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PubMed1988

Treatment of steatorrhoea in cystic fibrosis: a comparison of enteric-coated microspheres of pancreatin versus non-enteric-coated pancreatin and adjuvant cimetidine.

Enteric-coated microspheres of pancreatin were compared with non-enteric-coated pancreatin combined with cimetidine taken 40 min before meals in the treatment of patients with cystic fibrosis. Fourteen adults with steatorrhoea due to cystic fibrosis were investigated in an open, randomized crossover study, over two consecutive 28-day treatment periods. Lipase intake was adjusted to each patient's previous requirements and was the same during both months; they were instructed to continue with their normal diet. Patients collected faeces for 72 h at the end of each month and completed diary cards daily throughout. Bowel actions were less frequent on enteric-coated microspheres of pancreatin than on non-enteric-coated pancreatin/cimetidine (1.7 vs. 2.4/day; P less than 0.001) and stool character was improved (P less than 0.001). Mean daily faecal weight was similar on enteric-coated microspheres of pancreatin to that on the combination (254 g vs. 291 g; N.S.), whereas daily faecal fat excretion tended to be less on enteric-coated microspheres of pancreatin (21 g vs. 27 g; N.S.), and percentage fat absorption tended to be greater (81% vs. 73%; N.S.). Mean body weight increased by 0.3 kg on enteric-coated microspheres of pancreatin and fell by 0.1 kg on the combination (N.S.). These data indicate that enteric-coated microspheres of pancreatin are at least as effective as non-enteric-coated pancreatin with cimetidine in the treatment of steatorrhoea in cystic fibrosis.

Adult↗
PubMed1985

Relative contribution of different vascular beds to the pressor effects of alpha-adrenoreceptor agonists and vasopressin in pithed rats: radioactive microsphere determination.

The relative fractional distribution of 51Cr-labelled microspheres was evaluated in pithed rats during equieffective vascoconstrictor responses evoked by infusions of the alpha-adrenoreceptor agonists methoxamine (alpha 1-selective), UK-14,304 (alpha 2-selective) or vasopressin. The proportion of injected radioactive microspheres trapped in each tissue during a sustained pressor response relative to saline treated controls is considered a reflection of the degree of local vascoconstriction in the tissue analysed. All three agonists (methoxamine, UK-14,304 and vasopressin) decreased the number of microspheres trapped in the mesentery and tail. Only methoxamine reduced the blood flow to the kidney and spleen. UK-14,304 did not modify the number of microspheres in the sample of skeletal muscle, however, both vasopressin and methoxamine reduced the blood flow to this tissue. Vasopressin increased the counts in the lungs and particularly in the liver but decreased the number of spheres trapped in the stomach and skin. In contrast to the alpha-adrenoreceptor agonists, vasopressin did not increase the number of microspheres trapped in the heart. Since a reduction in the number of microspheres trapped in the tissue reflects a decrease in blood flow, to that organ it is reasonable to conclude that alpha 1-adrenoreceptor stimulation increases kidney, spleen, mesentery, caudal and skeletal muscle vascular resistance, whereas alpha 2-adrenoreceptors appear to preferentially vasoconstrict the mesenteric and the caudal vascular beds.

Adrenergic alpha-Agonists↗
PubMed1994

Effects of naftidrofuryl oxalate on microsphere embolism-induced decrease in regional blood flow of rat brain.

1. The purpose of the present study was to determine whether naftidrofuryl oxalate (naftidrofuryl), a vasodilator, is capable of improving brain regional blood flow of animals in sustained ischaemia. 2. Cerebral ischaemia was induced by injecting 900 microspheres (48 microns in diameter) into the right internal carotid artery of rats. Cerebral blood flow of brain regions was measured by a hydrogen clearance method on the 3rd, 7th and 28th days after the onset of ischaemia. Ischaemic animals were treated with naftidrofuryl, 15 mg kg-1 day-1 i.p., from the first to 28th day. 3. Microsphere-embolism caused a sustained decrease in cortical and striatal blood flow over a period of 28 days, whereas hippocampal blood flow was decreased on the 3rd day but not on the 7th or 28th day. On the 3rd day, the striatal and hippocampal but not cortical blood flow of naftidrofuryl-treated, microsphere-embolized rats was higher than untreated rats. On the 7th and 28th days, the cortical and striatal blood flow of the treated and untreated animals did not differ. 4. Brain slices from microsphere-embolized rats contained areas, which were not stained with triphenyltetrazolium chloride (TTC), to a similar degree on the 3rd, 7th and 28th days, indicating the genesis of cerebral infarction. TTC-unstained areas of microsphere-embolized rats that had received naftidrofuryl treatment were smaller than those of untreated rats on the 3rd and 7th days, but not on the 28th day. 5. The results suggest that naftidrofuryl improves cerebral circulation impaired by microsphere-induced ischaemia and this higher level of cerebral blood flow of the treated animal may account for the delayed development of cerebral infarction.

Animals↗
PubMed1996

Human epidermal melanocyte and keratinocyte melanocortin receptors: visualization by melanotropic peptide conjugated microspheres (latex beads).

The objectives of this research were to determine whether melanocortin receptors are characteristic (constant) membrane markers of human epidermal melanocytes. Methodologies were developed to visualize melanotropin receptors by scanning electron microscopy (SEM). Multiple copies (up to a hundred) of [Nle4,D-Phe7]alpha-MSH, a superpotent analog of alpha-melanocyte stimulating hormone (alpha-MSH), were conjugated to a macromolecular carrier (latex beads: microspheres). Incubation in the presence of the melanotropin-conjugated microspheres resulted in binding of human normal epidermal melanocytes to the beads. Almost every (possibly all) melanocyte possesses melanocortin receptors as visualized by SEM. Specificity of binding of the macromolecular conjugate was demonstrated by several studies: 1) Binding of melanocytes to the microspheres was specific since it could be blocked by prior incubation of the cells in the presence of the unconjugated hormone analog; 2) microspheres lacking bound ligand did not bind to the melanocytes; 3) microspheres that were first treated with reducing agents (e.g., dithiothreitol) did not subsequently bind to melanocytes; 4) another peptide hormone ligand (e.g., a substance-P analog) attached to the latex beads failed to bind to the cells; 5) B16/F10 mouse melanoma cells known to express melanocortin receptors bound to the microspheres; and 6) cells of nonmelanocyte origin (e.g., mammary cancer cells, small-cell lung cancer cells, fibroblasts) did not bind to the macromolecular conjugate. One exception was that human epidermal keratinocytes also expressed melanocortin receptors as determined by all the criteria established above for epidermal melanocytes. Thus, cell specific melanocortin receptors appear to be characteristic cell surface markers of epidermal melanocytes and keratinocytes.

Cells, Cultured↗
PubMed1993

Synthesis, properties, and intratumoral evaluation of mitoxantrone-loaded casein microspheres in Lewis lung carcinoma.

Smooth, round, uniform bovine casein microspheres of 1-5 and 10-20 microns size were readily prepared by a steric stabilization technique previously developed in this laboratory for synthesis of albumin microspheres. The avid phagocytic uptake of casein and albumin microspheres was demonstrated with fluorescein-labelled microspheres using a macrophage-like mouse myelomonocytic leukaemia cell line. Post-synthesis loading of 25% mitoxantrone was achieved for casein microspheres containing 20% polyglutamic acid. Preliminary intratumoural chemotherapy experiments with a mouse Lewis lung carcinoma indicated that mitoxantrone and mitoxantrone-loaded casein-polyglutamic acid microspheres exhibited lower toxicity when administered intratumorally.

Animals↗
PubMed2003

In vivo US monitoring of catheter-based vascular delivery of gene microspheres in pigs: feasibility.

In this study, the authors tested the feasibility of using ultrasonography (US) to monitor catheter-based vascular gene microsphere delivery. Polymeric biodegradable microspheres (mean diameter, 5 microm) were prepared by using a double-emulsion technique to encapsulate DNA-plasmid-encoding green fluorescent protein (GFP) genes. With use of gene-delivery catheters, GFP microspheres were locally delivered into the left femoral arterial walls of six pigs; the contralateral arteries were not infused with microspheres and thus served as negative control vessels. The delivery procedures were monitored with high-frequency (8-15-MHz) transducer US. The effectiveness of monitoring with US was compared with the effectiveness of monitoring with immunohistochemical anti-GFP staining. A highly echogenic "star burst" sign around the entire vessel wall was seen at US and correlated with immunohistochemical findings that showed the destination of the gene microspheres. Study results demonstrate the potential of US for monitoring catheter-based vascular gene microsphere delivery in vivo.

Animals↗
PubMed1997

Increased sciatic nerve blood flow in diabetic rats: assessment by "molecular" vs. particulate microspheres.

Sciatic nerve blood flow in diabetic rats in typically increased or unchanged when assessed by the reference sample microsphere method in our laboratory. In contrast, blood flow is generally reported to be decreased approximately 50% when assessed with laser Doppler flowmetry or hydrogen clearance polarography. To address concerns that increased blood flow observed with microspheres might be anomalous because of their particulate nature and/or because insufficient numbers of microspheres are captured in the nerve, a plasma-soluble "molecular microsphere" ([3H]desmethylimipramine, mol wt = 266) and 11.3-micron 153Gd-labeled microspheres were injected sequentially to assess blood flow in rats with streptozotocin diabetes of 2-4 wk duration. Nerve blood flows in diabetic rats were increased 1.5- to 2-fold (vs. control rats) with both tracers; these increases were prevented by tolrestat, an inhibitor of aldose reductase. These observations indicate that blood flow in sciatic nerve (like that in retina and kidney) is increased early after the onset of diabetes and is 1) demonstrable with a plasma-soluble tracer as well as with particulate microspheres and 2) linked to increased metabolism of glucose via the sorbitol pathway.

Aldehyde Reductase↗
PubMed1978

Regional blood flows measured in conscious rats by combined Fick and microsphere methods.

Regional blood flow measurements made by the radioactive microsphere technique were studied in conscious rats. A femoral arterial reference sample blood flow was measured directly, and at the same time indirectly by the combined use of direct Fick cardiac output and microsphere techniques. A significant correlation (r = .81, P less than .01) was obtained between direct and indirect blood flow values when 200--400 microspheres were trapped in the reference sample. When 100--200 microspheres were trapped, regional blood flow was 32% below true flow (P less than .01); and cardiac output, calculated by the reference sample method, was 57% greater than Fick cardiac output (P less than .01). When three consecutive Fick determinations and microsphere injections (20,000 per injection, 15 micrometer diam) were made in conscious rats, significant correlations were obtained among the first, second, and third regional blood flow measurements (r = .95, P less than .01). The results have demonstrated that cardiac output and reference blood flow can be measured with accuracy and precision in the conscious rat by the radioactive microsphere procedure.

Animals↗
PubMed1982

Acute and chronic microsphere loss from canine left ventricular myocardium.

We determined the effects of time, type of anesthesia, and myocardial infarction on loss of radioactive microspheres averaging 9 or 15 micrometers diameter from left ventricular myocardium. The principle used to compute losses was comparison of the number of microspheres injected directly into coronary arteries to the numbers remaining in myocardium, appearing within 2-4 min in the coronary sinus, or trapped in the lungs. Losses of 9-micrometers microspheres within 2 min of injection were significantly greater for halothane (mean 6.3%) than nitrous oxide anesthesia (mean 3.3%), and in the next 2 h increased to 11.7 and 7.9%, respectively. Over 5 wk in conscious dogs losses were as high as 40 and 11% for 9 and 15 micrometers microspheres, respectively. Losses were not greater for infarcted than normal muscle, and negligible radioactivity appeared in paracardiac lymph nodes. Microspheres leaving the heart were almost all below 10.3 micrometers diameter, so that microspheres with diameters 10-14 (mean 12) micrometers might be the best size to use for myocardial studies.

Anesthesia↗
PubMed1983

Precautions for measuring blood flow during anemia with the microsphere technique.

Preliminary data from a study of the effects of anemia on organ blood flow showed large discrepancies between cardiac output measured with the microsphere technique and simultaneous values calculated by the Fick principle. The most likely explanation was that the reference sample drawn according to our standard procedure underestimated the microsphere concentration in arterial blood, resulting in erroneously high blood flow values. In the present experiments we compared our usual reference sample, from a small catheter advanced from a peripheral artery into the brachiocephalic artery (withdrawal rate 1.3 ml/min), with a simultaneous sample from a larger catheter withdrawn at the much higher rate (7.89 ml/min). At hematocrits above 32%, microsphere concentrations from the two catheters were similar, but below 32% the concentration of microspheres in blood from the larger catheter was 30-50% more than from the smaller. The discrepancy was not altered by changing the injection site from left ventricle to left atrium and thus was probably not the result of poor mixing within the heart. It may have been the result of nonhomogeneous distribution of microspheres within larger vessels, perhaps as a consequence of laminar flow and axial streaming of both red blood cells and microspheres during anemia. Whatever the cause, it was possible to eliminate the difference by withdrawing from the smaller catheter at a more rapid rate (2.46 ml/min).

Anemia↗
PubMed1992

New nonradioactive microspheres and more sensitive X-ray fluorescence to measure regional blood flow.

We developed new nonradioactive microspheres and used more sensitive X-ray fluorescence spectrometers than used previously to measure regional blood flow in the heart and other organs. We demonstrated the chemical stability of eight kinds of heavy element-loaded microspheres and validated their use for regional blood flow measurement by comparing duplicate flows measured with radioactive and/or nonradioactive microspheres in both acute and chronic dog experiments. The wavelength-dispersive spectrometer (Philips PW 1480) has a higher sensitivity than the previously described X-ray fluorescent system and reduced the number of microspheres required for accurate measurement. The fine energy resolution of this system makes it possible to increase the numbers of different kinds of microspheres to be quantitated, but at present only eight kinds are available. We also used a synchrotron radiation-excited energy dispersive spectrometer. The monochromatic synchrotron radiation allowed us to obtain much higher signal-to-background ratios of X-ray fluorescence spectra than with the wavelength-dispersive system (50 dB more for Zr-loaded microspheres) and will enable analysis of fluorescent activity in smaller regions (< 20 mg) than the radioactive method does.

Animals↗
PubMed1995

Fluorescent microspheres to measure organ perfusion: validation of a simplified sample processing technique.

A disadvantage of nonradioactive microsphere techniques is that the processing of samples is time-consuming and complex. We developed and validated a simplified processing method for the fluorescent microsphere (FM) technique. In seven anesthetized dogs with coronary artery stenosis up to six different FM and five different radioactivity labeled microspheres (RM) were injected. Two FM and two RM labels were injected simultaneously to enable inter- and intramethod comparison. After gamma-counting samples of blood, myocardium (n = 168), and other organs (n = 59) were digested in test tubes with 2 N ethanolic KOH (60 degrees C, 48 h), microspheres were sedimented by centrifugation, dye was extracted in the same tube, and fluorescence was measured. With this processing method, recovery of FM was approximately 100%. Good correlations for inter- and intramethod comparisons were found [r = 0.985 +/- 0.01 (mean +/- SD)]. The lower intermethod correlation for blue microspheres (r = 0.958) indicates that the use of this label is less desirable. RM and FM endocardial-to-epicardial blood flow ratios correlated well (r = 0.974). With this one-vessel centrifugal sedimentation method and at least five fluorescently labeled microspheres, blood flow can be reliably measured in various organs, including ischemic myocardium.

Animals↗
PubMed1999

On the validity of blood flow measurement using colored microspheres.

The aim of this study was 1) to investigate the validity of repeated estimations of blood flow using colored microspheres (CMS) and 2) to develop and validate a method that permits four consecutive estimations in the same animal using nonradiolabeled microspheres (NRMS). Several mixtures of different types of microspheres were injected in dogs, with each mixture containing the radiolabeled microspheres (RMS; labeled with 113Sn) with either three CMS, four CMS, or three CMS and one type of fluorescent (crimson labeled) microsphere (FMS). The blood flows estimated with the use of any of the injected microspheres were compared with those measured using the RMS as the "gold standard." The results were analyzed by 1) regression analysis, 2) variance analysis (ANOVA I), and 3) estimation of the limits of agreement between RMS and NRMS flow rates. The results indicate that simultaneous estimations of blood flow obtained with the use of more than three CMS lack accuracy and reliability. A combination of three types of CMS with crimson-labeled FMS, however, offers the possibility to estimate consecutively four different flow rates in the same animal in an accurate way and with relatively high precision.

Analysis of Variance↗
PubMed1975

Measurement of gastric blood flow with radioactive microspheres.

The validity of using radioactive microspheres (15 +/- 5-mum diameter) to measure gastric blood flow and its partition between gastric wall layers was investigated in anesthetized dogs with a chambered segment of gastric corpus. Total flow measured by a venous effluent technique demonstrated close correlation with microsphere-measured flow (r = 0.98, slope = 0.95) in 12 dogs given histamine, gastrin, or isoproterenol. In 12 histamine-stimulated dogs, mucosal flow measured by aminopyrine clearance and by microspheres also showed good agreement (r = 0.96, slope = 0.83). No evidence was found to indicate that microspheres altered hemodynamic or gastric function. In all experiments less than 1% of the total gastric radioactivity passed through arteriovenous shunts. The mucosa always contained a statistically adequate number of spheres (greater than 400), but the submucosa and muscularis frequently did not. Microspheres of all sizes mixed adequately in large arteries, but a significant difference was found in the distribution of 16- and 26 mum spheres between mucosa and submucosa, presumably because of streaming of the larger spheres past mucosal arteries. It was concluded that, with the techniques developed in our laboratory, microspheres could be a highly useful tool for quantitating gastric regional blood flow under a variety of experimental conditions.

Aminopyrine↗
PubMedDate not supplied

Comparison between hydrogen clearance and microsphere technique for rCBF measurement.

Regional cerebral blood flow was measured repeatedly in anesthetized and immobilized cats under various experimental conditions by recording the clearance of inhaled hydrogen with inserted platinum electrodes and by recording the distribution of 15 mu microspheres labeled with 3 different radioisotopes. The values for both methods in normal cortical tissue were comparable (75.7 +/- 23.5 ml/100 g min for H2-clearance; 67.6 +/- 26.2 ml/100 g min for microsphere technique), but were below those recorded in awake cats. With both methods the values could be reliably reproduced (correlation coefficient between measurements: 0.903 for H2-clearance, 0.754 for microsphere technique). During ischemia induced by temporary occlusion of the middle cerebral artery the microsphere technique usually yielded higher flow values than the H2-clearance, and did not indicate severe ischemia in 6 out of 20 instances. After restoration of flow, hyperperfusion was observed by the microsphere technique in 2 cases only while H2-clearance indicated hyperemia in 6 instances. This limited comparability between the 2 methods was also expressed in a low correlation coefficient (0.486) calculated from 139 flow values obtained simultaneously with both methods. The discrepancy between the methods under pathological conditions might be due mainly to the different recording volumes: while Pt-electrodes record H2-clearance from a few mm3 or less, tissue samples of 300-700 mg were necessary for the microsphere technique and inhomogeneities of flow may thereby escape detection. The technique for measuring cerebral blood flow in an experimental setup should be selected according to the requirements of the study and according to the limitations of the various methods.

Animals↗
PubMed1993

Sustained decrease in brain regional blood flow after microsphere embolism in rats.

BACKGROUND AND PURPOSE: An experimental model that induces sustained ischemia and infarction may provide useful information relevant to prevention of the development of ischemic brain disease. The purpose of the present study was to elucidate the pathophysiological consequences of cerebral blood flow under sustained cerebral ischemia or oligemia and infarction in rats after microsphere embolism. METHODS: We injected 900 microspheres (48 microns in diameter) into the right internal carotid artery of 146 rats and determined the time course of changes in blood flow of the cerebral cortex, striatum, and hippocampus of both hemispheres by the hydrogen clearance method for a period of 28 days after the operation. Infarct area was determined by triphenyltetrazolium chloride staining and hematoxylin and eosin staining methods. RESULTS: Cortical and striatal blood flow of the right hemisphere of microsphere-injected rats was significantly decreased after the embolism, and this was sustained throughout the experiment. Hippocampal blood flow of the microsphere-injected hemisphere was also decreased on days 1 and 3 but tended to return toward control levels thereafter. In the left hemisphere, reduction in regional blood flow was detected in the cortex and hippocampus on day 1 and the striatum on day 3. A triphenyltetrazolium chloride-unstained area had developed by day 3 after the embolism. The extent of the area was similar to that on days 7 and 28. Microscopic examination revealed degenerative areas scattered mainly in the parietotemporal cortex, corpus callosum, hippocampus, thalamus, and lenticular nucleus of the embolized hemisphere, demonstrating the induction of widespread necrosis after embolism. CONCLUSIONS: Microsphere embolism resulted in a sustained decrease in regional blood flow and production of cerebral infarction in the brain regions of the microsphere-injected hemisphere.

Animals↗
PubMed2004

Incorporation of polymer microspheres within fibrin scaffolds for the controlled delivery of FGF-1.

The purpose of this work was to examine the feasibility of a hybrid scaffold in which fibroblast growth factor-1 (FGF-1)-encapsulated microspheres are embedded within a fibrin gel. Such a tissue-engineered scaffold could be incorporated into surgical procedures to promote healing while simultaneously delivering therapeutic agents that promote angiogenesis. Fibrin has been extensively studied as an adhesive in plastic and reconstructive surgery and the enhancement of wound healing with embedded growth factors is desirable. We report the release of a fluorescently-labeled model protein, bovine serum albumin (BSA-FITC), from poly(D,L-lactic-co-glycolic acid) microspheres embedded in the fibrin scaffold. The protein release was found to be significantly delayed as compared to microspheres alone during the initial 24 h of release. Additionally, FGF-1 was examined for efficient incorporation into these scaffolds as a potential mitogen for fibroblasts. The optimal concentration of FGF-1 in the media that enhanced NIH-3T3 fibroblast proliferation over 48 h was determined to be 0.1 microg/ml. The release of FGF-1 from microspheres embedded in fibrin gels was compared to FGF-1-encapsulated microspheres alone. The release of FGF-1 from the microsphere/scaffolds was delayed as compared to the release of FGF-1 from microspheres alone. This novel hybrid fibrin/microsphere scaffold is a feasible delivery system for growth factors.

Animals↗
PubMed2006

Formulation, characterization and release studies of alginate microspheres encapsulated with tetanus toxoid.

Alginate is a safe, non-immunogenic and inexpensive natural polymer with high mucoadhesive properties. Alginate microspheres can be used as a delivery system for antigens to mucosal surfaces. In the present study alginate microspheres were prepared by an emulsification technique. The effects of sonication time, concentration of alginate, emulsifier and calcium chloride, and also the volume of calcium solution, were evaluated on mean size, size range, surface roughness and porosity, sphericity and clumping of microspheres using an optical microscope and particle size analyzer. The most desirable conditions were 90 s sonication, 3% alginate solution, 2% surfactant and 60 ml of 0.33% CaCl2 in octanol. The resulting microspheres had a mean size of 1.34 +/- 0.3 microm and size range of 0.3 +/- 2.0 microm, with no surface roughness and porosity, low clumping and high sphericity. The encapsulation efficiency was about 47.7%. All batches showed nearly the same release profiles with a low burst release. The stability of the model antigen (tetanus toxoid (TT)) extracted from microspheres was confirmed by SDS-PAGE; and the antigenicity of TT was studied by ELISA and found to be 91 +/- 5% of the original TT. It can be concluded that, with regard to the size and morphological characteristics of the prepared microspheres and their ability in preserving the antigenicity of the encapsulated TT, they could be used as a delivery system for mucosal delivery of TT.

1-Octanol↗