Activity of enzymes involved in pyrimidine nucleotide synthesis during uterine growth in cyclic rats.

The pyrimidine nucleotide salvage enzymes, uridine and thymidine kinases, and the enzyme, aspartate carbamyltranferase, involved in de novo synthesis, were investigated to assess their relative contributions to the RNA and DNA precursor requirements of uterine growth in cyclic rats. Only aspartate carbamyltransferase reflected the known fluctuations in plasma oestradiol-17beta and uterine mitotic activity, being minimal at dioestrus 1 and maximal at pro-oestrus. Treatment of ovariectomized rats with oestradiol-17beta stimulated carbamyltransferase activity, but cycloheximide prevented this response, indicating the association between the enzyme and this hormone. Uridine kinase activity did not vary during the oestrous cycle, but there were peaks of thymidine kinase activity on the days of pro-oestrus and the 1st day of dioestrus.