If you have ever been to the ER, chances are you have been administered morphine to reduce pain. Have you ever wondered what morphine is and why it mitigates pain?
Morphine is the main alkaloid of opium, obtained from the milky fluids of the poppy plant (papaver somniferum). Like many useful chemicals found in plants, the morphine molecule is thought to have evolved as a natural insecticide. Although opium has been used medicinally since ancient times, the first person to isolate morphine was Friedrich Senturner in 1804. Morphine was first sold commercially in 1827. The name morphine comes from Morpheus, the Greek god of sleep, due to its powerful anesthetic and analgesic applications. It is important to note that morphine has the potential to produce addiction, either in its pure form or mixed with other chemicals in the form of opium. Ironically, at one point in history morphine was marketed as a cure to opium addiction.
Morphine binds to mu opioid receptors in nerve cells mimicking enkephalins, the body’s natural pain killing molecules. When activated, mu opioid receptors block the release of pain neurotransmitters and raise the threshold over which pain can be felt. Mu opioid receptors are found primarily in the brain, but are also present in the spinal cord and digestive tract. Thus, patients administered morphine also exhibit severe constipation, which can become very painful and mitigate the pain reducing properties of morphine. Other side effects include dizziness, drowsiness, headache, lightheadedness, nausea, restless mood, sweating, and vomiting.
Morphine and its receptors illustrate the form-function paradigm, seeing how the shape of the morphine molecule allows it to bind to the ligand site of mu opioid receptor. In fact, morphine is chemically similar to endorphin neurotransmitters, which are responsible for the feelings of pleasure and reward in the brain. Heroin (diacetylmorphine) is also chemically similar to morphine, as it is derived from morphine by substituting the alcohol groups (OH) with acetyl groups (COCH3). A “small” change in chemistry leads to increased solubility across the blood-brain barrier, creating substantial differences in the addictive properties and euphoric effects of heroin and morphine. Considering the damaging effects of addiction, morphine and its derivatives remain important in the modern world.