Detection and high performance liquid chromatography identification of the summer rises of vasopressin and oxytocin immunoreactivity in the rat pineal gland.

The vasopressin (VP) and oxytocin (OT) contents of the rat pineal gland during the summer period were determined by RIAs. Both the levels of VP immunoreactivity and OT immunoreactivity rose markedly in August. The highest level of VP immunoreactivity occurred on August 6 [82 +/- 19 fmol/gland (+/- SEM)], compared to basal levels of 14 +/- 2 fmol/gland. Basal levels of OT immunoreactivity of 20 +/- 8 fmol/gland increased to a peak level of 193 +/- 72 fmol/gland on August 14. Analysis of immunoreactive components by HPLC demonstrated that rises were due to the peptides coeluting with authentic VP and OT, respectively. Levels of immunoreactive VP and OT in the hypothalamus, pituitary gland, and hippocampus did not show variation during the summer. The results show that the VP and OT content of the pineal gland is regulated in a tissue-specific fashion by seasonal influences.