SUMMARY OF THE INVENTION
Dodecapeptides of the formula: ##STR2## where
X.sub.1 is either D- or L- Lys, Arg, His or Orn;
X.sub.2 is either D- or L- Asn, His, Glu, Asp, Tyr or Trp;
X.sub.3 is either D- or L- Trp;
the linear precursor intermediates thereof and pharmaceutically acceptable salts and