allatostatins or an active c terminal portion thereof containing at least the c terminal pentapeptide xaa 3 x 1 phe gly x 2 nh 2 xaa 3 being phe or tyr are modified at their n terminus by addition of a hydrophobic moiety which may be an aromatic amine aromatic acid or aliphatic fatty acid a variety of hydrophobic aromatic amines and acids are suitable for use herein preferred acids include phenyl alkanoic alkenoic or alkynoic acids such as 9 fluoreneacetic acid 6 phenyl hexanoic acid or 9 phenyl nonanoic acid while preferred amines include phenyl alkanoic alkenoic or alkynoic amines such as 4 phenyl butyl amine without being limited thereto examples of other suitable aromatic acids include 2 biphenylenecarboxylic acid 9 anthracenecarboxylic acid 1 fluorenecarboxylic acid and 1 pyrenebutyric acid while other suitable aromatic amines include 1 aminoanthracene 6 amino 3 4 benzocoumarin 2 amino 7 bromofluorene 6 aminochrysene 3 aminofluoranthene 9 aminophenanthrene and 1 pyrenemethylamine and suitable aliphatic fatty acids include palmitic acid caprylic acid decanoic acid lauric acid and valeric acid optionally the hydrophobic aromatic amines or acids or the aliphatic fatty acids may further include the amino acid arg conjugated thereto the analog of this second embodiment may be prepared from any member of the allatostatin family of neuropeptides a variety of these allatostatins have been previously described and are suitable for use herein as mentioned the allatostatin polypeptide to which the hydrophobic moiety is attached should include at least an active c terminal portion containing the c terminal pentapeptide xaa 3 x 1 phe gly x 2 nh 2 and may encompass the entire native allatostatin polypeptide however the polypeptide should not be so.