Flux ratio theorems for nonstationary membrane transport with temporary capture of tracer.

It has been shown recently that the ratio of unidirectional tracer fluxes, passing in opposite directions through a membrane which has transport properties varying arbitrarily with the distance from a boundary, is independent of time from the very first appearance of the two outfluxes from the membrane. This surprising proposition has been proved for boundary conditions defining standard unidirectional fluxes, and then generalized to classes of time-dependent boundary conditions. The operational meaning of all the resulting theorems is that when any of them appear to be refuted experimentally, the presence of more than one parallel transport pathway (that is, of membrane heterogeneity transverse to the direction of transport) can be inferred and analyzed.

Contractures complicating spinal cord injury: incidence and comparison between spinal cord centre and general hospital acute care.

One hundred and eighty-one spinal cord injured patients admitted to the Rehabilitation Institute of Chicago after acute care following a spinal cord injury were studied. The presence or absence of contractures as well as significant abnormalities with loss of range of motion greater than 15% was recorded. Patients were either admitted from general hospitals or the acute care unit of our spinal centre, Northwestern Memorial Hospital.

Extended theory of the early diffusion of multiple indicators: bounds on permeability ratios, with applications to intestinal capillaries.

The determination of ratios of capillary permeabilities to multiple indicators is secured by constructing upper bounds on effects of early back-diffusion following a single arterial injection. The analysis does not exclude highly extracted indicators, and it allows for effects of asymmetric blood-tissue exchange and of tissue concentration gradients. The concept of flow limitation of uptake is delimited operationally.

A case of spontaneous dislocated lenses.

There are a great number of causes of dislocated lenses. One such cause is the spontaneous dislocation of a mature or hypermature cataractous lens. The case of an 80-year-old black female with spontaneously dislocated lenses is reported.

Asymptotic forms of tracer clearance curves: theory and applications of improved extrapolations.

Tracer clearance curves are conventionally extrapolated beyond times of observation by using monoexponential asymptotic forms. The inadequacy of the resulting predictions, especially as to the mean transit time and quantities derived from it, has been previously demonstrated experimentally. Here improvements in extrapolations and in the resulting predictions are derived theoretically and tested on previously published data, venous as well as externally recorded.

Heterogeneity of splanchnic vascular transit times in man.

A new method of quantifying the heterogeneity of transit times through vascular beds, free from corrections for effects of recirculation, is applied to data of splanchnic transit times in eight normal subjects and three patients with cirrhosis and end-to-side portocaval shunts, as obtained by Bradley's method. There is proportionality between the heterogeneity, expressed as standard deviation and the mean transit time in the eight normal subjects. The heterogeneity of plasma transit times is not appreciably larger than that of red blood cells, despite the larger volume of distribution of plasma.

Saturation kinetics in hepatic drug removal: a statistical approach to functional heterogeneity.

Extraction of drugs and other substrates from blood passing through the intact liver (or other capillary beds), inferred from samples taken at the organ inlet and outlet, is influenced by two kinds of heterogeneity of capillaries: transverse and longitudinal with respect to the direction of blood flow. The transverse heterogeneity is exemplified by arteriovenous shunts of the extracting system; the longitudinal one by zones of liver function. These two clinically interesting examples are among transverse and longitudinal distributions of capillary properties that can be inferred from the way the organ transforms the influx of a substance (or of a pair of substances interacting via liver cells) into the outflux over a range of input concentrations or of rates of blood flow.

A Bayesian analysis of capillary heterogeneity in the intact pig liver.

Published experimental data on the steady elimination of galactose by five isolated perfused pig livers are interpreted in terms of a model of hepatic uptake, in which the functional properties of the individual liver capillaries (hepatic sinusoids) are not identical. Kinetic parameters, including the Michaelis constant for the local enzyme-substrate interaction, are determined for each preparation on the basis of this model and are compared with previously obtained values based on an earlier model in which the sinusoids were assumed to be functionally identical. Posterior distributions of the degree of functional heterogeneity and the value of the Michaelis constant are given for the case where the livers are considered as a statistically homogeneous group.

The Sdx antigen and antibody: biochemical studies on the inhibitory property of human urine.

Anti-Sdx is an IgM complement-binding autoantibody that defines a red cell antigen which is independent of I, i, Sp1 (Pr) and Gd. Hemagglutination by the antibody is unusually sensitive to variation in pH, salt, or other charged molecular species. The antibody is inhibited by urine from Sd(a+) persons, but inhibition is a nonspecific effect caused by charged molecules.

Estimates and implications of co-operativity for enzyme kinetics in the intact liver: method of flow invariants.

For substrates rapidly equilibrated between blood and liver cells, steady-state co-operative enzyme kinetics determines combinations of inlet and outlet substrate concentrations which do not change with the rate of blood flow recirculating through an isolated perfused liver. The mathematical forms of these combinations (here called flow invariants) are different for each value of the Hill co-operativity constant which can therefore be estimated, on a set of intact perfused preparations, from that flow invariant which is stochastically least dependent on experimental changes in the flow rate. This estimate, made in a narrow range of substrate concentrations, is illustrated using previously published data on the phosphorylation of galactose by galactokinase in rat liver.

Ostensible versus actual reasons for seeking pediatric attention: another look at the parental ticket of admission.

The presentation of parental anxiety that appears excessive in view of the nature of the child's "chief complaint" is a frequent occurrence in pediatric practice. This study reviews 370 sick-patient visits in one pediatric office during a three-month period. Additional questioning in the area of parental anxieties concerning these symptoms revealed that in 125 instances (33.

Capillary permeability of heterogeneous organs: a parsimonious interpretation of indicator diffusion data.

1. Calculations of capillary permeability of perfused organs from indicator diffusion data are reviewed, and reconsidered in terms of two kinds of organ heterogeneity of capillary extraction. 2.

Absolute stereochemistry and dopaminergic activity of enantiomers of 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine.

Resolution of the unique dopamine receptor agonist 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (1) was achieved by a stereospecific multistep conversion of the readily separated enantiomers of its O,O,N-trimethylated precursor 2. The absolute stereochemistry of the antipodes of 2-MeI was determined by single-crystal X-ray diffractometric analysis, thus permitting assignment of the configuration of stereospecifically related 1, as well as that of the synthetic intermediates. High-performance liquid chromatography of diastereoisomeric derivatives was utilized to determine the enantiomeric excess of the R (greater than 97%) and S (greater than 89%) isomers of 1.

A method of determining intrinsic hepatic clearance from the first-pass effect.

1. The relation between systemic hepatic clearance, intrinsic hepatic clearance and hepatic blood fow is considered from the point of view of the sinusoidal perfusion (parallel tube) model of the liver. 2.