Early childhood testing and school learning problems: a cross-validation.

Educators in the early school grades often find themselves in a dilemma when evaluating children's skills. Formal testing procedures are often inappropriate for young children and can wrongly identify them as deficient. The purpose of this study was to help teachers in making early decisions regarding individual children that would be accurate and helpful in designing educational programs. A screener was identified during the first year that discriminated between kindergarten children identified by their teachers as high-achieving or low-achieving. The results of a subsequent cross-validation yielded a relationship between the screener and the teachers' evaluations that was statistically significant.

The early prediction of school learning problems.

The purpose of this research was to determine a reliable and realistic set of variables for teachers to assist in early identification of children with special needs. Sixty-four kindergarten children participated in the study, 32 identified as high achieving and 32 identified as low achieving by their teachers. Variables included were information from questionnaires answered by parents and teachers and results of standardized tests. Based on the results of the analyses, variables and tests are suggested for distinguishing between groups of children who may experience school success or difficulties.

Glucose metabolism in the calf lens.

Carbohydrate metabolism in lens homogenates was evaluated using uniformly labeled [14C]-glucose. Metabolites were separated using HPLC and the distribution of 14C among metabolic pathways was determined. Under the standard incubation conditions employed (pH 7.4, 37 degrees C, 5 mM glucose) 40% of the glucose consumed forms lactate. The amount of 14C found in sorbitol and alpha-glycerol phosphate is 1-2%. This pathway distribution is essentially independent of glucose concentration from 2 to 35 mM. Over this range, lactate production is relatively constant at 2-3 mumol 7 hr-1. At 35 mM glucose, sorbitol production increases to 0.182 from 0.036 mumol 7 hr-1 at 5 mM glucose. The level of ATP is clearly a very significant factor in the regulation of glycolytic rate. An increase in ATP concentration from 1 to 3 mM results in a decrease in the rate of lactate production from 2.09 to 0.404 mumol 7 hr-1. The NAD/NADH ratio is significant in the distribution between lactate and alpha-GP. An increase in the level of NADP or NADPH increases sorbitol production as well as alpha-GP production. A computer program was developed to model the experimental incubation system. The calculated results are in agreement with the experimental in showing effects of ATP and perturbations of enzyme cofactor concentrations.

Depletion of sorbitol and fructose from young and older rat lenses.

Fasting for as little as 24 hr markedly reduced the levels of sorbitol and fructose in the adult rat lens. This depletion was found in both young (1 month) and older (8-12 month) rats. Two modes of depletion were examined: decreased synthesis and metabolic breakdown. The role of diffusion was discussed. In vitro experiments showed that in both age groups, decreased glucose in the medium resulted in a proportional decrease in glucose and sorbitol in the lens; the lenticular fructose level was not changed. In contrast to reports showing decreased glycolysis with age, the sorbitol-synthetic capacity of rat lenses was undiminished with age. Acceleration of glycolytic flux in lenses in vitro resulted in decreases in fructose, and to a lesser extent in sorbitol, in both age groups. These findings indicated that fructose can be removed from lenses by metabolism; and that, especially in the older lenses, glycolysis may represent a major route by which fructose, and hence sorbitol, are eliminated during fasting.

Age and the control of glycolysis in the rat lens.

Previous studies with lens dispersions indicated that the rate-limiting step in glycolysis shifts from hexokinase (HK) in the young lens to phosphofructokinase (PFK) in older lenses. Because the concentrations of the complex controlling factor for these enzymes could not be reproduced reliably in homogenates, the question of age-related control of glycolysis was re-examined in intact lenses. Toward this end, the levels of several metabolites of glucose were measured in fresh and incubated clear lenses. Of the substrates measured per fresh lens, only one changed significantly with age; fructose diphosphate was increased. When lenses were incubated in 2 to 12 mM glucose, the lactate production per lens was not significantly different with age. Together these results suggested that the glycolytic mass of the lens was constant with age. In both young and older lenses, increases in glucose in the medium led to increases in both glucose and glucose-6-phosphate in the lens. The lack of corresponding increase in lactate production suggested that the regulatory step lay downstream from HK, probably at PFK. This finding was corroborated by evidence that the initial acceleration of lactate production by the addition of cyanide (the Pasteur effect) was accompanied by decreases in the substrates of PFK, glucose-6-phosphate and fructose-6-phosphate. A secondary disinhibition of HK, as indicated by decreased lens glucose, became apparent after longer incubation with cyanide. This suggested that after disinhibition of PFK, HK became rate-limiting until the level of glucose-6-phosphate fell enough to allow the disinhibition of the latter enzyme as well. Thus PFK seemed to be the primary regulatory step in aerobic glycolysis in lenses of rats from 1 to 12 months of age.

The sorbitol pathway in the human lens: aldose reductase and polyol dehydrogenase.

The sorbitol pathway in human lenses is evaluated on the enzymic level. Adult lenses, normal and nondiabetic as well as diabetic cataracts, are found to contain limited levels of aldose reductase (AR) and high levels of polyol dehydrogenase (PD) relative to the animal lens. AR is confined primarily to the lens epithelium and is two to three times higher in juvenile lenses than in the adult lens. The level of AR in the epithelium of juvenile lenses is sufficient to cause significant osmotic stress. The Km of glucose of AR is roughly 200 mM, whereas the Km for NADPH is 0.06 mM. NADP inhibits human lens AR noncompetitively and has a Ki equivalent to the Km for NADPH. PD occurs in both the lens epithelium and cortex, remains persistently high with age, and decreases with increased cortical involvement. The Km of sorbitol for PD is 1.4 mM and for NAD is 0.06 mM. NADH (Ki 0.002 mM) competitively inhibits PD in the forward direction. PD purified 100-fold from diabetic and nondiabetic cataracts and normal lenses exhibit similar kinetic constants. PD has an extremely high Vmax in the fructose-to-sorbitol direction. The Km of fructose is 40 mM and for NADH is 0.02 mM. At high enough concentration, alrestatin also inhibits PD. The added activities of AR and PD in producing sorbitol and fructose in combination with decreased hexokinase with age may account for diabetic cataract formation in human lenses exposed to a high glucose stress. Nucleotide levels are reported for senile cataractous lenses.