An evaluation of four methods for measuring cholesterol absorption by the intestine in man

Critical comparisons have been made in 12 patients of four methods for measuring cholesterol absorption from the intestine. Methods I-III depend on the use of labeled cholesterol (intravenously or continuous labeling orally) in conjunction with sterol balance measurements; Method IV can be carried out with only a single test dose containing labeled cholesterol plus labeled beta-sitosterol. In the latter technique absorption is calculated as the loss of cholesterol relative to beta-sitosterol during intestinal transit. Method III (isotopic steady-state method) proved to be undependable because of uncertainties in determining the existence of an isotopic steady state. However, Method IV gave good agreement with Methods I and II, and it appears to have certain practical as well as theoretical advantages. Although Method IV requires collections of stools for up to 8 days, it is nevertheless the most rapid and the simplest of all the methods for estimating absorption. It can also be used in certain situations, such as in fur-licking animals, when Methods I and II are inadequate. Therefore, this method would seem to be a valuable addition to other isotopic techniques for estimating cholesterol absorption in man.     

Effects of dietary cholesterol on the regulation of total body cholesterol in man

Studies on the interaction of cholesterol absorption, synthesis, and excretion were carried out in eight patients using sterol balance techniques. Absorption of dietary cholesterol was found to increase with intake; up to 1 g of cholesterol was absorbed in patients fed as much as 3 g per day. In most patients, increased absorption of cholesterol evoked two compensatory mechanisms: (a) increased reexcretion of cholesterol (but not of bile acids), and (b) decrease in total body synthesis. However, the amount of suppression in synthesis was extremely variable from one patient to another; one patient had no decrease in synthesis despite a large increment in absorption of dietary cholesterol, and two patients showed a complete suppression of synthesis. In the majority of cases the accumulation of cholesterol in body pools was small because of adequate compensation by reexcretion plus reduced synthesis, but in a few patients large accumulations occurred on high cholesterol diets when absorption exceeded the compensatory mechanisms. These accumulations were not necessarily reflected in plasma cholesterol levels; these increased only slightly or not at all.     

Dietary beta-sitosterol as an internal standard to correct for cholesterol losses in sterol balance studies

In the course of carrying out sterol balance studies in 19 patients, we gathered the following evidence that, in some but not all patients, considerable amounts of neutral sterols are "lost" during their passage through the intestinal tract. (a) Since plant sterols are largely nonabsorbable in man, they should be totally recovered in the feces; yet in many patients significantly less plant sterol than expected was recovered, the loss amounting to as much as 56% of daily intake. (b) In two patients in whom cholesterol-(14)C and beta-sitosterol-(3)H were instilled into the terminal ileum, from which neither sterol is absorbed, the feces contained 25% less of each isotope than was instilled. (c) In four patients fed radioactive cholesterol daily until the isotopic steady state was closely approximated, 28-50% of the isotope could not be accounted for. On the other hand, in five patients fed radioactive bile acids until the isotopic steady state was approximated, input equalled output as predicted. Since the amount of -sitosterol absorbed in man is limited (5% or less), this sterol can be used as an internal standard for upward correction of the figure obtained for the amount of neutral steroids excreted. The use of beta-sitosterol for this purpose is based on three considerations: (a) it passes through the intestine in the same physicochemical state as cholesterol; (b) it accompanies cholesterol at every step of its isolation and chromatographic measurement; and (c) it is lost to the same extent as cholesterol. Excretion data for fecal neutral steroids can therefore be corrected for irregular fecal flow as well as for the "unexpected loss" referred to. This loss seems to be due not to errors in stool collection or to technical errors, but to intestinal bacterial degradation of neutral 3beta-OH,Delta(5)-sterols to products not recognized as steroids in the analytical methods used.     

Responses to mitogenic stimulation of lymphocytes taken during and after pregnancy

Serial blood samples were collected during pregnancy, after delivery and several months postnatally from 28 women. The blastogenic responses of lymphocytes to varying concentrations of phytohaemagglutinin (PHA) were tested using autologous plasma or fetal calf serum (FCS) to support the lymphocyte cultures. Using FCS, the blastogenic response decreased as pregnancy progressed and remained depressed months after delivery. In contrast, when autologous plasma was used a 10-fold higher concentration of PHA was required to give optimal stimulation. Blastogenic responses were still suppressed during pregnancy but had returned to initial values by the time of delivery and were greater still in the post-partum and postnatal periods. We conclude that the inherent ability of lymphocytes to undergo blastogenesis is suppressed during pregnancy but that this is over-shadowed by a humoral effect of pregnancy plasma. The significance of these results is discussed.     

Spatial pattern,regeneration and growth rates of Brachystegia spiciformis and Julbernardia globiflora

Past work on tree-to-tree interactions in semi-arid savannas, through the use of nearest neighbour analysis, has shown both a regular dispersion pattern and a positive correlation between the size of a tree and the distance to its nearest neighbour. From these results, the importance of competition has been inferred. In the present study, tree-to-tree interactions in a mesic savanna woodland at Marondera, Zimbabwe, dominated by relatively small-sized individuals of Brachystegia spiciformis and Julbernardia globiflora, were examined. Results show that the regular dispersion pattern is uncommon; that there are few significant positive correlations between size of individual and distance to nearest neighbour; and that growth rate is not consistently correlated with size and distance of nearest neighbour. Results of a study of regeneration relative to canopy cover suggest a possible mechanism for these findings: unlike semi-arid savannas, young plants often grow in under-canopy environments so that early spacing of young trees does not occur. Significant positive correlations between the size of a tree and the distance to its nearest neighbour were found in a stand of larger, presumably older, trees, suggesting that such a relationship only develops in mesic miombo woodland through a thinning process as the trees mature. Familial clumping, which is common in the study area, may mask spatial patterns.Abbreviations RBAI Relative basal area increment     

The Staphylococcus aureus ileS gene, encoding isoleucyl-tRNA synthetase, is a member of the T-box family.

The Staphylococcus aureus ileS gene, encoding isoleucyl-tRNA synthetase (IleRS), contains a long mRNA leader region. This region exhibits many of the features of the gram-positive synthetase gene family, including the T box and leader region terminator and antiterminator. The terminator was shown to be functional in vivo, and readthrough increased during growth in the presence of mupirocin, an inhibitor of IleRS activity. The S. aureus ileS leader structure includes several critical differences from the other members of the T-box family, suggesting that regulation of this gene in S. aureus may exhibit unique features.