Oxytocin affects the heart's response to social isolation

A team of researchers investigating the effects of oxytocin, a peptide produced by the brain that regulates social behavior, has found that it can prevent detrimental cardiac responses in adult female animals exposed to social isolation.

The findings may provide further insight into how these mechanisms affect humans.

The study was conducted by Angela J. Grippo, C. Sue Carter and Stephen W. Porges, all with the Department of Psychiatry and Brain-Body Center at University of Illinois at Chicago and is titled Chronic Oxytocin Treatment Mediates Heart Rate Responses Following Social Isolation. Dr. Grippo is presenting the team's findings at the 120th annual meeting of the American Physiological Society (APS; www.The-APS.org), being held as part of the Experimental Biology (EB '07) conference. More than 12,000 scientific researchers will attend the gathering being held April 28-May 2, 2007 at the Washington, DC Convention Center.

The social environment plays an important role in regulating both behavior and cardiovascular function in humans. Negative social interactions, such as loneliness or social isolation, may increase the risk of developing depression and anxiety as well as heart disease.

Prairie voles (ochrogaster) are small rodents that demonstrate features of social interactions similar to humans and therefore provide a useful animal model for investigating how the social environment influences behavior and cardiac function. Earlier studies by this research team showed that when prairie voles were isolated from their families, they displayed behaviors similar to depression and cardiovascular changes indicating a possible increased risk of heart disease (including elevated resting heart rate, reduced heart rate variability, and reduced parasympathetic regulation of the heart).

This study examines whether oxytocin plays a role in the heart's detrimental responses to social isolation.

Adult female prairie voles were placed under anesthesia and implanted with wireless, radio frequency transmitters. The animals were subsequently exposed to either social isolation or pairing with a female sibling (control conditions) for four weeks. They were treated with oxytocin or saline (control solution) daily for 14 days during the third and fourth week of the four-week isolation period. Electrocardiographic parameters (heart rate and heart rhythms) were recorded using the radio frequency transmitter. Following the period of isolation or pairing, all animals were exposed to a mild social stressor (a five minute social interaction test with an unfamiliar animal).

The researchers found that:

• the animals exposed to isolation had an increase in heart rate and a reduction in heart rate variability. The administration of oxytocin significantly improved both heart rate and heart rate variability;
• for the animals exposed to isolation, oxytocin significantly reduced the heart rate response following the five-minute resident intruder social interaction test;
• for the isolated animals, oxytocin significantly improved parasympathetic regulation of the heart; and
• for the paired prairie voles (control group) oxytocin did not alter the cardiac responses.

These findings suggest that oxytocin can prevent damaging cardiac changes in adult female prairie voles exposed to social isolation. While there are limitations to the study, including the lack of spontaneous puberty and estrous cycles in female prairie voles (unlike their human counterpart), the results serve as a springboard into better understanding the mechanisms that underlie the relations between social behavior and cardiac function in humans.

The American Physiological Society (APS) has been an integral part of the scientific discovery process since it was established in 1887. Physiology is the study of how molecules, cells, tissues and organs function to create health or disease.

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