On Oxytocin Research Articles

Development of Social Attention and Oxytocin Levels in Maltreated Children

Child maltreatment (CM) is a major risk factor for various psychopathologies but also adversely affects social development. Research on oxytocin (OT) is currently drawing attention as an endocrine basis for social development. In this study, we investigated the relationship between visual attention to social cues and salivary OT levels in children exposed to CM. The results revealed that the CM group had a significantly lower percentage of gaze fixation for the human face eye area and lower salivary OT levels compared to the typical development group. Moreover, a path analysis suggested that gaze fixation for the eye area was a mediator of the relationship between salivary OT levels and social-emotional problems in the CM group. These results suggest that lower endogenous OT levels in maltreated children may lead to atypical development of their visual attention to eyes as a social cue, resulting in social-emotional problems.

Salivary oxytocin in pigs, cattle, and goats during positive human-animal interactions

Research on oxytocin (OT) has provided crucial insight into the neuroendocrine mechanisms of social behavior and human-animal interactions. Nonetheless, this peptide hormone remains challenging to sample, usually requiring invasive measures in the brain or blood, which limits its use. We conducted an analytical validation of the measurement of OT in the saliva of three common farm animal species: pigs, cattle and goats. We then investigated the biological significance of salivary OT concentrations by using a positive human-animal interaction paradigm. The paradigm varied in terms of human familiarity and included a control condition where the animal was alone in the testing pen. A total of 18 pigs, 18 cattle and 9 goats were subjected to each condition using a within-individual counterbalanced design. Animals were free to choose to interact with the human. Saliva samples were collected immediately before and after the 10-min test, and behavior during the test was analyzed. Oxytocin could be reliably measured by ELISA in the saliva of goats (without extraction), and in the saliva of pigs and cattle after extraction. Salivary OT concentration did not change consistently according to testing condition. However, salivary OT concentration was significantly associated with some behaviors, with different relationships depending on the species. In conclusion, OT can be reliably measured in the saliva of goats and, after extraction, in the saliva of pigs and cattle. The relationships of OT with human-animal interactions and animal behavior were complex and to some extent species-dependent, possibly reflecting the perception of the interaction by the animal.

The effect of methylphenidate on social cognition and oxytocin in children with attention deficit hyperactivity disorder.

The current study aimed to explore the possible effect of stimulants on oxytocin (OT), a neuropeptide which regulates social behavior, as a mediator of the pro-social effect of methylphenidate (MPH) in children with attention deficit hyperactivity disorder (ADHD) compared to healthy controls (HCs). Utilizing a double-blind placebo-controlled design, we compared the performance of 50 children with ADHD and 40 HCs in "theory of mind" (ToM) tasks and examined the effect of a single dose of MPH/placebo on ToM and salivary OT levels in children with ADHD at baseline and following an interpersonal interaction. Children with ADHD displayed significantly poorer ToM performance; however, following MPH administration, their performance normalized and differences between children with ADHD and HC were no longer found. Salivary OT levels at baseline did not differ between children with ADHD and HCs. However, after a parent-child interaction, OT levels were significantly higher in the HC group compared to children with ADHD. Administration of MPH attenuated this difference such that after parent-child interaction differences in OT levels between children with ADHD and HC were no longer found. In the ADHD group, OT levels decreased from administration of placebo to the parent-child interaction. However, the administration of MPH to children with ADHD was associated with an increase in OT levels after the parent-child interaction. We conclude that OT might play a role as a mediator of social deficits in children with ADHD and that the reactivity of the OT system to social interaction in children with ADHD might be impaired. Stimulants may improve ToM and social functions in children with ADHD via its impact on the OT system. PRS: OT and Social Cognition in Children with ADHD: Impact of MPH.

Lack of association of OXTR variants with autism spectrum disorders in a south Indian population

Background: Absence of an effective treatment strategy for autism spectrum disorder (ASD) has necessitated the need for extensive research on oxytocin (OT) and oxytocin receptor gene (OXTR). However, studies on the role of genetic variants in OT and OXTR gene in determining ASD risk is not equivocal owing to the disparities across different ethnicities. We investigated the association of previously reported genetic variants in the OXTR gene with ASD individuals in a south Indian population. Methods: We recruited 222 subjects (110 ASD participants and 112 controls), from south India based on the diagnosis by the DSM-IV criteria. We genotyped single nucleotide polymorphisms (SNPs) rs2254298, rs2254295, rs60902022 and rs53576 in the OXTR gene and the allelic association between ASD participants and controls were determined. Results: We observed higher minor allelic frequency for the OXTR SNPs, which were in linkage disequilibrium in our population. However, the controls failed to exhibit any significant allelic association at rs2254298 (p=0.784), rs2254295 (p=0.661), rs60902022 (p=0.726), rs53576 (p=0.989) or genotypic association at rs2254298 (p=0.78), rs2254295 (p=0.66), rs60902022 (p=0.72), rs53576 (p=0.99) with ASD participants. Similarly, haplotype analysis also failed to prove any association. Conclusion: We suspect that the disparity in the allele frequencies for the SNPs selected in this study across populations might be the reason behind the lack of association as observed in previous studies. Thus, extensive research is necessary. Our study revealed that among south Indians, the rs2254298, rs2254295, rs60902022 and rs53576 SNPs in OXTR gene are unlikely to contribute to the susceptibility of ASD.

Oxytocin increases eye-gaze towards novel social and non-social stimuli

ABSTRACTResearch on oxytocin (OT) has revealed a substantial involvement of this neuropeptide in social cognition processes and attachment behavior.The rationale of the present project was to decipher the differential role of OT in basic social cognition processes towards non-erotic attachment stimuli vs. reproduction-related stimuli in human subjects.In a randomized double-blind repeated-measures cross-over design, N = 82 participants were investigated twice and received either intranasal OT or placebo at the first assessment followed by placebo or OT at second assessment. Participants were presented with standardized pictures of parent-child dyads, romantic couples engaging in non-erotic or explicit sexual activities, and non-social pictures while we assessed pupil dilation and eye focus on specific pre-defined areas of interest. Multilevel analyses suggest that during the initial presentation, OT increased pupil dilation towards all categories of stimuli and led the eye focus towards the eyes and body regions, followed by a strong decrease in pupil dilation and fixations at the second session.These carry-over effects indicate that hormonal treatment at an initial contact to social stimuli can determine how these stimuli are processed later. These results might have implications for OT as a treatment in interventions with repeated exposure to social material.

A dose-finding study of oxytocin using neurophysiological measures of social processing.

Recent interest has focused on oxytocin (OT), a neurotransmitter that promotes social processing, to improve social functioning in people with schizophrenia. However, little information is available regarding the doses of OT that are effective for influencing social processing in the brain (i.e., target engagement). In this study, we conducted a double-blind, placebo-controlled, cross-over dose ranging study of OT. In total 47 patients with schizophrenia were randomly assigned to one of eight doses of OT (8, 12, 24, 36, 48, 60, 72, or 84 IU). Patients completed two social processing tasks: one electroencephalography (EEG) task, a biological motion Mu-suppression task (i.e., identifying the gender, emotion, or direction of walking of point-light animations of human movement); and one pupillometry task, pupil dilation in response to viewing affective faces. Participants completed these tasks twice, one week apart, and were randomly administered drug or placebo intranasally 30 min prior to each session. Mu-suppression, i.e., suppression of oscillations in the 8-12 Hz range over central electrodes in response to social stimuli, was significantly enhanced at doses of 36 and 48 IU in comparison to placebo, but not at other doses. Significant pupil dilation was observed in response to faces vs. non-face stimuli, though there were no drug effects at any dose. Results suggest that OT affects central measures of social information processing in patients with schizophrenia and is optimal at a mid-range dose (36-48 IU). These results provide dosing guidance for future studies of OT to be used to enhance social processing in people with schizophrenia.

Maternal depression impacts child psychopathology across the first decade of life: Oxytocin and synchrony as markers of resilience.

While maternal depression is known to carry long-term negative consequences for offspring, very few studies followed children longitudinally to address markers of resilience in the context of maternal depression. We focused on oxytocin (OT) and mother-child synchrony - the biological and behavioral arms of the neurobiology of affiliation - as correlates of resilience among children of depressed mothers. A community birth-cohort was recruited on the second postbirth day and repeatedly assessed for maternal depression across the first year. At 6 and 10years, mothers and children underwent psychiatric diagnosis, mother-child interactions were coded for maternal sensitivity, child social engagement, and mother-child synchrony, children's OT assayed, and externalizing and internalizing problems reported. Exposure to maternal depression markedly increased child propensity to develop Axis-I disorder at 6 and 10years. Child OT showed main effects for both maternal depression and child psychiatric disorder at 6 and 10years, with maternal or child psychopathology attenuating OT response. In contrast, maternal depression decreased synchrony at 6years but by 10years synchrony showed only child disorder effect, highlighting the shift from direct to indirect effects as children grow older. Path analysis linking maternal depression to child externalizing and internalizing problems at 10years controlling for 6-year variables indicated that depression linked with decreased maternal sensitivity and child OT, which predicted reduced child engagement and synchrony, leading to higher externalizing and internalizing problems. OT and synchrony mediated the effects of maternal depression on child behavior problems and an alternative model without these resilience components provided less adequate fit. Maternal depression continues to play a role in children's development beyond infancy. The mediating effects of OT and synchronous, mutually regulated interactions underscore the role of plasticity in resilience. Results emphasize the need to follow children of depressed mothers across middle childhood and construct interventions that bolster age-appropriate synchrony.

<i>In vitro</i> inhibitory effect of methanol leaf extract of <i>Stachytarpheta jamaicensis</i> (Verbenaceae) on nonpregnant rat uterus

Purpose: To investigate the effect of the methanol extract of the plant, Stachytarpheta jamaicensis (Verbenaceae) (SJ) on uterine smooth muscles of non-pregnant female rats, with the aim of examining the oxytocic or otherwise effect of the extract. Methods: In the first phase of experiments, the effects of SJ (0.41 and 4.01 mg/ml) on oxytocin (OT) induced uterine contractions were determined and repeated after addition of salbutamol (SBL) (41.7 nM). In the second phase, verapamil (VER) (2.03 μM), SBL (41.7 nM), and SJ (0.41 and 4.01 mg/ml) were applied to the tissues after pre-contraction with K+ (80 mM). In the third phase, the effects of VER, SBL, and SJ on CaCl 2 -induced contractions (0.03 – 10.83 mM) were examined. In the fourth and final phases, the second phase experiments were repeated in a calcium-free medium and in the absence and presence of propranolol (1.54 mM) respectively. Results: SJ exhibited significant inhibitory effects on OT and CaCl 2 induced uterine contractions ( p < 0.05). The EC 50 for OT increased from 1.92 ± 0.12 to 7.16 ± 0.16 nM and that for CaCl 2 increased from 0.19 ± 0.09 to 0.76 ± 0.11 mM in the presence of the extract. SJ also significantly inhibited KCl- induced contraction by 39.15 ± 2.13 and 53.23 ± 1.58 % for 0.41 and 4.01 mg/ml of the extract, respectively ( p < 0.01); this inhibition was unaffected by propranolol. On the other hand, SBL and VER showed inhibition of 77.25 ± 1.85 and 79.44 ± 2.27 %, respectively. Conclusion: SJ exerts uterine inhibitory effects in rats which appear unrelated to β 2 -adrenergic receptor stimulation but possibly through inhibition of calcium entry into the cytoplasm. Keywords: Oxytocin, Calcium-free, Uterine contraction, β 2 -Adrenergic receptor stimulation, verapamil, salbutamol, Propranolol, S. jamaicensis

Oxytocin and Anxiety Disorders.

In the present chapter, we review the literature focusing on oxytocin (OT)-centered research in anxiety spectrum conditions, comprising separation anxiety disorder, specific phobias, social anxiety disorder (SAD), panic disorder, generalized anxiety disorder, and anxiety-related endophenotypes (e.g., trust behavior, behavioral inhibition, neuroticism, and state/trait anxiety). OT receptor gene (OXTR) polymorphisms have been implicated in gene-environment interactions with attachment style and childhood maltreatment and to influence clinical outcomes, including SAD intensity and limbic responsiveness. Epigenetic OXTR DNA methylation patterns have emerged as a link between categorical, dimensional, neuroendocrinological, and neuroimaging SAD correlates, highlighting them as potential peripheral surrogates of the central oxytocinergic tone. A pathophysiological framework of OT integrating the dynamic nature of epigenetic biomarkers and the summarized genetic and peripheral evidence is proposed. Finally, we emphasize opportunities and challenges of OT as a key network node of social interaction and fear learning in social contexts. In conjunction with multi-level investigations incorporating a dimensional understanding of social affiliation and avoidance in anxiety spectrum disorders, these concepts will help to promote research for diagnostic, state, and treatment response biomarkers of the OT system, advancing towards indicated preventive interventions and personalized treatment approaches.

Effect of oxytocin receptor blockade on appetite for sugar is modified by social context

Research on oxytocin (OT) has yielded two seemingly unrelated sets of discoveries: OT has prosocial effects, and it elicits termination of feeding, especially of food rich in carbohydrates. Here we investigated whether OT's involvement in food intake is affected by the social context in mice, with particular focus on the role of dominance. We used two approaches: injections and gene expression analysis. We housed two males per cage and determined a dominant one. Then we injected a blood–brain barrier penetrant OT receptor antagonist L-368,899 in either dominant or subordinate animals and gave them 10-min access to a sucrose solution in the apparatus in which social exposure was modified and it ranged from none to unrestricted contact. L-368,899 increased the amount of consumed sugar in dominant mice regardless of whether these animals had access to sucrose in the non-social or social contexts (olfactory-derived or partial social exposure). The antagonist also increased the proportion of time that dominant mice spent drinking the sweet solution in the paradigm in which both mice had to share a single source of sucrose. L-368,899-treated subordinate mice consumed more sucrose solution than saline controls only when the environment in which sugar was presented was devoid of social cues related to the dominant animal. Finally, we investigated whether hypothalamic OT gene expression differs between dominant and subordinate mice consuming sugar and found OT mRNA levels to be higher in dominant mice. We conclude that social context and dominance affect OT's effect on appetite for sucrose.

Prenatal Stress Produces Social Behavior Deficits and Alters the Number of Oxytocin and Vasopressin Neurons in Adult Rats

The present study investigated the long-lasting effects of prenatal repeated restraint stress on social behavior and anxiety, as well as its repercussions on oxytocin (OT) and vasopressin (VP)-positive neurons of the paraventricular (PVN) and supraoptic (SON) nuclei from stressed pups in adulthood. Female Wistar rats were exposed to restraint stress in the last 7 days of pregnancy. At birth, pups were cross-fostered and assigned to the following groups: prenatally non-stressed offspring raised by prenatally non-stressed mothers (NS:NS), prenatally non-stressed offspring raised by prenatally stressed mothers (S:NS), prenatally stressed offspring raised by prenatally non-stressed mothers (NS:S), prenatally stressed offspring raised by prenatally stressed mothers (S:S). As adults, male prenatally stressed offspring raised both by stressed mothers (S:S group) and non-stressed ones (NS:S group) showed impaired social memory and interaction. In addition, when both adverse conditions coexisted (S:S group), increased anxiety-like behavior and aggressiveness was observed in association with a decrease in the number of OT-positive magnocellular neurons, VP-positive magnocellular and parvocellular neurons of the PVN. The NS:S group exhibited a reduction in the amount of VP-positive magnocellular neurons compared to the S:NS. Thus, the social behavior deficits observed in the S:S and NS:S groups may be only partially associated with these alterations to the peptidergic systems. No changes were shown in the OT and VP cellular composition of the SON nucleus. Nevertheless, it is clear that a special attention should be given to the gestational period, since stressful events during this time may be related to the emergence of behavioral impairments in adulthood.

Effects of Oxytocin on Women's Aggression Depend on State Anxiety

Research on oxytocin (OT) indicates that it has stress reducing effects. This leads to opposing predictions of decreased and increased aggression which we examine in this study. Following completion of a state anxiety measure and administration of OT or a placebo, female participants took part in a competitive aggression game (PSAP) for a monetary prize which, if won, would be paid to a loved one. In the game, three options were available: participants could earn points; attack their opponent by deducting points; and defend themselves against point deduction by their opponent. There was no main effect of OT on these responses, however there was an interaction with state anxiety. In the placebo condition, women higher in state anxiety showed a significantly higher ratio of Attack-to-Earn responses than low anxiety women. Under oxytocin, there was a significant reduction in their Attack:Earn ratio resulting in no significant difference between high and low state anxiety groups. There was a similar trend for the Defend:Earn ratio. The reduction of reactive aggression in state anxious women supports the view that OT may decrease negative behavior and increase constructive behavior even under conditions of provocation.

A Preliminary Study of the Effects of Repeated Massage on Hypothalamic–Pituitary–Adrenal and Immune Function in Healthy Individuals: A Study of Mechanisms of Action and Dosage

This study gathers preliminary data about the biologic effects of repeated Swedish massage therapy compared to a light-touch control condition. The study design was a 5-week comparison of repeated Swedish massage and light touch on oxytocin (OT), arginine-vasopressin (AVP), adrenal corticotropin hormone (ACTH), cortisol (CORT), circulating phenotypic lymphocyte markers, and mitogen-stimulated cytokine function. The setting was an outpatient research unit in an academic medical center. The study subjects were medically and psychiatrically healthy young adults. The study comprised 45 minutes of Swedish massage or light touch, using highly specified and identical protocols, either weekly or twice weekly for 5 weeks. The outcome measures were mean differences between massage and light touch on OT, AVP, ACTH, CORT, lymphocyte markers, and cytokine levels. Compared to the touch control condition, weekly Swedish massage stimulated a sustained pattern of increased circulating phenotypic lymphocyte markers and decreased mitogen-stimulated cytokine production, similar to what was previously reported for a single massage session, while having minimal effect on hypothalamic-pituitary-adrenal function. Twice-weekly massage produced a different response pattern with increased OT levels, decreased AVP, and decreased CORT but little effect on circulating lymphocyte phenotypic markers and a slight increase in mitogen-stimulated interferon-γ, tumor necrosis factor-α, interleukin (IL)-1b and IL-2 levels, suggesting increased production of pro-inflammatory cytokines. There are sustained cumulative biologic actions for the massage and touch interventions that persist for several days or a week, and these differ profoundly depending on the dosage (frequency) of sessions. Confirmatory studies in larger samples are needed.

Enhanced Expression of Heme Oxygenase‐1 and Carbon Monoxide Excitatory Effects in Oxytocin and Vasopressin Neurones During Water Deprivation

A growing body of evidence indiates that carbon monoxide (CO) acts as a gas neurotransmitter within the central nervous system. Although CO has been shown to affect neurohypophyseal hormone release in response to osmotic stimuli, the precise sources, targets and mechanisms underlying the actions of CO within the magnocellular neurosecretory system remain largely unknown. In the present study, we combined immunohistochemistry and patch-clamp electrophysiology to study the cellular distribution of the CO-synthase enzyme heme oxygenase type 1 (HO-1), as well as the actions of CO on oxytocin (OT) and vasopressin (VP) magnocellular neurosecretory cells (MNCs), in euhydrated (EU) and 48-h water-deprived rats (48WD). Our results show the expression of HO-1 immunoreactivity both in OT and VP neurones, as well as in a small proportion of astrocytes, both in supraoptic (SON) and paraventricular (PVN) nuclei. HO-1 expression, and its colocalisation with OT and VP neurones within the SON and PVN, was significantly enhanced in 48WD rats. Inhibition of HO activity with chromium mesoporphyrin IX chloride (CrMP; 20 μm) resulted in a slight membrane hyperpolarisation in SON neurones from EU rats, without significantly affecting their firing activity. In 48WD rats, on the other hand, CrMP resulted in a more robust membrane hyperpolarisation, significantly decreasing neuronal firing discharge. Taken together, our results indicate that magnocellular SON and PVN neurones express HO-1, and that CO acts as an excitatory gas neurotransmitter in this system. Moreover, we found that the expression and actions of CO were enhanced in water-deprived rats, suggesting that the state-dependent up-regulation of the HO-1/CO signalling pathway contributes to enhance MNCs firing activity during an osmotic challenge.

Polymorphisms of candidate genes in Slovak autistic patients

Autism is one of the most genetically influenced neuropsychiatric disorders. However, its detailed genetic basis is far from being clear. Genome-wide association studies have revealed a number of candidate genes, mostly related to synaptogenesis and various neuroendocrine pathways. In our study we have focused on oxytocin (OT), oxytocin receptor (OXTR), GABA receptor gamma 3 (GABRG3), neuroligin (NLGN4X), and reelin (RELN). After signed consent, 90 autistic boys and 85 healthy controls were enrolled in the study. Polymorphisms of OT (rs2740204), OXTR (rs2228485), GABRG3 (rs28431127), and NLGN4X (rs5916338) were analyzed using restriction fragment length polymorphism. (GGC)n STR polymorphism in the 5' UTR of the RELN gene was genotyped using fragment analysis. The only significant association in autistic boys in Slovakia was found with higher number of GGC repeats in the RELN gene (P=0.001) potentially explaining lower RELN levels in blood and brain of autistic patients.

Nesfatin‐1 Stimulates Stress Hormone Secretion

Cellular actions of nesfatin‐1 on oxytocin (OT), vasopressin (AVP) and corticotropin releasing factor (CRF) neurons (J Neuroendocrinol 20:255,2008), the activation of early gene expression in those types of neurons following stress (Brain Res 1300:114,2009), and the ability of nesfatin‐1 to elicit fear and anxiety behaviors (Psychopharmacol 201:115,2008; AJP 297:R330,2009) suggested a role for nesfatin‐1 in the stress response. In conscious, unrestrained male rats i.c.v. administration of 180 pmole nesfatin‐1 resulted in significant increases in plasma levels of AVP (vehicle: 1.9±0.5, n=8; nesfatin‐1: 10.0±3.4 pg AVP/ml, n=8, p = 0.018) and ACTH (vehicle: 6.0±1.4; nesfatin‐1: 28.5±7.7 pg ACTH/ml; p&lt;0.01) 10 minutes later. Plasma OT levels were unchanged. The actions of nesfatin‐1 on food intake and cardiovascular function are dependent upon activation of POMC neurons (AJP 297:R330,2009) and roles for OT in those actions have been reported. We suggest that nesfatin‐1 activates stress hormone secretion by releasing AVP and CRF but that the ability of nesfatin‐1 to activate OT neurons reflects an action to release OT centrally and not into the peripheral plasma.

Hypothalamic gonadotropin-releasing hormone receptor activation stimulates oxytocin release from the rat hypothalamo-neurohypophysial system while melatonin inhibits this process

The present study was undertaken to investigate the influence of gonadotropin-releasing hormone (GnRH) and its agonist and antagonist on oxytocin (OT) release from the rat hypothalamo-neurohypophysial (H-N) system. An additional aim was to determine whether the possible response of oxytocinergic neurons to these peptides could be modified by melatonin through a cAMP-dependent mechanism. The results show that the highly selective GnRH agonist (i.e., [Des-Gly 10, d-His(Bzl) 6,Pro-NHEt 9]-LHRH; Histrelin) stimulates the secretion of OT from an isolated rat H-N system. Melatonin significantly inhibited basal and histrelin-induced release of OT in vitro, and displayed no significant influence on OT release in the presence of GnRH or its antagonist. Addition of melatonin to a medium containing forskolin resulted in significant reduction of OT secretion from the H-N system. On the other hand, addition of forskolin to a medium containing both histrelin and melatonin did not further alter the inhibitory influence of melatonin on the histrelin-dependent secretion of OT in vitro. Intracerebroventricular ( icv) infusion (experiment in vivo) of a GnRH antagonist resulted in substantial inhibition of OT release, thus revealing the stimulatory action of endogenous GnRH. In melatonin-treated animals, blood plasma OT levels were not changed in comparison to the vehicle. Our present data strongly suggests that activation of the GnRH receptor in the hypothalamus is involved in stimulation of OT secretion from the rat H-N system. It has also been shown, under experimental in vitro conditions, that melatonin fully suppresses the response of oxytocinergic neurons to the GnRH agonist – histrelin. The effect of melatonin on OT release is mediated by the cAMP-dependent mechanism, although other mechanisms of action are also possible.

Local and Systemic Effects of Embryos on Uterine Tissues During Early Pregnancy in Pigs

In the pig, the periimplantation period is critical for successful establishment of pregnancy. We studied the influence of embryos on oxytocin (OT) and progesterone (P(4)) regulated endometrial and myometrial secretion of 1) luteotrophic prostaglandin E(2) (PGE(2)) and 2) luteolytic prostaglandin F(2alpha) and its metabolite (PGFM) on days 12-14 of pregnancy in pigs. We used unilaterally pregnant pigs created by a surgical procedure in which one uterine horn remained intact and the second horn was cut transversely so that part of the horn was detached from the uterine body. The animals were divided into two groups, inseminated gilts (days 12-14 of pregnancy, n=6) and uninseminated cyclic gilts, which were used as controls (days 12-14 of estrous cycle, n=5). Embryos developed only in the patent part of the uterus and not in the occluded horn. The abundance of OTR mRNA was increased in the endometrium and decreased in the myometrium of the gravid uterine horn in the pregnant pigs compared with the non-gravid uterine horn or either uterine horn in the cyclic pigs, indicative of a local effect of the conceptus. The presence of embryos in the uterine horn during the periimplantation period determines endometrial metabolism of PGF(2alpha) and the local response of the endometrium to OT and P(4). OT stimulates PGF(2alpha) secretion and PGFM accumulation in endometrial cultures only from the non-gravid uterine horn and controls PGE(2) secretion from the endometrium and myometrium in the pregnant gilts. The results indicate a more systemic affect of pregnancy on the uterine response to OT and a possibly the local effect of the conceptus in promoting progesterone's inhibition of OT-stimulated PGE(2) secretion and uterine metabolism of PGF(2alpha).

Progesterone suppresses an oxytocin-stimulated signal pathway in COS-7 cells transfected with the oxytocin receptor

The present study was conducted to determine if progesterone (P4) would inhibit oxytocin-stimulated phosphoinositide hydrolysis in COS-7 cells expressing transfected ovine oxytocin receptor (OTR) with little or no nuclear P4 receptor (nPR) protein present. The relative absence of nPR in these cells was confirmed by immunocytochemistry and RT-PCR. To investigate the effects of P4 on oxytocin (OT) signaling, cells were transiently transfected with the ovine OTR. Radioreceptor assay for [ 3H]-OT binding confirmed the presence of a high affinity binding site for OT in transfected cells, while treatment with P4 and GTPγS (which uncouples the OTR from the heterotrimeric G-protein) increased the K d for OT binding slightly. Cells were then assayed for inositol phosphate hydrolysis 48 h post-transfection. Pre-treatment of cells with P4 for 10 min significantly interfered with rapid (20 min) OT-stimulated inositol trisphosphate (IP 3) production. This inhibition was specific to P4, because pre-treatment of cells with promegestone (R5020), testosterone, mifepristone (RU 486), or cortisol did not decrease OT-stimulated IP 3 levels. By radioreceptor assay for PR, no measurable specific binding of R5020 was observed for either transfected or non-transfected cells. We conclude that P4 can inhibit OTR-mediated phosphoinositide hydrolysis in COS-7 cells that express little or no nPR protein. These data support a role for a non-genomic action for P4 in OTR signaling via some mechanism other than by binding to a membrane progestin receptor in an immortalized, transfected cell.

Progesterone regulation of oxytocin receptor through non‐genomic actions

Although high dose steroids may interfere with G protein-coupled receptor activation through disruption of cholesterol-rich plasma membrane subdomains, the mechanism of non-genomic low dose progesterone (P4) effects on oxytocin (OT) receptor activation is unknown. Low dose P4 suppressed OT-induced prostaglandin F2<alpha> secretion and inositol phosphate accumulation (Bishop et al. Endocrinology 147:937) from ovine endometrial explants, and inhibited OT binding to OT receptors (Dunlap and Stormshak, Biol Reprod 70:65). To study the mechanism of the non-genomic effects of P4 on OT receptor, we developed transfected cell lines expressing ovine OT receptor in the absence of classic progesterone steroid hormone receptors. Both transiently and stably transfected cell lines expressed ovine OT receptor at moderate to high receptor levels that coupled to activation of phopholipase C and accumulation of inositol phosphates. Low dose P4 (2.5 ng/ml) inhibited OT-stimulated inositol phosphate accumulation in the transfected cell lines. Of interest, the ability of P4 to suppress OT-induced inositol phosphate accumulation in transfected cells varied with OT receptor expression levels, suggesting an allosteric effect of low dose P4 on ovine OT receptor function.