Enzyme immunoassay (EIA) of intracellular cAMP in human CD34⁺ cells. Highly enriched human CD34⁺ cells were stimulated with CRH (1 × 10^–6 M), orexin A (1 × 10^–6 M), or orexin B (1 × 10^–7 M). Afterward, intracellular cAMP concentration was measured by EIA and compared with untreated controls. CD34 cell samples of 6 patients were examined in duplicate. The lines in each bar represent one standard deviation. Significant changes (P < .001) are indicated (*).