Its poorly known role as a hormone producer
When I was 9 years old, our teacher asked us to name organs of the body, which she then would scribble on the blackboard. Of course everybody immediately shouted “The heart, the heart!”. Then came the stomach, then the lungs, and then…. a pause. The teacher asked “Isn’t there anything else?” So I replied: “Ovaries”, but she ignored me. I shouted two or three more times: “Ovaries, ovaries, ovaries!”, but she paid no attention to me. I was puzzled. I had seen a labelled drawing of the human anatomy in one of my grandfather’s books and I knew I was right, but the teacher only started writing on the board again, when another child suggested “bones”.
So, back to the heart, because that was (and still is) foremost on everybody’s mind, when discussing parts of the body. Traditionally, the heart was seen only as a pump that supplies oxygenated blood to the various organs of the body and assists in the delivery of nutrients to them and the removal of waste products from them. But that view of the heart changed in 1981, when the Canadian scientists Adolfo DeBold and Harold Sonnenberg showed that injected extracts from heart tissue into laboratory rats caused blood pressures to fall and extraction rates of salt to increase. The heart extract must have contained chemical messengers, in other words hormones.
But the heart, at least that of birds and mammals, consists of the two atria (the chambers of the heart that the blood enters first) and the two ventricles (the chambers that the blood flows into from the atria), which is why the question arose, where in the heart the hormones were produced. It was established that the atria were the main producers of the hormone, which turned out to be a new peptide that was given the name “atrial natriuretic peptide”, or abbreviated ANP. Suddenly it became popular to study the newly discovered heart hormones and researchers in countries as far part as Finland and Japan began to tackle questions like “Why and under what conditions would the atria of the heart produce and release the hormone?” and “How widespread in other vertebrate species was it to have a heart that also functioned as an endocrine, hormone-producing gland?”.
Apparently, ANP is released into circulation from the heart’s atria in response to an increase in blood pressure or stretch of blood vessels. If salt physiological solution is injected into a human being or an experimental animal, the result is an elevated blood concentration of ANP. The hormone then influences the kidneys to remove surplus salt and water. Inactivation of the ANP gene in mice causes hypertension. Since many species of fish (for example, eels and salmon) change from saltwater to freshwater (or vice versa) during their lives, it is obvious that in their bodies heart hormones must play particularly important roles. But the detection of the ANP molecule in the blood also helps doctors to obtain valuable information on a patient’s heart’s condition, because blood pressure, heart failure, and infarction are all associated with elevated levels of ANP.
Although the characterization of the heart as a producer of hormones occurred more than 20 years ago, the particular role of the heart as a producer of chemical messengers is still not widely known. Of course, it is far less romantic to think of the heart as an endocrine organ than as the seat of life and love. But one must not prematurely conclude that scientists, who unravel the functions of the heart, could not also be romantic. They can – as the poetry of cardiologist John Stone demonstrates!
© Dr V.B. Meyer-Rochow and http://www.bioforthebiobuff.wordpress.com, 2015.
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