Effects of Pantethine Supplementation to Diets on Hepatic Lipogenesis of Laying Hens Exposed

to a High Environmental Temperature

JENN-CHUN HSU*, Keiichi TANAKA, Shigeru OHTANI and CRISTINO M. COLLADO* *

Department of Poultry and Animal Science, Gifu University, Gifu-Shi 501-11 epartment of Animal Science, National Chung Hsing * D University, Taichung, Taiwan, Republic of China ** SEARCA , College, Laguna 3720, Philippines

(Received April 25, 1988)

Abstract This experiment was conducted to determine the effect of dietary pantethine supplementation on lipid accumulation and activities of lipogenic- related enzymes in the liver, on total cholesterol content of the egg yolk, and on the egg production of laying hens fed isocaloric and isonitrogenous diets

containing different cereals as the carbohydrate source, under 31℃ of environmental temperature. Pantethine added at 200ppm to the experimental diets did not affect daily feed consumption, but improved egg production and egg weight. Its supplementation to the barley-soy (BS) and corn-soy (CS) basal diets significantly increased liver weight but significantly reduced liver triglyceride. Total liver cholesterol was significantly reduced when pantethine was added to the CS basal diet. In a like manner, pantethine supplementation significantly reduced the concentrations of triglyceride,β-lipoprotein triglyceride

and estradiol-17 β in the plasma. Total plasma cholesterol was significantly decreased when pantethine was added to the BS or CS basal diet. It also suppressed the activities of several lipogenic-related enzymes in the liver, particulary that of HMG-CoA reductase. Further, it decreased total cholesterol (mg/g yolk) in the egg yolk. However, egg yolk weight increased. Thus, the amount of total cholesterol relative to the egg yolk was not significantly affected. The concentration of plasma thyroxine tended to increase when the experimental diets were supplemented with pantethine. In contrast, those of calcium and phosphorus did not show any significant change. Jpn. J. Zootech. Sci., 58 (12): 1059-1072, 1988 Key words : laying hen, pantethine, environmental temperature, hepatic lipogenesis, yolk cholesterol.

The chicken differs considerably from most mammalian species in many aspects of carbohydrate and lipid metabolism. In chickens, dietary fat is transported directly into the hepatic portal system as portomicrons1) and de novo fatty acid synthesis occurs mainly in the liver2). Hepatic lipogenesis in birds is dependent on the diet composition and dietary regimen. HSU et al.3) demonstrated that lipid content and lipogenic-related enzyme activities in the liver were higher in hens fed corn-soy diet

Jpn. J. Zootech. Sci., 59 (12): 1059-1072 1059 1988 HSU, TANAKA, OHTANI and COLLADO

than in those fed barley-soy diet. Environmental temperature, also, affects hepatic lipogenesis, that is, exposure to a high temperature results in an increased lipid deposition in laying hens4,5). AKIBA et al.6) found that chicks subjected to a

temperature of 34℃ had liver lipid and triglyceride levels significantly increased. ERB

et al.7) found that plasma estradiol-1713 β concentration was elevated when hens were

exposed to a high temperature. This was in contrast with the report of AKIBA et al. 8)

which indicated that there is an inverse relationship between plasma estradiol-17 β concentration and temperature. Several reports have suggested that the thyroid activity is affected by the environmental temperature. Thyroid size and thyroid secretion rate9) were decreased by high temperature and were increased by low temperature in chickens. BOBEK et al.10) also reported that the plasma thyroxine level of Japanese quails decreased accordindly as the envirnmental temperature decreased. Several studies have shown that vitamins and methionine supplementation to diets could regulate the lipid metabolism in the chicken liver5,11). The characterization of

pantethine [D-bis-(N-pantothenyl-β-aminoethyl) disulfide], a Lactobacillus bulgaricus factor, had been described in our previous report3). It may participate in the synthesis and catabolism of fat and steroids. In our previous study3), we showed that pantethine supplementation to a corn-soy diet significantly depressed lipogenesis and

lipid content in the liver of laying hens under 23℃ of environmental temperature. However, we observed different responses when pantethine supplemented to a barley- soy diet. It would seem that the dietary pantethine is effective in reducing the accumulation of liver lipid in laying hens fed a diet that induces high liver lipid content as demonstrated by the results obtained from the hens given the corn-soy diet3) Many investigators have studied the influence of various dietary factors on cholesterol contents in eggs and tissues. It has been reported that cholesterol contents of blood and/or eggs were reduced by increasing the level of dietary protein12), through the addition of pectin, gums and scleroglucan13), nicotinic acid14) and large amounts of vitamin A15) to the diet. Our previous study3) also indicated that laying hens fed the corn-soy basal diet supplemented with pantethine have a lower plasma concentration of total cholesterol than those fed the diet with no pantethine supplementation. However, nothing is known about the mechanism by which pantethine either accelerates the cholesterol degradation or depresses the cholesterol biosynthesis. The purpose of this study was to investigate the effect of dietary pantethine under high ambient temperature on the hepatic lipogenesis in the laying hens fed various isocaloric and isonitrogeneous diets. A corollary aim was to evaluate to the effect of dietary pantethine on total cholesterol content in the egg yolk.

Materials and Methods Animals and diets : Fifty Single Comb White Leghorn layers, approximately 32 weeks of age were selected from a commercial farm and housed in single bird laying

cages (30×39cm). All hens were fed commercial diet for two weeks, and the

1060

. Pantethine Supplementation and Hepatic Lipogenesis individual egg production and egg weight were recorded. Based on the egg production record, thirty-six hens were divided into six groups of six birds each, and housed individually in wire cages. At the start of the experiment, all the experimental birds were weighed individually. For a period of three weeks, the daily egg production and egg weight were recorded for each of the individual birds. Feed consumption, however, was determined and recorded on a group basis. Feed and water were supplied at libitum. Laying house temperature was 31±3℃ with a light: dark schedule of 16 : 8hr. A house moisture was not controlled. Table 1 shows the composition of the isocaloric, isonitrogenous corn-soy (CS), barley-soy (BS) and barley-corn-soy (BCS) basal diets. Each of them was fed either unsupplemented or supplemented with 200ppm pantethine (Pantosin powder was obtained from Daiichi Seiyaku Co., Ltd., Tokyo, Japan). General procedure : On the last day of the experiment, all hens were weighed individually. Thereafter, using a heparinized syringe, blood samples were taken from the wing vein of each bird for estradiol-17 β and thyroxine assays and for calcium and phosphorus determination. The hens were subsequently decapitated and blood samples were again collected for the determination of various lipid fractions concentration.

Plasma was later separated from each blood sample and then stored at -30℃ pending analysis. The sampling and killing of laying hens from each treatment were on a rotation basis. At necropsy, the liver and the abdominal fat were immediately

Table 1. Composition of basal diets of laying hens

BS=barley- soybean meal, CS=corn-soybean meal, BCS=barley-corn-soybean meal. Supplied per kilogram of diet: vitamin A, 5000IU; vitamin D, 1,000ICU; vitamin 1 E, 10IU; menadione, 3mg; niacin, 14mg; Ca-pantothenate, 10mg; riboflavin, 3mg; folic acid, 4mg; vitamin B12, 5μg; and choline chloride, 300mg. 2Supplied per kilogram of diet: MnSO4・4H3O , 30mg; FeSO4・7H2O, 25mg; ZnSO4・ 7H2O, 30mg; CuSO4・5H2O, 0.5mg; and KI, 1mg.

1061 HSU, TANAKA, OHTANI and COLLADO removed and weighed. Liver samples were placed in ice-cold saline solution (0.9%) for the determination of the various lipid fractions and the activities of lipogenic- related enzymes. Egg yolk samples were obtained from last three egg of each hen for the determination of total cholesterol. Preparation of liver homogenates : Each liver sample was homogenized in 0.25M sucrose solution containing 1mM ethylenediamine tetraacetate-2 Na. Then the homogenates were centrifuged (Model RS-18, Tomy Seiko) at 600×g at 4℃ for

15min. The supernatants were recentrifuged (Model 65p Rp 40-705 roter, Hitachi

Koki) at 105,000×g at 4℃ for 60 min and the resulting clear supernatants were used for assaying enzyme activity and total protein. Enzyme assays : Assays of the activities of citrate cleavage enzyme (EC 4.1.3.8 ; CCE) and NADP-malate dehydrogenase (EC 1.1.1.40 ; NADP-MDH) were carried out using the procedures previously reported by TANAKA et al.16). The activities of acetyl-CoA carboxylase (EC 6.2.1.3; ACC), fatty acid synthetase (FAS) and β- hydroxy-β-methylglutaryl-CoA reductase (EC 1.1.1.34; HMG-CoA reductase) were assayed according to the methods of HSU et al.17), QURESHI et al.18) and QURESHI et al.19), respectively. The protein content of the supernatant used for enzyme assay was determined by the method of LOWRY et al.20). Enzyme activities were expressed as nanomole or picomole of substrate converted to product per minute per mg protein at 25 or 38℃.

Analytical procedures : The concentrations of various plasma and liver lipid fractions and the cholesterol content in the egg yolk were analyzed by the method of TANAKA et al.16) . Calcium and phosphorus concentrations in the plasma were carried out in accordance with the simplified procedures suggested in the mini-manual enclosed

Table 2. Effect of pantethine supplementation to diets with different cereals on liver and abdominal fat weights of laving hens

1Diets with no pantethine . 2Diets with pantethine. 3Mean±S. E. for six birds. * ,**Significantly different (p<0.05, p<0.01) from the diets with no pantethine. different from one another among diets with no pantethine (p<0.05). ns=not

1062 Pantethine Supplementation and Hepatic Lipogenesis with the Calcium C-Test Kit (Wako Junyaku Kogyo K.K.) and Phosphorus-Test Kit (Wako Junyaku Kogyo K. K.). Plasma estradiol-17 β concentration was determined by the radioimmunoassay method as described by NAKAMURA et al .21). Plasma thyroxine concentration was assayed using the T-Test ELISA method . Data were analyzed using the two-way layout design of the analysis of variance22) . Significant differences among treatments were determined using Duncan's multiple range test23) and Student's t-test.

Results The effects of dietary pantethine supplementation on daily feed consumption, egg production, egg weight, egg shell thickness, liver weight and abdominal fat weight are presented in Table 2. Pantethine supplementation to the experimental diets improved egg production and egg weight. However, no effect was observed on daily feed consumption and egg shell thickness in all the dietary treatments. When pantethine was supplemented to the CS and the BS diets, liver weight (g/100g body weight) was significantly increased but abdominal fat weight (g/100g body weight) was not affected. Table 3 shows the influence of pantethine supplementation to various diets on the contents of various lipids in the liver and plasma of laying hens. Liver triglyceride content of laying hens fed the CS diet was significantly higher than that of those fed the BS diet. Meanwhile, when pantethine was supplemented to the CS and BS diets, the triglyceride content in the liver was significantly depressed. Similarly, the addition of pantethine to the CS diet caused significant reduction in the total cholesterol content of the liver. However, no effect was observed when pantethine was

body weight, feed consumption, egg production, egg weight, egg shell thickness,

a, bMean values in the same row having different superscript letters are significantly significant.

1063 HSU, TANAKA, OHTANI and COLLADO

Table 3. Effect of pantethine supplementation to diets with different cereals on

Table 4. Effect of pantethine supplementation to diets with different cereals on of laying hens

1Diets with no pantethine . 2Diets with pantethine. 3Mean±S. E. for six birds. *,** Significantly different (p<0 .05, p<0.01) from the diet with no pantethine. different from one another among diets with no pantethine (p<0.05). ns=not added to either BS or BCS diets. Differences were not significant among the dietary treatments for the phospolipid content in the liver. In comparison with the diets unsupplemented with pantethine, the diets supplemented with pantethine resulted in significantly lower plasma concentrations of triglyceride, β-lipoprotein triglyceride and non-esterified fatty acids (NEFA) in laying hens, with the exception of total cholesterol concentration in those fed the BCS diet and NEFA concentration in those fed the BS diet. Dietary treatments produced no significant effects on the phospholipid concentration in the plasma of laying hens. The effects of pantethine supplementation to diets with different cereals on the plasma concentrations of calcium, phosphorus, thyroxine and estradiol-17 β in laying

1064 Pantethine Supplementation and Hepatic Lipogenesis

the contents of various lipids in the liver and in the plasma of laying hens

a, bMean values in the same row having different superscript letters are significantly significant.

the concentrations of calcium, phosphorus, thyroxine and estradiol-17 β in the plasma

a,bMean values in the same row having different superscript letters are significantly significant.

hens are shown in Table 4. None of the dietary treatments significantly affected the concentrations of calcium and phosphorus in the plasma. However, when pantethine was added to various diets, there was an increase in the concentration of thyroxine and

a decrease in the concentration of estradiol-17 β in the plasma of laying hens.

Meanwhile, compared with laying hens fed the CS diet, those given the BS diet had significantly lower concentration of estradiol-17 β in the plasma of laying hens.

Estradiol-17 β concentration in the plasma of laying hens exposed 31℃ of environmental

temperature was three to four times as high as those exposed 23℃ of environmental

tremperature3). Table 5 shows the effects of dietary pantethine supplementation on the activities

1065 HSU, TANAKA, OHTANI and COLLADO

Table 5. Effect of pantethine supplementation to diets with different cereals on

1 Diets with no pantethine. 2Diets with pantethine. 3Activities expressed as substrate converted to product per minute per mg protein at 25 C. 5Mean±S. E. for six thine. a, bMean values in the same row having ACC, acetyl-CoA carboxylase; FAS, dehydrogenase; HMG-CoA reductase, 3-hydroxy-3-methylglutaryl-CoA reductase.

Table 6. Effects of pantethine supplementation to diets with different cereals on

1Diets with no pantethine . 2Diets with pantethine. 3Mean±S. E. for six birds. *,**Significantly different (p<0.05, p<0.01) from the diet with no pantethine. ns=not significant. of lipogenic-related enzymes in the liver of laying hens. The activities of FAS, NADP-MDH and CCE showed a lower level with pantethine treatments as compared to without pantethine treatments. Moreover, the activity of HMG-CoA reductase was significantly depressed in the liver of laying hens fed the diets supplemented with pantethine. The influences of dietary pantethine supplementation on the yolk weight and yolk content of total cholesterol are shown in Table 6. There was an increase in yolk weight (g/egg) and decrease in yolk total cholesterol content (mg/g yolk) resulting from the addition of pantethine to diets. However, there was no difference among the dietary treatments in the amont of total cholesterol in the egg yolk.

Discussion

The liver triglyceride content of laying hens fed the CS basal diet was significantly higher than those fed the BS basal diet (Table 3). This corroborates the results we reported in a previous paper3). This is also agreement with the result of JENSEN et al.24). It seems that the effects of pantethine supplementation to diets on liver triglyceride content are not as pronounced when laying hens are kept at a lower

1066 Pantethine Supplementation and Hepatic Lipogenesis

the activities of various enzymes in the liver of laying hens

rate converted to product per mg protein at 38 C . 4Activities expressed as subst- birds. *,**Significantly different (p<0.05, p<0 .01) from the diets with no pante- fatty acid synthetase; CCE, citrate cleavage enzyme; NADP-MDH , NADP-malate

yolk weight and yolk cholesterol content of laying hens

environmental temperature (23℃) as when they are reared at a higher environmental temperature (31℃). In a previous study3), we observed that a pantethine supplemented BS diet failed to show any significant effects on liver triglyceride content.

However, the present experiment, whereby laying hens were kept at 31℃, indicated significant decrease in the liver triglyceride level. These findings suggest that there are interactions among dietary composition, environmental temperature and hepatic lipid deposition in laying hens. The results reported by TAKAHASHI et al.26) similarly stated that environmental temperature, dietary composition, plasma estrogen level, and their interactions influenced hepatic lipid deposition of chickens. Added to this is our previous report3) which suggested that an interrelationship perhaps existed between experimental conditions and response to dietary supplementation with regard to liver fat accumulation. SCHEXNAILDER and GRIFFITH5) also showed that the response of liver lipid content of hens to the vitamin supplementation was inversely related to environmental temparatures. In the present experiment, total cholesterol concentration in the plasma was significantly reduced by pantethine supplementation to three basal diets. This result was in agreement with our previous study3) and was supported by our measurement of

1067 HSU, TANAKA, OHTANI and COLLADO

HMG-CoA reductase (the rate-limiting enzyme for cholesterol biosynthesis) activity in the liver of laying hens in the present experiment. That is, HMG-CoA reductase activity in the liver was altered in a parallel change with total cholesterol concentration in the plasma. In the present experiment, the activities of hepatic lipogenic-related enzymes, with the exception of NADP-MDH, were not affected by the dietary cereals feeding. These results differed from our previous report3) which indicated that laying hens fed the CS diet had significantly higher activities of CCE, NADP-MDH and FAS in the liver in comparison with those fed the BS diet. This may be attributed to the interaction between the cereal and the environmental temperature. However, pantethine supplementation to diets significantly depressed the activities of CCE, FAS and NADP-MDH in the liver of laying hens. These results were in accordance with the report of HSU et al.3). TANAKA et al.27) reported a positive correlation between hepatic fatty acid synthesis and the activities of CCE (r=0.996) and NADP-MDH (r=0.981) in the liver of chicks that received different levels of carbohydrate. It had also been shown that the increase of liver lipid caused by dienestrol diacetate was associated with an increase in fatty acid synthesizing activity when chicks were housed in air- conditioned room at 21℃6). These reports indicated that the reduction in the liver

lipid content was associated with the reduction in the hepatic lipogenic-related enzyme activities of laying hens fed the diets supplemented with pantethine. Then, the low liver lipid content would resulted in a reduction of lipid transportation from liver to blood stream. Thus, in the present experiment, it seems reasonable to say that the observed decreases In the plasma concentrations of triglyceride and β-lipoprotein

triglyceride in laying hens fed the diets with pantethine were, one way or another, responsible for the reduction in the liver lipid content.

The thyroid status and plasma estradiol-17 β concentration also affect hepatic lipid deposition. The administration of antithyroid substances, such as thiouracil and propylthiouracil, induces excessive lipid deposition in the liver of immature chickens27,28) and laying hens29). Thyroid secretion rate is decreased by high temperature and increased by low temperature in chickens30) and in laying hens31) . Exposing laying hens to high temperature resulted in an increase in hepatic lipid deposition4,5). Based on these reports, it is reasonable to suggest that hot environmental temperature resulted in a decrease in plasma thyroxine concentration and in an increase in hepatic lipid deposition in laying hens. Estrogen has profound effects on hepatic lipogenesis in both laying hens32) and immature estrogen-treated chicks33). Both in vitro and in vivo hepatic triglyceride syntheses were stimulated by estrogen treatment, whereas oxidation of palmitate was depressed34). This decrease in hepatic fatty acid oxidation seems responsible in making fatty acid available for the synthesis of triglyceride in the liver. TANAKA et al.35) have shown that plasma estradiol-17 β concentration is positively correlated to liver triglyceride content (r=

0.571). The same study demonstrated that a positive correlation also exists between plasma estradiol-17 β and plasma triglyceride (r=0.619), cholesterol (r=0.446),

1068 Pantethine Supplementation and Hepatic Lipogenesis

NEFA (r= 0.634) concentrations, and the activities of FAS (r=0.233), NADP-MDH (r=0.223), CCE (r=0.276) in the liver of laying hens. Several works34,36)have also indicated that the specific activities of lipogenic-related enzymes in the chick liver were significantly increased by estrogen treatment. In the present experiment, the circulating estradiol-17 β concentration was altered in a parallel fashion with lipogenic-related enzyme activities and triglyceride content in the liver, and triglyceride, total cholesterol,(β-lipoprotein triglyceride and NEFA concentrations in the plasma. Similar results were observed in the previous report3). It is well-known that cholesterol serves as the precursor of estradiol-17 β in the ovary. Thus, from the results of the present experiment, the effects demonstrated by pantethine supplementation and dietary cereals on lipid accumulation and lipogenic-related enzyme activities in the liver of laving hens appear at least partially due to the altered total cholesterol concentration in the plasma, which in turn altered the concentration of estradiol-17 β.

From Table 4, it can be seen that, compared with laying hens fed the BS or BCS basal diet, those given the CS basal diet had higher concentration of estradiol-17 β in the plasma. Furthermore, pantethine supplementation to the CS basal diet significantly depressed estradiol-17 β concentration in the plasma of laying hens. However, no similarly significant effect was observed in the BS or CBS basal diet despite pantethine supplementation. Another possibility is that the decrease in metabolism or degradation of estradiol-17 β by liver cells may have occurred as a result of feeding the CS diet. Steroids, such as estrogen, are mainly metabolized through the cytochrome p 450-linked mixed function oxidase (MFO) system in hepatic endoplasmic reticulum37) . Pantethine supplementation to diets resulting in reduced concentration of estradiol-

17 β in the plasma may result in an increase in the activity of the MFO system in laying hens. It has been reported that the cholesterol content of the plasma and/or the egg is increased by the addition of cholesterol38), certain vegetable oils39), a number of surface active agents40), bile acids41) and diethylstibestrol42) to the diet. On the other hand, the cholesterol content of the plasma and/or the egg is reduced by increasing dietary levels of protein12), fiber43), inclusion of pectin, gums and scleroglucan13), nicotinic acid14) and large amounts of vitamin A15). It has been suggested that an increase in the egg cholesterol content must be preceded by an increase in the plasma cholesterol concentration as occurs in the diets containing both fat and cholesterol fed to hens44,45) However, other reports do not always concur with this finding46). In spite of these conflicts, the present experiment indicated that the decreased yolk cholesterol content

(mg/g yolk) paralled the decreased cholesterol and β-lipoprotein triglyceride concentrations in the plasma of laying hens. These results can be explained by the assumption that pantethine supplementation to diets causes a decrease in cholesterol synthesis in the liver and a decline in the plasma levels of cholesterol and lipoprotein which, being the main source of yolk lipids, consequently diminished yolk cholesterol content. Another possibility could be the increase of metabolism or excretion of cholesterol by the liver may have occurred as a results of pantethine supplementation

1069 HSU, TANAKA, OHTANI and COLLADO to diets. From Table 1, it can be seen that egg production and egg weight were increased by pantethine supplementation to diets. However, in one of our earlier reports 3), we found out that at a temperature of 31℃, pantethine supplementation to the diets had no effect on the laying hens'egg production rate and egg weight. Thus, based on these results, we are inclined to conclude that the ability of pantethine supplementation to improve egg production rate and egg weight is evident only when the environmental temperature is high, but not when it is low.

Acknowlegements

This work was supported in part by the Japanese Government through the Ministry of Education's Scientific Research Grant Number 62480081.

References

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1071 HSU, TANAKA, OHTANI and COLLADO

高温環境下におけるパンテチンの飼料への添加が産卵中の

鶏の肝臓での脂質合成に及ぼす影響について

許振忠・田中桂一・大谷滋・C.M. COLLADO**

岐阜大学農学部,岐阜市501-11 *中興大学農学院 ,中華民国台中市 * * SEARCA , College, Laguna, Philippines

31℃ の高環塩下で産卵中の鶏を炭水化物の異なる飼含量が低下した.また,いずれの飼料にパンテチンを料で飼育した時,これらの飼料へのパンテチン添加によ添加しても,血漿中のトリグリセリドおよび β-リポ蛋って肝臓中の脂質合成にどのような影響を及ぼすかを検白質-トリグリセリドの濃度は低下したが,総コレステ討した. ロール濃度はトウモロコシ配合および大麦配合飼料にパ飼料中炭水化物源として,トウモロコシ,大麦あるいンテチンを添加した時に,低下が観察された.また同時はトウモロコシと大麦を配合した飼料と,さらにそれぞに肝臓中の脂肪酸合成関連酵素およびHMG-CoA還れの飼料に200ppmパンテチンを添加した6種類の飼元酵素の活性が低下した.血漿中サイロキシン濃度はい料を配合した.そして280日齢の産卵中の鶏(白色レグづれの飼料給与区においてもパンテチン添加によって高ホーン種)を1区6羽ずつ6区に分け,それぞれの実験い値を示し,一方血漿中エストラジオール濃度は低下あ飼料を3週間給与した.実験期間中の環境温度は31± るいは低下する傾向にあった.産卵率,卵重および卵黄 3℃ とした. 重量は,いずれの飼料給与区においても,パンテチンのトウモロコシ配合および大麦配合飼料へのパンテチン添加給与によって,改善された.また,卵黄中の総コレ添加は肝臓重量(g/100g体重)を増加させたが,肝臓ステロール含量はいずれの飼料給与区においても,パン中トリグリセリド含量を低下させた.トウモロコシ配合テチン添加によって低下した. 飼料にパンテチンを添加すると肝臓中総コレステロール日畜会報,59(12):1059-1072,1988

日畜会報,59(12):1059-1072 1072 1988