Protein turnover and growth in the whole body, liver and kidney of the rat from the foetus to senility.

Changes in the growth and protein turnover (measured in vivo) of the rat liver, kidney and whole body were studied between 16 days of life in utero and 105 weeks post partum. Tissue and whole-body growth were related to changes in both cellular hyperplasia (i.e. changes in DNA) and hypertrophy (protein/DNA values) and to the protein composition within the enlarging tissue mass. The suitability of using a single large dose of phenylalanine for measuring the rates of protein synthesis during both pre- and post-natal life was established. The declining growth rates in the whole animal and the two visceral tissues were then explained by developmental changes in the fractional rates of protein synthesis and breakdown, turnover rates being age-for-age higher in the liver than in the kidney, which in turn were higher than those measured in the whole animal. The declining fractional rates of synthesis in both tissues and the whole body with increasing age were related to changes in the tissues' ribosomal capacity and activity. The fall in the hepatic rate between 18 and 20 days of foetal life (from 134 to 98% per day) corresponded to a decrease in both the ribosomal capacity and the rate of synthesis per ribosome. No significant changes in any of these parameters were, however, found in the liver between weaning (3 weeks) and senility (105 weeks). In contrast, the fractional synthetic (and degradative) rates progressively declined in the kidney (from 95 to 24% per day) and whole body (from 70 to 11% per day) throughout both pre- and post-natal life, mainly as a consequence of a progressive decline in the ribosomal capacity, but with some fall in the ribosomal activity also during foetal life. The age-related contributions of these visceral tissues to the total amount of protein synthesized per day by the whole animal were determined. The renal contribution remained fairly constant at 1.6-2.9%, whereas the hepatic contribution declined from 56 to 11%, with increasing age. Approximate-steady-state conditions were reached at, and between, 44 and 105 weeks post partum, the half-life values of mixed whole-body, kidney and liver proteins being 6.4, 3.0 and 1.5 days, respectively, at 105 weeks.     

Pre- and post-natal growth and protein turnover in smooth muscle, heart and slow- and fast-twitch skeletal muscles of the rat.

The growth of one smooth and three individual striated muscles was studied from birth to old age (105 weeks), and where possible during the later stages of foetal life also. Developmental changes in protein turnover (measured in vivo) were related to the changing patterns of growth within each muscle, and the body as a whole. Developmental growth (i.e. protein accumulation) in all muscles involved an increasing proportion of protein per unit wet weight, as well as cellular hypertrophy. The contribution of the heart towards whole-body protein and nucleic acid contents progressively decreased from 18 days of gestation to senility. In contrast, post-natal changes in both slow-twitch (soleus) and fast-twitch (tibialis anterior) skeletal muscles remained reasonably constant with respect to whole-body values. Such age-related growth in all four muscle types was accompanied by a progressive decline in both the fractional rates of protein synthesis and breakdown, the changes in synthesis being more pronounced. Age for age, the fractional rates of synthesis were highest in the oesophageal smooth muscle, similar in both cardiac and the slow-twitch muscles, and lowest in the fast-twitch tibialis muscle. Despite these differences, the developmental fall in synthetic rates was remarkably similar in all four muscles, e.g. the rates at 105 weeks were 30-35% of their values at weaning. Such developmental changes in synthesis were largely related to diminishing ribosomal capacities within each muscle. When measured under near-steady-state conditions (i.e. 105 weeks of age), the half-lives of mixed muscle proteins were 5.1, 10.4, 12.1 and 18.3 days for the smooth, cardiac, soleus and tibialis muscles respectively. Old-age atrophy was evident in the senile animals, this being more marked in each of the four muscle types than in the animal as a whole. In each muscle of the senile rats the protein content and composition per unit wet weight, and both the fractional and total rates of synthesis, were significantly lower than in the muscles of younger, mature, animals (i.e. 44 weeks). In the soleus the decreased synthesis rate appeared to be related to a further fall in the ribosomal capacity. In contrast, the changes in synthesis in the three remaining muscles correlated with significant decreases in the synthetic rate per ribosome.(ABSTRACT TRUNCATED AT 400 WORDS)     

Respective influences of age and weaning on skeletal and visceral muscle protein synthesis in the lamb.

1. The influences of age and weaning on muscle protein synthesis were studied in vivo, by injecting a large dose of [3H]valine into 1-, 5- and 8-week-old suckling or 8-week-old weaned lambs. 2. The fractional rates of protein synthesis, in red- and white-fibre-type skeletal muscles or striated and smooth visceral muscles, were in 8-week-old suckling animals 24-37% of their values at 1 week of age. This developmental decline was related to decreased capacities for protein synthesis, i.e. RNA/protein ratios. 3. At 8 weeks of age, suckling and weaned lambs had similar fractional synthesis rates, capacities for protein synthesis and efficiencies of protein synthesis (i.e. rates of protein synthesis relative to RNA) in skeletal muscles. 4. In contrast, visceral-muscle fractional synthesis rates were lower in 8-week-old suckling lambs than in weaned animals, owing to decreased efficiencies of protein synthesis. It was concluded that developmental factors and the change to a solid diet, or weaning in itself, or both, affect differently skeletal and visceral muscle protein synthesis in the immature lamb.     

Protein Turnover and Growth of the Rat Brain from the Foetus to Old Age

Growth of the rat brain was studied between 16 days of foetal life and old age (105 weeks). Developmental changes in cerebral RNA, DNA, and protein contents are described. The age-related decline in brain growth rates correlates with progressive decreases in the fractional rates of protein synthesis (from 58 to 6.8% per day) and breakdown (from 36.4 to 4.1% per day).     

Intestinal protein synthesis in guinea pigs infected with Trichostrongylus colubriformis

The fractional synthesis rate (FSR) and daily synthesis of protein were measured in the small and large intestines of infected guinea pigs and uninfected animals fed ad libitum or quantitatively reduced rations. The FSR of the infected and parasite-free parts of the small intestine was unchanged but was increased by about 40% in the large intestine. Daily protein synthesis (mg/g body wt.) by infected guinea pig was greater by about 24% in the entire small intestine and by over 70% in the large intestine. These increases were not due to anorexia since the FSR and daily protein synthesis by the small and large intestines of the reduced ration animals were less than those of the infected group. Greater weight of the small intestine may explain increases in daily protein synthesis in the small, but not in the large intestine where weight was unchanged. Responses which may affect protein synthesis in the infected and parasite-free intestines are discussed.     

Pre- and post-natal growth and protein turnover in the lung of the rat.

The growth of the rat lung was studied at six ages, from 18 days of fetal life to old age (i.e. 105 weeks). Most of the increase in lung size appeared to involve cellular hyperplasia rather than hypertrophy, the DNA content of the lung increasing 96-fold from one extreme of life to the other. Pulmonary rates of protein turnover were high and were, age for age, consistently greater than the rates in the whole body. The age-related decline in the rate of lung growth corresponded to a marked decrease in the fractional rate of protein synthesis, i.e. from 93 to 33% per day during fetal and neonatal life. This in turn correlated with a 58% fall in the ribosomal capacity. From weaning onwards, synthesis rates remained between 30 and 40% per day. In contrast, the degradation of lung proteins was unchanged, at 28-38% per day throughout both fetal and post-natal life.     

The effects of age and chronic restricted feeding on protein synthesis and growth of the large intestine of the rat.

1. In vivo rates of protein synthesis and growth of the large intestine were studied in ad libitum fed control and chronic diet restricted rats between 3 and 149 weeks post partum. 2. Restricted feeding (50% reduced intake) when imposed from weaning significantly extends the life span of rodents through an unknown biochemical mechanism. 3. The change in nutritional status slows the accumulation of RNA, DNA and protein in the large intestine but does not modify the fractional rate of protein synthesis. 4. It was therefore deduced, that intracellular protein degradation, or the rate of mucosal cell extrusion into the gut lumen, is accelerated by chronic restricted feeding.     

The effect of chronic ethanol ingestion on protein metabolism in type-I- and type-II-fibre-rich skeletal muscles of the rat.

1. The effects of chronic ethanol feeding on muscles containing a predominance of either Type I (aerobic, slow-twitch) or Type II (anaerobic, fast-twitch) fibres were studied. Male Wistar rats, weighing approx. 90 g or 280 g, were pair-fed on a nutritionally complete liquid diet containing 36% of total energy as ethanol, or isovolumetric amounts of the same diet in which ethanol was replaced by isoenergetic glucose. After 6 weeks feeding, fractional rates of protein synthesis were measured with a flooding dose of L-[4-(3)H]-phenylalanine and muscles were analysed for protein, RNA and DNA. 2. Ethanol feeding decreased muscle weight, protein, RNA and DNA contents in both small and large rats. Type-II-fibre-rich muscles showed greater changes than did Type-I-fibre-rich muscles. Changes in protein paralleled decreases in DNA. 3. The capacity for protein synthesis (RNA/protein), fractional rates of protein synthesis and absolute rates of protein synthesis were decreased by ethanol feeding in both small and large rats. The amounts of protein synthesized relative to RNA and DNA were also decreased. Changes were less marked in Type-I than in Type-II-fibre-rich muscles. Loss of protein, RNA and DNA was greater in small rats, but protein synthesis was more markedly affected in large rats. 4. It was concluded that chronic ethanol feeding adversely affects protein metabolism in skeletal muscle. Fibre composition and animal size are also important factors in determining the pattern of response.     

Variation among chicken stocks in the fractional rates of muscle protein synthesis and degradation

Fractional rates (% · day^–1) of synthesis and degradation were determined by measuring the output of N-methylhistidine (MeHis) in the excreta at 4 and 8 weeks of age in the chicken. At 4 weeks of age, the fractional rate of synthesis of the meat-type stock was twice that of the egg-type stock (White Leghorn), but the fractional rates of synthesis at 8 weeks of age were similar (4.1–5.1% · day^–1) among stocks. The fractional rate of degradation (1.3–1.5% · day^–1) of the meat-type stock at 8 weeks of age was less than half the rate of the egg-type stock (2.9% · day^–1). The fractional rates of synthesis and degradation at 4 weeks of age in the Satsuma native fowl were relatively high compared with those in the other stocks. In particular, the rate of degradation (8.6% · day^–1) at 4 weeks of age was approximately twice that of other stocks. These results show that fractional rates of synthesis and degradation of muscle protein in the chicken differ among genetically diverse groups. The effect of changes in rates of synthesis and degradation on the change in fractional growth rate also differed. From regression coefficients (b_{K s · FGR} and b_{K d · FGR}) of these rates in skeletal muscle protein on the fractional growth rate, it was recognized that the change in growth rate accompanies the changes in both synthesis and degradation in White Leghorn and commercial broilers but only the change in synthesis in White Plymouth Rock (dw) and Satsuma native fowl.     

Synthesis of myelin basic proteins in the developing mouse brain.

Mice ranging in age from 14 to 39 days were injected intracerebrally with [³H]lysine and rates of incorporation of the isotope were measured into total trichloroacetic acid-precipitable protein and purified myelin basic proteins (MBPs). MBPs were isolated by O-(carboxymethyl)-cellulose chromatography of pH 3 extracts prepared from chloroform-methanol insoluble residues of whole brains. The MBPs prepared in this fashion were further separated by polyacrylamide gel electrophoresis. The gels were sliced and the radioactivity incorporated into each of the two proteins was determined. Analysis of the rates of synthesis of the two basic proteins (using a 2-h labeling period) as a function of age revealed that synthesis of both proteins appeared to peak at about 18 days of age in the mouse. These data suggest that the maximum rate of MBP synthesis coincides with the age of maximal myelin deposition in the mouse. Furthermore the relative rates of synthesis of L and S changed considerably over the developmental period examined. It was observed that the ratio of the rates of synthesis of the small:large basic protein (S/L) increased by approximately 50% between 2 and 4 weeks and declined thereafter. Throughout the developmental period examined, however, the small basic protein appeared to be synthesized at a greater rate than the large protein. The latter data are consistent with previous observations by us and other workers that mouse and rat myelin becomes increasingly enriched in the small relative to the large basic protein with maturation of the membrane.     

Regulation of indoleamine 2,3-dioxygenase activity in the small intestine and the epididymis of mice

Indoleamine 2,3-dioxygenase activity was found to be ubiquitously distributed in various tissues of mice, such as brain, lung, stomach, intestine, and epididymis. The highest enzyme activity was detected in the alimentary canal and the epididymis. Developmental and daily rhythmic changes of indoleamine 2,3-dioxygenase activity and the effects of various regulatory factors were studied with the supernatant fractions derived from the small intestine and the epididymis. The enzyme activity in these two tissues was absent during the first 2 weeks (the weaning period). From the third week, there was a rapid increase in activities and a maximum was reached when the mice were 8 to 10 weeks of age (adolescence). The enzyme activity in the small intestine then gradually diminished to zero level at 30 weeks of age (prime) or later, while that in the epididymis remained at the high level throughout 69 weeks of age (senescence). The enzyme activity of the small intestine from mice fed during the hours 9:00–13:00 showed daily rhythmic changes; high in the daytime and low at night. Under night feeding (21:00–1:00), the enzyme activity was high at night and low in the daytime. The epididymal enzyme activity showed no daily fluctuations by either feeding schedule. With regard to the developmental and daily rhythmic changes, indoleamine 2,3-dioxygenase activity in the small intestine was similar to that of hepatic tryptophan 2,3-dioxygenase. However, in contrast to the hepatic tryptophan 2,3-dioxygenase activity, indoleamine 2,3-dioxygenase activity in the small intestine and the epididymis was not affected by adrenalectomy or intraperitoneal administration of adrenal steroid or tryptophan.     

Effect of dietary lysine on muscle protein turnover in growing chickens.

Day-old male chickens were fed ad libitum isoenergetic diets containing 20% crude protein but differing in their lysine content (from 6.5 up to 11.3 g/kg). At 3 weeks of age, protein fractional synthesis rates in the pectoralis major muscle were determined using a large dose injection of 120 mumol per kg body weight of L-[4-3H] phenylalanine. Protein gain in the pectoralis major was measured between 19 and 23 days of age. Protein breakdown was obtained by calculating the difference between protein synthesis and deposition. Weight gain varied curvilinearly with dietary lysine intake and was maximum for 11.3 g lysine/kg of diet. In birds fed an adequate lysine intake (10.1-11.3 g/kg) protein fractional synthesis and breakdown rates were 23.6-25.9 and 17.8-19.8%/d respectively. Increasing lysine supplementation in the diet resulted in an impairment of protein fractional breakdown rates. By contrast, protein fractional synthesis rates remained unchanged owing mainly to an improvement in the synthesis efficiency (kRNA), until birds were fed an adequate lysine intake. These data suggest that the growth rate reduction of chickens fed lysine deficient diets was due to alterations in both rates of protein synthesis and breakdown in skeletal muscle. A maximum protein deposition is achieved when kRNA was optimal, ie for a dietary lysine content of about 9 g/kg, a value close to the requirement.     

Protein metabolism in the small intestine of the ethanol-fed rat

The effects of chronic ethanol feeding on the small intestine were investigated in young rats. Rats were fed a nutritionally-adequate liquid diet, containing 36 per cent of total energy as ethanol (treated, n = 7), or isovolumetric amounts of the same diet in which ethanol was substituted by isocaloric glucose (controls, n = 7). After six weeks the wet weight and total tissue contents of protein, RNA and DNA were significantly reduced by 21 per cent, 23 per cent, 16 per cent and 28 per cent respectively, (p less than 0.014). Rates of protein synthesis were measured with L[4(3H)]phenylalanine and fractional rates (defined as the percentage of constituent tissue protein synthesised each hour, i.e. ks, % h-1) were calculated from the specific radioactivity of free phenylalanine in both tissue homogenates and plasma. Ethanol-feeding reduced ks by approx 10 per cent (p less than 0.181). The amount of protein synthesized unit-1 RNA was also reduced by approx 15 per cent (p less than 0.059) but the amount of protein synthesis unit-1 DNA was unaffected by ethanol-feeding (p less than 1.000). In contrast, the absolute rates of protein synthesis were reduced by approximately 30 per cent (p less than 0.022). It was concluded that, as the small intestine contributes to approx. 20-25 per cent of whole body synthesis these results may have an important effect on whole body nitrogen homeostasis and may have implications for the gastrointestinal effects of ethanol seen during chronic alcoholic abuse.     

Ontogeny of pituitary gonadotrophin secretion in the fetal and post-natal pig in response to LHRH in vitro

Monolayer cultures of anterior pituitary cells from male or female pigs of 60, 80, 105 days of fetal life or of 60, 160 and 250 days of post-natal life were prepared and treated with LHRH (1 pM to 10 nM). Dose-related increases of LH were first seen at 80 days of gestation in both sexes, while only female fetuses responded to maximal LHRH at 60 days. Basal and stimulated LH release doubled in cultures from 105-day-old fetuses when compared with those at 80 days. Compared to late fetal stages LH release was 20- to 30-fold higher in cell cultures from 60-day-old (post-natal) donors without further change during the post-natal period. In all pre- and post-natal age groups basal and maximal LH release of pituitary cells from males was lower than that of females. FSH stimulation started in male and female cells at 80 days of gestation only at LHRH concentrations exceeding or equal to 0.1 nM. By 105 days FSH secretion was dose-related and pituitary cells of females responded with higher FSH values than did those of males. In general, post-natal cells released much higher amounts of FSH than did prenatal cells. Basal and maximal release of FSH decreased during post-natal development in both sexes. Basal as well as maximal FSH release of cultures from female donors was higher than that found in cultures from male donors. Determination of total LH and FSH content in fetal pituitary cell cultures indicated that the developmental increase in gonadotrophin release potential is a function of the total gonadotrophin content in vitro. We conclude that (1) the in-vitro release of gonadotrophins to LHRH is dose-, age- and sex-dependent; (2) in the female fetal pig LH responsiveness develops earlier than FSH responsiveness; (3) apparently, these maturational changes mainly reflect alterations in pituitary gonadotrophin content; and (4) there is no simple relationship between in-vitro release and circulating gonadotrophins.     

Age and the extent and topography of solitary lymphoid nodules in the wall of the human small and large intestine

Amount and topography of small lymphoid nodules (SLN) have been studied by means of the quantitative method in flat total preparations of the small and large intestine obtained from 111 corpses of persons of both sex (from newborn up to old age). Total amount of the SLN in the large intestine wall in all age periods exceeds that of the SLN in the small intestine wall. From birth up to the period of the 1 childhood total amount of the SLN increases successively, reaching (51 +/- 14) X 10(2) in the small and (74 +/- 11) X 10(2) in the large intestine at the age of 4-7 years. Beginning from 8 years of age up to old age, total amount of the SLN decreases successively, to a more degree in the wall of the small intestine than in the large intestine. The arrangement density of the SLN in the large intestine wall essentially exceeds that of the SLN in the small intestine wall during the all age periods. From birth up to early childhood the arrangement density of the SLN increases and then gradually decreases both in the small and large intestine. This demonstrates that development of the SLN takes place during the first 4-7 years of the human life, in contrast to the lymph nodes and tonsils, their greatest development takes place during juvenile and adolescent age.     

Ontogeny of a novel pituitary protein (7B2) in the human fetal intestine

The developmental profile of the concentration of a novel pituitary protein (7B2) was studied immunochemically in the human gastrointestinal tract from 12 weeks of gestation to 4 months after birth and was compared to the distribution in the adult. 7B2-like immunoreactivity (IR-7B2) was detected in all segments studied, but no gross changes were seen through fetal life. At term higher concentrations of IR-7B2 were found in the duodenum and the antrum, which is similar to the distribution of adult man. Gel permeation chromatography revealed that the main peak of 7B2 immunoreactivity in the fetal intestinal extract eluted with a Kav of 0.3. Similar elution profiles were also observed in extracts of human adult intestine.     

Relationships between the synthesis and breakdown of protein,dietary absorption and turnovers of nitrogen and carbon in the blue mussel,Mytilus edulis L.

Summary Seasonal and nutritionally induced changes of whole body protein metabolism have been studied in 45 to 57 mm shell-length Mytilus edulis from Whitsand Bay, southwest England. The subtraction of measured net protein balances from coincident rates of protein synthesis, determined in vivo by supplying ¹⁵N-labelled alga and monitoring the enrichment of excreted ammonia, enabled computation of protein breakdown rates. Over the range of protein absorption from zero to 0.58% of total soft tissue protein 24 h^-1, fractional rates of protein breakdown decreased from 0.41 to 0.03%, whereas protein synthesis and net protein balance both increased from 0.25% to 0.39% and from-0.16% to 0.36%, respectively. The progressive reduction in fractional protein degradation with elevated net protein balance represented a protein sparing effect, whereby the efficiency of protein synthesis (defined as net synthesis/overall synthesis) confirmed theoretical predictions of as much as 92% during periods of maximal growth. In addition, 38% of breakdown products were recycled directly to synthesis under conditions of zero net balance, with an increasing contribution evident upon further decreases of protein absorption. The overall response was characterized by a consistently conservative elemental turnover of nitrogen relative to carbon, so that as a fraction of each element absorbed, between 1.2 and 1.9 times as much nitrogen was incorporated within structural materials. Such conservation was most pronounced among mussels starved prior to experimentation, indicating nutritionally related efficiencies in the utilization of resources for synthesis. The changing balance between individual processes also effected large alterations in proportional size of the metabolic pool of free amino acids (0.2 to 14.5% of total soft tissue nitrogen). Finally, it is suggested that adjustments of protein synthetic rate may be significant in the regulation of energy expenditure, accounting for at least 16% of basal energy requirements. Results throughout have been compared and contrasted with those for mammals, and whole-body measurements of both protein synthesis and breakdown proposed as a valuable index for environmental effects on instantaneous growth and metabolism.     

The effect of protein depletion and repletion on muscle-protein turnover in the chick.

Rates of growth and protein turnover in the breast muscle of young chicks were measured in order to assess the roles of protein synthesis and degradation in the regulation of muscle mass. Rates of protein synthesis were measured in vivo by injecting a massive dose of L-[1-14C]valine, and rates of protein degradation were estimated as the difference between the synthesis rate and the growth rate of muscle protein. In chicks fed on a control diet for up to 7 weeks of age, the fractional rate of synthesis decreased from 1 to 2 weeks of age and then changed insignificantly from 2 to 7 weeks of age, whereas DNA activity was constant for 1 to 7 weeks. When 4-week-old chicks were fed on a protein-free diet for 17 days, the total amount of breast-muscle protein synthesized and degraded per day and the amount of protein synthesized per unit of DNA decreased. Protein was lost owing to a greater decrease in the rate of protein synthesis, as a result of the loss of RNA and a lowered RNA activity. When depleted chicks were re-fed the control diet, rapid growth was achieved by a doubling of the fractional synthesis rate by 2 days. Initially, this was a result of increased RNA activity; by 5 days, the RNA/DNA ratio also increased. There was no evidence of a decrease in the fractional degradation rate during re-feeding. These results indicate that dietary-protein depletion and repletion cause changes in breast-muscle protein mass primarily through changes in the rate of protein synthesis.     

The effects of surgical stress and short-term fasting on protein synthesis in vivo in diverse tissues of the mature rat.

1. We measured fractional rates of protein synthesis, capacities for protein synthesis (i.e. RNA/protein ratio) and efficiencies of protein synthesis (i.e. protein-synthesis rate relative to RNA content) in fasted (24 or 48 h) or fasted/surgically stressed female adult rats. 2. Of the 15 tissues studied, fasting caused decreases in protein content in the liver, gastrointestinal tract, heart, spleen and tibia. There was no detectable decrease in the protein content of the skeletal muscles studied. 3. Fractional rates of synthesis were not uniformly decreased by fasting. Rates in striated muscles, uterus, liver, spleen and tibia were consistently decreased, but decreases in other tissues (lung, gastrointestinal tract, kidney or brain) were inconsistent or not detectable, suggesting that, in many tissues in the mature rat, protein synthesis was not especially sensitive to fasting. 4. In fasting, the decreases in fractional synthesis rate resulted from changes in efficiency (liver and tibia) or from changes in efficiency and capacity (heart, diaphragm, plantaris and gastrocnemius). In the soleus, the main change was a decrease in capacity. 5. Surgical stress increased fractional rates of protein synthesis in diaphragm (where there were increases in both efficiency and capacity) by about 50%, in liver by about 20%, in spleen by about 40%, and possibly also in the heart. In liver and spleen, capacities were increased. In other tissues (including the skeletal muscles), the fractional rates of protein synthesis were unaffected by surgical stress.