Measurement of beam current and evaluation of scatter production in an 18-MeV accelerator.

Measurements of dose rate in a 10-MV x-ray beam may indicate considerable variation with collimator setting. This variation is observed even when the peak scatter factor is fixed by holding the field size at the phantom surface constant. The resulting output factor variation may be due to radiation backscattered from the collimators into the monitor chamber. Measurements of charge deposited in the accelerator target were compared with ionization readings for several field sizes. Evaluation of the data indicates that radiation backscattered into the monitor chamber contributes only a small amount to the output factor.

Lipogenesis in response to an oral glucose load in fed and starved rats.

Lipogenesis in livers of fed but not of starved rats is increased after intragastric feeding with glucose. In contrast, lipogenesis in brown adipose tissue increases in both fed and starved animals. These observations suggest that lipogenesis in brown adipose tissue is regulated by mechanisms in addition to, or other than, those operating in liver. The fate of newly synthesized lipid in brown adipose tissue is not known. However, the formation of palmitoyl-carnitine from palmitoyl-CoA and carnitine by mitochondria from brown fat was inhibited by malonyl-CoA. Although inhibition was not 100%, it is implied that mitochondrial uptake of the newly synthesized fat by the carnitine acyltransferase system is restricted under conditions of increased lipogenesis.

The human body burden of mirex in the southeastern United States.

Mirex is an organochlorine chemical with pesticidal and other industrial usages. Biologically, mirex was used as an insecticide for the control of imported fire ants in large areas of the southeastern United States. Evidence of mirex exposure in a national survey of chemicals in adipose tissue led to a more intensive survey of the general population in treated counties of the southeastern United States. Forty sites were selected randomly from 8 southeastern states where mirex was used widescale to combat fire ants; a total of 624 adipose tissue specimens were collected from these 40 sites. Tissue specimens were prepared by a modified Mills-Onley-Gather procedure and analyzed for mirex and selected other organochlorine compounds by electron-capture gas chromatography. Positive residue findings were confirmed by combined gas chromatography and mass spectrometry. Weighted statistical analysis of the data was conducted to estimate the level of mirex in the study area. It was estimated that 10.2% of the population of southern United States had quantifiable levels of mirex in adipose tissue. The estimated geometric mean of the quantifiable residue amounts was 0.286 ppm (lipid basis). Statistical tests of association and regression were used to investigate possible relationships between the presence and levels of mirex, and the Census Division or state of tissue-specimen collection, by age, race, and sex. These analyses indicated that region or location of tissue specimen collection (assumed to be area of residence) strongly related to both the presence of mirex residue and the amount of mirex residue detected. This may be correlated with the amount of mirex applied for fire ant control or with some other exposure patterns in different regions.