Relaxin activates BMDECs through the RXFP1 relaxin receptor. (A) The peptide B-R13/17K H2 (H2), a relaxin antagonist, was added as indicated to CD34⁺ BMDECs at a concentration of 1μM in the presence or absence of rhRLX (50 ng/mL). Shown is the DAF-FM fluorescence in arbitrary units (± SD) of 2 wells, 20 cells per well. *P < .002 versus all other treatments. Shown is a representative of 3 experiments. (B) BMDECs were isolated from the BM of wild-type littermates and Rxfp1 or Rxfp2 knockout mice and treated with vehicle (black bars) or rhRLX 50 ng/mL (white bars) for 10 minutes before the determining intracellular bioavailable NO by DAF-FM. The NO fluorescence from at least 20 cells was analyzed for each mouse. Shown is the mean DAF-FM fluorescence in arbitrary units (± SD). *P < .009 versus vehicle treated cells. †P < .05 versus untreated cells. n indicates the number of mice studied. (C) Wild-type (^+/+) littermates and Rxfp1 and Rxfp2 knockout (^−/−) mice were implanted with osmotic pumps containing rhRLX, and after 5 days their blood was collected and BMDEC-CFU were determined. Shown is the number of BMDECs (± SD). *P < .01 versus Rxfp1^+/+. n indicates the number of mice studied.