Summary. The absorption of cholesterol has been studied in man by perfusing the upper jejunum with a micellar solution of bile salt, 1-monoglyceride, and cholesterol-14C, with a triple lumen tube with collection sites 50 cm apart. The absorption of micellar components between the collection sites was calculated from their concentration changes relative to those of the watersoluble marker, polyethylene glycol. Control experiments were performed with cholesterol-free perfusions of saline or bile salt-monoglyceride solutions. Steady state conditions were obtained.Each of the components of the micelle was absorbed to a different extent during passage through the test segment of jejunum. Bile salt was not absorbed (mean, -3%), but micellar monoglyceride was rapidly hydrolyzed and absorbed almost completely (mean, 98%). Cholesterol radioactivity was absorbed to an intermediate extent (mean, 73%), and the absorption of chemically determined cholesterol (mean, 46%) indicated that much of the disappearance of radioactivity represented true absorption and not simple exchange.The specific activity of the perfused cholesterol fell during passage through the loop. This fall was interpreted as signifying the continuous addition of nonradioactive endogenous cholesterol by the test segment. However, the decrease in specific activity may also be considered to signify exchange, in that nonradioactive molecules entered the lumen as radioactive molecules were absorbed. Plant sterols appeared in the intestinal contents during the perfusion and must have been contributed by the perfused segment.The perfusate and samples taken from the upper and lower collection sites were examined by ultracentrifugation to define the physical state of cholesterol. It was found that cholesterol in the perfusate or upper collection site samples did not sediment, but that 23% of the cholesterol in the lower collection site samples was sedimentable (mean of three experiments); bile salt, as control, was not sedimentable. Solubility experiments in model systems showed that cholesterol possessed low solubility in bile salt solution; its solubility increased markedly and in linear proportion to the amount of

No abstract

A B S T R A C T In 35 patients maintained solely on liquid formula diets, chromic oxide has been evaluated as an internal standard for balance studies that require stool collections. In 28 patients the excretion of chromic oxide was ideal: steady states were attained in which mean daily output was 90% (or more) of mean daily intake. In these patients corrections for fecal flow could validly be applied.In patients who excreted the marker ideally, the availability of chromic oxide balance data made possible the calculation of pool sizes and turnover rates of unexcreted intestinal content. These indexes bore little relationship to the usual clinical descriptions of bowel habits. In some patient who had daily bowel movements, pool sizes were very large and daily turnover was small, i.e., a large proportion of the colonic contents was not excreted for surprisingly long periods. It is critically important for investigators to recognize this possibility when carrying out balance studies for fecal constituents that may be altered by bacterial action within the gut lumen: for instance, in 6 patients a significant inverse correlation was found between daily fecal turnover and degradative losses of large amounts of dietary /8-sitosterol.

In acute pulmonary oedema caused by lung irritants such as phosgene, pleura effusion is often observed. The fluid in the pleural cavities has a high protein content and is thought to come from the alveoli. If recovery occurs this fluid should, therefore, be absorbed chiefly by the pleural lymphatics. Little, however, is known of the rate of absorption of fluids from the pleural cavities, since most experimental studies have been concerned with suspended particles.In 1894, Starling & Tubby, experimenting upon anaesthetized dogs for periods up to 6 hr., showed that the dyestuffs indigo carmine and methylene blue were readily absorbed from the pleural cavities, appearing in the urine before the thoracic duct lymph, and in thoracic duct lymph only in concentrations approximating those in the plasma. They found that pleural fluid composition was so altered as to establish equilibrium with plasma values, as shown by decreased dye colour in residual pleural fluid, or falling glucose or saline concentrations when hypertonic solutions were injected. When hypertonic solutions were used, more fluid was recovered after 2-3 hr. than originally injected. In two out of three experiments with undiluted defibrinated blood, more fluid was recovered than originally injected. In the other experiment 10% of injected fluid was removed in 2 hr. In another experiment 6% of a mixture of equal parts serum and saline was removed in 2 hr. The total fluid injected varied in different experiments from 30 to 50 c.c. in dogs of 4-8 kg. weight.The results obtained by Starling & Tubby are quoted in some detail since they represent the main source, for the past 50 years, of quantitative information on pleural absorption. Drinker & Yoffey (1941) reviewed the available literature and concluded that lymphatic drainage of the pleural sacs is a slow process, and that one may expect the removal of exudates and transudates to be directly related to their protein concentrations, whole blood disappearing more slowly than diluted serum. They also suggest that, as in the case of the lungs, respiratory movements are of great importance in bringing about lymphatic absorption from the pleural sacs.

No abstract