The interaction of the bisbenzimidazole dye 33258 Hoechst with DNA and chromatin is characterized by changes in absorption, fluorescence, and circular dichroism measurements. At low dye/phosphate ratios, dye binding is accompanied by intense fluorescence and circular dichroism and exhibits little sensitivity to ionic strength. At higher dye/phosphate ratios, additional dye binding can be detected by further changes in absorptivity. This secondary binding is suppressed by increasing the ionic strength. A-T rich DNA sequences enhance both dye binding and fluorescence quantum yield, while chromosomal proteins apparently exclude the dye from approximately half of the sites available with DNA. Fluorescence of the free dye is sensitive to pH and, below pH 8, to quenching by iodide ion. Substitution of 5-bromodeoxyuridine (BrdU) for thymidine in synthetic polynucleotides, DNA, or unfixed chromatin quenches the fluorescence of bound dye. This suppression of dye fluorescence permits optical detection of BrdU incorporation associated with DNA synthesis in cytological chromosome preparations. Quenching of 33258 Hoechst fluorescence by BrdU can be abolished by appropriate alterations in solvent conditions, thereby revealing changes in dye fluorescence of microscopic specimens specifically due to BrdU incorporation.

Principal components analyses of subcutaneous fat measurements covering arm, trunk, and leg areas of the body were performed on 44 samples varying in sex, age, and ethnicity of subjects; measurement technique; and number of sites studied. Three major components emerged, similar in all samples: A first component of obesity, a second component of anatomical fat distribution contrasting trunk and extremity fat, and a third distributional component contrasting leg and arm fat. These components did not appear to vary with age (school children to older adults), sex, ethnicity (Black-White), technique (caliper, ultrasound, or X-rays), or number of sites (five to 13). The three major components are similar to vectors or obesity and relative fat patterning reported earlier by anthroposcopic (Skerlj et al., 1953) and graphic (Garn, 1955) methods. One of the pattern components (trunk-extremity) appears to correspond to a body build continuum associated with adult chronic diseases (Vague, 1956). The stability of these components among samples that differ in several characteristics suggests the validity of these components in describing aspects of body build of anthropological and epidemiological importance.

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In this pilot, case-controlled investigation of 43 colorectal and 41 control male patients, we compared associations of colorectal cancer with the aromatic amine acetyltransferase polymorphism, nutritional and demographic characteristics, medical histories, industrial and occupational histories, and exposures from home environments and personal habits. Persons with the "fast" acetylator trait were at greater risk of colorectal cancer (odds ratio: 2.48; 95% confidence interval: 1.02, 6.03). Results that differed from previous reports were positive associations of colorectal cancer with agricultural and manufacturing industries and with consumption of meats prepared by smoking, curing, and barbecueing. As expected, exercise frequency, cruciferous vegetables, and dietary fiber served as protective factors.

We measured serum levels of 11 pesticide residues and metabolites in 85 rural-dwelling persons. In general, the serum levels increased with age, with males having slightly higher levels than females. Consumption of eggs from home-raised hens contributed substantially to increased serum concentrations of trans-nonachlor, heptachlor epoxide, and oxychlordane; consumption of home-grown root vegetables likewise contributed to increased serum concentrations of trans-nonachlor and oxychlordane. Health risks, if any, that may be attributable to these "background" levels of exposure remain to be fully characterized in this, and all other, affected populations.