Plyometric exercise increases serum indices of muscle damage and collagen breakdown

The aim of the present study was to examine the effect of acute plyometric exercise on indices of muscle damage and collagen breakdown. Nine untrained men performed an intense bout of plyometric jumping exercises (experimental group) and nine men remained at rest (control group). Seven days before and 24, 48, and 72 hours after plyometric exercise or rest, several physiological and biochemical indices of muscle damage and two biochemical indices of collagen damage were determined. No significant changes in concentric and eccentric peak torque of knee extensors and flexors or flexion and extension range of motion were found after the plyometric exercise. Delayed-onset muscle soreness increased 48 hours after exercise. Creatine kinase increased 48 and 72 hours post exercise, whereas lactate dehydrogenase increased 24, 48, and 72 hours post exercise. Serum hydroxyproline increased 24 hours post exercise, peaked at 48 hours, and remained elevated up to 72 hours post exercise. Hydroxylysine (which was measured only before exercise and at 48 hours) was found increased 48 hours post exercise. No differences were found in any physiological or biochemical index in the control group. Intense plyometric exercise increased muscle damage, delayed-onset muscle soreness, and serum indices of collagen breakdown without a concomitant decrease in the functional capacity of muscles. Hydroxyproline and hydroxylysine levels in serum seem promising measures for describing exercise-induced collagen degradation. Coaches need to keep in mind that by using plyometric activities, despite the increased muscle damage and collagen turnover that follow, it is not necessarily accompanied by decreases in skeletal muscle capacity.     

Inhibition of collagen breakdown by diphenylhydantoin

Gingival tissue obtained from diphenylhydantoin-treated patients was cultured in the presence of [¹⁴C]proline for 24 h. The radioactive medium was removed and the tissue cultured for three days more. DNA, protein, hydroxyproline, proline and radioactivity determinations in the tissue indicated increased cellular proliferation, increased collagen contents and decreased breakdown of collagen in the affected tissues. The media were assayed for dialyzable and non-dialyzable hydroxyproline contents. It was found that the media in which diphenylhydantoin tissues were cultured contained more than twice as much non-dialyzable hydroxyproline than the controls. It was concluded that diphenylhydantoin brought about a reduction in collagen breakdown thus explaining the accumulation of hydroxylated collagen in the tissue.     

Multivitamin restriction increases adiposity and disrupts glucose homeostasis in mice

A strong association between obesity and low plasma concentrations of vitamins has been widely reported; however, the causality of this relationship is still not established. Our goal was to evaluate the impact of a multivitamin restriction diet (MRD) on body weight, adiposity and glucose homeostasis in mice. The mice were given a standard diet or a diet containing 50 % of the recommended vitamin intake (MRD) for 12 weeks. At the end of the experiment, total body weight was 6 % higher in MRD animals than in the control group, and the adiposity of the MRD animals more than doubled. The HOMA-IR index of the MRD animals was significantly increased. The adipose tissue of MRD animals had lower expression of mRNA encoding adiponectin and Pnpla2 (47 and 32 %, respectively) and 43 % higher leptin mRNA levels. In the liver, the mRNA levels of Pparα and Pgc1α were reduced (29 and 69 %, respectively) in MRD mice. Finally, the level of β-hydroxybutyrate, a ketonic body reflecting fatty acid oxidation, was decreased by 45 % in MRD mice. Our results suggest that MRD promotes adiposity, possibly by decreasing adipose tissue lipolysis and hepatic β-oxidation. These results could highlight a possible role of vitamin deficiency in the etiology of obesity and associated disorders.

Electronic supplementary material

The online version of this article (doi:10.1007/s12263-014-0410-x) contains supplementary material, which is available to authorized users.     

Acute food deprivation and chronic food restriction differentially affect hypothalamic NPY mRNA expression

Although acute food deprivation and chronic food restriction both result in body weight loss, they produce different metabolic states. To evaluate how these two treatments affect hypothalamic peptide systems involved in energy homeostasis, we compared patterns of hypothalamic neuropeptide Y (NPY), agouti-related protein (AgRP), proopiomelanocotin (POMC), and leptin receptor gene expression in acutely food-deprived and chronically food-restricted rats. Both acute food deprivation and chronic food restriction reduced body weight and circulating leptin levels and resulted in increased arcuate NPY and decreased arcuate POMC gene expression. Arcuate AgRP mRNA levels were only elevated in acutely deprived rats. NPY gene expression was increased in the compact subregion of the dorsomedial hypothalamus (DMH) in response to chronic food restriction, but not in response to acute food deprivation. Leptin receptor expression was not affected by either treatment. Double in situ hybridization histochemistry revealed that, in contrast to the situation in the arcuate nucleus, NPY and leptin receptor mRNA-expressing neurons were not colocalized in the DMH. Together, these data suggest that arcuate and DMH NPY gene expression are differentially regulated. DMH NPY-expressing neurons do not appear to be under the direct control of leptin signaling.     

Brief food restriction increases FA oxidation and glycogen synthesis under insulin-stimulated conditions

To determine the effects of brief food restriction on fatty acid (FA) metabolism, hindlimbs of F344/BN rats fed either ad libitum (AL) or food restricted (FR) to 60% of baseline food intake for 28 days were perfused under hyperglycemic-hyperinsulinemic conditions (20 mM glucose, 1 mM palmitate, 1,000 microU/ml insulin, [3-(3)H]glucose, and [1-(14)C]palmitate). Basal glucose and insulin levels were significantly lower (P < 0.05) in FR vs. AL rats. Palmitate uptake (34.3 +/- 2.7 vs. 24.5 +/- 3.1 nmol/g/min) and oxidation (3.8 +/- 0.2 vs. 2.7 +/- 0.3 nmol.g(-1).min(-1)) were significantly higher (P < 0.05) in FR vs. AL rats, respectively. Glucose uptake was increased in FR rats and was accompanied by significant increases in red and white gastrocnemius glycogen synthesis, indicating an improvement in insulin sensitivity. Although muscle triglyceride (TG) levels were not significantly different between groups, glucose uptake and total preperfusion TG concentration were negatively correlated (r(2) = 0.27, P < 0.05). In conclusion, our results show that under hyperglycemic-hyperinsulinemic conditions, brief FR resulted in an increase in FA oxidative disposal that may contribute to the improvement in insulin sensitivity.     

Immunological memory is compromised by food restriction in deer mice Peromyscus maniculatus

The immune system protects organisms against infection, but this protection presumably comes at a cost. Here, we asked whether food restriction would compromise the ability of an organism to generate an immune response on reexposure to an antigen, which would represent a functional cost of immunological memory. Immunological memory is generated when B and T lymphocytes sensitive to components of pathogens (i.e., antigens) proliferate after exposure and persist in circulation to hinder reinfection. To test the possibility that B cell memory, the component of the immune system responsible for antibody production, is expensive to maintain, secondary antibody production against a novel protein [keyhole limpet hemocyanin (KLH)] was compared in food-restricted and ad libitum-fed male deer mice (Peromyscus maniculatus). To determine whether compromised secondary antibody production was solely due to elevated corticosterone independent of resource availability, some food-restricted and ad libitum-fed mice were subjected to unpredictable, chronic (2 h/day) restraint. Mice fed 70% of their ad libitum diet 2 wk after primary antigen challenge produced approximately 95% less IgG against KLH after a second antigen challenge than mice fed ad libitum, even though all mice were fed ad libitum during the secondary antibody response period. Restraint had no effect on secondary IgG production in response to KLH, and corticosterone concentrations 1 day after food restriction did not differ between food-restricted and ad libitum-fed mice. Together, these data imply that secondary antibody responses and the benefits of immunological memory are energetically costly in this species.     

Interleukin 1 increases collagen type IV production by murine mammary epithelial cells

The effects of human interleukin 1 (IL 1) on collagen type IV production by normal mouse mammary epithelial cells were examined. Human IL 1 was derived from the culture media of peripheral blood monocytes or placental cells that were stimulated with silica. Although crude culture media of silica-stimulated monocytes or placental cells had no enhancing activity for type IV collagen production, IL 1-containing fractions obtained by Sephacryl S-200 gel chromatography and isoelectrofocusing from such media possessed considerable activity. To confirm the effects of IL 1 on collagen production, human monocyte-derived IL 1 was highly purified by sequential isoelectrofocusing, anion-exchange (AX 300), high-performance liquid chromatography (HPLC), and HPLC gel filtration (TSK 3000). The same HPLC gel filtration fractions contained both an activity that stimulated collagen synthesis by mammary cells and thymocyte growth-promoting activity. These activities of IL 1 differed from a number of other factors, such as epidermal growth factor and another factor produced by placental cells that stimulated type IV collagen production but not thymocyte proliferation. In fact, IL 1 induced 100-fold less collagen type IV production by mammary epithelial cells than was needed to induce thymocyte proliferation. Our data suggest that IL 1-like molecules, which reportedly are produced by many tissue cell types, may therefore play a role in promoting a basement membrane formation at stromal-epithelial boundaries.     

Ageing increases SOCS-3 expression in rat hypothalamus: effects of food restriction

Aged Wistar rats are characterized by leptin and insulin resistance. The expression of SOCS-3 in hypothalamus increases with ageing. Food restriction during 3 months decreases obesity Lee index in aged rats with respect to their ad libitum aged-mates and brings serum leptin concentrations to values close to those of young rats. Food restriction partially reverts the increases in SOCS-3 mRNA levels associated with ageing. These results suggest that SOCS-3 may be a mediator of hypothalamic leptin resistance in the aged Wistar rat and that the hyperleptinemia associated with ageing is, at least in part, responsible for the increase of SOCS-3 expression in hypothalamus.     

Trimer carboxyl propeptide of collagen I produced by mature osteoblasts is chemotactic for endothelial cells

During the second phase of osteogenesis in vitro, rat osteoblasts secrete inducer(s) of chemotaxis and chemoinvasion of endothelial and tumor cells. We report here the characterization and purification from mature osteoblast conditioned medium of the agent chemotactic for endothelial cells. The chemoactive conditioned medium specifically induces directional migration of endothelial cells, not affecting the expression and activation of gelatinases, cell proliferation, and scattering. Directional migration induced in endothelial cells by conditioned medium from osteoblasts is inhibited by pertussis toxin, by blocking antibodies to integrins alpha(1), beta(1), and beta(3), and by antibodies to metalloproteinase 2 and 9. The biologically active purified protein has two sequences, coincident with the amino-terminal amino acids, respectively, of the alpha(1) and of the alpha(2) carboxyl propeptides of type I collagen, as physiologically produced by procollagen C proteinase. Antibodies to type I collagen and to the carboxyl terminus of alpha(1) or alpha(2) chains inhibit chemotaxis. The chemoattractant is the propeptide trimer carboxyl-terminal to type I collagen, and its activity is lost upon reduction. These data illustrate a previously unknown function for the carboxyl-terminal trimer, possibly relevant in promoting endothelial cell migration and vascularization of tissues producing collagen type I.     

Evidence for phagocytosis of influenza virus-infected, apoptotic cells by neutrophils and macrophages in mice

Influenza virus-infected cells undergo apoptosis and become susceptible to phagocytosis by macrophages in vitro, and this leads to the propagation of the virus being inhibited. We previously showed that inhibitors of phagocytosis increased the rate of mortality among influenza virus-infected mice. However, the mode of the phagocytosis of influenza virus-infected cells in vivo has not been investigated. We, in this study, assessed this issue by histochemically analyzing bronchoalveolar lavage cells and lung tissue obtained from C57BL/6 mice infected with influenza A/WSN (H1N1) virus. Both neutrophils and macrophages accumulated in the lung soon after the viral challenge, and either type of cell was capable of phagocytosing influenza virus-infected, apoptotic cells. Changes in the level of phagocytosis and the amount of virus in lung tissue roughly correlated with each other. Furthermore, alveolar macrophages prepared from influenza virus-infected mice showed greater phagocytic activity than those from uninfected mice. The phagocytic activity of macrophages was stimulated in vitro by a heat-labile substance(s) released from influenza virus-infected cells undergoing apoptosis. These results suggested that the level of phagocytosis is augmented both quantitatively and qualitatively in the lung of influenza virus-infected animals so that infected cells are effectively eliminated. Finally, lack of TLR4 caused an increase in the rate of mortality among influenza virus-challenged mice and a decrease in the level of phagocytosis of apoptotic cells in the lung. TLR4 could thus play an important role in the host defense against influenza by positively regulating the phagocytic elimination of infected cells.     

Potential roles of hypochlorous acid and N-chloroamines in collagen breakdown by phagocytic cells in synovitis

We have tested the effects of the neutrophil/macrophage products, hypochlorous acid (HOCl) and N-chloroamines, on the structural integrity and proteolytic susceptibility of collagen to determine if these agents could play a role in inflammatory joint destruction. Rates of HOCl reaction with collagen, and collagen gelation were monitored by spectrophotometric methods. Direct fragmentation, and degradation by collagenase were measured by the release of acid-soluble counts from ³H-collagen. Physiologically relevant concentrations of HOCl (5–50 μM) reacted rapidly and quantitatively at several sites in the collagen polypeptide chain, causing extensive protein fragmentation and preventing collagen gelation. In contrast, reaction with (5–50 μM) N-chloroalanine induced little direct collagen fragmentation. Oxidative damage by N-chloroamines was, however, evident because collagen displayed greatly increased proteolytic susceptibility following N-chloroamine treatment. Collagen degradation by collagenase increased as much as 3-fold after exposure to N-chloroamine treatment. Collagen degradation by collagenase increased as much as 3-fold after exposure to N-chloroalanine. N-chloroleucine caused a small increase in proteolytic susceptibility, but N-chlorotaurine had no effect. Collagen fragmentation by HOCl, inhibition of gelation by HOCl, and N-chloroalanine-induced proteolytic susceptibility, all increased with linear kinetics at oxidant concentrations of 5 μM to 1.0 mM. In synovitis, phagocytes expose collagen to HOCl, N-chloroamines, and collagenase. It is known that HOCl can activate neutrophil procollagenase. Based on our new findings, we propose a model of inflammatory joint destruction that also includes collagen fragmentation, and increased susceptibility of collagen to degradation by collagenase. It may also be possible that taurine exerts a protective effect against HOCL/OCL⁻ damage by reacting to form what appears to be essentially an inert N-chloroamine. The validity of this model must now be tested.     

Vitronectin adsorption to chrysotile asbestos increases fiber phagocytosis and toxicity for mesothelial cells

Biological modification of asbestos fibers can alter their interaction with target cells. We have shown that vitronectin (VN), a major adhesive protein in serum, adsorbs to crocidolite asbestos and increases fiber phagocytosis by mesothelial cells via integrins. Because chrysotile asbestos differs significantly from crocidolite in charge and shape, we asked whether VN would also adsorb to chrysotile asbestos and increase its toxicity for mesothelial cells. We found that VN, either from purified solutions or from serum, adsorbed to chrysotile but at a lower amount per surface area than to crocidolite. Nevertheless, VN coating increased the phagocytosis of chrysotile as well as of crocidolite asbestos. VN coating of both chrysotile and crocidolite, but not of glass beads, increased intracellular oxidation and apoptosis of mesothelial cells. The additional apoptosis could be blocked by integrin-ligand blockade with arginine-glycine-aspartic acid peptides, confirming a role for integrins in the fiber-induced toxicity. We conclude that VN increases the phagocytosis of chrysotile as well as of crocidolite asbestos and that phagocytosis is important in fiber-induced toxicity for mesothelial cells.     

CCR7 ligand-enhanced phagocytosis of various antigens in mature dendritic cells-time course and antigen distribution different from phagocytosis in immature dendritic cells

CC chemokine receptor 7 (CCR7) is selectively expressed on mature dendritic cells (DC). The CCR7 ligands, CC chemokine ligand (CCL) 19 and CCL21, facilitate migration of mature DC from the peripheral tissues to regional lymph nodes. We previously demonstrated that CCR7 ligands induced rapid receptor-mediated endocytosis of dextran in mature DC. In the present study, we further examined the effects of CCR7 ligands on endocytosis of other kinds of antigen, mannosilated bovine serum albumin (Mann-BSA), Escherichia coli(E. coli), or ovalbumin-containing immune complex (OVA-IC), by mature DC. We found that CCR7 ligands enhanced the endocytosis of Mann BSA, E. coli, and OVA-IC in mature DC but not in immature DC. The endocytosis of BSA was not enhanced by CCR7 ligands. Furthermore, the phagocytosis of OVA-IC was significantly inhibited by anti-Fcgamma receptor III/II antibody. These results demonstrate that CCR7 ligands enhance only receptor-mediated endocytosis by mature DC. When rapidly phagocytosed E. coli were traced in CCL19-treated mature DC, most of the phagocytosed E. coli did not colocalize with the lysosomal marker: lysosome-associated membrane protein-1 (Lamp-1), whereas most of E. coli taken up relatively slowly by immature DC colocalized with Lamp-1. These results suggest that phagocytosis of antigens by immature and mature DC plays different functional roles.     

Role of integrins in regulation of collagen phagocytosis by human fibroblasts

Phagocytosis of collagen fibrils by fibroblasts is an important pathway for degradation of extracellular matrix in mature connective tissues. To study regulatory mechanisms in phagocytosis, 2-μm fluorescent beads coated with either collagen (COL) or bovine serum albumin (BSA) were incubated with human gingival fibroblasts in vitro. For these studies single cell suspensions were prepared by trypsinization, and bead internalization and collagen receptor expression were assessed by flow cytometry. After 3-h incubations, up to 8-fold more cells internalized COL beads than BSA-coated beads. Increased collagen coating concentration was associated with elevated proportions of cells that internalized COL beads, and was observed also in the presence of competing fibronectin-coated beads. The number of beads per cell and the percent of phagocytic cells increased proportionally with higher bead loadings. At > 4 beads per cell a maximum of ∼︁80% of cells were phagocytic. Cells reacted with mAbs against the α1, α2, and α3 integrin subunits were, respectively, 5%, 98% and 93% positively stained above background controls. All cells that internalized COL beads exhibited α2 staining but there were large proportions of phagocytic cells that were not stained for α1. In unfixed cells, bead internalization caused an immediate reduction of surface staining of membrane-bound α2 by ∼︁55% which returned to control levels within 3 h, indicating that cell-surface α2 was internalized by phagocytosis. Preincubation of cells with up to 8 COL beads per cell reduced the proportion of phagocytic cells and the number of internalized beads after a second COL bead incubation 4 h later. To assess the relationship between the percent of phagocytic cells and α2 integrin levels, serum starvation and cycloheximide experiments were conducted. Compared to controls, serum starvation for 24 h induced a 3.2-fold increase of cells internalizing COL beads but did not alter α2 staining levels. In contrast, 3 h cycloheximide treatment reduced α2 staining to 60% of control levels and this treatment also inhibited COL bead internalization. GRGDTP peptide as well as mAbs against the α1 and α2 subunits significantly reduced internalization of COL beads by 1.8 to 2.6-fold, whereas GRGESP peptide and α3 mAb exerted no effect. Internalization of BSA beads was not affected by any of these treatments. Collectively, these data indicate that the α2 integrin, along with other, as yet unidentified components, is likely involved in COL bead internalization. The α2 integrin subunit is rapidly recycled or synthesized following a phagocytic load. In contrast, the α1 integrin is not directly required for phagocytosis but may regulate the internalization step. © 1996 Wiley-Liss, Inc.     

Effects of germfree status and food restriction on longevity and growth of mice.

An investigation was undertaken to study the effects of germfree (GF) status and mild food restriction on life span in GF and specific pathogen-free (SPF) male ICR mice either full-fed (ad libitum) or on a restricted diet of 4.5 grams per day (equivalent to approximately 80% of full-fed intake) from five-week-old. The mean life span of the full-fed SPF and GF mice was 75.9 and 88.9 weeks respectively, while the mean life span of the food-restricted SPF and GF mice was 117.5 and 109.6 weeks, respectively. Mice in both GF and SPF food-restricted groups were characterized by lower body weight and increased survival. These findings suggest that the cessation of growth may be importantly and perhaps causally related to longevity. The GF mice survived longer than the SPF mice, but the combination of GF status with food restriction did not seem to extend life span more than food restriction alone.     

Tibial loading increases osteogenic gene expression and cortical bone volume in mature and middle-aged mice

There are conflicting data on whether age reduces the response of the skeleton to mechanical stimuli. We examined this question in female BALB/c mice of different ages, ranging from young to middle-aged (2, 4, 7, 12 months). We first assessed markers of bone turnover in control (non-loaded) mice. Serum osteocalcin and CTX declined significantly from 2 to 4 months (p<0.001). There were similar age-related declines in tibial mRNA expression of osteoblast- and osteoclast-related genes, most notably in late osteoblast/matrix genes. For example, Col1a1 expression declined 90% from 2 to 7 months (p<0.001). We then assessed tibial responses to mechanical loading using age-specific forces to produce similar peak strains (-1300 με endocortical; -2350 με periosteal). Axial tibial compression was applied to the right leg for 60 cycles/day on alternate days for 1 or 6 weeks. qPCR after 1 week revealed no effect of loading in young (2-month) mice, but significant increases in osteoblast/matrix genes in older mice. For example, in 12-month old mice Col1a1 was increased 6-fold in loaded tibias vs. controls (p = 0.001). In vivo microCT after 6 weeks revealed that loaded tibias in each age group had greater cortical bone volume (BV) than contralateral control tibias (p<0.05), due to relative periosteal expansion. The loading-induced increase in cortical BV was greatest in 4-month old mice (+13%; p<0.05 vs. other ages). In summary, non-loaded female BALB/c mice exhibit an age-related decline in measures related to bone formation. Yet when subjected to tibial compression, mice from 2-12 months have an increase in cortical bone volume. Older mice respond with an upregulation of osteoblast/matrix genes, which increase to levels comparable to young mice. We conclude that mechanical loading of the tibia is anabolic for cortical bone in young and middle-aged female BALB/c mice.     

Necroptosis increases with age and is reduced by dietary restriction

Necroptosis is a newly identified programmed cell death pathway that is highly proinflammatory due to the release of cellular components that promote inflammation. To determine whether necroptosis might play a role in inflammaging, we studied the effect of age and dietary restriction (DR) on necroptosis in the epididymal white adipose tissue (eWAT), a major source of proinflammatory cytokines. Phosphorylated MLKL and RIPK3, markers of necroptosis, were increased 2.7‐ and 1.9‐fold, respectively, in eWAT of old mice compared to adult mice, and DR reduced P‐MLKL and P‐RIPK3 to levels similar to adult mice. An increase in the expression of RIPK1 (1.6‐fold) and MLKL (2.7‐fold), not RIPK3, was also observed in eWAT of old mice, which was reduced by DR in old mice. The increase in necroptosis was paralleled by an increase in 14 inflammatory cytokines, including the pro‐inflammatory cytokines IL‐6 (3.9‐fold), TNF‐α (4.7‐fold), and IL‐1β (5.1‐fold)], and 11 chemokines in old mice. DR attenuated the expression of IL‐6, TNF‐α, and IL‐1β as well as 85% of the other cytokines/chemokines induced with age. In contrast, inguinal WAT (iWAT), which is less inflammatory, did not show any significant increase with age in the levels of P‐MLKL and MLKL or inflammatory cytokines/chemokines. Because the changes in biomarkers of necroptosis in eWAT with age and DR paralleled the changes in the expression of pro‐inflammatory cytokines, our data support the possibility that necroptosis might play a role in increased chronic inflammation observed with age.     

Effect of food restriction on reproduction and lactation in house mice mated post partum

Primiparous, post-partum mated BALB/c bom inbred mice were allowed to raise litters of 6 young until Day 22 of lactation: 11 of 25 females were restricted to 60% of food consumption of ad-libitum fed dams after stud male removal at Day 2 of lactation. Since weight gain of restricted females during lactation was not inhibited and infanticidal behaviour was not enhanced, food deprivation can be considered to have been relatively mild. However, none of the food-restricted dams gave birth to a second litter whereas 12 of the 14 ad-libitum fed mice littered. This pregnancy failure is suggested to be due to implantation failure or abortion shortly after implantation, which is attributed to maternal manipulation rather than to immediate consequences of energetic demands of lactated young. The dynamics of the weight changes of dams and young suggest that milk production in suckling house mice drops most markedly between Days 17 and 18 of lactation, irrespective of whether the dams are non-pregnant, pregnant, or food-restricted.     

Inhibition by oestrogen of collagen breakdown in the involuting rat uterus

1. Both the post-partum involution of the rat uterus and the rapid breakdown of collagen that accompanies it are extensively inhibited by oestrogenic hormones. In the normal rat, 85% of the uterine collagen is degraded within 4 days after parturition; in rats treated with 100μg. of 17β-oestradiol/day, only 35% of uterine collagen is broken down in the same period. 2. Similar effects are produced by diethylstilboestrol if the dose is increased tenfold. 3. Collagen breakdown is inhibited to a greater extent than is the loss of wet weight by oestradiol but not by diethylstilboestrol. 4. The oestrogens appear to act by blocking the breakdown of collagen. There is a greatly decreased concentration of free hydroxyproline in the uterus of treated animals. 5. Acid hydrolase concentrations (β-glucuronidase, β-galactosidase, cathepsin D and acid phosphatase) in the uterus are decreased by oestrogen treatment compared with controls, but the total amounts of these enzymes in the uterus are somewhat elevated. Oestrogens do not appear to inhibit collagen breakdown by altering the concentration and total amount of acid hydrolases.     

Gallium nitrate increases type I collagen and fibronectin mRNA and collagen protein levels in bone and fibroblast cells

Gallium is a Group IIIa transitional element with therapeutic efficacy in the treatment of metabolic bone disorders. Previously described antiresorptive effects of gallium on osteoclasts are not sufficient to account for the full range of effects of gallium on bone structure and metabolism. We have recently shown that gallium nitrate inhibits osteocalcin gene expression and the synthesis of osteocalcin protein, an osteoblast-specific bone matrix protein that is though to serve as a signal to trigger osteoclastic resorption. Here we present evidence for an additional mechanism by which gallium may function to augment bone mass by altering matrix protein synthesis by osteoblastic and fibroblastic cells. Rat calvarial explants exposed to gallium nitrate for 48 h showed increased incorporation of ³H-proline into hydroxyproline and collagenase digestible protein. In addition, gallium treatment increased steady-state mRNA levels for fibronectin and type I procollagen chains in primary rat calvarial osteoblast-enriched cultures, the ROS 17/2.8 osteoblastic osteosarcoma line, and nontransformed human dermal fibroblasts. These findings suggest that the exposure of mesenchymally-derived cells to gallium results in an altered pattern of matrix protein synthesis that would favor increased bone formation.