Hematopoiesis in the embryonic mouse spleen. II. Alterations after phenylhydrazine administration to the mothers

The effect of phenylhydrazine (PHZ) on the hematopoietic events in the embryonic spleeen of C₅₇Bl/6J mice was examined by light and electron microscopy. Following PHZ injections to the mothers, the embryonic spleen revealed a marked increase in erythroid precursors, with a shift to mature cells. This phenomenon was part of a more generalized stimulation of erythropoiesis, expressed by a shift to mature red cell precursors in the embryonic livers and an increase in the percentage of non‐nucleated cells in the embryonic peripheral blood. Concomitantly stimulation of phagocytosis in the spleen of embryos in the early gestational days and increased vascularity were observed, and a later effect of granulocytopoietic stimulation. The effect on erythropoiesis in the embryonic spleen might be a sequence of erythropoietin stimulation, either in the mothers or the fetuses, due to anemia and hypoxia following PHZ injections.