Caloric restriction abolishes enhanced metabolic efficiency induced by ectopic agouti protein in yellow mice.

Caloric restriction (CR), from approximately 3 months of age, at 70% of the ad libitum (AL) caloric intake prevented development of overt obesity in female "viable yellow" Avy/A (BALB/cStCrlfC3Hf/Nctr x VY/WffC3Hf/Nctr-Avy) F1 hybrid mice. In adult yellow Avy/A mice, caloric restriction eliminated the increased metabolic efficiency associated with the presence of agouti protein in ectopic sites. At 4 weeks of age, the yellow Avy/A mice were approximately 14% heavier and by 12 weeks of age, when caloric restriction began, they were approximately 24% heavier than the congenic agouti A/a mice. Between 4 and 12 weeks, the yellow mice gained approximately 63% in body weight, whereas the agouti mice gained only approximately 44%. While the comparable AL Avy/A mice gained approximately 128% and the AL A/a mice gained approximately 41% between 12 and 51 weeks of age, the CR Avy/A and A/a mice gained only 16% and 15%, respectively. Mean brain weights of CR mice of both genotypes were lower than those of the comparable ad libitum-fed (AL) groups; however, CR Avy/A mice had slightly, but significantly (P < 0.0001), higher brain weights than CR A/a mice. The larger mean brain weight and retention, during caloric restriction, of the somewhat greater prerestriction Avy/A mean body weight compared with prerestriction A/a mice were consonant with the hypothesis that ectopic agouti protein affects somatic growth directly or indirectly. This may be related to altered developmental/metabolic programming in yellow mice, indicated by greater metabolic efficiency and by an early transient increase in circulating IGF-1 levels. The specific cellular processes modulated by the agouti protein in ectopic sites remain to be identified.

Energy intake and prostate tumor growth, angiogenesis, and vascular endothelial growth factor expression.

BACKGROUND: A sedentary lifestyle coupled with excessive energy intake is speculated to be a factor associated with increased incidence of prostate cancer. We have investigated the effects of energy intake on prostate tumor growth in experimental animals. METHODS: Two transplantable prostate tumor models, i.e., the androgen-dependent Dunning R3327-H adenocarcinoma in rats and the androgen-sensitive LNCaP human carcinoma in severe combined immunodeficient mice, were studied. R3327-H tumor growth and relevant tumor biomarkers (proliferation index, apoptosis [programmed cell death], microvessel density, and vascular endothelial growth factor [VEGF] expression) were compared in ad libitum fed control rats, ad libitum fed castrated rats, and groups restricted in energy intake by 20% or 40%. A second set of experiments involving both tumor models examined tumor growth in ad libitum fed rats or in animals whose energy intake was restricted by 30% using three different methods, i.e., total diet restriction, carbohydrate restriction, or lipid restriction. All P values are two-sided. RESULTS: R3327-H tumors were smaller in energy-restricted or castrated rats than in control rats (P<.001). Tumors from energy-restricted rats exhibited changes in tumor architecture characterized by increased stroma and more homogeneous and smaller glands. In castrated rats, the tumor proliferation index was reduced (P<.0001), whereas apoptosis was increased in both energy-restricted (P<.001) and castrated (P<.001) rats. Tumor microvessel density and VEGF expression were reduced by energy restriction and castration (P<.003 versus control). Restriction of energy intake by reduction of carbohydrate intake, lipid intake, or total diet produced a similar inhibition of growth of R3327-H or LNCaP tumors. These effects were associated with reduced circulating insulin-like growth factor-I. CONCLUSIONS: Our observations are consistent with the hypothesis that energy restriction reduces prostate tumor growth by inhibiting tumor angiogenesis. Furthermore, dietary fat concentration does not influence prostate tumor growth when energy intake is reduced.

Carcinogenesis studies with the lyophilized mushroom Agaricus bisporus in mice.

Continuous administration of 10, 5, and 2.5% lyophilized Agaricus bisporus (AB) mushroom in the diet of six-week-old, randomly bred Swiss mice for life induced tumors in the lungs, forestomach, glandular stomach, and ovaries in certain groups. Some of the tumor incidences were found to be statistically significant, although no dose-response relationship was established. Histopathologically, the neoplasms were classified as adenomas and adenocarcinomas of lungs, glandular stomach, and ovaries and squamous cell papillomas and carcinomas of the forestomach. AB given in both raw and baked forms induced tumors in the same species in earlier experiments. Since this fungus is consumed in lyophilized form to a certain degree in the United States, the results may carry practical significance.

Lipid level and type alter stearoyl CoA desaturase mRNA abundance differently in mice with distinct susceptibilities to diet-influenced diseases.

Chronic diseases develop in susceptible individuals following exposure to environmental conditions including high fat diets. Inbred strains of mice differing in susceptibility to atherosclerosis, diabetes, obesity and certain cancers are models for understanding the genetic basis and molecular mechanisms whereby diet influences these polygenic and multifactorial disorders. Expression sequence tags (EST) and disease quantitative trait loci (QTL) are also being identified with these strains. Reported here are comparisons of food intake, growth, nonfasting serum lipids and expression of mRNA for hepatic apolipoprotein E (ApoE), hepatic stearoyl CoA desaturase (Scd1) and heart lipoprotein lipase (Lpl) in a 2 x 2 x 2 design with C57BL/6J and BALB/cByJ mice fed semipurified diets with 4 or 20% saturated (coconut) or unsaturated (corn) oils for 4 mo. Histological studies of aortas and coronary arteries are also reported for these animals. After 4 mo, BALB/cByJ mice were significantly heavier and had significantly higher total serum cholesterol, HDL cholesterol and triglyceride concentrations in the fed state than C57BL/6J mice. Efficiency of utilizing dietary energy did not differ consistently between strains. Oil level affected serum total cholesterol, triglycerides and HDL cholesterol, which were significantly greater in mice fed high fat diets. Lpl and ApoE mRNA expression levels were not significantly affected by mouse strain, oil source or oil level. Scd1 mRNA expression, however, was significantly higher in C57BL/6J than in BALB/cByJ mice and was lower in all mice fed 20% compared with those fed 4% fat diets. Genes regulated differently by diet among strains with distinct susceptibility to diet-influenced disease may be associated with molecular pathways contributing to incidence or severity.

Dietary fat and protein intake differ in modulation of prostate tumor growth, prolactin secretion and metabolism, and prostate gland prolactin binding capacity in rats.

The combined effects of dietary fat and protein concentration on prostate tumor growth and endocrine homeostasis were evaluated in male rats. A 2 x 2 factorial experiment examined the effects of protein (5 and 20% of energy as casein) and fat (10 and 40% of energy as corn oil) on the growth of the Dunning R3327-H transplantable prostate adenocarcinoma in Copenhagen x Fisher F1 rats. Rats fed protein-restricted diets for 20 wk exhibited lower energy intakes, final body weights and tumor growth rates. Weanling male Sprague-Dawley rats fed protein-restricted diets for 4 wk had serum concentrations of prolactin, growth hormone and testosterone which were 68, 17 and 85% of controls, respectively. After 16 wk of feeding, there were no effects of dietary protein on serum hormone concentrations despite reduced energy intake and body weight. The metabolic clearance rate of serum prolactin was lower in rats fed the low protein diets for 4 or 16 wk; however, no differences were noted when adjusted for body weight. In vivo studies employing intravenously injected 125I-labeled prolactin revealed slight alterations in the metabolism of circulating prolactin monomer or binding to serum proteins in protein-restricted rats. The maximal binding capacity of prolactin receptors on the prostate membrane fraction was 42% lower in rats fed diets restricted in protein despite normal serum hormone concentrations at 16 wk. Dietary fat had no effect on tumor growth or prolactin homeostasis although a slightly greater serum testosterone was noted in rats fed high fat diets. In contrast, restriction of dietary protein caused significant changes in energy intake, serum hormone concentrations, prolactin metabolism, prostatic prolactin binding capacity and prostate tumor growth rates. These studies support the hypothesis that dietary protein and energy intake, particularly during periods of rapid growth and development, may alter prostate biology and modulate the risk of future prostate cancer progression.

Temporal-regulation of serum lipids and stearoyl CoA desaturase and lipoprotein lipase mRNA in BALB/cHnn mice.

Databases for genes expressed in humans or cell cultures are being developed as a part of the Human Genome Project. Because genomes respond to nutritional and other environmental variables, quantitative analyses of mRNA abundance under defined nutritional and physiological states are required to understand normal metabolism and to clarify differences between normal and disease phenotypes. Reported here are comparisons of food intake, growthp5erum lipids and expression of mRNA for hepatic stearoyl CoA desaturase (Scd1) and heart lipoprotein lipase (Lpl) in female BALB/cHnn mice following food deprivation and refeeding at the end of 2 wk of feeding semipurified diets with 3, 10 or 20% corn oils. Body weights and utilization of dietary energy were similar for mice fed all three diets. There were no differences in serum lipid concentrations associated with the level of dietary fat during subsequent food deprivation and refeeding, but significant differences in serum triglycerides and total serum cholesterol were observed between food-deprived and fed mice. Heart lipoprotein lipase and hepatic Scd1 mRNA expression levels were affected significantly by concentration of corn oil and by time after eating. These and other studies examining gene regulation by dietary variables and nutrient availability are discussed in relation to development of diet-regulated gene databases for laboratory animals fed semipurified diets.

The e subunit gene of murine F1F0-ATP synthase. Genomic sequence, chromosomal mapping, and diet regulation.

Genomic sequences encoding murine Lfm1, whose predicted protein sequence is 96% and 98% similar to bovine and rat F1F0-ATP synthase e subunits (respectively), have been amplified from BALB/cByJ DNA, cloned, and sequenced. The 1.1-kilobase gene has 3 introns and 4 exons, and its coding sequence differs by two nucleotides compared to the previously published BALB/cHnn Lfm1 cDNA sequence. A PstI restriction site polymorphism in intron 2 between C57BL/6J and Mus spretus was used to map this gene to Chromosome 5 near D5Mit9. Related sequences were mapped on Chromosomes 8, 11, and 2 unlinked loci on Chromosome 2 using Southern blot analyses with the 1. 1-kilobase gene as probe. Previous studies from this laboratory indicated that the Lfm1/e subunit was regulated by the level of dietary fat and carbohydrate. Northern hybridization analyses demonstrated that e subunit mRNA abundance showed statistically significant differences (p < 0.025) between hearts of BALB/c mice fed 3% and those fed 20% corn oil for 2 weeks and in liver (p < 0. 05) from the same animals. Significant differences were also observed in hepatic and heart mRNA expression at different times after eating in animals subjected to a fast/refeed regimen. The implications of the high degree of sequence similarity to the e subunit for rat and bovine F1F0-ATP synthase and its regulation by diet are discussed.

The combined effects of dietary fat and estrogen on survival, 7,12-dimethylbenz(a)anthracene-induced breast cancer and prolactin metabolism in rats.

The relationships between dietary fat concentration (10 or 40% of energy), fat source (corn oil or beef tallow) and estrogen (control, ovariectomy or ovariectomy with estrogen replacement) to 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast carcinogenesis and survival in rats were studied in a 2 x 2 x 3 factorial experiment. Female Sprague-Dawley rats given DMBA (2.5 mg/100 g body wt, intragastric) at 55 d of age were randomly allocated to three groups 48 h later: sham ovariectomy (control), ovariectomy (OVX) or ovariectomy with a subcutaneous estrogen implant (OVX+E). Each group was subdivided into dietary groups fed 10 and 40% of energy as corn oil or beef tallow for 70 wk. OVX+E rats exhibited serum estrogen concentrations in excess of physiologic values. Survival at 70 wk for the 3 hormonal groups was control 51%, OVX 67% and OVX+E 13%. Mortality in controls was doubled by feeding a high fat diet; no diet effect was detected in OVX or OVX+E rats. Palpable tumors developed in 74, 14 and 60% of control, OVX and OVX+E rats, respectively. High fat diets approximately doubled the hazard of developing a palpable tumor. Adenocarcinoma prevalence was 58, 12 and 63% in control, OVX and OVX+E rats, respectively. The odds of having any tumor, an adenocarcinoma or an adenoma were multiplied by 3.6, 2.8 and 2.3, respectively, for rats fed high vs. low fat. Additional studies showed that diet had no effect on serum prolactin or estrogen concentrations or metabolism and clearance of intravenously administered radiolabeled prolactin. We demonstrated that high dietary fat concentration enhances breast carcinogenesis independently of cyclic ovarian function, although the presence of estrogen may be a prerequisite for significant dietary modulation. The effect of fat on breast cancer is not mediated by major changes in systemic prolactin metabolism.

Diet-disease interactions at the molecular level: an experimental paradigm.

High levels of dietary fat enhance the severity of certain cancers, obesity, and cardiovascular diseases in susceptible individuals usually after prolonged exposure. We have been developing methods for identifying and characterizing genes regulated by the level of dietary fat for the purpose of determining their role in diseases promoted by high levels of dietary fat, particularly cancer and atherosclerosis. Our protocol employs semi-purified diets of reproducible composition fed to normal inbred mice to obtain reagents for studying of molecular events that lead to pathology. Our early studies demonstrated that different levels of dietary fat cause the accumulation or change in expression of two genes, designated Lfm-1 and Lfm-2 (low fat mammary) in mouse mammary glands and selected other tissues. The Lfm-2 gene is stearoyl CoA desaturase, a gene known to be regulated by dietary fat and insulin levels. The Lfm-1 gene is highly similar to the e subunits of bovine and rat F1F0-ATPases. A Lfm-1 restriction fragment length polymorphism located on chromosome 8 is associated with atherosclerosis in certain inbred strains of mice warranting additional tests to determine whether it is involved in initiation or promotion of heart disease. The experimental approach has the potential for analyzing genes regulated by approximately 50 essential nutrients or other dietary constituents. A potential outcome of this research is the development of reagents which can be used to predict the risk of diet-related diseases in individuals.

F1Fo-ATPase subunit e gene isolated in a screen for diet regulated genes.

Described is a protocol for isolating genes differentially regulated by the level of an essential nutrient in the diet. One gene, designated LFM-1 (Low Fat Mammary), was identified by subtractive hybridization and plus/minus screening in a lambda-cDNA library constructed with mRNA from mammary glands of virgin, tumor-free Balb/c mice fed a low fat diet; a second gene, stearoyl CoA desaturase, known to be regulated by the level of fat intake, was also isolated. The procedure can be modified for use with other constituents. The differential expression of LFM-1 was noted in mammary glands, liver, and kidney but not other tissues of mice fed low fat compared to high fat. LFM-1 is 86% identical to the gene encoding the e subunit of bovine F1-Fo ATPase and 89% identical to an UV-light induced gene (DDIU4) from Chinese hamster fibroblasts. Differential hybridization analyses indicated that LFM-1 may belong to a gene family.

Nitrogen-stimulated orotic acid synthesis and nucleotide imbalance.

Orotic acid, first discovered in ruminant milk, is an intermediate in the pyrimidine biosynthesis pathway of animal cells. Its synthesis is initiated by the formation of carbamoyl phosphate (CP) in the cytoplasm, with ammonia derived from glutamine. Ureotelic species also form CP in the first step of urea synthesis in liver mitochondria. For that, ammonia is derived from tissue fluid. When there is insufficient capacity for detoxifying the load of ammonia presented for urea synthesis, CP leaves the mitochondria and enters the pyrimidine pathway, where orotic acid biosynthesis is stimulated, orotic acid excretion in urine then increases. Orotic acid synthesis is abnormally high with hereditary deficiencies of urea-cycle enzymes or uridine monophosphate synthase. It is also elevated by ammonia intoxication and during feeding of diets high in protein, high in lysine with respect to arginine, or deficient in arginine, ornithine, and citrulline. Rats fed 1% orotic acid or diets deficient in urea-cycle amino acids develop fatty livers, which has not been demonstrated in other species. Humans consuming 6 g of orotic acid daily have not shown adverse effects. Rats fed 1% orotic acid or arginine-deficient diets also showed more and larger foci positive for gamma-glutamyl transpeptidase and more liver tumors after administration of carcinogens and partial hepatectomy. Orotic acid feeding was also associated with the tendency for development of larger mammary tumors induced by chemical carcinogens in rats and with development of urinary bladder calculi containing high concentrations of orotic acid in mice. Conditions that raise tissue orotic acid change purine-pyrimidine ratios. It is unknown whether tissue orotate concentrations play a role in the recently observed enhanced proliferation of cells in the colon of rats fed high-protein, high-fat diets or in the promotion of chemically induced colon cancer by intrarectal administration of ammonium acetate.

The combined effects of dietary fat, protein, and energy intake on azoxymethane-induced intestinal and renal carcinogenesis.

Two 3 x 3 factorial experiments were conducted to examine the effects of dietary protein (8, 16, and 32% of energy from casein) and dietary fat (12, 24, and 48% of energy from corn oil) on the initiation and promotion of azoxymethane-induced carcinogenesis in rats. For the initiation study, 33 weanling male Sprague-Dawley rats were randomized to each of nine diets fed ad libitum. Azoxymethane was administered s.c. between the fourth to sixth weeks of feeding, providing a total dose of 6 mg/100 g body weight. All rats were subsequently fed a common diet containing 16% energy from protein and 24% energy from fat for an additional 30 to 38 weeks. For the promotion study, all rats were fed a common diet containing 16% of energy from protein and 12% of energy from fat until the completion of azoxymethane administration, when 33 rats were randomized to each of nine diets varying in fat and protein content and fed these diets until sacrifice. Low-protein diets during the initiation phase were associated with increased risk of renal adenocarcinomas (P less than 0.001) and mesenchymal (P = 0.005) malignancies. No other statistically significant relationships were found between the levels of dietary fat or protein and the prevalence of malignant lesions of the small intestine, colon, or kidney in either the initiation or promotion study (although polypoid adenocarcinoma of the colon increased suggestively from 13 to 19 to 26% of rats with increasing dietary protein during initiation). Results of a multiple logistic regression analysis, combining both studies, showed that ad libitum energy intake was significantly associated with intestinal carcinogenesis. The odds of finding an intestinal adenocarcinoma increased by 6.2 +/- 2.6% (SE) for each additional kilocalorie of mean daily ad libitum intake (P = 0.014). The quintile of rats which consumed the least averaged 60 kcal/day, while the most voracious quintile averaged 74 kcal/day. This 14 kcal/day difference in mean ad libitum intake corresponded to more than a doubling (146% increase) of the odds of developing an intestinal adenocarcinoma. These studies suggest that ad libitum energy intake is a critical factor modulating experimental colon carcinogenesis.

Large intestinal pH and ammonia in rats: dietary fat and protein interactions.

Mature male Sprague-Dawley rats were assigned to a 3 x 3 factorial experiment in which they were fed AIN-76A diets supplying 8, 16 and 32% of energy as protein and 12, 24 and 48% of energy as fat. During the 5 mo of feeding, 10 in vivo measurements of intracolonic pH were recorded on each rat with a flexible electrode. The pH ranged from 7.8 to 8.0 near the anus and declined to 7.4 to 7.5 at 12 cm from the anus. The mean percentages of dry matter in the contents of the colon, divided into three approximately equal segments, were as follows: proximal colon, 35; middle colon, 45; distal colon, 58. Ammonia concentrations in luminal fluid rose significantly with higher protein intake in the cecum, proximal colon and distal colon. The concentrations in the distal colon ranged from 39 to 74 mmol/L, depending upon protein intake. Thymidine incorporation by distal colon mucosal cells was higher in rats fed 32% of energy as protein and 48% of energy as fat compared with rats fed 8% of energy as protein and 12% as fat. The evidence suggests that increased intestinal cell proliferation in rats fed the high protein, high fat diet was due to greater concentrations of ammonia in the large intestine resulting from the high protein intake and greater concentrations of non-ionized ammonia resulting from the higher pH associated with increased fat intake. The actual determinations and calculations of ionized to non-ionized ammonia concentrations were compatible with the assumption that the large intestinal cells absorbed more ammonia at higher fat intakes.

Colon mucosal cell damage by ammonia in rats.

Colons of male Sprague-Dawley rats were perfused, in situ, with ammonium (NH4+) or sodium (Na+) and acetate (CH3COO-) or chloride (Cl-) to determine the effects of the cations and anions or their interactions on the colon mucosa. Solutions simulating ileal fluid were delivered at 0.4 mL/min at 38 degrees C via cannulae inserted at the cecal-colonic junction. Effluents were collected by cannulae inserted in the anus. In the first experiment, perfusion with the control solution or with the control solution having 35 mmol/L NaCl replaced by equimolar amounts of ammonium acetate, ammonium chloride or sodium acetate showed that only ammonium-containing solutions caused histological damage, loss of mucus, and significant losses of carbohydrate and DNA (P less than 0.05). The losses of carbohydrate and DNA expressed in microgram.cm-1.30 min-1 were as follows: control, 13.4 and 1.0; ammonium acetate, 31.8 and 1.6; sodium acetate, 16.0 and 0.6; ammonium chloride, 24.1 and 1.3, respectively. In the second experiment, perfusion with control fluid containing 35 or 70 mmol/L ammonium acetate at pH 6.8, 7.4 or 8.0 increased carbohydrate and DNA losses into the effluents compared with the pretest period (P less than 0.05), without significant effects related to influent pH. These studies are consistent with the concept that the life span of colon cells is shortened by concentrations of ammonia found in the colon under normal conditions and that ammonia enhances cell proliferation in the colon mucosa.

Dietary protein and chronic toxicity of 1,2-dimethylhydrazine fed to mice.

1,2-Dimethylhydrazine-HCl (DMH-2HCl) is derived from the natural toxin cycasin, and is extensively used to induce cancers in experiments with rodents. We examined the toxicity of DMH-2HCl, incorporated into purified diets varying in protein, to determine concentrations compatible with long-term survival in B6C3H1 mice. Initial studies showed single-dose oral LD50 values (95% confidence intervals) of 26 (18-32) mg DMH-2HCl/kg body weight for males, and 60 (53-65) for females. A 6-wk study was performed with diets containing 10 or 40% soybean protein with doses of 0, 11.25, 22.5, 45, 90, and 180 mg DMH-2HCl/kg diet. All mice fed the highest dose were removed from the study due to severe toxicity. Declines in food consumption and body weight occurred in both sexes, accelerated with increasing log(DMH) dose, and were substantially more severe in groups fed 10% protein. A 5-mo study was subsequently performed with male mice fed 10 or 40% protein diets containing doses of 0, 15, 30, or 45 mg DMH-2HCl/kg diet. In this longer study, dose-related declines of food intake and body weight were also more pronounced with 10% protein. Histopathologic examination of samples from 29 organs/tissues revealed hepatic changes most commonly, and these were more severe at higher DMH levels. Lesions ranged from focal centrilobular hepatocellular necrosis to severe toxic hepatitis, associated with lobular disorganization and hepatocellular hypertrophy. Frequent dose-dependent lesions were also found in kidneys, adrenals, and heart. Renal changes included focal subcapsular fibrosis with atrophy, and hyperplasia of the tubular epithelium. Adrenal cortical hypertrophy was noted at the two highest DMH doses. Focal cardiac myocytolysis was also noted at high DMH doses. Renal damage occurred only rarely in the absence of liver pathology, and adrenal hypertrophy only rarely without renal damage. Cardiac myocytolysis was found in 14% of mice without hepatic, renal, or adrenal damage, but in 62% of those with lesions in each of those organs. No evidence of gastrointestinal toxicity was observed. Hepatic, renal, and adrenal lesions were more frequent and severe in mice fed the low-protein diet. The protective effect of high protein was DMH-dose dependent. The lower doses in these studies could be used to investigate effects of diet, cocarcinogens, or chemopreventative agents on carcinogenesis resulting from chronic, low-level dietary exposure to DMH.

Kinetics of cell-mediated cytotoxicity in mice fed diets of various fat contents.

We previously reported lower mitogen-induced blastogenic and cytotoxic activity of splenocytes from C3H/OUJ female mice fed 20% soybean oil (SBO) in their diet compared to those fed 5% SBO. The present study examined the kinetics of cell-mediated cytotoxicity using the same animal model and dietary treatments. Kinetic parameters were determined by analyzing the lytic efficiency of splenocytes cultured for various times with several concentrations of radiolabeled P815 mastocytoma cells. The apparent avidity constant (K1/2) of the reaction was not changed by dietary SBO intake (1.0 +/- 0.2 x 10(5) cells for 20% SBO versus 1.3 +/- 0.3 x 10(5) cells for 5% SBO). However, the maximum velocity (Vmax) of the reaction for splenocytes from mice fed 20% SBO was significantly lower than that for splenocytes from mice fed 5% SBO (1.4 +/- 0.2 x 10(4) cells/h for 20% SBO versus 2.3 +/- 0.4 x 10(4) cells/h for 5% SBO, p less than 0.05). The evidence indicates that the rate of target cell lysis, but not the avidity of the lymphocytes for the target cell antigen, was altered by increasing dietary SBO concentration.

Priorities for nutrition content in a medical school curriculum: a national consensus of medical educators.

The ASCN Committee on Medical/Dental School and Residency Nutrition Education conducted a series of activities to establish guidelines for nutrition core content in a medical school curriculum. These activities included mail surveys of medical-nutrition educators and a representative group of medical school curriculum administrators and a national consensus workshop of nutrition educators. Results indicated close agreement between the nutrition educators and curriculum administrators (r = 0.89, p less than 0.0001) on the importance ratings of 41 nutrition topics and on the number of hours of nutrition course work that medical schools should provide (44 vs 37 h, respectively, p = 0.14). There was consensus among the nutrition educators that 26 topics should be given priority ratings as essential for inclusion in medical course work. Further prioritization of these topics resulted in a listing of core content topics and subtopics to serve as a guide to administrators and educators for planning nutrition course work in a medical school curriculum.

Orotic acid overproduction in experimental cirrhosis of rats.

Ammonia clearance, portal blood ammonia, and amino acid concentrations were studied during induction of cirrhosis by carbon tetrachloride in rats. Exposure to CCl4 vapors twice weekly for 7-16 weeks doubled orotic acid excretion. If exposure was discontinued for 7 days, the orotic acid excretion decreased despite the presence of cirrhosis proven histologically. Replacement of dietary casein with soybean protein eliminated the CCl4-induced orotic aciduria in growing rats but not in adults. Supplementation of casein with 1.5% arginine did not prevent CCl4-induced orotic aciduria. [14C]Orotate uptake into RNA and DNA of liver was not impaired. Perfusion of livers of cirrhotic animals with ammonia concentrations between 0.2 and 3.0 mM revealed no significant decreases in urea synthesis rates due to cirrhosis and no increase in the tendency to make orotic acid at a given ammonia concentration. However, ammonia uptake by cirrhotic livers was significantly reduced, resulting in higher ammonia concentrations in the effluent when there was moderate-to-severe cirrhosis. Portal blood samples taken from rats exposed to CCl4 had higher ammonia concentrations as cirrhosis worsened. The results lend support to the "intact hepatocyte" hypothesis of cirrhosis which attributes metabolic abnormalities to intrahepatic shunts.

Wheat bran and the induction of intestinal benzo(a)pyrene hydroxylase by dietary benzo(a)pyrene.

The mucosa of the intestine responds to polycyclic aromatic hydrocarbons (PAH) with the rapid induction of benzo(a)pyrene hydroxylase (BPH). Studies were conducted to determine if dietary fiber would reduce exposure of the intestine to dietary benzo(a)pyrene (BP) as indicated by intestinal BPH activity. In all studies, female Sprague-Dawley rats were fed a fiber-free purified diet for 7 d, whereupon they were switched to experimental diets for 48 h. After 48 h their small intestinal mucosa was assayed for BPH activity. Diets for the initial study contained 0, 100, 400, 800, or 1200 mg BP/kg diet, each with and without 10% soft white wheat bran. Enzyme induction with 100 and 400 mg BP/kg diet was partially inhibited by bran, but with higher concentrations of BP there was no protective effect. The inhibition in BP-induced intestinal BPH activity was observed with 10% wheat bran but not with 3.3 or 6.6%. Subsequent studies showed no significant inhibition in BPH induction with cellulose or lignin, whereas all forms of wheat bran (hard red, soft white, or finely ground soft white) caused significant inhibition. In the final study, a diet containing charcoal-broiled beef, a known source of PAH, was compared with diets containing raw beef or soybean protein, each with and without 10% soft white wheat bran. BPH activity remained low with raw beef and soybean protein whether or not fiber was added. However, intestinal BPH activity was raised ninefold by charcoal-broiled beef. The addition of bran reduced BPH activity to 65% of that observed with the fiber-free, charcoal-broiled beef diet.(ABSTRACT TRUNCATED AT 250 WORDS)