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Much evidence now exists to show that unbalanced DNA precursor pools cause DNA replicational infidelity in vitro. However, there are relatively few data with in vivo systems. Experiments were performed therefore, to determine if unbalanced precursor pools could be induced in vivo and if so, what affect this would have on various genetic markers. The nucleoside thymidine was shown to be completely non-toxic to the rat when administered orally, negative in the dominant lethal assay and was only marginally clastogenic in the micronucleus test. Treatment of human lymphocyte chromosomes with the essential amino acid arginine, arrested cell division possibly due to a predominance of arginine-rich histones limiting the chromatin-condensation during mitosis. Thymidine administered i. p. to mice induced marked increases in the proportions of abnormal sperm and the same effect, to a lesser extent, was seen in rats. The affected germ-cell stages were the mid - to late pachytene spermatocytes. These affects were probably due to base-misincorporation occuring during unscheduled DNA synthesis. The purine nucleoside adenine caused dose-related increases in the frequency of abnormal sperm in mice. In rats, a proportion of animals given 150mg/kg adenine showed high levels of abnormal sperm whilst others were unaffected. Examination of mice in the generation revealed that the damage to the germ-cells was transmissible. The simultaneous administration of deoxycytidine with excess thymidine to mice partly inhibited the effects on sperm morphology indicating that those effects were due to precursor pool imbalance. In addition, an analytical technique was developed to measure nucleosides and bases in the testes using HPLC. The method proved to be rapid, reproducible and quantitative and showed that 1hr following i. p. injection, thymidine levels in the testes increased markedly and thereafter quickly return to control levels. Finally, experiments were initiated to investigate the mechanisms underlying the formation of morphogically abnormal sperm. Polyacrylamide gel electrophoresis was used to identify membrane proteins in sperm from both control and treated animals.

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Consumer-driven nutrient cycling has been shown to be an important process in supplying inorganic nutrients to autotrophic and heterotrophic organisms in aquatic ecosystems. Theory indicates that consumer nutrient excretion is influenced primarily by an organism's nutrient composition; however, an organism's diet should also play an important role in nutrient excretion, especially if the consumer is nutrient limited. This study asks the question, how does diet influence nutrient excretion of consumers at different trophic levels? Macroinvertebrates and fish were collected from six streams and nitrogen (N) and phosphorus (P) excretion were quantified. Epilithon, leaf detritus, and seston (fine particulate organic matter in transport) were collected and analyzed for carbon (C), nitrogen (N), and phosphorus (P) content in an attempt to qualitatively assess the nutritional status of the diet of primary consumers. Macroinvertebrates were also analyzed for C, N, and P content to assess their nutritional composition in relation to their excretion and also to assess the nutritional composition of the diet of predatory insects and fish. Fish were also analyzed for C, N, and P. Similar to theoretical predictions, fish and macroinvertebrate P excretion was negatively related to P content and the N:P excretion ratio was negatively related to the body N:P ratio. However, this relationship was driven primarily by two phosphorus rich species, mottled sculpin in the fish and crayfish in the macroinvertebrates. Some relationships did emerge between consumer excretion and diet. For example, hydropsychid caddisflies had the highest macroinvertebrate P excretion, possibly explained by the low N:P of seston. However, shredders, eating on a very low N and P diet of leaf detritus, had very low N and P excretion. The relationship between consumers, their food, and nutrient excretion is a matter of mass balance. If the food N:P ratio is higher than that of the consumer, then the N:P excretion should be higher than the consumer N:P and the food N:P, especially if organisms are P-limited. However, N:P excretion by macroinvertebrates and fish were very similar despite large differences in diet. The majority of macroinvertebrates and fish had a lower N:P excretion ratio than the predicted N:P of their food, possibly indicating that 1) consumers were either selectively consuming more P-rich foods than the diets that I assigned them or 2) consumers are generally not N or P limited or influenced by the N or P in their diet. Mottled sculpin and crayfish were the only organisms with a higher N:P excretion than their resources and both had a higher %P than the other fish and macroinvertebrates, respectively. High N:P excretion along with high phosphorus content is indicative of P-limitation. Macroinvertebrates and fish, excluding mottled sculpin and crayfish, had a lower N:P excretion and the N:P ratio of the water column. If consumers do play a role in nutrient dynamics, then consumers could alter the relative abundance of nitrogen and phosphorus by supplying more phosphorus. However, the presence of a P-limited organism, such as mottled sclupin or crayfish, could alter the relative abundance of nitrogen and phosphorus by supplying less phosphorus. / Master of Science

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Yiu Kwan. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 106-117). / Abstract also in Chinese. / Abstract --- p.1 / Chinese abstract --- p.4 / Acknowledgment --- p.5 / Abbreviations --- p.7 / Content --- p.9 / Chapter I. --- Introduction --- p.11 / Chapter II. --- Literature Review --- p.14 / Chapter II. 1. --- Basic concepts --- p.14 / Chapter II.2. --- Clinical aspects of enzymology --- p.17 / Chapter II.3. --- Changes fetal enzymes in neonate --- p.34 / Chapter III. --- Materials and Methods --- p.48 / Chapter III. 1. --- Study population --- p.48 / Chapter III.2. --- Sample collection and storage --- p.49 / Chapter III.3. --- Determination of cardiac and hepatic enzymes in plasma --- p.51 / Chapter III.4. --- Data handling and statistical analysis --- p.67 / Chapter IV. --- Results --- p.68 / Chapter IV.1. --- Study population --- p.68 / Chapter IV.2. --- Enzyme reference values in cord blood --- p.72 / Chapter IV.3. --- Changes in fetal enzymes in relation to acid-base status at birth --- p.78 / Chapter IV. 4. --- Changes fetal enzymes in relation with other obstetric events --- p.80 / Chapter IV.5. --- Variables related to fetal enzymes levels --- p.85 / Chapter V. --- Discussion --- p.93 / Chapter V. 1. --- Reference value for cardiac and liver enzymes in cord blood for current study population --- p.93 / Chapter V.2. --- Changes fetal enzymes in relation to fetal acid-base status --- p.95 / Chapter V.3. --- Changes in fetal enzymes in relation with other obstetric variables --- p.99 / Chapter V.4. --- Analysis of inter-relationships between obstetric variables and fetal enzymes --- p.102 / Reference --- p.106

Une vision et une cohérence d’ensemble : telles sont les qualités qui manquaient à la notion de déséquilibre significatif inscrite dans trois règles du Code de la consommation, du Code de commerce, et nouvellement du Code civil. Tels sont également les objectifs que se propose d’atteindre cette étude, au travers d’une double démarche. Par la conception, en premier lieu, d’une méthode unitaire et séquencée de qualification du déséquilibre significatif, construite à partir des deux règles spéciales, et applicable à chacune d’elles, mais aussi généralisable, au-delà de celles-ci, à la règle de droit commun des contrats. Par l’élaboration, d’autre part, d’un principe de solution destiné à régir l’articulation entre ces trois règles, prenant la forme d’un principe de non-cumul et de non-option, lequel suppose, pour être pleinement réalisé, de procéder à une redéfinition du domaine d’application personnel de chacune d’elles. / A vision and an overall coherence: these are the qualities that were missing from the notion of Ŗsignificant imbalanceŗ inscribed in three rules of the Consumer code, the Commercial code, and, most recently, the Civil code. These are also the objectives that this study proposes to achieve through a double approach. First, it proposes a unitary and sequenced method of qualifying the significant imbalance constructed from the two special rules, and, while being applicable to each of special rules, it can also be generalized beyond them in the general rule of common law. Secondly, it elaborates to form a solution principle intended to govern the articulation between the new rule of common law and one of the pre-existing consumer or competition law, consisting of a principle of non-cumulation and non-option which requires, more broadly, a redefinition of the scope of both.