Biomedical subjects

H Oxlund

Publications and source records attributed to H Oxlund.

At least 73 records · Page 4Linked to original sources

PubMed1991

The influence of aminoguanidine on borohydride reducible collagen cross-links and wound strength.

The mechanical strength of skin wounds as well as the deposition of hydroxyproline and KB3H4 reducible hydroxylysinonorleucine (HLNL) and dihydroxylysinonorleucine (DHLNL) cross-links in subcutaneously implanted cellulose sponges have been investigated in rats treated with aminoguanidine (AG) or beta-aminopropionitrile (BAPN). Treatment with AG (25 mg/kg BW/day) did not influence the mechanical strength of the wounds, the deposition of hydroxyproline or the pattern of reducible collagen cross-links, whereas AG (125 mg/kg BW/day) reduced the maximum load by 17%, but did not influence the deposition of hydroxyproline or reducible cross-linking pattern. Treatment with BAPN (333 mg/kg BW/day) reduced the strength of the wounds by 59%, the HLNL by 50% and the DHLNL 57%, whereas the deposition of hydroxyproline did not seem to be influenced by BAPN treatment. In conclusion, AG at moderate dosage does not seem to influence the formation of lysyl oxidase dependent reducible cross-links of collagen.

Aminopropionitrile↗

PubMed1991

In vitro analysis of muscular contractile ability and passive biomechanical properties of uterine cervical samples from nonpregnant women.

We assessed the maximal muscular contractile ability, the passive biomechanical properties, and the hydroxyproline concentration in uterine cervical tissue samples from 28 nonpregnant women. Circular cervical tissue strips were mounted in organ baths and isometric tension was recorded. The mean (+/- SEM) maximal mechanical responses induced at the length of optimal mechanical performance by K+ (124 mmol/L) equaled 0.16 +/- 0.05 mN/mm2 in the distal cervix and 0.84 +/- 0.47 mN/mm2 in the proximal cervix, as compared with 4.85 +/- 1.0 mN/mm2 in tissues from the isthmus and 6.50 +/- 1.4 mN/mm2 in the fundus. The passive biomechanical properties were analyzed by a materials-testing machine. No significant differences were found between tissues from the distal and proximal cervix or between circular and longitudinal preparations. Tensile strength equaled 1.5-1.7 N/mm2, ie, 10(4)-fold the maximal muscular contractile ability. The extensibility was 0.63-0.76 and the stress-relaxation was 41-48%. The hydroxyproline concentration was 22.5 micrograms/mg wet weight in the distal cervix and 21.6 micrograms/mg in the proximal cervix, as compared with 16.6 micrograms/mg in the isthmus and 12.6 micrograms/mg in the fundus. A method for analysis of the biomechanical properties of the human cervix was designed, and from the measurements obtained it may be concluded that the passive biomechanical strength of the cervix markedly exceeds the active muscular contractile ability. This may be explained by a high collagen concentration and a low content of smooth muscle in the cervical tissue.

Adult↗

PubMed1990

Growth hormone increases the bursting strength of colonic anastomoses. An experimental study in the rat.

The effect of growth hormone on the bursting strength of left colonic anastomoses was investigated experimentally. Seventy-two 3 month-old female rats were randomized into two groups receiving daily injection of either saline (controls) or 2.0 mg biosynthetic human growth hormone per kg body weight per day. All injections were started 7 days before a left colonic resection and anastomosis, and continued until sacrifice at the 2nd, 4th or 6th post-operative day. The bursting strength of the anastomoses was tested in anaesthetized, living rats. The bursting pressure and the bursting wall tension of the growth hormone treated animals were increased two-fold on the second post-operative day (2p less than 0.005) and three-fold on the fourth post-operative day (2p less than 0.05), compared with controls. There was no difference in the bursting pressure or the bursting wall tension on the sixth postoperative day. The mass of the resected segment was increased by the pre-operative growth hormone treatment, whereas the hydroxyproline content was unchanged. In conclusion, treatment with biosynthetic human growth hormone increases the strength of colonic anastomoses in the early phases of healing.

Anastomosis, Surgical↗

PubMed1990

Biomechanical analysis of human chorioamniotic membranes.

The biomechanical properties of human fetal membranes were analyzed by means of a materials testing machine. Special attention was paid to the biomechanical properties of the intact chorioamniotic membrane and the amniotic and chorionic components, separately, and thickness and storage of membrane samples. The load-strain and stress-strain relationships, and parameters calculated from the curves: extensibility, strength, elastic stiffness and failure energy, express the visco-elastic behavior of these membranes. The mechanical properties of the chorioamniotic membranes are determined by the interaction between the amniotic and chorionic components of the membrane. The strength of the intact chorioamniotic membrane, however, is primarily determined by the amniotic component, because the amniotic component is much less extensible. Thus, the chorionic component only contributes 10-15% of the strength when the amniotic component breaks. The chorionic component is twice as extensible as the amniotic component. Samples of fetal membranes can be stored at -70 degrees C, with no significant changes in the biomechanical properties. No significant differences were found between specimens, which were oriented in parallel with and at right angles to the placental edge. Small samples can be analysed and the localization of samples in relation to the placental edge and rupture site of the membranes can be standardized. The method is well suited for studies of premature rupture of fetal membranes.

Amnion↗

PubMed1990

Growth hormone increases the mass, the collagenous proteins, and the strength of rat colon.

The effect of growth hormone treatment on the left colon was investigated in 4-month-old Wistar rats. The animals were injected with saline (controls) or biosynthetic human growth hormone (b-hGH) in doses of 1.0 and 5.0 mg b-hGH/kg/day for 30 days. The total body weight of the rats injected with 1.0 mg b-hGH/kg/day did not differ from that of the control group, whereas the body weight of the rats injected with 5.0 mg b-hGH/kg/day was increased by 37% compared with the control group. The colonic dry weight per unit length was increased by 57% and 46% by 1.0 mg and 5.0 mg b-hGH/kg/day, respectively. The defatted dry weight was increased by 52% and 44%, respectively. The hydroxyproline content per unit length was increased by 31% and 23%, respectively. Furthermore, the biomechanical strength was increased by the b-hGH injections. No difference between the two b-hGH doses was found in any of the data.

Animals↗

PubMed1990

Reduced strength of skin in Ehlers Danlos syndrome, type III.

The biochemical properties, ratio collagen type I/type III and the pattern of reducible collagen crosslinks were studied in skin biopsy samples from 10 patients with Ehlers Danlos syndrome type III (ED III) and 10 age- and sex-matched controls. The ED III patients had marked reductions in skin strength and stiffness (42% and 22%, respectively). The ultimate extensibility of the skin, however, was not different from that of the controls. Consequently, a certain load applied to the skin of these patients results in greater deformation than in that of the controls, due to reduced stiffness. The bursting limit is no different from that of the controls. Thus the skin in the ED III patients is not hyperextensible, it merely has reduced strength and stiffness. The reduction in strength could not be explained by differences in skin thickness or collagen content. Skin thickness, collagen content and ratio collagen type I/type III were the same as in the controls, as also was the pattern of reducible collagen crosslinks. These alterations in the mechanical properties of the skin of patients with ED III may be attributable to the molecular structure of the mature collagen or the arrangement of the collagen fibres.

Adult↗

PubMed1989

Increased aortic stiffness in patients with type 1 (insulin-dependent) diabetes mellitus.

The biomechanical properties of aortic samples from patients with Type 1 (insulin-dependent) diabetes mellitus and age- and sex-matched control subjects were analysed using a materials testing machine. The specimens were prepared from tissue outside areas of visible atherosclerosis in order to discriminate between primary Type 1 diabetic alterations in the aortae and secondary changes due to increased atherosclerosis. We paid special attention to the correction of biomechanical parameters for differences in wall thickness and registration of specimen length values. In the Type 1 diabetic aortae a marked reduction was found in the extensibility and an increase in their stiffness. The reduced extensibility was correlated significantly to the duration of Type 1 diabetes. The pronounced alterations in the mechanical properties could not be explained by the increase in the wall thickness which was observed among the Type 1 diabetic patients and the alterations could not be correlated to the grade of atherosclerosis in the thoracic aorta. The results of the present study, therefore, strongly suggest that Type 1 diabetic patients develop alterations in the arterial connective tissue independent of the presence of atherosclerosis. Such primary alterations in the vessel wall may play a role in the pathogenesis of large vessel disease among these patients.

Aorta, Thoracic↗

PubMed1988

Reduced strength of rat cortical bone after glucocorticoid treatment.

The aim of the present study was to examine the effect of therapeutic doses of glucocorticoids on the mechanical strength of rat femora. Groups of rats were treated with a glucocorticoid--methylprednisolone (Solu-Medrol)--1 mg/kg/day for 5, 10, 30, and 90 days. One group served as intact control, two control groups were injected with saline for 30 and 90 days and another group of rats had restricted access to food so that their weight gain was reduced to the same extent as the group treated with glucocorticoid for 90 days. The strength of the femora was analyzed by means of a materials testing machine. No differences were found in the short-term treated groups compared to the control groups, but in the group treated with glucocorticoid for 90 days, a reduction in the bending strength of the rat cortical bone was found. Furthermore, this reduction in strength was found after correction for the reduced thickness of cortical bone in the glucocorticoid-treated rats. The results could not be explained solely by the fact that glucocorticoid-treated rats had smaller bones. No alterations were found in bone density or bone ash weight relative to dry weight. The data indicate that the reduction in bone strength induced by glucocorticoids is not only caused by a reduction in bone quantity, but also by a decrease in bone quality.

Animals↗

PubMed1988

The role of elastin in the mechanical properties of skin.

The elastin fibers of rat skin samples were degraded by the use of a purified preparation of elastase to which soybean inhibitor was added, preventing the collagenolytic activity of the elastase on collagen. Control experiments ascertained degradation of elastin and no effect on collagen. The mechanical properties of the skin samples were studied before and after the enzymatic treatment and differences ascribed to the degraded elastin fibers. Elastin plays a role in the mechanical behaviour of rat skin at small stress values and small deformations. Especially, the elastin fibers are responsible for the recoiling mechanism after a stress or deformation has been applied.

Animals↗

PubMed1988

The influence of non-enzymatic glycosylation and formation of fluorescent reaction products on the mechanical properties of rat tail tendons.

Mechanical stability was examined in rat tail tendons after in vitro incubation in glucose at pH 7.4 using buffer systems of either phosphate or tris(hydroxymethyl)aminomethan. In the phosphate buffer system glucose and fluorescent compounds were found to be attached to the collagen molecules and the maximum 'stress' of the tendons was increased. In the tris(hydroxymethyl)aminomethan buffer system glucose was attached to the collagen molecules, but only small amounts of fluorescent compounds were attached to the collagen molecules and no changes in mechanical parameters were recorded. Initial incubation of tendons in a high concentration of glucose followed by incubation in either phosphate or tris(hydroxymethyl)aminomethan buffer solutions resulted in equal attachment of glucose to the collagen, but only the collagen reincubated in phosphate buffer developed a relatively high amount of fluorescent compounds and an increase in maximum mechanical 'stress' compared to the collagen reincubated in tris(hydroxymethyl)aminomethan buffer. This shows that the non-enzymatic glycosylation per se does not necessarily influence the mechanical properties of collagen. Additional reactions like transformation of glucose into fluorescent compounds or browning reaction products by Maillard's reaction seem to be essential.

Animals↗

PubMed1988

Serum aminoterminal type III procollagen peptide. Relation to biosynthesis of collagen type III in experimentally induced granulation tissue in rats.

Serum aminoterminal type III procollagen peptide was measured in rats during the development of granulation tissue induced by subcutaneous implantation of viscose cellulose sponges. Active collagen type III synthesis in granulation tissue during the first three weeks was accompanied by an increase in serum propeptide level. A positive correlation was observed between the increase in serum propeptide level on the one hand and the increase in granulation tissue collagen type III content and the in vitro formation of tissue 3H-hydroxyproline on the other hand. In some animals the serum propeptide level remained low, despite biochemical signs of collagen synthesis, indicating variations in the release into serum and/or the metabolism of circulating propeptide. The increase in propeptide antigen concentration was mainly due to an elevated content of material with molecular weight equal to or twice that of the propeptide. A minor fraction of the propeptide remained attached to the interstitial collagen fibres in the granulation tissue. The correlation between the serum propeptide level and the biosynthesis of collagen at the site of the focal fibroproliferative process suggests that the serum propeptide level may be a valuable indicator of fibrogenesis and thereby of disease activity in fibrotic conditions.

Animals↗

PubMed1988

Connective tissue changes in the cervix during normal pregnancy and pregnancy complicated by cervical incompetence.

When postpartum cervical biopsy specimens were compared with biopsy specimens from nonpregnant women, they revealed a 12-fold decrease in mechanical strength, a 50% reduction in the concentrations of collagen and sulfated glycosaminoglycans, a 35% reduction in hyaluronic acid, an increase in collagen extractability, and a fivefold increase in collagenolytic activity. Primiparas with relatively high concentrations of collagen and hyaluronic acid had relatively long cervical dilatation times during established labor, suggesting a physiologic importance to these variables. This correlation was not found in multiparas, even though the mean values of the biochemical parameters tested were similar to those in primiparas. Second-trimester biopsy specimens taken from patients with cervical incompetence contained normal collagen concentrations, but relatively high collagen extractabilities and collagenolytic activities, exceeding normal postpartum values. A biopsy specimen that was tested biomechanically had a very low strength and very high extensibility. Most likely, these data reflect a high turnover of collagen in incompetent cervices, resulting in a high proportion of newly synthesized collagen with low biomechanical strength.

Adult↗

PubMed1987

Histological and morphometric observations on the reticular fibers in the arterial beds of patients with ruptured intracranial saccular aneurysms.

Histological and morphometric studies on the collagenous, reticular, and elastic fibers of the tunica media were performed on the middle cerebral and brachial arteries of patients with ruptured intracranial saccular aneurysms and controls. There was no difference between aneurysm patients and controls in the amount of collagenous and elastic fibers. The amount of reticular fibers was, however, reduced about 35% in aneurysm patients within both the middle cerebral artery (P less than 0.01) and the brachial artery (P less than 0.02). The reticular fibers were irregularly distributed and often appeared shorter and coarser than normally. The observations point to a generalized abnormality of the arterial bed in some patients with rupture of saccular aneurysms.

Adult↗

PubMed1987

Changes in collagen and elastin of the rat aorta induced by experimental diabetes and food restriction.

The biochemical and biomechanical properties of aortas from diabetic rats were investigated after a period of three months. Diabetes caused increased non-enzymatic glycosylation of lysine and hydroxylysine residues of collagen, whereas no changes were found in the reducible collagen cross-links. Although diabetes caused a reduction in the thickness of the aortic wall and a decrease in the dry weight and amount of collagen and elastin per mm2, no changes were found in the mechanical strength and stiffness of the wall. When the mechanical parameters were corrected for the decrease in dry weight, the tensile strength of the aortic wall was found to be increased compared with the control group. This increase in the stability of aortic collagen can be explained by formation of reactive carbonyl compounds from the glycosyllysines, resulting in stabile cross-links between the collagen molecules.

Animals↗

PubMed1987

Collagen type III deficiency in patients with rupture of intracranial saccular aneurysms.

Samples of the middle cerebral artery (MCA) and the brachial artery were obtained post mortem from 14 patients who died following rupture of intracranial saccular aneurysms and from a control group of 14 age- and sex-matched patients who died of causes unrelated to aneurysm rupture. The biomechanical properties of ring-shaped arterial specimens were investigated by loading the specimens at a constant deformation rate until rupture. The relative amounts of collagen type I and type III were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) studies of cyanogen bromide peptides of collagen prepared from the arterial samples. A deficiency of collagen type III was demonstrated in specimens of the MCA in six of 14 patients with a ruptured intracranial saccular aneurysm. This deficiency was not accompanied by alterations in the mechanical arterial strength but resulted in a significant increase in the extensibility at stress values corresponding to blood pressures between 100 and 200 mm Hg. No difference was found between aneurysm patients and the control group in regard to the biomechanical properties of the brachial artery, despite the presence of a significant deficiency of collagen type III. The increase in vascular extensibility of the MCA may represent alterations in the fibrous structure and functional integrity of the cerebral arteries of aneurysm patients with collagen type III deficiency. Together with aggravating hemodynamic stresses, this deficiency may be an important factor in the pathogenesis of saccular aneurysms.

Brachial Artery↗

PubMed1986

Relationships between the biomechanical properties, composition and molecular structure of connective tissues.

Biomechanical, biochemical and morphological methods have been used in combination as analytical tools in the study of normal and pathological tissue functions. The biochemical studies described have been performed in vitro on whole tissue preparations and on individual components of connective tissues. Enzymatic degradation has been used to selectively remove components from the tissues. Collagen is the main load-bearing component in muscle tendon and skin. The mechanical properties of the aorta appear to depend on an interaction between collagen and elastin. Membranes of purified, reconstituted collagen type I itself exhibits the visco-elastic behavior which is characteristic for tissues like muscle tendon and skin. Applicability of the methods is shown in two examples: The strength of skin samples from patients with osteogenesis imperfecta was found to be reduced, and the skin from the patients with the lowest strength contained the highest proportions of collagen type III. Moreover, the stability of molecular collagen type I was decreased. In samples of the intracranial arteria cerebri media obtained at autopsy from patients with rupture of intracranial aneurysms the wall thickness, dry defatted weight and ratio collagen type I/type III were increased. The diameter of the arteries was reduced.

Aorta↗

PubMed1985

Thermal stability of collagen in relation to non-enzymatic glycosylation and browning in vitro.

Thermal stability measured by isometric contraction-relaxation force was examined in rat tail tendons after incubation in vitro in glucose or hydroxymethylfurfurale solutions at pH 7.4 using buffer systems of either phosphate or tris (hydroxymethyl)aminomethan. In the phosphate system, incubation with glucose (170 mmol/l) for 12 days was found to increase the thermal stability of the tendons by a factor 3. At the same time, glucose was found to be attached to the lysine and hydroxylysine residues of collagen, and reactive carbonyl compounds were formed in the solution. In the tris(hydroxymethyl)aminomethan system containing reactive amino groups (pK 8.1), glucose was also attached to the lysine and hydroxylysine residues, but only very small amounts of reactive carbonyl compounds were formed in the solutions and no changes in thermal stability were recorded. Incubation with hydroxymethylfurfurale itself was found to increase the thermal stability rapidly and markedly in the phosphate buffer systems. This effect was inhibited when the tris(hydroxymethyl)aminomethan buffer system was used. Buffer solutions with tris(hydroxymethyl)aminomethan, containing large amounts of free amino groups compared to the free amino groups of collagen, might interfere with the formation of cross-links formed by carbonyl groups derived from metabolic glucose and amino groups of collagen. The non-enzymatic glycosylation of lysine and hydroxylysine itself does not influence the thermal stability. Additional reactions appeared to be transformation into reactive carbonyl compounds, such as hydroxymethylfurfurale, with subsequent formation of thermally stable cross-links between the collagen molecules.

Animals↗

PubMed1985

Reduced strength of skin in osteogenesis imperfecta.

The biochemical properties and ratio collagen type I/type III of skin biopsies from nine patients with osteogenesis imperfecta and nine age- and sex-matched controls were studied. Four of six patients with osteogenesis imperfecta Sillence type I had pronounced reductions in skin tensile strength, decreased ratios of collagen type I/type III, primarily accomplished by reduced amounts of collagen type I, moderate or no disability. The three patients with osteogenesis imperfecta Sillence type III had severe skeletal deformities, but normal skin tensile strength, and ratios of collagen type I/type III within the normal range. These observations may be explained as resulting from various structural defects in the type I collagen of patients with osteogenesis imperfecta.

Adult↗