Cardiac inotropic actions of urocortin in conscious sheep

Urocortin (Ucn) is a recently isolated peptide related to the corticotropin-releasing factor (CRF) family, which can produce hemodynamic and hormonal actions in conscious rats. This study examined in detail the cardiovascular actions of Ucn and CRF after intravenous injection in chronically instrumented, conscious sheep. Injection of Ucn produced dose-dependent changes in cardiac contractility [rate of increase of aortic flow (dF/dt)], maximum aortic flow (Fmax), mean arterial pressure (MAP), heart rate (HR), cardiac output (CO), and coronary blood flow (CF). Ucn injected at 100 micrograms produced a potent increase in dF/dt, from 909 +/- 44 to a maximum of 1,849 +/- 901.min-1.s-1, and in Fmax, from 25.5 +/- 0.8 to 36.6 +/- 1.4 l/min. Cardiac contractility increased within 30 min of injection and remained significantly elevated for up to 24 h. MAP increased from 78 +/- 2 to 90 +/- 3 mmHg, and HR increased from 73 +/- 4 to 103 +/- 9 beats/min. CO rose from 5.0 +/- 0.1 to 5.8 +/- 0.2 l/min, whereas central venous pressure, total peripheral conductance, and stroke volume were unchanged. All Ucn-induced cardiovascular effects were inhibited by prior treatment with the CRF antagonist alpha-helical CRF-(9-41). Equimolar doses of CRF produced little change in any hemodynamic parameter. Both peptides increased plasma levels of adrenocorticotropin and cortisol, with Ucn having a more potent effect than CRF. We have shown for the first time that Ucn can produce potent and long-lasting actions to elevate cardiac contractility in conscious animals.