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Biomedical subjects

D A Martinez

Publications and source records attributed to D A Martinez.

29 records · Page 2Linked to original sources
PubMed1991

Nonreducible crosslink formation in tibial dyschondroplastic growth plate cartilage from broiler chicks fed homocysteine.

In the study of tibial dyschondroplasia, scientists have for a long time thought that an altered extracellular matrix might be involved in the etiology of the disease. The results presented in this paper show that the collagen content was increased in the dyschondroplastic cartilage when compared to normal growth plate and day-old hypertrophic cartilage. Furthermore, nonreducible crosslinks were found only in dyschondroplastic cartilage, with the greatest amounts occurring in the distal region of the lesion, approximately 10-fold higher than that found in the dyschondroplastic growth plate. Thus, intermolecular collagen bonding is altered in the extracellular matrix of dyschondroplastic cartilage. Possible models for the etiology of the disease are discussed.

Analysis of Variance↗
PubMed1991

Cortical bone maturation in young hypophysectomized rats.

Cortical bone growth and maturation were studied in young growing rats (62 days) that were hypophysectomized. After 10 days, femur bones were obtained for morphological and biochemical analysis of the middiaphysis. Hypophysectomy significantly decreased (42%) normal body growth demonstrated by reductions in body weight. Bone morphology data indicate that hypophysectomy significantly inhibits the circumferential growth of the middiaphysis as well as region-specific thickness compared with the control group. The effects of hypophysectomy on cortical bone mineral composition and density were significantly greater in the hypophysectomized rats. Bone density and total mineral density were significantly greater, 17% and 24%, respectively, in the hypophysectomized group compared with control animals. Bone collagen maturation, measured by the amount of the mature collagen cross-link hydroxylysylpyridinoline, in the hypophysectomized animals was significantly greater (130%). Also, collagen concentration and content per unit volume were significantly greater, 24% and 70%, respectively, in the hypophysectomized group. Our findings suggest that "normal" growth and maturation of cortical bone in rapidly growing animals is dependent upon the modulation of pituitary hormones. These data also suggest that an increased rate of mature collagen cross-link formation may be modified by the turnover rate of collagen and other matrix constituents. In addition, hormonal mechanisms associated with a suppression of bone growth may enhance the probability of mature collagen cross-link formation.

Animals↗
PubMed1990

Effects of spaceflight on rat humerus geometry, biomechanics, and biochemistry.

The effects of a 12.5-day spaceflight (Cosmos 1887 biosatellite) on the geometric, biomechanical, and biochemical characteristics of humeri of male specific pathogen-free rats were examined. Humeri of age-matched basal control, synchronous control, and vivarium control rats were contrasted with the flight bones to examine the influence of growth and space environment on bone development. Lack of humerus longitudinal growth occurred during the 12.5 days in spaceflight. In addition, the normal mid-diaphysial periosteal appositional growth was affected; compared with their controls, the spaceflight humeri had less cortical cross-sectional area, smaller periosteal circumferences, smaller anterior-posterior periosteal diameters, and smaller second moments of area with respect to the bending and nonbending axes. The flexural rigidity of the flight humeri was comparable to that of the younger basal control rats and significantly less than that of the synchronous and vivarium controls; the elastic moduli of all four groups, nonetheless, were not significantly different. Generally, the matrix biochemistry of the mid-diaphysial cross sections showed no differences among groups. Thus, the spaceflight differences in humeral mechanical strength and flexural rigidity were probably a result of the differences in humeral geometry rather than material properties.

Animals↗
PubMed1990

Spaceflight effects on biomechanical and biochemical properties of rat vertebrae.

The biomechanical and biochemical responses of lumbar vertebral bodies during a 12.5-day spaceflight (Cosmos 1887 biosatellite) were determined for rapidly growing rats (90-day-old, Czechoslovakian-Wistar). By use of age-matched vivarium controls (normal cage environment) and synchronous controls (simulated flight conditions), as well as a basal control group (killed before lift-off on the 1st day of flight), the combined influences of growth and space-flight could be examined. Centra of the sixth lumbar vertebrae (L6) were compressed to 50% strain at a fast strain rate while immersed in physiological buffer (37 degrees C). The body masses of vivarium and synchronous controls were significantly heavier than either the flight or basal controls. The flight group had an L6 vertebral body compressional stiffness that was 39% less than the vivarium controls, 47% less than the synchronous control, and 16% less than the basal controls. In addition, the average initial maximum load of the flight L6 was 22% less than vivarium controls and 18% less than the synchronous controls, whereas the linear compressional load of the flight group averaged 34% less than the vivarium and 25% less than the synchronous groups. The structural properties of the vertebrae from the 12.5-day-younger basal group closely resembled the flight vertebrae. Calcium, phosphorous, and hydroxyproline concentrations were not significantly different among the groups. Nevertheless, the lack of strength and stiffness development in spaceflight, coupled with a smaller proportion of mature hydroxypyridinoline cross-links, suggested that the 12.5 days of spaceflight slowed the maturation of trabecular bone in the vertebral bodies of rapidly growing rats.

Animals↗
PubMed1989

Biomechanical and biochemical changes in lumbar vertebrae of rapidly growing rats.

Although growth-related biochemical, morphological, and biomechanical properties of rat cortical bone have been investigated, similar properties of immature rat vertebral bone have not been well characterized. Information about these properties is necessary, however, for comparative analyses of rat vertebral bone adaptation. Thus a method was developed to characterize growth-related differences in immature rat vertebral bone. The centra of sixth lumbar vertebrae (L6) of 44-day-old and 54-day-old male Sprague-Dawley rats were compressed to 50% of their initial height at a 50%/s strain rate while immersed in a potassium phosphate buffer solution (pH 7.4, 37 degrees C). Structural and material properties for the 54-day-old group that were significantly greater than those for the 44-day-old group included load, stress, and energy at the proportional limit; initial maximum load and stress; and load and energy at 50% strain. The structural stiffness of L6, as well as its elastic modulus, was significantly greater in the older animals. The calcium concentrations and calcium-to-collagen ratios in 54-day-old vertebrae were significantly greater than in younger animals. These results indicated that the specimen preparation and testing protocol developed for rat vertebrae produced reliable biomechanical results, even with the relatively small size of rat vertebrae bodies, and that the quantity and quality of the matrix of immature rat vertebral bone changed significantly during this period of rapid growth. Our test protocol will be useful for investigating the responses of rat vertebral bone to exercise, disease, and spaceflight.

Animals↗
PubMed1981

Dermoid cysts of the ovary: their ultrasonographic appearances.

Ultrasonograms of 45 patients with 51 surgically proved benign cystic teratomas (dermoid cysts) of the ovary were reviewed to evaluate the ultrasonographic appearance of this entity. Contrary to several recent reports stressing a "typical" appearance for ovarian dermoid cysts, ie, an echogenic focus with acoustic shadowing situated within a predominantly cystic mass, the authors observed a much broader spectrum of appearances. Thirty-three percent of the cases demonstrated "typical" findings, 23.5% were predominantly solid, 20% were almost entirely cystic, and 23.5% were not visible. Ultrasound and conventional radiography in patients with dermoid cysts were compared: Ultrasonography contributed significantly to the correct diagnosis in the majority of cases. Because ultrasonography lacks ionizing radiation, and its use may reveal unrelated pelvic pathology, it should be the initial diagnostic modality in the examination of patients with suspected dermoid cysts of the ovary.

Dermoid Cyst↗
PubMedDate not supplied

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.

Adolescent↗
PubMedDate not supplied

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.

Animals↗
PubMedDate not supplied

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)

Adaptation, Physiological↗