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Psychosomatic Medicine 67:531-538 (2005)
© 2005 American Psychosomatic Society

ORIGINAL ARTICLES

Effects of Partner Support on Resting Oxytocin, Cortisol, Norepinephrine, and Blood Pressure Before and After Warm Partner Contact

Karen M. Grewen, PhD, Susan S. Girdler, PhD, Janet Amico, MD and Kathleen C. Light, PhD

From the Departments of Psychiatry (K.M.G., S.S.G., K.C.L.) and Psychology (S.S.G., K.C.L.), University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; and the Departments of Medicine, Pharmaceutical Sciences, and Pharmacy, University of Pittsburgh, Pittsburgh, Pennsylvania (J.A.).

Address correspondence and reprint requests to Karen Grewen, PhD, University of North Carolina, Medical Research Building A, CB #7175, Chapel Hill, NC 27599-7175. E-mail: karen_grewen{at}med.unc.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
 REFERENCES
 
Objective: We examined whether the magnitude of plasma oxytocin (OT), norepinephrine (NE), cortisol, and blood pressure (BP) responses before and after a brief episode of warm contact (WC) with the spouse/partner may be related to the strength of perceived partner support.

Methods: Subjects were 38 cohabiting couples (38 men, 38 women) aged 20 to 49 years. All underwent 10 minutes of resting baseline alone, 10 minutes of WC together with their partner, and 10 minutes of postcontact rest alone.

Results: Greater partner support (based on self-report) was related to higher plasma oxytocin in men and women across the protocol before and after WC. In women, higher partner support was correlated with lower systolic blood pressure (SBP) during solitary rest after WC but not before. Also, higher OT in women was linked to lower BP at baseline and to lower NE at all 4 measurements.

Conclusion: Greater partner support is linked to higher OT for both men and women; however, the importance of OT and its potentially cardioprotective effects on sympathetic activity and BP may be greater for women.

Key Words: warm contact • partner support • oxytocin • norepinephrine • cortisol • blood pressure

Abbreviations: ABP = ambulatory blood pressure; BMI = body mass index; BP = blood pressure; CVD = cardiovascular disease; DBP = diastolic blood pressure; HPA = hypothalamic–pituitary–adrenal; HR = heart rate; IV = intravenous; MI = myocardial infarction; NE = norepinephrine; OT = oxytocin; SBP = systolic blood pressure; SNS = sympathetic nervous system; SRI = Social Relationships Index; WC = warm contact.


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
METHODS
 RESULTS
 DISCUSSION
 NOTES
 REFERENCES
 
Althoughsocial connectedness may increase longevity by promoting healthier behaviors and increased tangible and informational support, emotional social support is reportedly one of the most consistent independent predictors of better health (1,2). Based on longitudinal data, Berkman asserted that for social support to have the greatest health benefits, it must engender feelings of intimacy and belonging (3). Similarly, Knox reported that a lack of intimate contact is associated with greater sympathetic nervous system activation (4), which is linked to increased risk of cardiovascular disease (CVD). Results from large-scale studies suggest that marriage, one of the most central and intimate sources of support for many adults, has a beneficial effect, and that divorce, bereavement, and social isolation have negative effects on cardiac and overall health. Married men and women are at reduced risk for all-cause and postmyocardial infarction (MI) death (5–11), whereas divorce is linked to increased total and cardiovascular mortality (10–13). Moreover, married people are also less likely to undergo surgery and enjoy better prognoses when they do receive a diagnosis of CVD (14). Some epidemiological studies suggest that men may receive greater cardioprotection from marriage compared with women (6,12,15), whereas other studies report similar benefits for both genders (9).

On closer inspection, however, not all marriages appear equally protective. The quality of the marital relationship seems to play an essential role in health outcomes (16,17), with greater levels of marital dissatisfaction and discord linked to enhanced health risk (8,18,19). In women with coronary heart disease, marital stress is a more potent predictor of cardiovascular outcomes than work stress (20), and reports of greater marital dissatisfaction have also been linked to greater physiological stress responses to the mere recollection of partner conflict, despite the absence of the stressful mate (21). Conversely, greater marital satisfaction and cohesion have been linked prospectively to reductions in left ventricular mass and smaller increases in 24-hour ambulatory blood pressure (ABP) over a 3-year follow up in patients with mild hypertension, especially when partners spent more time together (18,22). In healthy subjects, our own research group has reported lower mean 24-hour ABP in men and women reporting high compared with intermediate or low relationship quality and those with no partnered relationship (23). In another study of ABP at home and work, time spent with the spouse or partner was characterized by lower BP compared with times spent with others or alone (13). In a recent laboratory study, we reported that spending time in contact with a spouse/partner before stress markedly attenuated BP and heart rate (HR) increases to stress in both men and women (24). Taken together, these findings suggest that when the relationship is supportive and strong, time spent with the partner may be beneficial by reducing BP and protecting against future CVD. Therefore, the direct effects that emotionally supportive marital interactions exert on physiological processes are an important focus for researchers interested in the mechanisms underlying the cardioprotective influence of positive social relationships.

Oxytocin (OT), a hypothalamic neuropeptide active both centrally and peripherally, is an important potential mediator of cardiovascular health benefits of marriage and good relationships. As summarized by Uvnas-Moberg, recent advances in the study of the neurobiology of affiliation in mammals suggest that the OT system, which is uniquely responsive to the social environment, operates in parallel with known stress response systems both to bring about "calm and connection" effects in response to positive social cues, and to inhibit sympathetic and hypothalamic–pituitary–adrenal (HPA) activity after stress (25–27). Taylor has theorized that the OT system is a central factor in the "tend and befriend" behaviors that more women than men appear to use in response to both social contact and to stress (28). Animal studies have linked OT to important social behaviors, including social recognition, maternal behavior, and monogamous pair-bonding (29–31), and inform us that OT is produced in both male and females, with similar central oxytocinergic pathways and connections across genders. Although a single dose of OT increases BP and corticosterone in rats, daily OT administration for 5 to 14 days leads to enduring reductions in both measures, as well as decreased anxiety-like behaviors in novel environments, which are sustained long after OT administration is ended. An enhancing effect of female sex hormones is suggested by findings that these effects are prolonged in intact females (3 weeks) versus males and ovariectomized females (7–8 days) (32,33). Studies in several mammalian species have shown that enhanced OT activity of this kind leads to inhibition of both central alpha-adrenergic and HPA activity while promoting parasympathetic cardiac control (34–36). Conversely, lack of OT activity, associated with social isolation, is thought to promote multiple atherogenic factors involving platelet activity, endothelial function, and reductions in vagal tone (25).

Studies of OT responses in humans have been relatively few to date, and most have involved women in the postpartum period because of the established role of OT in the onset of maternal behavior and lactation. Mothers of infants who used both breast- and bottle-feeding methods reported less negative and more positive affect after breast feeding, which researchers interpreted as a probable effect of OT increases (37). Altemus reported that breast-feeding mothers demonstrated greater vagal control of HR in response to stress compared with bottle-feeders and controls (38). In a study of mothers of infants by our own research group, ABP levels were lower during the hour after infant feeding in breast-feeders compared with bottle-feeders (39). When OT responses to 10 minutes of baby holding followed by a speech stressor in the laboratory were examined in the same mothers, those who showed OT increases to stress demonstrated lower BP levels before, during, and after the speech task than mothers showing OT decreases. BP responses to the speech were lower in all mothers after baby contact compared with testing on another day when the baby was left at home, but this stress-buffering effect of baby contact was not correlated with the OT response. Similarly, Bonfiglio and Stoney (40) recently reported that during a speech stressor, presence of a supportive friend was linked to decreases in BP responses that were not associated with any increase in plasma OT levels. In one novel study involving women who were not postpartum and also not tested during stress, Turner and colleagues reported greater OT increases to positive emotion induction in partnered compared with single women and in those with fewer interpersonal relationship problems (41). OT effects in men are not well-documented; however, Heinrichs et al. (42) reported a decrease in cortisol stress reactivity in men given inhaled OT versus placebo. Although animal studies show that OT is present is both genders, and female sex hormones appear to potentiate the effects of OT on BP, no study to date has compared OT responses with a period of contact with spouses/partners in both men and women.

We hypothesized that a history of more frequent positive partner interactions would have cumulative effects leading to enhanced oxytocinergic activity. Thus, we attempted to determine whether a more supportive partner relationship was associated with higher levels of plasma OT before or after a brief period of warm physical and emotional contact with the partner in men and women currently in long-term partner relationships. Because pilot research indicated that plasma OT responses are significantly blunted or distorted in many individuals during stress, whereas OT responses are enhanced when solitary rest follows warm partner contact versus no contact (mean levels 2.34 versus 0.72 pg/mL, p < .02), we selected a protocol in which subjects simply rested alone before and after warm contact (WC) with their partners. We also examined the associations of both partner support and OT responses to other physiological measures, hypothesizing that BP, norepinephrine (NE), and cortisol levels would be lower after WC in people with higher partner support and/or higher OT levels. Finally, we examined whether OT meets statistical criteria to be a partial mediator of any observed effect of partner support on BP, NE, and/or cortisol.


   METHODS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
RESULTS
 DISCUSSION
 NOTES
 REFERENCES
 
Subjects
Healthy couples (38 women, 38 men), aged 20 to 49 years old, were recruited using local newspaper advertisements and fliers. Subjects were required to be living with their current spouse or monogamous partner for at least 1 year. Reasons for exclusion included current use of prescription medication affecting the cardiovascular or autonomic nervous systems, chronic systemic disease, current clinical depression or other psychiatric disorder, pregnancy, breast feeding, postmenopausal status, or being less than 11 months postpartum. There were no gender differences in racial distribution, with 82% of women and 79% of men describing themselves as "white" on an open-ended question of race.

Protocol
Subjects were screened during a brief telephone interview. Partners arrived together but were immediately separated. Each was instrumented with cardiovascular monitors and an intravenous (IV) catheter for blood sampling. A 20-minute period for instrumentation/adaptation was followed by solitary resting baseline alone (10 minutes). Subjects then joined their partners in a different room for the warm contact together period (10 minutes) and were separated again for the postcontact rest alone (10 minutes). Baseline alone period: Partners were seated in comfortable chairs in separate rooms. BP and HR data sampled at s 4, 6, and 8 was averaged to represent baseline levels. Blood was sampled at minute 8 for baseline NE, cortisol, and OT. Warm contact together period: Couples were seated on a loveseat in a quiet room and instructed to sit close together, holding hands if they felt comfortable doing so. They were asked to talk about a time they had spent together that had made them feel closer as a couple (2 minutes). They then watched a 5-minute segment of a romantic video they had previously seen. They then were instructed to talk for 2 minutes about a time when they felt close as a couple. During this time, couples were unmonitored and unobserved except when the experimenter entered the room to give instructions. At the end of this session, partners stood for a 20-second hug. Postcontact rest alone period: Subjects were moved to separate chambers to rest quietly alone for 10 minutes. BP and HR were measured at postcontact minutes 4, 5, 7, and 10. Plasma for OT and NE was sampled at postcontact minutes 4, 7, and 10 and serum for cortisol was sampled at minute 10 only.

Cardiovascular Assessment
Subjects were instrumented with the Accutracker II ambulatory blood pressure monitor (Suntech, Raleigh, NC), a device whose prototype has been validated against direct arterial and standard auscultatory measurements (43,44). To standardize the Accutracker readings to clinic BP assessments, a minimum of three seated BP readings were then taken with the Accutracker monitor, whereas simultaneous auscultatory BP readings were assessed by a trained technician. Monitor readings falling within 5 mm Hg of the stethoscopic values were considered acceptable, provided the Accutracker displayed no error codes.

Biochemical Analyses
The level of OT in EDTA plasma was determined by extraction and radioimmunoassay in the laboratory of Janet Amico (53,57). The intraassay coefficient of variation was 10% to 12% and the sensitivity was approximately 0.5 pg/mL. Norepinephrine was measured using reverse-phase high-performance liquid chromatography (sensitivity = 5 pg/mL, inter- and intraassay CV <10%). Serum cortisol levels were assessed using radioimmunoassay (ICN Pharmaceuticals, sensitivity = 0.07 µg/dL, inter- and intraassay CV <8%).

Partner Support
The spousal version of the Social Relationships Index (SRI), developed as a self-report version of the Social Support Interview (45), was used to assess partner support. Men and women reported similar levels of support (men: median = 26, mean = 25.6, standard deviation [SD] = 3.35, range = 17–30; women: median = 25, mean = 25.1, SD = 3.79, range = 15–30) and were grouped into high versus low partner support groups based on median split (high = 26–30, low = 15–25). In addition to individual assessments, partner support was also assessed as a function of the couple in two additional ways. A majority of subjects reported levels of partner support consistent with their partner (28% both high; 26% both low; 20% men high/women low; 26% women high/men low), and thus each subject was categorized by this dyadic consistency into high/high, low/low, or mixed groups. Each subject was also given a mean couple support score (partners’ mean SRI score) and grouped into high (top 25%), intermediate, or low (bottom 25%) couple partner support groups. This couple-based predictor yielded effects similar, but not as powerful, to the individual’s assessment of partner support in predicting outcome measures; therefore, results based on each individual’s assessment of partner support are reported.

Statistical Methods
The primary form of analysis was a 2 (gender) x 2 (high/low partner support) repeated measures multivariate analysis of covariance (MANOVA) with SBP, DBP, HR, NE, cortisol, and OT as dependent measures in separate models, using age and body mass index (BMI) as covariates when significant. Examination of within and between-subject mean differences was pursued only when the multivariate analysis of variance (MANOVA) overall F statistic was significant. Secondary analyses included simple regression analyses to examine relationships of OT to other measures under study and mediational analyses using the approach recommended by Baron and Kenny (46). Independent t tests were used to examine gender differences in dependent measures at baseline. Paired t tests were used to examine within-subject differences between OT levels at baseline versus postcontact samples separately for men and women.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
DISCUSSION
 NOTES
 REFERENCES
 
Sample Characteristics
Table 1 depicts baseline characteristics of subjects classified by gender. At baseline, men showed significantly lower HR and higher plasma NE (p’s < .05) than women, as well as marginally higher SBP. Gender groups were not different in baseline levels of DBP, OT, or cortisol, nor did they differ in age, BMI, or reports of support from their partners.


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  		TABLE 1. Sample Characteristics by Gender

 

Gender, Age, and Body Mass Index: Effects on Blood Pressure and Heart Rate
Separate repeated-measures MANCOVAs were then run for SBP, DBP, HR, NE, and cortisol to examine the effects of gender, high/low partner support group, and covariates (age and BMI) on these dependent measures across multiple measurements taken during the protocol. Main effects of gender were observed, with women exhibiting higher HR (F1,72 = 4.66), lower SBP (F1,71 = 6.29), and lower DBP (F1,71 = 6.74) compared with men across assessments (p’s < .05). Higher overall SBP (F1,70 = 13.58, p < .001) and DBP (F1,70 = 10.94, p < .01) were predicted by greater BMI, whereas higher DBP was also predicted by greater age (F1,70 = 6.71, p < .05).

Partner Support and Warm Contact: Effects on Blood Pressure, Heart Rate, Cortisol, and Norepinephrine
In these same analyses, partner support group was an independent predictor of the pattern of SBP changes between the precontact and the postcontact rest periods, both of which were spent alone (partner support group x time interaction: F3,213 = 3.47, p < .05). Subsequent univariate analyses revealed that subjects reporting high partner support showed lower SBP than those with low partner support in the postcontact period at minute 7 (b = –0.74, F = 4.25, p < .05). This group difference was evident although slightly weaker at minute 10 (b = –0.68, F = 3.53, p < .07), but was not present at precontact baseline. When the gender x support interaction term was added, a marginally significant gender x support x time interaction was present (F3,210 = 2.91, p < .06). Subsequent correlational analyses clarified that the SBP benefit of partner support was largely restricted to women and was evident after WC but not before it. In women, partner support was not significantly correlated with SBP at precontact baseline rest (Pearson r = –0.20, p = nonsignificant), but higher support was significantly related to lower SBP throughout the solitary postcontact rest at minute 4 (r = –0.38, p < .05), and minutes 5, 7, and 10 (r’s = –0.45, –0.43, and –0.46, respectively, p’s < .01). In men, none of these correlations between support and SBP approached significance (r’s = –0.01 to –0.09).

Repeated-measures analyses did not reveal effects of gender, age, BMI, partner support, or the support x gender interaction on DBP, HR, or levels of plasma NE. Cortisol levels were lower after WC than before it in both men and women (effect of time: F1,67 = 7.90, p < .01; means for men = 8.81 versus 7.52 µg/dL and for women = 7.79 versus 7.11 µg/dL). However, there were no differences in cortisol responses between subjects reporting high versus low partner support, and this observed cortisol decline in the sample as a whole may be the result of simple habituation rather than a specific effect of WC.

Partner Support: Effects on Plasma Oxytocin
We then examined the effect of partner support on plasma OT levels. Repeated-measures MANCOVA revealed a significant overall effect of partner support on OT levels across the laboratory session. Individuals reporting high versus low partner support exhibited greater OT across the protocol (between subjects F1,73 = 8.98, p < .005). Figure 1 shows mean age- and gender-adjusted OT levels in high and low partner support groups classified by median split. Pairwise comparisons revealed significantly greater mean OT levels in the high versus low partner support groups at all measurement times (all p’s < .05).



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  		Figure 1. Age- and gender-adjusted plasma oxytocin levels (pg/mL) during the precontact rest alone (base) and postcontact rest alone at 4, 7, and 10 minutes after termination of warm contact as a function of high versus low partner support (median split of total Social Relationships Index score). Presented as means ± standard error of mean.

 

The same effect was seen when partner support was treated as a continuous variable and examined by gender. The link between greater partner support and higher OT values was observed in both men and women at baseline (women: r = +0.36, men: r = +0.38, p’s < .05) and was present after WC with partner in women (postcontact rest alone minute 4: r = +0.34). When baseline OT was examined by partner support quartiles, a consistent pattern of increasing OT with increasing partner support was also seen (means, adjusted for age and gender ± standard error of mean: Q1 = 1.06 ± 0.24, Q2 = 1.51 ± 0.25, Q3 = 1.74 ± 0.25, Q4 = 2.21 ± 0.30 pg/mL).

When we categorized couples by dyadic consistency on the partner support measure (both partners reporting high, both low, or mixed support), we also saw a difference in baseline OT levels (F = 3.94, p < .05). Examination of least-square means revealed that individuals in dyads in which both partners endorsed low partner support had significantly lower baseline OT, adjusted for age and gender, than those in dyads in which one or both partners endorsed high partner support (low/low = 0.94 ± 0.26, high/high = 1.94 ± 0.23, and mixed = 1.74 ± 0.22 pg/mL, p’s < .05). Figure 2 illustrates these values for men and women, showing a comparable OT deficiency in men and women from dyads in which both partners endorsed low partner support (low/low group). OT levels were highly correlated within-subjects across the 4 samples (r’s = +0.79 to +0.89, all p’s < .0001), and wives’ OT levels were moderately correlated with their own husbands’ OT at baseline (r = 0.39, p < .05).



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  		Figure 2. Age- and gender-adjusted baseline oxytocin values (pg/mL) during precontact rest alone by dyadic consistency of partner support presented as means ± standard error of mean.

 

Gender Difference in Oxytocin Responses
Analyses also revealed a significant gender difference in OT response, independent of partner support (gender x time: F3,219 = 3.89, p < .05). Baseline OT levels were similar in men and women, and this similarity remained at all time periods except minute 7 of the post-WC solitary rest. Figure 3 depicts age-, gender- and partner support-adjusted means of plasma OT in men and women across the protocol. Subsequent paired t tests revealed that in women, OT was significantly higher at postcontact minute 7 than at precontact baseline (pre: 1.67 versus post: 2.00 pg/mL; mean difference +0.33 pg/mL ± 0.14 t = 2.24, p < .05) and postcontact minutes 4 (1.63 ± 0.17, t = 2.41, p < .05) and 10 (1.50 ± 0.17, t = 3.60, p < .001), whereas pre- and postcontact OT levels were not reliably different for men. Comparison of least-squared means also revealed women’s OT levels were marginally higher than men’s only at postcontact minute 7 (p < .052).



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  		Figure 3. Plasma oxytocin levels (pg/mL) during the precontact rest alone (base) and postcontact rest alone at 4, 7, and 10 minutes after termination of warm contact are displayed separately for men and women. Mean values ± standard error of mean are adjusted for age, gender, and partner support.

 

Gender Difference in the Association of Oxytocin With Blood Pressure and Norepinephrine
Although higher baseline OT was linked to higher partner support in both men and women, a link between higher baseline OT and lower baseline SBP and DBP was observed in women only (Pearson r’s = –0.36 and –0.34, p’s < .05 for women; r’s = +0.04 and +0.03, p’s = nonsignificant for men). Higher OT was also strongly correlated with lower NE in women but not in men at baseline and during the 3 postcontact samples obtained (see Table 2). OT values were also marginally correlated with age (baseline: r = –0.29, minutes 7 and 10: r’s = –0.28, all p’s < .10). In women only, partial correlations between OT and NE, adjusting for age, yielded even stronger associations (baseline: partial r (pr) = –0.51, p < .01; postcontact minute 4: pr = –0.35, p < .09, minute. 7: pr = –0.52, p < .01, and minute 10: pr = –0.43, p < .05).


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  		TABLE 2. Relationships Between Plasma Oxytocin and Norepinephrine in Women Only (n = 38)

 

Oxytocin Is a Partial Mediator of the Effect of Partner Support on Norepinephrine in Women
At baseline, lower age-adjusted NE was related to both better partner support (b = –10.41, t = –3.05, p < .01) and higher OT (b = –33.99, t = 3.34, p < .01) in women. Therefore, a series of linear regression analyses was performed to test whether the effect of partner support on baseline NE was mediated by plasma OT, as per the method described by Baron and Kenny (46). Evidence of mediation would be provided only if 1) partner support was related to plasma OT, 2) plasma OT was related to NE, and 3) the addition of OT into the model reduced the regression coefficient of NE regressed on partner support. Results, shown in Table 2, reveal that greater partner support predicted both higher OT (model 1) and lower NE (model 2) at baseline. Finally, when plasma OT was added (model 3), the effect of partner support on NE was reduced, suggesting that OT may be a partial mediator of the attenuating effect of partner support on resting levels of circulating NE in women.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
NOTES
 REFERENCES
 
Consistent with our a priori hypothesis that a history of more frequent positive partner interactions has cumulative long-term effects leading to enhanced oxytocinergic activity, we found that men and women reporting greater support from their partners showed higher plasma OT levels when resting alone both before and after a period of warm physical and emotional contact with their partners. It should be emphasized that participants were aware that the session would involve a period of warm physical and emotional partner contact, and their OT levels may have increased in anticipation of this event and then remained elevated. Thus, for a 30-minute interval surrounding a time of warm partner contact, greater sustained OT activity was shown by those with stronger partner relationships. To our knowledge, these are the first findings in humans linking OT to the strength of the partner relationship, and importantly, it was seen in both men and women. In animal models, OT activity has been shown to facilitate pair bonding and partner preference (47,48), and may also increase in response to warm physical contact and licking/stroking (49,50) in both males and females. In another study of 59 married/partnered women, the frequency of receiving hugs from the partner was directly related to both higher OT and lower BP (51). Thus, in a strong partner relationship, the higher OT levels we observed may both enhance the strength of that pair bond and be a result of more frequent episodes of warm contact between the partners in stronger relationships. That is, OT may be both a contributing cause and an effect of the strength of the pair bond. Repeated exposure to positive/supportive interactions may be necessary for enhanced OT activity reflected by greater tonic plasma OT levels in both genders. This interpretation is consistent with a recent report in which rats receiving daily massage eventually showed increases in central and peripheral OT levels, but not earlier than day 14 (52).

We also expected that greater partner support would influence BP and stress hormones after WC. Consistent with this prediction, we observed that the high support group showed lower SBP after contact, although this effect was also limited to women and to the same period when their OT increased. This complements our previous report of attenuation of BP and HR reactivity to an interpersonal speech stressor in both men and women after exposure to a similar period of warm partner contact compared with responses after solitary rest (24). Although we failed to find links between greater partner support and lower DBP, HR, NE, or cortisol response, we did obtain correlations of higher OT with lower SBP, DBP, and NE. Again, these associations were seen in women but not men, suggesting that beneficial cardiovascular effects of OT linked to partner support may be greater in women. This is most likely, in part, the result of the enhancing influence of estrogen on OT activity (33,54–56), availability (55–58), and receptor binding (29,59). A second factor, not mutually exclusive, is a possible contribution of OT’s sister peptide, vasopressin, which we did not measure. Studies in monogamous animal species suggest greater vasopressin activity in males in contrast to greater OT activity in females during pair bonding and mate contact (60,61). Vasopressin has powerful vasoconstrictive effects both systemically and in the renal bed that act to increase rather than decrease BP, effects that also may be more pronounced in males (62). Only in women were plasma OT levels transiently increased after partner contact (during minute 7), although men and women demonstrated similar levels after 10 minutes of solitary resting baseline. OT was not increased in blood sampled at 4 minutes after WC termination, suggesting it may be less than optimal to assess peripheral OT levels immediately after warm positive social contact, and that multiple assays may be needed to capture a short-term OT increase in plasma.

Higher OT in women was most strongly linked to lower plasma NE, an effect evident throughout the session. Furthermore, at baseline, greater OT met criteria to be a partial mediator of the attenuating effects of partner support on NE. This suggests that one potential pathway through which stronger partner relationships may be cardioprotective for women is through enhanced oxytocinergic activity that inhibits sympathetic nervous system (SNS) activity. It is important to note, however, that although strict statistical criteria were met for OT serving as a partial mediator for the effects of partner support on plasma NE, these relationships are correlational (regression-based) and do not verify causation in this cross-sectional design. Alternatively, other correlated factors (biological, behavioral, and/or cognitive) may be responsible for both increases in OT and reductions in SNS activity.

An important limitation of the current study is the lack of a comparison group that did not receive warm partner contact. This constrains our ability to infer that the short-term effects were specifically the result of the period of warm partner contact, allowing alternative explanations for the observed changes in cortisol and OT (habituation, anticipation of finishing the session, and rejoining the partner, and so on) and highlighting the need for further study. An additional limitation is that we did not assess whether subjects’ anxiety or negative affect were indeed lessened by WC; therefore, we cannot say whether changes observed after contact were the result of a change in mood/affect. In addition, the multiple components of the unmonitored WC condition—intimate conversation, viewing of a romantic video, and physical affection—make it difficult to identify a specific "magic bullet" responsible for the changes we observed. However, the multiple components, the ad lib nature, and the relative privacy of the task may have allowed the interaction to more closely resemble each dyad’s own typical behavior at home, thereby permitting a more accurate approximation of real-life responses. A new aspect of this protocol is the separate examination of the effect of a positive rather than negative partner interaction, which was measured without the influence of laboratory stressors. Finally, a strength of the current study is the use of multiple timed measurements of plasma OT following the contact condition which allowed us to identify timing of maximal OT response, and to compare response patterns in men versus women and high support versus low support groups.

In conclusion, our results suggest that a long-term effect of more positive/supportive couple relationships is enhanced production of plasma OT in both men and women. We speculate that greater OT levels may increase the probability of future positive interactions, so that OT and partner bonding reciprocate in a positive feedback loop. Women appear more likely than men to demonstrate transient contact-induced increases in peripheral OT, suggesting that women may be more physiologically responsive to this kind of nonsexual partner contact. Links between greater OT and reduced cardiovascular and sympathetic activity were also observed in women only. These results, combined with previous reports that women respond with greater cardiovascular and neuroendocrine reactivity to partner conflict (14,60), suggest that marriage and couple interactions may have the capacity to cause greater cardiovascular harm or protection in women compared with men over time based on qualitative factors such as partner support and relationship satisfaction (63). However, because marriage is also related to better long-term health in men, the extent to which higher OT and partner support contribute to maintaining the partner bond may provide cardiovascular benefit to men through other, as-yet undescribed, mechanisms. Thus, potentially cardioprotective benefits of positive partner relationships may involve increased OT for both men and women; however, the relative importance of OT and its effects on SNS activity and BP may be greater for women.


   NOTES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
REFERENCES
 

This research was supported by NIH grants HL64927 and RR00046.

DOI:10.1097/01.psy.0000170341.88395.47


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 METHODS
 RESULTS
 DISCUSSION
 NOTES
 REFERENCES
 

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