Blood's critical Taylor number and its flow behavior at supercritical Taylor numbers

When the inner cylinder of a fluid-filled Couette viscometer is rotated rapidly, a vortical flow pattern develops when a dimensionless value referred to as the critical Taylor number (Tc) is reached. We have determined its magnitude in our viscometer for three Newtonian fluids and for blood at 37 degrees C, using the inflection point of torque/RPM vs. RPM (sudden rise in apparent viscosity). Its position was identified by least squares line fitting. Because blood was studied, the viscosity used in Tc calculation was the apparent bob shear stress/shear rate ratio at the inflection marking vortical flow onset. For glycerol-water mixtures Tc was 41.8 +/- 0.3 (N = 11), for propylene glycol 42.0 +/- 0.2 (N = 14), for silicone oil 41.8 +/- 0.2 (N = 11). For healthy blood Tc was 40.7 +/- 0.9 (N = 140). This evidence against blood's increased resistance to flow instability was accompanied by a slower rate of rise in torque both above and below Tc compared to the three Newtonian fluids. Newtonian fluids and blood both developed wavy vortical flow at a rotation rate moderately higher than Tc. Blood resisted this unstable flow behavior more than the Newtonian fluids but it also experienced a slower rate of rise in torque with increasing rotation rate above the critical Taylor number. Shear-thinning is the simplest explanation for blood's mildly altered Taylor vortex behavior; blood's resistance to flow instability is otherwise not found to be sufficient to affect its flow stability in man.     

An investigation of the presence of ultramicrocells in natural mineral water

The presence of 'ultramicrocells' in natural mineral water, capable of passing through a 0.2 micron filter, has been demonstrated. Filters allowing the greatest proportion of viable (culturable) cells to pass ranked in the order, 0.4 micron polycarbonate (5.02%) > 0.2 micron polycarbonate (0.02%) > or = 0.45 micron cellulose nitrate (0.02%) > 0.2 micron cellulose acetate (< 0.002%). Following incubation for 4 d at 22 degrees C, viable counts in filtered mineral water increased from < 2-8.7 x 10(2) cfu ml-1(-2).8 x 10(4)-1.9 x 10(6) cfu ml-1. Successive filtration/incubation cycles of mineral water increased the proportion of cells passing through a 0.2 micron cellulose acetate filter from < 0.003% to 0.11% and 0.69%, suggesting selection for 'ultramicrocells'. Cells isolated from this process and grown on liquid R2A medium were thin, Gram-negative rods, of 0.15-0.40 micron wide and 0.50-6.20 microns long. Membrane filtration techniques used for pathogen detection in mineral waters will not retain all the cells present. If pathogens are able to form ultramicrocells, these may go undetected.     

Effect of different densities of live and dead Chlorella vulgaris on the population growth of rotifers Brachionus calyciflorus and Brachionus patulus (Rotifera)

In order to maintain rotifer populations during periods of low algal production, it is necessary to offer alternate diets, some of which include forms of preserved algae. The present work is based on the effect of live and dead Chlorella vulgaris on the population growth of Brachionus calyciflorus and Brachionus patulus. The experimental design consisted of three algal levels (0.5 x 10(6), 1.5 x 10(6) and 4.5 x 10(6) cells ml-1) offered in three forms (living, frozen and heat-killed). The maximal population density values for B. calyciflorus ranged from 55 +/- 1 ind. ml-1 (at 0.5 x 10(6) cells ml-1) to 471 +/- 72 ind. ml-1 (at 4.5 x 10(6) cells ml-1) with live Chlorella, but was much lower (6 +/- 1 to 26 +/- 6 ind. ml-1) with frozen or heat-killed alga under comparable food levels. However, the maximum population density of B. patulus under live or or heat-killed Chlorella was similar at comparable algal levels but when offered frozen algae it was four times less. The highest mean peak population density was 1,277 +/- 83 ind. ml-1 under 4.5 x 10(6) cells ml-1. The rate of population increase for B. calyciflorus varied from 0.50 to 0.79 using live Chlorella, but under comparable conditions, this range was lower (0.21 to 0.31) for B. patulus. Results have been discussed in light of possible application for aquaculture.     

Permeability of human granulocytes to water: rectification of osmotic flow

The permeability of human granulocytes to water was studied for samples of that population with an electronic particle counter. Changes in volume were monitored as these samples were introduced suddenly into hypo- and hypertonic osmotica. Temperature and concentration sensitivity analyses of the permeability coefficients were carried out. An apparent rectification of water flow seems to occur with the water permeability being three times higher for endosmotic flow than for exosmotic flow. The estimated water permeability at the reference temperature 20 degrees C was for exosmotic flow 2.04 +/- 0.02 x 10(-12) kgmol N-1 s-1 with an apparent transfer energy of 4.76 +/- 0.09 x 10(7) J kgmol-1, and for endosmotic flow 6.05 +/- 0.07 x 10(-12) kgmol N-1 s-1 with an apparent transfer energy of 4.9 +/- 0.1 x 10(7) J kgmol-1.     

Combined effect of concentrations of algal food (Chlorella vulgaris) and salt (sodium chloride) on the population growth of Brachionus calyciflorus and Brachionus patulus (Rotifera)

Salinity is an important variable influencing the density and diversity of rotifers. Studies on salt tolerance of rotifers have so far concentrated on euryhaline species while very little information is available on non-euryhaline taxa. In the present work, we have evaluated the combined effects of Chlorella vulgaris and sodium chloride on the population growth of two freshwater rotifers B. calyciflorus and B. patulus. A 24 hr acute tolerance test using NaCl revealed that B. calyciflorus was more resistant (LC50 = 3.75 +/- 0.04 g l-1) than B. patulus (2.14 +/- 0.09 g l-1). The maximal population density (mean +/- standard error) for B. calyciflorus in the control at 4.5 x 10(6) cells ml-1 (algal level) was 80 +/- 5 ind. ml-1, which was nearly a fifth of the one for B. patulus (397 +/- 7 ind. ml-1) under comparable conditions. Data on population growth revealed that regardless of salt concentration, the density of B. calyciflorus increased with increasing food levels, while for B. patulus, this trend was evident only in the controls. Regardless of salt concentration and algal food level, the day of maximal population density was lower (4 +/- 0.5 days) for B. calyciflorus than for B. patulus (11 +/- 1 day). The highest rates of population increase (r values) for B. calyciflorus and B. patulus were 0.429 +/- 0.012 and 0.367 +/- 0.004, respectively, recorded at 4.5 x 10(6) cells ml-1 of Chlorella in the controls. The protective role of algae in reducing the effect of salt stress was more evident in B. calyciflorus than B. patulus.     

Complex formation between endogenous toxin bilirubin and polyamidoamine dendrimers: a spectroscopic study

The effects of 4th and 5th generation cationic, neutral and anionic polyamidoamine (PAMAM) dendrimers on bilirubin absorbance and fluorescence were studied. Cationic and neutral PAMAM dendrimers shifted the bilirubin absorption maximum from 435 to 442-455 nm, increased the peak absorbance 1.5-fold, shifted the bilirubin fluorescence excitation and emission maxima, increased the fluorescence emission several-fold and significantly protected bilirubin against photodestruction. Using double fluorescence titration technique allowed to receive such constant of binding and the number of binding centers at 20 degrees C: for PAMAM G4 dendrimer, (2.4+/-1.4) x 10(6) (mol/l)(-1) and 0.07+/-0.012; for PAMAM G4-OH dendrimer, (3.1+/-1.3) x 10(6) (mol/l)(-1) and 0.08+/-0.014; for PAMAM G5 dendrimer, (7.6+/-3.6) x 10(6) (mol/l)(-1) and 0.09+/-0.02; and for PAMAM G5-OH dendrimer, (8.5+/-3.2) x 10(6) (mol/l)(-1) and 0.09+/-0.02. These effects can be explained by the formation of bilirubin-PAMAM dendrimer complexes and the formation of bilirubin monomers from tetramers. The formation of complexes sharply increased bilirubin solubility. We conclude that cationic and neutral PAMAM dendrimers bind bilirubin effectively and suggest that such dendrimers may serve as detoxication agents for hydrophobic endogenous toxins.     

Systemic hemodynamic and regional blood flow changes in response to chronic reductions in uterine perfusion pressure in pregnant rats

Preeclampsia (PE) is associated with increased total peripheral resistance (TPR), reduced cardiac output (CO), and diminished uterine and placental blood flow. We have developed an animal model that employs chronic reductions in uterine perfusion pressure (RUPP) in pregnant rats to generate a "preeclamptic-like" state during late gestation that is characterized by hypertension, proteinuria, and endothelial dysfunction. Although this animal model has many characteristics of human PE, the systemic hemodynamic and regional changes in blood flow that occur in response to chronic RUPP remains unknown. Therefore, we hypothesized that RUPP would decrease uteroplacental blood flow and CO, and increase TPR. Mean arterial pressure (MAP), CO, cardiac index (CI), TPR, and regional blood flow to various tissues were measured using radiolabeled microspheres in the following two groups of conscious rats: normal pregnant rats (NP; n = 8) and RUPP rats (n = 8). MAP was increased (132 +/- 4 vs. 99 +/- 3 mmHg) in the RUPP rats compared with the NP dams. The hypertension in RUPP rats was associated with increased TPR (2.15 +/- 0.02 vs. 0.98 +/- 0.08 mmHg x ml(-1) x min(-1)) and decreased CI (246 +/- 20 vs. 348 +/- 19 ml x min(-1) x kg(-1), P < 0.002) when contrasted with NP dams. Furthermore, uterine (0.16 +/- 0.03 vs. 0.38 +/- 0.09 ml x min(-1) x g tissue(-1)) and placental blood flow (0.30 +/- 0.08 vs. 0.70 +/- 0.10 ml x min(-1) x g tissue(-1)) were decreased in RUPP compared with the NP dams. These data demonstrate that the RUPP model of pregnancy-induced hypertension has systemic hemodynamic and regional blood flow alterations that are strikingly similar to those observed in women with PE.     

Cardiovascular responses to forskolin in the ovine fetus

Six near-term ewes were instrumented to measure regional blood flows in the maternal and fetal subthoracic structures and allowed to recover for 5 days. Control blood flows were measured and 10(-3) molar forskolin was infused in the fetal hindlimb vein at 1 ml/min. After 10 min of infusion, maternal and fetal regional blood flows were measured. The fetal blood pressure was 44 +/- 3 mmHg in the control state and 40 +/- 4 mmHg after forskolin, P less than 0.056. The fetal renal vascular resistance changed from 24.4 +/- 2.4 to 17.5 +/- 1.7 mmHg.ml-1.min.g, P less than 0.005. The placenta had a control resistance of 27.7 +/- 5.0 and 25.6 +/- 5.1 mmHg.ml-1.min.g after forskolin, P less than 0.05. The placental membranes showed vasodilation: control resistance was 261 +/- 49 and 168 +/- 39 mmHg.ml-1.min.g after forskolin, P less than 0.02. The generalized vasodilation of the fetal circulation was paralleled in the maternal circulation. Forskolin, a lipid soluble diterpene, apparently had a placental clearance close to the theoretical maximum. Vasodilation was seen in the maternal renal, placental and uterine vasculatures. Maternal blood pressure was unchanged. Maternal placental vascular resistance was 47.4 +/- 3.0 mmHg.ml-1.min.g in the control state and 40.6 +/- 3.3 mmHg.ml-1.min.g after forskolin, P less than 0.02. Forskolin is a vasodilator in both the fetal and maternal circulations. The maintenance of a relatively normal blood pressure in the face of regional vasodilation shows that forskolin may have a positive inotropic effect on the fetal heart. These results indicate that neither the fetal nor the maternal ovine placental vasculature is maximally dilated in the control state.     

Theoretical and experimental study of the time dependent flow of red blood cell suspension through narrow pores

The Hemorheometer has been adapted to allow the recording of the flow rate during the filtration process. For newtonian fluids, the flow rate variation versus time through the pores is well approximated by Poiseuille's law. For dilute red blood cell suspensions, the same analysis can be applied by introducing the concept of "apparent filtration viscosity" which is higher than the usual viscosity measured by Couette viscometry. The apparent filtration viscosity parameter is related to the deformations undergone by red blood cells as they pass through the narrow pores. Apparent filtration viscosity can be used to obtain a precise determination of the erythrocyte deformability. Measurements performed, for a given blood sample, with pores of different diameters (5 microns, 8 microns and 12 microns) show that the error on the value of apparent filtration viscosity is less than 3%. As a result, the sensitivity of the filtration method allows to discriminate among normal blood samples. High concentrations of erythrocytes or leucocytes are found to modify the apparent filtration viscosity. These factors are apparent in the recorded filtration curves. Their effects on filtration measurements can be easily estimated.     

Osmotic gradient-induced water permeation across the sarcolemma of rabbit ventricular myocytes

The mechanism of water permeation across the sarcolemma was characterized by examining the kinetics and temperature dependence of osmotic swelling and shrinkage of rabbit ventricular myocytes. The magnitude of swelling and the kinetics of swelling and shrinkage were temperature dependent, but the magnitude of shrinkage was very similar at 6 degrees, 22 degrees, and 37 degrees C. Membrane hydraulic conductivity, Lp, was approximately 1.2 x 10(-10) liter.N-1.s-1 at 22 degrees C, corresponding to an osmotic permeability coefficient, Pf, of 16 microns.s-1, and was independent of the direction of water flux, the magnitude of the imposed osmotic gradient (35-165 mosm/liter), and the initial cell volume. This value of Lp represents an upper limit because the membrane was assumed to be a smooth surface. Based on capacitive membrane area, Lp was 0.7 to 0.9 x 10(-10) liter.N-1.s-1. Nevertheless, estimates of Lp in ventricle are 15 to 25 times lower than those in human erythrocytes and are in the range of values reported for protein- free lipid bilayers and biological membranes without functioning water channels (aquaporin). Evaluation of the effect of unstirred layers showed that in the worst case they decrease Lp by < or = 2.3%. Analysis of the temperature dependence of Lp indicated that its apparent Arrhenius activation energy, Ea', was 11.7 +/- 0.9 kcal/mol between 6 degrees and 22 degrees C and 9.2 +/- 0.9 kcal/mol between 22 degrees and 37 degrees C. These values are significantly greater than that typically found for water flow through water-filled pores, approximately 4 kcal/mol, and are in the range reported for artificial and natural membranes without functioning water channels. Taken together, these data strongly argue that the vast majority of osmotic water flux in ventricular myocytes penetrates the lipid bilayer itself rather than passing through water-filled pores.     

Effect of contraction frequency on the contractile and noncontractile phases of muscle venous blood flow.

The purpose of this study was to test the hypothesis that increasing muscle contraction frequency, which alters the duty cycle and metabolic rate, would increase the contribution of the contractile phase to mean venous blood flow in isolated skeletal muscle during rhythmic contractions. Canine gastrocnemius muscle (n = 5) was isolated, and 3-min stimulation periods of isometric, tetanic contractions were elicited sequentially at rates of 0.25, 0.33, and 0.5 contractions/s. The O2 uptake, tension-time integral, and mean venous blood flow increased significantly (P < 0.05) with each contraction frequency. Venous blood flow during both the contractile (106 +/- 6, 139 +/- 8, and 145 +/- 8 ml x 100 g-1 x min-1) and noncontractile phases (64 +/- 3, 78 +/- 4, and 91 +/- 5 ml x 100 g-1 x min-1) increased with contraction frequency. Although developed force and duration of the contractile phase were never significantly different for a single contraction during the three contraction frequencies, the amount of blood expelled from the muscle during an individual contraction increased significantly with contraction frequency (0.24 +/- 0.03, 0.32 +/- 0.02, and 0.36 +/- 0.03 ml x N-1 x min-1, respectively). This increased blood expulsion per contraction, coupled with the decreased time in the noncontractile phase as contraction frequency increased, resulted in the contractile phase contribution to mean venous blood flow becoming significantly greater (21 +/- 4, 30 +/- 4, and 38 +/- 6%) as contraction frequency increased. These results demonstrate that the percent contribution of the muscle contractile phase to mean venous blood flow becomes significantly greater as contraction frequency (and thereby duty cycle and metabolic rate) increases and that this is in part due to increased blood expulsion per contraction.     

Effect of three food types on the population growth of Brachionus calyciflorus and Brachionus patulus (Rotifera: Brachionidae).

We compared the population growth of B. calyciflorus and B. patulus using the green alga Chlorella vulgaris, baker's yeast Saccharomyces cerevisiae or their mixture in equal proportions as food. Food was offered once every 24 h in two concentrations (low: 1 x 10(6) and high: 3 x 10(6) cells ml-1) separately for each species. The experiments were terminated after 15 days. In general, at any food type or concentration, B. patulus reached a higher population density. A diet of Chlorella alone supported a higher population growth of both rotifer species than yeast alone. B. calyciflorus and B. patulus achieved highest population densities (103 +/- 8 ind. ml-1 and 296 +/- 20 ind. ml-1, respectively) on a diet of Chlorella at 3 x 10(6) cells ml-1. When cultured using the mixture of Chlorella and yeast, the maximal population densities of B. calyciflorus were lower than those grown on Chlorella. Under similar conditions, the maximal abundance values of B. patulus were comparable in both food types. Regardless of food type and density the rate of population increase per day (r) for B. calyciflorus varied from 0.13 +/- 0.03 to 0.63 +/- 0.04. These values for B. patulus ranged from 0.19 +/- 0.01 to 0.37 +/- 0.01. The results indicated that even though Chlorella was a superior food for the tested rotifers, yeast can be effectively used at low concentrations to supplement algal requirements in rotifer culture systems.     

Systemic and regional hemodynamic effects of angiotensin-(1-7) in rats

The systemic and regional hemodynamics effects of ANG-(1-7) were examined in urethane-anesthetized rats. The blood flow distribution (kidneys, skin, mesentery, lungs, spleen, brain, muscle, and adrenals), cardiac output, and total peripheral resistance were investigated by using fluorescent microspheres. Blood pressure and heart rate were recorded from the brachial artery. ANG-(1-7) infusion (110 fmol x min(-1) x 10 min(-1) iv) significantly increased blood flow to the kidney (5.10 +/- 1.07 to 8.30 +/- 0.97 ml x min(-1) x g(-1)), mesentery (0.73 +/- 0.16 to 1.17 +/- 0.49 ml x min(-1) x g(-1)), brain (1.32 +/- 0.44 to 2.18 +/- 0.85 ml x min(-1) x g(-1)), and skin (0.07 +/- 0.02 to 0.18 +/- 0.07 ml x min(-1) x g(-1)) and the vascular conductance in these organs. ANG-(1-7) also produced a significant increase in cardiac index (30%) and a decrease in total peripheral resistance (2.90 +/- 0.55 to 2.15 +/- 0.28 mmHg x ml(-1) x min x 100 g). Blood flow to the spleen, muscle, lungs, and adrenals, as well as the blood pressure and heart rate, were not altered by the ANG-(1-7) infusion. The selective ANG-(1-7) antagonist A-779 reduced the blood flow in renal, cerebral, mesenteric, and cutaneous beds and blocked the ANG-(1-7)-induced vasodilatation in the kidney, mesentery, and skin, suggesting a significant role of endogenous ANG-(1-7) in these territories. The effects of ANG-(1-7) on the cerebral blood flow, cardiac index, systolic volume, and total peripheral resistance were partially attenuated by A-779. A high dose of ANG-(1-7) (11 pmol x min(-1) x 10 min(-1)) caused an opposite effect of that produced by the low dose. Our results show for the first time that ANG-(1-7) has a previously unsuspected potent effect in the blood flow distribution and systemic hemodynamics.     

Hyperglycemia reduces coronary collateral blood flow through a nitric oxide-mediated mechanism

We tested the hypothesis that hyperglycemia alters retrograde coronary collateral blood flow by a nitric oxide-mediated mechanism in a canine Ameriod constrictor model of enhanced collateral development. Administration of 15% dextrose to increase blood glucose concentration to 400 or 600 mg/dl decreased retrograde blood flow through the left anterior descending coronary artery to 78 +/- 9 and 82 +/- 8% of baseline values, respectively. In contrast, saline or L-arginine (400 mg x kg(-1) x h(-1)) had no effect on retrograde flow. Coronary hypoperfusion and 1 h of reperfusion decreased retrograde blood flow similarly in saline- or L-arginine-treated dogs (76 +/- 11 and 89 +/- 4% of baseline, respectively), but these decreases were more pronounced in hyperglycemic dogs (47 +/- 10%). L-arginine prevented decreases in retrograde coronary collateral blood flow during hyperglycemia (100 +/- 5 and 95 +/- 6% of baseline at blood glucose concentrations of 400 and 600 mg/dl, respectively) and after coronary hypoperfusion and reperfusion (84 +/- 14%). The results suggest that hyperglycemia decreases retrograde coronary collateral blood flow by adversely affecting nitric oxide availability.     

Efficiency of particle retention and clearance rate in the polychaete Sabellaria alveolata L

The development of Sabellaria alveolata, a gregarious reef-building polychaete species, is maximal in Mont-Saint-Michel Bay (France), where trophic capacity is now threatened by increasing shellfish farming. As no data are available concerning the ecophysiological response of this species, the purpose of the present study was to obtain clearance rate and retention efficiency values to provide a first order of magnitude for the trophic role of this species. Data were obtained using a flow-through system with novel troughs suitable for 225 cm2 reef blocks containing a mean number of 940 +/- 102 (S.E.) individuals. The experimental diet used consisted of a mixture of two live microalgae, Skeletonema costatum (3800 cell ml-1) and Isochrysis galbana (23,700 cell ml-1), chosen to cover a broad size range (2 to 16 microns equivalent spherical diameter, ESD), as determined by a particle counter. On the basis of a mean clearance rate of 0.7 lh-1 obtained with reef blocks, the mean rate for an individual was estimated at 7.5 x 10(-4) L h-1. Particles larger than 6 microns ESD were cleared with 100% efficiency, but S. alveolata was unable to retain particles smaller than 2 microns ESD. The results are compared with data obtained for other polychaete species, and clearance rate values are extrapolated to an entire reef.     

Interdependence of bronchial circulation and clearance of 99mTc-DTPA from the airway surface.

The extent to which the systemic vasculature is involved in soluble-particle uptake in the conducting airways has not been studied extensively. In anesthetized, ventilated sheep, 6-10 microl of technetium-99m-labeled diethylenetriamine pentaacetic acid (99mTc-DTPA) was delivered through a microspray nozzle to a fourth-generation airway. Perfusion of the cannulated bronchial artery was varied between control flow (0.6 ml x min(-1) x kg(-1)), high flow (1.8 ml x min(-1) x kg(-1)) or no flow (the infusion pump was stopped). Airway retention of the radioactive tracer was monitored using gamma camera imaging, and venous blood was sampled. During control perfusion, tracer retention at the site of deposition at 30 min averaged 20 +/- 6% (n = 7). With no flow, retention was significantly elevated to 32 +/- 8% (P = 0.03). In another group of sheep (n = 5) with a control retention of 13 +/- 4%, high flow resulted in an increase in tracer (25 +/- 4%; P = 0.04). Maximum blood uptake of tracer was calculated by estimating circulating blood volume and averaged 16% of total activity during control flow. Only during high-flow conditions was 99mTc-DTPA in the blood decreased (10%; P = 0.04). Most of the tracer was cleared by mucociliary clearance as visualized by imaging. This component was substantially decreased during no flow. The results demonstrate that both decreased and increased airway perfusion limit removal of soluble tracer applied to the conducting airways.     

Effects of maturation and aging on collateral ventilation in sheep

We studied collateral ventilation as a function of age by measuring the resistance (Rcoll) and time constant (Tcoll) of collateral airflow in young (2-10 mo), mature (16-24 mo), and old sheep (6-13 yr). Rcoll was 0.50 +/- 0.11 cmH2O X ml-1 X min (SE) in young sheep and decreased significantly to 0.05 +/- 0.02 and 0.02 +/- 0.01 cmH2O X ml-1 X min in mature and old sheep, respectively. Tcoll was 34.4 +/- 7.9 (SE) s in young sheep and decreased to 5.7 +/- 0.9 and 10.2 +/- 3.1 s in mature and old sheep, respectively. We conclude that a marked decrease in Rcoll and Tcoll occurs between birth and maturity but changes little with further aging. In the young an increased resistance and time constant of collateral airflow may accentuate ventilation perfusion imbalance and impair the removal of secretions in disease states.     

Heterogeneous responses of human limbs to infused adrenergic agonists: a gravitational effect?

Unlike quadrupeds, the legs of humans are regularly exposed to elevated pressures relative to the arms. We hypothesized that this "dependent hypertension" would be associated with altered adrenergic responsiveness. Isoproterenol (0.75-24 ng x 100 ml limb volume-1 x min-1) and phenylephrine (0.025-0.8 microg x 100 ml limb volume-1 x min-1) were infused incrementally in the brachial and femoral arteries of 12 normal volunteers; changes in limb blood flow were quantified by using strain-gauge plethysmography. Compared with the forearm, baseline calf vascular resistance was greater (38.8 +/- 2.5 vs. 26.9 +/- 2.0 mmHg x 100 ml x min x ml-1; P < 0.001) and maximal conductance was lower (46.1 +/- 11.9 vs. 59.4 +/- 13.4 ml x ml-1 x min-1 x mmHg-1; P < 0.03). Vascular conductance did not differ between the two limbs during isoproterenol infusions, whereas decreases in vascular conductance were greater in the calf than the forearm during phenylephrine infusions (P < 0.001). With responses normalized to maximal conductance, the half-maximal response for phenylephrine was significantly less for the calf than the forearm (P < 0.001), whereas the half-maximal response for isoproterenol did not differ between limbs. We conclude that alpha1- but not beta-adrenergic-receptor responsiveness in human limbs is nonuniform. The relatively greater response to alpha1-adrenergic-receptor stimulation in the calf may represent an adaptive mechanism that limits blood pooling and capillary filtration in the legs during standing.     

Hormonal interactions and renal function during mechanical ventilation and ANF infusion in humans

To investigate the influence of atrial natriuretic factor (ANF) on renal function during mechanical ventilation (MV), we examined the renal and hormonal responses to synthetic human ANF infusion in eight patients during MV with zero (ZEEP) or 10 cmH2O positive end-expiratory pressure (PEEP). Compared with ZEEP, MV with PEEP was associated with a reduction in diuresis (V) from 208 +/- 51 to 68 +/- 11 ml/h (P less than 0.02), in natriuresis (UNa) from 12.4 +/- 3.3 to 6.2 +/- 2.1 mmol/h (P less than 0.02), and in fractional excretion of sodium (FENa) from 1.07 +/- 0.02), 0.21 to 0.67 +/- 0.17% (P less than 0.02) and with an increase in plasma renin activity (PRA) from 4.83 +/- 1.53 to 7.85 +/- 3.02 ng.ml-1.h-1 (P less than 0.05). Plasma ANF levels markedly decreased during PEEP in four patients but showed only minor changes in the other four patients, and mean plasma ANF levels did not change (163 +/- 33 pg/ml during ZEEP and 126 +/- 30 pg/ml during PEEP). Glomerular filtration rate and renal plasma flow were unchanged. Infusion of ANF (5 ng.kg-1.min-1) during PEEP markedly increased V and UNa by 110 +/- 61 and 107 +/- 26%, respectively, whereas PRA decreased from 7.85 +/- 3.02 to 4.40 +/- 1.5 ng.ml-1.min-1 (P less than 0.05). In response to a 10 ng.kg-1.min-1 ANF infusion, V increased to 338 +/- 79 ml/h during ZEEP but only to 134 +/- 45 ml/h during PEEP (P less than 0.02), whereas UNa increased, respectively, to 23.8 +/- 5.3 and 11.3 +/- 3.3 mmol/h (P less than 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cellular composition of the cyclic corpus luteum of the cow

The cellular composition of CL from 6 cows on approximately Day 12 of the oestrous cycle, after synchronization with cloprostenol, was studied by ultrastructural morphometry. Point-count measurements of volume density (mean +/- s.d.) showed that large luteal cells occupied 40.2 +/- 7.0% of the luteal tissue, and small luteal cells 27.7 +/- 6.3%. Of the total of 393.4 +/- 52.0 x 10(3) cells per mm3 of luteal tissue, large luteal cells made up only 3.5% and small luteal cells 26.7%, a ratio of 1:7.6. Endothelial cells/pericytes, at 52.3%, were the most numerous cell type. The mean volume per large luteal cell was 29.6 +/- 6.3 x 10(3) microns 3, while that of small luteal cells was 2.7 +/- 0.4 x 10(3) microns 3. In spherical form, these volumes would represent mean diameters of 38.4 microns and 17.2 microns respectively, and are consistent with published measurements on dispersed luteal cells. However, the values for cell numbers are much higher than published values based on luteal tissue dispersion, suggesting that dispersion may result in substantial and possibly selective losses of luteal cells.