Corticotropin-releasing factor (CRF) has a coronary vasodilator effect and a positive inotropic effect on the isolated rat heart. Recently, expression of CRF receptor type 2 (CRF-R2) has been demonstrated in the heart. In addition, urocortin (Ucn), a new member of the CRF family, has been reported to have much greater affinity for CRF-R2 than CRF. It is suggested that the cardiac effects of Ucn may be more potent than those of CRF. We compared the effect of Ucn with that of CRF on isolated rat heart. The effects of Ucn were then analyzed to determine whether these effects were mediated by CRF receptors and/or any other mediators under the following conditions: perfusion buffer containing (1) alpha-helical CRF 9-41, (2) indomethacin, (3) N(G)-nitro-l -arginine methylester and (4) propranolol. Ucn exhibited a greater effect with a longer duration of action than CRF. Indomethacin significantly attenuated the vasodilator effects of Ucn (P<0.05). CRF receptor antagonist diminished both coronary vasodilation and the positive inotropic effects of Ucn (P<0.05). These results suggest that the cardiac effects of Ucn may be mediated by a CRF receptor, and prostaglandins may be involved in the vasodilator effect.

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