In pineal extracts several activities have been observed which cannot be explained on the basis of their content of melatonin or other pineal indoles to which an antigonadotropic activity is ascribed. The significance of structurally identified and unidentified substances is not fully understood. The list includes a neurohypophysial peptide, vasotocin (AVT), hypothalamic releasing factors and certain unidentified substances including the antigonadotropin under investigation in our laboratory. Our initial experiments demonstrated the presence of a non-melatonin antigonadotropin (PAG) in partially purified extracts of bovine, ovine, rat and human pineals. Purification by ion exchange chromatography and amino acid analyses have shown that this substance is not AVT. Recent purification studies include paper chromatography and high performance chromatography as final steps. It is concluded that if the active principle in a peptide, or contains a peptide moiety important for the biological activity, it may be present only in minute amounts in the puriest fractions derived and the quantities of recoverable material may be similar to those amounts of releasing factors recoverable from hypothalamic tissue. It is anticipated that large scale preparative methods will be required for structural determination. High performance chromatography may prove to be extremely useful in future studies.
