[2,4-Dileucine]oxytocin. A Polypeptide with Natriuretic and Diuretic Activities, and an Inhibitor of the Oxytocic Response of Oxytocin^1a,b

[2,4-Dileucine]oxytocin, an analog of oxytocin in which the tyrosine in position 2 and the glutamine in position 4 have both been formally replaced by leucine, has been synthesized from the corresponding protected nonapeptide intermediate. The analog was found to possess negligible pressor activity and no antidiuretic or oxytocic activities. However, [2,4-dileucine]oxytocin has a natriuretic activity and a weak diuretic effect. Furthermore, it was shown to be an inhibitor to oxytocin in the oxytocic in vitro assay system.