Urocortin

Urocortin is a 40-amino acid peptide that is the mammalian homologue of urotensin I (a fish CRF-like peptide) and a member of the corticotropin-releasing factor (CRF/CRH) peptide family. It was discovered in 1995 by Vaughan et al. in rat brain (Edinger nucleus) and is now known to be expressed in the hypothalamus, brainstem, heart, gut, skin, and reproductive tissues.

The CRF peptide family includes: CRF (41 aa), Urocortin (Ucn1, 40 aa), Urocortin 2 (Ucn2, 38 aa), and Urocortin 3 (Ucn3, 38 aa). They act through two G-protein-coupled receptors: - **CRF-R1**: Higher affinity for CRF and Ucn1; primarily mediates anxiety, HPA axis activation, and stress responses - **CRF-R2**: Higher affinity for Ucn2 and Ucn3; mediates stress adaptation, appetite suppression, and cardiac effects

**Receptor selectivity and functional distinction:** - CRF-R1 activation: Anxiogenic, HPA axis stimulation (ACTH→cortisol), suppresses appetite acutely - CRF-R2 activation: Anxiolytic (opposing CRF-R1), positive cardiac inotropy, sustained appetite suppression, stress coping

Urocortin (Ucn1) activates BOTH receptors and thus has complex, sometimes opposing effects depending on which receptor predominates in a given tissue.

**Cardiac research:** Urocortin's most therapeutically promising application is cardiac function. CRF-R2 is expressed on ventricular cardiomyocytes, and Ucn1/2/3 produce positive inotropic effects, increased coronary blood flow, and cardioprotection against ischemia-reperfusion injury via PKC-ε and MAPK. Phase II trials of Ucn2 (Corticotropin-releasing factor type-2 agonist) in heart failure have been conducted and show improved cardiac output.

**Appetite research:** CRF-R2-mediated appetite suppression complements CRF-R1-mediated effects. Ucn3 (CRF-R2 selective) reduces food intake more durably than CRF-R1 agonism without the anxiety component, making it a research target for obesity.