Pregnancy-induced changes in substance P and neurokinin 1 receptor (NK1-R) expression in the rat uterus

Elevated Neurokinin-1 Receptor Expression in Uterine Products of Conception Is Associated With First Trimester Miscarriages

Background

Miscarriage is a common complication of early pregnancy, mostly occurring in the first trimester. However, the etiological factors and prognostic and diagnostic biomarkers are not well known. Neurokinin-1 receptor (NK-1R) is a receptor of tachykinin peptide substance P (SP) and has a role in various pathological conditions, cancers, but its association with miscarriages and significance as a clinicopathological parameter are not studied. Accordingly, the present study aimed to clarify the localization and expression for NK-1R in human retained products of conception (POC). The role of NK-1R is not known in miscarriages.

Materials and Methods

NK-1R expression was assessed in POC and normal placental tissues by immunohistochemistry. Three- to four-micrometer-thin sections of formalin-fixed paraffin-embedded tissues were used for this purpose. Tissues were processed and then immunohistochemically stained with NK-1R antibody. Brain tissue was used as control for antibody. Protein expression was evaluated using the nuclear labeling index (%). Tissues were counterstained with 3,3'-diaminobenzidine (DAB), and microscopy was performed at 10×, 20×, and 40× magnifications.

Results

Ten human POC tissues and 10 normal placental tissues were studied by immunohistochemistry to demonstrate the localization of NK-1R. The expression of NK-1R protein was high in all the cases of both groups. NK-1R expression showed no notable differences among different cases of miscarriages as well as normal deliveries at full term regardless of the mother's age and gestational age at which the event occurred. Statistically, no difference was found in both groups, which is in agreement with our hypothesis and previous findings.

Conclusion

The expression of NK-1R was similar in all the cases, and it was intense. It shows that dysregulation of NK-1R along with its ligand SP might be involved in miscarriages and also involved in normal delivery. Our results provide fundamental data regarding this anti-NK-1R strategy. Thus, the present study recommends that SP/NK-1R system might, therefore, be considered as an emerging and promising diagnostic and therapeutic strategy against miscarriages. Hence, we report for the first time the expression and localization of NK-1R in POC. We suggest NK-1R antagonist in addition to the immunoglobulins and human chorionic gonadotropin to diagnose and treat spontaneous miscarriages.

The Myometrium: From Excitation to Contractions and Labour

We start by describing the functions of the uterus, its structure, both gross and fine, innervation and blood supply. It is interesting to note the diversity of the female's reproductive tract between species and to remember it when working with different animal models. Myocytes are the overwhelming cell type of the uterus (>95%) and our focus. Their function is to contract, and they have an intrinsic pacemaker and rhythmicity, which is modified by hormones, stretch, paracrine factors and the extracellular environment. We discuss evidence or not for pacemaker cells in the uterus. We also describe the sarcoplasmic reticulum (SR) in some detail, as it is relevant to calcium signalling and excitability. Ion channels, including store-operated ones, their contributions to excitability and action potentials, are covered. The main pathway to excitation is from depolarisation opening voltage-gated Ca²⁺ channels. Much of what happens downstream of excitability is common to other smooth muscles, with force depending upon the balance of myosin light kinase and phosphatase. Mechanisms of maintaining Ca²⁺ balance within the myocytes are discussed. Metabolism, and how it is intertwined with activity, blood flow and pH, is covered. Growth of the myometrium and changes in contractile proteins with pregnancy and parturition are also detailed. We finish with a description of uterine activity and why it is important, covering progression to labour as well as preterm and dysfunctional labours. We conclude by highlighting progress made and where further efforts are required.

Distribution of substance P (SP) and vasoactive intestinal peptide (VIP) in pseudocapsules of uterine fibroids

The authors examined the presence of Substance P (SP) and Vasoactive Intestinal Polypeptide (VIP) and their related fibers in the pseudocapsule of uterine fibroids (PUF) and in normal myometrium (NM) during myomectomies in 57 non-pregnant women. 4 samples were removed from the normal myometrium (NM) and from PUF. The samples were sent for histological and immune-fluorescent investigations. SP and VIP values were found non-significantly higher in PUF than in NM: SP values were 10.2±0.1 conventional units (C.U.) in PUF at the fundus of the uterus (FU) vs. 8.1±0.6C.U. of NM in the FU (p>0.05), and SP values were 25.1±0.9C.U. in PUF in the uterine body (UB) compared to. 23.2±1.4C.U. of NM in the myometrium of the UB (p>0.05). VIP values were 11.5±0.9C.U. in the PUF in FU compared to 9.8±1.4C.U. of NM in the FU (p>0.05), and VIP values were 33.9±3.9C.U. in the PUF in the UB vs. 32.6±4.8C.U. of the NM in the UB (p>0.05). These findings show that SP and VIP neurofibers are present in the fibroid pseudocapsule, similar to the values in the normal myometrium of a non-pregnant uterus. An intracapsular myoma excision which respects the pseudocapsule permits a physiological healing process of the uterine scar, due to a neurotransmitter sparing at the hysterotomic site. In women planning pregnancy, the myomectomy should be preferably performed respecting the pseudocapsule in order to preserve the neurotransmission.

Substance P (SP) and vasoactive intestinal polypeptide (VIP) in the lower uterine segment in first and repeated cesarean sections

The authors studied the presence of substance P (SP) and vasoactive intestinal polypeptide (VIP) and their related fibers in the lower uterine segment (LUS) in 133 women undergoing cesarean sections (CS) during active labor. These were divided into 2 groups: women undergoing repeat or first CSs. Specimens were collected from the LUS and were evaluated by light microscopy and by immunohistochemistry, for the morphometrical quantification of the SP and VIP fibers in the LUS. The SP amount was higher in the post-CS scar, while the VIP amount decreased: nerve fibers contained an SP amount of up to 13 ± 2.6C.U., while nerve fibers contained a VIP amount of up to 7 ± 1.9 C.U. The SP amount counts 10 ± 1.5% of the total Bodian fibers, and the ratio of the VIP is 10 ± 1.8% of their total amount. In normal conditions only 6.61 C.U. of the Bodian surface is occupied by SP related nerve fibers in contrast to 6.63 C.U. of the total surface by VIP; the amount of SP increased up to 13 ± 2.6C.U., while it decreased in the LUS previous scars. The SP levels are higher in repeat CS, while the VIP levels are reduced in the LUS. The increase of SP is probably linked to the attempt to achieve cervical ripening in a post-CS LUS, with the possible consequences of dystocia during vaginal birth after CS. Nevertheless, the decrease of VIP probably affects the relaxation of the internal uterine orifice, compromising the LUS formation and cervical ripening.

Regulation of the stimulant actions of neurokinin a and human hemokinin-1 on the human uterus: a comparison with histamine

Regulation of the contractile effects of tachykinins and histamine on the human uterus was investigated with biopsy sections of the outer myometrial layer. The effects of neurokinin A (NKA) and human hemokinin-1 (hHK-1) in tissues from pregnant but not from nonpregnant women were enhanced by the inhibition of neprilysin. The effects of NKA and eledoisin were blocked by the NK2 receptor antagonist SR 48968 but not by the NK1 receptor antagonist SR 140333 in tissues from both groups of women. Human HK-1 acted as a partial agonist blocked by SR 48968 and, to a lesser extent, by SR 140333; endokinin D was inactive. In tissues from pregnant women, responses to high potassium-containing Krebs solution were 2-3-fold higher than those from nonpregnant women. Mepyramine-sensitive maximal responses to histamine were similarly enhanced. The absolute maximum responses to NKA and its stable NK2 receptor-selective analogue, [Lys5MeLeu9Nle10]NKA(4-10), were increased in pregnancy, but their efficacies relative to potassium responses were decreased. Tachykinin potencies were lower in tissues from pregnant women than in those from nonpregnant women. These data 1) show for the first time that hHK-1 is a uterine stimulant in the human, 2) confirm that the NK2 receptor is predominant in mediating tachykinin actions on the human myometrium, and 3) indicate that mammalian tachykinin effects are tightly regulated during pregnancy in a manner that would negate an inappropriate uterotonic effect. The potencies of these peptides in tissues from nonpregnant women undergoing hysterectomy are consistent with their possible role in menstrual and menopausal disorders.

Coexpression of preprotachykinin A and B transcripts in the bovine corpus luteum and evidence for functional neurokinin receptor activity in luteal endothelial cells and ovarian macrophages

Nonneuronal cell sources of tachykinins, such as substance P (SP) and neurokinin B (NKB), have been demonstrated in leukocytes, endothelial cells and endocrine cells, and may play a role in corpus luteum (CL) development. For this reason, we analyzed mRNA presence for the two tachykinin precursors together with the neurokinin-1 receptor and the neurokinin-3 receptor (NK-1R and NK-3R, preferred by SP and NKB, respectively) in bovine CL at various stages in the luteal phase. Using the RT-PCR technique, we detected coexpression for the preprotachykinin A gene (PPT-A), which encodes SP and neurokinin A (NKA), and the preprotachykinin B gene (PPT-B) for NKB in the CL at the development, secretion and regression stages. Coexpression was also noted for NK-1R and NK-3R gene transcripts. Cultures of endothelial cells (ECs) derived from bovine CL expressed NK-1R and NK-3R mRNA, as did ovarian macrophages. Agonist treatment induced a stronger intracellular calcium ([Ca2+]i) increase after activation of NK-1R compared to NK-3R, a result that we verified by calcium imaging. This is the first evidence for functional tachykinin receptor activity in luteal ECs and ovarian macrophages from bovine CL.

Increased formation of corpora lutea in neurokinin 1-receptor deficient mice

There is evidence to suggest that the tachykinin-receptor system may be involved in female reproduction. Recently, we have shown that the mRNA transcripts of the preprotachykinin-A which encodes substance P (SP), a member of the tachykinin family, and of NK1-R (preferred receptor of SP) are expressed in the bovine corpus luteum (CL) of early developmental stage. The question arises whether the system is expressed at the protein level and influences the ovulatory process and CL formation. For this reason, ovaries from a mouse mutant in which the NK1-R gene had been disrupted were studied. By using RT-PCR, mRNA expression of NK1-R was confirmed in both the ovary and the uterus of wild-type mice. Weaning frequency and litter size, as recorded over 6 months, were similar in both groups. However, counting of CL in serial paraffin sections revealed a significant higher number of CL in the NK1-R deficient mice in comparison to the wild-type group (P < 0.01). The increased formation of CL in NK1-R deficient mice corresponded to a considerable number of CL with retained oocyte not found in ovaries of the wild-type group. We conclude: The CL with a retained oocyte may indicate that the muscular apparatus of the preovulatory follicle plays a role in oocyte expulsion and that contractility of the follicle wall is deficient in the mutant group. Our observation may have implications for the luteinized unruptured follicle syndrome in humans.

Transcripts of neurokinin B and neurokinin 3 receptor in superovulated rat ovaries and increased number of corpora lutea as a non-specific effect of intraperitoneal agonist application

Neurokinin B (NKB), a member of the tachykinin family, and its neurokinin 3 receptor (NK3-R) are preferentially found in the central nervous system. Others have recently reported on mRNA from this ligand-receptor system in the uterus and on NK3-R expression increasing with age. NKB and NK3-R mRNAs have also been noted in cumulus cells and oocytes from superovulated rats. Intact ovaries before and after puberty have not been studied. In this study, we stimulated 29-day-old rats by s.c. injections with gonadotropins for estrous cycle synchronization in order to elucidate the NKB-NK3-R system's expression and function in the ovary. Simultaneously, NaCl, the NK3-R agonist (Pro(7))-NKB, the antagonist SB 218795, or thiorphan, a neutral endopeptidase inhibitor of tachykinin degradation, were injected intraperitoneally (i.p.) for 3 1/2 consecutive days. First, we demonstrated NKB and NK3-R transcripts in one rat ovary by RT-PCR. No significant mRNA differences were noted between immature ovaries and superovulated ovaries in any of the i.p. applications. Second, the possible role of NK3-R on the ovulatory process was verified by counting corpora lutea (CL) and CL cysts in serial sections of the other ovary derived from the four different groups and embedded in paraffin wax. CL and CL cysts were noted in greater numbers in the pharmacologically treated groups than in the saline-treated group. To validate possible drug effects on the peritoneum, we additionally studied pieces of the omentum majus and retroperitoneal fat tissue. Both tissues were heavily infiltrated by granulocytes similar to a non-specific inflammatory response. The saline-treated group as well as the pharmacologically treated groups appeared to develop this unexpected side effect to a similar degree. We conclude that transcripts of NKB and NK3-R are present before and after puberty in the rat ovary and appear to be expressed at similar levels which may indicate a role for the NKB-NK3-R system in follicle growth. The effect of increased CL formation after application of the NK3-R agonist i.p. is related to a non-specific response.

Tachykinins and tachykinin receptors: effects in the genitourinary tract

Tachykinins (TKs) are a family of peptides involved in the central and peripheral regulation of urogenital functions through the stimulation of TK NK1, NK2 and NK3 receptors. At the urinary system level, TKs locally stimulate smooth muscle tone, ureteric peristalsis and bladder contractions, initiate neurogenic inflammation and trigger local and spinal reflexes aimed to maintain organ functions in emergency conditions. At the genital level, TKs are involved in smooth muscle contraction, in inflammation and in the modulation of steroid secretion by the testes and ovaries. TKs produce vasodilatation of maternal and fetal placental vascular beds and appear to be involved in reproductive function, stress-induced abortion, and pre-eclampsia. The current data suggest that the genitourinary tract is a primary site of action of the tachykininergic system.

Mammalian tachykinins and uterine smooth muscle: the challenge escalates

We review the actions of mammalian tachykinins on uterine smooth muscle. Derived from sensory neurones and non-neuronal cells within the female reproductive tract, tachykinins are potent uterotonic agents. Three tachykinin receptor genes, and the gene encoding neprilysin, the enzyme that inactivates tachykinins, are present in rat, mouse and human myometrium. In rat and human, the tachykinin NK(2) receptor is important in mediating the uterotonic effects of tachykinins; actions at this receptor remain relatively stable or vary only slightly in the face of changing hormonal and gestational status. In contrast, ovarian steroids and pregnancy regulate expression of the tachykinin NK(3), and to a lesser extent, the tachykinin NK(1) receptor, as well as the activity of neprilysin. In the oestrogen primed mouse uterus, the tachykinin NK(1) receptor primarily mediates tachykinin uterotonic effects, but there is a switch to the tachykinin NK(2) receptor by late pregnancy. The possible physiological and pathological roles of tachykinins, including hemokinins and endokinins, in normal and premature labour, stress-induced abortion and menstrual disorders are briefly discussed.