Vitamin A and marbling attributes: Intramuscular fat hyperplasia effects in cattle.

Twenty Angus steers were fed a diet low in ß-carotene and vitamin A for 10months. Ten steers were supplemented with vitamin A weekly, while the other ten steers did not receive any additional vitamin A. The results demonstrated that the restriction of vitamin A intake increased intramuscular fat (IMF) by 46%. This was a function of the total number of marbling flecks increasing by 22% and the average marbling fleck size increasing by 14%. Vitamin A restriction resulted in marbling flecks that were less branched (22%) and slightly more round (4%) with an increased minor axis length (7%). However, restricting vitamin A did not affect the size of the intramuscular or subcutaneous adipocyte cells or the subcutaneous fat depth. The results suggest that vitamin A affects the amount of marbling and other attributes of the marbling flecks due to hyperplasia rather than hypertrophy. This may explain why vitamin A restriction specifically affects IMF rather than subcutaneous fat deposition.

Expected and observed changes to descriptors of trabecular architecture with aging--a comparison of measurement techniques.

The fragility of trabecular bone depends not only on the amount of bone but also on its architecture. In order to assess fragility of bone, describe changes due to age, and monitor effect of disease or treatment, it is necessary to model the physical properties of trabecular bone architecture. An important feature of bone architecture is the degree of anisotropy (DA). Estimates of DA may be obtained from computed tomography data by characterizing orientation in images. Widely used image descriptors for estimating orientation in this setting include mean intercept length (MIL), line fraction deviation (LFD), star length distribution (SLD) and star volume distribution (SVD). In this study, estimates of DA computed via each of these image descriptors are compared on synthetic images for various combinations of trabecular thickness, separation and number. Estimates of DA are also computed for real images representing different stages of aging. It is found that estimates of DA vary substantially depending on the choice of image descriptor. In particular, the MIL tends to underestimate DA.

Why does the human factor IX gene have a G + C content of 40%?

The factor IX gene has a G + C content of approximately 40% in all mammalian species examined. In human factor IX, C----T and G----A transitions at the dinucleotide CpG are elevated at least 24-fold relative to other transitions. Can the G + C content be explained solely by this hot spot of mutation? Using our mathematical model, we show that the elevation of mutation at CpG cannot alone lower the G + C content below 45%. To search for other hot spots of mutation that might contribute to the reduction of G + C content, we assessed the relative rates of base substitution in our sample of 160 families with hemophilia B. Seventeen independent single-base substitutions are reported herein for a total of 96 independent point mutations in our sample. The following conclusions emerge from the analysis of our data and, where appropriate, the data of others: (1) Transversions at CpG are elevated an estimated 7.7-fold relative to other transversions. (2) The mutation rates at non-CpG dinucleotides are remarkably uniform; none of the observed rates are either more than twofold above the median for transitions or more than threefold above the median for transversions. (3) The pattern of recent mutation is compatible with the pattern during mammalian evolution that has maintained the G + C content of the factor IX gene at approximately 40%.

Sharpening radiographs.

This article describes a method for clarifying and sharpening radiographs. The method uses convolution with a computed tomography reconstruction kernel and a noise elimination procedure to control the noise amplification of the convolution. The effect is to flatten global variations and to sharpen and magnify local variations. Examples from industry and medicine are included.