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Food Intake Response of Genetically Selected High and Low-Weight Line Cockerels to Plasma Infusions from Fasted Fowl
Food Intake Response of Genetically Selected High and Low-Weight Line Cockerels to Plasma Infusions from Fasted Fowl M. P. LACY,1 H. P. VAN KREY, P. A. SKEWES, D. M. DENBOW, and P. B. SIEGEL Poultry Science Department, 2200 Animal Sciences Building, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
ABSTRACT Two experiments were conducted to determine if food intake of free-feeding chickens could be affected by infusions of plasma from fasted fowl. In the first experiment, chickens from two lines genetically selected for high or low body weight were infused intrahepatically with plasma collected from free-fed and fasted individuals from each line. Food intake of low-weight line birds was increased significantly by infusions of plasma from fasted high-weight line chickens when compared to food intake of low-weight line birds receiving plasma from free-fed low-weight line chickens. Food consumption in high-weight line birds was unaffected by any of the plasma treatments. In the second experiment, plasma from free-fed and fasted high-weight line chickens was infused intrahepatically into Single Comb White Leghorn cockerels. Again the birds receiving the plasma from the fasted fowl consumed significantly more food than those infused with plasma from free-fed fowl. The results of these experiments suggest that some property of plasma from fasted birds stimulates appetite. Selection for increased body weight may have intensified this hunger factor in high weight fowl. (Key words: food intake, hunger, plasma, hepatic infusion, chickens) 1987 Poultry Science 66:1224-1228 INTRODUCTION
Numerous studies have indicated that a satiety factor exists in the blood of sated animals. For example, plasma from sated goats and sheep reduced feeding in hungry rats when injected intraperitoneally (Baile, 1971). In both rats (Davis et al., 1969) and sheep (Seoane et al., 1972), transfusions from sated animals reduced food intake of fasted animals. Furthermore, transfusions from 1 to 4-h fasted rats into hungry recipients demonstrated that the longer the donors were fasted the less the food intake of recipients was depressed (Davis et al., 1971). A component, purported to play an inhibitory role in the regulation of food intake, has been isolated from human, rat, rabbit, and goose serum (Knoll, 1979; 1984). Skewes et al. (1986a,b) demonstrated that a constituent of chicken plasma inhibits food intake when injected intracerebroventricularly in the fowl. The existence of a blood-borne hunger factor to complement the well-documented satiety factor is equivocal. Food intake was stimulated in
'Present address: Extension Poultry Science Department, University of Georgia, Athens, GA 30602.
sated sheep cross-circulated with blood from fasted sheep (Seoane et al., 1972), and blood transfusions from 5-h fasted rats stimulated the food intake of recipient rats (Davis et al., 1971). However, neither plasma from fasted sheep nor blood from fasted goats had an effect on food intake of fasted rats when injected intraperitoneally (Baile, 1971). Similarly, Davis etal. (1969) reported that food intake of sated rats could not be elevated by transfusions from fasted rats. This has led some to question the role of hunger in food intake regulation. Recently, Strieker (1984) reviewed the literature on hunger and satiety in mammals and suggested there may be no stimulus for hunger. He reasoned that hunger may be due to the disappearance of inhibitory factors. Sykes (1983), after reviewing research on food intake in avian species, suggested that since birds appear to eat whenever food is available, there may be no requirement for short-term regulation of food intake. He postulated that birds eat continuously unless inhibited. Nevertheless, there is some evidence that hunger may influence food intake in the fowl. Feeding patterns suggest the relative importance of hunger and satiety in regulating food intake. Positive correlations between meal size and postmeal interval are believed to indicate that
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(Received for publication October 6, 1986)
PLASMA INFUSIONS AND FOOD INTAKE
MATERIALS AND METHODS
Experiment 1. This experiment was performed with genetically selected high and lowweight line fowl. It was hypothesized that chickens that are very dissimilar with respect to food consumption characteristics might respond differently to the treatments being investigated. Stock. The subjects used in the experiment were five high-weight (HW) line cockerels and five low-weight (LW) line cockerels 12 wk of age. These birds were progeny from parent lines of White Plymouth Rock chickens that had undergone 26 generations of divergent selection for body weight at 8 wk of age (Dunnington and Siegel, 1985). Body weights of the cockerels at the time of the experiment were 347 ± 45 g (mean ± standard deviation) for the LW and 991 ± 125 g for the HW line. Birds were housed in individual cages under continuous illumination with food and water available ad libitum. Cannulizations. To administer treatments intrahepatically, each bird was anesthetized with sodium pentobarbital (25 mg/kg body weight), and an indwelling Silastic® (Dow Corning Corp., Midland, MI) cannula(i.d. .76mm,o.d. 1.65 mm) was implanted into the hepatic portal circulation (Lacy et al., 1985). The cannula was exteriorized dorsally in the midthoracic region and was attached to a swivel system at the top of the cage so that an infusion could be made without handling the bird. The cockerels were
allowed 4 to 6 days to recover following surgery before the experiment was begun. Cannulae were flushed daily with 1 mL of heparinized saline (1,000 USP units/mL) to maintain patency. Treatments. Cockerels from both lines were infused with plasma and saline treatments via the intrahepatic cannulae. The treatments consisted of plasma collected from ad libitum-fed LW line chickens, 24-h fasted LW line chickens, ad libitum-fed HW line chickens, 24-h fasted HW line chickens and saline. The volume of the infusions was 20 mL/kg body weight, resulting in 7 mL for the LW line and 20 mL for the HW line cockerels. Infusions were made over a 30-min period using a multichannel syringe pump. Subjects were provided free access to food before and after but not during infusion. Experimental Design and Analysis. The five treatments were tested in each of the five HW and five LW line cockerels using a Latin square design in which birds and days were the blocking factors. Tests were conducted between 0800 and 1200 h with 24 h separating each test. Food intake of the birds was. measured hourly for 3 h post-infusion. Cumulative food intake at each hour was transformed to natural logarithms and tested within a line for day, bird, and treatment effects using analysis of variance. Duncan's multiple range test was used to examine significant (P=£.05) treatment differences. Experiment 2. The second experiment was conducted with Single Comb White Leghorn (SCWL) cockerels. The intent was to determine if stimulation of food intake could also be elicited in a light-breed commercial chicken. The subjects used in this experiment were eight SCWL cockerels 11 wk of age. Body weight at this age was 587 ± 54 g (mean ± standard deviation). Cockerels were maintained as described in the previous experiment. Birds were anesthetized and cannulated as in Experiment 1. Treatments. As only plasma from HW birds influenced food intake in Experiment 1, the plasma infused in this experiment was collected from 24-h fasted HW and ad libitum-fed HW chickens. A saline treatment was included as before, and an uninjected control was added. Volume of the plasma and saline infusates was 10 mL. The infusions were carried out as outlined in Experiment 1. Experimental Design and Analysis. The four treatments were tested in each of the eight cockerels using a replicated Latin square design. Tests were again conducted between 0800 to 1200 h with 24 h separating tests. Food intake
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hunger mechanisms initiate feeding while positive correlations between meal size and premeal interval suggest that satiety mechanisms control food intake (Le Magnen and Tallon, 1966). Studies with rats have shown meal size to be positively correlated with premeal but not postmeal interval (Le Magnen and Tallon, 1963; 1966), implying that sateity mechanisms are primary. In the chicken, both premeal and postmeal interval are positively correlated with meal size; however, postmeal correlations have been demonstrated more frequently (Duncan etal., 1970; Clifton, 1979a,b; Barbato et al., 1980). Thus, in fowl, unlike the rat, hunger may be important in food intake regulation. The objective of this study was to determine if food intake of free-feeding chickens could be stimulated by intrahepatic infusions of plasma collected from fasted chickens. Such a stimulation would suggest a blood-borne hunger factor exists in chicken plasma.
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LACY ET AL.
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RESULTS AND DISCUSSION
Experiment 1. At 3 h, post-infusion food intake of the LW birds treated with plasma from the fasted HW line birds was greater (P=s.05) than that of LW line birds infused with plasma from the other sources (Table 1). Results of the saline treatment did not differ from those of any of the plasma treatments. The response to saline was disturbing, for the purpose of the saline treatment was to establish whether stimulation of food intake was due to the presence of a hunger factor or to the absence of satiety factors. Since the saline treatment did not differ from the plasma treatments, the question remains unanswered. Nevertheless, the most important comparison in this experiment, the one between plasma from fed and fasted birds, showed that the food intake of LW birds was stimulated by plasma from fasted HW donors, suggesting the presence of a hunger factor. Seoaneefa/. (1972) obtained similar results with sheep; transfusions from fasted sheep increased food intake in sated sheep. Barbato et al. (1980) reported that the major difference in feeding behavior of HW and LW line birds is that HW line birds consume more meals with a concomitant decrease in the between meal interval. Thus, HW birds appear to be in a constant state of hunger, a feeding characteristic that suggests if a hunger factor does exist in fowl plasma, it is more prevalent in faster growing lines of chickens. Our results are congruent with this hypothesis.
TABLE 1. Mean cumulative food intake by ad libitum-fed cockerels 1, 2, and 3 h after intrahepatic infusions of plasma from fed and fasted high^weight (HW) and low^weight (LW) line birds LW Line
HW Line
source
lh
2h
3h
LW Fasted LW Fed HW Fasted HW Fed Saline
5.8 6.4 8.4 5.8 7.4
6.4 7.6 11.4 7.8 8.6
8.6 b 9.0 b 13.6 a 9.6b 10.6 a b
SEM1
1.1
1.1
1.1
- (g)
lh
2h
3h
18.4 18.4 18.4 14.6 21.1
26.0 24.6 25.8 20.2 26.8
29.0 26.6 28.4 26.4 29.4
2.1
2.3
2.6
-
a 'b Means within a column with differing superscripts are significantly different (P<.05). 1
Standard error of the mean.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
When plasma and saline treatments were infused into the HW line cockerels, no significant differences between any of the treatments were observed. The failure of plasma from fasted chickens to enhance feeding when infused into HW birds was not surprising. It has been shown consistently that meat-type chickens are less susceptible to factors controlling food intake than are light-breed chickens. Burkhart et al. (1983) demonstrated that ventromedial hypothalamic lesions caused hyperphagia in LW hens but had no effect in HW line hens. Lacy et al. (1982) found that the intubation of tyrosine stimulated food intake in light-breed chickens but did not increase food consumption in heavy-breed birds. Nir et al. (1978) demonstrated that heavy-breed birds normally consumed food at a volume close to the total capacity of their gastrointestinal tract (87%), while light-breed birds ate more to satisfy metabolic needs and normally filled only a relatively small percentage (30%) of their gastrointestinal capacity. Siegel (1978) concluded that genetic variation for increased growth was still present in the HW line, but physiological limits were blocking its expression. Since the property that stimulated food intake seems to be more prevalent in plasma of fasted HW line birds, it appears the diminution of appetite regulation observed in the HW birds is the result of insensitivity of food intake control mechanisms or receptors rather than a lack of appropriate signals. This suggestion has been made in previous studies. Burkhart et al. (1983) proposed that selection for increased body weight had resulted in a desensitization of hypothalamic satiety mechanisms; hepatic satiety mechanisms in heavy-breed birds have also
was measured and analyzed as in the previous experiment.
PLASMA INFUSIONS AND FOOD INTAKE TABLE 2. Mean cumulative food intake by ad libitumfed SCWL cockerels I, 2, and 3 h after intrahepatic infusions of plasma from fed and fasted high^weigbt (HW) line birds 1h
2h
3h
HW Fasted HWFed Saline Uninjected SEM1
5.6 3.1 3.8 6.8 .9
8.5 a b 4.9 C 5.1bc 10.5 a 1.2
(g) 11.6 a b 6.1b 7.6 a b 13.8 a 1.8
Means within a column with differing superscripts are significantly different (P<,05). 1
Standard error of the mean.
been theorized to be less sensitive than those in light-breed birds (Lacy et al., 1985). Experiment 2. Again, more food was consumed by subjects infused with plasma from the 24-h fasted HW birds than those infused with plasma from ad libitum-fed HW line birds, with the effect being significant at 2 h post-intubation (Table 2). As in Experiment 1, results of the saline treatment did not differ significantly from those of either plasma treatment. The uninjected control subjects, however, consumed significantly more food than subjects treated with either saline or plasma from ad libitum-fed HW line chickens, indicating that the infusion process itself may have inhibited food intake. In previous experiments (Lacy etal., 1985; 1986), intrahepatic saline infusions in volumes similar to those used in the present experiment had no affect on food intake, whereas larger volumes did affect food intake. There are several possible interpretations of the results obtained in this experiment. If the saline treatment did indeed inhibit food intake, then plasma from fasted birds may not have stimulated appetite as indicated in Experiment 1. Possibly, differences in food intake were due to inhibition of appetite produced by plasma from the ad libitum-fed birds. However, it does not seem likely that plasma from fed birds would have any major inhibitory effect on the food intake of similarly fed birds. Perhaps the most proper and conservative interpretation of these results is that appetite in the chicken is controlled by both hunger and satiety mechanisms. As previously discussed, there is considerable support for this hypothesis (Le Magnon and Tallon,
1966; Duncan et al., 1970; Clifton, 1979a,b; Barbato etal., 1980). The second experiment did not clarify whether the possible stimulatory property of the plasma from fasted birds was due to a hunger factor(s) or lack of satiety factor(s). Skewes et al. (1986b), using gel filtration techniques, characterized a low molecular weight fraction in plasma of ad libitum-fed fowl that inhibited food intake when administered centrally. Perhaps partitioning of the plasma from the HWfasted birds would provide information concerning the nature of the putative stimulatory mechanism operating here. In conclusion, the results of these experiments suggest that some property of plasma from fasted birds stimulates food intake. The questions of whether this putative stimulatory property is a humoral factor or whether satiety factors are absent remain unanswered. ACKNOWLEDGMENTS
This study was supported in part by a grant from the John Lee Pratt Animal Nutrition Program. REFERENCES Baile, C. A., 1971. Control of feed intake and fat depots. J. Dairy Sci. 54:564-582. Barbato, G. F., J. A. Cherry, P. B. Siegel, and H. P. Van Krey, 1980. Quantitative analysis of the feeding behavior of four populations of chickens. Physiol. Behav. 25:885-891. Burkhart, C. A., J. A. Cherry, H. P. Van Krey, and P. B. Siegel, 1983. Genetic selection for growth rate alters hypothalamic satiety mechanisms in chickens. Behav. Gen. 3:295-300. Clifton, P. G., 1979a. Temporal patterns of feeding in the domestic chick. I. ad libitum. Anim. Behav. 27:811820. Clifton, P. G., 1979b. Temporal patterns of feeding in the domestic chick. II. An operant situation. Anim. Behav. 27:821-828. Davis, J. D., C. S. Campbell, R. J. Gallagher, and M. A. Zurakov, 1971. Disappearance of a humoral satiety factor during food deprivation. J. Comp. Physiol. Psych. 75:476-482. Davis, J. D., R. J. Gallagher, R. F. Ladove, and A. J. Turausky, 1969. Inhibition of food intake by a humoral factor. J. Comp. Physiol. Psych. 67:407-414. Duncan, I.J.H., A. R. Horn, B. O. Hughes, and D.G.M. Wood-Gush, 1970. The pattern of food intake in female brown leghorn fowls as recorded in a Skinner box. Anim. Behav. 18:245-255. Dunnington, E. A., and P. B. Siegel, 1985. Long-term selection for 8-wk body weight in chickens: Direct and correlated responses. Theor. Appl. Genet. 71:305313. Knoll, J., 1979. Satietin: A highly potent anorexogenic sub-
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Plasma source
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LACY ET AL. in young chicks of light and heavy breeds. Br. J. Nutr. 39:27-35. Seoane, J. R., C. A. Baile, andF. H. Martin, 1972. Humoral factors modifying feeding behavior of sheep. Physiol. Behav. 8:993-995. Siegel, P. B., 1978. Response to twenty generations of selection for body weight in chickens. Proc. XVI World's Poult. Congr. 10:1761-1772. Skewes, P. A., D. M. Denbow, M. P. Lacy, and H. P. Van Krey, 1986a. Alteration of food intake following intracerebroventricular administration of plasma from free-feeding domestic fowl. Physiol. Behav. 36:295299. Skewes, P. A., D. M. Denbow, M. P. Lacy, and H. P. Van Krey, 1986b. Reduced food intake following intracerebroventricular administration of a low molecular weight fraction of plasma from free-feeding fowl. Poultry Sci. 65:172-176. Strieker, E. M., 1984. Biological bases of hunger and satiety: Therapeutic implications. Nutr. Rev. '42:333340. Sykes, A. H., 1983. Food intake and its control. Pages 1-29 in: Physiology and biochemistry of the Domestic Fowl. Vol. 4. B. M. Freeman, ed. Academic Press, London, UK.
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stance in human serum. Physiol. Behav. 23:497-502. Knoll, J., 1984. Satietin, a blood-borne anorectic glycoprotein, as the putative rate-limiting satiety signal in the negative feed-back of food intake. Z. Ernaehrungswiss. 23:85-103. Lacy, M. P., H. P. Van Krey, D. M. Denbow, P. B. Siegel, and J. A. Cherry, 1982. Amino acid regulation of food intake in domestic fowl. Nutr. Behav. 1:65-74. Lacy, M. P., H. P. Van Krey, P. A. Skewes, and D. M. Denbow, 1985. Effect of intrahepatic glucose infusions on feeding in heavy and light breed chicks. Poultry Sci. 64:751-756. Lacy, M. P., H. P. Van Krey, P. A. Skewes, and D. M. Denbow, 1986. Food intake in the domestic fowl: Effect of intrahepatic lipid and amino acid infusions. Physiol. Behav. 36:533-538. Le Magnen, J., and S. Tallon, 1963. Enregistrement et analyse preeliminaire de la periodicate alimentaire soontanee chez le rat blanc. J. Physiol. (Paris) 55:286297. Le Magnen, J., and S. Tallon, 1966. L'effect du jeune prealable sur les caracteristiques temporelles de la prise d'alimento chez le rat. J. Physiol. (Paris) 60:143-154. Nir, I., Z. Nitsan, Y. Dror, and N. Shapira, 1978. Influence of overfeeding on growth, obesity, and intestinal tract
ABSTRACT Two experiments were conducted to determine if food intake of free-feeding chickens could be affected by infusions of plasma from fasted fowl. In the first experiment, chickens from two lines genetically selected for high or low body weight were infused intrahepatically with plasma collected from free-fed and fasted individuals from each line. Food intake of low-weight line birds was increased significantly by infusions of plasma from fasted high-weight line chickens when compared to food intake of low-weight line birds receiving plasma from free-fed low-weight line chickens. Food consumption in high-weight line birds was unaffected by any of the plasma treatments. In the second experiment, plasma from free-fed and fasted high-weight line chickens was infused intrahepatically into Single Comb White Leghorn cockerels. Again the birds receiving the plasma from the fasted fowl consumed significantly more food than those infused with plasma from free-fed fowl. The results of these experiments suggest that some property of plasma from fasted birds stimulates appetite. Selection for increased body weight may have intensified this hunger factor in high weight fowl. (Key words: food intake, hunger, plasma, hepatic infusion, chickens) 1987 Poultry Science 66:1224-1228 INTRODUCTION
Numerous studies have indicated that a satiety factor exists in the blood of sated animals. For example, plasma from sated goats and sheep reduced feeding in hungry rats when injected intraperitoneally (Baile, 1971). In both rats (Davis et al., 1969) and sheep (Seoane et al., 1972), transfusions from sated animals reduced food intake of fasted animals. Furthermore, transfusions from 1 to 4-h fasted rats into hungry recipients demonstrated that the longer the donors were fasted the less the food intake of recipients was depressed (Davis et al., 1971). A component, purported to play an inhibitory role in the regulation of food intake, has been isolated from human, rat, rabbit, and goose serum (Knoll, 1979; 1984). Skewes et al. (1986a,b) demonstrated that a constituent of chicken plasma inhibits food intake when injected intracerebroventricularly in the fowl. The existence of a blood-borne hunger factor to complement the well-documented satiety factor is equivocal. Food intake was stimulated in
'Present address: Extension Poultry Science Department, University of Georgia, Athens, GA 30602.
sated sheep cross-circulated with blood from fasted sheep (Seoane et al., 1972), and blood transfusions from 5-h fasted rats stimulated the food intake of recipient rats (Davis et al., 1971). However, neither plasma from fasted sheep nor blood from fasted goats had an effect on food intake of fasted rats when injected intraperitoneally (Baile, 1971). Similarly, Davis etal. (1969) reported that food intake of sated rats could not be elevated by transfusions from fasted rats. This has led some to question the role of hunger in food intake regulation. Recently, Strieker (1984) reviewed the literature on hunger and satiety in mammals and suggested there may be no stimulus for hunger. He reasoned that hunger may be due to the disappearance of inhibitory factors. Sykes (1983), after reviewing research on food intake in avian species, suggested that since birds appear to eat whenever food is available, there may be no requirement for short-term regulation of food intake. He postulated that birds eat continuously unless inhibited. Nevertheless, there is some evidence that hunger may influence food intake in the fowl. Feeding patterns suggest the relative importance of hunger and satiety in regulating food intake. Positive correlations between meal size and postmeal interval are believed to indicate that
1224
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
(Received for publication October 6, 1986)
PLASMA INFUSIONS AND FOOD INTAKE
MATERIALS AND METHODS
Experiment 1. This experiment was performed with genetically selected high and lowweight line fowl. It was hypothesized that chickens that are very dissimilar with respect to food consumption characteristics might respond differently to the treatments being investigated. Stock. The subjects used in the experiment were five high-weight (HW) line cockerels and five low-weight (LW) line cockerels 12 wk of age. These birds were progeny from parent lines of White Plymouth Rock chickens that had undergone 26 generations of divergent selection for body weight at 8 wk of age (Dunnington and Siegel, 1985). Body weights of the cockerels at the time of the experiment were 347 ± 45 g (mean ± standard deviation) for the LW and 991 ± 125 g for the HW line. Birds were housed in individual cages under continuous illumination with food and water available ad libitum. Cannulizations. To administer treatments intrahepatically, each bird was anesthetized with sodium pentobarbital (25 mg/kg body weight), and an indwelling Silastic® (Dow Corning Corp., Midland, MI) cannula(i.d. .76mm,o.d. 1.65 mm) was implanted into the hepatic portal circulation (Lacy et al., 1985). The cannula was exteriorized dorsally in the midthoracic region and was attached to a swivel system at the top of the cage so that an infusion could be made without handling the bird. The cockerels were
allowed 4 to 6 days to recover following surgery before the experiment was begun. Cannulae were flushed daily with 1 mL of heparinized saline (1,000 USP units/mL) to maintain patency. Treatments. Cockerels from both lines were infused with plasma and saline treatments via the intrahepatic cannulae. The treatments consisted of plasma collected from ad libitum-fed LW line chickens, 24-h fasted LW line chickens, ad libitum-fed HW line chickens, 24-h fasted HW line chickens and saline. The volume of the infusions was 20 mL/kg body weight, resulting in 7 mL for the LW line and 20 mL for the HW line cockerels. Infusions were made over a 30-min period using a multichannel syringe pump. Subjects were provided free access to food before and after but not during infusion. Experimental Design and Analysis. The five treatments were tested in each of the five HW and five LW line cockerels using a Latin square design in which birds and days were the blocking factors. Tests were conducted between 0800 and 1200 h with 24 h separating each test. Food intake of the birds was. measured hourly for 3 h post-infusion. Cumulative food intake at each hour was transformed to natural logarithms and tested within a line for day, bird, and treatment effects using analysis of variance. Duncan's multiple range test was used to examine significant (P=£.05) treatment differences. Experiment 2. The second experiment was conducted with Single Comb White Leghorn (SCWL) cockerels. The intent was to determine if stimulation of food intake could also be elicited in a light-breed commercial chicken. The subjects used in this experiment were eight SCWL cockerels 11 wk of age. Body weight at this age was 587 ± 54 g (mean ± standard deviation). Cockerels were maintained as described in the previous experiment. Birds were anesthetized and cannulated as in Experiment 1. Treatments. As only plasma from HW birds influenced food intake in Experiment 1, the plasma infused in this experiment was collected from 24-h fasted HW and ad libitum-fed HW chickens. A saline treatment was included as before, and an uninjected control was added. Volume of the plasma and saline infusates was 10 mL. The infusions were carried out as outlined in Experiment 1. Experimental Design and Analysis. The four treatments were tested in each of the eight cockerels using a replicated Latin square design. Tests were again conducted between 0800 to 1200 h with 24 h separating tests. Food intake
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
hunger mechanisms initiate feeding while positive correlations between meal size and premeal interval suggest that satiety mechanisms control food intake (Le Magnen and Tallon, 1966). Studies with rats have shown meal size to be positively correlated with premeal but not postmeal interval (Le Magnen and Tallon, 1963; 1966), implying that sateity mechanisms are primary. In the chicken, both premeal and postmeal interval are positively correlated with meal size; however, postmeal correlations have been demonstrated more frequently (Duncan etal., 1970; Clifton, 1979a,b; Barbato et al., 1980). Thus, in fowl, unlike the rat, hunger may be important in food intake regulation. The objective of this study was to determine if food intake of free-feeding chickens could be stimulated by intrahepatic infusions of plasma collected from fasted chickens. Such a stimulation would suggest a blood-borne hunger factor exists in chicken plasma.
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1226
RESULTS AND DISCUSSION
Experiment 1. At 3 h, post-infusion food intake of the LW birds treated with plasma from the fasted HW line birds was greater (P=s.05) than that of LW line birds infused with plasma from the other sources (Table 1). Results of the saline treatment did not differ from those of any of the plasma treatments. The response to saline was disturbing, for the purpose of the saline treatment was to establish whether stimulation of food intake was due to the presence of a hunger factor or to the absence of satiety factors. Since the saline treatment did not differ from the plasma treatments, the question remains unanswered. Nevertheless, the most important comparison in this experiment, the one between plasma from fed and fasted birds, showed that the food intake of LW birds was stimulated by plasma from fasted HW donors, suggesting the presence of a hunger factor. Seoaneefa/. (1972) obtained similar results with sheep; transfusions from fasted sheep increased food intake in sated sheep. Barbato et al. (1980) reported that the major difference in feeding behavior of HW and LW line birds is that HW line birds consume more meals with a concomitant decrease in the between meal interval. Thus, HW birds appear to be in a constant state of hunger, a feeding characteristic that suggests if a hunger factor does exist in fowl plasma, it is more prevalent in faster growing lines of chickens. Our results are congruent with this hypothesis.
TABLE 1. Mean cumulative food intake by ad libitum-fed cockerels 1, 2, and 3 h after intrahepatic infusions of plasma from fed and fasted high^weight (HW) and low^weight (LW) line birds LW Line
HW Line
source
lh
2h
3h
LW Fasted LW Fed HW Fasted HW Fed Saline
5.8 6.4 8.4 5.8 7.4
6.4 7.6 11.4 7.8 8.6
8.6 b 9.0 b 13.6 a 9.6b 10.6 a b
SEM1
1.1
1.1
1.1
- (g)
lh
2h
3h
18.4 18.4 18.4 14.6 21.1
26.0 24.6 25.8 20.2 26.8
29.0 26.6 28.4 26.4 29.4
2.1
2.3
2.6
-
a 'b Means within a column with differing superscripts are significantly different (P<.05). 1
Standard error of the mean.
Downloaded from http://ps.oxfordjournals.org/ at Rutgers University Libraries/Technical Services on April 13, 2015
When plasma and saline treatments were infused into the HW line cockerels, no significant differences between any of the treatments were observed. The failure of plasma from fasted chickens to enhance feeding when infused into HW birds was not surprising. It has been shown consistently that meat-type chickens are less susceptible to factors controlling food intake than are light-breed chickens. Burkhart et al. (1983) demonstrated that ventromedial hypothalamic lesions caused hyperphagia in LW hens but had no effect in HW line hens. Lacy et al. (1982) found that the intubation of tyrosine stimulated food intake in light-breed chickens but did not increase food consumption in heavy-breed birds. Nir et al. (1978) demonstrated that heavy-breed birds normally consumed food at a volume close to the total capacity of their gastrointestinal tract (87%), while light-breed birds ate more to satisfy metabolic needs and normally filled only a relatively small percentage (30%) of their gastrointestinal capacity. Siegel (1978) concluded that genetic variation for increased growth was still present in the HW line, but physiological limits were blocking its expression. Since the property that stimulated food intake seems to be more prevalent in plasma of fasted HW line birds, it appears the diminution of appetite regulation observed in the HW birds is the result of insensitivity of food intake control mechanisms or receptors rather than a lack of appropriate signals. This suggestion has been made in previous studies. Burkhart et al. (1983) proposed that selection for increased body weight had resulted in a desensitization of hypothalamic satiety mechanisms; hepatic satiety mechanisms in heavy-breed birds have also
was measured and analyzed as in the previous experiment.
PLASMA INFUSIONS AND FOOD INTAKE TABLE 2. Mean cumulative food intake by ad libitumfed SCWL cockerels I, 2, and 3 h after intrahepatic infusions of plasma from fed and fasted high^weigbt (HW) line birds 1h
2h
3h
HW Fasted HWFed Saline Uninjected SEM1
5.6 3.1 3.8 6.8 .9
8.5 a b 4.9 C 5.1bc 10.5 a 1.2
(g) 11.6 a b 6.1b 7.6 a b 13.8 a 1.8
Means within a column with differing superscripts are significantly different (P<,05). 1
Standard error of the mean.
been theorized to be less sensitive than those in light-breed birds (Lacy et al., 1985). Experiment 2. Again, more food was consumed by subjects infused with plasma from the 24-h fasted HW birds than those infused with plasma from ad libitum-fed HW line birds, with the effect being significant at 2 h post-intubation (Table 2). As in Experiment 1, results of the saline treatment did not differ significantly from those of either plasma treatment. The uninjected control subjects, however, consumed significantly more food than subjects treated with either saline or plasma from ad libitum-fed HW line chickens, indicating that the infusion process itself may have inhibited food intake. In previous experiments (Lacy etal., 1985; 1986), intrahepatic saline infusions in volumes similar to those used in the present experiment had no affect on food intake, whereas larger volumes did affect food intake. There are several possible interpretations of the results obtained in this experiment. If the saline treatment did indeed inhibit food intake, then plasma from fasted birds may not have stimulated appetite as indicated in Experiment 1. Possibly, differences in food intake were due to inhibition of appetite produced by plasma from the ad libitum-fed birds. However, it does not seem likely that plasma from fed birds would have any major inhibitory effect on the food intake of similarly fed birds. Perhaps the most proper and conservative interpretation of these results is that appetite in the chicken is controlled by both hunger and satiety mechanisms. As previously discussed, there is considerable support for this hypothesis (Le Magnon and Tallon,
1966; Duncan et al., 1970; Clifton, 1979a,b; Barbato etal., 1980). The second experiment did not clarify whether the possible stimulatory property of the plasma from fasted birds was due to a hunger factor(s) or lack of satiety factor(s). Skewes et al. (1986b), using gel filtration techniques, characterized a low molecular weight fraction in plasma of ad libitum-fed fowl that inhibited food intake when administered centrally. Perhaps partitioning of the plasma from the HWfasted birds would provide information concerning the nature of the putative stimulatory mechanism operating here. In conclusion, the results of these experiments suggest that some property of plasma from fasted birds stimulates food intake. The questions of whether this putative stimulatory property is a humoral factor or whether satiety factors are absent remain unanswered. ACKNOWLEDGMENTS
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