Blog of the Society for Menstrual Cycle Research

What is a hormone?

March 5th, 2012 by Paula Derry

All too often, hormones are portrayed in the media, and even in professional articles, as strangers inside our bodies that control us.   Sometimes hormones are personified as bosses that order our bodies around.  Sometimes they are portrayed as akin in function to gasoline or motor oil, needed to keep the machinery of our body moving or smoothly gliding.  Hormone levels that oscillate rather than maintaining a reassuring stability might be especially suspicious or even uncanny.

Take oxytocin.  According to the website ScienceDaily.com, which summarizes recent scientific studies, the hormone oxytocin is the “cuddle chemical”, promoting positive feelings, especially between mothers and infants, but it also has a “dark side,” promoting envy and gloating.  An oxytocin nasal spray might help shy people behave in a less introverted manner, and can make “surly monkeys treat each other a little more kindly”.

Or, take estrogen.  Teenagers are at the mercy of their “raging hormones.”   Premenstrual syndromes, perimenopausal mood changes, menstrual migraines, and hot flashes have all been attributed to hormones that oscillate (i.e., go up and down), dip, or are present in the wrong amount; thus, the orders barked out by the hormones go awry.   Perimenopausal estrogen changes are feared to destabilize the brain, creating preconditions for cognitive decline, or to increase risks for bone or heart disease.   A recent article (2010, vol. 1204) published by the Annals of the N Y Academy of Sciences was titled  “Estrogen and the aging brain:  An elixir for the weary cortical network?”.  A Science Daily report on estrogen and menopause (Oct. 4, 2011) was entitled “This is your brain on estrogen”.  Of course, not all hormones have this mythic status.  Important as diabetes is as a public health problem, I don’t recall seeing an article entitled “This is your liver on insulin.”

Here’s another view of hormones:  Most introductory science textbooks define them as chemical messengers, typically released from special tissues called glands, into the bloodstream.  In order for a hormone to affect a cell, the cell must have a receptor for the hormone. If there is no receptor, the hormone does not affect the cell.  If there is a receptor, the hormone changes the rate at which cells work, it does not make cells do things they would not otherwise do.  Hormones are chemical messengers that are involved in coordinating physiology, behavior, and development.

Consider a simple case, a person who is sitting in a chair and wants to stand up.  The muscles in a variety of parts of her body have to work together.  She can’t, for example, lift her buttocks before her feet push down on the ground, or lean so far forward that she falls.  Other parts of the body have to get into the act, also.  For example, her blood pressure must go up before she starts to stand; otherwise she would become dizzy since as she rises less blood reaches her head. Mind and body work together; blood pressure rises in response to her mere intention to get up.  In a similar manner, purposiveness is typically coordinated by hormones, the nervous system, and other players.

The way I think about it is that hormones are team players in complex, multi-determined systems that have a purpose. Hormones help to coordinate what happens in the body, but in normal functioning they do not act alone; they are part of a larger whole. They are more like telephone wires than the content of the conversation.

For example, what are some natural effects of oxytocin?  As summarized in the textbook “Introduction to Behavioral Endocrinology” (Randy Nelson), oxytocin does indeed have strong effects on the behavior of female rats.  Rats who have never been pregnant avoid pups, but begin taking care of their own pups as soon as they give birth.  Do their hormones make them do it? Apparently. When the blood of a new mother (which will contain her hormones) was given to a rat who had never been pregnant, the never-pregnant rat began acting like a mother within 24 hours. However, when never-pregnant rats were housed with pups for an hour or two a day, after about 5 or 6 days they also began to behave maternally. That is, being around baby pups also resulted in behaving like a mother.  The hormone speeded things up but didn’t change the animal’s essential nature. Rat mothers retrieve their young if they wander off, but injecting a human with rat hormones does not make the human build nests.

Readers should note that statements published in re: Cycling are those of individual authors and do not necessarily reflect the positions of the Society as a whole.