Opium, analgesic effect

P-Endorphin. A peptide corresponding to the 31 C-terminal amino acids of P-LPH was first discovered in camel pituitary tissue (10). This substance is P-endorphin, which exerts a potent analgesic effect by binding to cell surface receptors in the central nervous system. The sequence of P-endorphin is well conserved across species for the first 25 N-terminal amino acids. Opiates derived from plant sources, eg, heroin, morphine, opium, etc, exert their actions by interacting with the P-endorphin receptor. On a molar basis, this peptide has approximately five times the potency of morphine. Both P-endorphin and ACTH ate cosecreted from the pituitary gland. Whereas the physiologic importance of P-endorphin release into the systemic circulation is not certain, this molecule clearly has been shown to be an important neurotransmitter within the central nervous system. Endorphin has been invaluable as a research tool, but has not been clinically useful due to the avadabihty of plant-derived opiates. 

Opium is the dried, powdered sap of the unripe seed pod of Papaver somniferum, a poppy plant indigenous to Asia minor. Theophrastus described its medical properties in the third century BC, but the Sumerians, ca BC 4000, probably perceived its utility. Arab physicians knew of the dmg, and Arab traders carried it to the Orient where it was used as a treatment for dysentery. Paracelsus is credited with repopularizing the dmg in western Europe in the early sixteenth century by formulating opium into "laudanum", which is still in use. More than 20 different alkaloids (qv) of two different classes comprise 25% of the weight of dry opium. The benzylisoquinolines, characterized by papaverine [58-74-2] (1.0%), a smooth muscle relaxant, and noscapine [128-62-1] (6.0%), an antitussive agent, do not have any analgesic effects. The phenanthrenes, the second group, are the more common and include 10% morphine (1, = R = H), 0.5% codeine [76-57-3], C gH2 N03, (1, R = H, R = CH3), and 0.2 thebaine [115-37-7], C 2H2 N03, (2). 

The most important other opium alkaloid is codeine. In contrast to morphine, codeine has a high oral-parenteral potency ratio due to less first-pass metabolism. Codeine is considered a prodrug, since it is metabolised in vivo to the primary active compounds morphine and codeine-6-glucuronide. Approximately 10% is demethylated to morphine. The analgesic effect of codeine is due to the formation of these metabolites as codeine itself has a very low affinity for opioid receptors. The half-life of codeine in plasma is 2 hours. 

An alkaloid is a complex organic chemical substance found in plants, which characteristically combines nitrogen with other elements, has a bitter taste, and typically has some toxic, stimulant, analgesic effects. There are many different alkaloids, 30 of which are found in the opium plant. While morphine is the most important alkaloid in opium—for its natural narcotic qualities as well as providing the chemical structure for heroin—another alkaloid, codeine, is also sought after for its medicinal attributes. Other alkaloids include papaverine, narcotine, nicotine, atropine, cocaine, and mescaline. While the concentration of morphine in opium varies depending on where and how the plant is cultivated, it typically ranges from 3 percent to 20 percent. 

Morphine has a strong analgesic effect and has been used for the alleviation of postoperative and cancer pain since antiquity, but its use is now restricted because of its drug dependency. Morphine and its homologues were called opiates after opium, which was extracted from poppy seeds. This class of drugs are now termed opioids. 

Thebaine was isolated from opium in 1835 by Pelletier (439). The therapeutic applicability of thebaine was studied by Balint et al. (440). It was found to be more toxic than morphine. It is a more effective narcotic but a weaker analgesic than morphine. The analgesic effect of thebaine in doses of 0.01 g/kg is greater than that of amidopyrine this effect persists, however, only over a period of 30 min. Dihydro-thebaine is somewhat more effective but it is more toxic (441). The number and the location of the double bonds in ring D of the morphinane skeleton is of importance for the analgesic effect. Teraoko... 

Narcotine was isolated by Derosne (592) and Robiquet (593) from opium. It has a mild antitussic and a relaxant effect on smooth muscles (similar to those of papaverine). The relaxant effect is about ten times smaller than that of papaverine (594-597). LaBarre and Plisnier (598, 599) found that narcotine is a better antitussic than codeine. j8-Narcotine proved to be much more effective than a-narcotine (600) the effect of the N-oxides of the two isomers was more marked than that of the base. /3-Narcotine N-oxide was much more effective than dihydrocodeine. Those substances did not increase the analgesic effect of morphine. Contrary to codeine they did not cause obstipation (601). The therapeutic dose of the hydrochloride is 25-50 mg three times daily for adults and 25 mg three times daily per os for children. For the effect of narcotine upon the cough reflex and upon the bronchial muscle, see (602-613). 

In the 19th century the major active agent in opium, morphine, was isolated. More potent than opium, morphine was prized for its analgesic effects but also became a major addiction problem. 

THC acts at both spinal and supraspinal levels to produce analgesia. As with opioids (opium derivatives), cannabinoids inhibit GABAergic synaptic transmission, while opioids also inhibit post-synaptic neurones. In this way THC and opioids have synergistic analgesic effects. Endogenous cannabinoids (anandamide) produce analgesia, but anandamide is less potent than THC and synthetic cannabinoids (Vaughan and Christie 2002). 

Narcotics Narcotic drugs have analgesic effects and tend to depress the CNS and promote sleep. Opiate alkaloids (drugs derived from the opium plant) cue the best-known narcotics and include morphine, codeine, heroin, hydromor-phone, oxycodone, and hydrocodone. 

Enkephalins and Endorphins. Morphine (142), an alkaloid found in opium, was first isolated in the early nineteenth century and widely used in patent medicines of that eta. It is pharmacologically potent and includes analgesic and mood altering effects. Endogenous opiates, the enkephalins, endorphins, and dynotphins were identified in the mid-1970s (3,51) (see Opioids, endogenous). Enkephalins and endorphins ate Hsted in Table 9. 

The development of the first effective analgesic drug, opium, was almost certainly adventitious, and occurred in prehistoric times. The use of the dried exudate from slitting the immature capsule of the opium poppy, Papaver somniferum, as an analgesic, sedative and euphoriant, has a long folkloric history. Isolation of the principal active component morphine (1) as a pure crystalline compound represented one of the early landmarks in organic chemistry. 

Opium and its derivatives have been employed for centuries for the treatment of pain. Morphine was first synthesized in 1805 and has proven to be one of the most effective analgesic agents available [1], Morphine and its analogs are particularly useful because they diminish pain sensation while maintaining consciousness. However, opiates induce severe side-effects including respiratory depression, nausea, bradycardia and constipation and long-term use of opiates can cause addiction [2]. 

During the nineteenth century, chemists had a good deal of success in isolating and purifying natural products from plant sources. Morphine was isolated as a pure compound from crude opium in 1804. Quinine was isolated from the bark of the cinchona tree in 1820 and was initially employed as a fever reducer. However, its effectiveness against malaria was soon discovered and it found an alternative highly important medical use. Sodium salicylate was isolated from the bark of the willow tree in 1821 and was also shown to have analgesic, antipyretic, and antiinflammatory properties. It took an additional 76 years, until 1897, to synthesize the acetyl derivative, acetylsalicyclic acid, commonly known as aspirin. 

Noscapine is a naturally occurring product of the opium poppy. It is a benzylisoquinoline with no analgesic or other CNS effects. Its antitussive effects are weak, but it is used in combination with other agents in mixtures for cough relief. 

Diphenoxylate (marketed in combination with atropine as Lomotil in the United States) is chemically related to both analgesic and anticholinergic compounds. It is as effective in the treatment of diarrhea as the opium derivatives, and at the doses usually employed, it has a low incidence of central opioid actions. Diphenoxylate is rapidly metabolized by ester hydrolysis to the biologically active metabolite difenoxylic acid. Lomotil is recommended as adjunctive therapy in the management of diarrhea. It is contraindicated in children under 2 years old and in patients with obstructive jaundice. Adverse reactions often caused by the atropine in the preparation include anorexia, nausea, pruritus, dizziness, and numbness of the extremities. 

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