Experimental Gerontology, Vol. 27, pp. 191-200, 1992
0531-5565/92 $5.00 + .00 Copyright© 1992 PergamonPressLtd.
Printed in the USA.All rightsreserved.
THE I N F L U E N C E OF AGE A N D CHRONIC RESTRICTED FEEDING O N PROTEIN S Y N T H E S I S IN THE SMALL INTESTINE OF THE RAT
BRIAN J. MERRY, ~ SHEENA
E.M. LEWIS 2 and DAVID F. GOLDSPINK 3
qnstitute of Human Ageing, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK, 2Department of Obstetrics and Gynaecology, School of Clinical Medicine, The Royal Victoria Hospital, Grosvenor Road, Belfast, BT 12 6BA, UK and 3Department of Cardiovascular Studies, The University, and The Cardiac Research Unit, Killingbeck Hospital, York Road, Leeds, LSI4 6UQ, UK
Abstract - - Rates of protein synthesis (measured in vivo) and growth of the small intes-
tine were studied as a function of age in ad libitum fed (control) and chronic dietaryrestricted rats. At weaning, the fractional rates of synthesis in the mucosal and muscularis externa and serosal layers of the small intestine of control animals were similarly high (90-100% per day). Although these rates subsequently declined with age in the muscularis externa and serosa, they remained constant in the mucosa. Restricted feeding (50% reduced intake), when imposed from weaning onwards, significantly extends the maximum life span of rodents. However, the change in nutritional status slows the accumulation of protein, RNA, and DNA in both layers of the small intestine. Although underfeeding did not prevent the age-related fall in muscularis externa and serosal protein synthesis, significantly higher rates (both fractional and per ribosome) were found when compared age for age with controls. Mucosal fractional synthetic rates were similarly increased by the reduced food intake. These changes in protein turnover in the small intestine are consistent with the higher rates of whole body turnover previously observed in chronically underfed rats. Key Words: age, chronic dietary restriction, RNA, DNA, protein synthesis, growth, mucosa, muscularis externa and serosa, small intestine
INTRODUCTION THERE IS now good evidence to indicate that the rates of protein synthesis decline with increasing age in many cell types from a wide range of organisms (Waterlow et al., 1978; Makrides, 1983). Since the protein mass of these tissues either increases or is maintained until senescence, it was predicted and has subsequently been confirmed experimentally that the rate of protein degradation must similarly decrease with age (Waterlow et al., 1978; Rothstein, 1981; Richardson and Cheung, 1982; Lewis et al., 1984). The increasing
Correspondence to: B.J. Merry. ( Ra'eived 21 June 1990; Accepted 24 June 1991 )
191
192
B.J. M E R R Y el al.
half-life of cellular proteins may therefore be a contributing factor in the accumulation of abnormal proteins and cell dysfunction in ageing (Adelman and Dekker, 1985). Using suspensions of freshly isolated kidney cells and hepatocytes, or cell free preparations from testis and spleen lymphocytes, it has been demonstrated (in vitro) that significantly higher rates of protein synthesis and degradation occur in tissues from rats which have been maintained on restricted feeding (Birchenall-Sparks et al., 1985; Richardson, 1985; Ward, 1988). Measured rates of protein synthesis (in vivo) and degradation at the level of the whole animal using ad libitum fed and chronically underfed rats (Lewis et al., 1985) have confirmed these observations. Evaluation of the changes in protein turnover in individual tissues, however, has revealed variable responses to long-term dietary restriction. For example, protein turnover in the ventricles of the heart (Goldspink et al., 1986) closely follows the higher turnover rates (Lewis et al., 1985) in the whole animal. In contrast, in underfed animals the skeletal musculature and lungs exhibit lower rates of protein synthesis, while hepatic rates are little changed (El Haj, et al., 1986: Goldspink et al., 1987; Goldspink and Merry, 1988). We have now extended our observations to investigate the effects of age and chronic dietary restriction on protein synthesis in the mucosal and muscularis externa and serosal layers of the small intestine, a tissue which has generally received little attention (McNurlan et al., 1979; McNurlan and Garlick, 1981; Wassner and Li, 1982: Goldspink et al., 1984). MATERIALS AND METHODS Male Sprague-Dawley (CFY strain) rats housed under barrier conditions were used throughout this study. All animals were weaned at 21 days and randomly allocated to control or experimental groups where they were caged individually and allowed free access to water. Dietary-restricted rats were pair-fed to 50% o f a d libitum fed controls (Merry and Holehan, 1981). Protein synthesis was measured in vivo in the mucosal and muscularis externa and serosal layers of the small intestine 10 min after receiving an intravenous injection of a large dose ofphenylalanine designed to flood the precursor pools (Garlick et al., 1980). This injection was administered via a lateral tail vein and contained 150 umol of the amino acid, including 65 uCi of L-[4-3H]phenylalanine (sp radioactivity 24 Ci/ mmol; from Amersham International PLC., Amersham, Bucks, UK) in 1 ml of 0.9% NaC1 per 100 g body weight. Animals were killed by decapitation, exsanguinated ( 15 s) and their abdominal cavities rapidly opened and immersed in ice-cold water to minimise further metabolism. The entire small intestine was rapidly isolated and flushed with ice-cold saline to remove all luminal contents. To ensure adequate chilling throughout, the small intestine was cut into several sections, each in turn being removed from the cold water to be treated accordingly. Each section was slit along its length, and the mucosal layer removed by scraping the tissue with the edge of a microscope slide. The remaining muscularis externa and serosa was wiped with paper tissue to remove any contaminating mucosal cells and then frozen in liquid N2. Before analysis the frozen tissues were pulverised in a cold room and homogenised in 0.3 M HC10, (1:50 wt/vol) in a ground glass homogeniser. The specific radioactivities of the phenylalanine both in the "flooded" tissue pool(s) and covalently bound in protein were measured in the mucosa and muscularis externa and serosa tissues by the method described by Garlick et al. (1980). This involved the prior hydrolysis of the washed protein
193
EFFECTS OF AGE AND UNDERFEEDING ON THE SMALL INTESTINE
pellets in 6 M HC1 at 110°C for 24 h and the conversion of phenylalanine into/3-phenethylamine. All measurements of radioactivity were made in a LKB scintillation counter (efficiency of 25% for tritium) in a Triton X- 100/xylene-based scintillant with the use of an external standard. The fractional rate of synthesis (i.e., ks, the percentage of the protein mass synthesised per day) was calculated from: SB
ks = SA---t× 100, where SA and SB are the specific radioactivities of phenylalanine in the free tissue pool and protein, respectively, and t is the time in days. Proteins were measured on the same tissue preparations by the method of Lowry et al. (1951), using bovine serum albumin (Sigma, Kingston upon Thames, Surrey, UK) as the standard. RNA and D N A were also extracted and measured as previously described (Goldberg and Goldspink, 1975). RESULTS The effects of both age and food intake were studied on the growth and rates of protein turnover in the mucosa and muscularis externa and serosa of the small intestine. Maximum increases (175-250%) in the wet weight, protein, RNA, and DNA contents of the muscularis externa and serosa were recorded between 3 and 103 weeks in ad libitum fed control rats (Table 1). Most of these increases (i.e., 145-180%), however, occurred during the rapid phase of growth following weaning (i.e., 3 to 7 weeks). This growth mainly
T A B L E 1 . C H A N G E S IN T H E P R O T E I N A N D N U C L E I C ACID C O N T E N T OF T H E MUSCULARIS E X T E R N A A N D SEROSA IN RESPONSE T O A G E I N G A N D D I E T A R Y I N T E R V E N T I O N
Age (week.~ 3 7
Tissue weight (g) Zero-time Control Control DR
52
Control DR
103
Control DR
149
Control DR
2.4 ± 0.07 . 6.7 ± 0.4 2.7 ± 0.3 (-60*) 6.9 ___0.3 4.2 ± 0.2 (-39*) 9.1 ± 0.7 6.2 ± 0.4 (-32*) . 8.6 ± 0.6
Total protein (g) 0.39 + 0.03 . 1.04 _+ 0.1 0.49 _+ 0.04 (--53*) 0.95 _+ 0.08 0.58 _+ 0.03 (-59*) 0.94 _+ 0.05 1.03 _+ 0.1 (+9) . . 1.08 _+ 0.17 .
Total RNA P (mg)
Total DNA P (rag)
1.5 + 0.1 . 3.7 + 0.1 2.4 _+ 0.2 (-46*) 3.0 _+ 0.2 2.4 _+ 0.2 (-21"*) 5.0 + 0.5 3.2 _+ 0.2 (-36*) . 5.0 _+ 0.6
1.0 ± 0.06 . . 2.6 ± 0.3 1.8 ± 0.2 (--31"*) 2.6 ± 0.2 1.8 ± 0.1 ( 31"*) 3.4 _+ 0.6 2.5 ± 0.2 (-26**) . . 2.6 ± 0.2
RNA P DNAP
Protein/ DNA P (g/ rag)
1.5 +_ 0.1
0.38 _+ 0.02
1.5 ± 0.1 1.3 _+ 0.03 ( - 12) 1.2 ± 0.1 1.4 ± 0.1 (+15) 1.6 _+ 0.2 1.4 _+ 0.1 ( - l l)
0.41 _+ 0.03 0.30 _+ 0.03 (-26**) 0.34 _~ 0.02 0.30 +_ 0.04 (-11) 0.32 _+ 0.06 0.44 _+ 0.03 (+38**)
1.9 _+ 0.2
0.42 ± 0.5
Each value is the mean _+ SEM of measurements made on the muscularis externa and serosal layers of the small intestine taken from five ad lib±rum fed control and dietary restricted (DR) rats at each of five ages studied. Statistical significance values (*p < 0.01, **p < 0.025) between the means of control and experimental tissues were determined at each age using Student's t test. The percentage differences between control and experimental values at each age are shown in parentheses.
B.J. MERRYet al.
194
arose from increased cellular proliferation (i.e., a 160% increase in the DNA content), with little increase (8%) in cell size (i.e., protein/DNA; Table 1). Between 7 and 103 weeks, both the total and fractional rates of protein synthesis (Table 2) declined (p < 0.01); this was mainly a consequence of age-related decreases in ribosomal efficiency (i.e., synthesis/RNA) rather than changes in ribosomal capacity (i.e., RNA/protein; Table 2). Similar age-related decreases in the rate of protein degradation must occur in the muscularis externa and serosa in order to preserve the tissue weight and protein mass between 7 and 103 weeks. These declining age-related changes in muscularis externa and serosal protein turnover are similar to those previously described for this (Goldspink et al., 1984) and several other body tissues (Waterlow et al., 1978; Goldspink et al., 1985). Such changes in the muscularis externa and serosa could possibly be linked with reported decreases in gut motility as a function of age (Rothstein, 1975); presumably effects primarily expressed on the turnover of the longitudinal and circular smooth muscle layers. By comparison with the muscularis externa and serosa, larger gains (345-650%) in the wet weight, protein, and nucleic acid content were observed in the mucosa between weaning and senescence (Table 3). Although these increases in the mucosal layer (i.e., 55-200%) were initially (3 to 7 weeks) less rapid than in the muscularis externa and serosa, they continued for longer to reach plateau levels closer to 52 weeks. As with the serosa, cellular hyperplasia rather than hypertrophy was the major contributor to the observed growth. In contrast to the muscularis externa and serosa, the accumulation and maintenance of the mucosal protein mass (Table 3) was not accompanied by significant age-related changes
T A B L E 2. C H A N G E S 1N T H E R A T E OF P R O T E I N SYNTHESIS IN T H E MUSCULARIS E X T E R N A A N D SEROSA W I T H A G E I N G AND D I E T A R Y I N T E R V E N T I O N
Fractional rate ~/synthe~is (%/dal')
AA'e (week,~9 3 7
Zero-time Control Control DR
52
Control DR
103
Control DR
149
Control DR
100.0 _+ 4.0 . 92.6 + 9.8 101 _+ 8.0 (+9) 43.1 _+ 2.9 81.3 _+ 3.7 ( + 89*) 55.0 ± 4.1 88.8 ± 5.0 ( + 62") . 63.6 _+ 4.9
Total protein synthesized (g/da)9 0.39 + 0.03 . 1.06 + 0.02 0.49 _+ 0.03 ( 54*) 0.49 + 0.04 0.47 _+ 0.01 ( - 4) 5.21 ± 0.7 0.95 _+ 0.06 ( - 84*) . . 0.67 _+ 0.09 .
(g/day/g ~[RNAP)
R:~¢4P~ protein Ong/A')
265 ± 18
4.0 + 0.3
268 ± 9.1 163 ± 16 (-38**) 130 ± 2.6 186 _+ 7.4 ( + 42*) 93 ± 16 277 ± 40 ( + 198*)
3.6 _+ 0.3 4.3 ± 0.4 (+17) 3.5 _+ 0.3 4.6 ± 0.3 ( + 30**) 5.5 _+ 0.6 3.2 ± 0.2 (-40*)
136 ± 16
4.9 ± 0.6
.
.
T h e values represent the means _+ SEM of measurements made on five preparations of muscularis externa and serosa from the control and dietary restricted (DR) animals used in Table 1. Protein synthesis was measured in vivo exactly 10 min after an intravenous injection of 150 u m o l of3H-phenylalanine/100 g body weight. The total amount of protein synthesised/day represents the product of the fractional rate and the protein mass (Table 1). Values in parentheses indicate the percentage change between age-matched control and dietary-restricted rats; significance levels were determined using Student's t test: *p < 0.01 ; **p
0531-5565/92 $5.00 + .00 Copyright© 1992 PergamonPressLtd.
Printed in the USA.All rightsreserved.
THE I N F L U E N C E OF AGE A N D CHRONIC RESTRICTED FEEDING O N PROTEIN S Y N T H E S I S IN THE SMALL INTESTINE OF THE RAT
BRIAN J. MERRY, ~ SHEENA
E.M. LEWIS 2 and DAVID F. GOLDSPINK 3
qnstitute of Human Ageing, University of Liverpool, P.O. Box 147, Liverpool, L69 3BX, UK, 2Department of Obstetrics and Gynaecology, School of Clinical Medicine, The Royal Victoria Hospital, Grosvenor Road, Belfast, BT 12 6BA, UK and 3Department of Cardiovascular Studies, The University, and The Cardiac Research Unit, Killingbeck Hospital, York Road, Leeds, LSI4 6UQ, UK
Abstract - - Rates of protein synthesis (measured in vivo) and growth of the small intes-
tine were studied as a function of age in ad libitum fed (control) and chronic dietaryrestricted rats. At weaning, the fractional rates of synthesis in the mucosal and muscularis externa and serosal layers of the small intestine of control animals were similarly high (90-100% per day). Although these rates subsequently declined with age in the muscularis externa and serosa, they remained constant in the mucosa. Restricted feeding (50% reduced intake), when imposed from weaning onwards, significantly extends the maximum life span of rodents. However, the change in nutritional status slows the accumulation of protein, RNA, and DNA in both layers of the small intestine. Although underfeeding did not prevent the age-related fall in muscularis externa and serosal protein synthesis, significantly higher rates (both fractional and per ribosome) were found when compared age for age with controls. Mucosal fractional synthetic rates were similarly increased by the reduced food intake. These changes in protein turnover in the small intestine are consistent with the higher rates of whole body turnover previously observed in chronically underfed rats. Key Words: age, chronic dietary restriction, RNA, DNA, protein synthesis, growth, mucosa, muscularis externa and serosa, small intestine
INTRODUCTION THERE IS now good evidence to indicate that the rates of protein synthesis decline with increasing age in many cell types from a wide range of organisms (Waterlow et al., 1978; Makrides, 1983). Since the protein mass of these tissues either increases or is maintained until senescence, it was predicted and has subsequently been confirmed experimentally that the rate of protein degradation must similarly decrease with age (Waterlow et al., 1978; Rothstein, 1981; Richardson and Cheung, 1982; Lewis et al., 1984). The increasing
Correspondence to: B.J. Merry. ( Ra'eived 21 June 1990; Accepted 24 June 1991 )
191
192
B.J. M E R R Y el al.
half-life of cellular proteins may therefore be a contributing factor in the accumulation of abnormal proteins and cell dysfunction in ageing (Adelman and Dekker, 1985). Using suspensions of freshly isolated kidney cells and hepatocytes, or cell free preparations from testis and spleen lymphocytes, it has been demonstrated (in vitro) that significantly higher rates of protein synthesis and degradation occur in tissues from rats which have been maintained on restricted feeding (Birchenall-Sparks et al., 1985; Richardson, 1985; Ward, 1988). Measured rates of protein synthesis (in vivo) and degradation at the level of the whole animal using ad libitum fed and chronically underfed rats (Lewis et al., 1985) have confirmed these observations. Evaluation of the changes in protein turnover in individual tissues, however, has revealed variable responses to long-term dietary restriction. For example, protein turnover in the ventricles of the heart (Goldspink et al., 1986) closely follows the higher turnover rates (Lewis et al., 1985) in the whole animal. In contrast, in underfed animals the skeletal musculature and lungs exhibit lower rates of protein synthesis, while hepatic rates are little changed (El Haj, et al., 1986: Goldspink et al., 1987; Goldspink and Merry, 1988). We have now extended our observations to investigate the effects of age and chronic dietary restriction on protein synthesis in the mucosal and muscularis externa and serosal layers of the small intestine, a tissue which has generally received little attention (McNurlan et al., 1979; McNurlan and Garlick, 1981; Wassner and Li, 1982: Goldspink et al., 1984). MATERIALS AND METHODS Male Sprague-Dawley (CFY strain) rats housed under barrier conditions were used throughout this study. All animals were weaned at 21 days and randomly allocated to control or experimental groups where they were caged individually and allowed free access to water. Dietary-restricted rats were pair-fed to 50% o f a d libitum fed controls (Merry and Holehan, 1981). Protein synthesis was measured in vivo in the mucosal and muscularis externa and serosal layers of the small intestine 10 min after receiving an intravenous injection of a large dose ofphenylalanine designed to flood the precursor pools (Garlick et al., 1980). This injection was administered via a lateral tail vein and contained 150 umol of the amino acid, including 65 uCi of L-[4-3H]phenylalanine (sp radioactivity 24 Ci/ mmol; from Amersham International PLC., Amersham, Bucks, UK) in 1 ml of 0.9% NaC1 per 100 g body weight. Animals were killed by decapitation, exsanguinated ( 15 s) and their abdominal cavities rapidly opened and immersed in ice-cold water to minimise further metabolism. The entire small intestine was rapidly isolated and flushed with ice-cold saline to remove all luminal contents. To ensure adequate chilling throughout, the small intestine was cut into several sections, each in turn being removed from the cold water to be treated accordingly. Each section was slit along its length, and the mucosal layer removed by scraping the tissue with the edge of a microscope slide. The remaining muscularis externa and serosa was wiped with paper tissue to remove any contaminating mucosal cells and then frozen in liquid N2. Before analysis the frozen tissues were pulverised in a cold room and homogenised in 0.3 M HC10, (1:50 wt/vol) in a ground glass homogeniser. The specific radioactivities of the phenylalanine both in the "flooded" tissue pool(s) and covalently bound in protein were measured in the mucosa and muscularis externa and serosa tissues by the method described by Garlick et al. (1980). This involved the prior hydrolysis of the washed protein
193
EFFECTS OF AGE AND UNDERFEEDING ON THE SMALL INTESTINE
pellets in 6 M HC1 at 110°C for 24 h and the conversion of phenylalanine into/3-phenethylamine. All measurements of radioactivity were made in a LKB scintillation counter (efficiency of 25% for tritium) in a Triton X- 100/xylene-based scintillant with the use of an external standard. The fractional rate of synthesis (i.e., ks, the percentage of the protein mass synthesised per day) was calculated from: SB
ks = SA---t× 100, where SA and SB are the specific radioactivities of phenylalanine in the free tissue pool and protein, respectively, and t is the time in days. Proteins were measured on the same tissue preparations by the method of Lowry et al. (1951), using bovine serum albumin (Sigma, Kingston upon Thames, Surrey, UK) as the standard. RNA and D N A were also extracted and measured as previously described (Goldberg and Goldspink, 1975). RESULTS The effects of both age and food intake were studied on the growth and rates of protein turnover in the mucosa and muscularis externa and serosa of the small intestine. Maximum increases (175-250%) in the wet weight, protein, RNA, and DNA contents of the muscularis externa and serosa were recorded between 3 and 103 weeks in ad libitum fed control rats (Table 1). Most of these increases (i.e., 145-180%), however, occurred during the rapid phase of growth following weaning (i.e., 3 to 7 weeks). This growth mainly
T A B L E 1 . C H A N G E S IN T H E P R O T E I N A N D N U C L E I C ACID C O N T E N T OF T H E MUSCULARIS E X T E R N A A N D SEROSA IN RESPONSE T O A G E I N G A N D D I E T A R Y I N T E R V E N T I O N
Age (week.~ 3 7
Tissue weight (g) Zero-time Control Control DR
52
Control DR
103
Control DR
149
Control DR
2.4 ± 0.07 . 6.7 ± 0.4 2.7 ± 0.3 (-60*) 6.9 ___0.3 4.2 ± 0.2 (-39*) 9.1 ± 0.7 6.2 ± 0.4 (-32*) . 8.6 ± 0.6
Total protein (g) 0.39 + 0.03 . 1.04 _+ 0.1 0.49 _+ 0.04 (--53*) 0.95 _+ 0.08 0.58 _+ 0.03 (-59*) 0.94 _+ 0.05 1.03 _+ 0.1 (+9) . . 1.08 _+ 0.17 .
Total RNA P (mg)
Total DNA P (rag)
1.5 + 0.1 . 3.7 + 0.1 2.4 _+ 0.2 (-46*) 3.0 _+ 0.2 2.4 _+ 0.2 (-21"*) 5.0 + 0.5 3.2 _+ 0.2 (-36*) . 5.0 _+ 0.6
1.0 ± 0.06 . . 2.6 ± 0.3 1.8 ± 0.2 (--31"*) 2.6 ± 0.2 1.8 ± 0.1 ( 31"*) 3.4 _+ 0.6 2.5 ± 0.2 (-26**) . . 2.6 ± 0.2
RNA P DNAP
Protein/ DNA P (g/ rag)
1.5 +_ 0.1
0.38 _+ 0.02
1.5 ± 0.1 1.3 _+ 0.03 ( - 12) 1.2 ± 0.1 1.4 ± 0.1 (+15) 1.6 _+ 0.2 1.4 _+ 0.1 ( - l l)
0.41 _+ 0.03 0.30 _+ 0.03 (-26**) 0.34 _~ 0.02 0.30 +_ 0.04 (-11) 0.32 _+ 0.06 0.44 _+ 0.03 (+38**)
1.9 _+ 0.2
0.42 ± 0.5
Each value is the mean _+ SEM of measurements made on the muscularis externa and serosal layers of the small intestine taken from five ad lib±rum fed control and dietary restricted (DR) rats at each of five ages studied. Statistical significance values (*p < 0.01, **p < 0.025) between the means of control and experimental tissues were determined at each age using Student's t test. The percentage differences between control and experimental values at each age are shown in parentheses.
B.J. MERRYet al.
194
arose from increased cellular proliferation (i.e., a 160% increase in the DNA content), with little increase (8%) in cell size (i.e., protein/DNA; Table 1). Between 7 and 103 weeks, both the total and fractional rates of protein synthesis (Table 2) declined (p < 0.01); this was mainly a consequence of age-related decreases in ribosomal efficiency (i.e., synthesis/RNA) rather than changes in ribosomal capacity (i.e., RNA/protein; Table 2). Similar age-related decreases in the rate of protein degradation must occur in the muscularis externa and serosa in order to preserve the tissue weight and protein mass between 7 and 103 weeks. These declining age-related changes in muscularis externa and serosal protein turnover are similar to those previously described for this (Goldspink et al., 1984) and several other body tissues (Waterlow et al., 1978; Goldspink et al., 1985). Such changes in the muscularis externa and serosa could possibly be linked with reported decreases in gut motility as a function of age (Rothstein, 1975); presumably effects primarily expressed on the turnover of the longitudinal and circular smooth muscle layers. By comparison with the muscularis externa and serosa, larger gains (345-650%) in the wet weight, protein, and nucleic acid content were observed in the mucosa between weaning and senescence (Table 3). Although these increases in the mucosal layer (i.e., 55-200%) were initially (3 to 7 weeks) less rapid than in the muscularis externa and serosa, they continued for longer to reach plateau levels closer to 52 weeks. As with the serosa, cellular hyperplasia rather than hypertrophy was the major contributor to the observed growth. In contrast to the muscularis externa and serosa, the accumulation and maintenance of the mucosal protein mass (Table 3) was not accompanied by significant age-related changes
T A B L E 2. C H A N G E S 1N T H E R A T E OF P R O T E I N SYNTHESIS IN T H E MUSCULARIS E X T E R N A A N D SEROSA W I T H A G E I N G AND D I E T A R Y I N T E R V E N T I O N
Fractional rate ~/synthe~is (%/dal')
AA'e (week,~9 3 7
Zero-time Control Control DR
52
Control DR
103
Control DR
149
Control DR
100.0 _+ 4.0 . 92.6 + 9.8 101 _+ 8.0 (+9) 43.1 _+ 2.9 81.3 _+ 3.7 ( + 89*) 55.0 ± 4.1 88.8 ± 5.0 ( + 62") . 63.6 _+ 4.9
Total protein synthesized (g/da)9 0.39 + 0.03 . 1.06 + 0.02 0.49 _+ 0.03 ( 54*) 0.49 + 0.04 0.47 _+ 0.01 ( - 4) 5.21 ± 0.7 0.95 _+ 0.06 ( - 84*) . . 0.67 _+ 0.09 .
(g/day/g ~[RNAP)
R:~¢4P~ protein Ong/A')
265 ± 18
4.0 + 0.3
268 ± 9.1 163 ± 16 (-38**) 130 ± 2.6 186 _+ 7.4 ( + 42*) 93 ± 16 277 ± 40 ( + 198*)
3.6 _+ 0.3 4.3 ± 0.4 (+17) 3.5 _+ 0.3 4.6 ± 0.3 ( + 30**) 5.5 _+ 0.6 3.2 ± 0.2 (-40*)
136 ± 16
4.9 ± 0.6
.
.
T h e values represent the means _+ SEM of measurements made on five preparations of muscularis externa and serosa from the control and dietary restricted (DR) animals used in Table 1. Protein synthesis was measured in vivo exactly 10 min after an intravenous injection of 150 u m o l of3H-phenylalanine/100 g body weight. The total amount of protein synthesised/day represents the product of the fractional rate and the protein mass (Table 1). Values in parentheses indicate the percentage change between age-matched control and dietary-restricted rats; significance levels were determined using Student's t test: *p < 0.01 ; **p
