Alternative futures for nutrition in health and agriculture.

Four alternative futures for nutrition programs within the areas of agriculture and health are considered. The first, based on current trends, will lead to a continued emphasis on the quality of the food supply in agriculture and on the relationship of diet to disease in the area of health. Under these conditions both areas will continue their nutrition research and education programs related to health maintenance and the promotion of health; the funding of nutrition programs will grow slowly. An alternative future, based on revolutionary advances in understanding of gene-nutrient interactions, could lead to greatly increased funding to apply this understanding toward improved nutrition and health. Alternatively, changes in the nation's health care system could lead to emphasis on health promotion and significantly increased funding would follow for nutrition research and education in support of health promotion. A final consideration involves the possibility that food insecurity will become politically unacceptable around the world and this change will significantly alter the direction and the support of food programs.

The dynamic nature of zinc availability from foods in vivo. Implications for in vitro methods.

This paper presents a review of data from animal experiments demonstrating that the relative availability of zinc from foods is affected by an interaction between the source and amount of zinc consumed. Zinc availability from foods was determined by whole body counting after feeding 65Zn-labeled meals containing varying amounts of zinc. Relative to availability from zinc chloride, zinc availability from foods such as chicken, milk, and peanut butter was greater when determined using 98 rather than 16 micrograms zinc in the meal. In rats fed the higher dose of zinc, there were greater differences in zinc availability among the 15 foods studied, and zinc availability was greater from some foods than from zinc chloride. After an in vitro enzymatic digestion, neither zinc solubility nor the partitioning of zinc between low and high molecular weight substances was useful for predicting zinc availability in vivo. These data indicate that zinc availability from food is not a constant proportion of availability from a zinc salt. In view of the dynamic nature of zinc availability in vivo, the inability to accurately simulate different physiological responses to varying quantities of certain foods may limit the usefulness of in vitro methods.

Dietary conditions influencing relative zinc availability from foods to the rat and correlations with in vitro measurements.

Zinc availability from a series of foods was determined using 65Zn-labeled test meals fed to rats. Zinc availability relative to zinc chloride depended on the amount of the zinc source in the test meal. Zinc availability from several foods was similar to that from zinc chloride when tested in smaller amounts, but enhanced when fed in larger amounts. The range of zinc availability was similar for foods of plant and animal origin. Rats retained significantly more zinc from pork, chicken, peanut butter, egg or milk than from rice, beef, soybean flour or navy beans. Foods with intermediate zinc availability were sweet corn, whole wheat bread, cheese and oysters. Several food characteristics were examined for possible relationships with zinc availability, including the solubility or molecular size of zinc compounds after an in vitro enzymatic digestion and the contents of phytic acid, minerals, amino acids, carbohydrate and fatty acids relative to the zinc content of the food. Protein and several amino acids predicted about half of the variance in zinc availability. Following in vitro enzymatic digestion, neither zinc solubility nor the partitioning of zinc between low and high molecular weight substances was a strong predictor of zinc availability.

Influence of usual zinc intake and zinc in a meal on 65Zn retention and turnover in the rat.

The influences of zinc in a meal and usual zinc intake on zinc retention and turnover were investigated in 7-wk-old male rats fed diets containing 12-151 mg Zn/kg for 3 wk before and after consuming a 65Zn-labeled meal containing ZnCl2. Retention corrected to zero time and turnover rate were determined by whole-body counting. Percent zinc retention was inversely proportional to the natural logarithm of the meal zinc, between 0.09 and 26 mumol. In comparison to lower doses, higher doses resulted in lower percent retention but greater amounts of zinc retained. Although the latter relationship was slightly curvilinear, there was no indication of a limited capacity for zinc retention with high doses. However, doses above 4 mumol resulted in higher turnover rates in rats accustomed to lower zinc intakes. Percent retention and the reciprocal of the turnover rate were proportional to the reciprocal of the dietary zinc concentration. The greatest differences in retention and turnover occurred between 12 and 26 mg Zn/kg diet. The zinc dose in a meal and the usual dietary zinc separately influenced percent zinc retention. These factors also interacted, such that greater dose effects were observed at lower zinc intakes and greater dietary zinc effects were observed at lower doses.

The effect of three hypolipidemic drugs on catalase activity and peroxisomal and mitochondrial palmitate oxidation in rat cardiac and skeletal muscle.

Catalase activity and peroxisomal and mitochondrial palmitate oxidation have been investigated in cardiac and skeletal muscle from rats fed clofibrate, ciprofibrate or nafenopin in an unrefined diet for different periods of time. Nafenopin was also added to either a high carbohydrate (70% of kilocalories from glucose) or high fat (70% of kilocalories from lard) diet and fed to rats for either 1 or 3 weeks. Catalase activity was elevated in all muscles from rats fed the hypolipidemic drugs. The response of catalase activity in muscle to clofibrate was dose-dependent. The response time of catalase activity was different in individual muscles. Peroxisomal palmitate oxidation was elevated in the heart and soleus muscle from rats fed nafenopin in either the high-carbohydrate or the high-fat diet. There was no change in peroxisomal palmitate oxidation in psoas or extensor digitorum longus muscle from rats fed the drugs. Mitochondrial palmitate oxidation was only slightly increased by nafenopin in the heart and soleus muscles after 3 weeks of nafenopin feeding. The results suggest that the cardiac muscle, like the liver, responds to hypolipidemic drug treatment with an increase in peroxisomal fat oxidation. The skeletal muscle response is less specific and that tissue may not contribute to the hypolipidemic effect of the drugs. The findings also suggest that these drugs do not induce peroxisome proliferation in skeletal muscle.

Effect of level of dietary protein and total or partial starvation on catalase and superoxide dismutase activity in cardiac and skeletal muscles in young rats.

In cells the level of potentially toxic superoxide radical (O2-) is controlled by superoxide dismutase (SOD); the level of hydrogen peroxide (H2O2), also potentially toxic, is controlled by catalase and glutathione peroxidase. To study the effects of altered food intake or dietary protein content on SOD and catalase in cardiac and skeletal muscles, young rats were fed ad libitum diets containing 3, 6 or 25% casein or were subjected to total or partial food restriction (resulting in similar body weight losses). Rats fed a diet containing 3 or 6% casein had much lower growth rates than those fed 25% casein, but the muscle catalase activities were similar in all three groups. Catalase activities in muscles of rats whose food intake was restricted were twice those in rats fed ad libitum. Rats fed ad libitum had higher muscle SOD activities at 41 days of age than did 25-day-old rats, irrespective of the amount of dietary protein or the rate of growth. Twenty-five-day-old rats whose food intake was totally restricted for 2 days had skeletal muscle SOD activities similar to the higher activities seen at 41 days of age in ad libitum-fed rats, but SOD activity in the heart was unchanged after food restriction. The responses of catalase and SOD in muscles differ from the responses reported for these enzymes in liver and erythrocytes when food intake or dietary protein is altered.

Evidence for increased peroxidative activity in muscles from streptozotocin-diabetic rats.

The ability of cardiac and skeletal muscles from diabetic rats to metabolize superoxide and hydrogen peroxide was determined by the activities of superoxide dismutase (SOD) and catalase, respectively. Male and female Sprague-Dawley rats, 43 days old, were made diabetic with a single intravenous injection of streptozotocin (70 mg/kg body weight). On the 80th day after injection the blood glucose concentration of these rats was increased fourfold, and the plasma insulin concentration was decreased four- to fivefold compared to controls. Body weights of male diabetic rats were 61% and those of female diabetic rats were 66% of their ad libitum-fed controls. The seven different skeletal muscles examined weighed less in the diabetic rats than in controls of the same age and body weight. The hearts of the diabetic rats weighed more than those of controls of the same age and body weight. Comparison to the body weight controls allowed the distinction of specific effects due to lack of insulin from effects due to retardation in muscle growth. Increased catalase activity in all muscles examined from diabetic rats (plantaris, gastrocnemius, and heart) suggested a response in catalase activity similar to that of starved rats. SOD activity was not altered in the diabetic rat skeletal muscles and erythrocytes, but was somewhat decreased in the heart.

Copper-zinc and manganese superoxide dismutase activities in cardiac and skeletal muscles during aging in male rats.

The activities of total superoxide dismutase (SOD) and the manganese (Mn SOD) and copper-zinc (Cu-Zn SOD) forms were determined in the supernatant fraction of heart, liver and six skeletal muscles from rats during aging. Total SOD activity increased in most muscles between 3 and 23 months of age. There was no change in activity in liver between 3 and 19 months of age. The increase in total activity in heart was due to increased Mn SOD activity, whereas increases in skeletal muscles were due to Cu-Zn SOD or to both Cu-Zn and Mn SOD. The nutritional implications during aging are discussed.

Changes in aerobic and anaerobic metabolism in rat cardiac and skeletal muscles after total or partial dietary restrictions.

This study examined the effects of acute dietary restriction on aerobic and anaerobic metabolic capacity of skeletal and cardiac muscles. Male weanling Sprague-Dawley rats were fed a 28% casein diet to a body weight of 100 g. The control group was killed at 100 g and the experimental groups were starved to 70 g body weight by either 4-day total restriction (TR) or 9-day partial restriction (PR). The heart, soleus, extensor digitorum longus (EDL), biceps brachii, psoas and red and white portions of the gastrocnemius (GR and GW) were assayed for oxygen uptake and succinic dehydrogenase (SDH) and pyruvate kinase (PK) activity. Cytochrome c was also measured in the gastrocnemius and psoas. The decrease in muscle weight was similar to the 30% decrease in body weight with the exception of the soleus which decreased by only 10% due to either TR or PR. PK, an estimate of anaerobic capacity, appeared to increase per unit weight in all tissues after both TR and PR; however, total muscle PK remained unchanged. Total cytochrome c and SDH activity, estimate of aerobic capacity, decreased in all muscles after either treatment. The largest decreases in SDH were 38% in the soleus and 51% in the heart after TR and 50% in the GR and 48% in the GW after PR. Oxygen uptake increased in the soleus (20%) and heart (70%) but decreased in all other skeletal muscles with the greatest effect after PR (50%). This study has shown that there is a decrease in aerobic capacity during acute starvation and that total muscle anaerobic metabolic capacity remains near normal.

The effect of acute dietary restriction on muscle fibre number in weanling rats.

1. Male Sprague-Dawley rats were allocated at 100 g into either an ad lib.-fed control group or a food-restricted group. The restricted group was fed for 9 d at 25% of ad lib. intake. Controls were killed at a body-weight of 100 g and 29 d of age. 2. The effects of food restriction on muscle weight, fibre number, fibre diameter, DNA, and protein were examined in three skeletal muscles, the soleus, plantaris and extensor digitorum longus (EDL). 3. Acute dietary restriction caused body- and muscle-weight loss and a decrease in both the number and cross-sectional area of muscle fibres in each of the muscles. 4. The restriction halted growth-related increases in DNA in all muscles and decreased the protein:DNA value in the plantaris and EDL. 5. These results indicate that present theories describing cellular development are not adequate to define growth potential or growth retardation of skeletal muscle.

Effect of starvation and refeeding on catalase and superoxide dismutase activities in skeletal and cardiac muscles from 12-month-old rats.

Catalase and superoxide dismutase (SOD) activities were determined in muscles from 12-month-old rats after severe starvation and after subsequent refeeding. Catalase increased in most muscles after starvation and decreased after refeeding, while SOD remained unchanged.

Comparison of morphological and biochemical parameters of growth in rat skeletal muscles.

Morphological and biochemical parameters of cellular growth of four skeletal muscles were examined in male Sprague-Dawley rats from 25 to 165 days of age. The number of muscle fibres decreased in the soleus (41%), plantaris (20%), extensor digitorum longus (25%), and biceps brachii (19%) from 25 to 165 days of age, while nuclear number increased in each muscle until approximately 81 days, with no additional change up to 165 days of age. Fusion of muscle fibres may possibly explain the apparent loss of fibres. During this period of growth, nuclear number correlated equally well with both fibre length and cross sectional area. However, transverse growth accounts for approximately 60% to the post-weanling increase in nuclear number.

Metabolism of D- and L-tryptophan in dogs.

The metabolism of D- and L-[benzene ring-U-14C]tryptophan by dogs was studied. The distribution of label from each isomer in urine, feces, CO2 and various tissues was determined. Thirteen different urinary tryptophan metabolites were isolated by ion exchange cellulose chromatography. D-[14C]Tryptophan was poorly converted to 14CO2 relative to the L-isomer, while giving rise to nearly three times as much urinary 14C as did the L-isomer. The major urinary metabolites of D-tryptophan were unchanged D-tryptophan via indolepyruvic acid appeared to be the major fate of ingested D-tryptophan, with renal excretion of the unchanged D-isomer the next most important fate. The dog apparently utilizes D-tryptophan more efficiently than does the human but much less efficiently than does the rat. The dog appears to be a reasonable animal model for the human in studies of D-tryptophan metabolism.