Embryonic production of nitric oxide and its role in implantation: a pilot study

Plasma and amniotic fluid concentrations of nitric oxide: Effects on uterine artery and placental vasculature in women who underwent voluntary pregnancy termination and in women with missed and threatened abortion. A pilot study

OBJECTIVES

First trimester miscarriage is a multifactorial event. Various angiogenic factors have been proposed as possible early markers of non-viable pregnancies. The aim of the present study was to evaluate the systemic nitric oxide (NO) production in healthy early pregnancy and its possible role in first trimester miscarriage.

STUDY DESIGN

We prospectively enrolled women referred to our Unit for elective termination of pregnancy, threatened abortion or missed abortion. Blood samples were taken for testing circulating NO plasma levels. Subsequently, all patients underwent 2-D ultrasonographic analysis and Color Doppler imaging to assess the pulsatility index of the uterine arteries. 3-D ultrasonographic and power Doppler analysis allowed a volumetric and vascular reconstruction of the placenta. During dilatation and vacuum aspiration, amniotic fluid was collected.

RESULTS

Seventy-two patients were enrolled: 25 with elective termination of pregnancy (Group I); 17 with threatened abortion (Group II); 30 with missed abortion (Group III). Group II showed greater placental volume and lower uterine arteries PI than others. The plasma NO concentration resulted statistically higher in women with threatened abortion, while amniotic fluid NO concentration were higher in the viable pregnancies (Group I) than in the aborted fetuses (Group III). Plasma NO was inversely correlated with both mean arterial pressure and uterine artery PI and was positively correlated with amniotic fluid NO and CRL; amniotic fluid NO was positively correlated with placental Vascularization Index and Vascularization-Flow Index.

CONCLUSION

Amniotic NO concentration was higher in viable pregnancies and positively related to Doppler 3D indices of vascularization and blood flow within the placenta. Further studies are needed to elucidate its role in first trimester miscarriage.

Novel Insights on the Role of Nitric Oxide in the Ovary: A Review of the Literature

Nitric oxide (NO) is formed during the oxidation of L-arginine to L-citrulline by the action of multiple isoenzymes of NO synthase (NOS): neuronal NOS (nNOS), endotelial NOS (eNOS), and inducible NOS (iNOS). NO plays a relevant role in the vascular endothelium, in central and peripheral neurons, and in immunity and inflammatory systems. In addition, several authors showed a consistent contribution of NO to different aspects of the reproductive physiology. The aim of the present review is to analyse the published data on the role of NO within the ovary. It has been demonstrated that the multiple isoenzymes of NOS are expressed and localized in the ovary of different species. More to the point, a consistent role was ascribed to NO in the processes of steroidogenesis, folliculogenesis, and oocyte meiotic maturation in in vitro and in vivo studies using animal models. Unfortunately, there are few nitric oxide data for humans; there are preliminary data on the implication of nitric oxide for oocyte/embryo quality and in-vitro fertilization/embryo transfer (IVF/ET) parameters. NO plays a remarkable role in the ovary, but more investigation is needed, in particular in the context of human ovarian physiology.

Nitric oxide as an early marker of human embryo metabolic cleavage in ART using fresh or thawed oocytes

OBJECTIVE

To study a possible role of nitric oxide (NO) as a marker of development in the early phases of human embryo cleavage during assisted reproduction.

STUDY DESIGN

179 women having ART were included. 123 women used fresh oocytes and 56 oocyte thawing cycles in the Center of Reproductive Medicine, Department of Obstetrics and Gynecology, Arcispedale S. Maria Nuova, between July 2005 and June 2006; 57 patients had IVF and 122 patients had ICSI. NO concentrations in IVF or ICSI embryo culture media were assessed by monitoring levels of NO stable oxidation products (nitrites/nitrates). Analysis of embryo quality was performed. Student's t-test or Mann-Whitney and logistic regression model tests were applied to the data.

RESULTS

In patients using fresh oocytes, there were greater NO production in embryos derived from ICSI than from IVF after 52 h of culture (38.64 micromol/L vs 11.2 micromol/L, p<0.05). No correlation with embryo quality was observed. Embryos derived from fresh oocytes produce more NO than embryos from thawed oocytes both after 48 and 52 h of culture (16.12 micromol/L vs 6.83 micromol/L and 25.93 micromol/L vs 2.98 micromol/L respectively, p<0.05).

CONCLUSION(S)

NO in embryo culture media is not a metabolic cleavage marker or a marker of embryo quality in ART. However, it could be an important parameter in the investigation of metabolism in frozen/thawed oocytes.

Nitric oxide metabolite production in the human preimplantation embryo and successful blastocyst formation

Eleven patients underwent controlled ovarian hyperstimulation yielding 72 embryos for evaluation. Mean nitric oxide metabolite levels in the insemination media were 2.6 times higher in embryos that progressed to blastocysts by culture day 5 than in those that did not. A comparison of the receiver operating characteristic curves between morphological predictors and nitric oxide metabolite levels revealed a trend toward a stronger association of insemination media nitric oxide metabolite with blastocyst formation.

Uterine vascularization and pregnancy outcome in patients undergoing intracytoplasmatic sperm injection: the role of nitric oxide

PURPOSE

To evaluate whether, after pituitary desensitisation, the impedance to flow in the uterine vessels may be an indicator of an ICSI programme outcome, and to test the relationship between intrafollicular nitric oxide and oocyte/embryo quality.

METHODS

Thirty-eight women, on the basis of impedance to flow at the level of uterine artery, evaluated on the first day of COH, were divided in patients with normal (Pulsatility Index--PI, 2.5; Group II, n=27) PI values. The patients were submitted to hormonal, ultrasonographic and Doppler evaluations. Plasma and follicular fluid concentrations of nitrites/nitrate (NO(2) (-)/NO(3) (-)) were assayed.

RESULTS

In the Group I, the impedance to flow remained lower than in Group II and was associated to good quality embryos and to a higher pregnancy rate. Follicular fluid NO(2) (-)/NO(3) (-) levels were inversely correlated with the embryo quality. The uterine artery PI and the pregnancy rate were inversely correlated. The PIs analysed on the day 1 of stimulation, were positively correlated with those registered on day 8 and on the day of ovum pick-up.

CONCLUSIONS

A Doppler analysis done on day 1 of controlled ovarian hyperstimulation may be an useful indicator of ART outcome.

Embryo transfer: factors involved in optimizing the success

PURPOSE OF REVIEW

Embryo transfer is arguably the most critical step in assisted reproduction. The purpose of this article is to review the different aspects of the procedure in the light of recent evidence.

RECENT FINDINGS

Randomized trials have shown that significantly higher pregnancy rates are obtained when embryo transfer is performed under ultrasound guidance, the embryos are deposited in the middle part of the uterine cavity, an atraumatic technique is used and when low-dose aspirin is routinely administered following the procedure. Blood in the catheter and leaving the embryos inside it for more than 120 s diminish the pregnancy rate significantly. Air in the catheter, immediate removal of the catheter, performing two transfers in the same cycle, prolonged bed rest, sexual intercourse after embryo transfer or the use of sildenafil do not affect the results. Based on currently available evidence, Cochrane reviews have concluded that the live birth rate is not increased by delaying embryo transfer from day two to three or to the blastocyst stage, and that single embryo transfer leads to lower live birth rates than the transfer of two embryos. The value of a mock transfer a few days before the actual procedure has been challenged as the position of the uterus may change. The effect of holding the cervix with a volsellum, routinely administering antibiotics and the superiority of one catheter over the others is still to be determined.

SUMMARY

Recent studies confirm the importance of the various aspects of embryo transfer. More randomized studies are needed to further evaluate them.

Nitric oxide in blastocyst implantation in the rhesus monkey

Successful blastocyst implantation depends on the interaction between cells of maternal endometrium and conceptus, as well as adequate blood supply to the site of blastocyst implantation. Nitric oxide (NO) generally plays a significant role in the local regulation of vascular physiology in a variety of mammalian tissue systems, however, its role in blastocyst implantation and placentation in the primate is not known. The aim of the present study was to examine: (i) NADH-diaphorase activity and expression of three isoforms of nitric oxide synthase (NOS), namely endothelial NOS (eNOS), inducible NOS (iNOS) and neuronal NOS (nNOS) in pre-implantation stage monkey embryos, morula (n= 4) and blastocyst (n= 10), as well as, in different compartments of conceptus and maternal endometrium at primary implantation sites during lacunar (n= 6) and villous (n= 9) stages of placentation in the rhesus monkey, and (ii) the potential anti-nidatory effect of vaginal administration of NOS inhibitor during the peri-implantation period of conception cycles in rhesus monkeys. Pre-implantation stage blastocysts exhibited marked NADPH-diaphorase activity along with immunopositive iNOS mainly in the inner cell mass. During the lacunar stage, marked eNOS expression was observed in cytotrophoblast cells lining the embryonic cavity. However, cytotrophoblast cells lining villi, forming columns, and constituting anchoring villi expressed all the three isoforms of NOS in villous placenta stage tissue. During the lacunar stage, eNOS and iNOS protein expressions were observed in epithelial and decidual cells of endometrium. As gestation advanced, mRNAs for all three isoforms of NOS were observed to increase in epithelial and decidual cells, however, with no marked change in protein expression. Vaginal administration of a NOS inhibitor (NG-nitro-l-arginine methyl ester, L-NAME, 4, 6, and 8 mg/kg body weight or aminoguanidine, AG, 4 mg/kg body weight) during days 6 to 12 after ovulation resulted in pregnancy failure in a higher number of animals (L-NAME: 8 confirmed pregnancies in 25 animals; AG: 2 confirmed pregnancies in 8 animals) compared with control animals (5 pregnancies in 7 animals). It appears that NO may play an important role in the establishment of pregnancy in the rhesus monkey.