Uptake Of Microspheres Research Articles

Microvascular hemodynamics in experimental arthritis: Disparity between the distribution of microspheres and plasma flow in bone

The microcirculation in normal and arthritic juxtaarticular bone was studied in 16 young dogs with carragheenan-induced arthritis of one knee. The regional blood flow was determined by the tissue uptake of intracardially injected 15-μm 141Ce-labeled microspheres, and the microvascular plasma volume was determined by the distribution space of circulating 125I-fibrinogen. Disparities between the distribution of plasma flow and microspheres, introduced by plasma skimming or nonentrapment of spheres in the intraosseous circulation, were estimated by 59Fe-transferrin, a third intravascular tracer, injected as a bolus intracardially and trapped peripherally after 15 sec by prompt circulatory arrest. The tissue uptake of the plasma flow tracer was compared to that of microspheres by the ratio between observed and expected activity of 59Fe-transferrin, the expected activity being calculated from the microsphere distribution. The transferrin and microsphere uptake agreed well in patella, marginal epiphyseal bone, and cortical bone, whereas observed activity of transferrin was twice the expected in central epiphyseal bone, three times higher in marrow, and up to eightfold higher in metaphyses adjacent to growth plates. This discrepancy was significantly greater in arthritic bone when the metaphyses were examined in toto. The microsphere method thus appears to underestimate blood flow to cancellous bone and marrow due to uneven distribution of plasma and formed elements from profound plasma skimming and perhaps also by AV shunting.

Size Effects on the Uptake of Particles by Populations of Tetrahymena pyriformis Cells

ABSTRACTFlow cytometry has been used to make direct measurements of rates of uptake of latex microspheres from dilute, monodisperse suspensions by Tetrahymena pyriformis. Measurements were made for five different sizes of microspheres, ranging from 1.09 to 6.17 μm diameter. Fractions of cells in the population that did not ingest the microspheres offered were also determined. In addition, the size distributions, as indicated by the forward angle light scattering intensity which is measured by the instrument, were determined for the whole population and for the subpopulations of cells that did and did not ingest the particles, for each particle size used. It was found that the fraction of cells that did not ingest the particles was small and independent of particle size when this was less than about 2.7 μm, but increased with particle size when particle size was increased above this value. The so‐called maximum clearance rate, which can be calculated from the data, was found to increase monotonically with particle size if it were based only on those cells which actually ingested the particles offered. However, a plot of maximum clearance rate vs. particle size exhibited a maximum if the clearance rate were based on all cells present in the population.

Intestinal uptake of fluorescent microspheres in young and aged mice.

Rhodamine B-labeled synthetic latex particles (microspheres), 1.8 micron in diameter, were administered by gavage 5 days per week to young (24 days) and aged (18 months) mice. After 25 days (19 gavages), the particles were assayed in solubilized tissues by depositing them on filters and counting under fluorescence microscopy. Aged mice exhibited significantly more fluorescent particle accumulation in Peyer's patches but significantly less in lungs than young mice. Mesenteric lymph nodes and Peyer's patch-free intestinal segments contained measurable latex, but differences between young and aged animals were not significant. Liver contained only trace amounts of latex, and spleen and kidney were latex free in both young and aged animals. Nonquantitative observations on KOH-glycerol-cleared whole Peyer's patches and slices of liver, lung, and mesenteric lymph node were similar.

Regional differences in phagocytosis by the corneal endothelium in the domestic cat.

The phagocytosis of IgG-coated latex microspheres by the central and peripheral regions of the corneal endothelium in the domestic cat was investigated by organ culture. The endothelium was exposed to 1.357 X 10(7) microspheres/mm2, and counts of ingested microspheres were made by scanning electron microscopy. Initial assessments of phagocytosis over 8-h and 24-h periods of culture gave extremely low levels of incorporation. Therefore, subsequently, a 48-h period of culture was adopted. Microsphere uptake levels per square millimeter over 48 h were as follows: peripheral endothelium 6,021 +/- 3,162; central endothelium 2,000 +/- 1,529; overall 4,011 +/- 3,294. The greater uptake of microspheres in the peripheral cornea was statistically significant (P less than 0.002, paired t-test). The involvement of microvilli in phagocytosis by corneal endothelial cells was proposed.

Phagocytosis of Bioactive Microspheres

The influence of several proteins on the uptake of microspheres was investigated using mouse peritoneal macrophages. Thioglycollate-stimulated macrophages were cultivated for 3 h with protein-grafted and protein-coated cellulose microspheres smaller than 2 μm in the presence and the absence of serum. Bovine serum albumin reduced the phagocytosis of microspheres, while y-globulin, human fibronectin, bovine tuftsin, and gelatin enhanced the phagocytosis. This trend was not influenced substantially by the presence of serum and the mode of surface binding of the proteins; that is, covalent grafting or physical adsorption (coating). However, in the case of gelatin binding, phagocytosis was greatly enhanced by the presence of serum as compared with the other proteins.

The variation with flow-rate of the extraction of bone-seeking tracers in recirculation experiments.

Radioactive microspheres were injected into the hearts of anesthetized dogs and the reference organ technique used to determine cardiac output. Blood flow to the leg bones was then obtained from microsphere uptake. Simultaneous injections of the bone-seeking radiotracers 85Sr and, in fewer animals, 18F and 99mTc methylene diphosphonate similarly gave their clearances from the blood by bone over a period of 5 min. The ratio of clearance to flow (extraction ratio) was found to be flow-dependent, falling from near unity at low flow rates to about 0.4 at higher flow rates. The results are in general accordance with the Renkin theory of capillary permeability but do not fit exactly to the concept of a constant product of permeability and surface area, perhaps due to the heterogeneity of the model. The findings confirm conclusions based on tibial nutrient artery perfusion experiments and demonstrate that skeletal blood flow cannot be measured by the clearance of bone-seeking tracers. There were substantial differences of blood flow normalized for weight between the bones of a given animal.

Measurement of tendon blood flow in rabbits by microsphere uptake and 133Xe washout

Blood flow was measured in the calcaneal tendons of rabbits using the techniques of labelled microsphere uptake and 133Xe washout simultaneously. There was no correlation between the results obtained with the two methods in individual animals. It is doubtful if the assumptions underlying the 133Xe washout technique are valid when it is used to measure blood flow in tendons.

Asynchronous transmural perfusion during coronary reactive hyperaemia.

Dynamic variation in the transmural distribution of myocardial blood flow was studied in 36 anaesthetised open-chest dogs during the course of the reactive hyperaemia following a 90 s occlusion of the left anterior descending coronary artery. Myocardial blood flow was estimated from tissue uptake of radioactive microspheres, 9 to 10 micrometers in diameter. Endo/epi flow ratios indicated asynchronous reactive hyperaemic responses across the free wall of the left ventricle; flow was preferentially to subepicardium during the initial (pre-peak) phase, whereas flow was preferentially to subendocardium during the prolonged recovery phase. The mean of endo/epi flow ratios obtained during the peak plateau of coronary artery reactive hyperaemia indicated essentially uniform transmural distribution. However, further analysis indicated that this was result of ratios less than 1 early in the peak plateau and ratios greater than 1 late in the peak plateau. Reversal of the endo/epi flow ratios due to regionally asynchronous maximum flows is responsible for the prolonged plateau at peak flow observed in measurements of coronary artery reactive hyperaemia. Transmural asynchrony of peak reactive hyperaemic flow may also account for underestimates in vasodilator capability of ischaemia based on measurements of either coronary artery or myocardial blood flow.

The effect of a natriuretic atrial extract on renal haemodynamics and urinary excretion in anaesthetized rats.

1. An extract of cardiac atrial tissue, when injected intravenously into anaesthetized rats, caused a large and rapid increase in renal excretion of sodium chloride. 2. The renal response to atrial extract was associated with increases in total and medullary blood flow in the kidney, as measured by microsphere and albumin uptake methods, respectively. 3. The data suggest that these changes in renal haemodynamics may contribute to, but are unlikely to be the complete cause of, the natriuresis and chloriuresis following injection of atrial tissue extract.

Distribution of blood flow in the dog kidney. I. Saturation rates for inert diffusible tracers, 125I-iodoantipyrine and tritiated water, versus uptake of microspheres under control conditions.

Disparate reports on intrarenal blood flow distribution prompted a direct comparison between microspheres (Ms) and inert diffusible tracers (DT). The "tissue sampling technique" for estimating local flow with DT (Kety) was adapted for the dog kidney, using 125I-iodoantipyrine (1-Ap) and tritiated water (THO). Ms (15 micron) were injected 2-3 min prior to 10-15 s DT infusion made during continuous 1 s arterial blood sampling. Tracers were measured in 7 to 20 samples from each of the following zones: Outer, middle and inner cortex (C1, C2, C3), outer and inner halves of outer medulla (OM1, OM2), and inner medulla (IM). I-Ap and THO gave closely similar flow distribution, and average total renal blood flow (RBF) of 3.90 and 3.78 as compared to 3.94 ml/min . g with Ms. Flow in C2 (ml/min . g) was similar with all tracers, and in per cent thereof average local flows were: C1 102, C3 70, OM1 34, OM2 12, and IM 2 with DT versus 117, 53, 12, 3, and 0 with Ms. Zonal flow fractions of total RBF obtained with DT were: C1 0.41, C2 0.33, and C3+medulla 0.26 versus 0.51, 0.33 and 0.16 with Ms. Thus, a Ms surplus in C1 relative to DT flow, representing 10% of total RBF, matched a Ms deficit in C3+medulla. This disparity might result from: (1) Failure of Ms to enter deep afferent arterioles in proportion to blood flow, (2) diffusion of DT from deep portions of the interlobular arteries, and/or (3) postglomerular inward flow of blood and DT.

Evaluation of methods of measuring glomerular and nutrient blood flow in rat kidneys.

In normal rats, glomerular plasma flow rates (GPF) were estimated from the uptake of microspheres, and single-nephron filtration rates were estimated by Hanssen's technique in order to calculate single-nephron filtration fractions (SNFF) for outer (C1), middle, (C2), and deep (C3) nephrons. With large microspheres (15 micron), SNFF averaged 0.19, 0.41, and 0.63, and with small microspheres (9 micron), SNFF averaged 0.25, 0.48, and 0.42 for areas C1, C2, and C3, respectively. Kidney filtration fractions (FF) averaged 0.36. Because microsphere experiments in normal rats have generally suggested that SNFF-C1 and FF are similar, we conclude that both types of microspheres overestimated outer cortical plasma flow rates, and probably underestimated inner cortical plasma flow rates. In addition, not all of the smaller microspheres were trapped in the glomeruli. Nutrient blood flow rates were estimated from the uptake of 86Rb. Values ranged from 7.3 ml/g per min in the outer cortex to 4.7 ml/g per min in the inner cortex. Because these values are very similar to measurements made by several other techniques, we conclude that 86Rb uptake adequately estimates cortical blood flow. Medullary blood flow estimates, however, increased with time and were probably too high.

Intrarenal distribution of blood flow and glomerular filtration during chronic unilateral ureteral obstruction.

Paired hydronephrotic (HN) and hypertrophic (HT) rat kidneys were studied after 6 days with complete unilateral ureteral obstruction without exposing the kidneys. Total HN renal blood flow (RBF), estimated by total microsphere (MS) uptake and from local 125I-antipyrine (Ap) uptake, averaged about 3/4 of control. HN kidney GFR was reduced to about 1/2 of control level as estimated from inulin clearance of HT kidney times the HN to HT ratio for mean single nephron filtration rate, determined by 14C-ferrocyanide. Whereas blood flow (Ap) was proportionately reduced in outer and inner cortex (OC and IC), fractional flow to the outer medulla (OM) was doubled as compared to controls (p less than 0.01). Filtration was well preserved in deep as compared to superficial glomeruli with a smaller deep nonfiltering fraction (p less than 0.02). Thus the results oppose the current concept that HN is characterized by disproportionate circulatory damage to IC and OM with little or no filtration in deep nephrons. In HT kidneys average RBF (MS) and GFR rose by about 1/2. Whereas total blood flow (Ap) rose proportionately in OC and IC, it remained at control level in OM, indicating dissociation between the total RBF and GFR and the effective blood flow to the OM zone.

Flow of blood to the ovaries of ewes throughout the estrous cycle.

A Doppler ultrasonic blood flow procedure was evaluated to determine if it could be adapted for use on vessels as small (I.D. ≅ 0.5 mm) as the ovarian artery in sheep. When blood was pumped through silastic tubing (I.D. = 0.38 and 0.57 mm) the values calculated for blood flow using the Doppler procedure were highly correlated (P<0.01) with the known flow rates. A second experiment was conducted to compare the Doppler ultrasonic procedure for measuring blood flow to the ovaries of ewes and the uptake of radioactive microspheres. Although it was not possible to measure blood flow directly (ml/min) with the radioactive microsphere method, when the cpm/g of ovarian tissue were compared to the ml/min blood flow calculated using the Doppler procedure, there was a high degree of correlation (r = 0.94, P<0.01). These results suggested that the Doppler ultrasonic procedure was reliable for the quantification of blood flow to the ovaries of ewes. In a final experiment the flow of blood to the ovaries of four ewes was quantified throughout an estrous cycle. Blood samples for hormone analysis and blood flow data were collected at 2–6 h intervals. Significant correlations were noted between serum levels of LH and FSH (P<0.05), LH and prolactin (P<0.05), and FSH and prolactin (P<0.01). Systemic levels of progesterone and blood flow to the ovary bearing the corpus luteum were also correlated (P<0.05). Blood flow to the luteal ovary increased from approximately 0.7 ml/min during the estrual phase of the cycle to 3 to 5 ml/min during the mid-luteal phase. This observation suggests that the amounts of LH and prolactin, as well as other substances, such as oxygen, glucose, cholesterol, etc., which reach the corpus luteum were increased. This mechanism probably plays a very important role in supporting the increased function of the corpus luteum during the mid-luteal phase of the estrous cycle.

Evaluation of blood flow in the submandibular gland of the dog by fractional uptake of ionic and particle tracers.

SummaryThis study examined the fractional uptake of 169Yb-labeled microspheres (about 25 μ in diam) and an ionic tracer (42K or 86Rb) by the same unstimulated submandibular gland as an index of its blood flow (total and/or functional). Cardiac outputs were measured to calculate a “blood flow” from these uptakes. To examine any changes in the uptake of the 42K or 86Rb with time, tissues were sampled 40-60 or 120-180 sec after injecting the ionic tracer for uptake of the ionic and particle tracers. For the 40-60-sec group of dogs, fractional uptake of the ionic tracer appeared to be similar to that of the microspheres. In the other group, uptake of the ionic tracer was significantly larger than that for the labeled microspheres. Injection of two differently labeled spheres (169Yb and 85Sr) sequentially demonstrated that uptakes of the spheres injected secondly were not different from those injected initially. Fractional uptakes of each type of sphere per unit weight were similar in the right and left gland,...