“…Many PRH candidates have been suggested, but overwhelming evidence suggests oxytocin (OT) as the main PRH. The cell membrane of lactotrophs bear OT receptors (Chadio and Antoni, 1989), administration of OT stimulates PRL secretion (Chadio and Antoni, 1993;Lumpkin et al, 1983;Salisbury et al, 1980;Samson et al, 1989) and antagonism of OT prevents PRL release (Arey and Freeman, 1989;Arey and Freeman, 1990;Johnston and Negro-Vilar, 1988;McKee et al, 2007;Sarkar, 1988). Estradiol also influences OT synthesis (Breton et al, 1995) and secretion (Yamaguchi et al, 1979), suggesting an additional permissive role of E 2 on PRL secretion via control of OT.…”