Regulation of pyrimidine nucleotide synthesis in rat hematopoiesis

In an attempt to define a regulation of pyrimidine nucleotide synthesis in hematopoietic cells, we investigated the activities of thymidylate synthetase and thymidine kinase, and the cell cycle by flow cytometric DNA analysis and bromodeoxyuridine-immunohistochemistry during the recovery phase of hematopoietic cells in bone marrow after the hypoplastic period induced by cyclophosphamide treatment in rats. The hematopoietic cells first entered into cell cycle via the de novo pathway in pyrimidine nucleotide synthesis, and were secondly proliferated and differentiated via the salvage pathway. S-phase cells associated with a myeloid hematopoiesis increased earlier than those associated with an erythroid hematopoiesis in the recovery phase of in rat bone marrow.