Characterization of vasopressin and oxytocin immunoreactivity in the sheep and rat pineal gland: absence of vasotocin and detection of a vasopressin-like peptide.

The presence of arginine-vasopressin (VP), arginine-vasotocin (VT) and oxytocin (OT) were studied in sheep and rat pineal gland by the combination of HPLC and radioimmunoassays. Three immunoreactive substances, which had the same retention time as OT, VP and VT, were detected in sheep and rat pineal extracts after HPLC separation. Parallelism of dilution curve and standard curve demonstrated that two of them were identical to OT and VP respectively. The third component was distinct from VT on basis of its immunological reaction with two different antibodies; it resembled the immunoreactivity of VP. This substance was also detected in the hypothalamus, brain cortex and pituitary gland, but not in the hippocampus and adrenal gland. The results support the notion that VT is absent in the adult mammalian pineal gland and point to the existence of another, possibly related peptide.