Substrate utilization and oxygen consumption by canine jejunal mucosa in vitro.

Oxygen consumption, carbon dioxide production, and substrate utilization by small pieces of canine jejunal mucosa have been measured in vitro. In the absence of added substrate, the Qo2 was 0.21 mumol/h per mg dry wt and the respiratory quotient (RQ) was 0.73 indicating the endogenous substrate to be lipid in nature. When glucose or galactose was added, Qo2 and RQ increased. Metabolism of the endogenous substrate was depressed by fructose but not by glucose or galactose. Less than 15% of the metabolized glucose and fructose was degraded to Co2; 80% of the metabolized glucose was recovered as lactate. Galactose disappeared at one-seventh the rate of glucose, but 40% of that metabolized was degrated to CO2. In all experiments Qo2 showed marked cyclic fluctuations with an amplitude of 30-40% of the mean value and a period of 30-40 min. For tissues from a single animal, the cycles were in phase on a clock time basis, indicating that the cycles were synchronized by some in vivo mechanism.

Countercurrent exchange of water in canine jejunum.

The possibility of countercurrent exchange of water molecules in canine intestinal villi has been examined. Tritium-labeled water (3H2O) molecules were introduced either into the fluid lavaging the intestinal lumen or into the arterial blood supply for varying periods of time. Quickly frozen samples of intestinal tissue were sectioned such that isotopic concentrations at the villus tip, midvillus, villus base, and underlying submucosa and muscle could be determined. The villus concentration gradients observed were consistent with the existence of a countercurrent exchange but could also be explained by alternative arrangements. More convincing evidence of a countercurrent was obtained from experiments in which [14C]inulin was introduced simultaneously with 3H2O into the intestinal artery. The villus tip-to-base concentration ratio for 3H2O was less than one while the ratio for inulin was greater than one, thus vitiating the alternative explanations and leading to the conclusion that the labeled water molecules must have undergone a countercurrent exchange.

Unstirred water layer in canine jejunum.

The thickness of the unstirred water layer in in vivo-lavaged canine jejunum has been estimated by observations on the kinetics of entrance of [14C]inulin into the intervillus space (IVS) from the luminal fluid. Concentrations of the inulin in the IVS at three different levels (upper, 350 micrometers; middle, 250 micrometers; and lower, 250 micrometers) were determined as a function of duration of lavage. The concentrations rose slowly, indicating that there was little or no convective mixing of the fluid between the villi. After 1-2 h of lavage, mean concentrations in the IVS were three to seven times higher than in the lavage fluid, indicating that water absorption occurred from the IVS and that solvent drag as well as diffusion played a role in the entrance of inulin into the IVS. Because the concentration was always greatest at the uppermost level of the IVS, water absorption from the IVS must have been restricted to that level. Analysis of the data also required the inclusion of a small secretory stream (5% of the absorptive flow) from the crypts to explain the experimental observations. The results demonstrate that substances absorbed into the villus tips must penetrate an unstirred layer of 500-1,000 micrometers; for those absorbed into the lateral surfaces of the villi, an additional barrier of as much as 800 micrometers exists.

The gravimetric method for the determination of residual moisture in freeze-dried biological products.

The gravimetric test for the determination of residual moisture in freeze-dried biological products performed in a humidity- and temperature-controlled room with the use of scrupulous gravimetric analytical technique can be used to accurately determine residual moisture in freeze-dried biological products such as antihemophilic factor (human) or honey bee venom allergenic extract. This method determines the first water of hydration of sodium tartrate dihydrate (7.93%) to within 1.3% of the calculated value with a relative standard deviation of 0.3% for 10 replicates. For this gravimetric procedure, freeze-dried samples containing from 1.12 to 4.4% residual moisture had relative standard deviations ranging from 3.6 to 9.1%. Samples containing less than 1.0% residual moisture by the gravimetric method such as intravenous immune globulin and antihemophilic factor (human) had relative standard deviations ranging from 16.7 to 47.0%. Relative standard deviations for residual moisture tests performed on comparable samples by the Karl Fischer and thermogravimetric methods showed similar variability.