No abstract

The effects of fasting were examined on the rhythmic changes in the activities of maltase [EC 3.2.1.20] and leucine aminopeptidase [EC 3.4.11.1] in the small intestine of rats which has been kept under scheduled feeding conditions. Irrespective of whether the rats had been kept on a daytime or nighttime feeding schedule, the rhythms of maltase and leucine aminopeptidase persisted when the animals were starved. However, the amplitude of the leucine aminopeptidase rhythm began to decrease from the first day of fasting, while that of maltase did not. Conspicuous rhythms persisted for at least 2 days during fasting, but they gradually became vague and disappeared after 5 days. When rats were refed after fasting, the leucine aminopeptidase activity increased within a few hours, but the maltose activity did not. It is suggested that the rhythms of the digestive enzymes in the small intestine of rats are not a direct consequence of food intake, but are triggered off by the anticipatory mechanism which operates when rats expect to be fed. The rhythmic change of leucine aminopeptidase seemed to be intensified by food intake.

This study describes the age-related changes of vitamin D metabolism and its related hormones, immunoreactive PTH (iPTH) and calcitonin (CT) in normal human subjects. The objective was to assess their roles in the changes in metabolism of calcium and phosphorus with age. Serum calcium and phosphorus levels declined linearly with age from newborn infants to older adults (r = -0.385, P less than 0.01; r = -0.568, P less than 0.01). The serum calcium and phosphorus levels in adults of 51 yr of age or more were significantly lower than those in children and younger adults of 50 yr of age or less (P less than 0.025, P less than 0.01), whereas the calcium and phosphorus levels in cord blood were significantly higher than those in children and younger adults (P less than 0.025, P less than 0.01). The serum concentration of 1 alpha,25-dihydroxyvitamin D (1 alpha,25-(OH)2-Vit D) did not change in children and younger adults, being 42.0 +/- 1.4 (SE) pg/ml, but it significantly decreased to 31.4 +/- 1.9 pg/ml in older adults (P less than 0.01). There were no significant age-related changes in the serum concentrations of 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, or vitamin D-binding protein (DBP) among children, younger adults and older adults. The concentrations of all vitamin D metabolites and DBP in cord serum were significantly lower than those in children and younger adults (P less than 0.01). Serum iPTH levels were higher in older adults (P less than 0.05) and lower in cord blood (P less than 0.1), compared with those in children and younger adults, whereas the serum CT level was higher in cord serum (P less than 0.01). No sex differences were found in the serum concentrations of calcium, phosphorus, vitamin D metabolites, DBP, iPTH, and CT. The serum concentration of calcium or phosphorus did not correlate significantly with that of 1 alpha 25-(OH)2-Vit D by simple correlation analysis. Multivariate analysis, however, showed that the change in the serum concentration of 1 alpha,25-(OH)2-Vit D, as well as iPTH and CT, contributed to their correlation with the change in the serum concentrations of calcium and phosphorus. These data indicate that change in vitamin D metabolism might play some role in the age-related change of serum calcium and phosphorus levels in children and adults, but that calcium and phosphorus metabolism in the fetus might be regulated by some mechanisms other than vitamin D metabolism.

Quality assurance (QA) of clinical electron beams is essential for performing accurate and safe radiation therapy. However, with advances in radiation therapy, QA has become increasingly labor-intensive and time-consuming. In this paper, we propose a tissue-equivalent plastic scintillator for quick and easy QA of clinical electron beams. The proposed tool comprises a plastic scintillator plate and a charge-coupled device camera that enable the scintillation light by electron beams to be recorded with high sensitivity and high spatial resolution. Further, the Cerenkov image is directly subtracted from the scintillation image to discriminate Cerenkov emissions and accurately measure the dose profiles of electron beams with high spatial resolution. Compared with conventional methods, discrepancies in the depth profile improved from 7% to 2% in the buildup region via subtractive corrections. Further, the output brightness showed good linearity with dose, good reproducibility (deviations below 1%), and dose rate independence (within 0.5%). The depth of 50% dose measured with the tool, an index of electron beam quality, was within  ±0.5 mm of that obtained with an ionization chamber. Lateral brightness profiles agreed with the lateral dose profiles to within 4% and no significant improvement was obtained using Cerenkov corrections. Field size agreed to within 0.5 mm with those obtained with ionization chamber. For clinical QA of electron boost treatment, a disk scintillator that mimics the shape of a patient's breast is applied. The brightness distribution and dose, calculated using a treatment planning system, was generally acceptable for clinical use, except in limited zones. Overall, the proposed plastic scintillator plate tool efficiently performs QA for electron beam therapy and enables simultaneous verification of output constancy, beam quality, depth, and lateral dose profiles during monthly QAs at lower doses of irradiation (small monitor units, MUs).

The seco-steroid hormone 1,25-dihydroxyvitamin D3 is known to induce the expression of a calcium binding protein termed calbindin-D28K in a variety of target tissues. In order to comprehend the mechanism of induction we have cloned and sequenced the chicken calbindin-D28K gene. The gene spans some 18.5 kilobases (kb) of chromosomal DNA from the putative Cap site to the polyadenylation site of the 2.8 kb mRNA. It is split into 11 coding exons by 10 intervening sequences. The promoter region of this gene is markedly G + C-rich (60-80%) extending from -225 to +400. Within this region we find 70 CpG dinucleotides, four G-C boxes, and numerous known promoter regulatory signals. These putative regulatory signals include a TATA box (ATAAATA) at -30 and a CAT box (CCAAT) at -326. Ten additional variant CAT boxes are found in the upstream promoter region (-218 to -770) of this gene. Furthermore we have identified a glucocorticoid-like responsive element at -410 (TCTACACACTGTTCC) and this element overlaps a metal responsive element (TGCACTC) and a variant CAT box (CCAAAT) and juxtaposes an enhancer-like core element (AAATGGT) on its 3'-side. In addition, the calbindin-D28K promoter is composed of a variety of simple repeated sequences, some of which are components of putative regulatory signals. All splice junctions were found to conform to the GT-AG rule. A consensus sequence of the 5'-splice junction reads AG/GTAAG-TTATA. A consensus sequence of the 3'-splice site consists of two elements: a pyrimidine track (mainly T) followed by ACAG/G-T. A two-dimensional model of calbindin-D28K was constructed which projects the existence of 6 alpha-helix-loop-alpha-helix regions characteristic of calcium binding domains. The 3'-end of the gene consists of a single large (2039 base pair) uninterrupted exon, an organizational feature common to other members of the calcium binding protein gene family which include calmodulin, parvalbumin, Spec I, myosin light chains, etc. Another feature common to the gene family is the presence of the repeated sequence ATTT or TTTA located in the 3'-untranslated exons. These simple repeat sequences could be involved in regulating mRNA degradation by serving as a ribonuclease recognition signal.