MORPHINE - NEW ASPECTS IN THE STUDY OF AN ANCIENT COMPOUND

Morphine is the most widely used compound among narcotic analgesics an d remains the gold standard when the effects of other analgetic drugs are compared. Apart from its presence in the poppy plant Papaver somni ferum, morphine has been shown to be present in milk, cerebrospinal fl uid and also in nervous tissue extracts. Recent evidence suggests that biosynthetic pathways for morphine exist in animal and even human tis sues such as liver, blood and brain. The most characteristic effect of morphine is the modulation of pain perception resulting in an increas e in the threshold of noxious stimuli. Antinociception induced by morp hine is mediated via opioid receptors and therefore can be inhibited b y opioid antagonists, e.g., naloxone. Nevertheless, consideration of m orphine as endogenous ligand for opioid receptors seems to be speculat ive. Recently, the primary receptor for morphine-type drugs called the CI-opioid receptor has been cloned from rat brain. There is accumulat ing evidence that morphine actions are, at least partly, due to one of its major metabolite morphine-6-glucuronide in man. It is concluded t hat further investigations are necessary to elucidate the mechanisms, whereby multiple actions of morphine are expressed in the nervous syst em.