Effect of parathyroid hormone and 1,25-dihydroxyvitamin D₃ on RNA and heme synthesis by erythroid precursors

Parathyroid hormone (PTH) was shown to stimulate RNA and heme synthesis in 12- to 13-day embryonic mouse liver erythroid cells, thus expressing an erythropoietin-like effect. Incubation of erythroid precursors with 1,25-dihydroxyvitamin D₃ (1,25 (OH)₂D₃) had no effect on heme synthesis, and only slightly increased the RNA synthesis, thus showing no enhancement effect of 1,25 (OH)₂D₃ on the PTH stimulating effect on erythropoiesis. The recent data show that even a short period of 15 min incubation with PTH was sufficient to increase RNA synthesis by the erythroid precursors. However, high concentration of PTH was essential for its inhibitory effect and upon removal of the hormone the synthetic capacity of the erythroid precursors has returned to control levels.