Training increases the in vivo strength of the lower leg: an experimental study in the rat.

The effect of training on bone strength has been investigated in rats. After 7 weeks of training, fracture strength of the tibia in vivo during muscle contraction and after resection was assessed. A group of 30 male rats 11 weeks old were randomized to exercise on a treadmill, sedentary (ordinary caging), and inactivity (right-sided patellar tendonectomy) groups. The training group ran on a treadmill with a 10% inclination for 1 h per day. After 4 weeks the animals in all groups were anesthetized and the right lower legs loaded in three-point ventral bending until fracture during electrically induced muscle contraction. The contralateral tibiae were tested correspondingly after resection. Ultimate bending moment, energy absorption to failure, bending stiffness, and deflection were assessed for the in vivo and the resected tibiae. The body weight gain was 37% higher in the sedentary and 57% higher in the inactive animals than in the training group (P < 0.05), indicating a physiologic effect of the training. In the dissected tibiae there were no significant group differences in any of the mechanical parameters, indicating that neither training nor inactivity changed the structural capacity of the tibiae per se. In contrast, there were significant differences between the in vivo tibiae. Ultimate bending moment was 12% higher in the training group than in the sedentary and inactive groups (P = 0.03). Energy absorption in the training group was 11 and 12% higher (not significant) than in the sedentary and inactivity groups, respectively. Bending stiffness was 7 and 17% higher in the training group compared to sedentary and inactivity groups (P = 0.018).(ABSTRACT TRUNCATED AT 250 WORDS)

Muscle contraction increases the in vivo structural strength to the same degree in osteopenic and normal rat tibiae.

The increase in structural capacity due to muscle contraction in the lower leg was investigated in osteopenic and normal rats. Osteopenia was induced by ovariectomy combined with a low-calcium diet (0.01%). The control rats were sham operated and fed a diet containing 1.1% calcium. After 7 weeks the right lower leg of all animals were fractured in three-point ventral cantilever bending during muscle contraction induced by electrical stimulation of the ischiatic nerve. The left tibiae were resected and fractured as each animal's control. During muscle contraction in vivo, the ultimate bending moment, energy absorption, bending stiffness, and deflection were significantly lower in the osteopenic than in the sham-operated animals. However, the increase in mechanical parameters due to muscle contraction comparing the in vivo and resected tibiae in each animal were equally high in the osteopenic and sham-operated animals. Ultimate bending moment in the resected tibiae was 10% higher in the sham-operated animals compared with the ovariectomized, proving mechanically weaker tibiae in the osteopenic rats. In accordance with this, the medullary area of the osteopenic rats was 46% larger in the distal tibial diaphysis, and the ultimate stress the tibiae could withstand was 15% lower in the osteopenic compared with the sham-operated rats. The trabecular bone volume in the distal tibial metaphysis of the osteopenic rats was reduced by 70% compared with the sham operated. This study shows that muscle protection against fracture can be substantial in osteopenic tibia and that it is of the same magnitude as in rats with normal bone mass.

Cerebral blood flow measured with intracerebral laser-Dopplerflow probes and radioactive microspheres.

We have measured cerebral blood flow with intracerebral laser-Doppler microprobes in pentobarbital-anesthetized pigs. We compared the results with measurements from laser-Doppler probes placed on the surface of the brain and with blood flow estimation by the radioactive microsphere method. The cerebral blood flow was varied by alterations in inspired carbon dioxide, hemorrhagic hypotension, and high cerebrospinal fluid pressure. The intracerebral probes and the surface probes showed parallel responses to variations in cerebral blood flow. The correlation was closest between surface probes and the intracerebral probes measuring from the cerebral cortex (r = 0.46; P < 0.005). The r value between laser-Doppler flowmetry and radioactive microspheres was 0.41 (P < 0.0005) for all measurements. The correlation to microspheres was best for the probes located 3 or 10 mm into the brain and poorest for the surface probe. In conclusion, intracerebral laser-Doppler flow measurements reflect changes in blood flow, and the technique appears useful for continuous estimates of cerebral blood flow.

Regional blood flow and strontium-85 incorporation rate in the rat hindlimb skeleton.

Regional distribution of radioactive microspheres and 85Sr incorporation rate in the os ilium, femur, and tibia were determined in 44 rats. In 15 additional animals, regional blood flow was measured with the reference sample technique. Highest numbers of microspheres were found in the distal femoral and proximal tibial metaphyses. Highest blood flow rates were found in the os ilium, the caput femoris, and distal femoral and proximal tibial metaphyses. The diaphyses and epiphyses of the femur and tibia had a relatively lower perfusion. The regional 85Sr incorporation rate was correlated (r = 0.67) to the regional distribution of the microspheres. The dispersion of the data was large and this was mainly due to biological variation. The results describe the regional distribution of blood flow in the rat hindlimb and demonstrate a close association between blood flow and mineral turnover in normal rat skeletal tissue as shown by the correlation between microsphere and 85Sr incorporation rate distribution.

Carvedilol reduces ischaemic skeletal muscle necrosis.

Carvedilol is an alpha1 and nonselective beta-adrenergic receptor antagonist with antioxidative properties known to protect against reperfusion injury in the heart, brain, and kidneys. The aim of this study was to test the hypothesis that carvedilol improves postischaemic reperfusion and tissue survival in skeletal muscle. Sixteen Wistar rats underwent tourniquet ischaemia of the left hindlimb for 3 hours and 15 minutes at 27 degrees C. Single-fiber laser Doppler probes were inserted in the left and right anterior tibial muscles, and microvascular perfusion was measured until 2 hours after removal of the tourniquet. Perfusion indices for each 15-minute interval were calculated for the left hindlimb (tourniquet ischaemia) by dividing the postischaemic by the pre-ischaemic laser Doppler flowmetry values, and the geometrical areas under the curves representing a plot of perfusion index relative to time, measured in arbitrary units, were compared. Laser Doppler flowmetry values for the right anterior tibial muscle were compared. Tissue damage was measured by histomorphometry of necrotic areas and no-reflow zones in cross sections from the anterior tibial muscle 72 hours after ischaemia. Neutrophils were counted in the same sections. The treatment group received 1 mg carvedilol/kg body weight before ischaemia and 1 mg/kg immediately before removal of the tourniquets. The areas under the curves representing the plot of perfusion index relative to time were larger for the rats treated with carvedilol: 9.5 compared with 3.0 arbitrary units (p = 0.0003). Treatment did not change the laser Doppler flowmetry values for the right hindlimbs. The histomorphometric areas of necrosis in cross sections from the muscles were reduced from 88% (38-96%) in the control animals to 41% (7-85%) in those treated with carvedilol (p = 0.01), and the area of no-reflow was reduced from 20% (2-52%) to 0% (0-7%) (p = 0.006). The number of neutrophils did not differ between groups. The study supports the hypothesis that carvedilol improves early reperfusion and protects skeletal muscle subjected to 3 hours and 15 minutes of ischaemia.

Effect of reduced cerebral perfusion pressure on cerebral blood flow following inhibition of nitric oxide synthesis.

OBJECT: The authors tested the hypothesis in a porcine model that inhibition of nitric oxide synthesis during reduced cerebral perfusion pressure (CPP) affected the relative cerebral blood flow (CBF) and the cerebrovascular resistance. METHODS: The CPP was reduced by inducing high cerebrospinal fluid pressure and hemorrhagic hypotension. With continuous blood and intracranial pressure monitoring, relative CPP was estimated using the laser Doppler flowmetry technique in nine pigs that received 40 mg/kg nitro-L-arginine methyl ester (L-NAME) and in nine control animals. The L-NAME caused a decrease in relative CBF (p < 0.01) and increases in cerebrovascular resistance (p < 0.01), blood pressure (p < 0.05), and CPP (p < 0.001). During high intracranial pressure there were no significant differences between the treated animals and the controls. After hemorrhage, there was no significant difference between the groups initially, but 30 minutes later the cerebrovascular resistance was decreased in the control group and increased in the L-NAME group relative to baseline (p < 0.05). Combined hemorrhage and high intracranial pressure increased the difference between the two groups with regard to cerebrovascular resistance (p < 0.05). CONCLUSIONS: These results suggest that nitric oxide synthesis inhibition affects the autoregulatory response of the cerebral circulation after cardiovascular compensation has taken place. Nitric oxide synthesis inhibition enhanced the undesirable effects of high intracranial pressure during hypovolemia.

Effect of alpha-adrenergic blockade on the cerebrovascular response to increased intracranial pressure after hemorrhage.

OBJECT: In this study the authors tested the hypothesis that hemorrhagic hypotension and high intracranial pressure induce an increase in cerebrovascular resistance that is caused by sympathetic compensatory mechanisms and can be modified by alpha-adrenergic blockade. METHODS: Continuous measurements of cerebral blood flow were obtained using laser Doppler microprobes placed in the cerebral cortex in anesthetized pigs during induced hemorrhagic hypotension and high cerebrospinal fluid pressure. Eight pigs received 2 mg/kg phentolamine in 10 ml saline, and 13 pigs served as control animals. During high intracranial pressure occurring after blood loss, cerebral perfusion pressure (CPP) (p < 0.01) and cerebral blood flow (p < 0.01) decreased in both groups. Cerebrovascular resistance increased (p < 0.05) in the control group and decreased (p < 0.005) in the phentolamine-treated group. The cerebrovascular resistance was significantly lower in the phentolamine-treated group (p < 0.05) than in the control group. Cerebrovascular resistance increased at lower CPPs in the control group (linear correlation, r = 0.39, p < 0.01) and decreased with decreasing CPP in the phentolamine-treated group (linear correlation, r = 0.76, p < 0.001). CONCLUSIONS: This study shows that the deleterious effects on cerebral hemodynamics induced by blood loss in combination with high intracranial pressure are inhibited by alpha-adrenergic blockade. This suggests that these responses are caused by alpha-adrenergically mediated cerebral vasoconstriction.

Cardiovascular response to blood loss during high intracranial pressure.

The authors hypothesized that the combination of hemorrhage and increased intracranial pressure (ICP) has deleterious effects on cardiovascular function. The effect of blood loss during normal and increased ICP was studied in eight pigs. The mean arterial pressure (MAP), pulmonary arterial pressure, pulmonary capillary wedge pressure, cardiac output, and cerebrospinal fluid (CSF) pressure were measured. The regional tissue blood flow was determined with radioactive microspheres labeled with four different nuclides. High ICP (80% of MAP) was induced by infusion of artificial CSF into the cisterna magna. The response to rapid arterial bleeding of 25% of blood volume was measured. The decrease in blood flow to the intestine, skeletal muscle, and the kidneys after blood loss was significantly greater during high ICP. The decrease in blood flow to the spleen and pancreas tended to be greater during high ICP, whereas the changes in blood flow to the liver, adrenal glands, and heart muscle showed no such tendency. The fall in cardiac output and heart stroke volume after blood loss were more pronounced when the ICP was high, and the increase in systemic vascular resistance was considerably greater. These observations suggest that during high ICP the physiological protective mechanisms against blood loss are impaired in the systemic circulation, and a loss of 25% of the blood volume, normally well compensated for, may induce a state of shock.

Effect of hemorrhage on cerebral microcirculation during normal and high cerebrospinal fluid pressure in pigs.

Studies on cerebral blood flow during hypotension and high intracranial pressure are scarce. Accordingly, this study examines the effects of increased cerebrospinal fluid (CSF) pressure on the cerebral circulatory response to hemorrhage. Measurements of cerebral microcirculation with laser Doppler flowmetry was performed in 12 pentobarbital-anesthetized pigs during hemorrhage, with and without high CSF pressure. Arterial and CSF pressures were monitored. Laser Doppler microprobes were positioned on the brain surface and in the gray and white matter. High CSF pressure (80% of mean arterial pressure) was induced by infusion of artificial CSF into the cisterna magna in eight pigs, whereas four animals served as controls. The response to rapid arterial bleeding at normal and high CSF pressure was recorded. When CSF pressure was normal, bleeding of 15% and 25% of the total blood volume caused a drop of cerebral perfusion pressure to 73 and 71 mmHg, respectively, causing a decrease in the laser Doppler signal to 90+/-8% of the baseline value. During high CSF pressure, the cerebral perfusion pressure was 23 mmHg and the laser Doppler signal was 52+/-29% of baseline. Bleeding of 15% of blood volume reduced the laser Doppler signal to 0 (equal to postmortem values) in three pigs, and bleeding of 25% of the blood volume reduced the laser Doppler signal to 0 in seven of eight pigs. Consequently, a blood loss that is of minor importance for the cerebral microcirculation in the normal state may be deleterious to the circulation when combined with high CSF pressure.

Cerebrovascular effects of high intracranial pressure after moderate hemorrhage.

Patients with head injuries often develop increased intracranial pressure after hemorrhage. The authors studied the effect of moderate hemorrhage followed by elevated intracranial pressure on cerebrovascular variables. Cerebral blood flow in 13 pigs was measured with laser Doppler flowmetry, and cerebral venous blood gases were taken from the sagittal sinus. High intracranial pressure (80% of mean arterial pressure) was induced by infusion of artificial cerebrospinal fluid into the cisterna magna, and blood pressure was reduced by bleeding to a mean of 78% of the prebleeding values in eight pigs. Five pigs served as secondary controls. High intracranial pressure before hemorrhage caused a decrease in cerebral blood flow to 34% of the baseline values, a decrease in sagittal sinus oxygen saturation to 46%, and a decrease in cerebral perfusion pressure to 36%, but did not change cerebrovascular resistance. High intracranial pressure after hemorrhage decreased cerebral blood flow to 14% of baseline values. Sagittal sinus oxygen saturation decreased to 22%, cerebral perfusion pressure decreased to 30%, and the cerebrovascular resistance increased by 355%. The moderate hypotension after hemorrhage caused a considerable enhancement of the effects of high intracranial pressure on cerebral hemodynamics.

Revascularisation of bone grafts in rats.

Revascularisation of syngeneic and allogeneic intramuscular bone grafts have been studied using radioactive microspheres to measure the ingrowth of blood vessels. New bone formation and resorption were measured by 85strontium uptake and by graft weight reduction. Revascularisation, and mineralisation rate were significantly higher in syngeneic grafts than in allogeneic grafts at two, three and six weeks after implantation. The syngeneic grafts lost weight faster indicating that the allogeneic grafts resorbed more slowly. The ingrowth of new vessels is impaired in allogeneic bone, and this probably inhibits the rate of bone formation and resorption of the grafts.

Fracture weakens ipsilateral long bones: mechanical and metabolic changes after femoral or tibial injury in rats.

We have studied the effect of tibial osteotomy on mechanical and metabolic properties of the femur, and the effects of femoral osteotomy or fracture on mechanical properties of the tibia in rats. In the bone ipsilateral to the trauma, there was a significant reduction of mechanical strength and stiffness, both in bending and torsion, compared with the contralateral side. The ipsilateral bone lost weight and the blood flow was increased. The mineral incorporation rate was not affected. This may be due in part to disuse of the traumatized limb, but the fracture itself may affect the other bones in the extremity.

Cerebral nitric oxide concentration and microcirculation during hypercapnia, hypoxia, and high intracranial pressure in pigs.

Intracerebral nitric oxide (NO) concentration was measured to establish the technique and to investigate the response of the NO concentration to CO(2)variations, hypoxia, and reduced cerebral perfusion pressure. An intracerebral nitric oxide sensor was used in 10 pigs. Cerebral microcirculation was measured by laser Doppler flowmetry. Five pigs received 40 mg/kg nitro-1-arginine methyl ester (L-NAME). Baseline NO concentration was 246 +/- 42 nM. Hypercapnia increased cerebral microcirculation (P< 0.05) and NO concentration (P< 0.05). Hypoxia decreased NO concentration (P< 0.05). During high intracranial pressure, cerebral microcirculation decreased (P< 0.05) before the NO concentration decreased (P< 0.05), and after normalisation of the intracranial pressure the NO concentration increased, but more slowly than the cerebral microcirculation. L-NAME caused a decrease in cerebral microcirculation (P< 0.05) and NO concentration (P< 0.05) to a new steady state, and L-NAME attenuated the changes in NO concentration after hypoxia (P< 0.05) and high intracranial pressure (P< 0.05). In conclusion, the electrochemical sensor appears to reliably detect changes in localised intracerebral NO concentration and seems to be a promising tool for direct measurement of this chemically unstable substance.

Fresh, frozen, or decalcified bone grafts: a study of early vascularisation and mineralisation of allogeneic and syngeneic bone grafts in rats.

The incorporation of syngeneic and allogeneic bone grafts pretreated by freezing or demineralisation was studied in 10 rats. Fresh, decalcified, or frozen cancellous bone of syngeneic or allogeneic origin was transplanted to intramuscular pouches. Revascularisation was evaluated with radioactive microspheres; formation of new bone was assessed by incorporation of strontium, and resorption was assessed by measuring the reduction of graft weight. Three weeks after grafting, fresh syngeneic and allogeneic bone differed significantly in all three variables. Frozen syngeneic bone was revascularised significantly better than frozen allogeneic bone, but there was no difference in formation of new bone or resorption. There were no significant differences between syngeneic and allogeneic decalcified bone in any of the variables studied. We conclude that differences in incorporation between syngeneic and allogeneic bone grafts are reduced by pretreatment with deep-freezing or demineralisation. Both forms of pretreatment affect the incorporation of the grafts.

Circulation in corticocancellous bone grafts measured with laser Doppler flowmetry. An experimental study in rats.

Laser Doppler flowmetry has been evaluated for measurement of the microcirculation (flux) in corticocancellous bone grafts. Corticocancellous tibial grafts were transplanted between four donor and eight recipients rats of two histocompatibility-mismatched strains. The microcirculations in the grafted and the intact tibias were measured after 12 weeks. Variation of the method in a single animal was 0.3-0.4 in both normal and grafted bone. The flux variation between the animals was of similar magnitude. The variation did not depend upon the magnitude of the flux values. Grafts had between 26% and 53% lower circulation than normal bone, but the graft bone interface, which contained callus, had a 56% higher flux than normal bone. We conclude that laser Doppler flowmetry might be useful in research into bone grafts.

Revascularisation of fresh compared with demineralised bone grafts in rats.

Revascularisation of bone grafts is influenced by both the anatomical origin and the pre-implantation processing of the graft. We investigated the revascularisation by entrapment of 141Ce (cerium)-labelled microspheres in large, fresh and demineralised syngeneic grafts of predominantly cancellous (iliac bone) or cortical (tibial diaphysis) bone three weeks after heterotopic implantation in rats. The mean (SD) 141Ce deposition index (counts per minute (cpm) of mg recovered implant/cpm of mg host iliac bone) was higher in fresh iliac bone grafts, 0.98 (0.46) compared to that of demineralised iliac bone, 0.32 (0.20), p < 0.001, and fresh tibial bone grafts, 0.51 (0.27), p = 0.007. We found no significant difference in the mean 141Ce deposition index between fresh tibial bone grafts and demineralised tibial bone grafts, 0.35 (0.42), p = 0.4, or between demineralised tibial grafts and demineralised iliac bone grafts, p = 0.8. The results suggest that whereas fresh cancellous grafts are revascularised more completely than fresh cortical grafts, there is no difference in the revascularisation of demineralised cancellous and cortical grafts. In addition, fresh cancellous bone is revascularised more completely than demineralised cancellous bone, whereas there is no difference between fresh and demineralised cortical bone.

[Biological background of clinical bone transplantation]. / Biologisk bakgrunn for klinisk beintransplantasjon.

The biologic incorporation of bone grafts into host bone is dependent upon the type of graft, but the aim in all cases is to replace the graft with host bone by bone resorption and new bone formation. This is best achieved by transplanting fresh autogeneic bone. Allogeneic bone grafts are less efficient because of immunological reactions to the grafts, but they are the only alternative in clinical practice. There are several methods of preparing the allogeneic grafts to make them more suitable for clinical use, e.g. deep-freezing, freeze-drying, or demineralization. Experimentally attempts have been made to reduce the immunological reactions to allogeneic bone, or to combine the graft with bone-inducing substances. The basic knowledge of bone transplant biology has improved greatly in recent years, but is still inadequate to achieve an improvement in the established clinical practice.

Bone metabolism and repair are normal in athymic rats.

Several reports indicate that the thymus gland is important in the regulation of bone metabolism. Anatomic or physiologic abnormalities in the bones of athymic animals could therefore be expected. The mechanical properties, circulation, and mineralization rate of intact femora, tibiae, ossa ilia, and of an osteotomized tibia of athymic Lewis rats were compared with those of normal Lewis rats. The results were not significantly different in the two groups. The absence of the thymus thus does not seem to have any major influence on bone structure, function, or regenerative properties.

Intestinal ischemia after a single intravenous injection of deslanoside. A case report.

Nonocclusive intestinal ischemia is closely associated with heart disease and digitalization. Animal experiments and indirect evidence in man suggest that digitalis significantly decrease splanchnic blood flow. A case is described where peroperative intravenous digitalis caused profound intestinal ischemia. The report constitutes the first direct observation relating heart glycosides with intestinal ischemia in man.