Crosstalk between foetal vasoactive peptide hormones and placental aminopeptidases regulates placental blood flow: Its significance in preeclampsia.

In pregnancy, placental circulation occurs through two independent circulation systems: foetoplacental and uterine (spiral artery)-placental lake. Crosstalk between the foetal peptide hormones, angiotensin II (A-II) and vasopressin (AVP), and their degrading placental aminopeptidases (APs), aminopeptidase A for A-II and placental leucine aminopeptidase for both AVP and oxytocin, primarily regulate placental circulation. On the other hand, placental circulation represents an arteriovenous shunt. In normal pregnancy, the blood pressure decreases, despite increased cardiac output and plasma volume, probably due to the arteriovenous shunt in the growing placenta. Actually, the foetal vasoactive hormones in the foetoplacental circulation are much higher than those in the maternal circulation throughout pregnancy. In normal pregnancy, AP activity derived from the placenta in maternal blood increases with gestation and placental growth. Foetal hypoxia increases the secretion of foetal both AVP and A-II. Although there is an increase in both AP activities in the maternal blood in normal pregnancy, their activities increase more than those in normal pregnancy during mild preeclampsia. However, both AP activities decline significantly compared than those in severe preeclampsia. This suggests that AP prevents leakage of increased foetal vasoactive hormones into the maternal blood in mild preeclampsia, and its protective role breaks down in severe preeclampsia, leading to a massive leak of the hormones into maternal circulation and consequent marked contraction of both the maternal vessels and the uterus. Consequently, AP activity in both placenta and maternal blood acts as the foeto-maternal barrier for foetal vasoactive hormones and thus contributes to the onset of preeclampsia.

The Multifaceted Nature of Aminopeptidases ERAP1, ERAP2, and LNPEP: From Evolution to Disease.

In the human genome, the aminopeptidases ERAP1, ERAP2 and LNPEP lie contiguously on chromosome 5. They share sequence homology, functions and associations with immune-mediated diseases. By analyzing their multifaceted activities as well as their expression in the zoological scale, we suggest here that the progenitor of the three aminopeptidases might be LNPEP from which the other two aminopeptidases could have derived by gene duplications. We also propose that their functions are partially redundant. More precisely, the evolutionary story of the three aminopeptidases might have been dictated by their role in regulating the renin-angiotensin system, which requires their controlled and coordinated expression. This hypothesis is supported by the many species that lack one or the other gene as well as by the lack of ERAP2 in rodents and a null expression in 25% of humans. Finally, we speculate that their role in antigen presentation has been acquired later on during evolution. They have therefore been diversified between those residing in the ER, ERAP1 and ERAP2, whose role is to refine the MHC-I peptidomes, and LNPEP, mostly present in the endosomal vesicles where it can contribute to antigen cross-presentation or move to the cell membrane as receptor for angiotensin IV. Their association with autoinflammatory/autoimmune diseases can therefore be two-fold: as "contributors" to the shaping of the immune-peptidomes as well as to the regulation of the vascular response.

Social behaviour is altered in the insulin-regulated aminopeptidase knockout mouse.

Oxytocin, and the closely related neuropeptide, vasopressin, are both known to modulate social behaviours. The pro-social effects of oxytocin are well-documented and have generated much interest into its suitability as a therapeutic for disorders characterised by social dysfunction. This study investigated the social phenotype of mice with a targeted deletion of the gene for insulin-regulated aminopeptidase, an enzyme involved in the degradation of oxytocin and vasopressin. In the 3-chamber sociability test, a genotype effect was observed and subsequent post hoc analysis revealed that male, but not female, insulin-regulated aminopeptidase knockout mice made significantly more approaches to the enclosure holding a stranger mouse than did wildtype mice (p = 0.0039). Male insulin-regulated aminopeptidase knockout mice also displayed decreased rearing (t = 2.309, df = 24, p = 0.0299) and locomotor activity (t = 2.134, df = 24, p = 0.043) in the open field test, suggestive of a reduced stress response to a novel environment. Our findings provide support for the role of insulin-regulated aminopeptidase in influencing social behaviour, possibly via modulation of oxytocin and vasopressin levels. The increase in social interaction observed in the male, but not female, insulin-regulated aminopeptidase knockout mice is in agreement with reports of sex differences in effects of oxytocin and vasopressin on social behaviours and should be explored further.

27-Hydroxycholesterol impairs neuronal glucose uptake through an IRAP/GLUT4 system dysregulation.

Hypercholesterolemia is associated with cognitively deteriorated states. Here, we show that excess 27-hydroxycholesterol (27-OH), a cholesterol metabolite passing from the circulation into the brain, reduced in vivo brain glucose uptake, GLUT4 expression, and spatial memory. Furthermore, patients exhibiting higher 27-OH levels had reduced 18F-fluorodeoxyglucose uptake. This interplay between 27-OH and glucose uptake revealed the engagement of the insulin-regulated aminopeptidase (IRAP). 27-OH increased the levels and activity of IRAP, countered the IRAP antagonist angiotensin IV (AngIV)-mediated glucose uptake, and enhanced the levels of the AngIV-degrading enzyme aminopeptidase N (AP-N). These effects were mediated by liver X receptors. Our results reveal a molecular link between cholesterol, brain glucose, and the brain renin-angiotensin system, all of which are affected in some neurodegenerative diseases. Thus, reducing 27-OH levels or inhibiting AP-N maybe a useful strategy in the prevention of the altered glucose metabolism and memory decline in these disorders.

New insights into the role of sex steroid hormones in pregnancy: possible therapeutic approach by sex steroid hormones for the treatment of both preeclampsia and preterm labor.

Fetal peptide hormones are essential for the development of fetus, which increase in accordance with pregnancy term. Concentration of these hormones within the feto-placental unit is normally higher than that of maternal circulation. Since these hormones are biologically active, the leakage of these hormones into the maternal circulation is regulated by degradation activity by placental aminopeptidases, in order to maintain the balance between carriage of pregnancy and onset of labor.Because the concentration of these hormones, being regulated by the amount of endogenous production and by physiological degradation by enzymes in the blood and tissue, the balance between production and degradation is a definitive element for maintaining normal gestation and term delivery.The changes of the balance between fetal angiotensin II (A-II) and vasopressin (AVP) andA-II and AVP degrading enzymes, between aminopeptidase A (APA) and placental leucine aminopeptidase( P-LAP) - in the placenta and maternal blood due to fetal stress such as hypoxia - are the provable causes of preeclampsia or preterm labor.Induction of APA and P-LAP by estradiol benzoate (E2) and progesterone (P) from placenta has been demonstrated. They are involved in the regulation of fetal peptide hormones via placental aminopeptidases in homeostasis of pregnancy.Recently it was shown that both APA and P-LAP could be potentially safe and effective drugs for preeclampsia and preterm labor. The authors' proposed sex steroid treatment with dose increasing manner by gestational week (sex steroid treatment) for severe preeclampsia and preterm labor could be candidates replacing conventional treatments. In light of lacking safe and effective medication, the proposed sex steroid treatment is worthwhile for the prospective controlled studies for the treatment of both preeclampsia and preterm labor.

Deletion of insulin-regulated aminopeptidase in mice decreases susceptibility to pentylenetetrazol-induced generalized seizures.

The peptide angiotensin IV (Ang IV) influences seizure susceptibility in rat and mouse models. Indeed, Ang IV has been shown to protect rats from limbic seizures in the focal pilocarpine model. Moreover, both anticonvulsive and antiepileptogenic effects of Ang IV have been reported in the acute pentylenetetrazol (PTZ) and kindling model of generalized seizures in mice. It has been hypothesized that the latter effects on seizures could be established via a modulatory effect on dopamine receptors in the basal ganglia or via an indirect interaction between Ang IV and adenosine A1 receptors. However, a possible role for insulin-regulated aminopeptidase (IRAP), the high affinity binding site for Ang IV, has not been studied yet. To unequivocally unravel the involvement of IRAP in generalized seizure generation, we investigated the susceptibility of male IRAP wild-type (IRAP(+/+)) and knock-out (IRAP(-/-)) mice to PTZ-induced seizures. Challenging these mice intravenously with PTZ resulted in significantly increased thresholds for myoclonic twitch and generalized clonic seizures with loss of righting reflexes in IRAP(-/-) mice compared to their IRAP(+/+) littermates. These behavioural data were confirmed by video-electrocorticography monitoring. Our study shows that IRAP(-/-) mice are less sensitive to the development of PTZ-induced seizures and suggests that IRAP is involved in generalized seizure generation.

Hypothalamus-pituitary-thyroid axis disruption in rats with breast cancer is related to an altered endogenous oxytocin/insulin-regulated aminopeptidase (IRAP) system.

Associations of breast cancer with diseases of the thyroid have been repeatedly reported, but the mechanism underlying this association remains to be elucidated. It has been reported that oxytocin (OXT) attenuates the thyroid-stimulating hormone (TSH) release in response to thyrotrophin-releasing hormone (TRH) and decreased plasma levels of TSH as well as the thyroid hormones by an effect mediated by the central nervous system. Oxytocinase (IRAP) is the regulatory proteolytic enzyme reported to hydrolyze OXT. Changes in IRAP activity have been reported in both human breast cancer and N-methyl-nitrosourea (NMU)-induced rat mammary tumours. Here, we measure IRAP activity fluorometrically using cystyl-ß-naphthylamide as the substrate, in the hypothalamus-pituitary-thyroid axis together with the circulating levels of OXT, and its relationship with circulating levels of TSH and free thyroxine (fT4), as markers of thyroid function in control rats and rats with breast cancer induced by NMU. We found decreased thyroid function in rats with breast cancer induced by NMU, supported by the existence of lower serum circulating levels of both TSH and fT4 than their corresponding controls. Concomitantly, we found a decrease of hypothalamic IRAP activity and an increase in circulating levels of OXT. We propose that breast cancer increases OXT pituitary release by decreasing its hypothalamic catabolism through IRAP activity, probably due to the alteration of the estrogenic endocrine status. Thus, high circulating levels of OXT decreased TSH release from the pituitary, and therefore, of thyroid hormones from the thyroid, supporting the association between breast cancer and thyroid function disruption.

A new approach regarding the treatment of preeclampsia and preterm labor.

Both preeclampsia and preterm delivery are important complications in pregnancy and are leading causes for maternal and perinatal morbidity and mortality. The underlying molecular mechanisms of both diseases remain unknown, thus treatments (beta2-stimulants and magnesium sulfate) are essentially symptomatic. Both molecules have molecular weights less than 5-8 kDa and cross the placental barrier thus exerting their effects on the fetus. In addition, the fetus produces peptide hormones that are highly vasoactive and uterotonic and increase in response to maternal stress and with continued development. Fetal peptides are also small molecules that inevitably leak across into the maternal circulation. Aminopeptidases such as placental leucine aminopeptidase (P-LAP) and aminopeptidase A (APA) are large molecules that do not cross the placental barrier. We have shown that APA acts as an antihypertensive agent in the pregnant spontaneously hypertensive rat by degrading vasoactive peptides and as a result returns the animal to a normotensive state. We have also noted that P-LAP acts as an anti-uterotonic agent by degrading uterotonic peptides, and as a result prolongs gestation in the pregnant mouse. Thus, P-LAP and APA represent promising agents for the treatment of preeclampsia and preterm labor by degrading bioactive hormones derived from the feto-placental circulation.

Systemic arterial vasodilation, vasopressin, and vasopressinase in pregnancy.

Systemic arterial vasodilation in early pregnancy is accompanied by a compensatory rise in cardiac output and a decline in BP. This relative arterial underfilling in early pregnancy is coupled to stimulation of the renin-angiotensin-aldosterone system and hypotonicity. Arterial underfilling induces the nonosmotic stimulation of arginine vasopressin and upregulation of aquaporin 2 followed by trafficking of this water channel to the apical membrane of principal cells along the collecting ducts. In middle and late pregnancy, there also is a four-fold increase in vasopressinase, a cystine aminopeptidase produced by placental trophoblasts, which enhances the metabolic clearance of vasopressin. In the setting of preeclampsia, twins or triplets, or subclinical central diabetes insipidus, a transient diabetes insipidus may ensue from this vasopressinase-mediated degradation of N-terminal amino acids from the vasopressin molecule. Because desmopressin is already deaminated at the N-terminal, it is resistant to the effect of vasopressinase and therefore is the treatment of choice for transient diabetes insipidus of pregnancy.

Therapeutic targeting of insulin-regulated aminopeptidase: heads and tails?

Insulin-regulated aminopeptidase, IRAP, is an abundant protein that was initially cloned from a rat epididymal fat pad cDNA library as a marker protein for specialized vesicles containing the insulin-responsive glucose transporter GLUT4, wherein it is thought to participate in the tethering and trafficking of GLUT4 vesicles. The same protein was independently cloned from human placental cDNA library as oxytocinase and is proposed to have a primary role in the regulation of circulating oxytocin (OXY) during the later stages of pregnancy. More recently, IRAP was identified as the specific binding site for angiotensin IV, and we propose that it mediates the memory-enhancing effects of the peptide. This protein appears to have multiple physiological roles that are tissue- and domain-specific; thus the protein can be specifically targeted for treating different clinical conditions.

A novel role for placental leucine aminopeptidase (P-LAP) as a determinant of chemoresistance in endometrial carcinoma cells.

In several recent studies, we have shown that P-LAP can be a poor prognostic factor and a factor of chemoresistance in endometrial carcinoma, especially in the advanced patients. In our study, we investigated whether P-LAP alters the expression of apoptosis regulatory proteins as a mechanism of drug resistance. We transfected P-LAP cDNA into A-MEC cells (endometrial adenocarcinoma cell line), and A-MEC-LAP cells displayed a 1.8-fold, 2.0-fold and 1.7-fold increase in IC(50) against paclitaxel, carboplatin and cisplatin respectively. Translational downregulation by siRNA2 to P-LAP on A-MEC-LAP cells demonstrated 60%, 51% and 58% decrease in IC(50). To investigate the mechanism of P-LAP-induced chemoresistance, we also assessed whether P-LAP transfection had an effect on carboplatin-induced apoptotic death of A-MEC cells. A-MEC and A-MEC-pc (transfected with vector alone) cells exhibited a strong apoptotic response to carboplatin, while A-MEC-LAP cells exhibited a weak apoptotic response. In an attempt to identify the mechanism of the inhibitory effect on apoptotic response to carboplatin, we next assessed the expression of cleaved caspases and PARP cleavage. While treatment of A-MEC-pc cells with carboplatin exhibited increased levels of cleaved caspase 3, caspase 7 and caspase 9 compared to that after no treatment, A-MEC-LAP cells did not show any expression of these caspases. These results suggest that P-LAP reduces sensitivity to anticancer drugs via inhibition of mitochondria-mediated apoptosis, and may be a molecular target for conquering anticancer drug resistance.

Gene regulation and physiological function of placental leucine aminopeptidase/oxytocinase during pregnancy.

Human pregnancy serum and placenta have the ability to degrade uterotonic peptide oxytocin (OT). Placental leucine aminopeptidase (P-LAP), which is also called cystine aminopeptidase, is the only membrane aminopeptidase known to functionally degrade OT as oxytocinase (OTase). P-LAP/OTase hydrolyzes several peptides other than OT including vasopressin and angiotensin III. P-LAP/OTase predicted from cDNA sequence is a type II integral membrane protein, which is converted to a soluble form existing in maternal serum by metalloproteases, possibly ADAM (a disintegrin and metalloproteinase) members. P-LAP/OTase activity increases with normal gestation, while decreases in the patients with preterm delivery and severe preeclampsia. In placenta, P-LAP/OTase is predominantly expressed in differentiated trophoblasts, syncytiotrophoblasts. Activator protein-2 (AP-2) and Ikaros transcription factors play significant roles in exerting high promoter activity of P-LAP/OTase in the trophoblastic cells. Moreover, P-LAP/OTase is transcriptionally regulated in a trophoblast-differentiation-dependent fashion via up-regulation of AP-2, putatively AP-2alpha. P-LAP/OTase may be involved in maintaining pregnancy homeostasis via metabolizing peptides such as OT and vasopressin.

The insulin-regulated aminopeptidase: a companion and regulator of GLUT4.

The insulin-regulated membrane aminopeptidase (IRAP) was originally identified in fat and muscle cells as a major protein in intracellular vesicles that also harbor the insulin-responsive glucose transporter GLUT4. IRAP, like GLUT4, predominantly localizes to these intracellular vesicles under basal conditions. In response to insulin IRAP, like GLUT4, translocates to the plasma membrane. Purification and cloning of IRAP revealed that it was a novel member of the family of zinc-dependent membrane aminopeptidases. Upon the cloning of the human placental oxytocinase (P-LAP) it was discovered that IRAP and P-LAP were the rat and human homologues of the same protein. The expression of IRAP/P-LAP is not limited to fat and muscle cells, and the subcellular distribution of IRAP/P-LAP is regulated by different peptide hormones and exercise. IRAP/P-LAP cleaves several peptide hormones in vitro. In insulin- and oxytocin-treated cells, concomitant with the appearance of IRAP/P-LAP at the cell surface, aminopeptidase activity toward extracellular substrates increases. A physiological function for IRAP/P-LAP may thus be the processing of circulating peptide hormones. These extracellular substrates, however, would be processed efficiently only when IRAP/P-LAP gets access to them after translocation to the cell surface upon stimulation of cells with insulin or other factors. The in vivo substrates for IRAP/P-LAP remain to be determined. The initial characterization of mice in which IRAP/P-LAP was deleted (IRAP -/- mice) revealed that GLUT4 protein levels were dramatically decreased in all fat and muscle tissues. This finding suggests a function for IRAP/P-LAP in the regulation of GLUT4 levels. Further characterization of the IRAP -/- mice is required to elucidate the role IRAP/P-LAP may play in the control of peptide hormone metabolism.

Possible role of placental leucine aminopeptidase in the antiproliferative effect of oxytocin in human endometrial adenocarcinoma.

PURPOSE: Oxytocin (OT) was reported to inhibit the proliferation of various neoplastic tissues and cells, however, the regulation system remains unclear. This study examined the role of OT and its regulatory ability in endometrial adenocarcinoma. EXPERIMENTAL DESIGN: To investigate the possible function of placental leucine aminopeptidase (P-LAP) in endometrial adenocarcinoma, we transfected P-LAP cDNA into A-MEC cells, showing the lowest enzyme activity of P-LAP. Also we examined P-LAP protein expression in human endometrial adenocarcinoma. RESULTS: We demonstrated the presence of P-LAP, which is identical to cystine aminopeptidase as oxytocinase, in human endometrial adenocarcinoma tissues and found that the expression of P-LAP increase with advances in the grade. Exposure of endometrial adenocarcinoma cell lines to OT caused dose- and time-dependent inhibition of growth. Treatment with 10(-7) M OT for 72 h reduced cell growth by 62, 25, and 30% in A-MEC, HEC1A, and Ishikawa cells, respectively. P-LAP-transfectant cells not only partially recovered from OT-induced growth inhibition but also showed a higher growth rate than parental cells under condition without OT. An OT receptor antagonist and a protein kinase A inhibitor blocked OT-induced growth inhibition in A-MEC and A-MEC-pc cells but not in A-MEC-LAP cells. CONCLUSIONS: These findings suggested that P-LAP might be functionally positive on carcinoma cell growth by degrading suppressive peptides such as OT.

Oxytocinase as the most important marker of fetal development.

Enzymes as biochemical markers come within the entire scope of the live mother-fetus system. The most important are the enzymes which regulate physiological processes, of which oxytocinase (a type of aminopeptidase) has a much wider scope of action than its name suggests, as it regulates also the level of aminopeptide hypothalamic hormones. Thus, it determines neurological, endocrinological and immunological regulation of entire steroidogenesis. Under the influence of gestational enlargement of the uterine cavity, the mothers hypothalamus produces an increasing amount of hormones, which in turn induces an increasing oxytocinase synthesis in the placenta in order to prevent the hormone in the blood reaching the level which could bring about uterine contractions. Also, the growing fetus additionally induces the production of oxytocinase by releasing its own hormones. All this occurs in combined action of the mother, fetus, placenta and even fetal membranes in one space-time process called pregnancy. When in the late pregnancy the enzyme remains at constant level or decreases without appearance of uterus contractions, labour induction is necessary due to fetus life hazard of as much as several percent. Reduction in enzyme level and even its insufficient growth in the second trimester of pregnancy, occur several weeks before preterm birth or death of the fetus. On the other hand, in the event of treatment of diseases accompanying the pregnancy,normalization of oxytocynasaemia shows the effectiveness of treatment. With the dominating profile of the steady increase of oxytocinase (>90% of cases), the target values are higher than in the case of irregular growth. Their close values are a result of the hormonal treatment of threatened pregnancies with ACTH depot. In the cases of the primary hypothalamic insufficiency, this treatment reduces the rate of fetal deaths, which would stand at several dozen percent. It is a classical example of biological pregnancy monitoring since the risk of fetal death can be predicted several weeks earlier when assessment of chemical compounds or physical changes still gives accurate results within physiological limits.

Two molecular species of oxytocinase (L-cystine aminopeptidase) in human placenta: purification and characterization.

Two different forms of oxytocinase (L-cystine aminopeptidase, CAP; EC 3.4.11.3) were purified from the 9000 g and 105000 g precipitate fractions of human placenta homogenate by sequential chromatography on columns of hydroxyapatite, DE-32, nickel ion affinity, and Sephadex G-200. One species (CAP-I) purifed from the mitochondrial/lysosomal fraction migrated on sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis with an apparent molecular mass of 61 kDa; the other (CAP-II) from the microsomal fraction was composed of two subunits with molecular masses of 56 and 40 kDa. The molecular masses of CAP-I and CAP-II estimated by gel filtration were 64 and 97 kDa, respectively. The specific activities of the two species for S-benzyl-L-cysteine p-nitroanilide increased by 357- (for CAP-I) and 139-fold (for CAP-II) compared with the starting preparations. The optimal pH values toward the artificial substrate were approx. 7.4-8.0 for CAP-I and 6.8-8.0 for CAP-II. The Km and Vmax values toward oxytocin were 5.6 microM and 23.4 micromol/h/mg protein for CAP-I, and 38 microM and 15.6 micromol/h/mg protein for CAP-II. Both enzymes were inhibited by the metal-chelating agents, EDTA and o-phenanthroline, whereas they were specifically activated by addition of Co2+: CAP-I was more sensitive to these reagents than CAP-II. L-Methionine strongly inhibited CAP-I, while CAP-II activity was only slightly affected. CAP-II was more sensitive to amastatin than CAP-I. Thus, the two enzymes are quite distinct in their molecular nature and biochemical properties. They may play a regulatory role in the metabolism of oxytocin and other biologically active peptides in intact placenta.

Immunohistochemical localization of placental leucine aminopeptidase/oxytocinase in normal human placental, fetal and adult tissues.

While oxytocinase is known to exist in pregnancy serum and placenta, the present study describes the expression of the mRNA for this enzyme in a wide variety of other human tissues. Northern blot analysis was used to detect the mRNA, with a probe derived from a cDNA for oxytocinase/placental leucine aminopeptidase (P-LAP). Both the distribution and localization of immunoreactive oxytocinase/P-LAP protein have been determined immunohistochemically by use of an anti-P-LAP antibody in normal placental, fetal and adult tissues. In placental tissues, only syncytiotrophoblasts were stained positively. In both fetal and adult tissues, positive staining was obtained in vascular endothelial cells, gastrointestinal mucosal cells, epithelial cells of hepato-biliary, pancreato-biliary, bronchial-alveolar and renal tubular systems as well as islet cells of pancreas and neurons in the central nervous systems. Sweat-gland cells, seminal vesicles and prostate gland in the adult, as well as adipocytes and skeletal muscle cells in the fetus were also stained. The widespread distribution of P-LAP suggests its involvement in a variety of physiological events not restricted to the regulation of the amounts of bioactive peptides such as arginine vasopressin (AVP) and oxytocin (OT) in pregnancy. The presence of P-LAP in syncytiotrophoblasts supports the idea that P-LAP in pregnancy serum is derived from the placenta.

[Possible role of placental proteases via degradation of vasoactive peptides in the maternal and fetal blood pressure].

Both fetal and maternal blood pressure is regulated mainly by the humoral factor, vasoactive peptides such as angiotensin II and vasopressin, but not by autoregulation and the autonomic nervous system. It is known that the normal musculoelastic tissue in the vessel wall of the coiled artery, which supplies blood to the uteroplacental blood pool, is replaced by fibrinous tissue with advancing gestation. Therefore uteroplacental circulation is similar to arterio-venous shunt; it is possibly important for the homeostasis of maternal blood pressure. It is known that hypoxemia results in both the redistribution of feto-placental blood flow, the increase of blood flow in the placenta, and the increase of fetal vasoactive peptides. Since placental proteases (vasopressinase and angiotensinase) degrade vasoactive peptides, placental proteases protect the placental vessels from the vasoconstriction by vasoactive peptides and might contribute to the redistribution of feto-placental blood flow. Therefore placental proteases effect on fetal blood pressure via regulation of fetal vasoactive peptides, which regulate placental blood flow. Although human and animal pregnancy is normally associated with a refractory response to the pressor effect of exogenously infused angiotensin II, patients with pre-eclampsia as well as nonpregnant women are sensitive to angiotensin II; thin phenomenon has been studied as one of the causes of pre-eclampsia. Since the administration of placental angiotensinase was effective in lowering blood pressure in rats with hypertension induced by the infusion of angiotensin II, placental proteases are possibly involved in the refractory response to exogenously infused angiotensin II.(ABSTRACT TRUNCATED AT 250 WORDS)

Human fetal membrane contribution to the prevention of parturition: uterotonin degradation.

This investigation was conducted to evaluate the potential capacity of the human fetal membranes-decidua parietalis, and in particular the chorion laeve, to degrade uterotonins that are produced in amnion, are present in amniotic fluid, or both. The four uterotonins that have been evaluated most frequently as myometrial contractants potentially involved in the initiation of human parturition are prostaglandins, oxytocin, endothelin-1, and platelet-activating factor. We assessed the levels of mRNA and the specific activities (SAs) of enkephalinase (the plasma membrane endopeptidase that degrades endothelins) and prostaglandin dehydrogenase (PGDH) in human fetal membranes, i.e. amnion and chorion leave, and in decidua parietalis. The SA of oxytocinase (which inactivates oxytocin) in these tissues also was determined. The SA of enkephalinase in chorion laeve from all anatomical sites (singleton and diamnionic-dichorionic twin placentae) in all pregnancies studied (mean +/- SEM, 95 +/- 7.9 ng/min.mg protein; n = 28) is similar to that in human fetal kidney (89.5 +/- 2.8; n = 6). Kidney tissue is believed to be one of the richest sources of enkephalinase. The SAs of enkephalinase in amnion (18.3 +/- 2.3 nmol/min.mg protein; n = 29) and in decidua parietalis (31.8 +/- 6.7; n = 20) also were high, but significantly less than that in chorion leave. The level of enkephalinase mRNA in chorion laeve in singleton pregnancies is high, as is the SA of enkephalinase (111.9 +/- 10.6 nmol/min.mg protein; n = 17). In paired chorion laeve tissues from five diamnionic-dichorionic twin placentae, the SAs of enkephalinase in reflected chorion laeve (74 +/- 12.8; P < 0.06 compared with singletons) and fused chorion laeve (64.8 +/- 6.5; P < 0.001 compared with singletons) were similar. The SA of PGDH in reflected chorion leave (46.3 +/- 6.9 nmol/min.mg protein; n = 19) was significantly greater than that in decidua (16 +/- 5.5; n = 15). There was a significant correlation between the levels of PGDH mRNA and PGDH enzyme SA. In fused chorion laeve of diamnionic-dichorionic twin placentae, the SA of PGDH (14.9 +/- 7.3; n = 4) was much less than that in reflected chorion laeve of the same twin pregnancy (70.5 +/- 14.7; n = 4). PGDH mRNA was not detectable in amnion tissue (n = 5) by northern analysis, and the SA of PGDH (< 1.2 +/- 1.0; n = 6) in amnion was undetectable or near the lower limit of assay detection.(ABSTRACT TRUNCATED AT 400 WORDS)