Postresonance electromagnetic absorption by man and animals

A surface integral equation (SIE) method is used to calculate the specific absorption rate (SAR) in spherically capped cylindrical models irradiated by an axially incident electromagnetic plane wave (K polarization) in a frequency range for which calculations previously have not been available (80–400 MHz for man models). In the SIE method, the electromagnetic (EM) field relations are formulated in terms of electric and magnetic currents on the surface of the model. The average SAR is calculated from the far scattered EM fields by means of the forward scattering theorem. SAR data calculated by the SIE method agree with data calculated by the extended boundary condition method (EBCM) for frequencies up to 80 MHz (the upper frequency limit of the EBCM) for man models. For rat models exposed to 1–3 GHz radiation, reasonable agreement was also obtained with the limited experimental data available.     

The effects of zinc deficiency on pancreatic carboxypeptidase activity and protein digestion and absorption in the rat

1. Proteolytic enzyme activities were examined in the pancreas of zinc-deficient and control rats. 2. No change was detected in trypsin-plus-chymotrypsin activity. 3. Carboxypeptidase activity was appreciably lowered in zinc deficiency and returned rapidly to normal on zinc therapy. 4. In experiments in which U-¹⁴C-labelled Chlorella protein was fed no evidence was obtained which suggested that the reduction in carboxypeptidase activity had limited the rate of protein digestion or absorption. 5. The specific activity of pancreatic protein synthesized during these experiments was appreciably lower in zinc-deficient than in control rats. 6. A higher proportion of the total activity present, in each organ examined, was in the non-protein fraction in zinc-deficient rats.     

Comparative aspects of protein digestion and amino acid absorption in fish and other animals

1. Molar concentrations of amino acids in the content of subsequent parts of alimentary tract of rainbow trout and common carp have been calculated. 2. The ratio of free amino acid concentration in intestinal content to blood of carp most commonly was between 10 and 20 and decreased as digestion proceeded. 3. Free amino acid concentration in gut content of fish appeared several times higher than that in reptiles or mammals. 4. Absorption rate of amino acids in carp was most intense during the first 3 hr after feeding and generally similar to that found in caymans. 5. Release rate of amino acids from dietary protein was most intense in the second segment of carp intestine where most of amino acids were also absorbed. 6. Requirements of essential amino acids based on their absorption rate were determined.     

New techniques for studying digestion and absorption of nutrients by ruminants

Physical constraints on ruminal digestion have received concentrated research attention in the past 10 years. With scanning electron microscopy, microbial attack and digestion of forage components in the rumen have been observed. Limits to passage through the digestive tract have been explored with digesta flow markers and particle-sizing devices. Diet composition analysis has been simplified by near-IR reflectance. NMR procedures, and histological indexing. Rumen microbial function and genetics are being examined by new procedures and genetically altered microbes are being used for production of specific nutrients. Isolated microbial enzymes are being used in feed analysis. The site of digestion in vivo has received detailed attention with new cannula designs, digesta flow markers, and constitutive microbial markers. Ruminants are being maintained by intragastric or i.v. infusion of purified nutrients to quantitate nutrient requirements. Static and dynamic models of digestive function are aiding in the interpretation of research data. Unfortunately, many new procedures have not been critically standardized against traditional methods. The complexity of certain new techniques and models complicates critical review, publication, and comprehension of research results. The most important laboratory tool for increasing research knowledge is still the alert, fertile human imagination.     

Flavanols: digestion,absorption and bioactivity

Flavanols, or flavan-3-ols, are a family of bioactive compounds present in cocoa, red wine, green tea, red grapes, berries and apples. With a basic monomer unit of (−)-epicatechin or (+)-catechin, flavanols can be present in foods and beverages as monomers or oligomers (procyanidins). Most, but not all, procyanidins are degraded into monomer or dimer units prior to absorption. The bioavailability of flavanols can be influenced by multiple factors, including food processing, cooking, digestion, and biotransformation. Flavanols are potent antioxidants, scavenging free radicals in vitro and in vivo. While some of the actions of flavanols can be linked to antioxidant activities, other modes of action may also occur, including modulation of intracellular signaling, effects on membrane fluidity and regulation of cytokine release or action. Physiologically, flavanol-rich foods and beverages can affect platelet aggregation, vascular inflammation, endothelial nitric oxide metabolism, and may confer protective effects against neurodegeneration. Epidemiological data suggests that intake of cocoa, a rich source of flavanols, is inversely associated with 15-year cardiovascular and all-cause mortality in older males. (−)-Epicatechin and its metabolite, epicatechin-7-O-glucuronide, have been identified as independent predictors of some of the vascular effects associated with the consumption of a flavanol-rich beverage. Targeted dietary components and nutrition supplements that can influence the vascular system will be of great value in the prevention and treatment of chronic disease.     

The concentration of protein solutions by normal freezing

An apparatus is described which is designed for preparative freeze concentration experiments by the technique of normal freezing. It has a capacity of approximately 22 liters distributed over twelve vessels. The influence of various geometrical and chemical parameters such as stirring speed, crystallization rate, and sample composition on the normal freezing of protein solutions are discussed. For dilute protein solutions (<0.1%) the concentration factor generally was 8- to 10-fold with recoveries of 90–100 percent. With higher protein concentrations and at ionic strengths higher than approximately 0.05, the recovery was decreased. No loss of activity was detected when concentrating enzyme solutions.     

The interaction of cholesterol absorption and cholesterol synthesis in man

The total miscible pool of cholesterol in the body is determined largely by the interaction of cholesterol absorption and synthesis. In the present study we have examined the net effects of this interplay in one normal and five hypercholesteremic subjects when various amounts of cholesterol were made available for absorption. Feeding large amounts of cholesterol to the normocholesteremic patient caused an expansion of body pools by as much as 20 g before the amount of cholesterol re-excreted as fecal neutral steroids each day came into balance with the cholesterol absorbed from the diet. There was no detectable decrease in total body synthesis of cholesterol nor any increase in conversion of cholesterol into bile acids. However, feedback control of cholesterol synthesis was demonstrable when large quantities of plant sterols were fed: in the hypercholesteremic patients thus studied, the absorption of both endogenous and exogenous cholesterol was then greatly reduced, and a compensatory increase in synthesis occurred. Thus, the plant sterol experiments, but not the cholesterol feeding experiment, demonstrated that feedback control by dietary cholesterol does occur in man. That feedback control by dietary cholesterol is relatively unimportant in man seems to be due to the fact that in the metabolic "steady state" the absorption mechanism is essentially saturated by the large amounts of endogenous cholesterol available for reabsorption. These findings demonstrate that there are important differences between man and various laboratory animals in regard to the interaction of absorption and synthesis as factors controlling the size of tissue pools of cholesterol.     

Immunological demonstration of intestinal absorption and digestion of protein macromolecules in the trout (Salmo gairdneri)

Summary An immunofluorescence technique using antibodies against the Fc and Fab fragments of human IgG (IgG_H) was used to study the absorption of proteins by the intestinal epithelial cells of rainbow trout after oral or anal administration. Cellular absorption of a high molecular weight protein, hepatitis-B surface antigen (HBsAg), was also studied by using two monoclonal antibodies, one specific for the conformation of the antigen (implying disulfide bridges), and the other that reacts with the constituent polypeptides. Both absorbed IgG_H and HBsAg were seen to be segregated in the apical vacuolar system, a characteristic feature of intestinal epithelial cells. The same antibodies were used with an everted sac technique in conjunction with immunofluorescence, to show the intravacuolar degradation of IgG_H and HBsAg following absorption. By using an antibody against cathepsin D, it was possible to demonstrate, by immunofluorescence, the localization of this enzyme in the same vacuolar system. After coupling the antibody to peroxidase or to the protein A/colloidalgold complex, the ultrastructural antigenic sites of cathepsin D could be seen to be localized in the interior of the vacuoles. The vacuolar localization of a cathepsin B activity was determined by incubating sections of intestinal mucosa, or isolated epithelial cells, with a specific synthetic substrate (Z-Ala-Arg-Arg-methoxynaphthylamide). The supranuclear hyaloplasmic vacuoles of intestinal epithelial cells may be considered to be phagolysosomes that assure the degradation of absorbed proteins. This function may be of fundamental importance in the nutritional processes of this species.