Abstract
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.