Is oxytocin present in platelets?

For arginine-vasopressin (AVP) it has been suggested that about 90% of the total amount present in peripheral blood is platelet-membrane bound. Oxytocin (OT) and AVP are nonapeptides which are similar in many respects. We investigated the possibility that OT might be found in platelet-rich plasma samples from patients undergoing ovarian super-stimulation for in-vitro fertilization purposes. These plasma samples were treated with acid repeated freezing/thawing and sonification in an attempt to solubilize or expose the possible bound OT. No differences between OT concentrations in platelet-rich or -poor plasma samples were found. We conclude that plasma OT is not bound or confined to platelets.