Search PubMed⌕ Search

Biomedical subjects

L H Allen

Publications and source records attributed to L H Allen.

At least 91 records · Page 5Linked to original sources
PubMed1984

A comparison of amino acid-induced hypercalciuria in sham-operated and parathyroidectomized rats.

In previous studies we have demonstrated that the reduced renal reabsorption of calcium and hypercalciuria resulting from protein consumption are associated with serum insulin levels. Arginine stimulation of insulin secretion also results in hypercalciuria. The present study was designed to test whether the calciuria associated with arginine-stimulated insulin secretion is mediated by insulin inhibition of parathyroid hormone (PTH) activity. Parathyroidectomized (PTX) and sham-operated rats were infused with physiological saline, or with 12 mmol X kg-1 X hour-1 arginine in saline at 1.2 ml/hour. Analysis of data from clearance periods 90-150 minutes after infusions commenced show that arginine infusion increased urine volume, and calcium excretion (nanograms/minute and nanograms/milliliter glomerular filtration rate), to the same extent in PTX and sham-operated animals. PTH does not, therefore, appear to be involved in the calciuretic response to amino acid infusion.

Amino Acids↗
PubMed1984

Dark/Light modulation of ribulose bisphosphate carboxylase activity in plants from different photosynthetic categories.

Ribulose bisphosphate carboxylase/oxygenase (RuBPCase) from several plants had substantially greater activity in extracts from lightexposed leaves than dark leaves, even when the extracts were incubated in vitro with saturating HCO(3) (-) and Mg(2+) concentrations. This occurred in Glycine max, Lycopersicon esculentum, Nicotiana tabacum, Panicum bisulcatum, and P. hylaeicum (C(3)); P. maximum (C(4) phosphoenolpyruvate carboxykinase); P. milioides (C(3)/C(4)); and Bromelia pinguin and Ananas comosus (Crassulacean acid metabolism). Little or no difference between light and dark leaf extracts of RuBPCase was observed in Triticum aestivum (C(3)); P. miliaceum (C(4) NAD malic enzyme); Zea mays and Sorghum bicolor (C(4) NADP malic enzyme); Moricandia arvensis (C(3)/C(4)); and Hydrilla verticillata (submersed aquatic macrophyte). It is concluded that, in many plants, especially Crassulacean acid metabolism and C(3) species, a large fraction of ribulose-1,5-bisphosphate carboxylase/oxygenase in the dark is in an inactivatable state that cannot respond to CO(2) and Mg(2+) activation, but which can be converted to an activatable state upon exposure of the leaf to light.

Journal Article↗
PubMed1984

Regulation of calcium metabolism in streptozotocin-induced diabetes.

Sixty-nine-day-old female Wistar rats that had been made diabetic 9 days earlier by an intraperitoneal injection of streptozotocin were studied by a combination radioisotope and balance technique that evaluates calcium absorption, excretion, and bone calcium deposition and resorption rates. Streptozotocin-induced diabetes was associated with a marked drop in calcium absorption and a threefold rise in urinary calcium excretion, changes that greatly exceeded the expected effects from the hyperphagia and increased calcium intake of the experimental animals. Bone calcium deposition was halved in the diabetic rats, with bone resorption unchanged and equal to the deposition rate. As a result, the bone and body calcium balances were zero in the experimental animals. To maintain plasma calcium near normal under these circumstances, the diabetic animals turned over their skeletal calcium in relationship to the central pool much more rapidly than the controls. Although the skeleton in the normal animals serves as both storehouse and regulator of the plasma calcium, in short-term streptozotocin-induced diabetes there is no calcium storage in bone, with the skeleton only playing the role of regulator of calcium homeostasis.

Animals↗
PubMed1983

Evidence for insulin involvement in arginine- and glucose-induced hypercalciuria in the rat.

Urinary calcium excretion is increased after the consumption of protein and carbohydrate by both the human and the rat due to a decreased efficiency in the renal reabsorption of calcium. We have previously shown that the magnitude of the postprandial change in urine calcium in human subjects fed a high protein meal was correlated with the protein-induced changes in serum insulin levels. The present study investigates further the relationship between plasma insulin and urinary calcium excretion. Renal calcium clearance studies were performed in rats infused with the insulin secretagogues glucose or arginine, in the presence and absence of mannoheptulose, a drug which suppresses insulin secretion. The hypercalciuretic effect of arginine was also examined in streptozotocin (SZ) diabetic rats. Arginine and glucose infusion increased urinary calcium excretion by 575 and 225%, respectively, by a mechanism which could be inhibited by mannoheptulose. A linear relationship (r = 0.86) was observed between plasma insulin and urinary calcium excretion. Arginine infusion had no effect on urinary calcium excretion in the SZ diabetic rat, in marked contrast to its effect on normal animals. We conclude that insulin is an important mediator of arginine- and glucose-induced hypercalciuria in the rat.

Animals↗
PubMed1983

Effects of Light and Elevated Atmospheric CO(2) on the Ribulose Bisphosphate Carboxylase Activity and Ribulose Bisphosphate Level of Soybean Leaves.

Soybean (Glycine max L. Merr. cv Bragg) was grown throughout its life cycle at 330, 450, and 800 microliters CO(2) per liter in outdoor controlled-environment chambers under solar irradiance. Leaf ribulose-1,5-bisphosphate carboxylase (RuBPCase) activities and ribulose-1,5-bisphosphate (RuBP) levels were measured at selected times after planting. Growth under the high CO(2) levels reduced the extractable RuBPCase activity by up to 22%, but increased the daytime RuBP levels by up to 20%.Diurnal measurements of RuBPCase (expressed in micromoles CO(2) per milligram chlorophyll per hour) showed that the enzyme values were low (230) when sampled before sunrise, even when activated in vitro with saturating HCO(3) (-) and Mg(2+), but increased to 590 during the day as the solar quantum irradiance (photosynthetically active radiation or PAR, in micromoles per square meter per second) rose to 600. The nonactivated RuBPCase values, which averaged 20% lower than the corresponding HCO(3) (-) and Mg(2+)-activated values, increased in a similar manner with increasing solar PAR. The per cent RuBPCase activation (the ratio of nonactivated to maximum-activated values) increased from 40% before dawn to 80% during the day. Leaf RuBP levels (expressed in nanomoles per milligram chlorophyll) were close to zero before sunrise but increased to a maximum of 220 as the solar PAR rose beyond 1200. In a chamber kept dark throughout the morning, leaf RuBPCase activities and RuBP levels remained at the predawn values. Upon removal of the cover at noon, the HCO(3) (-) and Mg(2+)-activated RuBPCase values and the RuBP levels rose to 465 and 122, respectively, after only 5 minutes of leaf exposure to solar PAR at 1500.These results indicate that, in soybean leaves, light may exert a regulatory effect on extractable RuBPCase in addition to the well-established activation by CO(2) and Mg(2+).

Journal Article↗
PubMed1983

Dietary protein level and skeletal development in the golden Syrian hamster.

The hamster was used as a model for investigating the effect of low, moderate, and high protein intake (12, 18, and 36% casein) on bone mineral content. Animals fed the low level of protein between 3 and 8 months of age had a reduction in the weight of all skeletal components measured, with the exception of the diaphyseal portion of the long bones. Diaphyseal weight and calcium remained significantly lower when expressed as a percentage of body weight. However, urinary calcium excretion was not lower than that of animals consuming an adequate protein intake. Ingesting a high protein diet resulted in a significant increase in urinary calcium excretion, and a reduced amount of both mineral and organic material in the diaphyses. We conclude that long-term consumption of a high protein ration led to the development of a mild osteoporotic condition in the hamster which was limited to the diaphyseal portions of the long bones.

Aging↗
PubMed1982

Pregnancy outcome in North American women. I. Effects of diet, cigarette smoking, and psychological stress on maternal weight gain.

This study examined the roles of diet, cigarette smoking, and psychological stress in pregnancy weight gain. The 60 were selected by defined criteria to minimize variation in anthropometric, socioeconomic, and medical variables which also affect weight gain. To maximize variation in weight gain, subjects were also selected on the basis of low weight gain (less than or equal to 15 lb) and adequate weight gain (greater than 15 lb). Each weight gain group contained smokers and nonsmokers. Smokers consumed more calories than nonsmokers (2119 versus 1810 kcal/day, p less than 0.01). for nonsmokers, differences between the intakes of low weight gain (1617 kcal/day) and adequate weight gain (1905 kcal/day) women were significant (p less than 0.02) and calorie intake was correlated with weight gain (r=0.44 p, less than 0.02). Psychological stress negatively correlated with weight gain (r=0.37, p less than 0.01) but not with calorie intake. We conclude that low weight gain is associated with a lower food intake. In contrast, smoking and stress may cause low weight gain by reducing the utilization of calories for weight gain.

Body Weight↗
PubMed1982

Pregnancy outcome in North American women. II. Effects of diet, cigarette smoking, stress, and weight gain on placentas, and on neonatal physical and behavioral characteristics.

This study evaulated the effects of diet, weight gain (low = LWG, less than or equal to 15 lb; adequate greater than 15 lb), smoking, and stress on the pregnancy outcomes of 60 women. LWG mothers, compared to adequate weight gain, had lower calorie intakes, shorter gestations (0.5 wk, Dubowitz) smaller placentas (345 +/- 65 versus 373 +/- 75 g), and infants with lower birth weight 2640 +/- 329 versus 3192 +/- 307 g), ponderal indices (2.37 versus 2.62), and growth rates. Mothers who smoked had increased calorie intake, but showed no alterations in gestational age of infants or placenta weights. Infants of smokers weighed less than those of nonsmokers (2875 +/- 522 versus 309 +/- 511 g), but had a normal ponderal index. LWG or smoking were associated with impaired motor performance, visual habituation and orientation, and reflexes. Smoking adversely affected auditory habituation and orientation, and autonomic regulation. LWG and smoking have significant, but separate, detrimental effects on pregnancy outcome.

Anthropometry↗
PubMed1980

Oestrogen use and survival in endometrial cancer.

Of 860 women with endometrial cancer registered in a regional cancer treatment centre, 259 (30%) gave a history of oestrogen use for 6 months or more at some time before diagnosis, and 568 (66%) were non-users. OEstrogen use was associated with younger age, earlier stage, lower grade of tumour, less common myometrial invasion, and preferred treatment including radiation and hysterectomy. The 5-year survival of oestrogen users was 92 +/- 2% compared with 68 +/- 2% for non-users. Further analysis controlling for differences in the distribution of the variables associated with survival showed that for women who have endometrial cancer, the risk of any death for non-users is approximately 2-7 times greater than for oestrogen users, and the risk of death from endometrial cancer is 5.4 times greater for non-users. A history of oestrogen use is not associated with superior survival of women who have poorly differentiated tumours or myometrial invasion.

Adult↗
PubMed1980

A comparison of the effects of feeding sulfur amino acids and protein on urine calcium in man.

It has been suggested that the sulfur amino acids in protein are responsible for the calciuria observed after protein ingestion. This hypothesis was tested by feeding meals containing either 15 g protein (control), 45 g protein (high protein), or 15 g protein plus sulfur amino acids equivalent to those in the high protein diet. Compared to the control, the high protein diet caused an increase in urinary calcium and sulfate and a decrease in the renal reabsorption of calcium. In contrast, the sulfur amino acid supplement had no effect on calcium excretion or reabsorption. Net acid excretion was unaffected by dietary treatment.

Adult↗
PubMed1979

Polyethylene glycol as a quantitative fecal marker in human nutrition experiments.

Data are summarized from five experiments in which polyethylene glycol (PEG) was fed to 51 subjects as a quantitative fecal marker. In three experiments PEG was fed continuously for 35 to 106 days. Preexperimental diet was assumed to have been completely excreted when the ratio of fecal PEG to fecal dry solids became constant. This took more than 7 days to occur in 50% of the subjects. Fecal recovery of PEG averaged only 93% of that consumed. PEG was a valid fecal marker for nitrogen, calcium, magnesium, iron, and zinc, but was less valid for sodium. In one experiment where PEG and chromic oxide (Cr2O3) were fed simultaneously, PEG was excreted faster on average than Cr2O3. In most subjects, small amounts of Cr2O3 were excreted sporadically for 42 days after Cr2O3 feeding had ceased. Inclusion of quantitative fecal markers permitted identification of the time when preexperimental diet had been completely eliminated, subjects who showed marked pooling of intestinal contents, and changes in the amount of fecal dry solids. However, an average fecal recovery of only 93% of the PEG or Cr2O3 consumed suggests that further work is needed before the recovery of either of these markers can be used with confidence for the correction of nutrient balance data.

Calcium↗
PubMed1979

Protein-induced hypercalciuria: a longer term study.

Urine calcium excretion is known to be directly correlated with the level of dietary protein intake. In this experiment we examined the persistence of the hypercalciuria induced by the consumption of high protein diets, and the mechanism of the calciuric response. In a 95-day metabolic study, each of six adult male subjects received formula diets supplying 12 g nitrogen or 36 g nitrogen, and approximately 1400 mg calcium per day. Urine calcium increased rapidly and significantly from an average of 191 mg/day on the 12 g nitrogen diet to 277 mg/day on the 36 g nitrogen diet. There was no significant difference in the apparent absorption of calcium, so that overall calcium balance was -37 mg/day on the 12 g nitrogen diet, and significantly lower at -137 mg/day in subjects consuming the high protein diet. Levels of urinary hydroxyproline, serum insulin, and parathyroid hormone were not significantly increased by high intakes of protein. A decrease in the fractional reabsorption of calcium by the kidney seems to be the most likely cause of the protein-induced hypercalciuria. The consumption of high calcium diets is unlikely to prevent the negative calcium balance and probable bone loss induced by the consumption of high protein diets.

Adult↗
PubMed1979

Reduction of renal calcium reabsorption in man by consumption of dietary protein.

This experiment was designed to test whether protein consumption reduces the amount of filtered calcium reabsorbed by the kidney. Nine subjects were each fed meals containing 18 g protein and 54 g protein. The intake of energy, sodium, calcium, phosphorus, magnesium and zinc was similar in the two meals. For 4 hours after the meal, measurements were made of serum calcium (total and filterable), serum creatinine, and urinary calcium, creatinine, zinc and nitrogen. Calcium reabsorption was calculated in five clearance periods, as (filterable calcium X GFR) minus urinary calcium. Urinary calcium, zinc and nitrogen were significantly higher between 2 and 4 hours after consumption of the high protein meal. Protein level did not affect urine pH or volume, serum total or filterable calcium & or GFR. The percentage reabsorption of filtered calcium was significantly lower 0.5 hours after the high protein meal, so that at 2.5 hours, reabsorption was 98.0% compared to 98.7% after the lower protein meal. We conclude that protein consumption reduces the amount of calcium reabsorbed by the kidney.

Adult↗
PubMed1978

Calcium metabolism, intestinal calcium-binding protein, and bone growth of rats fed high protein diets.

The rat was used as a model for investigating the mechanism by which the consumption of high diets causes calciuria. Using a combined balance and kinetics study, calcium (Ca) metabolism was studied in 56-day old male rats which had been consuming a control (18% casein) or a high protein (36% casein) diet for 2, 14, or 28 days. Urine Ca was significantly increased to 1.7 mg/day and 1.1 mg/day in rats which consumed the high protein diet for 2 or 14 days respectively. After 29 days of consuming the high protein diet, urinary Ca excretion was 0.7 mg/day, the same as that of controls. No other criteria of calcium metabolism were significantly affected by the high protein intakes. Intestinal calcium-binding protein activity was not affected by consumption of the 36% casein diet for 7 days, nor was bone mineralization after consumption of this diet for 32 days. Since the rat excretes a low percentage of dietary Ca via the urinary route, it is not a useful model for studying Ca kinetics in protein-induced calciuria.

Animals↗
PubMed1975

Water Use Efficiency of Field-grown Maize during Moisture Stress.

Theoretical analysis of the CO(2) assimilation and water loss by single leaves suggests that the water use efficiency of C(4) species decreases as stomatal resistance increases. To confirm this hypothesis for a complete maize crop, results from computer simulations and a field experiment were compiled for varying stomatal resistances. A soil-plant-atmosphere model allowed simulations of the many simultaneous interactions between a crop canopy and its environment. The simulations for varying stomatal resistances clearly indicated that as stomatal resistance increased, water use efficiency of the maize crop decreased. The field experiment data also confirmed that water use efficiency was significantly decreased under water stress conditions when stomatal resistance increased. We concluded that management practices for maize, which induce moisture stress conditions resulting in increased stomatal resistance, reduce both crop photosynthetic productivity and water use efficiency.

Journal Article↗