524
Differences in Growth Hormone and Prolactin Secretion Associated with Environmental Temperature and Energy Intake 1
2
Summary The combined effects of environmental temperature and level of energy intake on plasma concentrations of growth hormone (GH) and prolactin (PRL) have been investigated in 14 week old pigs acclimated to 35 or 10 °C on a high (H) or low (L) energy intake (H = 2L). Measurements were made at 15 min intervals between 08.00 and 18.00 hours, after feeding at 17.00 hours on the previous day. Mean values of G H were greater in pigs on the L than H intake and there was a tendency for values to be higher at 35 than 10 °C. However, there was wide individual vaiation within each treatment group and the differences were not statistically significant. Mean PRL concentrations were greater at 35 than 10 °C (P < 0.05). It is concluded that circulating levels of plasma G H do not have a major role in maintaining the differences in growth and morphology of young pigs kept in widely different environmental conditions. However, these differences could be related at least in part to the GH-like properties of PRL.
With respect to energy intake, plasma IGF-I concentrations decline on a low intake (Clemmons, Klibanski, Underwood, McArthur, Ridgway, Beitins and Van Wyk 1981; Phillips, Goldstein and Gavin 1988). By contrast, G H tends to be inversely related to level of nutrition (Bassett, Weston and Hogan 1971) and increases with time after feeding (McCusker, Wangsness, Griel and Kavanaugh 1985). It was therefore of relevance to investigate the extent to which energy intake interacts with any effects of environmental temperature on G H secretion. There is an inter-relation between G H and prolactin (PRL) in the regulation of growth. Moreover, there is some evidence of seasonal variation in PRL secretion in wild pigs (Ravault, Martinat-Botte, Mauget, Martinat, Locatelli and Bariteau 1982) which could be a response to both environmental temperature and photoperiod. In the present investigation, therefore, the secretory patterns of G H and PRL have been investigated in young pigs living at 35 or 10 °C on a high or low level of energy intake. Materials and Methods
Key words Growth Hormone — Prolactin — Temperature — Energylntake
Introduction Acclimation of young pigs to a warm or cold temperature and a high or low level of energy intake has a striking influence on growth and morphology (Weaver and Ingram 1969; Dauncey, Ingram, Walters and Legge 1983; Ingram and Dauncey 1986). At both temperatures, those on a low intake are smaller than those on a high intake. Animals living in the warm have longer limbs, larger ears and a longer snout compared with littermates in the cold on the same food intake. More recently, plasma concentrations of insulin-like growth factor-I (IGF-I) have been found to be greater in animals living in the warm than the cold and on a high than a low energy intake (Dauncey, Shakespear, Rudd and Ingram 1990). It was therefore decided to investigate whether there are any differences in the plasma concentration of G H in animals living in a warm or cold environment under conditions of controlled energy intake. Horm.metab.Res.22(1990)524-527 © Georg Thieme Verlag Stuttgart • New York
Animals Six litters of pigs from the Large White herd kept at the Institute (Cambridge) were used. For each litter, four males were taken from the sow at 14 days of age and kept at 30 °C for 3 days. Animals were then separated into two groups and housed singly in wire cages. For one group the environmental temperature was increased to 35 °C and for the other it was gradually reduced to 10 °C over the next 2—3 weeks. At each temperature one pig received a high (H) energy intake and the other a low (L) intake of standard feed (Ultra-Wean, Dalgety U. K.). Animals were fed once daily at 17.00 hours and the absolute amount of food was increased as the animals grew, although the ratio H:L was always 2:1 (Dauncey et al. 1983). A light:dark cycle with illumination from 06.00 to 18.00 hours was provided. At 14 weeks of age, a vinyl catheter was inserted into the jugular vein under general anaesthesia (Halothane, ICI) and sterile conditions. Four days later, blood samples were taken at 15 min intervals between 08.00 and 18.00 hours. The animals had last been fed at 17.00 hours on the previous day and were not fed again until the last sample had been taken. All food was eaten within 3—4 h. At the time of investigation, mean body weights (kg) ± SEM for the four treatment groups were: 35H, 31.8 ±3.2; 35L, 20.9 ±1.6; 10H, 22.4 ± 1.8; 10L, 12.9 ±0.8. Physical appearance of the pigs was similar to that described previously, with marked differences in lengths of extremities between those living at 35 compared with 10 °C (Ingram and Dauncey 1986).
Received: 12 Dec. 1989
Accepted: 26 March 1990
Downloaded by: Universite Laval. Copyrighted material.
M. J. Dauncey and H. L. Buttle AFRC Institute of Animal Physiology and Genetics Research, Cambridge AFRC Institute for Grassland and Animal Production, Hurley, United Kingdom
Growth Hormone, Prolactin and Environment
Horm. metab. Res. 22 (1990)
525
Table 1 Plasma concentrations of growth hormone and prolactin in 14 week old pigs living at 35 or 10 °C on a high (H) or low (L) energy intake. Measurements were made between 15 and 25 h after the last meal at 15 min intervals. Treatment Group 35H
35L
10H
10L
Growth hormone: Mean±SEM (ng/ml) Number of peaks/10 h Amplitude of peaks+ SEM (ng/ml)
2.26 + 0.67 2.3 13.4 + 2.46
3.24 + 0.34 3.2 15.3 + 2.27
1.98 + 0.45 2.5 13.2 + 2.32
2.97+1.18 2.3 12.2 + 2.99
Prolactin: Mean + SEM (ng/ml)
1.71+0.54
1.02 ±0.35
0.65 + 0.15
0.71+0.22
Procedures
Homologous double antibody radioimmunoassays were used to measure GH and PRL concentrations in plasma samples. The assays were similar to those used by Klindt and Stone (1984) and have been described previously {Buttle 1987). All samples from each group of four littermates were analysed within the same assay.
Results Growth
Hormone
Table 1 gives the mean values over 10 h for all animals and Fig. 1 illustrates individual values for two pigs from each treatment group. Episodic secretion occurred in all animals, with peaks at intervals of 3—4 h. Peak height was variable both within and between animals and ranged from 6 to 29 Growth Hormone ng GH/ml plasma. Basal values between peaks were less than 1 ng/ml for all treatments. The mean G H concentration was The first antiserum was raised in a guinea-pig (HLB on average 48% greater on the low compared with the high 1/2) using as antigen a mixture of porcine GH preparations kindly supplied by Professor A. E. Wilhelmi (pig GH P476 C) and by Dr. G. S. energy intake (P < 0.1). Values were also slightly greater, by G. Spencer and was used at a final dilution of 1:160,000 in assays. approximately 14%, in the warm than the cold (P > 0.5). USDA pig growth hormone pGH-Bl was iodinated by the method of However, in neither case did the differences reach statistical Goldfine, Amir, Petersen and Ingbar (1974) and was also used as a refsignificance because of the wide variation within treatments. erence preparation. The assay showed no cross-reaction (
Differences in Growth Hormone and Prolactin Secretion Associated with Environmental Temperature and Energy Intake 1
2
Summary The combined effects of environmental temperature and level of energy intake on plasma concentrations of growth hormone (GH) and prolactin (PRL) have been investigated in 14 week old pigs acclimated to 35 or 10 °C on a high (H) or low (L) energy intake (H = 2L). Measurements were made at 15 min intervals between 08.00 and 18.00 hours, after feeding at 17.00 hours on the previous day. Mean values of G H were greater in pigs on the L than H intake and there was a tendency for values to be higher at 35 than 10 °C. However, there was wide individual vaiation within each treatment group and the differences were not statistically significant. Mean PRL concentrations were greater at 35 than 10 °C (P < 0.05). It is concluded that circulating levels of plasma G H do not have a major role in maintaining the differences in growth and morphology of young pigs kept in widely different environmental conditions. However, these differences could be related at least in part to the GH-like properties of PRL.
With respect to energy intake, plasma IGF-I concentrations decline on a low intake (Clemmons, Klibanski, Underwood, McArthur, Ridgway, Beitins and Van Wyk 1981; Phillips, Goldstein and Gavin 1988). By contrast, G H tends to be inversely related to level of nutrition (Bassett, Weston and Hogan 1971) and increases with time after feeding (McCusker, Wangsness, Griel and Kavanaugh 1985). It was therefore of relevance to investigate the extent to which energy intake interacts with any effects of environmental temperature on G H secretion. There is an inter-relation between G H and prolactin (PRL) in the regulation of growth. Moreover, there is some evidence of seasonal variation in PRL secretion in wild pigs (Ravault, Martinat-Botte, Mauget, Martinat, Locatelli and Bariteau 1982) which could be a response to both environmental temperature and photoperiod. In the present investigation, therefore, the secretory patterns of G H and PRL have been investigated in young pigs living at 35 or 10 °C on a high or low level of energy intake. Materials and Methods
Key words Growth Hormone — Prolactin — Temperature — Energylntake
Introduction Acclimation of young pigs to a warm or cold temperature and a high or low level of energy intake has a striking influence on growth and morphology (Weaver and Ingram 1969; Dauncey, Ingram, Walters and Legge 1983; Ingram and Dauncey 1986). At both temperatures, those on a low intake are smaller than those on a high intake. Animals living in the warm have longer limbs, larger ears and a longer snout compared with littermates in the cold on the same food intake. More recently, plasma concentrations of insulin-like growth factor-I (IGF-I) have been found to be greater in animals living in the warm than the cold and on a high than a low energy intake (Dauncey, Shakespear, Rudd and Ingram 1990). It was therefore decided to investigate whether there are any differences in the plasma concentration of G H in animals living in a warm or cold environment under conditions of controlled energy intake. Horm.metab.Res.22(1990)524-527 © Georg Thieme Verlag Stuttgart • New York
Animals Six litters of pigs from the Large White herd kept at the Institute (Cambridge) were used. For each litter, four males were taken from the sow at 14 days of age and kept at 30 °C for 3 days. Animals were then separated into two groups and housed singly in wire cages. For one group the environmental temperature was increased to 35 °C and for the other it was gradually reduced to 10 °C over the next 2—3 weeks. At each temperature one pig received a high (H) energy intake and the other a low (L) intake of standard feed (Ultra-Wean, Dalgety U. K.). Animals were fed once daily at 17.00 hours and the absolute amount of food was increased as the animals grew, although the ratio H:L was always 2:1 (Dauncey et al. 1983). A light:dark cycle with illumination from 06.00 to 18.00 hours was provided. At 14 weeks of age, a vinyl catheter was inserted into the jugular vein under general anaesthesia (Halothane, ICI) and sterile conditions. Four days later, blood samples were taken at 15 min intervals between 08.00 and 18.00 hours. The animals had last been fed at 17.00 hours on the previous day and were not fed again until the last sample had been taken. All food was eaten within 3—4 h. At the time of investigation, mean body weights (kg) ± SEM for the four treatment groups were: 35H, 31.8 ±3.2; 35L, 20.9 ±1.6; 10H, 22.4 ± 1.8; 10L, 12.9 ±0.8. Physical appearance of the pigs was similar to that described previously, with marked differences in lengths of extremities between those living at 35 compared with 10 °C (Ingram and Dauncey 1986).
Received: 12 Dec. 1989
Accepted: 26 March 1990
Downloaded by: Universite Laval. Copyrighted material.
M. J. Dauncey and H. L. Buttle AFRC Institute of Animal Physiology and Genetics Research, Cambridge AFRC Institute for Grassland and Animal Production, Hurley, United Kingdom
Growth Hormone, Prolactin and Environment
Horm. metab. Res. 22 (1990)
525
Table 1 Plasma concentrations of growth hormone and prolactin in 14 week old pigs living at 35 or 10 °C on a high (H) or low (L) energy intake. Measurements were made between 15 and 25 h after the last meal at 15 min intervals. Treatment Group 35H
35L
10H
10L
Growth hormone: Mean±SEM (ng/ml) Number of peaks/10 h Amplitude of peaks+ SEM (ng/ml)
2.26 + 0.67 2.3 13.4 + 2.46
3.24 + 0.34 3.2 15.3 + 2.27
1.98 + 0.45 2.5 13.2 + 2.32
2.97+1.18 2.3 12.2 + 2.99
Prolactin: Mean + SEM (ng/ml)
1.71+0.54
1.02 ±0.35
0.65 + 0.15
0.71+0.22
Procedures
Homologous double antibody radioimmunoassays were used to measure GH and PRL concentrations in plasma samples. The assays were similar to those used by Klindt and Stone (1984) and have been described previously {Buttle 1987). All samples from each group of four littermates were analysed within the same assay.
Results Growth
Hormone
Table 1 gives the mean values over 10 h for all animals and Fig. 1 illustrates individual values for two pigs from each treatment group. Episodic secretion occurred in all animals, with peaks at intervals of 3—4 h. Peak height was variable both within and between animals and ranged from 6 to 29 Growth Hormone ng GH/ml plasma. Basal values between peaks were less than 1 ng/ml for all treatments. The mean G H concentration was The first antiserum was raised in a guinea-pig (HLB on average 48% greater on the low compared with the high 1/2) using as antigen a mixture of porcine GH preparations kindly supplied by Professor A. E. Wilhelmi (pig GH P476 C) and by Dr. G. S. energy intake (P < 0.1). Values were also slightly greater, by G. Spencer and was used at a final dilution of 1:160,000 in assays. approximately 14%, in the warm than the cold (P > 0.5). USDA pig growth hormone pGH-Bl was iodinated by the method of However, in neither case did the differences reach statistical Goldfine, Amir, Petersen and Ingbar (1974) and was also used as a refsignificance because of the wide variation within treatments. erence preparation. The assay showed no cross-reaction (
