It is shown that a rigid sphere transported along in Poiseuille flow through a tube is subject to radial forces which tend to carry it to a certain equilibrium position at about 0.6 tube radii from the axis, irrespective of the radial position at which the sphere first entered the tube. It is further shown that the trajectories of the particles are portions of one master trajectory and that the origin of the forces causing the radial displacements is in the inertia of the moving fluid. An analysis of the parameters determining the behaviour is presented and a phenomenological description valid at low Reynolds numbers is arrived at in terms of appropriate reduced variables. These phenomena have already been described in a preliminary note (Segré & Silberberg 1961). The present more complete analysis confirms the conclusions, but it appears that the dependence of the effects on the particle radius go with the third and not the fourth power as was then reported. It is also shown that the description of the phenomena becomes more complicated at tube Reynolds numbers above about 30.
Thiazolidine-4-carboxylic acid (TC) (a precursor of intracellular cysteine) was administered to rats at 50 mg/kg and at 400 mg/kg by an i.p. route and at 800 mg/kg per os, and the levels of glutathione (GSH) in gastric mucosa, gastric wall and liver were determined. GSH levels in the eyes were measured after oral administration of TC. No changes in GSH levels were observed at 50 mg/kg from 1 to 48 h. An initial increase of liver GSH levels was followed by a decrease (up to 12 h) at 400 mg/kg i.p. After oral administration of 800 mg/kg an initial increase of GSH levels in the liver and gastric mucosa was followed by a decrease (up to 24 h); the GSH levels in the gastric wall showed a persistent decrease. No significant changes were seen in the GSH levels of the eyes.
A model with two compartments (glucose and insulin) by and a negative feedback has been used to fit the values of blood glucose obtained experimentally by infusing intravenously glucose (0.5 gm. min−1) or insulin (0.055 U. min−1) for about 250 minutes. Glucose was infused to normal ambulatory or hospitalized subjects and to diabetic patients; insulin was infused to normal subjects. The model employed fits the data of all the groups. The SAAM program and a digital computer (IBM 7094) were used. The model cannot be solved completely due to the number of degrees of freedom of the system but values related to the transfer constants of the model can be computed, as the damping constant a, the natural frequency w, the natural period T and the free frequency b of the system, which shows damped oscillations in normal subjects; in diabetic patients the system passes through states of overdamping until no oscillations can be seen in the more severe cases. The effect of ten days of treatment with prednisone (25 mg. m per day, per os) has been evaluated in a group of normal subjects. Discriminant analysis between normal and diabetic subjects and between glucose and insulin infusion has been carried out by using a BMD program and a digital computer.
The kinetics of rosaprostol (9-hydroxy-19,20-bis-norprostanoic acid, Rosal) and of its metabolite (3-(2-n-hexyl-5-hydroxy-cyclopentyl)propionic acid) has been determined in plasma and in urine of 10 healthy volunteers after oral administration of 500 mg of rosaprostol. The peak of rosaprostol (of 524 ng/ml) appears at 4 h, whereas that of the metabolite (of 503 ng/ml) appears earlier (2 h); therefore the relationship between the two substances does not follow the precursor-successor relationship in plasma and a compartmental model has been used to fit the data. In this model the biotransformation process occurs before entering the central compartment (first-pass effect). The mean half-life of rosaprostol is equal to about 5 h and that of the metabolite is equal to 3 h. All of rosaprostol is biotransformed and only the metabolite is partially eliminated by the urine. The urinary excretion of the metabolite represents only a small fraction of the administered dose. The urinary clearance of the metabolite is equal to 5.3 l/h. The volume of distribution of both substances is equal to 21.2 l.
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