb) to the drinking water of 5-week-old rats for 35 days produced toxicity (decreased growth rate and lead-induced anemia) in rats fed semipurified diet, but not in rats fed Purina Rat Chow (Chow). Blood and tissue lead levels also were higher in rats fed semipurified diet than in rats fed Chow. In order to determine whether rats fed semipurified diet could be used as animal models in the determination of permissible levels of lead in the environment, the susceptibility to lead toxicity of these rats to lead-based paints was tested. The addition of 1% paint chips containing 10% lead octoate to the diets resulted in lead toxicity (reduction in growth rates and hematocrit values) only in rats fed the semipurified diet. Rats fed a semipurified diet that permits normal growth are more susceptible to the toxic effects of lead and can be used more effectively in lead toxicity studies than rats fed Chow.     

Hepatic transmethylation and blood alcohol levels

Golden Syrian hamsters that have elevated hepatic alcohol dehydrogenase activity were divided into four groups and group-fed on four different liquid diets for five weeks. Group I was fed a control diet formulated for hamsters. Group II was fed the control diet containing 20 micrograms of 4 methylpyrazole per litre. Group III was fed the hamster ethanol liquid diet (ethanol amounting to 36% of total calories). Group IV was fed the ethanol diet to which 4-methylpyrazole (20 micrograms/litre) was added. Groups I, II and III were group-fed the amount consumed by Group IV on a daily basis. Upon killing the animals, blood alcohol levels were found to be elevated in Group IV but not in Group III. Hepatic methionine synthetase (MS) was inhibited in Group IV. Betaine-homocysteine methyltransferase was induced in this group to compensate for the MS inhibition and liver betaine was lowered reflecting this induction. None of these changes were seen in Group III. Since none of the animals showed an aversion to their respective diets and gained weight normally, these data indicate that it was the elevated blood levels of ethanol rather than nutritional factors that were related to the changes in methionine metabolism.     

Dietary soy and soy isoflavones have gender-specific effects on plasma lipids and isoflavones in golden Syrian f(1)b hybrid hamsters

The specific components of soy responsible for its beneficial effects on plasma lipids are unknown. Golden Syrian F(1)B Hybrid hamsters (75 male, 74 female) were evaluated for the effect of dietary soy and soy isoflavones on plasma lipids. They were fed the following diets for 16 wk: casein/lactalbumin (C/L), soy protein with isoflavones [Soy(+)], soy protein with isoflavones removed [Soy(-)], Soy(-) plus isoflavone extract (IF), and C/L + IF. At necropsy, plasma total cholesterol, HDL cholesterol (HDLC), LDL + VLDL cholesterol (LDL + VLDLC), isoflavones, and uterine and accessory gland weights were measured. Male hamsters fed the three soy-containing diets had lower LDL + VLDLC concentrations than those fed the two C/L diets (P < 0.01), and those fed Soy(-) + IF did not differ from those fed Soy(+). In females, diet did not affect plasma LDL + VLDLC concentration. Females fed Soy(+) or Soy(-) had higher HDLC (P < 0.05) than those fed C/L. HDLC was not affected by diet in males. Due to higher equol production (P < 0.01), males had greater plasma isoflavone concentrations (P < 0.01) than females. There was a positive association between plasma total isoflavones and LDL + VLDLC (r = 0.65, P < 0.05) in females. These data suggest gender differences in plasma lipid and isoflavone responses to soy- based diets in Syrian F(1)B Hybrid hamsters, which offer an opportunity to explore effects of sex hormones on isoflavone metabolism and the effects of isoflavones on lipid metabolism.     

The effect of the level of dietary corn oil on mouse skin carcinogenesis

To investigate the effects of two levels of dietary corn oil on tumorigenesis, semipurified diets containing 5% or 10% corn oil were fed during the promotion stage of a mouse skin carcinogenesis model. Sencar mice were initiated with 10 nmol dimethylbenz[a]anthracene (DMBA) and promoted with either 1 microgram 12-O-tetradecanoylphorbol-13-acetate (TPA) or 40 mg benzoyl peroxide twice weekly for 24 or 52 weeks, respectively. No significant differences in kilocalories of food consumed or body weights were observed between the diet groups during the study. Fatty acid profiles of the epidermal phospholipids reflected dietary fat intake. For example, high levels of linoleate and low levels of arachidonate were found in the phosphatidylcholine fraction from mice fed the 10% corn oil diet compared with 5% corn oil. When the diets were fed during TPA promotion, the papilloma incidence after 11 weeks of treatment for the 5% corn oil group was 77% and 37% for the 10% corn oil group. By 15 weeks of TPA treatment, papilloma incidence between the diet groups was similar, and later, carcinoma incidence and yield were not different between the two groups. For the animals treated with benzoyl peroxide, there was only a slight but not significant difference in papilloma and carcinoma appearance. In parallel studies, ornithine decarboxylase activity, vascular permeability, hyperplasia, and prostaglandin E2 (PGE2) levels were elevated in the epidermis after promoter treatment, but only hyperplasia and PGE2 synthesis tended to reflect the dietary effects on tumor appearance. These data suggest that the quantity of dietary corn oil at the two levels tested, 5% and 10%, altered epidermal phospholipid fatty acid composition and PGE2 levels and had modest effects on the modulation of tumorigenesis in this skin model.     

Dietary fat and cholesterol modulate the plasma lipoprotein distribution and production of pigment or cholesterol gallstones in hamsters.

To evaluate the impact of key dietary factors on plasma lipoproteins and gallstone induction, male Syrian hamsters were fed either cholesterol and fat-supplemented purified diets containing glucose or lactose, or cholesterol and fat-free diets with or without fiber, for 13 wk. Fat-supplemented hamsters were hyperlipidemic in comparison to those fed fat-free diets. The former group revealed a greatly expanded VLDL fraction, whereas a normal HDL2 pool predominated in the latter group. Plasma fatty acids indicated that hamsters fed the fat-free diet were essential fatty acid deficient whilst the hamsters fed the fat-supplemented diet were subnormal in essential fatty acids. Ninety-three percent of the hamsters fed the fat-supplemented diet had gallstones (mostly cholesterol), whereas 62% of hamsters fed the fat-free diet had gallstones (almost all pigmented). Lactose increased cecal weight and prevented pigment stone formation in the fat-supplemented hamsters, whereas adding fiber to the fat-free diet contributed essential fatty acids, eliminated cholesterol stones and enhanced pigment stone formation. Thus, diets containing casein, rice flour, glucose and fiber with minimal essential fatty acids but no cholesterol promoted pigment stones (associated with a normal lipoprotein profile); a low fat diet limited in essential fatty acids but containing cholesterol and lactose, promoted cholesterol gallstones (associated with an expanded VLDL pool).     

Effects of dietary proteins and trypsin inhibitor on growth and lipid metabolism in hamsters

The purpose of this study was to determine trypsin inhibitor (TI) activity in sweetpotato and soy flour diets and their effects on the growth and lipid metabolism of hamsters. Male Golden Syrian hamsters were fed different types of dietary protein containing casein, soyprotein, transgenic sweetpotato plus soy flour (TSPF+SF), nontransgenic sweetpotato (NTSPF) plus soy flour (NTSPF+SF), transgenic sweetpotato (TSPF) and nontransgenic sweetpotato flour for 28 days. The TI activity was highest in TSPF+SF (19.30 TIU/mg) and NTSPF+SF (17.20 TIU/mg) diets that induced growth retardation in animals, lowest in TSPF (5.80 TIU/mg) and NTSPF (5.50 TIU/mg) diets, which did not affect the growth of the animals, and negligible in casein (<1.00 TIU/mg) and soyprotein (2.00 TIU/mg) diets. Plasma total cholesterol (TC), high density lipoprotein-cholesterol (HDL-C), low density lipoprotein-cholesterol (LDL-C) and triglyceride (TG) concentrations were significantly higher in hamsters fed the casein diet compared to those fed the soy protein, TSPF+SF, NTSPF+SF, TSPF and NTSPF diets. A positive correlation was observed between plasma TC concentrations of hamsters and dietary methionine, lysine, leucine content and methionine/glycine ratios. Liver TC and TG concentrations of hamsters fed casein were significantly higher than those of all other diet groups. The supplementation of sweetpotato flour with soy flour increased both protein and TI activity in the diets and the lipid metabolism of hamsters were unaffected by TI activity.     

Influence of dietary carbohydrates upon the metabolism of lipids and minerals in rabbits

Rabbits were fed purified diets containing either corn starch, sucrose, glucose or fructose as 39.5% of the caloric content, or were fed a commercial diet. At the end of the 12-week trial period, glucose tolerance tests did not reveal a difference by treatment, and males had a lower tolerance than females. The serum cholesterol concentrations of the various density lipoproteins varied by treatment as determined weekly; often the HDL cholesterol was higher in the rabbits fed corn starch, and the VLDL cholesterol was higher in the rabbits fed corn fructose. Cholelithiasis at the end of the trial was prevalent in rabbits fed sucrose, glucose or fructose, was infrequent in the rabbits fed corn starch, and was absent in the rabbits fed the commercial diet. Lipid and cholesterol concentrations in the liver were greater in the rabbits fed the purified diets than in those fed the commercial diet. Cholesterol concentration in the thoracic aorta was greater in the rabbits fed the commercial diet than in those fed the purified diet. Analyses of liver and kidneys for Cr, Mn, Cu and Zn revealed treatment differences only in the case of the kidneys where Cr concentration was greater in the kidneys when the commercial diet was fed.     

The hypocholesterolemic effect of lemon peels,lemon pectin,and the waste stream material of lemon peels in hybrid F<Subscript>1</Subscript>B hamsters

Summary Background We found in preliminary studies with hamsters that citrus peels have a cholesterol lowering effect comparable to that of pectin extracted from these peels. Aim of the study We wanted to examine whether the cholesterol lowering effect of the peels could be completely accounted for by the pectin in the peels. Methods We fed cholesterol enriched (0.1 %,w/w) semipurified diets containing 3 % (w/w) of cellulose, lemon peels, lemon pectin, and the waste stream material of the lemon peels to hybrid F₁B hamsters for a period of 8 weeks. The waste stream of the lemon peels is the left over after extraction of the lemon pectin. Results Feeding the semipurified diets resulted in an increase of plasma cholesterol levels in all the dietary groups after 2 and 4 weeks on the diets. Cholesterol concentrations in the cellulose fed hamsters continued to increase after 4 weeks on the diet, whereas cholesterol levels in the other groups had reached a plateau. As a consequence, the plasma cholesterol levels in the hamsters fed the peels (5.59 ± 0.74 mmol/L, mean ± SD, n = 14), pectin (5.19 ± 0.48 mmol/L), or waste stream (5.53 ± 0.94 mmol/L) were lower than those in the hamsters fed cellulose (6.71 ± 1.52 mmol/L) after 8 weeks on the diets. Differences in total plasma cholesterol were reflected in differences in both VLDL and LDL cholesterol concentration, but this effect was more distinct for the VLDL. There was no effect of the type of fiber on HDL cholesterol levels. Liver cholesterol concentrations paralleled the concentrations of plasma cholesterol and the liver cholesterol concentrations in the hamsters fed the peels (3.57 ± 1.01 μmol/g liver, mean ± SD, n = 14), pectin (4.86 ± 1.42), and the waste stream (4.96 ± 1.89) were lower than those in the cellulose group (7.19 ± 2.32). The hamsters fed the peels, pectin, or waste stream tended to have a higher excretion of fecal bile acids and neutral sterols then the cellulose fed hamsters. Conclusion The results of this study suggest that lemon peels and the waste stream of the lemon peels are as effective in lowering plasma and liver cholesterol in hamsters as the pectin extracted from the peels and that also compounds other than pectin are probably responsible for the cholesterol lowering effect of the citrus peels. Received: 20 September 2001, Accepted: 17 December 2001     

Unusual proliferation of the pancreatic endocrine cells in adults, suggestive of islet cell metaplasia

We present two adult autopsy cases with malignancy, in which unusual proliferation of the pancreatic endocrine cells was observed. Histopathological examination revealed extensive proliferation of the pancreatic endocrine cells throughout the pancreata in both cases. The islets of the pancreas were enlarged with irregular contours. An admixture of the islet cells, acinar cells and ductular epithelial cells was also observed. Immunohistochemically, these islets were composed of the endocrine cells of various types, i.e. A-, B-, D- and PP-cells, and they showed a predominance of PP-cells. Clinically, endocrine hyperfunction of the pancreas was not detected in either cases. Although this histological change may be described as endocrine cell hyperplasia or dysplasia, the close connection of the islet cells, acinar cells and ductular epithelial cells might rather suggest metaplastic change of the acinar or ductular cells into the islet cells under unknown stimuli.     

Effect of dietary Laminaria angustata (brown seaweed) on azoxymethane-induced intestinal carcinogenesis in male F344 rats

The effect of dietary Laminaria angustata (brown seaweed) on azoxymethane (AOM)-induced intestinal carcinogenesis was studied in male F344 rats. Five-week old rats were fed semipurified diets containing 0 and 10% seaweed. When the rats were 7 weeks old, all except the vehicle-treated groups received weekly subcutaneous injections of AOM in normal saline for two weeks (20 mg/kg body wt/week). All animals were fed the experimental diets until the termination of the experiment, which was 28 weeks after the last AOM injection. The incidence (percent of animals with tumors) and multiplicity (tumors/animal) of small intestinal tumors did not differ significantly between the control and seaweed groups. The incidence and multiplicity of colon adenomas along with the size of colon tumors were increased in rats fed the seaweed diet compared with those fed the control diet. Dietary seaweed had no major effect on the concentration of fecal bile acids; however, the concentration of fecal cholesterol and total neutral sterols was decreased in the seaweed group. These results suggest that dietary seaweed increases the risk for colon tumors.     

Cholesterol-lowering in hamsters fed rice bran at various levels, defatted rice bran and rice bran oil.

This study was conducted to determine the relative cholesterol-lowering effects of several levels of full-fat rice bran in hamsters. In addition, the separate effects of defatted rice bran and/or crude rice bran oil were investigated at levels equivalent to those present in 43.7% full-fat rice bran. Diets containing 10.9, 21.8, 32.8 or 43.7% full-fat rice bran, 35% defatted rice bran and/or 9% rice bran oil were fed to 4-wk-old male hamsters. All diets contained 10% total dietary fiber, 9% fat and 3.2% nitrogen; hypercholesterolemic diets contained 0.3% cholesterol; two diets were cholesterol-free, i.e., 10% cellulose and 43.7% full-fat rice bran. After 21 d, plasma and liver cholesterol, plasma triglycerides and liver weights were significantly greater in hamsters fed the 10% cellulose diet with 0.3% cholesterol compared with those fed the cholesterol-free cellulose diet. In animals fed cholesterol-free diets, plasma cholesterol values were significantly lower in those fed the 43.7% full-fat rice bran diet than in those fed the cellulose diet. In animals fed cholesterol-containing diets, plasma and liver cholesterol were significantly lower in animals fed the 43.7% full-fat rice bran diet than in those fed the cellulose diet. Plasma cholesterol reductions were significantly correlated to the level of rice bran in the diet. In cholesterol-fed hamsters, total liver cholesterol content was significantly lower in those fed the defatted rice bran diet with rice bran oil compared with those fed the cellulose diet. Full-fat rice bran was the only treatment that significantly lowered both plasma and liver cholesterol.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of colon tumor development and dietary fat on the immune system of rats treated with DMH

We examined the effect of dietary fat and colon tumorigenesis on the morphology and function of the rat mesenteric lymph node (MLN) and spleen at two stages of tumor development. Male Sprague-Dawley rats were fed semipurified diets of varying fat content (5% mixed fat, 24% beef fat, 24% corn oil, or 24% Crisco) and treated for five weeks with either the colon carcinogen 1,2-dimethylhydrazine (DMH) or the vehicle (saline). Animals consuming high-fat diets had an increased incidence of splenic follicular and germinal center hyperplasia. Carcinogen treatment had no significant effect on the histological morphology of the spleen. MLN morphology was not dramatically affected by either diet or DMH treatment. At this time period, the splenic lymphocyte transformation response induced by concanavalin A (Con A), phytohemagglutinin, or pokeweed mitogen was significantly depressed in the group fed 24% corn oil (vehicle-treated) and in the DMH-treated groups fed 5% fat compared with the vehicle-treated group fed 5% fat. In contrast, the MLN transformation response was elevated in the group fed 24% Crisco. DMH treatment did not significantly influence the MLN response. Four months after carcinogen or vehicle treatment, at the point of colon tumor development, no statistically significant differences were seen in the splenic or MLN blastogenic responses of DMH- or saline-treated animals. Splenic natural killer cell cytotoxic activity was also not significantly affected by dietary fat, carcinogen treatment, or tumor development.     

Influence of iron and the sex of rats on hematological, biochemical and immunological changes during copper deficiency

The influence of dietary iron and the sex of rats on suppressed lymphocyte functions caused by copper deficiency was examined. Male and female weanling Lewis rats were fed two concentrations of copper (0.6 or 5.6 micrograms Cu/g diet) and iron (50 or 300 micrograms Fe/g diet) for 42 d. Regardless of dietary iron concentrations, male and female rats consuming low copper diets had lower serum ceruloplasmin activity and serum and liver copper concentrations than those fed the high copper diet. However, hemoglobin and hematocrit levels were higher in copper-deficient females than in copper-deficient males and were unaffected by copper deficiency in females fed the high iron diet. Copper-deficient females also had higher serum and liver iron concentrations than copper-deficient males. Proliferation of concanavalin A (Con A)-stimulated spleen lymphoid cells (SLC) was suppressed in copper-deficient males and females, but the suppression was less in the females. Thus, the primary cause of suppressed SLC proliferation in copper-deficient rats is poor copper status; poor iron status induced by copper deficiency had little influence on proliferation.     

Exocrine pancreatic secretion is stimulated in piglets fed fish oil compared with those fed coconut oil or lard.

An experiment was conducted to study the effect of feeding diets containing fat sources with different fatty acid composition (fish oil, coconut oil or lard, 10 g/100 g diet) on exocrine pancreatic secretion in piglets after weaning. A total of 16 barrows were weaned at 4 wk of age; 3 d later, they were surgically fitted with a catheter in the pancreatic duct for continuous collection of pancreatic juice. Collections of pancreatic juice were made every other day starting 4 d postsurgically. Piglets fed the fish oil diet secreted a significantly greater volume of pancreatic juice than piglets fed the coconut oil or lard diets. The output [U/(h. kg(0.75))] of lipase was higher in piglets fed fish oil than in piglets fed lard or coconut oil. The output of colipase was greater in piglets fed fish oil and coconut oil than in those fed lard. The dietary treatments did not affect the output of carboxylester hydrolase. The output of trypsin was significantly lower in piglets fed lard than in piglets fed fish oil or coconut oil diets and the output of carboxypeptidase B was greater in those fed the fish oil diet. Protein, chymotrypsin, carboxypeptidase A, elastase and amylase outputs did not differ among the dietary treatment groups. The apparent digestibilities of nutrients and energy were measured in feces and did not differ among groups. Thus, the greater output of lipase in fish oil-fed piglets did not result in a greater digestibility of fat in this diet.     

Effect of colon tumor development and dietary fat on the immune system of rats treated with DMH

We examined the effect of dietary fat and colon tumorigenesis on the morphology and function of the rat mesenteric lymph node (MLN) and spleen at two stages of tumor development. Male Sprague‐Dawley rats were fed semipurified diets of varying fat content (5% mixed fat, 24% beef fat, 24% corn oil, or 24% Crisco) and treated for five weeks with either the colon carcinogen 1,2‐dimethylhydrazine (DMH) or the vehicle (saline). Animals consuming high‐fat diets had an increased incidence of splenic follicular and germinal center hyperplasia. Carcinogen treatment had no significant effect on the histological morphology of the spleen. MLN morphology was not dramatically affected by either diet or DMH treatment. At this time period, the splenic lymphocyte transformation response induced by concanavalin A (Con A), phytohemagglutinin, or pokeweed mitogen was significantly depressed in the group fed 24% corn oil (vehicle‐treated) and in the DMH‐treated groups fed 5 %fat compared with the vehicle‐treated group fed 5% fat. In contrast, the MLN transformation response was elevated in the group fed 24% Crisco. DMH treatment did not significantly influence the MLN response. Four months after carcinogen or vehicle treatment, at the point of colon tumor development, no statistically significant differences were seen in the splenic or MLN blastogenic responses of DMH‐ or saline‐treated animals. Splenic natural killer cell cytotoxic activity wasalso not significantly affected by dietary fat, carcinogen treatment, or tumor development.