Reverse-phase HPLC elution profile of oxytocin immunoreactivity in rat tissues. Tissue extracts, lyophilized and reconstituted in 20% acetonitrile in 0.1% TFA, were applied to a C 18 Bondapak column and were eluted with acetonitrile gradient (20–50%) in 0.1% TFA. ( A ) The extract from the right atrium. ( B ) The extract from the heart perfusates. ( C ) The HPLC profile of OT synthetic standard. ( D ) The extract from the pituitary gland.