Takeda S, Kuwabara Y, Mizuno M
Department of Obstetrics & Gynecology, Faculty of Medicine, Tokyo University, Tokyo, Japan.
Nihon Naibunpi Gakkai Zasshi. 1989 Mar 20;65(3):182-9. doi: 10.1507/endocrine1927.65.3_182.
Oxytocin metabolism seems to occur mainly in the kidney and the liver. Placental cystine amino peptidase (CAP), which inactivates oxytocin by cleavage of the bond between the N-terminal cystine residue and adjacent tyrosine, rises progressively with advancing gestation. The role of CAP in oxytocin metabolism is not clear. To clarify this issue, the authors measure oxytocin metabolic clearance rate(MCR) by the constant infusion of 3mU/min and 6 mU/min synthetic oxytocin in 14 adult subjects: 5 pregnant women (38 approximately 41 weeks gestation), 4 puerperal women and 5 nonpregnant women. Oxytocin MCR (mean +/- SE) during infusion of 3 mU/min was 20.9 +/- 2.6 ml/kg/min in pregnant women; 16.9 +/ 2.4 ml/kg/min in puerperal women; 19.7 +/- 3.3 ml/kg/min in pregnant women. Oxytocin MCR during infusion of 6 mU/min was 22.1 +/- 3.3 ml/kg/min in pregnant women and 22.7 +/- 3.1 ml/kg/min in nonpregnant women. These values were statistically similar. Mean (+/- SE) CAP values were 143.5 +/- 7.8 mU/ml in pregnant women, 60.8 +/- 3.0 mU/ml in puerperal women, and 13.8 +/- 2.7 mU/ml in nonpregnant women. CAP levels in pregnant women were significantly higher than others. 3H-oxytocin degradation was studied in vitro in pooled plasma of pregnant and nonpregnant women. 85% of original 3H-oxytocin was destroyed in pregnant plasma during 1 hour but only below 10% was destroyed in nonpregnant plasma in 2 hours. These results suggest that CAP in pregnant women may not play a role in the inactivation of oxytocin in vivo, thus differing from its role in vitro.
催产素的代谢似乎主要发生在肾脏和肝脏。胎盘胱氨酸氨基肽酶（CAP）通过裂解N端胱氨酸残基与相邻酪氨酸之间的键来使催产素失活，其活性随着妊娠进展而逐渐升高。CAP在催产素代谢中的作用尚不清楚。为了阐明这个问题，作者通过以3mU/分钟和6mU/分钟的速度持续输注合成催产素，对14名成年受试者进行了催产素代谢清除率（MCR）的测量：5名孕妇（妊娠38至41周左右）、4名产后妇女和5名非孕妇。在输注3mU/分钟时，孕妇的催产素MCR（平均值±标准误）为20.9±2.6ml/kg/分钟；产后妇女为16.9±2.4ml/kg/分钟；孕妇为19.7±3.3ml/kg/分钟。在输注6mU/分钟时，孕妇的催产素MCR为22.1±3.3ml/kg/分钟，非孕妇为22.7±3.1ml/kg/分钟。这些值在统计学上相似。孕妇的平均（±标准误）CAP值为143.5±7.8mU/ml，产后妇女为60.8±3.0mU/ml，非孕妇为13.8±2.7mU/ml。孕妇的CAP水平显著高于其他人。对孕妇和非孕妇的混合血浆进行了体外3H-催产素降解研究。在1小时内，孕妇血浆中85%的原始3H-催产素被破坏，但在2小时内非孕妇血浆中只有不到10%被破坏。这些结果表明，孕妇体内的CAP可能在体内催产素失活过程中不起作用，因此与其在体外的作用不同。
