Nathan Lifson

Theory of use of the turnover rates of body water for measuring energy and material balance

Abstract The theory is developed for the use of the isotopically determined turnover rates of the hydrogen and oxygen of body water for measurement of total energy and material balance of an animal. After a consideration of several simplifying assumptions, a summary is given of tests of the extent to which theoretical expectations are realized. The results of these appear to be in general accord with theoretical expectations.

Regional tissue uptake of D2O in perfused organs: rat liver, dog heart and gastrocnemius.

Regional tissue D2O concentrations were measured in the isolated dog heart, dog gastrocnemius and rat liver following relatively brief perfusions with D2O-labeled fluid. Results indicate heterogeneity of tissue concentrations in all three organs. A venous outflow concentration curve for the liver was reconstructed on the assumptions that each regional tissue sample represented an equally probable portion of a composite organ and that in each region D2O transport was flow-limited. The agreement between this curve and the observed outflow curve was sufficiently good to suggest that the discrepancies between the observed venous curve and that for the theoretical case of a completely flow-limited organ can be largely explained for the liver by macroscopic regional perfusion heterogeneity without invoking microscopic tissue transport limitation. In the case of the heart and the gastrocnemius, the observed macroscopic tissue heterogeneity was insufficient to account for the discrepancies between the respective venous outflow concentration curves and the theoretical case. However, in the heart, regions of low tissue concentration were apparently systematically missed in the sampling procedure. The actual heterogeneity in both organs was probably underestimated.

Note on the blood supply of the ducts of the rabbit pancreas

Abstract The adventitia of the pancreatic ducts contains extensive vascular plexuses. Microscopic examination of rabbit pancreases injected with various materials (silicone latex, India ink, hematoxylin, microspheres) has led to the following conclusion: The blood entering the plexuses is venous blood draining from the acini, and the blood leaving the plexuses drains into the extralobular pancreatic veins. A possibly unique feature of the pancreatic circulation is that a significant fraction of pancreatic blood flows through four vascular exchange beds in series before returning to the heart: islets of Langerhans → acinar capillaries → ductal plexuses → hepatic sinusoids.

Determination of the Total Carbon Dioxide Outputs of Rats By the D2O18 Method

The doubly-labeled water (D2O18) method for measuring CO2 output has been tested in eight rats by comparing the value obtained by this procedure with the total CO2 actually collected. The average absolute discrepancy between the two values was 3 (±3)%, and the average discrepancy when account was taken of algebraic sign was +2 (±4)%. (The values in parentheses are standard deviations of the distributions.)

Determination of Evans Blue Dye in Blood and Tissues.

Summary 1. A method is described for determination of Evans blue dye in various animal tissues. In brief it consists of (1) homo-genization of tissue in a concentrated solution of urea, (2) splitting of the Evans blue-protein complex and partial precipitation of protein and chromogens with acetone, and (3) complete precipitation of chromogens by addition of Somogyi reagents. 2. The method has been employed to follow the fate of the dye after intravenous injection into rats. After such administration of 12.5 mg of Evans blue, about 90% of the injected dye apparently left the blood but only about 15% could not be recovered from the body in 40 hours. At 140 hours after injection about 67% of the injected dye could still be recovered from the body.

Simple Method for Visualization of the Islets in Fixed But Otherwise Intact Pancreas

A simple, inexpensive, reproducible method is described for prominently displaying the islets of Langerhans. The method consists of sequential arterial perfusion of the organ of the sacrificed animal with saline, formalin, hematoxylin, and water, followed by clearing in methyl salicylate. The procedure should be useful whenever islet tissue needs to be quantitatively distinquished from non islet tissue and fixation is allowable.

Support of Water Absorption by Rat Jejunum in vitroby Glucose in Serosal Fluid

Summary Glucose in the Ringers fluid bathing the serosal surface supports water absorption by isolated jejunal loops of rat intestine. The rate of water absorption increased with increasing glucose concentration up to 1/2 isosmotic. This maximum rate was about 65% of that found when 1/10 isosmotic glucose was present in the Ringers fluid bathing the mucosa.

Heterogeneity of macroscopic and single villus blood flow in rabbit small intestine.

Abstract Heterogeneity of single villus blood flow in the small intestine was estimated from frequency distributions of 9-μm microspheres per villus in villus fields of 100–200 villi. The microspheres, which were nonradioactive, were administered, with or without 26-μm spheres in addition, by a brief injection into the left ventricle of unfasted, anesthetized rabbits. The spheres were counted and localized microscopically in cleared pieces of jejuno-ileum. It was found that gamma distributions of single villus flow would generate frequency distributions of beads per villus similar to those observed when the average villus contained up to four beads. This agreement, together with other relevant information, suggests the following view: The frequency distribution of values of single villus flow in a small area is unimodal, is skewed toward the high flow direction, has a coefficient of variation of, at most, 0.5–0.6, and is approximated by a gamma distribution. Reasons are given for believing that the coefficient of variation may be significantly smaller. The dispersion of values for total perfusion and its distribution to the layers of the intestine in small (about 25 mm 2 ) adjacent macroscopic pieces of intestine typically had a coefficient of variation of 0.2–0.3.

Validation study of D218O method for determination of CO2 output of the eastern chipmunk (Tamais striatus)

Abstract o 1. The doubly labeled water (D 2 18 O) method for measuring CO 2 output has been tested in two eastern chipmunks ( Tamias striatus ) by comparing over a 5-day period the value calculated by this procedure with the value actually collected. 2. The error of the D 2 18 O method was 1 and 8 per cent for the two chipmunks studied. 3. The method appears to have the same applicability to this species as to the previously studied small mammals and birds.

Metabolism of C13-carboxyl-labeled malonate by the intact mouse.

Summary When C13 - carboxyl - labeled malonate was injected subcutaneously into mice, 20-32% of the labeled carbon was recovered in the respiratory carbon dioxide in 6 hours. At body temperature, dog plasma showed little or no ability to decarboxylate malonate. These results are interpreted to indicate the probable occurrence in mammalian cells of enzymatic mechanisms for conversion of malonate to carbon dioxide.