An intraluminal prosthesis may improve healing of a one-layer colonic anastomosis: an experimental study in pigs.

OBJECTIVE: To compare healing of one-layer colonic anastomoses with or without a soluble intraluminal prosthesis (* SBS-tube). DESIGN: Randomised, partly blinded controlled study. SETTING: University hospital, Denmark. SUBJECTS: 16 female Danish country strain pigs, of which 8 had the SBS tube inserted and 8 acted as controls. INTERVENTIONS: One-layer colonic anastomoses either hand-sewn (n = 8, controls) or hand-sewn onto an SBS tube (n = 8). MAIN OUTCOME MEASURES: Macroscopic evaluation, leakage test, breaking strength, histology, oxygen tension in and near the anastomosis peroperatively and 4 days postoperatively. RESULTS: Three quarters of the tubes (n = 8) dissolved in less than 2 hours. Histological examination showed significantly better structured layers and more mucosal epithelial covering in the SBS group. The other histological variables examined were: tissue gap (p < 0.08), inflammation (p < 0.10), breaking strength (p < 0.46) and amount of granulation tissue (p < 0.71), but the last findings were not significant. Oxygen tension at the anastomotic line was better in the SBS tube group, but not significantly so. CONCLUSIONS: We conclude that the SBS tube facilitates the sewing of the anastomosis and may improve healing, possibly because of better apposition of the cut ends and reduced tension in the sutures.

Strength of colonic anastomoses and skin incisional wounds in old rats - influence by diabetes and growth hormone.

The influence of advanced age on the mechanical strength of colonic anastomoses and skin incisional wounds in diabetic rats was investigated after 0 (suture binding capacity) and after 7 days of healing. Furthermore, the effects of growth hormone (GH) injections to old diabetic rats were investigated. Diabetes in old rats did not influence the strength of colonic anastomoses after 0 and 7 days. However, in these diabetic animals, the strength of skin incisional wounds was reduced by 27% after 7 days of healing (P< 0.01). GH injections administered to old diabetic rats doubled the mortality compared with that of saline-injected old diabetic rats (P< 0.01). GH injections did not influence the strength formation of either colonic anastomoses or skin incisional wounds in old normal rats. In conclusion, the healing of colonic anastomoses in diabetic rats was not compromised by old age, while the strength of skin wounds was decreased.

Methylprednisolone does not inhibit the release of growth hormone after intravenous injection of a novel growth hormone secretagogue in rats.

The present study was undertaken to study the growth hormone-releasing properties and growth-promoting effect of a GH secretagogue ipamorelin (IPA) in rats given the synthetic glucocorticoid methylprednisolone (MP). In a first experiment, rats received either saline or MP (5.0 mg/kg) for 8 days. Treatment with MP significantly (P< 0.001) decreased body weight gain, but the acute response to either IPA or growth hormone releasing hormone (GHRH) in terms of plasma GH was not changed. In a second experiment, venous catheters were surgically implanted. On the next day, rats were randomly allocated to receive saline alone, MP alone (5.0 mg/kg) or MP plus IPA in doses of 0.4 or 1.6 mg/kg/day for 10 days. IPA was administered intravenously four times a day.MP treatment significantly (P< 0.05) retarded recovery from surgery in terms of body weight. Thus, saline treated animals lost 4.0 +/- 3.5 g over the entire experimental period, whereas animals receiving MP lost 13. 6 +/- 2.9 g. When IPA was given together with MP, losses in body weight were significantly (P< 0.05) reduced to 2.3 +/- 2.0 and 1.6 +/- 2.0 g in animals given the high and low dose of IPA, respectively. In parallel with this IGF-I levels increased. In conclusion, this work shows that MP does not disrupt the response of the GH-IGF-I axis to an exogenous stimulus like IPA, and repeated stimulation leads to increases in IGF-I and of body weight gain.

Bisphosphonate maintains parathyroid hormone (1-34)-induced cortical bone mass and mechanical strength in old rats.

This study was designed to determine the fate of new parathyroid hormone (PTH)-induced cortical bone after withdrawal of PTH treatment, and to evaluate whether subsequent treatment with a bisphosphonate would influence this. Six groups of 21-month-old rats were used: a baseline group killed at the beginning of the experiment, three groups injected with human PTH (1-34) (62 mug/kg) daily for 8 weeks (day 1-56), then one group was killed and the other two groups were injected for another 8 weeks (day 57-112) with either saline or bisphosphonate (risedronate 5 mug/kg twice a week). Two control groups were injected with vehicle for the first 8 weeks, then one group was killed and the other group injected with saline the next 8 weeks. All animals were labeled with tetracycline and calcein on day 35 and day 49 of the experiment, respectively. PTH increased periosteal (35%) and in particular endosteal mineralizing surfaces (188%), mineral appositional rates, and bone formation rates at the femur diaphysis, leading to an increase in cortical cross-sectional area of 31%. Withdrawal of PTH induced a fast and pronounced endosteal bone resorption whereas risedronate prevented this resorption. No differences were seen in apparent density of dry defatted bone and ash among the groups. PTH increased the mechanical strength of the femur diaphysis; ultimate load increased by 64% and ultimate stress by 25%. A pronounced decrease in mechanical strength and competence was found after withdrawal of PTH: ultimate load decreased by 31% and ultimate stress by 21%. Risedronate, however, prevented this decrease in mechanical strength and competence in these 2-year-old rats.

Biomechanical properties of normal and varicose internal spermatic veins.

To investigate possible differences in biomechanical properties between varicose spermatic veins and controls. During surgery on 12 patients for grade 3 left-sided varicocele testis, 2 cm of the vein was obtained for comparison with: (i) samples of the left internal spermatic vein taken from the same anatomical localization from 8 patients without scrotal disease, and (ii) samples from the right internal spermatic vein from 7 other patients also without scrotal disease. The biomechanical properties of ring-shaped venous specimens were investigated by loading the specimen at a constant deformation rate until rupture. The relative amounts of collagen in the specimens were determined as the contents of hydroxyproline. There was a significant difference between varicocele testis/right spermatic vein in UC (unit collagen), F-max (maximum strength), Strain (ultimate extensibility) and E-fail (relative failure energy), but not in LD (diameter) and Tan-a (stiffness of the specimen). There were no significant differences between left and right spermatic vein in LD, UC, F-max, Strain, Tan-a and E-fail. There was a significant difference in LD between varicocele testis/left spermatic vein, but no relationship in UC, F-max, Strain, Tan-a and E-fail. Biomechanical analyses of the spermatic veins from patients operated for varicocele seem to support the hypothesis that a difference in biomechanical properties plays a part in the development of varicocele because a significant increase in extensibility of varicocele samples was found compared with normal right spermatic vein samples.

No effects of human relaxin on the active and passive biomechanical properties of isolated cervical specimens from nonpregnant women.

OBJECTIVE: To evaluate the effect of human relaxin (hRLX-2) on the active and passive biomechanical properties of cervical tissue in vitro. MATERIAL: Cervical samples were obtained from the middle part of the cervix in 22 nonpregnant women undergoing hysterectomy. METHODS: The effect of hRLX-2 (10(-7) M) on the active biomechanical properties was studied on vasopressin (10(-8) M) induced smooth muscle contractions in an organ bath model. The effect on the passive biomechanical properties were studied after incubation of the strips for 48 h with hRLX-2 (10(-8) M and 10(-9) M). Subsequently, the specimens were stretched in a material testing machine until they broke. The load applied and the elongation were simultaneously recorded and the results translated into stress-strain curves. RESULTS: hRLX-2 did not influence the vasopressin-induced contractility of cervical strips from nonpregnant women in this study. No synergistic effect of progesterone could be demonstrated. The passive biomechanical properties (tensile strength, extensibility, stiffness of failure energy) did not change significantly after relaxin incubation. The results obtained in vitro do not suggest an important physiological effect of relaxin on the human nonpregnant cervix.

The effect of oophorectomy on mechanical properties of rabbit cerebral and coronary isolated small arteries.

OBJECTIVE: Our purpose was to study the effect of oophorectomy on the passive and active mechanical characteristics of rabbit small cerebral and small coronary arteries. STUDY DESIGN: Ring preparations of small cerebral and small coronary arteries from rabbits that had undergone oophorectomy and sham operation were mounted on myographs 6 weeks after operation. Experiments were performed as follows. (1) concentration-response relations for vasopressin (10(-11) to 10(-7) mol/L), U46619 (10(-10) to 10(-6) mol/L), 5-hydroxytryptamine (10(-7) to 10(-5) mol/L), and endothelin (10(-13) to 10(-7) mol/L); (2) relaxing effects of acetylcholine (10(-8) to 10(-4) mol/L); (3) length-tension relations after addition of high potassium (124 mmol/L), vasopressin (10(-7) mol/L), and a mixture composed of potassium (124 mmol/L), vasopressin (10(-7) mol/L), and prostaglandin F 2 alpha (10(-5) mol/L); (4) calculation of vessel morphologic features and determination of hydroxyproline as a measure of collagen content. RESULTS: Oophorectomy did not influence basal tone, relaxant effects of acetylcholine, vessel morphologic features, elastic characteristics, or hydroxyproline content of the vessels. However, in cerebral arteries at a normalized lumen diameter, oophorectomy induced a marked increase in the force development after stimulation with agonists but not after depolarization with high potassium. The reason for this was a leftward shift in the active length-tension curves (vasopressin activation). In coronary arteries none of these changes were seen after oophorectomy. CONCLUSION: These data demonstrate that withdrawal of ovarian hormones changes the position of the active length-tension curve for pharmacomechanical but not electromechanical coupling of small cerebral arteries without interference with the elastic characteristics of these vessels.

Collagen structural organization of healing colonic anastomoses and the effect of growth hormone treatment.

PURPOSE: This experimental study was designed to investigate the collagen fibrils of colonic anastomoses in rats and to compare normal healing with rats treated with biosynthetic growth hormone (bGH). METHODS: The healing zone of left colonic anastomoses was studied at days 2, 4, and 6 after surgery by means of scanning electron microscopy. RESULTS: After four days of healing a normal anastomosis was filled with loosely packed and unorganized collagen fibrils, which were organized into collagen fibers after six days. Compared with normal anastomoses, rats treated with bGH showed a more organized healing, characterized by a dense structure of a new-formed collagen framework of fibrils and immature collagen fibers after six days. CONCLUSIONS: Healing colonic anastomoses are characterized by new-formed collagen fibrils at postoperative day 4, and bGH seems to stimulate structural organization of the anastomotic collagen fibrils into fibers.

Growth hormone increases the collagen deposition rate and breaking strength of left colonic anastomoses in rats.

BACKGROUND: The purpose was to investigate how growth hormone exerts its stimulating effect on the healing of experimental colonic anastomoses. METHODS: Rats were treated with biosynthetic growth hormone (bGH); the anastomotic breaking strength, collagen content, and collagen deposition rate (labeling of collagen with 14C-proline) were compared to saline treated controls. RESULTS: bGH increased the breaking strength when the rats were treated before and after the operation and when bGH treatment was started at operation and continued during the healing period. No effect on these parameters was seen, however, when treatment was given only before operation. The collagen deposition rate of the intact colon was accelerated from 0.6% to 1.0% per hour at operation after 7 days of preoperative treatment. The anastomotic collagen deposition rate was increased on day 4 from 4.4% in the controls to 9.0% in the anastomosed rats given bGH from operation and to 12.9% in rats given bGH from 7 days before operation until day 4 after operation, resulting in a higher anastomotic collagen content. CONCLUSIONS: Treatment of rats with bGH in the healing phase increases the breaking strength of colonic anastomoses caused by a stimulation of the collagen deposition rate of the anastomotic segment.

Different biomechanical properties of human fetal membranes obtained before and after delivery.

The aim of this study was to elucidate whether the mechanical properties of fetal membranes change during late pregnancy and labour. Membranes delivered by elective caesarean section in week 38 showed different load-strain curves to membranes obtained after spontaneous vaginal delivery at term. A major change in mechanical properties was a decrease in strength of the intact chorioamniotic membrane from 1.39 N to 0.98 N (width of biopsy 4 mm), mainly due to loss of strength of the amniotic component, from 1.27 N to 0.72 N. Moreover, the extensibility of the chorionic component (epsilon Fmax) increased after vaginal delivery from 0.42 to 0.54, resulting in a two-component behaviour of the intact chorioamniotic membrane and further decrease of strength. Based on these observations it is suggested that the amnion is attached to the chorion, act biomechanically in parallel and possess relatively high mechanical strength during pregnancy. After vaginal delivery the two membranes are separated, and pronounced changes are induced in their mechanical properties.

Glucocorticoid treatment or food deprivation counteract the stimulating effect of growth hormone on rat cortical bone strength.

Growth hormone (GH) has been found to increase the length, thickness and bending strength of rat femora. The present study was designed to investigate if glucocorticoid treatment or food restriction would interfere with the effect of exogenous GH on bone growth. Male rats treated with GH for 30 days experienced a weight gain of 30-35% and longitudinal and periosteal femoral growth. A dose-related increase in the bending strength of the femora was found and was explained by an increased thickness of the femora. In spite of a reduced real density, biomechanical competence was preserved after GH treatment. GH treatment combined with a relatively small dose of glucocorticoid, which in itself had no significant effect on bone growth and strength, reduced the stimulating effect of GH on body weight gain, femoral growth and strength. GH-treated rats that were food restricted, so as to limit their body weight gain to that of the saline group, experienced significant longitudinal and periosteal femoral growth. Bone strength, however, was not increased, which conforms to a reduced mineralization and increased porosity of the femora. Young's modulus (normalized bone stiffness) was significantly decreased in this group, probably as a result of decreased mineralization. Furthermore, the combination of GH treatment and food restriction resulted in a reduced apparent density indicating increased bone resorption.

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.

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.

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.

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.

Long term local cortisol treatment of tendons and the indirect effect on skin. An experimental study in rats.

The mechanical properties of muscle tendon after long term local cortisol treatment were studied as well as those of skin with regard to possible systemic effects. Rats received cortisol injections 10 mg/kg into each hind limb, around the peroneal tendons every third day for 55 days. A control group was injected in the same way, but with saline. The local cortisol treatment did not alter the mechanical properties of the peroneous longus tendon, even though its dry weight and hydroxyproline content was reduced. A systemic effect on skin from the dorsum was observed. The thickness and hydroxyproline content were reduced, and in spite of that, the strength of the skin specimens increased. The hydroxyproline/nitrogen ratio in purified, insoluble skin collagen was not changed after the cortisol treatment. Two different effects of corticosteroids on collagenous tissues are suggested to act here: (1) within the first one to two weeks corticosteroids induce a relatively fast increase in the stability of the collagenous tissue, (2) followed by a progressive thinning and reduction in collagen of the tissue, caused mainly by an inhibited collagen synthesis. Thus the strength of the muscle tendon is not reduced, even though its collagen content is reduced after local cortisol treatment for 55 days.

The influence of cortisol on wound healing of the skin and distant connective tissue response.

The effect of moderate dosage cortisol treatment on healing wounds and on the response in skin distant to the wounds was investigated. The stress-strain characteristics of a skin wound and intact skin specimens were examined. Also, skin thickness, water content and collagen content were measured. Cortisol treatment resulted in reduced extensibility and increased stiffness for ten day wounds, but unchanged failure energies; for 20 day wounds, failure energies were reduced, indicating reduced ability to withstand rupturing forces. Thus, the mechanical properties of healing wounds under moderate dosage, long term corticosteroid treatment were found to be slightly impaired. A systemic effect of wounding at day 10 resulted in decreased stiffness and increased collagen content of the skin distant to the wound.