Large Scale,Analytical Method for Isolating Basal Lateral Plasma Membranes from Rat Duodenum

A procedure is described for obtaining large amounts of basal lateral plasma membranes from the rat duodenal epithelium. The yield is approximately 50%, and the purification factor is 18; preparations from 25 rats routinely contain 100 mg of protein. The procedure depends on mild homogenization with a nitrogen cavitation bomb, followed by removal of brush borders by sedimentation in a weak centrifugal field. Basal lateral membranes in the resulting supernatant are partially purified by differential centrifugation in a medium which approximates their equilibrium density, and then further purified by equilibrium density gradient centrifugation in a high capacity zonal rotor. Brush border membranes may be isolated from the 450 x g pellet. Since both brush border and basal lateral membranes may be isolated from the same homogenate, this preparative procedure is suitable for such analytical purposes as determinations of distributions of enzyme activities between the two surfaces of the epithelium. The large scale of the isolation procedure makes it an appropriate starting point for purification of specific basal lateral membrane components.     

Methods to Maximize Retention in Weight Loss Studies

GREENWAY, FRANK L., GEORGE A. BRAY, AND ROBERT L. MARLIN. Methods to maximize retention in weight loss studies. Obes Res. Objective: Dropouts from clinical trials decrease quality and increase costs. Free participation, paid participation, and contingency contracting are three study retention methods. Contingency contracting, or depositing a fee to be refunded contingent upon attendance in a clinical trial, has been reported to decrease dropouts without affecting weight loss. These three methods of retention were compared with a commercial weight loss clinic's practice of charging non-refundable fees. Methods and Procedures: Dropouts were compared in two studies testing mazindol, with one study using free care and the other using contingency contracting; two studies testing phenylpropanolamine, one using free care and the other using contingency contracting; and in studies with phenylpropanolamine on file with Thompson Medical Company using free care, paid participation, and contingency contracting. Results: The dropout rate was 50% at 8 weeks in a trial of mazindol with free care vs. 7% for contingency contracting (p <0. 001). The two phenylpropanolamine studies gave the same weight losses, but the dropouts were 37% at 8 weeks for free care vs. 11 % for contingency contracting (p<0. 001). The studies of phenylpropanolamine on file at the Thompson Medical Company had 28% dropouts at 8 weeks using free care vs. 19% for paid participation (p<0. 001), and 11% for contingency contracting (p<0.005). Dropouts with contingency contracting (11%) were not different from the commercial weight loss program (13%). Discussion: Contingency contracting can decrease dropouts, improve quality, and decrease costs without affecting weight loss in clinical trials for obesity.     

The Green sea turtle (Chelonia mydas): mating, nesting and hatching on a farm

The collection of eggs from wild rookeries for incubation and hatching on the Mariculture Ltd farm on Grand Cayman Island, BWI, was described in the previous paper. It was realized, however, that this method of stocking the farm must sooner or later be superseded by the production of farm-laid eggs, and at an early stage a start was made on the task of establishing a breeding colony. The necessary collection of adult turtles and progress in breeding to the end of 1973 is described in the present paper.     

Stimulation of bone resorption in organ culture by salt-free extracts of Solanum glaucophyllum.

Addition of a desalted aqueous extract made from dried leaves of Solanum glaucophyllum produced a marked stimulation of bone resorption in a culture system in vitro. This result indicates that, like the biologically active forms of vitamin D, the active material in the plant not only stimulates intestinal calcium absorption but increases bone mobilization as well.     

Body macronutrient composition is predicted by lipid and not protein content of the diet

Diet is an important determinant of fitness‐related traits including growth, reproduction, and survival. Recent work has suggested that variation in protein:lipid ratio and particularly the amount of protein in the diet is a key nutritional parameter. However, the traits that mediate the link between dietary macronutrient ratio and fitness‐related traits are less well understood. An obvious candidate is body composition, given its well‐known link to health. Here, we investigate the relationship between dietary and body macronutrient composition using a first‐generation laboratory population of a freshwater fish, the three‐spine stickleback (Gasterosteus aculeatus). Carbohydrate is relatively unimportant in the diet of predatory fish, facilitating the exploration of how dietary protein‐to‐lipid ratio affects their relative deposition in the body. We find a significant effect of lipid intake, rather than protein, on body protein:lipid ratio. Importantly, this was not a result of absorbing macronutrients in relation to their relative abundance in the diet, as the carcass protein:lipid ratios differed from those of the diets, with ratios usually lower in the body than in the diet. This indicates that individuals can moderate their utilization, or uptake, of ingested macronutrients to reach a target balance within the body. We found no effect of diet on swimming endurance, activity, or testes size. However, there was an effect of weight on testes size, with larger males having larger testes. Our results provide evidence for the adjustment of body protein:lipid ratio away from that of the diet. As dietary lipid intake was the key determinant of body composition, we suggest this occurs via metabolism of excess protein, which conflicts with the predictions of the protein leverage hypothesis. These results could imply that the conversion and excretion of protein is one of the causes of the survival costs associated with high‐protein diets.     

Highly purified basal lateral plasma membranes from rat duodenum. Physical criteria for purity

Summary Preparations of intestinal epithelial cell basal lateral plasma membranes were analyzed with free flow electrophoresis and density pertubation with digitonin. The initial basal lateral membrane preparations were obtained by equilibrium density gradient centrifugation after two different schemes of homogenization and differential sedimentation (A.K. Mircheff, C.H. van Os, and E.M. Wright. 1978.Membr. Biochem. 1: 177, and A.K. Mircheff, S.D. Hanna, M.W. Walling, and E.M. Wright. 1979.Prep. Biochem. 9:33. In these preparations, Na,K-ATPase, a marker for the basal lateral mambrane, was purified 16- to 18-fold over the initial homogenate. The preparations were also enriched in NADPH-cytochromec reductase, alkaline phosphatase, acid phosphatase, and galactosylstransferase.Both free-flow electrophoresis, which separates on the basis of surface charge, and density perturbation with digitonin, which depends on a specific interaction of digitonin with cholesterol-rich membranes, resolved the preparation into three populations of particles. The major population, which represented basal lateral membranes purified 20- to 32-fold with respect to the initial homogenate, contained Na,K-ATPase, alkaline phosphatase, adenylate cyclase, and acid phosphatase. A second population was defined by its content of NADPH-cytochromec reductase, and the third was defined by its content of galactosyltransferase. Guanylate cyclase appeared to be partitioned between the Na,K-ATPase-rich and NADPH-cytochromec reductase-rich populations. Galactosyltransferase is also present in fractions which contain the Na,K-ATPase-rich membranes, but the present data cannot exclude the possibility of spillovers by the adjacent, galactosyltransferase-rich population. This work emphasize the importance of multiple, physical criteria for purity in the isolation of subcellular components.