Influence of sarcosine or N-methylalanine in position 7 on the antagonistic properties of [1-deaminopenicillamine]- and [1-(beta-mercapto-beta, beta-cyclopentylmethylene-propionic acid)]-vasopressin.

Substituting sarcosine or N-methylalanine for proline in the inhibitory vasopressin analogs dPAVP and d(CH2)5AVP had the following effects: 1) milk ejection and antidiuretic activities were severely depressed, 2) pressor antagonism was maintained but weakened somewhat, and 3) antagonism in the uterus in vitro was maintained, but no consistent pattern was seen.