A noninvasive analysis of urinary musculoskeletal collagen metabolism markers from rhesus monkeys subject to chronic hypergravity.

A decrease in load-bearing activity, as experienced during spaceflight or immobilization, affects the musculoskeletal system in animals and humans, resulting in the loss of bone and connective tissue. It has been suggested that hypergravity (HG) can counteract the deleterious effects of microgravity-induced musculoskeletal resorption. However, little consensus information has been collected on the noninvasive measurement of collagen degradation products associated with enhanced load-bearing stress on the skeleton. The purpose of this study is to assess the urinary collagen metabolic profiles of rhesus monkeys (Macaca mulatta) during 1) 2 wk of basal 1 G (pre-HG), 2) 2 wk of HG (2 G), and 3) two periods of post-HG recovery (1 G). Urine was collected over a 24-h period from six individual rhesus monkeys. Hydroxyproline (Hyp) and collagen cross-links (hydroxylysylpyridinoline and lysylpyridinoline) were measured by reverse-phase HPLC. Urinary calcium, measured by atomic absorption, and creatinine were also assayed. The results indicate no changes in nonreducible cross-links and Hyp during HG. Collagen cross-link biomarker levels were significantly elevated during the 2nd wk of HG. Urinary calcium content was significantly lower during HG than during the 1-G control period, suggesting calcium retention by the body. We conclude that there is an adaptation of the nonhuman primate musculoskeletal system during hyperloading and that noninvasive measurements of musculoskeletal biomarkers can be used as indicators of collagen and mineral metabolism during HG and recovery in nonhuman primates.

Temporal extracellular matrix adaptations in ligament during wound healing and hindlimb unloading.

Previous data from spaceflight studies indicate that injured muscle and bone heal slowly and abnormally compared with ground controls, strongly suggesting that ligaments or tendons may not repair optimally as well. Thus the objective of this study was to investigate the biochemical and molecular gene expression of the collagen extracellular matrix in response to medial collateral ligament (MCL) injury repair in hindlimb unloaded (HLU) rodents. Male rats were assigned to 3- and 7-wk treatment groups with three subgroups each: sham control, ambulatory healing (Amb-healing), and HLU-healing groups. Amb- and HLU-healing animals underwent bilateral surgical transection of their MCLs, whereas control animals were subjected to sham surgeries. All surgeries were performed under isoflurane anesthesia. After 3 wk or 7 wk of HLU, rats were euthanized and MCLs were surgically isolated and prepared for molecular or biochemical analyses. Hydroxyproline concentration and hydroxylysylpyridinoline collagen cross-link contents were measured by HPLC and showed a substantial decrement in surgical groups. MCL tissue cellularity, quantified by DNA content, remained significantly elevated in all HLU-healing groups vs. Amb-healing groups. MCL gene expression of collagen type I, collagen type III, collagen type V, fibronectin, decorin, biglycan, lysyl oxidase, matrix metalloproteinase-2, and tissue inhibitor of matrix metalloproteinase-1, measured by real-time quantitative PCR, demonstrated differential expression in the HLU-healing groups compared with Amb-healing groups at both the 3- and 7-wk time points. Together, these data suggest that HLU affects dense fibrous connective tissue wound healing and confirms previous morphological and biomechanical data that HLU inhibits the ligament repair processes.

Evaluation of bone and collagen metabolism by assessing urinary biomarkers in non-human primates.

The purpose of this investigation was to evaluate mineralized and non-mineralized connective tissue responses of non-human primates to microgravity by non-invasive analysis of urinary biomarkers.

Cortical bone responses to 2G hypergravity in growing rats.

BACKGROUND: Rat cortical bone adaptation to chronic hypergravity (2G) was studied using young growing male Wistar rats (60 d). METHODS: Animals (10 rats) were subjected to chronic hypergravity (14 d) in order to understand the plastic nature of bone under a constant hypergravity stress using a special rodent habitat that was attached to a 12-ft. radius centrifuge. Also, an equal number of stationary controls were housed in a rodent vivarium containing identical cages that were used for centrifugation. After 14 d of centrifugation, femur bones were excised and prepared for morphological and biochemical measurements. RESULTS: Results showed that 2G had significantly shortened the femurs (3%) and reduced the cortical bone area (13%). In particular, hypergravity induced significant reductions in the thicknesses of cortical bone at the anterior (13%) and medial regions (15%) of the mid-diaphysis. However, femoral bone density, collagen and calcium concentrations were unaltered. The content of mature, stable bone collagen cross-links hydroxylysylpyridinoline (HP), lysylpyridinoline (LP), were significantly greater in bones from centrifuged animals. CONCLUSION: Our findings suggest that short term exposure to 2G does not enhance bone formation or induce changes in cortical bone composition, or alter specific gravity. These data also suggest that bone maturation as reflected by collagen cross-linking is upregulated. However, it is undetermined at this time whether the enhanced content of mature bone collagen in the centrifuged rats is a result of either an increased rate of cross-linking or reduction in the degradation of "older collagen."

Ultrasonic wave velocity measurement in small polymeric and cortical bone specimens.

A system was refined for the determination of the bulk ultrasonic wave propagation velocity in small cortical bone specimens. Longitudinal and shear wave propagations were measured using ceramic, piezoelectric 20 and 5 MHz transducers, respectively. Results of the pulse transmission technique were refined via the measurement of the system delay time. The precision and accuracy of the system were quantified using small specimens of polyoxymethylene, polystyrene-butadiene, and high-density polyethylene. These polymeric materials had known acoustic properties, similarity of propagation velocities to cortical bone, and minimal sample inhomogeneity. Dependence of longitudinal and transverse specimen dimensions upon propagation times was quantified. To confirm the consistency of longitudinal wave propagation in small cortical bone specimens (< 1.0 mm), cut-down specimens were prepared from a normal rat femur. Finally, cortical samples were prepared from each of ten normal rat femora, and Young's moduli (Eii), shear moduli (Gij), and Poisson ratios (Vij) were measured. For all specimens (bone, polyoxymethylene, polystyrene-butadiene, and high-density polyethylene), strong linear correlations (R2 > 0.997) were maintained between propagation time and distance throughout the size ranges down to less than 0.4 mm. Results for polyoxymethylene, polystyrene-butadiene, and high-density polyethylene were accurate to within 5 percent of reported literature values. Measurement repeatability (precision) improved with an increase in the wave transmission distance (propagating dimension). No statistically significant effect due to the transverse dimension was detected.

Effects of exercise on knee joints with osteoarthritis: a pilot study of biologic markers.

OBJECTIVE: To determine the effects of low intensity weight-bearing exercise on osteoarthritis (OA) of the knee. METHODS: Synovial fluid keratan sulfate (KS) and hydroxyproline were measured as markers of cartilage degradation. The Arthritis Impact Measurement Scales (AIMS) were used to measure health status, and a visual analog scale for pain assessment was used before and after intervention. An exercise (EX) group (n = 15) received a thrice-weekly 12-week low intensity exercise program and a weekly educational program, and a minimal treatment (Min RX) group (n = 15) received only the education program. RESULTS: Pain levels declined in the EX group, and the Min RX group showed improvement on the AIMS. Synovial fluid was obtained in 11 subjects before and after the intervention. Levels of KS and hydroxyproline did not change. CONCLUSION: Further study of exercise effects should include both clinical and biologic parameters to examine the outcome of exercise as a therapeutic intervention in OA of the knee.

Effect of a growth hormone treatment on bone orthotropic elasticity in dwarf rats.

A refinement of the current ultrasonic elasticity technique was used to measure the orthotropic elastic properties of rat cortical bone as well as to quantify changes in elastic properties, density, and porosity of the dwarf rat cortex after a treatment with recombinant human growth hormone (rhGH). The ultrasonic elasticity technique was refined via optimized signal management of high-frequency wave propagation through cubic cortical specimens. Twenty dwarf rats (37 days old) were randomly assigned to two groups (10 rats each). The dwarf rat model (5-10% of normal GH) was given subcutaneous injections of either rhGH or saline over a 14-day treatment period. Density was measured using Archimedes technique. Porosity and other microstructural characteristics were also explored via scanning electron microscopy and image analysis. Statistical tests verified significant decreases in cortical orthotropic Young's (-26.7%) and shear (-16.7%) moduli and density (-2.42%) concomitant with an increase in porosity (+125%) after rhGH treatments to the dwarf model (p < 0.05). A change in material symmetry from orthotropy toward planar isotropy within the radial-circumferential plane after GH treatments was also noted. These results demonstrate some alteration in bone properties at this time interval. Structural implications of these changes throughout physiological loading regimens should be explored.

Noninvasive markers of bone metabolism in the rhesus monkey: normal effects of age and gender.

Measurement of bone turnover in conditions such as osteoporosis has been limited by the need for invasive iliac bone biopsy to reliably determine parameters of bone metabolism. Recent advances in the area of serum and urinary markers of bone metabolism have raised the possibility for noninvasive measurements; however, little nonhuman primate data exist for these parameters. The purpose of this experiment was to define the normal range and variability of several of the newer noninvasive bone markers which are currently under investigation in humans. The primary intent was to determine age and gender variability, as well as provide some normative data for future experiments in nonhuman primates. Twenty-four rhesus macaques were divided into equal groups of male and female according to the following age groupings: 3 years, 5-10 years, 15-20 years, and > 25 years. Urine was collected three times daily for a four-day period and measured for several markers of bone turnoverm including pyridinoline (PYD), deoxypyrodinoline (DPD), hydroxyproline, and creatinine. Bone mineral density measurements of the lumbar spine were performed at the beginning and end of the study period. Serum was also obtained at the time of bone densitometry for measurement of osteocalcin levels by radioimmunoassay. There were no significant differences in bone mineral density, urine PYD, or urine DPD based on gender. Bone density was lowest in the youngest animals, peaked in the 15-20-year group, but again decreased in the oldest animals. The osteocalcin, PYD, and DPD levels followed an inversely related pattern to bone density. The most important result was the relative age insensitivity of the ratio of PYD:DPD in monkeys up to age 20 years. Since bone density changes take months or years to become measurable and iliac biopsies are invasive, the PYD/DPD marker ratio may have important implications for rapid noninvasive measurement of the effects of potential treatments for osteoporosis in the non-human primate model.

The effect of nonablative laser energy on joint capsular properties. An in vitro histologic and biochemical study using a rabbit model.

The purpose of this study was to evaluate the effect of laser energy at nonablative levels on joint capsular histologic and biochemical properties in an in vitro rabbit model. The medial and lateral portions of the femoropatellar joint capsule from both stifles of 12 mature New Zealand White rabbits were used. Specimens were divided into three treatment groups (5 watts, 10 watts, and 15 watt) and one control group using a randomized block design. Specimens were placed in a 37 degrees bath of lactated Ringer's solution and laser energy was applied using a holmium:yttrium-aluminum-garnet laser in four transverse passes across the tissue at a velocity of 2 mm/sec with the handpiece set 1.5 mm from the synovial surface. Histologic analysis revealed thermal alteration of collagen (fusion) and fibroblasts (pyknosis) at all energy densities, with higher laser energy causing significantly greater morphologic changes over a larger area (P < 0.05). Application of laser energy did not significantly alter the biochemical parameters evaluated, including type I collagen content and nonreducible crosslinks (P > 0.05). This study demonstrated that nonablative laser energy caused significant thermal damage to the joint capsular tissue in an energy-dependent fashion, but type I collagen content and nonreducible crosslinks (P > 0.05). This study demonstrated that nonablative laser energy caused significant thermal damage to the joint capsular tissue in an energy-dependent fashion, but type I Collagen content and nonreducible corsslinks were not significantly altered.

Effect of a hypergravity environment on cortical bone elasticity in rats.

There is considerable interest in determining whether hypergravity can be used as a countermeasure for microgravity-induced bone loss. This study was conducted on 20 immature male rats in order to investigate possible elastic adaptations of cortical bone in rapidly growing rats exposed to chronic hypergravity. Ten rats were continuously centrifuged for 14 days at twice gravitational acceleration (2G) on a 12.75 foot radius centrifuge and 10 rats concurrently acted as stationary controls. The effect of hypergravity on the elastic characteristics of cortical bone was quantified via ultrasonic wave propagation. Propagation velocities of longitudinal and shear waves were measured through cubic cortical specimens from the posterior femoral diaphyses. Density was measured with an Archimedes' technique. The orthotropic elastic properties were calculated and used to compare the difference between groups. Results showed an average increase in both the Young's moduli (Eii, + 2.2%) and shear moduli (Gij, + 4.3%) with a statistically significant increase only in G12 (+15.7%, P = 0.046). The ratio of transverse to axial strain (Poisson's ratio, nuij) demonstrated statistically significant changes in nu12, nu21, nu13, and nu31 (P < 0.05). These findings suggest that although slight elastic changes were incurred via a hypergravity environment, the treatment level or duration in this study do not dramatically perturb the normal elastic behavior of cortical bone and that dramatic biomechanical differences noted in previous studies were due more to structural changes than material elasticity changes. Hypergravity applied post facto to a microgravity environment would offer further illucidation of this method as treatment for a degenerative spaceflight experience.

Cortical bone growth and maturational changes in dwarf rats induced by recombinant human growth hormone.

The growth hormone (GH)-deficient dwarf rat was used to investigate recombinant human (rh) GH-induced bone formation and to determine whether rhGH facilitates simultaneous increases in bone formation and bone maturation during rapid growth. Twenty dwarf rats, 37 days of age, were randomly assigned to dwarf plus rhGH (GH; n = 10) and dwarf plus vehicle (n = 10) groups. The GH group received 1.25 mg rhGH/kg body wt two times daily for 14 days. Biochemical, morphological, and X-ray diffraction measurements were performed on the femur middiaphysis. rhGH stimulated new bone growth in the GH group, as demonstrated by significant increases (P < 0.05) in longitudinal bone length (6%), middiaphyseal cross-sectional area (20%), and the amount of newly accreted bone collagen (28%) in the total pool of middiaphyseal bone collagen. Cortical bone density, mean hydroxyapatite crystal size, and the calcium and collagen contents (microgram/mm3) were significantly smaller in the GH group (P < 0.05). Our findings suggest that the processes regulating new collagen accretion, bone collagen maturation, and mean hydroxyapatite crystal size may be independently regulated during rapid growth.

Changes in diaphragm muscle collagen gene expression after acute unilateral denervation.

The purpose of the present study was to examine the effects of acute (3 days) unilateral diaphragm denervation (DNV) on 1) levels of alpha 1(I) and alpha 1(III) procollagen mRNA; 2) collagen concentration [hydroxyproline (HYP)]; 3) amount of the nonreducible collagen cross-link hydroxylysylpyridinoline (HP); and 4) the passive force-length relationship of the muscle. The levels of alpha 1(I) and alpha 1(III) procollagen mRNA, HYP concentration, and amount of HP were measured in muscle segments from the midcostal region of DNV and intact (INT) hemidiaphragms of adult male Fischer 344 rats (250-300 g). The in vitro passive force-length relationship of DNV and INT hemidiaphragm was determined by lengthening and shortening the diaphragm muscle segments from 85 to 115% of optimal length at a constant velocity (0.6 optimal length/s). Three days after DNV, the level of alpha 1(I) procollagen mRNA was increased over 15-fold in the DNV hemidiaphragm compared with INT (P < 0.05), whereas the level of alpha 1(III) procollagen mRNA was increased by approximately sixfold in the DNV hemidiaphragm compared with INT (P < 0.05). Collagen (HYP) concentration did not differ between groups, averaging 8.7 and 8.9 micrograms/mg dry wt for the DNV and INT hemidiaphragms, respectively. In addition, there was no difference in the amount of the mature nonreducible collagen cross-link HP between the DNV and INT hemidiaphragms (0.66 vs. 0.76 mole HP/mole collagen, respectively). The amount of passive force developed during lengthening did not differ between DNV and INT hemidiaphragms. These data indicate that acute DNV of the hemidiaphragm is associated with an increase in the mRNA level of the two principal fibrillar collagen phenotypes in skeletal muscle. However, despite extensive muscle remodeling, the passive force-length relationship of the DNV hemidiaphragm is unaffected compared with the INT muscle.

Compatibility of adaptive responses with combining strength and endurance training.

Impairment in strength development has been demonstrated with combined strength and endurance training as compared with strength training alone. The purpose of this study was to examine the effects of combining conventional 3 d.wk-1 strength and endurance training on the compatibility of improving both VO2peak and strength performance simultaneously. Sedentary adult males, randomly assigned to one of three groups (N = 10 each), completed 10 wk of training. A strength-only (S) group performed eight weight-training exercises (4 sets/exercise, 5-7 repetitions/set), an endurance-only (E) group performed continuous cycle exercise (50 min at 70% heart rate reserve), and a combined (C) group performed the same S and E exercise in a single session. S and C groups demonstrated similar increases (P < 0.0167) in 1RM squat (23% and 22%) and bench press (18% for both groups), in maximal isometric knee extension torque (12% and 7%), in maximal vertical jump (6% and 9%), and in fat-free mass (3% and 5%). E training did not induce changes in any of these variables. VO2peak (ml.kg-1.min-1) increased (P < 0.01) similarly in both E (18%) and C (16%) groups. Results indicate 3 d.wk-1 combined training can induce substantial concurrent and compatible increases in VO2peak and strength performance.

Morphological and biochemical effects of strenuous exercise on immature long bones.

To determine the effects of intense exercise on the growth of long bones in immature animals, young male white leghorn chickens were run five days per week starting at four weeks of age on motor-driven treadmills. Work intensity was determined on the basis of maximal oxygen consumption (VO2 max) with the exercise intensity maintained at 70-80 percent VO2 max. Young animals ran continuously for 30 minutes, older animals 45 to 60 minutes each day. Runners and controls (10 animals per group) were sacrificed at 8, 12, 14 and 20 weeks of age. The lengths of the femurs and tibiotarsus were significantly stunted at 8-, 12- and 14 weeks in the runners but had nearly recovered at 20 weeks of age. Both bones also demonstrated significantly decreased total cross-sectional areas in 8-, 12- and 14 week-old runners as well as decreased cortical cross-sectional areas. The tibiotarsus also remained significantly smaller in the 20-week-old runners, but the femur had recovered in terms of radial growth. Intermolecular pyridinoline collagen crosslinks were identical in amount in the two groups with the femur collagen significantly less cross-linked than the tibiotarsus. The delayed growth of the exercised avian young bone is consistent with data obtained from children and young mammalian models. The osteogenic response to exercise that produces an increased bone mass in adult tissue appears either suppressed or overcome in young avian bone indicating that it may be erroneous to assume that data obtained from adult tissue are also applicable to young growing bone.

Regional and age variations in growing tendon.

Gastrocnemius tendons of 10 White Leghorn chickens at 6, 8, and 12 weeks of age were divided into proximal, middle, and distal portions to assess regional variability in composition and growth. Body weight increases approximately 150% during the period examined, whereas the lateral gastrocnemius muscle and tendon increase approximately 193% and 227%, respectively. No significant changes in cellularity (DNA concentration) or hydroxypyridinium (OHP) crosslinks occur with increasing age. Hydroxyproline (HYP) concentration increases by 12 weeks of age, as hexuronate, glucosamine, and galactosamine decrease. Composition shows some regional variation: the distal region of the tendon has a lower HYP concentration and increased GAGs and OHP crosslinks compared to either the proximal or middle regions, which do not differ from each other. The mean collagen fibril diameter increases with age, but the oldest tendons also contain more small diameter fibrils (< 40 nm). There is a unimodal fibril distribution at all three ages, although this has broadened by 12 weeks. The data from this study suggest that rapid tendon growth occurs throughout the time period examined and that changes characteristic of mature tendon, such as increased OHP crosslink concentration, have not yet developed in hatchlings because of the large amount of new tissue being produced. Whereas all three regions of the tendon are similar in size, composition of the distal region differs from that of the proximal and middle regions, suggesting that this portion of the tendon should be avoided when sampling a tendon.

Passive length-force properties of senescent diaphragm: relationship with collagen characteristics.

The purpose of this study was to examine the effect of aging on collagen concentration and extent of nonreducible collagen cross-linking as well as with the passive length-force relationship of the diaphragm muscle. Midcostal diaphragm muscle strips from young (6 mo) and senescent (24 mo) Fischer 344 rats were perfused in a tissue bath containing mammalian Ringers solution (25 degrees C) aerated with 95% O2-5% CO2. The segments were lengthened and shortened from 85 to 115% of optimal length (L(o)) at a constant velocity (0.6 L(o)/s), and the passive force was measured. Hydroxyproline (HYP) and the mature nonreducible collagen cross-link, hydroxylysylpyridinoline (HP), were measured by high-pressure liquid chromatography. The resting force at Lo did not differ between young and senescent diaphragm muscles. However, the senescent diaphragm exhibited greater passive force compared with the young (P < 0.05) at lengths > 110% of L(o). High-pressure liquid chromatography analysis revealed a higher concentration of HYP in the senescent compared with the young diaphragm (9.32 +/- 0.83 and 6.59 +/- 0.78 g HYP/mg dry wt, respectively; P < 0.05). Additionally, the content of HP was greater in the senescent compared with the young diaphragm (1.16 +/- 0.05 and 0.91 +/- 0.05 mol HP/mol collagen, respectively; P < 0.05). These results suggest that diaphragm collagen metabolism, maturation, and the passive length-force characteristics of the muscle are altered with senescence.

Mechanical and biochemical analyses of tibial compartment fascia in chronic compartment syndrome.

Increases in compartment pressure associated with chronic compartment syndrome (CCS) may be due to changes in the mechanical properties and/or thickness of fascia (4,22). To explore this possibility, we compared the mechanical and biochemical characteristics (stiffness, thickness, time-dependent response, collagen content, and collagen crosslinking) of fascia from patients with symptomatic anterior compartment syndrome to fascia from adjacent collateral compartments. We tested 43 specimens harvested from 20 individuals during surgical fasciectomy. Properties of normal (lateral)-compartment (NC) and pathological (anterior)-compartment (PC) fascia were mechanically tested in the axial and transverse directions forming four groups. An external control group (EX) of six specimens of anterior and lateral-compartment fascia harvested from amputated legs was also included in the study. PC fascia was found to be thicker and structurally stiffer (elastic modulus times thickness) in the axial direction than was NC fascia (p < or = 0.05). No significant differences were found between NC and PC time-dependent response, although significant differences between percent relaxation in the pooled axial and transverse direction specimens were observed. No differences were found in the collagen content, as measured by hydroxyproline (Hyp) concentration, between NC and PC fascia. PC fascia was found to have less collagen crosslinking by hydroxylyslpyridinoline (HP) concentration. In conclusion, although this study does not elucidate etiological factors in CCS, the changes found in PC fascia suggest that fascial mechanical properties contribute to the pathology.

Non-reducible collagen cross-linking in cartilage from broiler chickens with tibial dyschondroplasia.

Recent work has shown that hydroxylysylpyridinoline (HP), a non-reducible cross-link that stabilizes the collagen fibril network, is significantly greater (over 10-fold) in dyschondroplastic cartilage than in normal growth-plate cartilage in the tibiotarsi of chickens with homocysteine-induced tibial dyschondroplasia (TD). In the present study, broiler chicks with a genetic disposition to TD, as well as normal broiler chicks on a copper-deficient diet alone or supplemented with copper and thiram, were raised for 3 to 4 weeks (Expts. 1 and 2). Their dyschondroplastic cartilage from the proximal tibiotarsus was collected and analyzed for HP as well as lysylpyridinoline (LP) cross-links. Normal growth plate cartilage was obtained from chicks on the copper-deficient diet supplemented with copper. In a third experiment, another set of broiler chicks was raised on a corn/soybean meal-based diet with or without homocysteine, and their articular and sternal cartilage were isolated for cross-link analysis. In the first two experiments, dyschondroplastic cartilage from all birds with induced TD had higher HP and LP concentrations than growth-plate cartilage from birds without TD, although the ratios of HP to LP varied. In the third experiment, the sternal and articular cartilage from birds with homocysteine-induced TD appeared normal, having similar HP concentrations in the same types of cartilage in birds without TD.

Adaptations of immature trabecular bone to moderate exercise: geometrical, biochemical, and biomechanical correlates.

Strenuous endurance exercise can adversely affect the mechanical integrity of immature bone, but it is unclear whether a more moderate exercise regimen would have a positive effect. Thus, to investigate the response of immature trabecular bone to moderate exercise, we randomly assigned female Sprague-Dawley rats (8 weeks old) to either a basal-control, exercise, or age-matched control group. The basal-control rats were killed at 8 weeks of age, while the other two groups were killed at 18 weeks of age. Between 8 and 18 weeks, one group remained sedentary, while another group was trained progressively on a motor-driven treadmill at a moderate level of intensity. Rat femoral necks (FN) were tested in cantilever bending to failure, and the sixth lumbar vertebral bodies (L6) were compressed to 50% of their initial height. Both tissues were analyzed for calcium, hydroxyproline, and collagen-crosslinking concentrations, and for changes in geometry. The adrenal mass per unit body mass was significantly greater in the exercised group, compared to the age-matched controls. L6 calcium content, compressional stress, and elastic modulus were significantly less in the exercise group as compared to the age-matched control group. Nonreducible collagen crosslinks (hydroxylysylpyridinoline [HP] and lysylpyridinoline [LP]) were significantly greater in the older exercise and age-matched control L6 and FN. In the weightbearing FN--but not L6--the LP concentration of the exercise group was significantly greater than the age-matched controls.(ABSTRACT TRUNCATED AT 250 WORDS)

The presence of lysylpyridinoline in the hypertrophic cartilage of newly hatched chicks.

The presence of lysylpyridinoline (LP) as a nonreducible cross-link in appreciable quantities has primarily been limited to the mineralized tissues, bone and dentin. However, the results reported here show that LP is not only present in the hypertrophic cartilage of the tibiotarsus isolated from newly hatched broiler chicks, but it is approx. 4-fold as concentrated as hydroxylysylpyridinoline (HP). Bone and articular cartilage surrounding the hypertrophic cartilage do not contain measurable quantities of LP. Purified LP has a fluorescent scan similar to purified HP and literature values, confirming that we indeed were measuring LP. Also, the cartilage lesion produced by immature chondrocytes from birds with tibial dyschondroplasia had LP but the HP:LP ratio was > 1. Thus, the low HP:LP ratio could be a marker for hypertrophic cartilage in avians.