X1-X2-X3-X4-X5-X6-X7-R¹   (I)

wherein,

X1 represents Nle or X-Nle, wherein X represents an amino acid or a di-, tri-, tetra- or penta-peptide consisting of polar or hydrophilic amino acid residues selected from the D and L forms of Asp, Glu, His, Arg, homoArg, Tyr, Asn, Ser, Thr, Lys, Orn, Dap, Dab and Gln and wherein X may furthermore contain one or two amino acid residues selected from Gly, β-Ala or the D and L forms of Pro, Hyp, and Ala;

and wherein the N-terminal amino group of X1 may optionally be acylated with an acyl moiety, R—C(O)—, wherein R presents an alkyl or alkenyl with up to 6 carbon atoms, wherein said alkyl may optionally be substituted with one or more substituents selected from hydroxyl and amino;

X2 represents Glu or Asp;

X3 represents Cit, Dab, Dap, cyclohexylglycine, cyclohexylalanine, Val, Ile, tert-butylglycine, Leu, Tyr, Glu, Ala, Nle, Met, Met(O), Met(O₂), Gln, Gln(alkyl), Gln(aryl), Asn, Asn(alkyl), Asn(aryl), Ser, Thr, Cys, Pro, Hyp, Tic, 2-PyAla, 3-PyAla, 4-PyAla, (2-thienyl)alanine, 3-(thienyl)alanine, (4-thiazolyl)Ala, (2-furyl)alanine, (3-furyl)alanine, Phe, wherein the phenyl moiety of said Phe is optionally substituted by halogen, hydroxyl, alkoxy, nitro, benzoyl, methyl, trifluoromethyl, amino, or cyano;

X4 represents D-Phe, wherein the phenyl moiety in D-Phe may optionally be substituted with one or more substituents selected from halogen, hydroxy, alkoxy, nitro, methyl, trifluoromethyl and cyano;

X5 represents Arg;

X6 represents Trp;

X7 represents Lys or Orn, wherein to make the peptide of formula I cyclic an amide bond is formed between the side chain carboxyl of X2 and the side chain amine group of X7;

R1 represents —N(R″)₂ or —OR″ with each R″ independently representing hydrogen or C_1-6alkyl, which may optionally be substituted with one or more amine or hydroxyl;

provided that if X3 represents Hyp, Ala, Pro, Glu, Lys or Gln, and X1 represents Ac-Nle, then X2 does not represent Asp; or