Oxytocin oxytocinase

Oxytocin is metabolized by oxytocinase, which is produced by the placenta and appears to regulate uterine oxytocin. Oxytocinase does not appear to affect plasma oxytocin, which is metabolized by the liver and kidney. 

M. Naruki, S. Mizutani, K. Goto, M. Tsujimoto, H. Nakazato, A. Itakura, M. Mizuno, O. Kurauchi, F. Kikkawa, Y. Tomoda, Oxytocin Is Hydrolyzed by an Enzyme in Human Placenta That Is Identical to the Oxytocinase of Pregnancy Serum , Peptides 1996, 17, 257-261. 

Dispostion Oxytocin is subject to enzymatic hydrolysis, primarily by tissue oxytocinase. 

Because of the metabolic lability of peptide bonds, metabolic inactivation is likely to play a particularly important role in the overall action of the peptide hormones. Structural alterations in the hormone molecule which increase metabolic stability would be expected to increase the duration of hormone action. Oxytocin is well known to be inactivated by an enzyme present in the serum of pregnant primates ( serum oxytocinase" see (1) but also more generally by homogenates of various tissues including the kidneys and liver. The major pathway of oxytocin inactivation by liver cell-sap has been shown to involve reductive fission of the disulphide bond followed by aminopeptidase degradation of the peptide chain (2). In an effort to obtain peptides resistant to aminopeptidase action we introduced D-hemicystine and N-methylhemicystine into the amino terminal position of... 

Oxytocinase (EC 3.4.1), an o-aminopeptide amino acid hydrolase which inactivates oxytocin, is present in blood during pregnancy. It contains sialic acid (Tuppy et al., 1963) which, according to Sjoholm... 

Sjoholm, L, 1967, Biochemical studies on oxytocin and oxytocinase, Acta Pharm. Suedcica 4 81-96. 

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