Abstract: Maggy UI (Urotensin I) or flathead sole urotensin, obtained from Hippoglossides Elassodon has the formula: H-Ser-Glu-Glu-Pro-Pro-Met-Ser-Ile-Asp-Leu-Thr-Phe-His-Met-Leu-Arg-Asn-Met- Ile-His-Arg-Ala-Lys-Met-Glu-Gly-Glu-Arg-Glu-Gln-Ala-Leu-Ile-Asn-Arg-Asn-Leu -Leu-Asp-Glu-Val-NH.sub.2. Analogs have been synthesized that are at least as potent as Maggy UI, and Maggy UI or such an analog or a biologically active fragment of either or pharmaceutically acceptable salts of any of the foregoing, dispersed in a pharmaceutically acceptable liquid or solid carrier, can be administered to mammals to achieve a substantial elevation of ACTH, .beta.-endorphin, .alpha.-lipotropin and corticosterone levels and/or an increase in intestinal blood flow and/or a lowering of systemic blood pressure and/or a changing of regional blood distributio over an extended period of time.