Abstract: A peptide is provided for use as a diagnostic imaging, radiotherapeutic, or therapeutic agent, which peptide has a conformationally constrained global secondary structure obtained upon complexing with a metal ion. The peptide is of the general formula:R.sub.1 --X--R.sub.2where X is a plurality of amino acids and includes a complexing backbone for complexing metal ions, so that substantially all of the valances of the metal ion are satisfied upon complexation of the metal ion with X, resulting in a specific regional secondary structure forming a part of the global secondary structure; and where R.sub.1 and R.sub.2 each include from 0 to about 20 amino acids, the amino acids being selected so that upon complexing the metal ion with X at least a portion of either R.sub.1 or R.sub.2, or both, have a structure forming the balance of the conformationally constrained global secondary structure.

Abstract: High affinity linked, branched or linear repeat peptides containing two or more biological-function domains and at least one medically useful metal ion-binding domain are labeled with medically useful metal ions for use in a variety of diseases and pathologic conditions, including diagnosis and treatment of diseases. Such peptides include high affinity chemotactic peptides containing a biological-function domain which includes at least two linked N-formyl-MLF (SEQ. ID NO. 2) sequences and high affinity repeat and branched peptides containing two or more YIGSR (SEQ. ID NO. 1) sequences.

Abstract: Cyclic lactam peptides, seven amino acids in length, having D-2'-naphthylalanine (D-2'-Nal) or D-para-iodo-phenylalanine D-(p-I)Phe at position 4 of the peptide provided potent and specific antagonists of the two neural melanocortin receptors and of the peripheral receptor. In particular, the peptide ##STR1## was found to be a potent antagonist of the MC3 and MC4 receptors with partial agonist activity, and a full agonist of the MC1 and MC5 receptors; the peptide ##STR2## was found to be a potent antagonist of the MC3 and MC4 receptors with partial agonist activity. Both peptides have antagonist activities in the classical frog skin bioassay for pigmentation at the MC1 receptor.

Abstract: A novel class of cyclic bridged analogs of .alpha.-MSH are described herein. With the described analogs, when administered in pharmaceutical compositions, it is now possible to achieve normalization of hypopigmentation dysfunctions and to achieve darkening of the skin in the total absence of sun or UV light irradiation.