Corticotropin-releasing factor(CRF), which activates the hypothalamic-pituitary-adrenal axis under stress, also has proinflammatory peripheral effects possibly through mast cells. The purpose of this study was to investigate the effect of urocortin (UCN), a 40-amino-acid CRF family peptide, on degranulation and intracellular calcium of rat lung mast cells. The activation and degranulation of mast cells were observed by Toluidine blue staining and transmission electron microscope. The intracellular calcium was investigated using confocal laser scanning microscopy and flow cytometry. The results indicated that all the three different concentrations of UCN(0.1, 1 and 10 mu M) significantly induced the activation and degranulation of rat lung mast cells in vitro. This effect was markedly blocked by selective CRF receptor 1(CRF-R1) antagonist antalarmin, but not by specific CRF receptor 2(CRF-R2) antagonist antisauvagine-30(anti-Svg-30). The results also showed that UCN caused a rapid peak increase inCa2+(i) at point of 300s after UCN treatment, followed by a decrease to a sustained plateau phase. The peak increase inCa2+(i) induced by UCN was significantly inhibited by antalarmin, but not by anti-Svg-30. This effect of UCN onCa2+(i) in rat lung mast cells was also found by flow cytometry. Regression analysis revealed a positive correlation between mast cells degranulation extent and the maximum value ofCa2+(i)(P < 0.01). Taken together, our present study suggested that UCN induced the increase of Ca2+(i) and degranulation of rat lung mast cells through CRF-R1. These findings may have implications for the pathophysiology of allergic and inflammatory lung disorders such as asthma, which is closely associated with mast cell activation and degranulation. Copyright (c) 2008 S. Karger AG, Basel. The purpose of this study was to investigate the effect of urocortin (UCN), a 40-amino (CIN), a pro-inflammatory cytokine -acid CRF family peptide, on degranulation and intracellular calcium of rat lung mast cells. The activation and degranulation of mast cells were observed by Toluidine blue staining and transmission electron microscope. The intracellular calcium was investigated using confocal laser scanning microscopy and flow cytometry. The results indicated that all the three different concentrations of UCN (0.1, 1 and 10 mu M) significantly induced the activation and degranulation of rat lung mast cells in vitro. This effect was markedly blocked by selective CRF receptor 1 (CRF-R1) antagonist antalarmin , but not by specific CRF receptor 2 (CRF-R2) antagonist antisauvagine-30 (anti-Svg-30). The results also showed that UCN caused a rapid peak The increase in Ca2 + (i) induced by UCN was significantly inhibited by antalarmin, but not by anti-Svg-30. This effect of UCN onCa2 + (i) in rat lung mast cells was also found by flow cytometry. Regression analysis revealed a positive correlation between mast cells degranulation extent and the maximum value of Ca2 + (i) (P <0.01). Taken together, our present study suggested suggested that UCN induced the increase of Ca2 + (i) and degranulation of rat lung mast cells through CRF-R1. These findings may have implications for the pathophysiology of allergic and inflammatory lung disorders such as asthma, which is closely associated with mast cell activation and degranulation Copyright (c) 2008 S. Karger AG, Basel.