Growth hormone is permissive for skeletal adaptation to mechanical loading

Hip Structure Analyses in Acromegaly: Decrease of Cortical Bone Thickness After Treatment: A Longitudinal Cohort Study

Long‐standing growth hormone (GH) excess causes the skeletal clinical signs of acromegaly with typical changes in bone geometry, including increased cortical bone thickness (CBT). However, a high prevalence and incidence of vertebral fractures has been reported. The aim of this study was to assess the course of cortical bone dimensions in the hip by comparing patients with acromegaly and clinically nonfunctioning pituitary adenomas (NFPAs) at baseline and 1 year after pituitary surgery (1‐year PO) in a longitudinal cohort study. DXA was performed in patients with acromegaly (n = 56) and NFPA (n = 47). CBT in the femoral neck (CBTneck), calcar (CBTcalcar), and shaft (CBTshaft) were determined by hip structural analysis (HSA). CBT at baseline and the change to 1‐year PO were compared. Test results were adjusted for differences in gender distribution, age, and gonadal status. Cortical thickness analyses showed higher values [mm] at baseline in patients with acromegaly compared with NFPA: CBTneck median [25th; 75th] 6.2 [4.7; 8.0] versus 5.1 [4.1; 6.4] (p = 0.006), CBTcalcar 4.8 [4.2, 5.7] versus 4.0 [3.2, 4.5] (p < 0.001), CBTshaft 6.2 [5.1, 7.2] versus 5.2 [4.6, 6.0], (p = 0.003). In acromegaly, GH was correlated with CBTneck (r = 0.31, p = 0.020), whereas IGF‐1 was correlated with CBTcalcar (r = 0.39, p = 0.003) at baseline. In acromegaly, CBTneck decreased by 11.2%, p = 0.002 during follow‐up. Finally, the decrease in CBTneck and CBTcalcar in acromegaly was significant compared with NFPA (p = 0.023 and p = 0.017, respectively). Previous observations of increased CBT in acromegaly were confirmed with DXA‐derived HSA in a large, well‐defined cohort. The decline in CBT in acromegaly could contribute to the increased fracture risk in acromegaly despite increased bone dimensions and disease control. © 2019 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Age and sex effects on the relationship between body composition and hip geometric structure in males and females from East China

The study finds bone mineral density is the principal determinant of hip geometry and lean mass is a better determinant than fat mass in Chinese. Moreover, the impact of fat on skeleton differs with age, with a negative effect in young people but a more positive effect in elderly.

PURPOSE

The aim of this study was to examine whether the correlation between body composition including bone mineral density (BMD), lean mass (LM) and fat mass (FM), and hip geometric structure change with aging in males and females from East China.

METHODS

It was a cross-section study. A total of 1168 healthy male and 1066 healthy females in Shanghai were divided into six groups based on their age and sex. All participants were evaluated by assessing the BMD of lumber spine and proximal hip, total LM, total FM, and geometric parameters of the hip such as the cross-sectional area (CSA), average cortical thickness (ACT), and the buckling ratio (BR) at the narrow neck (NN), the intertrochanter (IT), and the shaft (FS).

RESULTS

Among the three body composition, the correlation between hip BMD and hip geometric structure was strongest. LM showed significantly positive correlations with CSA. FM showed negative or little positive correlation with hip geometry in the young group. However, the degree of the contribution of FM to hip geometric structure became substantially positive with aging. Limb LM produced the largest positive contribution to CSA and ACT at all three regions in young males. However, in older males the trunk LM produced the largest positive contribution to CSA and ACT.

CONCLUSIONS

Among all body composition parameters, hip BMD showed the largest correlation with hip geometric structure, with LM showing the second largest. The impact of FM and LM on hip geometry changed with aging and with different distributions of lean mass and fat mass.

Protective Role of Testicular Hormone INSL3 From Atrophy and Weakness in Skeletal Muscle

Androgens are primarily involved in muscle growth, whilst disease-driven muscle wasting is frequently associated with hypogonadism. The Leydig cells of the testes also produce the peptide-hormone Insulin-like peptide 3 (INSL3). INSL3 displays anabolic activity on bone, a target tissue of androgens, and its plasma concentrations are diminished in male hypogonadism. Here we tested the role of INSL3 on muscle mass regulation, in physiological and pathological conditions. Studies on C2C12 cell line showed that INSL3, acting on his specific receptor RXFP2, promotes skeletal muscle protein synthesis through the Akt/mTOR/S6 pathway. Next, studies on Rxfp2 ^-/- mice showed that INSL3 is required to prevent excessive muscle loss after denervation. Mechanistically, denervated Rxfp2 ^-/- mice lacked the compensatory activation of the Akt/mTOR/S6 pathway and showed an abnormal ubiquitin-proteasome system activation. Lack of INSL3 activity resulted also in reduced contractile force. These findings underlie a role of INSL3/RXFP2 in protein turnover, contributing to muscle wasting in male hypogonadism.

Stress and Alterations in Bones: An Interdisciplinary Perspective

Decades of research have demonstrated that physical stress (PS) stimulates bone remodeling and affects bone structure and function through complex mechanotransduction mechanisms. Recent research has laid ground to the hypothesis that mental stress (MS) also influences bone biology, eventually leading to osteoporosis and increased bone fracture risk. These effects are likely exerted by modulation of hypothalamic-pituitary-adrenal axis activity, resulting in an altered release of growth hormones, glucocorticoids and cytokines, as demonstrated in human and animal studies. Furthermore, molecular cross talk between mental and PS is thought to exist, with either synergistic or preventative effects on bone disease progression depending on the characteristics of the applied stressor. This mini review will explain the emerging concept of MS as an important player in bone adaptation and its potential cross talk with PS by summarizing the current state of knowledge, highlighting newly evolving notions (such as intergenerational transmission of stress and its epigenetic modifications affecting bone) and proposing new research directions.

Relaxin and insulin-like peptide 3 in the musculoskeletal system: from bench to bedside

Skeletal muscles and bones form a joined functional unit sharing a complex mechanical, biochemical and hormonal crosstalk. A number of factors, including sex hormones, physiologically regulate the musculoskeletal system. Striking gender differences in muscle and bone mass, and function are mainly caused by distinct actions exerted by oestrogens and androgens. However, relaxin and relaxin-related peptides, such as insulin-like peptide 3 (INSL3), might contribute to these sex-associated differences in physiological and pathological conditions (such as osteoporosis and sarcopenia). Relaxin is a 'pregnancy' hormone, but it is also produced from the prostate gland, and has recently attracted attention as a potential drug for cardiovascular disorders and fibrosis. In contrast, INSL3 is a male-specific hormone produced by the Leydig cells of the testis with a fundamental role in testicular descent during fetal life. Recent evidence suggests that both hormones have interesting roles in the musculoskeletal system. Relaxin and INSL3, by finely tuning bone formation and resorption, are involved in bone remodelling processes, and relaxin contributes to the healing of injured ligaments and promotes skeletal muscle regeneration. Here, we review the most recent findings on the effects of relaxin and INSL3 on skeletal muscle and the cell components of bone. In the light of the experimental evidence available and animal models, their clinical implications are also discussed.

LINKED ARTICLES

This article is part of a themed section on Recent Progress in the Understanding of Relaxin Family Peptides and their Receptors. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.10/issuetoc.

Sarcopenia and fragility fractures: molecular and clinical evidence of the bone-muscle interaction

➤ Bone and muscle tissues are in close relationship, and the aging process is a factor involved in the loss of the functionality of both bones and muscles.➤ Sarcopenia and osteoporosis are linked from a biological and functional perspective and are related to an increased fracture risk in the elderly.➤ The increased fracture risk in sarcopenic and osteoporotic subjects is due to the decline of muscle mass and strength, the decrease in bone mineral density, and limited mobility.

Growth Hormone and Craniofacial Tissues. An update

Growth hormone is an important regulator of bone homeostasis. In childhood, it determines the longitudinal bone growth, skeletal maturation, and acquisition of bone mass. In adulthood, it is necessary to maintain bone mass throughout life. Although an association between craniofacial and somatic development has been clearly established, craniofacial growth involves complex interactions of genes, hormones and environment. Moreover, as an anabolic hormone seems to have an important role in the regulation of bone remodeling, muscle enhancement and tooth development. In this paper the influence of growth hormone on oral tissues is reviewed.

WISE-2005: bed-rest induced changes in bone mineral density in women during 60 days simulated microgravity

To better understand the effects of prolonged bed-rest in women, 24 healthy women aged 25 to 40 years participated in 60-days of strict 6° head-down tilt bed-rest (WISE-2005). Subjects were assigned to either a control group (CON, n=8) which performed no countermeasure, an exercise group (EXE, n=8) undertaking a combination of resistive and endurance training or a nutrition group (NUT, n=8), which received a high protein diet. Using peripheral quantitative computed tomography (pQCT) and dual X-ray absorptiometry (DXA), bone mineral density (BMD) changes at various sites, body-composition and lower-leg and forearm muscle cross-sectional area were measured up to 1-year after bed-rest. Bone loss was greatest at the distal tibia and proximal femur, though losses in trabecular density at the distal radius were also seen. Some of these bone losses remained statistically significant one-year after bed-rest. There was no statistically significant impediment of bone loss by either countermeasure in comparison to the control-group. The exercise countermeasure did, however, reduce muscle cross-sectional area and lean mass loss in the lower-limb and also resulted in a greater loss of fat mass whereas the nutrition countermeasure had no impact on these parameters. The findings suggest that regional differences in bone loss occur in women during prolonged bed-rest with incomplete recovery of this loss one-year after bed-rest. The countermeasures as implemented were not optimal in preventing bone loss during bed-rest and further development is required.

Relationship of cranial robusticity to cranial form, geography and climate in Homo sapiens

Variation in cranial robusticity among modern human populations is widely acknowledged but not well-understood. While the use of "robust" cranial traits in hominin systematics and phylogeny suggests that these characters are strongly heritable, this hypothesis has not been tested. Alternatively, cranial robusticity may be a response to differences in diet/mastication or it may be an adaptation to cold, harsh environments. This study quantifies the distribution of cranial robusticity in 14 geographically widespread human populations, and correlates this variation with climatic variables, neutral genetic distances, cranial size, and cranial shape. With the exception of the occipital torus region, all traits were positively correlated with each other, suggesting that they should not be treated as individual characters. While males are more robust than females within each of the populations, among the independent variables (cranial shape, size, climate, and neutral genetic distances), only shape is significantly correlated with inter-population differences in robusticity. Two-block partial least-squares analysis was used to explore the relationship between cranial shape (captured by three-dimensional landmark data) and robusticity across individuals. Weak support was found for the hypothesis that robusticity was related to mastication as the shape associated with greater robusticity was similar to that described for groups that ate harder-to-process diets. Specifically, crania with more prognathic faces, expanded glabellar and occipital regions, and (slightly) longer skulls were more robust than those with rounder vaults and more orthognathic faces. However, groups with more mechanically demanding diets (hunter-gatherers) were not always more robust than groups practicing some form of agriculture.

Functional adaptation to mechanical loading in both cortical and cancellous bone is controlled locally and is confined to the loaded bones

In order to validate whether bones' functional adaptation to mechanical loading is a local phenomenon, we randomly assigned 21 female C57BL/6 mice at 19 weeks of age to one of three equal numbered groups. All groups were treated with isoflurane anesthesia three times a week for 2 weeks (approximately 7 min/day). During each anaesthetic period, the right tibiae/fibulae in the DYNAMIC+STATIC group were subjected to a peak dynamic load of 11.5 N (40 cycles with 10-s intervals between cycles) superimposed upon a static "pre-load" of 2.0 N. This total load of 13.5 N engendered peak longitudinal strains of approximately 1400 microstrain on the medial surface of the tibia at a middle/proximal site. The right tibiae/fibulae in the STATIC group received the static "pre-load" alone while the NOLOAD group received no artificial loading. After 2 weeks, the animals were sacrificed and both tibiae, fibulae, femora, ulnae and radii analyzed by three-dimensional high-resolution (5 mum) micro-computed tomography (microCT). In the DYNAMIC+STATIC group, the proximal trabecular percent bone volume and cortical bone volume at the proximal and middle levels of the right tibiae as well as the cortical bone volume at the middle level of the right fibulae were markedly greater than the left. In contrast, the left bones in the DYNAMIC+STATIC group showed no differences compared to the left or right bones in the NOLOAD or STATIC group. These microCT data were confirmed by two-dimensional examination of fluorochrome labels in bone sections which showed the predominantly woven nature of the new bone formed in the loaded bones. We conclude that the adaptive response in both cortical and trabecular regions of bones subjected to short periods of dynamic loading, even when this response is sufficiently vigorous to stimulate woven bone formation, is confined to the loaded bones and does not involve changes in other bones that are adjacent, contra-lateral or remote to them.

Craniofacial morphology in the Argentine Center-West: consequences of the transition to food production

The Argentine Center-West was the southernmost portion of the Andes where domestication of plants and animals evolved. Populations located in the southern portion of this area displayed a hunter-gatherer subsistence economy up to historical times, and coexisted with farmers located to the north. Archaeological and biological evidence suggests that the transition to food production was associated with the consumption of a softer diet and a more sedentary way of life. This study tests the hypothesis that diet-related factors influenced morphological differentiation, by comparing functional cranial components of farmers and hunter-gatherers. Three-dimensional changes on eight minor functional components (anteroneural, midneural, posteroneural, otic, optic, respiratory, masticatory, and alveolar) were measured on skulls derived from both subareas. Volumetric and morphometric indices were calculated to estimate the absolute and relative size of components, respectively. Results of a paired t-test indicated that farmers have a smaller craniofacial size than hunter-gatherers. The components that varied the most were masticatory and posteroneural, showing smaller absolute and relative sizes in farmers. Discriminant analyses indicated that lengths and widths were the most affected dimensions of these and other components. The pattern of differentiation, which involves specific components, enabled us to exclude differential gene flow and stochastic mechanisms as the main causes. Instead, results support the hypothesis that diet-related factors associated with both subsistence economies influenced craniofacial morphology. A proportion of the observed variation associated with size differences can be explained by two systemic factors: the lesser quality of nutrition due to a low protein content in the diet, and a decrease of growth hormone circulation induced by a lower mobility due to sedentism. However, differentiation is better explained by a localized factor: the reduction in the masticatory and posteroneural components in farmers resulted from a decrease of masticatory stresses and workload on the head and neck, linked to the consumption of a softer diet.

Modeled microgravity stimulates osteoclastogenesis and bone resorption by increasing osteoblast RANKL/OPG ratio

Mechanical unloading causes detrimental effects on the skeleton, but the underlying mechanisms are still unclear. We investigated the effect of microgravity on osteoblast ability to regulate osteoclastogenesis. Mouse osteoblast primary cultures were grown for 24 h at unit gravity or under simulated microgravity, using the NASA-developed Rotating Wall Vessel bioreactor. Conditioned media (CM) from osteoblasts subjected to microgravity increased osteoclastogenesis and bone resorption in mouse bone marrow cultures. In these osteoblasts, the RANKL/OPG ratio was higher relative to 1g. Consistently, treatment with high concentrations of OPG-inhibited osteoclastogenesis and bone resorption in the presence of CM arising from osteoblasts cultured under microgravity. Microgravity failed to affect osteoblast differentiation and function in the time frame of the experiment, as we found no effect on alkaline phosphatase mRNA and activity, nor on Runx2, osteocalcin, osteopontin, and collagen1A2 mRNA expression. In contrast, microgravity induced a time dependent increase of ERK-1/2 phosphorylation, while phospho-p38 and phospho-JNK remained unchanged. Apoptosis, revealed by bis-benzimide staining, was similar among the various gravity conditions, while it was increased under microgravity after treatment with the MEK-1/2 inhibitor, PD98059, suggesting a protection role by ERK-1/2 against cell death. In conclusion, microgravity is capable to indirectly stimulate osteoclast formation and activity by regulating osteoblast secretion of crucial regulatory factors such as RANKL and OPG. We hypothesize that this mechanism could contribute to bone loss in individuals subjected to weightlessness and other unloading conditions.

The past, present, and future of bone morphometry: its contribution to an improved understanding of bone biology

It was not until the 1950s that a better paradigm for bone biology evolved, which led to the birth of bone histomorphometry. Two clinicians, Harold Frost (1958-1964) and Lent Johnson (1964), were responsible for the paradigm stating that the primary function of bone is mechanical load bearing with subsidiary function to participate in plasma calcium homeostasis to support hematopoesis. Dynamic bone histomorphometry was born when Milch et al. (1958) discovered bone localization of tetracycline and Frost generated the methodology to study tetracycline-based dynamic histological analysis of cortical bone remodeling (1961-1965). Dynamic bone histomorphometry did not blossom until Frost, while a Sun Valley Workshop participant, developed it to address trabecular bone dynamics. The combination of Arnold (1948) producing thin sections of plastic-embedded undecalcified bone and Frost's (1977-1983) modification of dynamic cortical bone histology for cancellous bone made it possible to study tetracycline-based dynamic histomorphometry of cancellous bone. It led to the better understanding of basic metabolic unit (BMU) remodelling and to Frost's mechanostat hypothesis, and characterized the rat model to accelerate the development of several drugs in the treatment of bone diseases. Currently, dynamic bone histomorphometry has contributed to studies in bone's mechanical usage windows, mechanical usage setpoint hypothesis, muscle-bone relations, marrow-bone relations, the Utah paradigm of musculoskeletal physiology, apoptosis, genetics (transgenic mice) and bone structure, bone quality, the lacunocanalicular network and bone modelling, and remodeling hypothesis, osteocyte role as mechanosensory, chemosensory, and regulatory in bone maintenance, targeted and untargeted remodeling, the role of permissive agents, etc., items in bone biology expounded briefly by Lent Johnson (1965) and continuously by Harold Frost at the Sun Valley Workshop (1965-2003). Finally, "What's next?" covers how to improve and perpetuate the employing of qualitative histomorphometry in research opportunities in hard tissue research.

Bone's mechanostat: a 2003 update

The still-evolving mechanostat hypothesis for bones inserts tissue-level realities into the former knowledge gap between bone's organ-level and cell-level realities. It concerns load-bearing bones in postnatal free-living bony vertebrates, physiologic bone loading, and how bones adapt their strength to the mechanical loads on them. Voluntary mechanical usage determines most of the postnatal strength of healthy bones in ways that minimize nontraumatic fractures and create a bone-strength safety factor. The mechanostat hypothesis predicts 32 things that occur, including the gross anatomical bone abnormalities in osteogenesis imperfecta; it distinguishes postnatal situations from baseline conditions at birth; it distinguishes bones that carry typical voluntary loads from bones that have other chief functions; and it distinguishes traumatic from nontraumatic fractures. It provides functional definitions of mechanical bone competence, bone quality, osteopenias, and osteoporoses. It includes permissive hormonal and other effects on bones, a marrow mediator mechanism, some limitations of clinical densitometry, a cause of bone "mass" plateaus during treatment, an "adaptational lag" in some children, and some vibration effects on bones. The mechanostat hypothesis may have analogs in nonosseous skeletal organs as well.

Abnormal bone collagen morphology and decreased bone strength in growth hormone-deficient rats

Patients with growth hormone deficiency (GHD) have an increased risk of bone fractures. In these patients, the well-described decrease in bone mineral density (BMD) and content (BMC) may, however, not alone explain the increase in fracture rate. Accordingly, the aim of this study was to evaluate collagen morphology and bone mineralisation in cortical bone as well as bone strength in GHD rats to try to clarify the explanation for the increased fracture rate. The Dw-4 rat was used as a model for GHD. This strain of rats has an autosomal recessive disorder, reducing GH synthesis to approximately 10% and growth rate to approximately 40-50% when compared to normal control rats. Five male Dw-4 rats were examined at age 12 weeks and five healthy Lewis rats served as age-matched controls. The animals were examined for (1) bone mineral status by dual energy X-ray absorptometry (DXA) and ash weight/bone volume, (2) biomechanical properties, (3) serum insulin-like growth factor I (IGF-I) and IGF binding protein 3 (IGFBP-3), and (4) collagen morphology of cortical bone from the right femurs was examined by scanning and transmission electron microscopy. A significant decrease was found in serum IGF-I, IGFBP-3 and biomechanical properties in GHD rats compared to controls (P < 0.009). While DXA-derived BMD was decreased, no significant difference was found in ash weight/bone volume. Electron microscopy showed a significant decrease in the number and a significant increase in the diameter of collagen microfibrils in GHD rats as compared to their controls (P < 0.009). In conclusion, we report for the first time that collagen morphology in bone is markedly altered in rats with isolated GHD. Whether similar conditions are present in GHD patients need further investigations. The changes described, however, may provide a co-explanation for the increased fracture rate in GHD.

Physical stress by magnetic force accelerates differentiation of human osteoblasts

We examined the effect of magnetic force on differentiation of cultured human osteoblasts. Magnetic microparticles (MPs) were introduced into the cytoplasm of a human osteoblast cell line and the cells were cultured in a magnetic field (MF) in group MP-MF. Three groups of controls were used: cells without MPs were cultured out of MF (group C), cells without MPs were cultured in MF (group MF), and cells with MPs were cultured out of MF (group MP). The cells in group MP-MF became larger and were elongated along the axis of the magnetic poles. Appearance of alkaline phosphatase (AlPase) activity, formation of bone nodules, and calcium deposition were accelerated depending on the intensity of the magnetic field. It takes longer culture in the other three groups to exhibit these changes. Core-binding factor A1 (Cbfa1: transcription factor for osteoblast differentiation) and osteocalcin (a bone-matrix protein involved in controlling osteogenesis) were expressed earlier or stronger in group MP-MF than the other groups. Then we compared phosphorylation of mitogen-activated protein kinase (MAPK) between group MP-MF and group C. Phosphorylation of p38(MAPK) (p38) was increased in group MP-MF, while total p38 as well as total and phosphorylated forms of MAPK/ERK 1/2 and SAPK/JNK were not changed between the two groups. When a p38 inhibitor, SB 203580, was added to the culture medium in group C, AlPase activity, formation of bone nodules, and calcium deposits were completely inhibited. On the other hand, they were inhibited only partially by a MAPK/ERK 1/2 inhibitor, U-0126. Based on these results, it is concluded that (1) osteoblast differentiation is accelerated by a magnetic force, (2) this acceleration is mainly attributed to the activation of p38 phosphorylation, and (3) the stimulus induced by a magnetic field offers a new approach to osteoblast differentiation.

Effects of hypophysectomy and recombinant human growth hormone on material and geometric properties and the pre- and post-yield behavior of femurs in young rats

To study the musculoskeletal effects of hypophysectomy (Hx) and a partial replacement treatment with recombinant human growth hormone (rhGH) in rats, we determined the stiffness (elastic modulus, E) and volumetric BMD (vBMD) of cortical bone; the periosteal and endosteal perimeters, area and bending moment of inertia (xCSMI) of the cross sections, and the structural stiffness and pre- and post-yield strength of the femur diaphyses by pQCT and mechanical tests, and the gastrocnemius weight of rats that were either intact (n = 9) or Hx at 15 days of age (20). The latter were otherwise untreated (Hx controls, 4) or given 0.4 (8) or 2.0 (8) IU kg(-1) day(-1), s.c., of rhGH for 45 days starting 15 days after surgery. Hx delayed musculoskeletal development (gastrocnemius weight, bone geometric properties), thus affecting the diaphyseal stiffness and strength. It also reduced the cortical vBMD through an undefined mechanism, and increased the elastic modulus of cortical bone. The Hx also affected the correlation between bone geometric and material properties (xCSMI vs. E), suggesting an antianabolic interaction with the biomechanical control of bone modeling in response to strains caused by mechanical usage. As a result, Hx reduced the stiffness, post-yield, and ultimate strength of the diaphyses. These effects should reflect changes in bone tissue microstructure, perhaps associated with crack generation and progress, but unrelated to bone mineral mass. They are compatible with the induction of a delay in collagen turnover with associated increases in fibers' diameter and crystals' size that may have resulted from the suppression of some other hormones, such as thyroid, prolactin, or other hormones regulated by ACTH. The above doses of rhGH significantly but incompletely prevented the negative Hx effects on bone and muscle development (bone geometric properties, muscle mass). However, rhGH treatment failed to prevent the demineralizing and stiffening effect of Hx on bone tissue and the unusual effects on the post-yield strength (less clearly related to muscle development than the former). Consequently, rhGH treatment tended to preserve the natural relationship between muscle function and bone geometry but not bone strength. The effects of larger rhGH doses and the interaction of other hormones with the described effects remain to be investigated. Nevertheless, these findings would deserve special attention because they challenge the prevailing view that in endocrine-metabolic bone-weakening diseases the bone matrix always has a normal composition.

Growth and maturational changes in dense fibrous connective tissue following 14 days of rhGH supplementation in the dwarf rat

The purpose of this study was to investigate the impact of recombinant human growth hormone (rhGH) on patella tendon (PT), medial collateral ligament (MCL), and lateral collateral ligament (LCL) on collagen growth and maturational changes in dwarf GH-deficient rats. Twenty male Lewis mutant dwarf rats, 37 days of age, were randomly assigned to Dwarf + rhGH (n = 10) and Dwarf + vehicle (n = 10) groups. The GH group received 1.25 mg rhGH/kg body wt twice daily for 14 days. rhGH administration stimulated dense fibrous connective tissue growth, as demonstrated by significant increases in hydroxyproline specific activity and significant decreases in the non-reducible hydroxylysylpyridinoline (HP) collagen cross-link contents. The increase in the accumulation of newly accreted collagen was 114, 67, and 117% for PT, MCL, and LCL, respectively, in 72 h. These findings suggest that a short course rhGH treatment can affect the rate of new collagen production. However, the maturation of the tendon and ligament tissues decreased 18-25% during the rapid accumulation of de novo collagen. We conclude that acute rhGH administration in a dwarf rat can up-regulate new collagen accretion in dense fibrous connective tissues, while causing a reduction in collagen maturation.