Sunlight, cholesterol and coronary heart disease

We investigated the relationship between geography and incidence of coronary heart disease, looking at deficiency of sunlight and thus of vitamin D as a factor that might influence susceptibility and thus disease incidence. Sunlight deficiency could increase blood cholesterol by allowing squalene metabolism to progress to cholesterol synthesis rather than to vitamin D synthesis as would occur with greater amounts of sunlight exposure, and the increased concentration of blood cholesterol during the winter months, confirmed in this study, may well be due to reduced sunlight exposure. We show evidence that outdoor activity (gardening) is associated with a lower concentration of blood cholesterol in summer but not in the winter. We suggest that the geographical variation of coronary heart disease is not specific, but is seen in other diseases and sunlight influences susceptibility to a number of chronic diseases, of which coronary heart disease is one.      

Underuse of screening mammography by family physicians

Although the American College of Radiology, the National Cancer Institute, and the American Cancer Society recommend screening mammography for women more than 40 years old, there is little compliance with these recommendations. Primary-care physicians are often reluctant to refer patients for the procedure, whereas the patients are usually willing to undergo the procedure. This survey documents the underuse of screening mammography by family physicians who are members of the Michigan Academy of Family Physicians. The underuse of mammography by this physician sample was due to two main factors: The physicians perceived far more disadvantages than advantages with mammography and perceived problems (with, e.g., equipment, effectiveness, and patient acceptance) as pervasive. To change the attitudes and referral behavior of family physicians, one must take into account the specific, negative perceptions of the procedure and place an emphasis on the initial referral, since subsequent referrals are easier to implement.     

Systematic assessment of the quality of osteoporosis guidelines

Background  

Numerous agencies have developed clinical practice guidelines for the management of postmenopausal osteoporosis. The study objective was to conduct a systematic assessment of the quality of osteoporosis guidelines produced since 1998.     

Human hepatoma cells secrete single chain factor X, prothrombin, and antithrombin III

The human hepatoma cell line, Hep G2, was analyzed for the ability to synthesize and secrete several coagulation proteins. Using specific radioimmunoassays, factor X, prothrombin, and antithrombin III were present in 8-day culture supernatants at 62, 405, and 1,220 ng/mL, respectively. Factor IX was not detected, either in supernatants or in cell extracts. Intrinsically labeled factor X was secreted as a single- chain polypeptide of 66,000 daltons, as measured by sodium dodecylsulfate-polyacrylamide gels under nonreduced and reduced conditions. Immunoblots of Hep G2 supernatants and normal human plasma also indicate the presence of single-chain factor X. These findings support the hypothesis of a postsecretion proteolytic cleavage of factor X into the two-chain form. Prothrombin and antithrombin represented their plasma protein counterparts structurally, with molecular weights of 73,000 and 61,000, respectively. Secreted factor X, prothrombin, and antithrombin III were biologically active, as determined in coagulation or chromogenic assays, and all three activities were neutralized by monospecific antibodies. Vitamin K increased the quantity of prothrombin secreted by twofold, without affecting the rate of secretion over a five-day culture period, and had an apparent transient inhibitory effect on secretion of antithrombin III. Warfarin caused a three to fourfold decrease in the rate and quantity of secreted prothrombin, but did not affect intracellular concentrations. The intracellular and extracellular concentrations and rate of secretion of antithrombin III were not modulated by warfarin. These data suggest that the Hep G2 cell line may provide a useful model for assessing the regulation of biosynthesis and secretion of human coagulation proteins.     

Evidence for early recruitment of granulocyte precursors during high- dose methotrexate infusions in mice

The effects of constant exposure to high concentrations of methotrexate in vivo on the committed stem cell (CFU-C) were studied by in vitro culture of mouse bone marrow. Bone marrow samples were obstained from animals receiving a continuous infusion, and were cultured in a methotrexate-free semisolid gel system. The effects of methotrexate infusion on the pluripotent stem cell population (CFU-S) were studied as well. Constant exposure to 10(-5) M methotrexate produced a rapid decrease in total nucleated cells per femur, reaching 35% of control at 12 hr and remaining at approximately this level throughout 48 hr of drug infusion. A decrease in the number of both CFU-C and CFU-S per femur was observed, which paralleled the drop in nucleated cells during the first 24 hr. However, in contrast to an additional drop in the number of CFU-S, an increase of CFU-C number per femur was observed from 24 to 48 hr. These data indicated a self-limited cell kill of nucleated bone marrow cells, and suggested recruitment of CFU-C from the CFU-S pool between 24 and 48 hr of infusion despite continued methotrexate infusion.     

Immunochemical studies on Tn erythrocyte glycoprotein

Glycoproteins were extracted from membranes of erythrocytes that displayed Tn polyagglutination and were compared chemically and immunologically with glycoproteins of group O, MN cells. Tn glycoprotein had lower than normal NANA : protein and sugar : protein ratios, as revealed by direct analysis and polyacrylamide gel electrophoresis, and displayed slower immunoelectrophoretic mobility than glycoproteins of group O, MN cells. Agglutination of Tn cells by Salvia sclarea lectin was inhibited by Tn glycoprotein but not by O, MN glycoprotein. Tn and MN glycoproteins were equally potent inhibitors of influenza virus HA. Our findings indicate than Tn-specific determinants are part of the glycophorin molecule.