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M L Smith

Publications and source records attributed to M L Smith.

At least 397 records · Page 22Linked to original sources
PubMed1984

Models for studying long-term recovery following forebrain ischemia in the rat. 2. A 2-vessel occlusion model.

A model is described in which transient ischemia is induced in rats anaesthetized with N2O:O2 (70:30) by bilateral carotid artery clamping combined with a lowering of mean arterial blood pressure to 50 mm Hg, the latter being achieved by bleeding, or by bleeding supplemented with administration of trimetaphan or phentolamine. By the use of intubation, muscle paralysis with suxamethonium chloride, and insertion of tail arterial and venous catheters, it was possible to induce reversible ischemia for long-term recovery studies. Autoradiographic measurements of local CBF showed that the procedure reduced CBF in neocortical areas, hippocampus, and caudoputamen to near-zero values, flow rates in a number of subcortical areas being variable. Administration of trimethaphane or phentolamine did not affect ischemic and postischemic flow rates, nor did they alter recovery of EEG and sensory-evoked responses, but trimetaphan blunted the changes in plasma concentrations of adrenaline and noradrenaline. Recovery experiments showed that 10 min of ischemia gave rise to clear signs of permanent brain damage, with a small number of animals developing postischemic seizures that led to the death of the animals in status epilepticus. After 15 min of ischemia, such alterations were more pronounced, and the majority of animals died. It is concluded that the short revival times noted are explained by the fact that the model induces near-complete ischemia, and that recovery following forebrain ischemia is critically dependent on residual flow rates during the period of ischemia.

Animals↗
PubMed1983

Proton-translocating ATPase and lysosomal cystine transport.

A proton-translocating ATPase was identified in highly purified lysosomes from Epstein-Barr virus-transformed human lymphoblasts. Activity of this ATPase caused acidification of highly purified, fluorescein isothiocyanate dextran-loaded lysosomes and correlated with the ATP-dependent efflux of lysosomal cystine. The lysosomal ATPase was distinct from mitochondrial F1-ATPase in its responses to a variety of inhibitors. Although ATP-dependent lysosomal cystine efflux is not demonstrable in cultured lymphoblasts from individuals with nephropathic cystinosis, ATPase activity and acidification in lysosomes from these cells is comparable to that in noncystinotic lysosomes. ATPase activity in lymphoblasts from normal individuals was 543 +/- 79 nmol/mg/min while in lymphoblasts from cystinotic individuals this activity was 541 +/- 25 nmol/mg/min. ATP-dependent acidification of lysosomes from normals was -0.5 +/- 0.1 pH units compared to -0.5 +/- 0.1 pH units in cystinotic lysosomes. Activity of the lysosomal proton-translocating ATPase is a necessary, but not sufficient, condition for lysosomal cystine efflux.

Animals↗
PubMed1983

Ab initio calculations of electron distributions in heme-CO models.

We have, by the use of ab initio calculations, found a back-bonding state of pi symmetry close to the Fermi level for CO bound to FeN5C14. We thus find it likely that small shifts of the redox potential magnitude of EF - EV magnitude of will cause relatively large changes of the CO vibrational frequency. The separation of Fe 3d orbitals in our heme model is found to agree with what is predicted by ligand field theory for Oh symmetry. This paper presents nonrelativistic Hartree-Fock-Slater calculations of the 5 sigma bonding and 2 pi back-bonding between CO and Fe. The effects of up to 19 additional atoms are discussed for models of heme (COFe to COFeN5C14). The filled back-bonding state is found to be strongly influenced by second nearest neighbor atoms. By use of symmetry orbitals we have resolved the Fe 3d orbitals into the T2g and Eg representations of the Oh point group and find the former states to be occupied whereas the latter are unoccupied. The difference in occupancy is reduced when the CO ligand is removed which also causes an increased density of states at the Fermi level, i.e., the highest occupied and lowest unoccupied orbitals. Possible correlations between our data and experimental results are discussed for heme proteins as well as for metal surfaces.

Carbon Monoxide↗
PubMed1983

Local cerebral blood flow in the recovery period following complete cerebral ischemia in the rat.

This study examines reflow patterns in the recirculation period following complete, global ischemia. Cerebrospinal fluid (CSF) compression ischemia was induced in ventilated rats for 5-30 min, and local cerebral blood flow (CBF) was measured autoradiographically after 5, 60, and 90 min of recirculation. Ischemia of 15 min duration was induced by four-vessel occlusion combined with arterial hypotension in two additional groups, with recovery periods of 5 or 60 min. In the immediate recirculation period (5 min), following 15 min of ischemia, local CBF was markedly heterogeneous. Thus, whereas most structures gave clear evidence of "reactive hyperemia," others showed perfusion defects of the "no-reflow" type. Typically these defects affected the striatum, thalamus, and hippocampus, as well as the frontal, sensorimotor, and parietal cortices. Areas of no-reflow appeared after 10 min, were more extensive after 15 min, and occupied a major part of the brain after 30 min of ischemia. When recirculation was instituted for 60 or 90 min, following 15 min of ischemia, flow returned in previously unperfused areas. However, a delayed hypoperfusion developed, which differed widely between structures (range of CBF values, 20-80% of control). When the ischemic period was prolonged to 30 min, some perfusion defects remained, even after 90 min of recirculation.

Animals↗
PubMed1983

Recirculation in the rat brain following incomplete ischemia.

The objective of this study was to characterize local cerebral blood flow (CBF) in the recirculation period following incomplete forebrain ischemia. Specifically, we wished to determine whether perfusion defects developed in the immediate recirculation period, to study how initial hyperemia and delayed hypoperfusion at the local level were related to the severity of the preceding ischemia, and to find out whether reflow was influenced by the nutritional state of the animals. To that end, forebrain ischemia of 15 min duration was induced in fed and fasted ventilated rats under 70% N2O. Local CBF was measured with an autoradiographic technique at the end of ischemia, as well as at 5 and 60 min following the start of recirculation. Control experiments were performed to examine the influence of ischemia on cerebral metabolic state in fed and fasted animals. The ischemia reduced CBF to excessively low values (less than 5% of control) in many forebrain structures, including the cerebral cortices, caudoputamen, and hippocampus. In spite of this, perfusion defects failed to appear after 5 min of recirculation. Instead, moderate to marked hyperemia was present in all previously ischemic structures. After 60 min of recirculation, pronounced hypoperfusion developed. The magnitude of the initial hyperemia was poorly related to the severity of the preceding ischemia, but the latter partly determined the degree of delayed hypoperfusion. Thus, little or no hypoperfusion developed in structures whose flow rates exceeded 30-40% of control during ischemia. Fasted animals had a better preserved flow to many structures than did fed animals, indicating that the detrimental effect of feeding (or glucose infusion) is also reflected in lower perfusion rates.

Animals↗
PubMed1983

Effect of the calcium antagonist nimodipine on the delayed hypoperfusion following incomplete ischemia in the rat.

Regional cerebral blood flow (CBF) was measured autoradiographically in the recovery period following 15 min of forebrain ischemia in rats pretreated with either nimodipine (0.1 mg kg-1) or vehicle. The results showed that although nimodipine increased postischemic CBF, the flow enhancement was regionally heterogeneous, sometimes resulting in zones of gross hypoperfusion and overt hyperemia within the same structures. This patchy improvement of delayed postischemic hypoperfusion was not accompanied by recovery of sensory evoked responses, and return of EEG activity was not enhanced.

Animals↗
PubMed1983

Cyclo-oxygenase inhibition by indomethacin and recirculation following cerebral ischemia.

In this study we examined the effect of pretreatment with the cyclo-oxygenase inhibitor indomethacin (10 mg . kg-1) on local cerebral blood flow (DBF) in the immediate recirculation period following complete and incomplete ischemia. Ischemia of 15 min duration was induced in lightly anaesthetized and artificially ventilated rats, and local CBF was measured with a 14C-iodoantipyrine autoradiographic technique after recirculation periods of 5 min. Following complete ischemia indomethacin-treated animals showed a reduced incidence of perfusion defects of the "no-reflow" type. Perfused structures had somewhat higher flow rates than in untreated rats. A similar enhancement of immediate reflow was observed following incomplete ischemia provided that the structures in question had been severely ischemic. In structures that suffered only mild ischemia, the drug reduced postischemic CBF. It is concluded that, in the rat brain, cyclo-oxygenase inhibition does not curtail postischemic reactive hyperemia. Furthermore, the previously reported beneficial effect of indomethacin on brain circulation following complete ischemia seems to be due to an enhancement of immediate reflow, and to amelioration of an initial hindrance to reflow.

Animals↗
PubMed1983

Cerebral circulatory responses to hypercapnia and hypoxia in the recovery period following complete and incomplete cerebral ischemia in the rat.

In this study we examined the reactions of cerebral vessels to hypercapnia and hypoxia during the recovery period following cerebral ischemia. We used ventilated, lightly anesthetized rats and induced complete ischemia by CSF compression, incomplete ischemia by bilateral carotid occlusion combined with hypotension. After 15 min of ischemia and 60 min of recirculation the animals were rendered hypercapnic or hypoxic for 2-3 min and local CBF was then measured autoradiographically with 14C-iodoantipyrine. Following complete ischemia vascular CO2 responsiveness was abolished or attenuated in most structures analysed. However, there was a considerable interstructural heterogeneity. For example, in the cerebellum and the red nucleus flow rates were observed which approached values obtained in hypercapnic control animals, whereas CO2 responsiveness was abolished in several cortical areas and hippocampus. The response to CO2 following incomplete ("forebrain") ischemia varied considerably. In the cerebral cortices areas with low flow rates were often mixed with hyperemic zones, and in most structures that had very low flow rates during ischemia, CO2 responsiveness was lost or grossly attenuated. Structures that had suffered moderate or only mild ischemia had better retained or completely preserved CO2 response. The cerebrovascular reaction to hypoxia was found to be attenuated in most, but not abolished in any of the structures examined. In general, the vascular response to hypoxia was better preserved than that to hypercapnia. Reactivity was similar following complete and incomplete ischemia. As observed during hypercapnia, there were pronounced interstructural variations with considerable increases in flow rates e.g. in the substantia nigra and the cerebellum.

Animals↗
PubMed1983

Relative distribution of diphosphonate between bone and soft tissue at 4 and 24 hours: concise communication.

Digital bone scintigrams were obtained in 19 patients using Tc-99m hydroxyethylidene diphosphonate (HEDP). These were quantitated for skeletal, soft-tissue and renal uptake of tracer using a contrast-enhancement technique to define the regions of interest. Twenty-four hr whole-body retention (WBR) of HEDP was also measured. It was found that approximately 70% of retained diphosphonate was localized in the skeleton at 24 hr, with 26% in soft tissue and 4% in kidneys. However, we have shown that over a wide spectrum of whole-body retention measurements (18 to 70%) the 24-hr soft-tissue component, as a percentage of administered dose, remained relatively constant whereas skeletal tracer accumulation mirrored WBR (r = 0.98, p less than 0.001). The present study indicates that, despite a significant but essentially stable soft-tissue component, measurement of 24-hr WBR of HEDP accurately reflects skeletal metabolism.

Bone and Bones↗
PubMed1983

The mechanism of spontaneous heme release from horseradish peroxidase isoenzyme A2.

We have investigated the spontaneous release of heme from chromatographically homogeneous horseradish peroxidase A2 at varying temperature, pH and iron ligands. A "biphasic" rate of heme release was observed under all conditions. Upon further purification of HRP A2, a component was isolated that was homogeneous by polyacrylamide gel electrophoresis and exhibited a single first order rate of heme release. The rate of the release increased with pH and temperature, decreased in the presence of cyanide and increased slightly in the presence of fluoride. These results are consistent with the idea that the rate of heme release is a measure of the flexibility of the protein lining the heme "pocket" with iron bonding playing a secondary, though important role in heme-protein interactions.

Animals↗
PubMed1983

Delayed vaginal reconstruction in the fibrotic pelvis following radiation or previous reconstruction.

Vaginal reconstruction was performed in 14 patients who had developed vaginal stenosis secondary to extensive pelvic fibrosis after pelvic radiation therapy (12 patients) or prior vaginal reconstruction (2 patients). Sixteen procedures were performed using a split-thickness skin graft. All patients had satisfactory vaginal restoration, and 12 patients reported good vaginal function. No fistula developed as a result of the operative procedure, but one patient later developed a rectovaginal fistula resulting from tumor recurrence. Successful vaginal reconstruction can be achieved even years after initial therapy in patients who develop an obliterated vagina from previous radiation or surgery.

Adult↗
PubMed1982

ATP-dependent lysosomal cystine efflux is defective in cystinosis.

Lysosomes containing large amounts of the amino acid, cystine, were obtained from transformed, cultured, human lymphoblasts which had been exposed to cystine dimethyl ester. Lysosomal cystine efflux was greatly enhanced by exogenous ATP in cell lines from normal individuals. Cystine efflux was unresponsive to ATP in lysosomes from individuals with the disorder, cystinosis. Efflux of cystine from normal cell lysosomes was inhibited by both the ATP analog, 5-adenylylimidodiphosphate, and the proton translocator, carbonyl cyanide m-chlorophenylhydrazone. Efflux was not affected by ouabain or oligomycin. Thus, lysosomal cystine efflux is dependent upon the functioning of a proton-pump ATPase. ATPase-dependent cystine efflux appears to be aberrant in cystinotic cell lysosomes.

Adenosine Triphosphate↗