Abstract: Two 32,000-dalton proteins with inhibin activity were isolated from porcine follicular fluid using heparin-Sepharose affinity chromatography, followed by gel filtration on Sephacryl S-200 and then four steps of reverse-phase high-performance liquid chromatography. Each isolated molecular is composed of two chains having molecular weights of about 18,000 and about 14,000 daltons, respectively, which are bound together by disulfide bonding. Microsequencing revealed the NH.sub.2 -terminal portion of the 18K chain of both to be Ser-Thr-Ala-Pro-Leu-Pro-Trp-Pro-Trp-Ser-Pro-Ala-Ala-Leu-Arg-Leu-Leu-Gln-Ar g-Pro-Pro-Glu-Glu-Pro-Ala-Val, of one of the 14K chains to be Gly-Leu-Glu-Cys-Asp-Gly-Arg-Thr-Asn-Leu-Cys-Cys-Arg-Gln-Gln-Phe-Phe-Ile-As p-Phe-Arg-Leu-Ile-Gly-Trp, and of the other 14K chain to be Gly-Leu-Glu-Cys-Asp-Gly-Lys-Val-Asn-Ile-Cys-Cys-Lys-Lys-Gln-Phe-Phe-Val-Se r-Phe-Lys-Asp-Ile-Gly-Trp-Asn-Asp-Trp-Ile-Ile-Ala-Pro.

Abstract: 28-member residue and 25-member residue peptides have been synthesized containing the tetradecapeptide somatostatin that are more potent than somatostatin. Somatostatin-28 has the formula: ##STR1## The three N-terminal amino acid residues are absent in somatostatin-25. Somatostatin-28 or somatostatin-25 or a pharmaceutically acceptable addition salt thereof, dispersed in a pharmaceutically acceptable liquid or solid carrier, can be administered to mammals in the same manner as somatostatin.