Clearance Rate Of Particles Research Articles

The effects of the toxic dinoflagellate Protogonyaulax tamarensis on the feeding and behaviour of bivalve molluscs

A series of experiments was carried out to assess the effects of the toxic dinoflagellate Protogonyaulax tamarensis on shell-valve activity, rates of particle clearance, preingestive, and postingestive particle selection in seven species of bivalve molluses from three geographic localities: Maine, Rhode Island, and Spain. The responses observed were species-specific and varied with collection locality. Responses included shell-valve closure and/or siphon retraction ( Mya arenaria, Mytilus edulis, Geukensia demissa), reduced rates of particle clearance ( M. arenaria, G. demissa), increased rates of particle clearance ( Ostrea edulis), production of mucus ( M. edulis from Spain and Rhode Island, Placopecten magellanicus, G. demissa). Mortalities were noted in M. edulis from both Spain and Rhode Island. Two species ( Modiolus modiolus and Spisula solidissma) exhibited no effects of the toxic dinoflagellates. Data are also presented for particle selection, clearance and filtration rates for the seven species. It is suggested that species which are periodically exposed to dinoflagellate blooms may have evolved mechanisms permitting them to exploit the toxic organisms as food with no ill effects.

Airborne acidity: estimates of exposure and human health effects.

Human health effects have resulted from the inhalation of ambient acidic aerosols, and there is suggestive evidence that current North American levels of exposure are producing excesses in respiratory morbidity. Annual mean mortality rates have been correlated with ambient aerosol concentration indices, with SO4(2-), FP, IP, and TSP having a descending order as predictive coefficients. These pollutant indices also contain H+ in descending mass ratios, and may all be surrogates for H+ as an active agent. Controlled exposure studies in humans and animals provide evidence that acidic aerosols produce greater changes in respiratory mechanical function and rates of particle clearance than other constituents of ambient particulate matter. The strong acid content of the ambient aerosol has not been measured in any of the population based pollutant effects studies in which it is a likely causal factor. The absence of direct measurement data on acidic aerosol in these studies, and their reliance on surrogate indices such as SO2 and SO4(2-), precludes firm conclusions about exposure-response relationships. High priority areas for further investigation include systematic investigation of the spatial and temporal distribution of population exposures; extension and refinement of population response studies in relation to acid aerosol exposures; responses of normal healthy and asthmatic human volunteers to mixtures of acidic aerosols and oxidant vapors under controlled conditions of exposure and exercise intensity; and progression of changes in lung epithelia during repetitive daily exposures of experimental animals to acidic aerosols, oxidants, and their mixtures, with concurrent measurements of particle clearance and respiratory function.

Airborne Acidity: Estimates of Exposure and Human Health Effects

Human health effects have resulted from the inhalation of ambient acidic aerosols, and there is suggestive evidence that current North American levels of exposure are producing excesses in respiratory morbidity. Annual mean mortality rates have been correlated with ambient aerosol concentration indices, with SO4(2-), FP, IP, and TSP having a descending order as predictive coefficients. These pollutant indices also contain H+ in descending mass ratios, and may all be surrogates for H+ as an active agent. Controlled exposure studies in humans and animals provide evidence that acidic aerosols produce greater changes in respiratory mechanical function and rates of particle clearance than other constituents of ambient particulate matter. The strong acid content of the ambient aerosol has not been measured in any of the population based pollutant effects studies in which it is a likely causal factor. The absence of direct measurement data on acidic aerosol in these studies, and their reliance on surrogate indices such as SO2 and SO4(2-), precludes firm conclusions about exposure-response relationships. High priority areas for further investigation include systematic investigation of the spatial and temporal distribution of population exposures; extension and refinement of population response studies in relation to acid aerosol exposures; responses of normal healthy and asthmatic human volunteers to mixtures of acidic aerosols and oxidant vapors under controlled conditions of exposure and exercise intensity; and progression of changes in lung epithelia during repetitive daily exposures of experimental animals to acidic aerosols, oxidants, and their mixtures, with concurrent measurements of particle clearance and respiratory function.

Alteration of airway reactivity by mucus

In 11 beagles with permanent tracheostomies we investigated whether mucus hypersecretion alters airway reactivity to inhaled aerosols. Mucus was collected from the dogs while awake by resting a cytology brush on the lower tracheal mucosa; the mucus collection rate was used as an index of mucus flux. Mucus linear velocity was determined under light sedation by bronchoscopically observing the rate of particle clearance in the trachea. Mucus depth was then computed from the flux and velocity. On a separate occasion, under pentobarbital anesthesia, methacholine aerosols (1 min duration) were given at 10 min intervals in doubling doses up to at least 2 mg/ml. Pulmonary resistance R l was determined prior to and 2 min after each dose. After a 1 h pause, methacholine was infused at a constant rate of 40 μg·kg −1·min −1 for 10 min. This dose produced a plateau in R l after approximately 3 min; the mean rise in R l was similar to that achieved with the 2 mg/ml aerosol. The infusion response R inf was defined as the change in R l 4–5 min post infusion; the aerosol response R aer was defined ad the change in R l 2 min post 2 mg/ml aerosol. There was no significant correlation between R inf and R aer, nor between either R inf or R aer and mucus flux. There was, however, a strong positive association between R inf/R aer and mucus flux and a similar positive association between R inf/R aer and mucus depth. These associations indicate that dogs with elevated secretion levels are relatively unresponsive to aerosolized as opposed to infused methacholine. Thus, to the extent that infusion reactivity reflects innate airway reactivity, the reactivity to inhaled aerosol may underestimate the true value when mucus hypersecretion occurs.

Methods for reducing particle concentrations ofAspergillus fumigatusconidia and mouldy hay dust

The effectiveness of commercially available domestic air purifiers to reduce airborne Aspergillus fumigatus conidia and mouldy hay dust was investigated. It was found that the rate of particle clearance is a function of the volume of air passing through the purifiers but that the low throughflow of air makes their use of little value in clearing particles from a normal sized room. Vacuum cleaners were more effective than air purifiers because of their higher air throughput, so too were high volume fan systems in conjunction with simple filtration units. Ionizers had no effect but steam condensation was very efficient at clearing airborne particles.

Clearance rates of bacteria-sized particles by freshwater ciliates, measured with monodisperse fluorescent latex beads.

Monodisperse fluorescent latex particles with diameters of 0.57 and 1.04 μm have been used to measure the clearance rates of bacteria-sized particles by two ciliates from a Norwegian lake. The clearance rates by Epistylis rotans on these particles were in the range 0.23 to 1.26 μl ind-1h-1, and by Strombidium sp. 0.26 to 0.90 μl ind-1 h-1. The clearance rates varied with food level and temperature. Possibilities and limitations of the suggested method are discussed.

Effect of cadmium on particle clearence by the Sydney rock oyster, Saccostrea commercialis (I. & R.)

Sydney rock oysters, S. commercialis (I. & R.); were exposed to a control and 10. 50 and 100 �g 1-1 cadmium in a flowing seawater system in the laboratory for 45 days. After this period the rates of particle clearance, assessed by using killed 14C-labelled Escherichia coli in suspension, were determined for each group of oysters. A small proportion of 14C-label from the E. coli was recovered from the non-gut tissues of the oyster, suggesting that the oyster digested, and may have derived some energy from, the bacteria. All cadmium- treated oysters displayed reduced efficiency of clearance compared to controls. If this sublethal effect of cadmium occurs in natural populations, oysters could suffer impaired feeding efficiencies with subsequent effects on growth and reproduction.

Cytoprotective actions of prostacyclin during hypoxia in the isolated perfused cat liver.

The cytoprotective effect of prostacyclin (PGI2) was examined using hypoxic cat livers perfused with Krebs-Henseleit buffer at constant flow. PGI2 infusion (10 ng . g-1 . min-1) showed no direct vasodilator effect on the hepatic circulation under conditions of normoxia or hypoxia, as studied by changes in perfusion pressure. Hypoxia induced a marked decline in hepatic oxygen consumption, an increase in perfusion pressure, and in perfusate cathepsin D and LDH activity in the hepatic effluent indicating lysosomal and cytoplasmic leakage. Tissue samples, obtained 150 min after hypoxic perfusion, showed higher percent-free cathepsin values (82 +/- 4%, mean +/- SE, 7 livers, P less than 0.025) compared to that of normoxia (58 +/- 4). Phagocytic activity, measured by the clearance rate of colloidal carbon particles, was also depressed by hypoxia. PGI2 infusion significantly inhibited the posthypoxia leakage of liver cathepsin D and LDH into the recirculating perfusate, restored the percent-free cathepsin D to 64 +/- 3%, and preserved the phagocytic activity during hypoxia, indicating preservation of lysosomal and cytoplasmic membrane integrity and Kupffer cell phagocytic function. The preservation of lysosomal integrity by PGI2 was further confirmed by electron microscopy. It is evident that PGI2 has a significant protective effect in hypoxic hepatocytes that may not be related to its vasodilation and inhibition of platelet aggregation.

Preservation of hepatic cell integrity by aprotinin in hypoxia

Perfused cat livers subjected to 2.5 hr of hypoxia exhibited dramatic increases in perfusate cathepsin D and lactic acid dehydrogenase (LDH) activities, amino nitrogen concentrations, and a 60% depression in the clearance rate of carbon particles by the reticuloendothelial system (RES). Addition of aprotinin (250 KIU/ml) to the perfusate prior to hypoxia prevented the increases in circulating cathepsin D, LDH, and amino-nitrogen observed at 150 minutes. In addition, aprotinin prevented the reduction in carbon clearance during severe hypoxia. However, aprotinin had no effect on the percent free cathepsin D activity indicating that this agent did not directly prevent increases in lysosomal fragility occurring in response to hypoxia. Thus, addition of pharmacologic doses of aprotinin to the perfusate protected RES cells, and markedly reduced the release of cytoplasmic and lysosomal enzymes. The prevention of cell membrane dissolution appears to be a critical factor in hepatic preservation, and may be related to the inhibition of proteolysis by aprotinin. These effects may help explain the therapeutic effectiveness of this agent in shock and in myocardial ischemia.

Protection of hypoxic cytotoxicity by glucocorticoid in the liver

Induction of hypoxia for 2.5 h in perfused cat livers resulted in a 10-fold increase in cathepsin D and a 15-fold increase in lactic dehydrogenase (LDH) activities in the perfusate and a 42% depression of the clearance rate of particles by the reticuloendothelial system (RES). Addition of 10(-3) M methylprednisolone (MP) to the perfusate only slightly retarded the release of LDH, but significantly (P<0.05) inhibited cathepsin D release by 90% at 150 min. Liver flow did not change during the perfusion period when MP was added to control or hypoxic livers. Similarly, MP did not significantly alter oxygen consumption in perfused livers. However, MP protected against the reduction in carbon clearance during hypoxia without inducing blockade of colloidal carbon clearance. Moreover, opsonization of carbon with autologous plasma did not improve the clearance of colloidal carbon above that observed in nonopsonized experiments. Thus, pharmacologic doses of a synthetic glucocorticoid protected RES cells and release of lysosomal hydrolases during severe hypoxia in isolated perfused cat livers probably by stabilization of cellular and intracellular (lysosomal) membranes.

Experimental tests of suspension feeding in Atlantic reef corals

The ability of 15 species of Atlantic reef corals to act as suspension feeders was demonstrated by their removal of suspended particles from sea water in culture vessels. Mean clearance rates varied from 16.6 to 145.5 ml water cleared/h/cm2 of live coral tissue. The lowest rates was found in Porites porites which is primarily a tentacle feeder, and the highest in Diploria clivosa which acts as both a tentacle feeder and suspension feeder. Rates of particle clearance in Agaricia agaricites, which is primarily a suspension feeder, were influenced by current velocity and type of food.

Regional deposition and clearance of particles in the human nose

The sites of particle deposition and clearance rates in the human nose have been investigated for inhaled monodisperse particles in the size range 2–10 μm. At least 45 per cent of the retained material was deposited in the anterior region of the nasal passages and the site of maximum deposition was 2–3 cm behind the tip of the nose. Although clearance of particles from this region was very variable, a long-term retention with a biological half-life greater than 3 hr was always observed. In approximately half the experiments, the site of maximum deposition in the nose was in the region of the junction between the ciliated and nonciliated epithelia: particles deposited on the ciliated epithelium were rapidly removed by the mucociliary clearance mechanism, while particles deposited in the unciliated region were removed relatively slowly. In some cases, as much as 60 per cent of the particles initially deposited in the anterior region were removed with half-lives of less than 20 min.

Papain-induced emphysema and the elimination of TiO2 particulates from the lungs.

The deposition, retention, and clearance of TiO2 particles in normal rats under varying conditions were determined. Assuming that the particle parameters are constant, the deposition can be predicted if the lung weight, concentration of TiO2 in the air, and time of exposure are known. The clearance of particles was followed up to 140 days. The retention half-time after exposure is 14 days for approximately the first 8 days and 88 days thereafter. Experimental emphysema produced by aerosol inhalation and intratracheal injection of papain reduces the clearance rate of TiO2 particles.

Deposition and clearance following inhalation and intratracheal injection of particles.

The pulmonary deposition patterns and the clearance rates of insoluble particles from the lungs of rats were measured during the early post-exposure period following inhalation and intratracheal injection. The data were analyzed by assuming that the pulmonary system consists of a series of compartments and that these compartments are cleared sequentially in time via the trachea. Based on these assumptions, the intratracheal injection technique produced a relatively greater deposition of particles in the lower respiratory tract as compared with inhalation. The clearance kinetics of particles from the lungs were similar for particles deposited in equivalent compartments of the pulmonary system by the two methods of exposure, suggesting that clearance from a given lung compartment is independent of the distribution of particles within that compartment. If this inference is valid, the clearance kinetics obtained following intratracheal injection of particles should not differ from those obtained following inhalation, even though the fractional deposition of particles in lung compartments may differ following the two methods of exposure.

Role of reticulo-endothelial system in blood clearance of cholesterol.

The clearance rate of colloidal carbon particles is only slightly impaired in rabbits rendered hypercholesteremic by overfeeding cholesterol. Rabbit serum cholesterol injected into rats is cleared by phagocytosis of the reticulo-endothelial cells whether the cholesterol is in the form of chylomicra (cloudy serum) or not (clear serum from fasting animals). The clearance of the foreign serum cholesterol from the blood follows an exponential function with respect to time as for many other colloids and the rate of clearance is inversely proportional to the quantity injected. Interference is observed between the clearance of cholesterol and other colloids when injected simultaneously. Pretreatment of rats with high doses of heparin increases substantially the speed of clearance of foreign serum cholesterol. The mechanism of the action of the R.E.S. in the metabolism of cholesterol is discussed.