Inactivation of Oxytocin by Human Myometrial Preparations:I.Preliminary Evidences for the Presence of a Thiol-Oxido-Reductase Activity and an Amino-Peptidase Activity in Crude Extracts

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Abstract
In a planned series of studies of the ways in which human myometrial preparations inactivate oxytocin a pilot study was made with the three synthetic model substrates L‐Cystyl‐di‐β‐Naphthylamide, S‐Benzyl‐L‐Cy‐steinyl‐β‐Naphthylamide, S‐Benzyl‐β‐Mercaptopropionyl‐β‐Naphthylamide and with Oxytocin and Deamino‐oxytocin. The syntheses of S‐benzyl‐β‐cysteinyl‐β‐naphthyl‐amide and S‐benzyl‐β‐mercaptopropionyl‐β‐naphthylamide are described. Incubations with crude extracts from myometria of non‐pregnant women and pregnant women in the three trimesters liberated β‐naphthylamine from L‐cystyl‐di‐β‐naphthylamide and S‐benzyl‐L‐cysteinyl‐β‐naphthylamide but not from S‐benzyl‐β‐mercaptopropio‐nyl‐β‐naphthylamide. The liberation of β‐naphthylamine from L‐cystyl‐di‐β‐naphthylamide was competitively inhibited by oxytocin and non‐competitively inhibited by deamino‐oxytocin. The results are interpreted as giving preliminary evidence for the presence of a thiol‐oxido‐reductase activity and an amino‐peptidase activity in the extracts.

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