Using item mean squares to evaluate fit to the Rasch model.

Throughout the mid to late 1970's considerable research was conducted on the properties of Rasch fit mean squares. This work culminated in a variety of transformations to convert the mean squares into approximate t-statistics. This work was primarily motivated by the influence sample size has on the magnitude of the mean squares and the desire to have a single critical value that can generally be applied to most cases. In the late 1980's and the early 1990's the trend seems to have reversed, with numerous researchers using the untransformed fit mean squares as a means of testing fit to the Rasch measurement models. The principal motivation is cited as the influence sample size has on the sensitivity of the t-converted mean squares. The purpose of this paper is to present the historical development of these fit indices and the various transformations and to examine the impact of sample size on both the fit mean squares and the t-transformations of those mean squares. Because the sample size problem has little influence on the person mean square problem, due to the relatively short length (100 items or less), this paper focuses on the item fit mean squares, where it is common to find the statistics used with sample sizes ranging from 30 to 10,000.

Effect of aldonic acids on the uptake of ascorbic acid by 3T3 mouse fibroblasts and human T lymphoma cells.

1. Previously, we reported that calcium L-threonate caused a dose-related increase in uptake of ascorbic acid (AA) by human T-lymphoma cells. Preincubation of mouse fibroblasts with calcium L-threonate also resulted in a dose-related augmentation in uptake of AA as compared to non-treated controls. 2. Potassium L-lyxonate increased AA uptake by lymphoma cells, but did not significantly affect uptake by fibroblasts. Tartaric acid decreased uptake of AA by both cell lines. 3. Ouabain and dinitrophenol had no effect on AA uptake nor on the ability of threonate to augment AA uptake by fibroblasts. However, in T-lymphoma cells ouabain and dinitrophenol reduced AA uptake and prevented augmentation of AA uptake by calcium L-threonate.

Effects of d-alpha-tocopherol supplementation on experimentally induced primate atherosclerosis.

Prevention and regression of induced atherosclerosis by d-alpha-tocopherol was investigated in 24 male M. fascicularis. One group received a basal diet, while three others consumed an atherogenic diet. Two of the latter groups also received tocopherol, one at the onset of the study (prevention) and the other after atherosclerosis was established by ultrasound evaluation (regression). Atherosclerosis was monitored over a 36-month period by duplex ultrasound imaging of the common carotid arteries. At termination, 24 arterial sites were examined for histopathology. In those animals receiving an atherogenic diet, mean percent ultrasound stenosis at 36 months posttreatment was lower in the tocopherol-supplemented groups (61 and 18%) than in the unsupplemented group (87%). Plasma tocopherol concentration was negatively correlated with percent ultrasound stenosis (p less than 0.002). Percent stenosis in the regression group decreased from 33 to 8% (p less than 0.05) 8 months after tocopherol supplementation. Although not consistently significant, histopathological changes were greater in untreated compared to treated animals. These results, if confirmed, indicate that d-alpha-tocopherol may be prophylactically and therapeutically effective in atherosclerosis.

Effect of cytochalasin B on the uptake of ascorbic acid and glucose by 3T3 fibroblasts: mechanism of impaired ascorbate transport in diabetes.

Hyperglycemia and/or hypoinsulinemia have been found to inhibit L-ascorbic acid cellular transport. The resultant decrease in intracellular ascorbic acid may de-inhibit aryl sulfatase B and increase degradation of sulfated glycosaminoglycans (sGAG). This could lead to a degeneration of the extracellular matrix and result in increased intimal permeability, the initiating event in atherosclerosis. The present studies show that the glucose transport inhibitor cytochalasin B blocked the uptake of 3H-2-deoxy-D-glucose (2.5 mg%) by mouse 3T3 fibroblasts. Cytochalasin B also blocked the uptake of 14C-L-ascorbic acid (1.25 mg%). The results of these studies further support the hypothesis that glucose and ascorbate share a common transport system. This may have important implications concerning the vascular pathology associated with diabetes mellitus.

Clinical profile of a 4-year primate atherosclerosis model.

Twelve male M. fascicularis monkeys were divided into two groups of 6 animals each. One group (BASAL) was fed a diet containing 24% protein, 38% carbohydrate and 20% fat, while the other group (ATHER) received an identical diet with the addition of 4.08 g/kg diet cholesterol. The animals were studied over a 4-year period. Blood samples were regularly collected, ECGs taken and carotid artery status evaluated by duplex ultrasound scanning. Lipid xanthomas were monitored by visual inspection. The ATHER group experienced a rapid and sustained rise in serum total cholesterol, concomitant with depression of HDL-cholesterol. In general, triglycerides were significantly higher in ATHER animals. Routine clinical analysis revealed lower hematocrit and hemoglobin, and elevated BUN and alkaline phosphatase in the treated group. Lipid xanthomas were detected early in the ATHER animals, progressing until infiltration was evident on the entire body surface. There were no differences in ECGs between the groups. At approximately 17 months posttreatment, stenosis was apparent in the carotid arteries of treated animals, rising to an average of 90% at study termination. These results indicate that diet-induced carotid atherosclerosis can be monitored non-invasively in the primate with minimum risk to the animal.

An acute study on the relative gastro-intestinal absorption of a novel form of calcium ascorbate.

Several functions of L-ascorbic acid (vitamin C) have been suggested in addition to its role in the prevention of scurvy. Consequently, a controversy has arisen over the daily intake of the vitamin which will afford maximum benefits. Rapid cellular uptake and delayed renal excretion of ascorbic acid would be conducive to providing optimum cellular concentration for biochemical activity. ESTER-C (patent pending), a complex consisting of L-ascorbic acid and Ca++, has been recently developed by Inter-Cal Corporation (421 Miller Road, Prescott, AZ 86301). It has been proposed that the structure of ESTER-C may render it more readily absorbed and less rapidly excreted than the acid or salt form of the vitamin. To test this hypothesis, ESTER-C and L-ascorbic acid were administered to two groups of rats. Blood was sampled at 20, 40, 80, 160 and 240 minutes and plasma analyzed for ascorbic acid. As urine appeared in collection cups, it was tested qualitatively for the presence of ascorbic acid. The plasma concentration of ascorbic acid was higher in ESTER-C treated rats at 20, 40 and 80 minutes than in rats given L-ascorbic acid. Ascorbic acid was detected in the urine of animals administered ESTER-C later than in those treated with L-ascorbic acid. These results support the hypothesis that ESTER-C is absorbed more readily and excreted less rapidly than L-ascorbic acid.

Diet-induced changes in selected clinical chemistry parameters in M. fascicularis.

Thirty-six male M. fascicularis monkeys were fed a basal diet (180 g/day, 24% protein, 38% carbohydrate and 20% fat) for a period of 17 months. At that time, the animals were divided into two groups. One group (6 animals) continued on the basal diet (BASAL group), while the others (30 animals) received an atherogenic diet (ATHER group) containing 4.08 g/kg cholesterol. Blood samples were drawn for clinical chemistry analyses. Serum cholesterol rose dramatically in the ATHER group, an average increase of 350 mg/dl over basal-diet values after two weeks on the atherogenic diet. Serum triglycerides followed the same pattern. HDL-cholesterol in the atherogenic-diet group decreased sharply. These animals also had slightly elevated BUN, uric acid and SGOT levels. Skin lipid xanthomas were also observed in the ATHER group, but were absent in animals fed the basal diet. Body weight among all animals remained relatively constant. Minimal changes in clinical chemistry values other than those noted above are evidence of the low physiological stress placed on the animals by this dietary regimen.

Changes in selected serum biochemical and EKG values with age in cynomolgus macaques.

Normal serum values for alkaline phosphatase were significantly higher in juvenile male cynomolgus monkeys compared to adults. Conversely, blood urea nitrogen (BUN) was significantly lower in juveniles than adults. A comparison of selected EKG parameters from each group revealed no significant differences; however, there was a trend towards mean left axis deviation in adult animals.

Role of the adenylate cyclase system in altered insulin release from islets of Langerhans of aging rats.

In attempting to understand the causes of the hyperglycaemia observed in aging populations and to determine the mechanism(s) for the diminished in vitro insulin release from islets of Langerhans of older rats, the adenylate cyclase-cyclic AMP system was studied in isolated islets from 12 month old and 2 1/2 month old (control) male rats to determine its role in this altered insulin secretion. Islets of Langerhans were isolated by collagenase digestion and then either incubated in the presence of low or high concentrations of glucose for studies of insulin release or were sonicated and assayed for determinations of activities of adenylate cyclase and phosphodiesterase. Insulin release was identical from islets of 12 month old and 2 1/2 month old rats to 2.8 mM D-glucose, while in the presence of 16.7 mM D-glucose, insulin release was decreased by 33% (P less than 0.02) from islets of the older animals. Adenylate cyclase activity was diminished by 60% (P less than 0.005) from the 12 month old rats as compared with islets from the 2 1/2 month old controls, while low Km phosphodiesterase activity was similar in islets from both groups of animals. From these studies it appears that the adenylate cyclase-cyclic AMP system may play a role in the altered insulin release from islets of aging rats.