• Journal of Yeungnam Medical Science
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• v.18 no.1
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• pp.94-100
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• 2001

Background: It is doubtful that aging causes deteriorated glucose metabolism and insulin resistance of skeletal muscle. Some researchers had different results about it. So we have studied the mechanism responsible for the abnormal glucose tolerance associated with aging in rapidly growing and matured rats. Materials and Methods: Animals were used S.D. rats. Growing rats were 7 weeks old (BW: 160-190 gm) and matured rats were 28 weeks old (BW: 420-525 gm). Results: Fasting blood glucose and plasma insulin levels were significantly elevated in matured rat compared with growing rats. And during oral glucose tolerance test the glucose level was also significantly elevated in matured rats. These results confirmed an insulin resistant state of aging. Insulin levels at 30 minutes of oral glucose tolerance test was significantly elevated in growing rat. But at 120 minutes it was maintained at higher level in matured rats than in growing rats. It suggested the possibility of increased insulin secretion by initial stimulation of beta-cells in growing rats, and increased secretion and decreased catabolic rate of insulin in matured rats. Glucose uptake rate of soleus muscle in matured rats was lower than that of growing rats, but the difference was not statistically significant. The dose(insulin)-responsive(glucose uptake) curve of soleus muscle was only slightly deviated to the right side. Conclusion: Glucose metabolism of rat skeletal muscle was worsened by aging. The data of glucose uptake experiments suggested the possibility of insulin resistance of skeletal muscle in matured rats. but the mechanism of insulin resistance of skeletal muscle need further studies.

• Journal of Nutrition and Health
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• v.28 no.9
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• pp.817-824
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• 1995

This study was performed to evaluate the effect of dietary protein level on Ca efficiency in bone mineral density in growing male rats. Twenty male rate were divided into two groups. The rats in one group were fed on casein 20% diet as control group and the others were fed on casein 40% diet as protein group. All rats were fed on experimental diet and deionized water ad libitum for 9 weeks. The total body, spine and femur bone mineral density and bone mineral content were measured using dual energy-x ray absorptiometry. Urinary calcium, phosphate, pyridinoline and creatinine, serum calcium, phosphate, total protein, albumin, alkaline phosphatase(ALP) and osteocalcin were measured. Urinary Ca excretion, pyridinoline and crosslinks value and serum ALP content seem to be increased in high protein group. It appears that the growing rats in high protein group had a higher bone resprption and bone formation than those in control group. Animal fad a high protein diet had a siginficantly higher Ca efficiency in BMD, BMC of total body, spine and femur. The results of this show that increasing of dietary protein level (40%) is beneficial of improvement of Ca efficiency during growing period.

• Journal of Nutrition and Health
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• v.38 no.5
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• pp.344-351
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• 2005

The purpose of this study was to examine the impact of isoflavones on lipid concentrations and hepatic LDL receptor mRNA level in growing female rats. Twenty four rats (body weight $75\pm5g$) were randomly assigned to one of two groups, consuming control diet or isoflavones supplemented diet (57mg isoflavones/100g diet). All rats has been fed on experimental diet and deionized water ad libitum for 9 weeks. The concentration of triglyceride and total cholesterol were measured in serum and liver. Serum HDL cholesterol was measured. Hepatic LDL receptor mRNA level was tested by RT-PCR. Supplementation of isoflavones did not affect weight gain, mean food intake and food efficiency ratio. Serum total cholesterol and non-HDL cholesterol of isoflavones supplemented rats were significantly lower than those of control rats (p<0.05). But hepatic cholseterol was not influenced by supplementation of isoflavones. Hepatic LDL receptor mRNA level not significantly different between control group and isoflavones supplemented group. Therefore, isoflavones may be beneficial on serum cholesterol and non-HDL cholesterol lowering in growing female rats.

• Journal of Nutrition and Health
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• v.36 no.5
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• pp.452-458
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• 2003

Soybean is a rich source of isoflavones such as genistein and daidzein. Soy isoflavones have both weak estrogenic and anti-estrogenic effects and are structurally similar to tamoxifen, an agent that has an effect similar to that of estrogen in terms of reducing postmenopausal bone loss. The purpose of this study was to determine the effects of differences in protein source (casein vs soy) and isoflavone levels (reduced vs higher levels) on selected bone markers and hormones in growing male rats. Thirty weanling Sprague-Dawley young rats were divided into 3 groups: The control group was fed a casein-based diet, the soy concentrate group was fed soy protein with totally reduced isoflavones content (isoflavones 0.07 mg/g protein), and the soy isolate group was fed soy protein with a higher than normal isoflavones content (isoflavones 3.4 mg/g protein). The degree of bone formation was estimated by measuring serum osteocalcin and alkaline phosphoatase (ALP). By determining collagen cross-linkage by immunoassay and correcting with creatinine values, the bone resorption rate was compared. Serum osteocalcin, growth hormone, estrogen and calcitonin were analyzed using radio immunoassay kits. The bone formation marker and ALP activity were differentiated by protein source, showing higher values than casein in feeding either soy isolate or soy concentrate. In this study using growing rats, the differences in isoflavone contents were not a significant factor in either bone formation or bone reaborption markers. Moreover, the soy isolate group had significantly higher levels of growth hormone than the casein group. The findings of this study suggest that growth hormone is partially responsible for its bone-formation effects in young growing rats. Soy protein and the isoflavones in soy protein are beneficial for bone-formation in growing male rats. Therefore, exposure to soy protein and isoflavones early in life may have long-term health benefits in preventing bone diseases such as osteoporosis. Further study to evaluate the mechanism of action of isoflavones on bones is warranted. (Korean J Nutrition 36(5): 452∼458, 2003)

• Journal of Nutrition and Health
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• v.39 no.3
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• pp.236-243
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• 2006

A recent study reported that a diet rich in isoflavones is beneficial for bone formation in growing rats. It therefore seemed desirable to find out whether the beneficial effect of isoflavones in ovariectomized rats could also be reproduced with same amount of isoflavones which used for growing rats. To study the effect of isoflavones, an equal amount of isoflavones which used for growing rats, on bone mineral density and bone mineral content in ovariectmized rats were performed. Forty female Sprague-Dawley rats (body weight $210{\pm}5g$) were divided into two groups, ovariectomy and sham groups, which were each randomly divided into two subgroups that were fed casein and casein supplemented with isoflavones diets for 9 weeks after operation. All rats were fed on experimental diet and deionized water ad libitum for 9 weeks. Bone mineral density (BMD) and bone mineral content (BMC) were measured using PIXImus (GE Lunar Co, Wisconsin) in spine and femur. Serum alkaline phosphatase activity (ALP) and osteocalcin and urinary DPD crosslinks value were measured as markers of bone formation and resorption. The results of this study indicate that body weight gain and food intake were higher in ovariectomy groups than in sham groups regardless of diets. Serum Ca concentration was lower in ovariectomy groups than in SHAM groups. Serum ALP, osteocalcin, and crosslink value were increased in ovariectomy groups. Spine BMD/weight, femur BMD/weight, and femur BMC/weight of ovariectomy groups were significantly lower than SHAM groups after 9 weeks. However, isoflavones supplemented group in ovariectomy groups, serum ALP and osteocalcin concentrations, spine BMD/weight and spine BMC, femur BMD/weight and femur BMC/weight were significantly increased after 9 weeks. In conclusion, the beneficial effect of isoflavones on bone in ovareiectomized rats was shown on 9 weeks after feeding with an equal amount of isoflavones supplementation which used for growing rats.

• Journal of Nutrition and Health
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• v.36 no.6
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• pp.549-558
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• 2003

The purpose of this study was to determine which differences in the source of protein (soy vs casein) and isoflavones in soy protein are responsible for the differential effects of bone marks and hormones in growing female rats. Forty-two 21-day-old Sprague-Dawley female rats were randomly assigned to one of three groups, consuming casein (control group), soy protein isolate (57 mg isoflavones/100 g diet), or soy protein concentrate (about 1.2 mg isoflavones/100 g diet). All rats were fed on experimental diet and deionized water ad libitum for 9 weeks. Bone formation was measured by serum osteocalcin and alkaline phosphatase (ALP) concentrations. And bone resorption rate was measured by deoxypyridinoline (DPD) crosslinks immunoassay and corrected for creatinine. Serum osteocalcin, growth hormone, estrogen and calcitonin were analyzed using radioimmunoassay kits. Diet did not affect weight gain and mean food intake. Food efficiency ratio was lower in the soy protein groups. The soy isolate group had a higher ALP and osteocalcin concentration and lower crosslinks value than the casein group. Therefore, the soy isolate groups had a higher bone formation/resorption ratio than the casein group. And, the soy group had significantly higher growth hormone than the casein group. The findings of this study suggest that soy protein and isoflavones are beneficial for bone formation in growing female rats. Therefore, exposure to these soy protein and isoflavones early in life may have benefits for osteoporosis prevention.

• Journal of Nutrition and Health
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• v.40 no.3
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• pp.235-241
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• 2007

The aim of this study was to define an arginine effect when added to a diet. The influence of arginine supplements on bone mineral density and content were studied in young female Sprague-Dawley rats fed either an arginine supplemented diet or control diet. Twenty four rats (body weight $83{\pm}5g$) were randomly assigned to one of two groups, consuming casein or casein with supplemented arginine diet. All rats were fed on experimental diet and deionized water ad libitum for 9 weeks. Bone mineral density (BMD) and bone mineral content (BMC) were measured using PIXImus (GE Lunar Co, Wisconsin, USA) in spine and femur 3, 6, and 9 weeks after feeding. The serum and urine concentrations of Ca and P were determined. Diet did not affect weight gain and mean food intake. The serum concentration of Ca and P were not changed by arginine supplementation. Urinary Ca excretion was significantly decreased by arginine supplementation. Spine BMD was significantly increased by arginine supplementation on 3 and 6 weeks after feeding. Femur BMD was significantly increased in the group of arginine supplementation on 3, 6, and 9 weeks. Rats fed the arginine-supplemented diet had better bone mineral content than did control diet rats in the experimental period. Therefore, arginine supplementation may be beneficial on spine and femur BMD increment in growing female rats. These are thought to be associated with an arginine-induced growth hormone release. The exact mechanism of this effect remains to be elucidated.

• Asian-Australasian Journal of Animal Sciences
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• v.24 no.9
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• pp.1274-1281
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• 2011

Dietary protein restriction affects lipid metabolism in rats. This study was performed to determine the effect of a low protein diet on hepatic lipid metabolism and insulin sensitivity in growing male rats. Growing rats were fed either a control 20% protein diet or an 8% low protein diet. Feeding a low protein diet for four weeks from 8 weeks of age induced a fatty liver. Expression of acetyl-CoA carboxylase, a key lipogenic enzyme, was increased in rats fed a low protein diet. Feeding a low protein diet decreased very low density lipoprotein (VLDL) secretion without statistical significance. Feeding a low protein diet down-regulated protein expression of microsomal triglyceride transfer protein, an important enzyme of VLDL secretion. Feeding a low protein diet increased serum adiponectin levels. We performed glucose tolerance test (GTT) and insulin tolerance test (ITT). Both GTT and ITT were increased in protein-restricted growing rats. Our results demonstrate that dietary protein restriction increases insulin sensitivity and that this could be due to low-protein diet-mediated metabolic adaptation. In addition, increased adiponectin levels may influences insulin sensitivity. In conclusion, dietary protein restriction induces a fatty liver. Both increased lipogenesis and decreased VLDL secretion has contributed to this metabolic changes. In addition, insulin resistance was not associated with fatty liver induced by protein restriction.

• Journal of Nutrition and Health
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• v.40 no.4
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• pp.320-326
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• 2007

An important related question is whether arginine has influence bone metabolism. The effect of arginine supplements on bone markers and related hormones were studied in young female Sprague-Dawley rats fed either an arginine supplemented diet or control diet. Twenty four rats (body weight 83${\pm}$5 g) were randomly assigned to one of two groups, consuming casein or casein with supplemented arginine diet. All rats were fed on experimental diet and deionized water ad libitum for 9 weeks. Bone formation was measured by serum osteocalcin and alkaline phosphatase (ALP) concentrations. And bone resorption rate was measured by deoxypyridinoline (DPD) crosslinks immunoassay and corrected for creatinine. Serum osteocalcin, growth hormone, estrogen, insulin-like growth factor-1 (IGF-1), parathyroid hormone (PTH) and calcitonin were analyzed using radioimmunoassay kits. The weight gain and mean food intake were not affected regardless of diets. The rats fed arginine-supplemented diet had not significantly different in ALP, osteocalcin, crosslinks value, PTH, estradiol, and IGF-1 compared to those fed casein diet group. The arginine-supplemented group had significantly higher growth hormone and calcitonin than casein group. This study suggests that arginine is beneficial for bone formation in growing female rats. Therefore exposure to diet which rich in arginine early in life may have benefits for bone formation and osteoporosis prevention.

• Nutritional Sciences
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• v.9 no.2
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• pp.74-81
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• 2006

The present study examined the effect of soy isoflavones on lipid metabolism in growing female rats. Rats were randomly assigned to three different groups and provided experimental diets for 9 weeks. The experimental groups were classified into 1) a control group, 2) a soy protein isolate group: soy (+)) group and 3) a soy protein concentration group: soy (-)) group. Diets contained either casein or one of two soy proteins with (soy (+)) or without isoflavones (soy (-)). Serum triglyceride concentration showed no significant differences among the experimental groups. Serum total cholesterol concentration was significantly lower in both the soy (+) and soy (-) groups than in the control group and LDL-cholesterol concentration was significantly lower in the soy (+). Serum HDL-cholesterol concentration was significantly higher in the control group than in the soy protein groups but the HDL-cholesterol share rate in total cholesterol tended to be lower in the control group than in the soy protein groups, insignificant as it was. Hepatic IDL receptor mRNA level was significantly increased in the soy (+) group when compared to the other two groups to be 20% higher than the control group. In conclusion, soy protein isolate, soy protein rich with isoflavones reduced serum total cholesterol and LDL-cholesterol concentration and increased hepatic IDL receptor mRNA expression in growing female rats. Therefore, it is considered that the intake of soy isoflvones during puberty can be advantageous in terms of the long-tenn control of serum lipid.