Muscular Growth Research Articles

Differential growth retardation and Myofibrillar fragmentation in rats submitted to feed restriction and realimentation

Feed regimens alter muscle growth rate, hence they might impact the proteolytic system involved in tenderization during meat conditioning. The aim of this project was to verify the effects of feed restriction regimens on muscular and animal growth and their impact on postmortem myofibrillar fragmentation. The regimens were: 1) Feeding ad libitum for 11 d (Al/2); 2) Feed restriction (60% of Net Energy for maintenance - NEm) for 11 d (Rt/2); 3) Ad libitum for 22 d (Al); 4) Ad libitum for 4 d and feed restriction (60% NEm) for 18 d (Rt); 5) Ad libitum for 19 d and 3 d of fast (Ft); 6) Feed restriction (60% NEm) for 11 d and ad libitum until 22 d (Ral). The regimens Al/2 and Rt/2 had different intestine weights (19.3 ± 1.1 and 15.8 ± 1.9 g, respectively; P < 0.07). At 22 d, Al animals had higher (P < 0.07) intestine weight (21.8 ± 3.8). Moreover, Ral animals had heavier intestine (19.9 ± 1.5) as compared to Rt (16.6 ± 1.6) or Ft (12.8 ± 1.9). The intestine/live weight percentage ratio was lower (P < 0.05) for Ft (6.3%) as compared to Al (8.4%) and to Ral (9.2%), but it was similar to Rt (7.6%). Liver weight (g) in the Ral (9.5 ± 1.1) did not differ from Al (10.7 ± 2.5) or Rt (8.5 ± 1.1), although the two latter were different (P < 0.05). There was an effect of feed restriction over muscle protein degradation verified by Myofibrillar Fragmentation Index (MFI). The animals at Rt, Ft or Ral showed the lowest MFI 0d (42 ± 1.9; 40 ± 2.7; 40 ± 3.6; respectively) and MFI 5d (77 ± 2.7; 74 ± 3.0; 74 ± 2.9; respectively) as compared to Al, whose indexes were 54 ± 3.0 and 82 ± 3.3. Even though the MFI 5d were lower for the restricted animals, the rates of fragmentation postmortem were higher. Feed restriction altered myofibrillar protein degradation, reflected in lower extended fragmentation of the myofibrils.

Myostatin preferentially down-regulates the expression of fast 2x myosin heavy chain in cattle

Myostatin is involved in an inhibitor of muscular growth and differentiation. Myoblasts derived from double-muscled Japanese shorthorn cattle (DM myoblasts) with absence of functional myostatin had higher abilities to proliferate and differentiate than myoblasts derived from normal-muscled cattle (NM myoblasts). In DM myoblasts, mRNA expressions of fetal myosin heavy chain (MyHC) in growth medium and of fast 2a and 2x MyHC in fusion medium were significantly greater than that in NM myoblasts. No significant difference existed in expressions of embryonic and slow MyHC mRNA between DM and NM myoblasts. The expression of MyoD mRNA was suppressed in myoblasts by administration of myostatin. Two cloned DM myoblast strains (DMc) were established. Addition of myostatin for DMc resulted in less myotube formation and suppression of mRNA expression of fast 2x MyHC. These findings suggest that the endogenous myostatin preferentially down-regulates the expression of the fast 2x MyHC and participates in differentiation of myofiber types during early bovine myogenesis.

Effect of dietary phosphorus and its interaction with genetic background on global gene expression in porcine muscle

Environmental concerns and costs associated with dietary phosphorus (P) supplementation have lead to attempts to minimize the amount of P added to swine diets. In addition to its requirement for bone growth, dietary P is also necessary for muscular growth. To examine the effects of genetic background and dietary P on global gene expression in the muscle of young pigs, we utilized muscle tissue from 36 gilts sired from two different sire lines. These animals were fed either a P adequate, P deficient or P repletion diets for 14 days and showed differences in growth performance and bone integrity in response to the interaction of genetic background and dietary P. Total RNA from the loin muscle of these animals was obtained for microarray analysis. Significant differences (p<0.01) in gene expression were seen based on the effect of sire line (339 genes), dietary P (18 genes) and the interaction between sire line and dietary P (31 genes). The microarray data were validated by semi-quantitative real-time PCR. These results support our hypothesis that genetic background and dietary P treatment can affect the homeorhetic control of P metabolism in pigs. Genes identified as differentially expressed in this study may be excellent candidate genes for additional work to elucidate genotype specific P requirements as well as to identify a genetic background that can maintain superior growth in a more environmentally friendly manner.

Motor Neuron Degeneration in a 20-Week Male Fetus: Spinal Muscular Atrophy Type 0

Neuropathological changes in degenerating motor neurons are well documented in the term neonate with spinal muscular atrophy, but not at midgestation. Postmortem neuropathological examination was performed in a 20-week male fetus with a hypoplastic left cardiac anomaly. Selective degeneration of spinal and hypoglossal motor neurons was an incidental finding. Degenerating motor neurons were not immunoreactive with neuronal nuclear antigen (NeuN) or neuron-specific enolase (NSE), as were the normal motor neurons. Synaptophysin reactivity was reduced around the soma of degenerating normal motor neurons. Ubiquitin and tau were expressed in degenerating motor neurons. Gliosis, inflammation and microglial activation were lacking in the ventral horns of the spinal cord. Laryngeal striated muscle was unaltered for age. No cerebral malformations or hypoxic-ischaemic changes were found. This case represents an early motor neuronal degeneration and corresponds to the recently described "type 0" spinal muscular atrophy. Lack of contractures is attributed to the early fetal age, since most muscular growth occurs in the second half of gestation.

Cataract Blindness Among Scheduled Tribes in Mysore District, Karnataka: Problems and Perspectives

In the present study an attempt is made to understand the problems and perspectives of cataract blindness among Scheduled Tribes in H.D. Kote Taluk, Mysore District, Karnataka. The members of Scheduled tribes covered in the study are Jenukurubas, Bettakurubas and Yeravas. Ten tribal settlements known as hadis were selected for the present study. These settlements are located in the fringe area of Rajiv Gandhi National Park, Nagarahole. In-depth interviews were conducted on 160 informants, 80 males and 80 females. Out of 80 females 28 were suffering from cataract blindness and remaining were healthy individuals. Out of 80 males, 31 were suffering from cataract blindness and remaining were healthy persons. In the present study the emic perspective frequently mentioned is ‘not able to see properly’ (126). The major signs and symptoms of cataract blindness recorded are ‘foggy vision’ (99), and ‘abnormal muscular growth over the eyes’ (62). The constraints for underutilization of eye care services among members of scheduled tribes were ‘no money (137), ‘fear of surgery or treatment’ (79), ‘lack of information on eye care services’ (61) and ‘lack of family members who are willing to help the blinds to get treatment’ (51). The major causes of cataract blindness recorded are ‘carrying heavy load of firewood on head’ (59), ‘aging’ (47) and ‘not oiling the hair regularly’ (46)according to the present study

Electrical stimulation based on chronaxie reduces atrogin‐1 and myoD gene expressions in denervated rat muscle

Denervation induces muscle fiber atrophy and changes in the gene expression rates of skeletal muscle. Electrical stimulation (ES) is a procedure generally used to treat denervated muscles in humans. This study evaluated the effect of ES based on chronaxie and rheobase on the expression of the myoD and atrogin-1 genes in denervated tibialis anterior (TA) muscle of Wistar rats. Five groups were examined: (1) denervated (D); (2) D+ES; (3) sham denervation; (4) normal (N); and (5) N+ES. Twenty muscle contractions were stimulated every 48 h using surface electrodes. After 28 days, ES significantly decreased the expression of myoD and atrogin-1 in D+ES compared to the D group. However, ES did not prevent muscle-fiber atrophy after denervation. Thus, ES based on chronaxie values and applied to denervated muscles using surface electrodes, as normally used in human rehabilitation, was able to reduce the myoD and atrogin-1 gene expressions, which are related to muscular growth and atrophy, respectively. The results of this study provide new information for the treatment of denervated skeletal muscle using surface ES.

Poster 90: Expression of Muscular Growth Factor on Passive Stretching in the Rat Skeletal Muscle

Objective: To investigate the effect of muscle growth by passive stretching exercise on the rat skeletal muscle. Design: Case-control study. Setting: University laboratory. Animals: 10 male Wistar rats weighing 250 to 350g. Intervention: Continuous passive stretching of unilateral gastrocnemius muscle under anesthesia by ankle dorsiflexion for 15 minutes a day, and 4 procedures were done within the week. Then muscles were removed and ribonucleic acid (RNA) was extracted. Main Outcome Measure: Semiquantitation of the messenger RNA was done for the mechanogrowth factor, that is, an autocrine variant of insulin-like growth factor secreted from muscle, and myogenin, a myogenic transcription factor that enhances the gene expression of the muscle, using the reverse transcription polymerase chain reaction method. Results: Messenger RNA of the mechanogrowth factor was significantly increased in stretched gastrocnemius muscle as compared with the unstretched contralateral one. The expression of myogenin messenger RNA trend to increase, however, the difference was not significant. Conclusions: Brief passive stretching exercise induces the mechanogrowth factor. This finding suggests that passive stretching may prevent the disuse atrophy of patients in an unconscious state or with neurologic defects.

Age-Dependent Effects of Physical Activity on Lean Mass Accrual

Physical activity may be one of the most important modifiable factors for the development of lean mass (an index of muscular growth) in childhood and adolescence. However, the effects of normal growth and maturation may mask the effects of physical activity. To distinguish the age-dependent effects of physical activity from those of growth and maturation, individual growth trajectories must be identified; this can only be achieved using longitudinal data. PURPOSE: To investigate the independent effects of physical activity at each measurement occasion on total body lean mass (TBLM) accrual. METHODS: 105 boys and 103 girls, participating in the Saskatchewan Pediatric Bone Mineral Accrual Study (PBMAS), were repeatedly assessed during the circumpubertal years. At study entry they were 8 and 15 years of age; a 13-year developmental pattern (8 to 21 years) was constructed based on seven years of annual data. Height and physical activity were assessed biannually. TBLM was assessed annually by dual energy X-ray absorptiometry (DXA) (Hologic 2000). Physical activity was determined using the physical activity questionnaires for children and adolescence (PAQ-C/A). Biological age, a measure of maturity, was denned as years from age of peak height velocity. Data were analyzed using random effects models. RESULTS: The fixed coefficients that significantly predicted TBLM were biological age (years) (−722g ± 127g, p>0.05), height (cm) (607g ± 18g, p>0.05), body mass (g) (213g ± 12g, p>0.05), sex (0=boy;1=girl) (−2410g ± 434g, p>0.05) and physical activity (1=low;5=high) (214g ± 81g, p>0.05). CONCLUSIONS: For boys of the same biological age, height and body mass TBLM is predicted to be 2.2% higher in the most active boy compared to the least active boy; a 3.2% difference was found in girls. The results indicate that physical activity has a significant independent effect on total body lean mass accrual during childhood and adolescence.

Growth improvement by probiotic in European sea bass juveniles ( Dicentrarchus labrax, L.), with particular attention to IGF-1, myostatin and cortisol gene expression

In the present study a Lactic Acid Bacteria (LAB) strain Lactobacillus delbrueckii delbrueckii, acting as probiotic, was administered to Dicentrarchus labrax (European sea bass) juveniles for a short (25 days) and a long (59 days) time and the effects of the bacteria on gut colonization in sea bass juveniles cortisol level and growth were evaluated with respect to fish fed on live preys solely (control group). Measures of body weight and standard length (S.L.) were performed to assess juveniles growth, while cortisol, a hormone directly involved in stress responses, was chosen as a stress marker. In addition, the expression of two antagonistic genes involved in muscular growth (IGF-I and myostatin (MSTN) was analyzed through real-time PCR. Fish fed on live preys added with L. delbrueckii delbrueckii showed a high gut colonization by this Lactic Acid Bacteria strain. In the same fish a significantly ( p < 0.05) lower cortisol level was observed with respect to those fed on live preys solely (control 5.1 ± 0.47 ng/g; group A: 3.6 ± 0.36 ng/g; group B: 4.5 ± 0.48 ng/g). In addition, an increase of IGF-I transcription was observed in fish treated with LAB, being IGF-I mRNA levels six times higher in both treated groups with respect to the control (control: 1 ± 0.01 a.u.; group A: 6.63 ± 0.18 a.u.; group B: 6.16 ± 0.15 a.u.). On the contrary, MSTN mRNA transcription was significantly inhibited in treated groups (control 1 ± 0.02 a.u.; group A: 0.71 ± 0.01 a.u.; group B: 0.26 ± 0.003 a.u.). These results are in agreement with the increase of body weight recorded in this study. Fish fed on LAB showed 81% higher body weight in long treated group and 28% in short treated one with respect to control.

Identification of genetic variants in differentially expressed sequences in cattle of different metabolic type – potential genetic markers of nutrient utilization

Abstract. Two cattle breeds serve as a model to identify genes and genetic variants, respectively, that are potentially associated with nutrient transformation: Holsteins bred for high milk production mainly, and Charolais bred for high body weight with outstanding muscular growth. The major differences between Charolais and Holstein regarding many general body parameters originate from differences in pathways and deposition of nutrients. In an initial experiment, expressed sequence tags (ESTs) differentially displayed between both cattle breeds were isolated by mRNA differential display in liver and intestine. Of the in total identified 277 ESTs, 79 showing the most prominent differences, were screened for single nucleotide polymorphisms (SNPs). Thirty four SNPs were detected in 30 ESTs In a direct sequencing approach based on the comparative sequencing of the corresponding amplicons generated by PCR from genomic DNA pools of 20 animals each of both cattle breeds,. Eighteen of these SNPs showed breed specific distribution of allelic variants. Occurrence of ESTs with a breed specific SNP distribution and localisation of the respective ESTs to chromosome regions known to be affecting carcass and growth traits in cattle suggest a trait association of the respective SNPs. The polymorphic nature of the SNP markers suggests that they will be useful for evaluating whether variation in these genomic regions influences nutrient pathways in cattle.

The German Musical Exile and the Course of American Musicology

On the face of it, the subject would seem not to need a paper. Musicology was a European discipline fed from many sources, named by Friedrich Chrysander (1863, 1867), defined by Guido Adler (1885), and, during its early twentieth-century course, shaped by Friedrich Ludwig and Hugo Riemann. Like other humanities during the muscular growth of Wilhelmine Germany, it became a German province. As America had taken its classical music from Germany during the nineteenth century, so it took its musicology from Germany in the early years of the twentieth. But our pioneers soon set out to create a distinctly American musicology, and were on their way to doing so from the founding of the Musical Quarterly in 1915 to the creation of the New York Musicological Society in 1931 and its reorganization as the American Musicological Society (AMS) three years later.3 They were soon overtaken by an unexpected influx of emigre scholars in flight from central Europe whose numbers and prestige charted the course of the fledgling discipline anew. Eventually, as the emigres passed from the scene, and the generations of those they had taught began to pass from it as well, their influence eroded and American musicology reclaimed its national character, however that character would come to be construed. It seems a straightforward story. It isn’t. That story tells us little about why we did what we did during the early decades of our Society’s existence. It narrates the meteoric rise of the emigres’ influence, but fails to account for its seemingly sudden collapse. When in 1985 Joseph Kerman published a stunning critique of postwar Anglo-American scholarship-he had been fighting the battle for twenty years before that-Margaret Bent responded as President of the AMS with an Address at the Society’s annual meeting that year in Vancouver, defending the classic paradigm with the authority of one who was its elegant voice and the passion of one who recognized what was at stake (Kerman 1985; Bent 1986). But by the annual meeting in 1990 in Oakland the field had become a Babel of voices.

Effects of protein deficiency on the mRNA levels of insulin‐like growth factors and myostatin in skeletal muscle of weaned lambs

ABSTRACTWe investigated the effect of protein deficiency on mRNA levels of insulin‐like growth factors (IGF‐I and ‐II) and myostatin in skeletal muscle of weaned lambs. Weaned lambs were given a control diet (crude protein, 18%) or a low protein diet (crude protein, 5.7%) for 20 days. A small piece of the M. longissimus thoracis was collected by surgical biopsy at the end of feeding trial. The mRNAs of IGFs and myostatin were determined using a real‐time reverse transcription polymerase chain reaction. Blood samples were also collected to measure plasma concentrations of IGF‐I and serum urea nitrogen. Control lambs gained normally, whereas the bodyweight of the animals given the low protein diet was maintained and was significantly lower than that of the control from 10 days of the onset of feeding trial. Protein deficiency affected neither IGF mRNAs nor myostatin mRNA in the muscle. The expression of these mRNAs was unlikely to respond sensitively to protein deficiency in the muscle. However, serum IGF‐I concentration was significantly lower in the protein deficient lambs than in the control animals. Therefore, we consider that the retardation of muscular growth does not depend on the local mRNA expression of these factors in protein deficient lambs, but the reduction of serum IGF‐I, at least, partly contributes to the suppression of growth.

Increases in Skeletal Muscle Size Following Moderate Vascular Occlusion in Standardbred Horses

2343 Moderate vascular occlusion increases muscular activity and can be used in populations that cannot tolerate high intensity exercise to promote muscular growth. PURPOSE: To demonstrate whether moderate vascular occlusion would result in changes to limb muscle size in horses. Methods: Six healthy, unfit Standardbred mares (age 14 ± 4, body mass 529 ± 49 kg, mean ± SD) were used. Horses (standing at rest) wore an occlusion cuff at the most proximal position of the left foreleg. The right foreleg was used as control. An occlusion pressure of 200 mmHg was set for 5 min followed by 10 min recovery. Three sets of occlusions were given to each horse. Ulnaris lateralis/flexor digitorum profundus and extensor digitorum communis muscle thickness were measured using B-mode ultrasound. Foreleg and 1st phalanx circumference was st measured using a flexible-tape measure. Pulse wave Doppler was performed on the radialis artery with a 5–10 mHz mechanical transducer three times at baseline and twice during each occlusion. A final measurement was also obtained 2 to 3 min after removal of the cuff. Peak flow velocity (PFV), and the flow integral (FVI) were measured each time. Results: Mid-foreleg but not 1st phalanx girth was increased (p<0.05) in st the occluded but not the control leg following occlusionFlextensor and flexor MTH was increased (p<0.05) in the occluded but not the control leg. There were no changes (p>0.05) in PFV or FVI at any measured time-point. Conclusion: Moderate vascular occlusion may be a suitable and safe model to study muscle hypertrophy in horses.

Effect of Kaiyu Qingwei granule on insulin receptor in liver and skeletal muscular cell membrane in diabetes mellitus rats

Objective: To investigate the effect of Kaiyu Qingwei granule (KYQWG) on the insulin binding capacity of liver and skeletal muscular cell membrane and serum insulin-like growth factor-1 (IGF-1) in streptozotocin-induced diabetic rats.Methods: Rats in four experimental groups were investigated: the control group, the model group, the KYQWG group and the Metformin group. The insulin binding rate (IBR) of liver and skeletal muscular cell membrane was detected by receptor-ligand radiometric method and changes of serum levels of glucose, insulin and IGF-1 were observed before and after 4 weeks of medication.Results: The KYQWG group had a lower blood glucose level and IBR of liver and muscular cell membrane, as compared with those in the model group (P<0.01 or P<0.05), and a higher level of IGF-1 than that in the model group(P<0.01), but had no obvious changes in the serum level of insulin.Conclusion: KYQWG may increase the serum level of IGF-1 in diabetic rats, thus to decrease the insulin resistance at ante-receptor sites and improve the sugar metabolic disturbance in rats with diabetes mellitus.

Lógica clínica en cirugía ortopédica de la parálisis cerebral

The evolution of muscular contractures and skeletal deformities in cerebral palsy, and criteria for prevention or therapeutical decisions are analized. Developmental brain damage produces a disbalance between bone and muscular growth. Orthopaedic palliative treatments try to avoid malposition of the extremities and to compensate mechanical disbalance during the entire skeletal growth. Therapeutical options are based is on the distinction between dynamic situations and rigid ones; and also on the presence or absence of articular fixed deformities.

Effect of dietary fats on hepatic lipid metabolism in the growing turkey

The influence of dietary fatty acids on hepatic capacity of lipid synthesis and secretion was investigated in 7-week-old male turkeys. They were fed 10% of either lard (rich in saturated and monounsaturated fatty acids) or linseed oil (rich in polyunsaturated fatty acids, especially 18:3n-3). Fattening was identical with both diets (0.15–0.20% of abdominal adipose tissue), but the proportion of muscle Pectoralis major was lower with linseed oil (6.6 vs. 7.4%). Specific activities of lipogenic enzymes (ME, G6PDH, ACX, and Δ9-desaturase) were not influenced by the diet, however, FAS activity was lower with linseed oil (14.3 vs. 25.4 nM NADPH fixed/min). Fasting concentrations of lipoproteins synthesized and secreted by the liver, VLDL and HDL, were also lower with linseed oil, as well as plasma concentrations of phospholipids and cholesteryl esters. However, when VLDL catabolism was inhibited by injection of an antiserum against LPL, VLDL concentration was identical in both groups (100–120 mg/l), whereas that of phospholipids and cholesteryl esters, that are transported by HDL mainly, remained lower with linseed oil. Thus, in the growing turkeys, and contrary to mammals and the chicken, feeding n-3 polyunsaturated fatty acids did not decrease hepatic triglyceride synthesis and secretion, nor fattening. By contrast, in this species, n-3 polyunsaturated fatty acids appear to influence mostly HDL metabolism, with a negative impact on muscular growth.

Content and localization of myostatin in mouse skeletal muscles during aging, mechanical unloading and reloading.

Changes in myostatin content and localization in mouse skeletal muscles were investigated during aging, hindlimb suspension (HS) and reloading after HS. During aging, the content of myostatin among solubilized proteins in gastrocnemius and plantaris muscles (Gast/Plant) was initially low and increased until their wet weight/body weight ratio reached a peak. It remained unchanged with further aging, although gradual atrophy of the muscles was seen to occur. Also, the myostatin content did not change significantly during HS (up to 14 days) in both Gast/Plant and soleus muscles, though the muscles showed morphological signs of atrophy. However, reloading for 2 days after a 14-day HS caused significant decreases in the myostatin content in both of these muscles. Immunohistochemical observations showed the sarcoplasmic existence of myostatin, the amount of which appeared to decrease after reloading. The results suggest that myostatin plays a part in the processes of muscular growth and loading-induced hypertrophy, but is not involved in either aging-related or unloading-induced muscular atrophy.

The effects of dietary energy restriction on overloaded skeletal muscle in rats

We evaluated the effects of three levels of energy intake, 73 % (CON73), 81 % (CON81) and 100 % (CON100) of the ad libitum intake of the control diet, on skeletal muscle growth induced by functional overload in male rats. Unlike most previous studies which have employed chronic or acute food restriction where all nutrients are reduced in the diet, the present study tested the effects of energy deprivation as a single factor without inducing other nutritional deficiencies. Muscular growth of plantaris and soleus muscles was induced by removal of synergist gastrocnemius muscles in one hindlimb; muscles in the other leg were used as sham-operated intra-animal controls. After 30 d, rats on the energy-restricted CON73 and CON81 diets gained less weight and had smaller livers, kidneys, hearts and fat pads (epididymal, retroperitoneal and omental) than CON100 rats They also had smaller sham-operated plantaris muscles (CON73 --13 %, CON81 --9 %) containing less total protein (CON73 --14 %; CON81 --10 %) than CON100 rats However, the same measurements in overloaded plantaris muscles were similar among groups. Soleus muscle mass and protein contents were not significantly affected by energy restriction in our study. Percentage distributions of myosin heavy-chain isoforms (types I, IIa, IIx and IIb) were similar among rats in CON100, CON81 and CON73 groups for both plantaris and soleus muscles. We conclude that the growth reduction of plantaris muscle induced by energy restriction at 73 % and 81 % for 30 d was prevented by functional overload in male rats.

Dietary Protein Does Not Affect Overloaded Skeletal Muscle in Rats

We compared the effects of three levels of dietary protein, i.e., 7% (low protein; LP); 17.5% (adequate protein; CON); or 30% (high protein; HP) on growth of functionally overloaded muscle in Sprague-Dawley male rats. Growth of plantaris and soleus muscles was induced by the surgical removal of gastrocnemius muscles in one hindlimb; muscles in the other leg were used as sham-operated, intra-animal controls. After 4 wk, rats fed the 7% LP diet gained less weight (-29%) and had lighter livers (-20%) and kidneys (-16%) than rats fed the CON diet (P < 0.05). Measurements of rats fed the 30% HP diet were not different from those of CON rats except that their kidneys were larger (+6%) (P < 0.05). The level of dietary protein did not affect the experimentally induced muscular growth in either plantaris or soleus muscles. Gains in overloaded plantaris muscles over sham-operated muscles were not different among rats fed LP, CON and HP diets for muscle mass (+42 to +45%), total protein (+42 to +46%) and myofibrillar protein (+40 to +44%). Soleus muscles also did not differ among diet groups for gains in mass (+20 to +33%), total protein (+20 to +33%) and myofibrillar protein (+21 to +33%). No dietary protein effects were found on myosin heavy chain isoform (I, IIa, IIx, IIb) expression in either plantaris or soleus muscles. We conclude that gains in plantaris and soleus muscle mass, total protein and myofibrillar protein induced by functional overload are not affected by low (7%) or high (30%) protein feeding in young male rats for 4 wk.

Osteopenic syndromes in the adolescent female.

Low bone density in growing girls and mature young women is usually a finding that needs an explanation and further clinical investigation. Population-based epidemiologic studies on osteoporosis in young persons do not exist. As a disease, osteoporosis among children and adolescents is rate, and since 1965 only 100 cases of idiopathic juvenile osteoprososis have been reported. When osteoporosis occurs in children, it is usually secondary to an underlying medical disorder (e.g., anorexia nervosa, leukemia) or to medications, but occasionally no identifiable primary cause can be detected. It may also be the result of a genetic disorder such as osteogenesis imperfecta. On the other hand, osteopenia in growing and young persons seems much commoner and needs further investigation. Adolescence is a period of increased calcium requirement, and girls with an underlying bone disease are at higher risk for bone demineralization. An additional point of interest is the changes in the geometry of bones through their continuous adaptation to simultaneous skeletal and muscular growth. Bones, through the mechanostat mechanism, adapt to mechanical loading by differentiating their geometry. A recent finding in this direction is that before and during the teenage years there is an environmental effect of physical activity and nutrition on hip geometry. Another important finding is an age-dependent increase in bone cross-sectional area and bone strength index in the absence of an increase in volumetric spongiosa bone density and cortical bone density. Girls, in comparison to boys, deposit more calcium in their bones during puberty, thus probably preparing their skeleton for the forthcoming events of pregnancy and lactation.