Growth Plate Height Research Articles

TGF-β2 prevents the impaired chondrocyte proliferation induced by unloading in growth plates of young rats

Growth plate width and cartilage organization are altered during skeletal unloading in growing rats. Immunohistochemical studies have identified TGF-β in calcified cartilage, and TGF-β is known to induce mitogenic effects on chondrocytes in vitro. On the other hand, IGF-1 was shown to be expressed in the proximal tibial growth plate and to mediate GH-induced longitudinal bone growth in rats. We therefore investigated the effect of recombinant human (rh) IGF-1 and rhTGF-β2 infusion on the changes induced by unloading in the cellular organization of the growth plate in growing rats. Hindlimb unloading for 14 days induced a 13% reduction in growth cartilage height in the proximal tibia. This effect was mostly related to a 17% and 14% decrease in the proliferative zone height and chondrocyte number, respectively. In unloaded rats treated with a systemic infusion of rhTGF-β2 (2μg/kg/day) the number of chondrocytes in the proliferative zone was not different from those of normal loaded animals. In contrast, rhIGF-1 treatment at a 2mg/kg/day dose was not effective in counteracting the effects of unloading on growth plate height and chondrocyte number. These results show that systemic administration of rhTGF-β2 prevents in large part the reduced growth of chondrocytes in the proliferative zone and the reduced epiphyseal growth plate growth induced by unloading in rats.

Effect of 17-Beta-Estradiol on the Healing of Tibial Bone after Marrow Ablation

The present study has been undertaken to demonstrate the effect of 17 beta-estradiol on the healing of tibial bones after marrow ablation. Ninety-six 4-month-old female rats were divided into three experimental groups: group 1 was subjected to ablation in both tibiae and to injection of vehicle; group 2 to ablation in both tibiae and estradiol administration, and group 3 to estradiol administration without ablation. Before the rats were killed, all on the same day, 8 animals of each group underwent treatment for 3, 6, 14 and 21 days, respectively: every second day, 0.1 ml arachis oil was injected intramuscularly into group 1 and 17 beta-estradiol into groups 2 and 3. An additional 8 untreated animals were used as controls. Tibial bones were studied chemically and morphologically. While the control and ablated animals gained weight, there was a significant decrease in the gain in body weight of estradiol-treated rats. Bone and ash weight were increased in all experimental groups. The ratios (%) of tibial ash weight and of tibial Ca and Mg contents to body weight significantly increased in all experimental groups, compared to the controls; whereas P increased only at 6 and 14 days. As shown by computerized histomorphometry, the height of the proximal tibial growth plate was increased following ablation, but not with estradiol treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth-plate modifications after drilling.

Thirty 5-week-old male rats were used to discern the local modifications of the growth plate after drilling. A 1-mm wide drill hole was made on the right femur from the intercondylar notch to the diaphysis crossing the growth plate, with the left femur acting as a sham-operated control. Animals were killed in four five-unit groups at 1, 2, 8, and 16 weeks, respectively, after the surgical procedure. Soft tissues were removed and bone length measured. Distal growth plates of both femora were histologically, histomorphometrically, and histochemically studied. There were no significant differences in length or growth-plate height between drilled bones and their controls. Drill holes were filled by bony trabeculi formed progressively from metaphyses and adjacent cartilage metaplasia. This bone bridge grew wider as time passed after the surgical procedure. These experimental findings suggest that caution should be taken when pinning fractures through the growth plate. Failed attempts can produce permanent epiphysiodesis bridges.

HISTOMORPHOMETRIC ANALYSIS OF THE EPIPHYSEAL GROWTH PLATE IN RATS AFTER PRENATAL ALCOHOL EXPOSURE

We studied the effect of prenatal alcohol exposure on growth in the proximal tibial growth plate in 0- and 15-day-old rats, using histomorphometric methods. Body weight and tibial length were reduced in all alcohol-exposed rats. In 15-day-old rats, these parameters were lower than in the 15-day-old controls, thus showing a persistence of the effects of ethanol. The proximal tibial growth plate showed alterations, principally in 15-day-old rats. The most notable of these was a decrease in growth plate height produced by a significant reduction in hypertrophic zone height. Likewise, there were fewer cells in this zone in alcohol-exposed rats than in controls. This work shows that prenatal ethanol exposure induces growth retardation which may be due to growth plate alterations that might reflect impaired cell function.

Is longitudinal bone growth influenced by diurnal variation in the mitotic activity of chondrocytes of the growth plate?

The diurnal variations in the mitotic index, height, and rate of linear bone growth were determined and correlations between these parameters examined. Young, unweaned, female Wistar rats were housed under standardized conditions, labeled with a fluorochrome 60 h before sacrifice, and killed at intervals throughout a 24-h period, specifically 0600, 1200, 1800, and 2400. The proximal tibial epiphyseal growth plates were collected and processed, and the mitotic index, growth plate height, and the rate of linear bone growth were measured. The mitotic index measured at 0600 was significantly higher than that measured at 1800 and 2400. Growth plates of rats sacrificed at 1200 were taller than those of rats sacrificed at 1800, but there was no difference between heights of growth plates from rats sacrificed at other times. Daily growth rate for all rats averaged 283.9 microns/day and there were no statistically significant differences between daily growth rates measured at any time period. Our findings imply that in comparative, quantitative structural studies of animal groups, sacrifice should be carried out at identical times of the day, since, given a constant speed of vascular ingrowth and diurnal variation in width, relative diurnal accumulation and depletions of cells may take place. We also suggest that the daily growth rate and mitotic index be measured directly and not be considered a function of the height of the growth plate.

Morphologic and histologic abnormalities in female and male rats treated with anabolic steroids.

A two-part study was performed to determine the effects of high doses of anabolic steroids on weight, appetite, and organ histology. Initially, 30 white Wistar rats, 15 males and 15 females, were treated weekly with either 0.52 cc of physiologic saline or nandrolone decanoate. After 6 weeks, female treated and control rats had comparable weight gains, but male treated rats were significantly lighter than controls. Rats were sacrificed and organs dissected for histologic preparation. Treated male livers had less lipid than control males. The uteri of treated females displayed abnormal vacuolization, stromal edema, and peliosis. In Part II, 12 male rats, 6 treated and 6 control, were given the drug or saline in a manner identical to that in Part I. Treated rats had lower weights from Weeks 1 through 6 and ate less than controls. Upon sacrifice, treated rats' kidneys were heavier, and testes and liver were lighter compared to controls. Roentgenographic studies of tibias from Parts I and II showed no significant differences in tibial length or height of growth plate between treated and control groups. In summary, when anabolic steroid use is studied in the rat model, numerous pathological and anatomical changes occur.

Physiological mechanisms adopted by chondrocytes in regulating longitudinal bone growth in rats.

1. Chondrocyte activities within growth plate cartilage are the principal determinants of longitudinal bone growth, and it was the aim of this investigation to assess how these cell activities are modulated under various growth rate conditions. Using proximal tibial growth plates from rats of different ages, growth rate was determined by fluorochrome labelling and incident light fluorescence microscopy. Various cellular parameters contributing to longitudinal bone growth were quantified by light microscopic stereology. The size of the proliferating cell population ('growth fraction') was estimated by autoradiography (using [3H]thymidine labelling). 2. A comparison between data for suckling (21-day-old) and fast-growing (35-day-old) rats revealed that growth acceleration is achieved almost exclusively by cell-shape modelling, namely by an increase in final cell height and a decrease in lateral diameter, whereas final cell volume and surface area are slightly reduced. Cell proliferation rate in the longitudinal direction and net matrix production per cell remain unchanged. The physiological increase in linear growth rate thus appears to be based principally upon a controlled structural modulation of the chondrocyte phenotype. On the other hand, a physiological reduction in growth rate (i.e. growth deceleration) effected during the transition from pre-puberty (35-day-old rats) to maturity (80-day-old rats) is achieved by simultaneous decreases in several chondrocyte parameters, including cell height (i.e. phenotype modulation), cell volume and proliferation rate (in the longitudinal direction). However, chondrocytes continue to produce matrix at a level comparable to that attained during the period characterized by high growth rates (i.e. at 21 and 35 days). Cartilage matrix thus appears to play a subordinate role in regulating longitudinal bone growth rate. The duration of the hypertrophic cell activity (i.e. phenotype modulation) phase remains constant (at approximately 2 days) under the various growth rate conditions. 3. The findings presented in this study indicate that measurement of bulk parameters such as [35S]sulphate incorporation into matrix components, [3H]thymidine uptake by cells and growth plate height are of limited value as estimators of longitudinal bone growth, since changes in the parameters that these measurements quantify bear little relationship to changes in linear growth rate, and may be useful only as indicators of total growth plate activity.

Chubby: a new autosomal recessive skeletal mutation producing dwarfism in the mouse.

The chubby (cby) mutant is a previously undescribed skeletal mutation in the mouse. Breeding experiments showed that cby is a recessive mutant with complete viability, full penetrance and fertility in both sexes. Tests for allelism showed that the cby mutant is genetically unlike the somewhat similar mutants, stumpy (stm), pituitary dwarf (dw), spondylometaphyseal chondrodysplasia (smc), brachymorphic (bm), and achondroplasia (cn). The defects seem to occur mainly in growth cartilage. Microradiography revealed increased height of the epiphyseal growth plate and irregular bone trabeculae in the metaphysis. Light microscopy showed disturbed columnar organization of proliferative chondrocytes and pronounced signs of cellular disintegration. The hypertrophic zone, however, contained normally shaped chondrocytes arranged in regular columns. In spite of the normal cellular hypertrophy the pattern of cartilage mineralization was disturbed. The electron microscopy studies revealed very high amounts of matrix vesicles and numerous larger membrane coated structures in the extracellular matrix. Biochemical analysis of the affected growth cartilage revealed a slightly modified pattern of proteoglycan subpopulations and considerably longer chondroitin sulfate chains when compared with controls. From the present study it can be concluded that the cby mutant is a genetically and morphologically distinct condition with characteristic, somewhat rickets-like stigmata. The pathogenetic mechanism underlying the condition remains to be clarified.

Tibial epiphyseal development: a cross-sectional histologic and histomorphometric study in the New Zealand white rabbit.

Sequential histomorphometric studies on the developing rabbit tibia from birth to skeletal maturity demonstrate that growth plate height lessens as longitudinal growth diminishes. Differing rates of development proximally and distally are documented. Distally, growth plate height, width, and area and total epiphyseal area peak or reach near maximum values by 3 weeks, whereas proximally, they do so by 8 weeks (except for height, which also peaks at 3 weeks). The distal growth plate is being obliterated by 16 weeks, at which time the proximal growth plate remains well structured and open. The distal tibia and fibula develop as one tissue mass. The articular cartilage and epiphyseal cartilage are continuous from birth, whereas a single ossification center and a single growth plate are present by 8 weeks. The data point to the presence of intrinsic growth plate, as well as systemic, control mechanisms affecting skeletal growth. Knowledge of temporal and quantitative features of epiphyseal and growth plate development will greatly aid in the elucidation of the underlying controls.