Sensitivity of parametric link functions in generalized linear models.

A common method of choosing the link function in generalized linear models is to specify a parametric link family indexed by unknown parameters. The maximum likelihood estimates of such link parameters, however, may often depend on one or several extreme observations. Diagnostics are derived to assess the sensitivity of the parametric link analysis. Two examples demonstrate that the proposed diagnostics can identify jointly influential observations on the link even when masking is present.

Dietary fiber, Hispanics, and breast cancer risk?

The cancer rates of immigrant populations in the United States must be taken into account when looking at the importance of diet and culture as it relates to cancer prevention. Unfortunately, some nutrition studies targeted toward nontraditional white populations have not adequately confronted the issue of cultural meaning in efforts to gather dietary data accurate enough to support nutritional analyses, identify marginal diets, or relate risk to dietary patterns. The study presented here resolves many of the culturally specific issues utilizing awareness, attention, and judicious combination of culturally sensitive qualitative and quantitative research techniques. The importance of such a study in an Hispanic population is based on the fact that the age-adjusted rate of breast cancer in countries such as Mexico is among the lowest in the world. In addition, although one of the fastest-growing minority groups in the United States, Hispanic women living in this country have been shown to have the lowest incidence of the mortality rates from this disease across most geographic regions of the United States. Therefore, one might speculate that dietary factors, which have been shown to play a role in breast cancer prevention, may account for this difference. It is well recognized that the traditional Hispanic diet is rich in protective nutrients such as dietary fiber. It is known that through complex mechanisms, dietary fiber works to reduce the amount of estrogens in the body. Research also indicates that it is the level of endogenous estrogen in the body that may influence the onset of breast cancer. In order to better understand how dietary factors may be associated with breast cancer in Hispanic women, it is important that one develop the proper tools to discern any potential differences. Therefore, we developed an approach to obtaining dietary fiber information from a small cohort of 22 Houston-area Hispanic women as a vanguard study for a larger breast cancer prevention trial. Two separate dietary assessment instruments were utilized, a three-day food record and the Southwest Food Frequency Questionnaire. The mean intake of dietary fiber was 16 g/day according to the food record and 21 g/day according to the SWFFQ. Fruits, vegetables, breads, cereals, and beans provided for most of the participants' dietary fiber intake. These results support evidence that the Hispanic population's dietary fiber intake is higher than that for other groups, and this may help explain the lower incidence of breast cancer among some Hispanic populations.

Glutamine stability in biological tissues evaluated by fluorometric analysis.

Although glutamine has been considered unstable during storage and therefore difficult to quantitate, recent results suggest this amino acid is stable at low pH ranges. We evaluated the stability of glutamine in plasma and tissue extracts, using fluorometric analysis. The measured concentration of glutamine detected varied linearly up to 0.8 mmol/L for the aqueous solution (r2 = 98.7, P = 0.0001) with a mean (+/- SD) coefficient of variation of 2.41% +/- 0.79%. When glutamine was dissolved in 50 g/L trichloroacetic acid (TCA), the values were essentially unaltered. Glutamine in an aqueous solution and stored at -70 degrees C was stable for at least 16 days; glutamine in TCA was stable for 6-8 days, then decreased to a concentration significantly lower than that of the aqueous solution. The expected and observed concentrations in plasma were equal (r2 = 0.99975) for increasing amounts of added glutamine. Glutamine concentrations in plasma were stable for > 1 year when stored at -70 degrees C. The glutamine of a transplantable rat sarcoma and a normal rat liver could be extracted with 50 g/L TCA with high efficiency (88.6% +/- 1.9% and 90.2% +/- 0.04%, respectively); the extracted glutamine is stable in TCA for at least 7 days without neutralization when stored at -70 degrees C. Fluorometric analysis of glutamine required only a small quantity of plasma (25 microL) or tissue (200 mg) and is a convenient method for quantifying this important amino acid.

Stage-dependent variation in the radiosensitivity of DNA in developing male germ cells.

The induction and rejoining of gamma-ray-induced DNA single-strand breaks (SSBs) were measured in the spermatogenic cells of mice using the alkaline elution technique. The animals were injected with [3H]thymidine and sacrificed on subsequent days to examine selectively cohorts of radiolabeled cells in the successive stages of maturation. A significantly increased frequency of SSB was observed in the unirradiated early spermatocytes and late spermatids, associated with genetic recombination and chromatin compaction, respectively. The frequency of SSBs induced by irradiation of animals in vivo remained constant from the early spermatocyte through mid-spermatid stages and decreased significantly only after the cells matured to the late spermatid stage. The frequency of SSBs after in vitro irradiation of testicular cell suspensions also decreased as round spermatids matured to late spermatids. Such decreases for both modes of irradiation may result from maturation-dependent alterations in chromatin in late spermatids, such as condensation and replacement of histones with protamines, rather than from changes in oxygen tension. Rejoining of SSBs in vivo was efficient in the spermatocytes and early spermatids but declined in late spermatids. Possible reasons for the discrepancy between the greater number of unrepaired lesions and lower susceptibility to mutation induction in late spermatids than in round spermatids are discussed.