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Receptors for Neuropeptides: Ligand Binding Studies
Published in Edwin E. Daniel, Neuropeptide Function in the Gastrointestinal Tract, 2019
Sultan Ahmad, Hans-Dieter Allescher, Chiu-Yin Kwan
The presence of opioid receptors in the gastrointestinal tract using the ligand binding approach was first suggested by Terenius,38 who reported the “specific uptake” of 3 H-labeled dihydromorphine by a crude membrane fraction from the guinea pig ileum longitudinal muscle (perhaps containing myenteric plexus) preparation. With a refinement of binding techniques, better characterization followed. Pert and Snyder,39 using a crude membrane preparation, reported the presence of opioid receptors in guinea pig ileum myenteric plexus, no binding to the longitudinal muscle could be observed. In 1975, Terenius40 and Creese and Snyder41 separately reported the detailed characterization of opioid receptors in guinea pig ileum longitudinal muscle/myenteric plexus. Good correlation was found between receptor binding and pharmacological potency of both agonists and antagonists.41 Since then, specific opioid binding has been reported in several GI systems, including parietal cells from guinea pig ileum42 and rat small intestine.43 No binding, however, was found on rat intestinal epithelial cells.44 Opioid receptors have even been demonstrated in the midgut of the insect Leucophaea madierae.45
Disposition and Metabolism of Drugs of Dependence
Published in S.J. Mulé, Henry Brill, Chemical and Biological Aspects of Drug Dependence, 2019
Dihydromorphine is prepared by the catalytic hydrogenation of morphine. The monohydrate colorless, crystalline base and the water-soluble hydrochloride (pKa 8.55) melt at 157°C (decomp.) and 280 C, respectively. It is considered equipotent to morphine in analgesic activity.142
Information on level of drugs into breastmilk
Published in Wendy Jones, Breastfeeding and Medication, 2018
Dihydrocodeine is the preferred opiate analgesic due to a cleaner metabolism than other opiates. It has a slightly weaker action but retains effective analgesic activity along with paracetamol and/or a non steroidal. As with all opiates it should be taken at the lowest possible dose for the shortest possible time. Dihydrocodeine is metabolised via CYP2D6 to the active metabolite dihydromorphine, which has a potency similar to morphine (Kirkwood 1997). The oral bio-availability of dihydrocodeine is only about 20% and it is subject to extensive first-pass metabolism limiting the amount in breastmilk.
Substance use disorders: diagnosis and management for hospitalists
Published in Journal of Community Hospital Internal Medicine Perspectives, 2020
Ahmed K. Pasha, Arnab Chowdhury, Sanah Sadiq, Jeremiah Fairbanks, Shirshendu Sinha
The most commonly used opioids, which vary in potency, include heroin, morphine, codeine, hydrocodone, oxycodone, methadone, tramadol, fentanyl, buprenorphine. Morphine and heroin are equivalent in terms of potency as heroin is converted to morphine and monoacetylmorphine during metabolization. Codeine, hydrocodone and tramadol are considered the ‘weak’ opioids among the above. These differ from ‘strong’ opioids by a dose limit which results from the accumulation of side effects [26]. Codeine is a prodrug that is converted to morphine. Hydrocodone is a prodrug that is converted to dihydromorphine. Oxycodone has active metabolites which contributes to its euphoria thereby increasing its abuse potential. Methadone is a long-acting opioid. Tramadol is an opioid agonist that affects 5HT receptors in addition to opioid receptors. Buprenorphine is a partial opioid receptor agonist (activates receptors at a lower level) and is sometimes formulated with naloxone (a pure opioid antagonist) to decrease its abuse risk [26,27] Heroin, methadone, and oxycodone are highly reinforcing and the most abused opioid types.