Experiments were conducted to investigate the effect of reducing dietary anion-cation balance (AC-balance), defined as meq $ sp circ$(Sodium + Potassium)-(Chloride + Sulfur) S, on calcium (Ca) metabolism. Reducing the dietary AC-balance from +314 to $-22$ (meq kg$ sp{-1}$ dry matter (DM)) did not affect plasma Ca level but reduced Ca retention mainly due to a 10-fold increase in urinary Ca excretion with similar rate of apparent absorption. It also decreased urine pH and titratable acidity. The response to induced hypocalcemia created by the infusion of 4.6% EDTA solution revealed that reducing dietary AC-balance from +354 to +37 (meq kg$ sp{-1}$DM) did not affect the volume of the compartment, within which there was rapid equilibration of free Ca but tended to increase the rate of Ca mobilization from it during the infusion. The Ca kinetic study with a four-compartment model indicated that reducing dietary AC-balance from +338 to $-127$ (meq kg$ sp{-1}$DM) during the eucalcemic period and from +429 to $-147$ (meq kg$ sp{-1}$DM) during an EGTA-infusion period (simulated lactational Ca loss) caused hypercalciuria and increased ionized form of plasma Ca. Increased true intestinal Ca absorption and reduced bone accretion were observed in the lowest AC-balance diet only during the EGTA-infusion period. There were no differences in the size of total exchangeable Ca pool but the amount of Ca movement between them tended to increase in reduced AC-balance diets during both periods. Results indicated that feeding reduced AC-balanced diet may have a beneficial role in preventing parturient paresis (milk fever) by increasing Ca flux through the exchangeable Ca pool and Ca mobilization capability.

D.Sc. (Botany) / Please refer to full text to view abstract

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The experiment was designed to demonstrate the effects of exercise and confinement on the calcium metabolism of rats. A subsidiary purpose was to determine if any such effects are mediated by a humoral agent. Twenty-four male Sprague Dawley rats were divided into three groups. One group was exercised in motorized activity cages for one hour per day five days per week; one group was confined in small individual metabolism cages for 26 days and in body holders for 12 days; one group was housed in individual metabolism cages and served as controls. Half of the rats of each of the above three groups received 2 ml whole blood from rats similarly treated (exercised, confined or control), on each of the last five days of the experiment. Thus the exercised rats received blood from confined rats, the confined rats received blood from exercised rats and the control rats received blood from control rats. A calcium balance study was carried out for the last 26 days of the 38 day experiment and a calcium-45 balance study was carried out for the last six hours of the experiment. Thus the following specific parameters of calcium metabolism were measured: calcium balance, per cent calcium utilization, food intake, faecal calcium, urinary calcium, total carcass calcium, femur calcium, calcium-45 absorption and femur calcium-45. The entire experiment was performed twice and the data analyzed using a randomized complete block design analysis of variance. The exercise or confinement did not significantly alter the calcium metabolism of the male Sprague Dawley rat under the conditions of this study. Two possible conclusions were discussed. Either this experiment casts some doubt on the current concepts regarding immobilization and osteoporosis, or that the humane conditions adopted in this study did not successfully immobilize the rats. The present experiment also suggests that regular vigorous exercise may not affect the calcium metabolism of the rat to a greater extent than normal activity or mild exercise. No conclusions could be drawn about the role of the blood in regulating or controlling the effects of exercise or confinement on calcium metabolism. / Medicine, Faculty of / Cellular and Physiological Sciences, Department of / Graduate

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Although the therapeutic benefits of calcium supplementation have yet to be fully determined, popular literature has promoted this practice to combat osteoporosis. This study examined the potential bioavailability of calcium from various supplement and antacid forms. Four dosage levels were studied for each of five sources, including leading supplements Caltrate and Os-Cal, two "calcium rich" antacids, Tums and Rolaids, and a calcium carbonate control. These samples were subjected to four gastric treatments in an in vitro digestion procedure designed to observe the influence of acid secretion on calcium solubility. Depending on the degree of acidity of these solutions, solubility behavior of CaCO3 was highly variable. Normal and reduced acid treatments adequately solubilized between 85 and 88% of the total calcium, whereas negligible quantities were dissolved in deionized water or the achlorhydric solution. Relative availability of calcium from the various sources differed according to gastric treatment. Tums, Caltrate and Os-Cal had dissolution rates that were similar to reagent grade CaCO3. Rolaids provided a significantly lower amount of soluble calcium under all of the experimental conditions (P < 0.001). Amounts of available calcium increased with increasing dosages. The effectiveness of fortification techniques used to increase the calcium content of various food systems was also examined. Fortified orange juice and yogurt samples were found to contain a quantity of available calcium comparable to that found in milk. It was concluded that both of these approaches are reasonable for increasing calcium intakes in individuals with normal gastric secretion. / Master of Science

Calcium is an important factor in many cellular activities and in the maintenance of structural integrity of membranes. Calcium accumulation in the rat lens above the normal physiological range (0.11 µmol/g wet weight) has been associated with formation of cataracts. Selenite is known to influence the histological characteristics of the lens and also alter important biochemical functions. In the selenite induced cataract calcium levels increase as much as 5-fold above normal, the increase preceding appearance of mature opacity by 24 hours. Calcium in the lens rapidly exchanges with labelled calcium in the incubation medium and. establishes equilibrium within 30 minutes. Selenite, accumulated in lens in vivo, causes a 5-6 fold increase in lens calcium over controls during a 24 hour incubation in modified Hank's medium at 37°C. In vitro lmM selenite in the culture medium results in a 15-fold increase in lens calcium, a 17-fold increase in sodium/potassium ratio, and a 60% increase in lens hydration. Efflux of calcium from in vivo and in vitro selenite-treated lens is not impaired. The lens retains the capability to transport 3-4 fold greater calcium over controls from lenses which have accumulated excess calcium in the presence of selenite. In vivo selenite treatment results in a 2.5-fold increase only of extracellular water. In in vitro selenite-treated lenses, however, there is a 2.6-fold increase in extracellular water and a 1.8-fold increase of intracellular water. Selenite treatment of the lenses in vivo and in vitro causes a greater influx of calcium into the lens. Calcium accumulation may act in a nonspecific manner altering lens biochemical functions, membranes and structure, causing development of relationships between selenite induced lens fiber opacities. cataract and cell the associated changes in lens calcium content further validates this model for studying the biochemical changes which impact cataract formation. / Master of Science

by Wong Ka-Hing. / "September 2004." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2004. / Includes bibliographical references (p. 226-279). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy