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The Effect of Dried and Fresh Eggs on Plasma Cholesterol and Atherosclerosis in Chickens1
The Effect of Dried and Fresh Eggs on Plasma Cholesterol and Atherosclerosis in Chickens1 PAUL GRIMINGER and HANS FISHER Department of Nutrition, Rutgers University, New Brunswick, New Jersey 08904 (Received for publication June 28, 1985)
1986 Poultry Science 65:979-982 INTRODUCTION
Taylor et al. (1979) showed that oxidation products of cholesterol, fed to rabbits over short or long time periods, were angiotoxic. It was later demonstrated in the same laboratory that many of the oxidation products of cholesterol, which can be found in cholesterolcontaining foods such as powdered eggs, are cytotoxic for cultured rabbit aortic smooth muscle cells, whereas purified cholesterol is not (Peng et al., 1979). The authors of these reports proposed the hypothesis that certain autooxidation products of cholesterol are the probable prime cause of atherosclerotic lesions. Similar conclusions were drawn by Imai et al. (1980), who injected rabbits intravenously with oxygenated sterols. In the feedback mechanism inhibiting cholesterol synthesis, certain oxidative products of cholesterol, especially 7-keto- and 25hydroxycholesterol, are more effective than cholesterol itself. This was demonstrated by several researchers, including Bell et al. (1976) with cell cultures and Kandutsch et al. (1977) with mice. Working with chickens, Naber et al. (1985) also observed a significant reduction in hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting enzyme in the
1 New Jersey Agricultural Experiment Station Publication No. D-14408-1-85 supported by state funds.
synthesis of cholesterol, when dietary cholesterol oxides replaced cholesterol. Chickens are known to develop aortic lesions spontaneously, but dietary cholesterol will increase the severity of these lesions. If the hypothesis of the primary responsibility of oxidized derivatives of cholesterol for atherosclerosis is correct and generally applicable, the feeding of heat spray-dried powdered eggs should cause more severe atherosclerosis in chickens than the feeding of fresh eggs. The experiment reported here was undertaken to study this suggestion further. MATERIALS AND METHODS
Ninety Single Comb White Leghorn males were randomly assigned to six groups of 15 birds each at 6 weeks of age. They had been raised on a commercial starter diet for the first 4 weeks, followed by 2 weeks on the experimental, cholesterol-free control diet (Diet 3). At this time (6 weeks), the chickens were switched from heated starting cages to unheated growing cages and at 11 weeks of age were transferred to individual cages in a climatically controlled room. Two of the six experimental groups received a diet containing 20% heat-dried, whole egg powder (Treatment 1), two other groups received the equivalent of the egg powder in the form of fresh yolks and egg white solids (Treatment 2), and the last two groups received the egg protein equivalent, but not the fat or cholesterol, as supplemental
979
Downloaded from http://ps.oxfordjournals.org/ at Fudan University on May 5, 2015
ABSTRACT Oxidation products of cholesterol, which have been observed to be formed in powdered eggs and other dehydrated cholesterol-containing foods, have been suspected as the probable primary cause of atherosclerotic lesions. The feeding of powdered vs. fresh egg yolks to young male chickens up to 30 and 43 weeks of age, respectively, produced approximately the same increase in plasma cholesterol, liver fat, and liver cholesterol when compared to the feeding of a soybean-based cholesterol-free diet. Aortic atherosclerosis, however, was found to be more severe in a group of birds fed fresh egg yolks than in those fed powdered egg or the cholesterol-free diet. A previously demonstrated, enhanced feedback inhibition of cholesterol synthesis by oxidized cholesterol derivatives may at least partly explain these results. (Key words: atherosclerosis, plasma cholesterol, egg yolks, dietary cholesterol)
GRIMINGER AND FISHER
980
histopathological evaluation of the aortas as previously reported (Fisher et al, 1967). Total liver lipids were determined gravimetrically after chloroform:methanol (2:1) extraction and liver cholesterol was determined as described for plasma. Before killing the second group of birds (B replica), fecal cholesterol was determined on two occasions. RESULTS
At every measurement, plasma cholesterol levels were similar for the egg powder and the fresh egg groups but were significantly lower for the birds fed the cholesterol-free control diet (Table 2). Average values for all plasma cholesterol measurements were 165, 155, and 94 mg/100 ml for Treatments 1, 2, and 3, respectively. The differences between Treatment 3 and the other two treatments were statistically significant (P<.001). The same observations also held true for liver fat and liver cholesterol (Table 2). Both the visual and the histological scores showed greater atherosclerotic involvement for
TABLE 2. Liver fat and liver and plasma cholesterol response to fresh and dried egg yolks Dietary treatment 1
TABLE 1. Composition of the experimental diets
Ingredient
1
2
Soybean meal, dehulled Whole egg powder Egg white solids Mineral mix 2 Vitamin mix2 DL-Methionine Choline-chloride, 70% Olive oil Fiber 3 Corn starch Glucose monohydrate
25.0 20.0
Egg powder, Treatment 1
(wk)
Treatment 1
Age
3
30 43"
3
-(g/100g)25.0 45.0
4.4 .2 .2 .2 1.0 2.0
7.0 4.4 .2 .2 .2 1.0 2.0
4.4 .2 .2 .2 1.0 2.0
20.0 27.0
20.0 20.0
20.0 27.0
Fresh yolk, Treatment 2
Control, Treatment 3 2
Plasma cholesterol (mg/100 ml) 169 162
± 6.7 + 6.2
162 149
± 4.7 ± 4.3
± 2.4 ± 2.6
97 91
Liver fat (% of fresh liver) 30 43
12.0 ± .85 11.8 ± .63
11.6 ± .57 13.5 ± .71
5.0 ± .17 5.8 ± .16
Liver cholesterol (% of fresh liver) — 30 43
3.8 ± .42 2.8 ± .34
3.6 ± .36 3.8 ± .36
.5 ± .03 .4+ .02
1 Arithmetic average ± standard error of the mean (SE).
1 Fresh yolk added daily to basal diet to simulate yolk content of whole egg powder.
2 Control values differ significantly (P<.001) from "egg powder" and "fresh yolk" values for all measurements. The latter two treatments do not differ significantly from each other.
2 For (1980).
Griminger
3 Averages (three determinations 40 to 45 birds each) of birds killed at 6 months of age.
3 Solka Floe (The Brown Co., Berlin, NH) consisting of 99.5% pure cellulose.
"Averages (four determinations 40 to 45 birds each) of birds killed at 9 months of age.
composition,
see
Bauer
and
Downloaded from http://ps.oxfordjournals.org/ at Fudan University on May 5, 2015
soybean meal (Treatment 3). Between Weeks 6 and 9, the diets provided 2.5% more protein, but neither olive oil nor a separate source of fiber, than the diets fed the chickens after 9 weeks of age (for composition, see Table 1). For Treatment 2, fresh yolks, equivalent to the yolk contained in the egg powder of Treatment 1, were mixed into the feed daily; leftover feed from the previous day was weighed back, recorded, and discarded. For Treatments 1 and 3, feed consumption was recorded weekly. The birds were weighed at monthly intervals. Blood for plasma cholesterol determinations was drawn each month from half the chickens (alternatively from the A or B replica of each treatment). Blood was drawn from the brachial vein and cholesterol determined by the extraction procedure of Searcy and Berquist (1960) and the colorimetric method of Zlatkis et al. (195 3). The A replica birds were killed at 30 weeks of age, the B replica birds at 43 weeks, and the aortas and livers were removed. The aortas were cleaned of adhering tissue, cut open lengthwise, and graded visually for encroachment of the lumen by thickening of the intimal surface and atherosclerotic plaques, using a scale from 1 to 4, where a value of 1 denotes an essentially clean aorta, and a value of 4 denotes one practically occluded by plaques and intimal thickening. This was followed by
EGGS AND PLASMA CHOLESTEROL IN CHICKS
DISCUSSION
This experiment did not demonstrate that the feeding of a diet containing powdered eggs was more atherogenic than a diet providing equivalent amounts of lipids and cholesterol from fresh yolks. In fact, the fresh-yolk diet was somewhat more atherogenic. It also showed that the plasma cholesterol levels, which were similar for the two egg treatments, and much higher than for the cholesterol-free control group, did not correlate well with the degree of atherosclerotic involvement of the chickens. On
TABLE 3. Visual and histological aortic scores Dietary treatment Egg powder, Treatment 1
Fresh yolk, Treatment 2
30' 43
1.54 ±.15 1.46 ± .10
2.32 ±.20 1.94 ±.23
30 43
6.84 ±.62 5.75 ± .75
Age (wk)
Control, Treatment 3
Visual score 1.58 ± .13 1.62 ± .19
Histological score 8.14 ±.75 6.23 ± .98
the other hand, the similarity between the plasma and liver cholesterol levels, as well as between the fecal cholesterol excretions for Treatments 1 and 2 (the egg diets), suggested that similar amounts of dietary cholesterol were absorbed from the two diets. The differences in atherosclerotic response between heat-dried and fresh egg yolk cannot, therefore, be due to differences in rate of cholesterol absorption. It also cannot be assumed that the short exposure to air of the fresh yolks, which were added to the feed daily and consumed by the chickens within a short time, could have caused significant formation of oxidation products. Pike and Peng (1985) have shown that shell eggs and liquid yolks manifest an unusual stability toward lipid oxidation. It is of interest to note that recently Naber et al. (1985) observed that the feeding of oxidized cholesterol to laying hens produced a similar increase in blood cholesterol as the feeding of purified cholesterol, and that neither of the two cholesterol supplements had any significant effect on body weights, feed intake, or egg production. Assuming that heat spray-dried egg powder contains oxidation products of cholesterol, while fresh egg yolks do not, the conclusion that oxidized, rather than pure cholesterol, is responsible for atherosclerotic lesions was not substantiated by this investigation. To the contrary, it appears that the spray-drying process affected the yolk lipids in a manner that made them less atherogenic than the fresh product. The previously cited observations on an inhibitory effect by oxidation products of cholesterol on cholesterol synthesis may help to explain this phenomenon. It is also possible that the oxidative products affect atherosclerosis in more than one way. While they may have a direct atherogenic effect on aortic tissue, they may indirectly also have the opposite effect by reducing cholesterol synthesis, even if this is not expressed by lowered plasma cholesterol levels. The species of experimental animal, as well as the nature of the oxidation products, may all affect the results. Differentiation of the cholesterol-containing lipoproteins in future exploration of these phenomena would be of interest.
6.69 ± .39 5.75 ± .72 ACKNOWLEDGMENTS
'Scores for Treatment 2 differed significantly from scores for Treatments 1 and 3 (P<.01). Other differences were not statistically different.
The authors express their appreciation to W. G. Siller, Poultry Research Centre, Roslin
Downloaded from http://ps.oxfordjournals.org/ at Fudan University on May 5, 2015
the chickens fed fresh egg yolks, but little difference was noted between the egg powder and the control groups (Table 3). However, only the visual score differences of the 30week-old chickens reached statistical significance (P<.01). Food intake was highest for the control birds; this was not surprising, since their diet, low in fat, provided fewer calories per unit of weight than the other two diets. The fresh yolk-fed chickens also ate slightly more than the egg powder-fed groups. While the yolk-fed chickens were slightly heavier, these differences were significant (P<.02) only between Groups 2B and 3B at the final weighing. At the start of the experimental period (6 weeks of age) the chickens averaged 484 g; at 30 weeks, 2142 g; and at 43 weeks (B replica only), 2261 g. Feed consumption averaged 19 g/day. Fecal cholesterol was lower for the control group, except for one measurement. On the average, birds excreted between 34 and 92 mg cholesterol/day in 12 to 22 g of dry feces/bird/day.
981
982
GRIMINGER AND FISHER
Outstation, Midlothian, Scotland, for the microscopic assessment of the aortas in this study and to Anna Sekowski for technical assistance. REFERENCES
Downloaded from http://ps.oxfordjournals.org/ at Fudan University on May 5, 2015
Bauer, K. D., and P. Griminger, 1980. Effect of dietary carbohydrates and biotin level on cecal size and biotin concentration of growing chickens. Poultry Sci. 59:1493-1498. Bell, J. J., T. E. Sargeant, and J. A. Watson, 1976. Inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in hepatoma tissue culture cells by pure cholesterol and several cholesterol derivatives. J. Biol. Chem. 251: 1745-1758. Fisher, H., P. Griminger, and W. G. Siller, 1967. Effect of pectin on atherosclerosis in the cholesterol-fed rabbit. J. Atheroscler. Res. 7:381-386. Imai, H., N. T. Werthessen, V. Subramanyam, P. W. Lequesne, A. H. Soloway, and M. Kanisawa, 1980. Angiotoxicity of oxygenated sterols and possible precursors. Science 207:651—653. Kandutsch, A. A., H. J. Heiniger, and H. W. Chen,
1977. Effects of 25-hydroxycholesterol and 7-ketocholesterol, inhibitors of sterol synthesis, administered orally to mice. Biochim. Biophys. Acta 486:260-272. Naber, E. C , J. B. Allred, C. J. Winget, and A. E. Stock, 1985. Effect of cholesterol oxidation products on cholesterol metabolism in the laying hen. Poultry Sci. 64:675-680. Peng, S-K., P. Tham, C. B. Taylor, and B. Mikkelson, 1979. Cytotoxicity of oxidation derivatives of cholesterol on cultured aortic smooth muscle cells and their effect on cholesterol synthesis. Am. J.Clin. Nutr. 32:1033-1042. Pike, O. A., and I. C. Peng, 1985. Stability of shell egg and liquid yolk to lipid oxidation. Poultry Sci. 64:1470-1475. Searcy, R. L., and L. M. Berquist, 1960. A new color reaction for the quantitation of serum cholesterol. Clin. Chim. Acta 5:192-199. Taylor, C. B., S-K. Peng, N. J. Werthessen, P. Tham, and K. T. Lee, 1979. Spontaneously occurring angiotoxic derivatives of cholesterol. Am. J. Clin. Nutr. 32:40-57. Zlatkis, F., B. Zak, and A. J. Boyle, 1953. A new method for the direct determination of serum cholesterol. J. Lab. Clin. Med. 41:486-492.
1986 Poultry Science 65:979-982 INTRODUCTION
Taylor et al. (1979) showed that oxidation products of cholesterol, fed to rabbits over short or long time periods, were angiotoxic. It was later demonstrated in the same laboratory that many of the oxidation products of cholesterol, which can be found in cholesterolcontaining foods such as powdered eggs, are cytotoxic for cultured rabbit aortic smooth muscle cells, whereas purified cholesterol is not (Peng et al., 1979). The authors of these reports proposed the hypothesis that certain autooxidation products of cholesterol are the probable prime cause of atherosclerotic lesions. Similar conclusions were drawn by Imai et al. (1980), who injected rabbits intravenously with oxygenated sterols. In the feedback mechanism inhibiting cholesterol synthesis, certain oxidative products of cholesterol, especially 7-keto- and 25hydroxycholesterol, are more effective than cholesterol itself. This was demonstrated by several researchers, including Bell et al. (1976) with cell cultures and Kandutsch et al. (1977) with mice. Working with chickens, Naber et al. (1985) also observed a significant reduction in hepatic 3-hydroxy-3-methylglutaryl-coenzyme A reductase, the rate-limiting enzyme in the
1 New Jersey Agricultural Experiment Station Publication No. D-14408-1-85 supported by state funds.
synthesis of cholesterol, when dietary cholesterol oxides replaced cholesterol. Chickens are known to develop aortic lesions spontaneously, but dietary cholesterol will increase the severity of these lesions. If the hypothesis of the primary responsibility of oxidized derivatives of cholesterol for atherosclerosis is correct and generally applicable, the feeding of heat spray-dried powdered eggs should cause more severe atherosclerosis in chickens than the feeding of fresh eggs. The experiment reported here was undertaken to study this suggestion further. MATERIALS AND METHODS
Ninety Single Comb White Leghorn males were randomly assigned to six groups of 15 birds each at 6 weeks of age. They had been raised on a commercial starter diet for the first 4 weeks, followed by 2 weeks on the experimental, cholesterol-free control diet (Diet 3). At this time (6 weeks), the chickens were switched from heated starting cages to unheated growing cages and at 11 weeks of age were transferred to individual cages in a climatically controlled room. Two of the six experimental groups received a diet containing 20% heat-dried, whole egg powder (Treatment 1), two other groups received the equivalent of the egg powder in the form of fresh yolks and egg white solids (Treatment 2), and the last two groups received the egg protein equivalent, but not the fat or cholesterol, as supplemental
979
Downloaded from http://ps.oxfordjournals.org/ at Fudan University on May 5, 2015
ABSTRACT Oxidation products of cholesterol, which have been observed to be formed in powdered eggs and other dehydrated cholesterol-containing foods, have been suspected as the probable primary cause of atherosclerotic lesions. The feeding of powdered vs. fresh egg yolks to young male chickens up to 30 and 43 weeks of age, respectively, produced approximately the same increase in plasma cholesterol, liver fat, and liver cholesterol when compared to the feeding of a soybean-based cholesterol-free diet. Aortic atherosclerosis, however, was found to be more severe in a group of birds fed fresh egg yolks than in those fed powdered egg or the cholesterol-free diet. A previously demonstrated, enhanced feedback inhibition of cholesterol synthesis by oxidized cholesterol derivatives may at least partly explain these results. (Key words: atherosclerosis, plasma cholesterol, egg yolks, dietary cholesterol)
GRIMINGER AND FISHER
980
histopathological evaluation of the aortas as previously reported (Fisher et al, 1967). Total liver lipids were determined gravimetrically after chloroform:methanol (2:1) extraction and liver cholesterol was determined as described for plasma. Before killing the second group of birds (B replica), fecal cholesterol was determined on two occasions. RESULTS
At every measurement, plasma cholesterol levels were similar for the egg powder and the fresh egg groups but were significantly lower for the birds fed the cholesterol-free control diet (Table 2). Average values for all plasma cholesterol measurements were 165, 155, and 94 mg/100 ml for Treatments 1, 2, and 3, respectively. The differences between Treatment 3 and the other two treatments were statistically significant (P<.001). The same observations also held true for liver fat and liver cholesterol (Table 2). Both the visual and the histological scores showed greater atherosclerotic involvement for
TABLE 2. Liver fat and liver and plasma cholesterol response to fresh and dried egg yolks Dietary treatment 1
TABLE 1. Composition of the experimental diets
Ingredient
1
2
Soybean meal, dehulled Whole egg powder Egg white solids Mineral mix 2 Vitamin mix2 DL-Methionine Choline-chloride, 70% Olive oil Fiber 3 Corn starch Glucose monohydrate
25.0 20.0
Egg powder, Treatment 1
(wk)
Treatment 1
Age
3
30 43"
3
-(g/100g)25.0 45.0
4.4 .2 .2 .2 1.0 2.0
7.0 4.4 .2 .2 .2 1.0 2.0
4.4 .2 .2 .2 1.0 2.0
20.0 27.0
20.0 20.0
20.0 27.0
Fresh yolk, Treatment 2
Control, Treatment 3 2
Plasma cholesterol (mg/100 ml) 169 162
± 6.7 + 6.2
162 149
± 4.7 ± 4.3
± 2.4 ± 2.6
97 91
Liver fat (% of fresh liver) 30 43
12.0 ± .85 11.8 ± .63
11.6 ± .57 13.5 ± .71
5.0 ± .17 5.8 ± .16
Liver cholesterol (% of fresh liver) — 30 43
3.8 ± .42 2.8 ± .34
3.6 ± .36 3.8 ± .36
.5 ± .03 .4+ .02
1 Arithmetic average ± standard error of the mean (SE).
1 Fresh yolk added daily to basal diet to simulate yolk content of whole egg powder.
2 Control values differ significantly (P<.001) from "egg powder" and "fresh yolk" values for all measurements. The latter two treatments do not differ significantly from each other.
2 For (1980).
Griminger
3 Averages (three determinations 40 to 45 birds each) of birds killed at 6 months of age.
3 Solka Floe (The Brown Co., Berlin, NH) consisting of 99.5% pure cellulose.
"Averages (four determinations 40 to 45 birds each) of birds killed at 9 months of age.
composition,
see
Bauer
and
Downloaded from http://ps.oxfordjournals.org/ at Fudan University on May 5, 2015
soybean meal (Treatment 3). Between Weeks 6 and 9, the diets provided 2.5% more protein, but neither olive oil nor a separate source of fiber, than the diets fed the chickens after 9 weeks of age (for composition, see Table 1). For Treatment 2, fresh yolks, equivalent to the yolk contained in the egg powder of Treatment 1, were mixed into the feed daily; leftover feed from the previous day was weighed back, recorded, and discarded. For Treatments 1 and 3, feed consumption was recorded weekly. The birds were weighed at monthly intervals. Blood for plasma cholesterol determinations was drawn each month from half the chickens (alternatively from the A or B replica of each treatment). Blood was drawn from the brachial vein and cholesterol determined by the extraction procedure of Searcy and Berquist (1960) and the colorimetric method of Zlatkis et al. (195 3). The A replica birds were killed at 30 weeks of age, the B replica birds at 43 weeks, and the aortas and livers were removed. The aortas were cleaned of adhering tissue, cut open lengthwise, and graded visually for encroachment of the lumen by thickening of the intimal surface and atherosclerotic plaques, using a scale from 1 to 4, where a value of 1 denotes an essentially clean aorta, and a value of 4 denotes one practically occluded by plaques and intimal thickening. This was followed by
EGGS AND PLASMA CHOLESTEROL IN CHICKS
DISCUSSION
This experiment did not demonstrate that the feeding of a diet containing powdered eggs was more atherogenic than a diet providing equivalent amounts of lipids and cholesterol from fresh yolks. In fact, the fresh-yolk diet was somewhat more atherogenic. It also showed that the plasma cholesterol levels, which were similar for the two egg treatments, and much higher than for the cholesterol-free control group, did not correlate well with the degree of atherosclerotic involvement of the chickens. On
TABLE 3. Visual and histological aortic scores Dietary treatment Egg powder, Treatment 1
Fresh yolk, Treatment 2
30' 43
1.54 ±.15 1.46 ± .10
2.32 ±.20 1.94 ±.23
30 43
6.84 ±.62 5.75 ± .75
Age (wk)
Control, Treatment 3
Visual score 1.58 ± .13 1.62 ± .19
Histological score 8.14 ±.75 6.23 ± .98
the other hand, the similarity between the plasma and liver cholesterol levels, as well as between the fecal cholesterol excretions for Treatments 1 and 2 (the egg diets), suggested that similar amounts of dietary cholesterol were absorbed from the two diets. The differences in atherosclerotic response between heat-dried and fresh egg yolk cannot, therefore, be due to differences in rate of cholesterol absorption. It also cannot be assumed that the short exposure to air of the fresh yolks, which were added to the feed daily and consumed by the chickens within a short time, could have caused significant formation of oxidation products. Pike and Peng (1985) have shown that shell eggs and liquid yolks manifest an unusual stability toward lipid oxidation. It is of interest to note that recently Naber et al. (1985) observed that the feeding of oxidized cholesterol to laying hens produced a similar increase in blood cholesterol as the feeding of purified cholesterol, and that neither of the two cholesterol supplements had any significant effect on body weights, feed intake, or egg production. Assuming that heat spray-dried egg powder contains oxidation products of cholesterol, while fresh egg yolks do not, the conclusion that oxidized, rather than pure cholesterol, is responsible for atherosclerotic lesions was not substantiated by this investigation. To the contrary, it appears that the spray-drying process affected the yolk lipids in a manner that made them less atherogenic than the fresh product. The previously cited observations on an inhibitory effect by oxidation products of cholesterol on cholesterol synthesis may help to explain this phenomenon. It is also possible that the oxidative products affect atherosclerosis in more than one way. While they may have a direct atherogenic effect on aortic tissue, they may indirectly also have the opposite effect by reducing cholesterol synthesis, even if this is not expressed by lowered plasma cholesterol levels. The species of experimental animal, as well as the nature of the oxidation products, may all affect the results. Differentiation of the cholesterol-containing lipoproteins in future exploration of these phenomena would be of interest.
6.69 ± .39 5.75 ± .72 ACKNOWLEDGMENTS
'Scores for Treatment 2 differed significantly from scores for Treatments 1 and 3 (P<.01). Other differences were not statistically different.
The authors express their appreciation to W. G. Siller, Poultry Research Centre, Roslin
Downloaded from http://ps.oxfordjournals.org/ at Fudan University on May 5, 2015
the chickens fed fresh egg yolks, but little difference was noted between the egg powder and the control groups (Table 3). However, only the visual score differences of the 30week-old chickens reached statistical significance (P<.01). Food intake was highest for the control birds; this was not surprising, since their diet, low in fat, provided fewer calories per unit of weight than the other two diets. The fresh yolk-fed chickens also ate slightly more than the egg powder-fed groups. While the yolk-fed chickens were slightly heavier, these differences were significant (P<.02) only between Groups 2B and 3B at the final weighing. At the start of the experimental period (6 weeks of age) the chickens averaged 484 g; at 30 weeks, 2142 g; and at 43 weeks (B replica only), 2261 g. Feed consumption averaged 19 g/day. Fecal cholesterol was lower for the control group, except for one measurement. On the average, birds excreted between 34 and 92 mg cholesterol/day in 12 to 22 g of dry feces/bird/day.
981
982
GRIMINGER AND FISHER
Outstation, Midlothian, Scotland, for the microscopic assessment of the aortas in this study and to Anna Sekowski for technical assistance. REFERENCES
Downloaded from http://ps.oxfordjournals.org/ at Fudan University on May 5, 2015
Bauer, K. D., and P. Griminger, 1980. Effect of dietary carbohydrates and biotin level on cecal size and biotin concentration of growing chickens. Poultry Sci. 59:1493-1498. Bell, J. J., T. E. Sargeant, and J. A. Watson, 1976. Inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in hepatoma tissue culture cells by pure cholesterol and several cholesterol derivatives. J. Biol. Chem. 251: 1745-1758. Fisher, H., P. Griminger, and W. G. Siller, 1967. Effect of pectin on atherosclerosis in the cholesterol-fed rabbit. J. Atheroscler. Res. 7:381-386. Imai, H., N. T. Werthessen, V. Subramanyam, P. W. Lequesne, A. H. Soloway, and M. Kanisawa, 1980. Angiotoxicity of oxygenated sterols and possible precursors. Science 207:651—653. Kandutsch, A. A., H. J. Heiniger, and H. W. Chen,
1977. Effects of 25-hydroxycholesterol and 7-ketocholesterol, inhibitors of sterol synthesis, administered orally to mice. Biochim. Biophys. Acta 486:260-272. Naber, E. C , J. B. Allred, C. J. Winget, and A. E. Stock, 1985. Effect of cholesterol oxidation products on cholesterol metabolism in the laying hen. Poultry Sci. 64:675-680. Peng, S-K., P. Tham, C. B. Taylor, and B. Mikkelson, 1979. Cytotoxicity of oxidation derivatives of cholesterol on cultured aortic smooth muscle cells and their effect on cholesterol synthesis. Am. J.Clin. Nutr. 32:1033-1042. Pike, O. A., and I. C. Peng, 1985. Stability of shell egg and liquid yolk to lipid oxidation. Poultry Sci. 64:1470-1475. Searcy, R. L., and L. M. Berquist, 1960. A new color reaction for the quantitation of serum cholesterol. Clin. Chim. Acta 5:192-199. Taylor, C. B., S-K. Peng, N. J. Werthessen, P. Tham, and K. T. Lee, 1979. Spontaneously occurring angiotoxic derivatives of cholesterol. Am. J. Clin. Nutr. 32:40-57. Zlatkis, F., B. Zak, and A. J. Boyle, 1953. A new method for the direct determination of serum cholesterol. J. Lab. Clin. Med. 41:486-492.