hGH promotes proplatelet formation and platelet production by cultured megakaryocytes. (A) Human cord blood-derived CD34⁺ cells were cultured with rhTPO (20 ng/ml) for 7 days and then treated with rhGH (100 ng/ml) for 3 days. Proplatelet formations in representative megakaryocytes were detected by phase contrast imaging (i), and visualized by confocal microscopy (iii) after being stained with anti-β1-tubulin (green) and DAPI (blue). Arrows indicate typical proplatelet formations. (ii) Histogram showing the number of proplatelet-forming megakaryocytes for each group. Data are from 3 independent experiments. Error bars denote SD. **P < .01. (B) Human cord blood-derived CD34⁺ cells were treated with rhSCF (20 ng/ml) in the presence or absence of rhGH (100 ng/ml) for 13 days. (i) Culture-derived platelets were stained with APC-CD41, FITC-CD42b, and PI, and analyzed by flow cytometry. (ii) Mean percentages of CD41⁺CD42b⁺PI⁻ culture-derived platelets are shown. Data are representative of 3 independent experiments. Error bars denote SD. **P < .01. (C) Human cord blood-derived CD34⁺ cells were treated with rhTPO (20 ng/ml) for 7 days and then treated with rhGH (20, 50, or 100 ng/ml) or rhTPO (20 ng/ml) for 6 days. (i) Culture-derived platelets stained with APC-CD41, FITC-CD42b, and PI was analyzed by flow cytometry. (ii) Histogram showing the percentage of CD41⁺CD42b⁺PI⁻ culture-derived platelets in 3 independent experiments. Error bars denote SD. *P < .05; **P < .01.