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Logo of nihpaAbout Author manuscriptsSubmit a manuscriptNIH Public Access; Author Manuscript; Accepted for publication in peer reviewed journal;
Schizophr Res. Author manuscript; available in PMC Dec 1, 2011.
Published in final edited form as:
PMCID: PMC2981685
NIHMSID: NIHMS241335

Peripheral oxytocin is associated with reduced symptom severity in schizophrenia

Abstract

Background

Emerging evidence from clinical trials suggests that oral estrogen and intranasal oxytocin might reduce symptom severity in schizophrenia. Whether increases in endogenous hormones are similarly associated with improved symptoms is unknown. We investigated the effects of menstrual cycle phase and related fluctuations in peripheral hormone levels on clinical symptoms in women with chronic schizophrenia.

Method

Twenty-three women with schizophrenia were administered the Positive and Negative Syndrome Scale (PANSS), a measure of clinical symptom severity, at two menstrual cycle phases: 1) early follicular (Days 2–4; low estrogen/progesterone) and 2) midluteal (Days 20–22; high estrogen/progesterone). Twenty-seven males with schizophrenia and 58 controls (31 female) completed testing at comparable intervals. Men were included to examine whether the relationships between clinical symptoms and hormone levels in women generalize to men. Plasma hormone assays of estrogen, oxytocin, progesterone, and testosterone were obtained.

Results

Female patients showed less severe symptoms during the midluteal versus early follicular phase (p’s<0.01). Oxytocin did not fluctuate across phases, but in female patients (p’s<0.01) higher oxytocin levels were associated with less severe positive symptoms and overall psychopathology. In both sexes, higher oxytocin levels were associated with more prosocial behaviors (p<0.05).

Conclusion

Consistent with previous findings in acutely ill patients, our results suggest that clinical symptoms vary across the menstrual cycle in patients with chronic schizophrenia. Similar to recent findings regarding benefits of intranasal oxytocin, these new findings indicate that high levels of endogenous oxytocin might improve positive symptom severity and general psychopathology in women and social behaviors in both sexes.

Keywords: oxytocin, estrogen, progesterone, schizophrenia, menstrual cycle

1. Introduction

Sex modulates the clinical presentation and course of schizophrenia. The course of the disease is more benign in women than in men; females generally have a later age of onset, shorter and less frequent acute episodes of psychosis, less severe negative symptoms, better premorbid functioning, and a better treatment response to antipsychotic medication compared to males (Riecher-Rossler and Hafner, 2000, Halbreich and Kahn, 2003, Rao and Kolsch, 2003). These sex differences suggest involvement of hormonal factors. In this study, we use a menstrual cycle paradigm to explore changes in clinical symptoms in relation to fluctuating peripheral hormone levels.

Patients with schizophrenia show reduced levels of estrogen and other sex hormones such as progesterone and testosterone (Oades and Schepker, 1994, Goyal et al., 2004, Huber et al., 2004, Bergemann et al., 2005a, Huber et al., 2005, Howes et al., 2007, Ko et al., 2007), and alterations in neurohormones such as oxytocin (Linkowski et al., 1984, Beckmann et al., 1985, Legros et al., 1992, Mai et al., 1993, cf., Glovinsky et al., 1994, Goldman et al., 2008, Keri et al., 2009). Impressively, four (Kulkarni et al., 2002, Akhondzadeh et al., 2003, Louza et al., 2004, Ko et al., 2006, Kulkarni et al., 2008) of five (Bergemann et al., 2005b) randomized, placebo-controlled clinical trials (RCT) demonstrate beneficial effects of short-term adjunctive estrogen treatment on clinical symptoms including overall, positive, negative, and/or general psychopathology in premenopausal women with chronic schizophrenia. The one neutral trial differed from the other four positive trials in its use of high-dose oral estrogen (Bergemann et al., 2005b).

Following promising findings from open label studies (Bujanow, 1972, Bakharev et al., 1984), intranasal oxytocin is now being examined in RCTs as a therapy for schizophrenia. A randomized clinical trial of short-term adjuvant intranasal oxytocin (versus placebo) demonstrated therapeutic effects on clinical symptoms in a small sample of predominantly male schizophrenia patients with residual symptoms (Feifel et al., 2010). Oxytocin has widespread effects beyond its characteristic roles in pregnancy and lactation, including effects on behaviors that are impaired in schizophrenia such as emotional processing, stress management, affiliative behavior, and certain aspects of cognition (Carter et al., 2008, Heinrichs et al., 2009). Whether natural changes in endogenous estrogen or oxytocin influence clinical symptoms in women with schizophrenia is unknown.

Menstrual cycle paradigms provide insights into how clinical symptoms might change in relation to physiological changes in estrogen and progesterone (which reliably change across cycle phases) and oxytocin (which changes in some studies)(Salonia et al., 2005, Liedman et al., 2008). These paradigms allow for assessment of symptoms in relation to significant change in hormone levels across specific menstrual phases as well as average hormone levels across different phases. Four (Hallonquist et al., 1993, Riecher-Rossler et al., 1994, Choi et al., 2001, Bergemann et al., 2007) of six (Harris, 1997, Thompson et al., 2000) studies in premenopausal women with schizophrenia demonstrate improved clinical symptoms in relation to natural fluctuations across the menstrual cycle; specifically, symptom improvement was evident in the midluteal (high estrogen/progesterone) versus the early follicular (low estrogen/progesterone) phase. In two of these studies, higher estradiol levels were associated with improved clinical symptoms and in particular positive symptoms (Riecher-Rossler et al., 1994, Bergemann et al., 2007). Of the two studies finding no cycle-related changes, one did not validate menstrual cycle phase with hormone assays (Harris, 1997) and the other did not tightly control menstrual cycle phase (Thompson et al., 2000), allowing for a wide range of estradiol and progesterone levels. Animal studies suggest that estrogen can upregulate the synthesis of oxytocin (Young et al., 1998, Patisaul et al., 2003), but the relationship between oxytocin and clinical symptoms has not been investigated in a menstrual cycle study, and no previous study has examined endogenous oxytocin levels over time in relation to clinical symptom severity.

The purpose of this study was to investigate the effects of menstrual phase and hormone levels on clinical symptom severity in women with chronic schizophrenia. We hypothesized that like acutely ill women with schizophrenia, women with chronic schizophrenia would show improvements in clinical symptoms during the midluteal versus early follicular phase, and that these improvements would relate to increases in estradiol. We also extended previous studies by including measures of oxytocin. We predicted that oxytocin levels would be inversely related to clinical symptom severity in patients with schizophrenia. We examined progesterone and testosterone because metabolites of both hormones as well as testosterone can influence clinical symptom expression in schizophrenia (Ko et al., 2008, Marx et al., 2009, Ritsner et al., 2010). We also evaluated relationships between clinical symptoms and hormone levels in men with schizophrenia and included male controls. Male patients were included to examine whether the relationships between hormone levels and clinical symptoms in female patients generalize to men.

2. Methods

2.1. Participants

The sample included 108 participants, including 50 patients (23 women, 27 men) and 58 controls (31 women, 27 men). Inclusion criteria for all participants were: (1) age 18–40; (2) English as first language; (3) for patients, Structured Clinical Interview for DSM (SCID; First et al., 1995) diagnosis of schizophrenia or schizoaffective disorder depressed type; (4) for patients, reported medication compliance and consistency in treatment medication for two months prior to the study; and (5) for women, regular menstrual cycles (28+5days). Additional inclusion criteria for women helped to validate menstrual phase based on the normal range for the estradiol assay (Diagnostic Products, Los Angeles, CA), including (6) early follicular levels <90pg/ml and (7) midluteal levels between 27–246pg/ml. Exclusion criteria for all participants were: (1) history of moderate/severe head trauma or other neurological disorder; (2) history of substance abuse/dependence, excluding cigarettes; (3) high intake of phytoestrogens (3>servings of soy/day or supplements); (4) conditions resulting in abnormal gonadal hormone secretion; (5) significant medical illness; (6) use of hormone treatments; and (7) for women, pregnancy/lactation within the last year. Controls were also excluded if they (8) currently used medications known to influence the central nervous system or (9) had an Axis I psychiatric disorder (based on SCID interview).

Controls were recruited from the community, and patients from outpatient clinics and residential facilities in the Chicago metropolitan area. Patients were diagnosed with schizophrenia (68%) or schizoaffective disorder—depressed type (32%), were clinically stable, and self-reported stable medication regimens for the prior three months. Most patients (84%) were prescribed second generation antipsychotics. Antipsychotic medication dosages ranged from 40–1133mg chlorpromazine equivalents (Woods, 2003, Lehman et al., 2004) per day (median dosage, 400mg/day). Forty-six percent of patients were taking antidepressants, 4% were taking mood stabilizers, and 38% met criteria for hyperprolactinemia (>20ng/mL). Written informed consent was obtained from all participants. Study procedures were approved by the UIC Institutional Review Board.

Table 1 shows demographic and clinical information for the 108 participants. The sample had high body mass index scores (BMI; 42% obese; 21% overweight according to standard criteria (1998)). Compared to controls, patients were older by 3–4 years and had higher BMIs (p’s<0.05). Controlling for age and BMI did not affect the significance of the results. Male and female patients were similar across most clinical variables, but male patients received higher doses of antipsychotic medication (p<0.05).

Table 1
Demographics and Other Descriptive Information.

2.2. Measures

2.2.1. Clinical Symptoms

The Positive and Negative Symptom Scale (PANSS; Kay et al., 1987) was administered to patients at each study visit to generate measures of positive symptoms, negative symptoms, general psychopathology, and a total score. A PANSS prosocial factor derived from an exploratory factor analysis in a sample of outpatients with SCID diagnoses within the schizophrenia spectrum was also examined (Purnine et al., 2000). Items in this subscale were active social avoidance, emotional withdrawal, passive social withdrawal, stereotyped thinking, hallucinatory behavior, and suspiciousness/paranoia.

2.2.2. Serum Hormone Assays

To account for circadian rhythm effects (Brambilla et al., 2009), blood samples were drawn once at the same time of day during both sessions. Samples were stored in plain tubes, centrifuged (2400xg for 15 minutes at 4°C), placed into −80°C freezers, and assayed in duplicate. Batched samples (placed in dry ice; shipped overnight) were sent to the University of Alabama at Birmingham’s General Clinical Research Center for analysis (Gower and Nyman, 2000). Serum concentrations were analyzed using commercial kits: estradiol by double-antibody radioimmunoassay (RIA; Diagnostic Products, Los Angeles, CA)(sensitivity 1.61pg/ml, intra-assay CV=4.01%), progesterone by “Coat-a-Count” coated tube RIA (Diagnostic Products, Los Angeles, CA)(sensitivity 0.05ng/ml, intra-assay CV=2.33%), prolactin (for determination of possible hyperprolactinemia, >20ng/mL) by a two-site immunoenzymometric assay (TOSOH Bioscience, CA) (sensitivity=1ng/mL, intra-assay CV=1.5%), and sex hormone binding globulin by immunoradiometric assay (Diagnostic Systems Laboratories, Webster, TX)(sensitivity=3nmol/L; intra-assay CV=1.37%). Free testosterone was calculated using the method of Stephen J. Winters (University of Louisville; Louisville, KY) (sensitivity 0.82ng/dl; intra-assay CV=2%). Oxytocin was quantified at UIC with an EIA kit (Assay Designs, Ann Arbor, MI)(sensitivity 16pg/mL, intra-assay CV<11%) that is highly specific for oxytocin versus other peptides, as determined by HPLC (Carter et al., 2007). Samples were initially run undiluted. Twenty of 203 samples showed values greater than 600pg/ml. Dilution (1:2 ratio) was subsequently used to confirm the accuracy of those samples.

2.3. Procedures

Women were evaluated once during the early follicular phase (Day 2–4; low estradiol/progesterone) and once during the midluteal phase (Day 20–22; high estradiol/progesterone). Phase at first session was counterbalanced across participants. Sessions were held during two separate cycles about 42 days apart. Menstrual phase was initially estimated by counting back to Day 1 of the last menstrual cycle, and was later validated with estradiol and progesterone levels. Examiners were blinded to menstrual cycle status. Men were tested in separate sessions approximately 42 days apart. Given that half of the women were randomly assigned to follicular phase first and half to luteal phase first, half of the men were randomly assigned to have their second session data reversed with that of the first session. This counterbalancing reduces confounds related to carry over effects (e.g., change in symptom ratings due to increased comfort with the examiner).

2.4. Statistical Analyses

Our hypotheses were tested using multilevel random coefficient models in which the two measurement time points (i.e., follicular and midluteal) were nested within individuals. The first analyses examined changes in hormone levels across the menstrual cycle (follicular and midluteal), with menstrual phase as a within-subjects variable (Level 1 in model) and Group (patients, controls) as a between-subjects variable (Level 2 in model). The second analyses (benchmark model) examined the effect of menstrual phase (Level 1 in model) on clinical symptoms (primary outcome) in female patients. Next, we examined the degree to which individual variations in hormone levels that fluctuate across the menstrual cycle (i.e., estradiol, progesterone) were associated with clinical symptoms that change across the menstrual cycle in female patients. To accomplish this, we added estradiol and progesterone levels as time-varying covariates (Level 1 in model) to our benchmark model. These models provide an estimate of how individual variation in a specific hormone (e.g., estradiol) is associated with changes in clinical symptoms while controlling for variations in other hormones (e.g., progesterone). Finally, we examined the degree to which hormone levels that did not change across the menstrual cycle (e.g., testosterone) predicted average symptom presentation in female patients. This was accomplished by adding these hormones as time-invariant covariates to the model (Level 2 in model). Parallel analyses were conducted in male patients to examine changes in hormones and clinical symptoms across sessions spaced at equivalent time intervals. Analyses in patients examined the following covariates: BMI, primary SCID diagnosis (schizophrenia vs. schizoaffective), type of antipsychotic medication (first vs. second generation) and dosage, use of SSRI or mood stabilizer, and hyperprolactinemia (>20ng/ml). Non-significant covariates were eliminated from the models. Regression coefficients are presented as unstandardized beta weights (standard errors). Only p values< 0.10 are reported (so that trend-level effects are noted). Multilevel models were analyzed with SAS (v.9.02 for Windows; SAS, Cary, NC).

3. Results

3.1. Hormone levels in women and men

Table 2 shows average hormone levels for female participants. As expected for females overall, estradiol and progesterone levels were significantly higher during the midluteal versus early follicular phase, (p’s<0.001). Testosterone and oxytocin levels did not change significantly across the cycle. Progesterone levels were lower in patients compared to controls (p<0.01), but levels of estradiol, free testosterone, and oxytocin did not differ between female groups. Both groups showed similar progesterone levels during the early follicular phase, but patients showed lower progesterone levels compared to controls during the midluteal phase (p<0.001). Patients and controls showed a similar magnitude of change in estrogen, testosterone, and oxytocin across phase.

Table 2
Endogenous Serum Hormone Levels (M and SD) in a Function of Menstrual Cycle Phase (early follicular, midluteal) in Female Patients and Healthy Controls.

Table 3 presents hormone levels for men. Free testosterone levels were lower in male patients compared to controls (p<0.05), but estradiol and oxytocin levels did not differ between the two groups. As expected, no hormone levels differed as a function of test session, and there were no Group by Session interactions.

Table 3
Endogenous Serum Hormone Levels (M and SD) in Male Patients and Controls over Two Study Sessions (A, B).

3.2. Changes in clinical symptoms in women with schizophrenia across the menstrual cycle

Table 4 shows PANSS ratings for female patients at each cycle phase as well as the change score. Scores on the positive (Cohen’s d=0.15) and general psychopathology (Cohen’s d=0.50) subscales and the total symptom score (Cohen’s d=0.34) were lower during the midluteal versus early follicular phase (p’s<0.01), whereas scores on the negative symptom subscale and prosocial factor did not change. Clinical symptoms in male patients did not differ significantly from Session A and B.

Table 4
The Effects of Menstrual Cycle Phase in Female Patients and Test Session in Male Patients on the Positive and Negative Syndrome Scale Ratings (PANSS).

3.3. Relationships between clinical symptoms and hormone levels in women and men with schizophrenia

Individual variation in estradiol and progesterone levels did not significantly account for changes in clinical symptom scores. Average levels of oxytocin, which was very consistent over time (test-retest reliability r=0.81, p<0.001), were associated with average symptom presentation in female patients (Table 5). Specifically, higher levels of oxytocin were associated with lower scores on the total symptom, and positive, general psychopathology, and prosocial measures (p’s<0.01; see Figure 1). There was a trend for higher oxytocin levels to be related to lower negative symptom scores in women (p=0.06). In men, higher oxytocin levels were associated with better prosocial scores (p<0.05). Testosterone did not relate to symptoms in either sex.

Figure 1
Fitted subscale scores on the Positive and Negative Syndrome Scale (PANSS) using multilevel random coefficient models as a function of plasma oxytocin levels in female patients for three scales: positive subscale (p<0.001), general psychopathology ...
Table 5
The Effects of Menstrual Cycle Change, Fluctuating and Non-fluctuating Hormones in Female Patients on the Positive and Negative Syndrome Scale Ratings (PANSS).

Exploratory analyses on individual PANSS items indicated that in female patients, higher levels of oxytocin were significantly associated with better clinical symptoms on delusions, hallucinatory behavior, suspiciousness/paranoia, passive social withdrawal, and tension (p’s<0.05). Trends were also noted on blunted affect, emotional withdrawal, and depression (p<0.10). In male patients, trends were noted on active social avoidance and hostility (p<0.10).

4. Discussion

The primary goal of this study was to examine the effects of menstrual cycle phase and peripheral hormone levels on clinical symptom severity in women with schizophrenia. In women, menstrual cycle-related changes on the PANSS were observed, with lower positive symptoms, total symptoms, and general psychopathology in the midluteal compared to early follicular phase. Individual variations in hormone levels across the cycle were not related to these cycle-related changes in symptoms. Although oxytocin did not vary significantly across the menstrual cycle, higher average levels of oxytocin predicted less severe positive, general, and prosocial symptoms in women. In men, higher levels of oxytocin predicted better prosocial symptom scores. These findings in chronic patients extend previous work in acutely ill patients showing that symptoms fluctuate across the menstrual cycle. Additionally, our findings support continued investigation of hormones in relation to symptom severity in schizophrenia, and continued investigation of exogenous oxytocin as an adjunctive treatment in schizophrenia.

4.1. Clinical Symptoms, Menstrual Cycle, and Hormones in Women with Schizophrenia

Our finding that clinical symptoms improve during the midluteal versus follicular phase is consistent with previous studies (Hallonquist et al., 1993, Riecher-Rossler et al., 1994, Bergemann et al., 2007). We observed small to medium improvements (i.e., according to Cohen’s d effect sizes) in positive, general, and total symptoms in the midluteal versus follicular phase. This finding is similar to that of Bergemann (2007), who studied changes in symptoms across the menstrual cycle in 125 premenopausal women with schizophrenia. The negative symptom subscale was only marginally affected by menstrual cycle in the Bergemann (2007) study and was not significantly related to menstrual cycle in our study, possibly because our study was underpowered to detect a subtle change. Our study did not replicate previous reports that estrogen levels related to clinical symptoms (Riecher-Rossler et al., 1994, Bergemann et al., 2007). This difference may reflect different characteristics of our patient populations; in earlier studies, patients showed reduced estrogen levels across the entire menstrual cycle and were either acutely ill or tested following recent hospitalization. In contrast, our study involved an outpatient female sample with similar estradiol compared to controls, regular menstrual cycles, stable drug therapy, and comparatively low and stable psychopathology scores. Thus, our study provides evidence that menstrual cycle fluctuations in symptoms are evident not only in acutely ill women with high levels of symptoms, but also in chronically ill stable women with lower levels of symptoms.

In this study, we also related clinical symptoms to endogenous levels of oxytocin, progesterone, and testosterone. Progesterone levels in female patients were not significantly associated with changes in clinical symptoms. However, we found reduced midluteal progesterone levels, as in other studies (Bergemann et al., 2005a, Bergemann et al., 2007) and reduced overall progesterone levels in women with schizophrenia, similar to some (Riecher-Rossler et al., 1994, Howes et al., 2007) but not all studies (Huber et al., 2004). Reduced levels of progesterone may indicate anovulatory cycles and insufficient follicular maturation (Bergemann et al., 2007) or could be due to stress or nutritional deficiencies (Huber et al., 2004).

Consistent with previous studies, we found indications of reduced free testosterone levels in men with schizophrenia (Goyal et al., 2004, Huber et al., 2005, Akhondzadeh et al., 2006, Ko et al., 2007, Konarzewska et al., 2009). There are a number of factors reported to affect testosterone level in both men with and without schizophrenia including obesity(Zumoff et al., 1990, Jensen et al., 2004) and over half of the male patients in our sample were overweight (56% with BMI scores>30). Further work is needed to examine the impact of idiopathic or drug-induced obesity factors in hormone-psychopathology relationships in schizophrenia patients.

4.2. Oxytocin and Clinical Symptoms in Men and Women with Schizophrenia

High oxytocin levels were associated with reduced prosocial symptoms in both sexes. The relationship between oxytocin and prosocial behaviors may reflect the well-established role of oxytocin in affiliative behaviors (Carter et al., 2008). There are several neurobiological mechanisms by which oxytocin might influence prosocial behaviors in schizophrenia. Oxytocin/glutamate interactions have been documented in two preclinical studies involving prepulse inhibition (PPI), a widely used measure of sensorimotor gating. PPI is impaired in schizophrenia and is used to test the efficacy and action of antipsychotic drugs in preclinical models. In one study, oxytocin treatment in male rats reversed deficits in PPI induced by dizocilpine, a non-competitive NMDA antagonist. Oxytocin had smaller benefits following PPI induced by amphetamine, and was ineffective in reversing apomorphine-induced deficits in PPI (Feifel and Reza, 1999). In the second study, oxytocin knock-out mice show disrupted PPI following treatment with phencyclidine, a non-competitive NMDA antagonist, but not following treatment with amphetamine or apormorphine (Caldwell et al., 2009). Oxytocin also reversed social deficits in male rats caused by chronic phencyclidine (Lee et al., 2005).

Oxytocin was also associated with positive, general, and overall symptoms in female but not male patients. The novel of finding of oxytocin relating to positive symptoms was in part due to decreasing suspiciousness/paranoia, hallucinations, and delusions, as indicated by the exploratory item analysis. Intranasal oxytocin given to healthy individuals increases trust (Kosfeld et al., 2005, Theodoridou et al., 2009), and peripheral oxytocin levels are associated with increased trustworthiness (Zak et al., 2005). The relationship between oxytocin and lower levels of general symptoms in women was in part due to decreasing depression and tension. Oxytocin may have a more global effect on general psychopathology due to its role in emotional processing, stress management, affiliative behavior, and depression (Scantamburlo et al., 2007, Carter et al., 2008, Heinrichs et al., 2009, Parker et al., 2010).

The relationship between oxytocin and positive symptoms in particular might be influenced by dopamine/neuropeptide interactions (Shahrokh et al., Rosenfeld et al., 2010). Mesolimbic dopamine projections are thought to be hyperactive, especially in the acute phase of schizophrenia (Abi-Dargham and Moore, 2003). Peripheral administration of oxytocin has been shown to inhibit dopamine transmission in mesolimbic pathways (Sarnyai and Kovacs, 1994). Animal and clinical studies demonstrate that antipsychotic medication increases both central (Beckmann et al., 1985) and peripheral (Uvnas-Moberg et al., 1992) oxytocin levels, suggesting that enhancing endogenous oxytocin may play a role in the therapeutic effects of antipsychotic drugs.

In men, oxytocin levels were not related to most symptom domains. Our analytic model examined the relationship between oxytocin and symptoms while controlling for the effects of other hormones, including estrogen. When estrogen was taken out of the model, a significant relationship between oxytocin levels and positive and overall symptoms was evident in men(p < .05). This pattern suggests that the relationship between oxytocin and symptoms in men may be influenced by estradiol levels.

4.3. Limitations

One limitation to our study is that statistical controls for medication effects (antipsychotic type, SSRIs, mood stabalizers) only partially adjust for the diverse neurochemical effects of different antipsychotic drugs. Studies suggest that antipsychotic medications may impact oxytocin (Beckmann et al., 1985, Uvnas-Moberg et al., 1992), particularly clozapine and olanzapine (20% on these medications in current study) and less by risperidone and haloperidol (36% on these medications in current study)(Kiss et al. 2009)(Beckmann et al., 1985, Uvnas-Moberg et al., 1992). Future studies should examine untreated acutely ill first episode patients where biology/symptom associations can be examined early in the course of illness without confounding influence of psychiatric medications. Second, the EIA measurement of oxytocin was done in unextracted samples, which is associated with higher levels of this peptide. However, earlier work separating samples with HPLC prior to assay revealed that this assay is highly specific for oxytocin (Carter et al., 2007). Also, in the present study oxytocin samples showed comparable values when rerun after dilution; within and between assay coefficients of variation were less than 11%. Third, we measured oxytocin once at each of two menstrual phases. Although, test-retest reliabilities were high (r=0.81), oxytocin secretion may be pulsatile and measurement at multiple time points during each cycle phase might yield a more fine-grained understanding of oxytocin secretion. However, we were only able to measure oxytocin at one point at each phase of the menstrual cycle due to funding limitations. Fourth, neuropeptides do not readily cross the blood brain barrier. However, most endogenous oxytocin is synthesized within the brain, and there is some evidence in animals that central and peripheral oxytocin are correlated (Landgraf and Neumann, 2004). Peripheral administration of oxytocin as well as peripheral levels may influence behavior by bypassing the brain through circumventricular organs. Furthermore, peptide effects on mood and behavior may result from effects on peripheral receptors, which are abundant in visceral organs, including organs innervated by the vagus. Finally, while the prosocial factor has been used in two additional studies (Loebel et al., 2004, Docherty et al., 2010) it has not been revalidated.

4.4. Conclusions

In summary, the present study examined the effect of menstrual cycle phase and hormones on clinical symptoms in women with schizophrenia. Earlier studies involving acutely ill patients demonstrated that clinical symptoms fluctuate across the menstrual cycle (Riecher-Rossler et al., 1994, Bergemann et al., 2007). Here we show the same pattern of findings in chronically ill, clinically stable female patients. Peripheral hormone levels did not account for these cycle-related changes but peripheral measures are an imperfect index of CNS levels, and secondary effects of hormones or other cycle-related factors were not measured. Endogenous oxytocin levels, which had not been examined in previous menstrual cycle studies, were significantly associated with improvements in positive symptoms in female patients and prosocial symptoms in male and female patients. This work supports the general hypothesis that endogenous hormones can modulate symptoms in chronically-treated men and women with schizophrenia. It may be important to consider sex when evaluating oxytocin in the management of schizophrenia.

Acknowledgments

Role of funding score

The funding agencies had no role in the design and conduct of the study collection, management, analysis, and interpretation of the data; and preparation, review, or approval of the manuscript.

This work was supported by Award Number F31MH082480 from the National Institute of Mental Health. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Center for Research Resources or the National Institutes of Health. Other support for this work was by a Psi Chi Graduate Research Grant, by the Alice J. Dan Dissertation Award from the UIC Center for Research on Women and Gender (CRWG), and by the University of Illinois at Chicago (UIC) Center for Clinical and Translational Science (CCTS), Award Number UL1RR029879 from the National Center for Research Resources, and by the Core Lab of the GCRC/CNRU at the University of Alabama, which is supported by NIH grants M01-RR-00032, P30-DK56336). Validation of the oxytocin assay was supported by MH 072935 (CSC). Dr. Sweeney is supported by a Humboldt Research Award for Senior Research Scientists. We would also like to thank Erin Eatough, Antonia Savarese, Jill Breit, Pamela Perschler, Stephanie Klenotich, Jessica Jandak, and Melissa Arcabos for their assistance with this study. Special thanks goes to Ellen Herbener, Jim Pellegrino, Julie Dumas, Cherise Rosen, Sheila Dowd, Sandra Wilkniss and the Thresholds Psychiatric Rehabilitation Center, and the Center for Cognitive Medicine at the University of Illinois at Chicago.

Footnotes

Contributors

Drs. Rubin and Maki conceived the idea and methodology for the study. Dr. Carter developed the methodology to explore oxytocin and served as an advisor and resource on this project for understanding oxytocin. Dr. Sweeney served as an advisor on this project and provided his expertise in schizophrenia. Dr. Pournajafi-Nazarloo and Ms. Drogos ran the oxytocin assays. Dr. Rubin, Dr. Maki’s lab, and the Center for Cognitive Medicine were involved in recruitment and clinical assessments. Dr. Rubin conducted the statistical analyses and wrote the first draft. Drs. Rubin, Maki, Carter, and Sweeney exchanged multiple versions of the manuscript. All authors contributed to the writing of the manuscript and approval of the final version.

Conflict of interest

Dr. Sweeney is a consultant to Pfizer and has a research grant from Janssen. Dr. Maki received honoraria from the American Nutraceutical Association and research support from the Soy Health Research Program. All other authors declare that, except for income received from their primary employer, no financial support or compensation has been received from any individual or corporate entity over the past 3 years for research or professional service, and there are no personal financial holdings that could be perceived as constituting a potential conflict of interest.

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