Prolactinis well-known for its role in stimulating milk production in nursing mothers but a new study published in the online journal PLoS One identifies a previously unrecognized function of this hormone – its contribution to sexual behavior and pair-bonding.
The study used cotton-top tamarins, a socially-monogamous, small monkey native to Colombia that live in family groups where both parents help care for the young.
The study found that chronic peripheral levels of prolactin correlated significantly with both sexual behavior and contact affiliation (time spent in grooming and huddling) in both sexes. Prolactin levels were high among pairs that frequently had sex and cuddled, and low among mothers that had finished nursing.
These results substantiate few recent studies suggesting a parallel between oxytocin and prolactin.
Charles Snowdon, first author of the study and an emeritus professor of psychology at University of Wisconsin-Madison believes that “the behavioral aspects of prolactin have received less study than those of oxytocin”.
According to him the discovery 25 years ago that oxytocin had an important role in pair bonding “was a conceptual breakthrough that oxytocin was not just about parenting, or the mother-infant bond, but about the pair bond between the adults;” “now we are finding something similar for prolactin, which is a hormone with different physical effects.”
Other recent research indicates increased prolactin levels after orgasm in humans and during infant carrying in marmosets. The authors of the PLoS One study believe that these results taken together with their results suggest that prolactin may be acting as a reward for parenting as well as for social sexual interactions with a partner.