Urotensin II (UII) and urotensin II-related peptide (URP) are functionally selective, suggesting that these two hormones might play distinct physiological role through different interactions with their cognate receptor UT. Hypothesizing that the Phe3 residue of URP, which is also present in UII, is a key-element of its specific UT activation, we evaluated the impact of its replacement by non-natural amino acids in URP. Each compound was evaluated for its ability to bind UT, induce rat aortic ring contraction, and activate Gq, G12, and β-arrestin 1 signaling pathways. Such modifications impaired contractile efficacy, reflected by a reduced aptitude to activate G12 in URP but not in the truncated but equipotent UII4-11. Moreover, we have identified two structurally different UT modulators: [d-Phe(pI)3]URP and [Bip3]URP, which exert a probe-dependent action against UII and URP. These compounds should help us understand the specific roles of these hormones as well as guide further therapeutic development.