Pharmacological Studies on 7-Hydroxymitragynine, Isolated from the Thai Herbal

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    The research data: http://mitizane.ll.chiba-u.jp/metadb/up/assist1/Y2006-17.pdf

    the tl;dr:

    “Competition binding assays revealed that 7-hydroxymitragynine bound to opioid receptors in homogenates of guinea-pig brain membrane. Its affinities for three opioid receptor types were determined by evaluating the inhibition of binding of ligands to µ-, δ- and κ-opioid receptors. As a result, 7-hydroxymitragynine interacted with all three opioid sites, but bound preferentially to µ-opioid receptors”*
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    “We studied the opioid agonistic effects of the constituents of Mitragyna speciosa using in vitro assays. Among them, 7-hydroxymitragynine showed most potent opioid effect which was 17 fold more potent than that of morphine. …. 9-hydroxycorynantheidine showed partial agonistic effect on opioid receptors.”
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    Interestingly, [ 7-hydroxymitragynine] is very effective when administered orally. *The effect was 14–22 fold more potent than that of morphine when orally administered, and had a favorable bioavailability (oral/subcutaneous dose ratio). In addition, it induced a more rapid effect than morphine.

    “In general, *partial agonists have not only agonistic but also antagonistic effects.** To determine the µ-opioid partial agonistic properties of 9-hydroxycorynantheidine, we investigated the agonistic and antagonistic effect of 9-hydroxycorynantheidine in guinea-pig ileum. 9-Hydroxycorynantheidine shifted the concentration-response curves for µ-selective agonist DAMGO slightly to the right. Logically, a partial agonist antagonizes the pharmacological effect of a full agonist, which acts on the same receptor, at the concentration that shows maximal response… *
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    “It is widely accepted that a full maximum response was elicited by a full agonist at very low concentrations, which can only occupy certain fractions among in all specific receptors present. Those receptors that are unoccupied when a full maximum response is already elicited by an agonist are termed “spare receptors”. Drugs with high intrinsic activity require fewer drug–receptor interactions than drugs with low intrinsic activity to produce a maximal effect leading to the concept of spare receptors…
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    “In general, full agonists do not need to bind spare receptors for their maximum effect, and thus full agonists can induce the maximum effect in the presence of some concentration of an irreversible antagonist, but partial agonist needs to bind all specific receptors inducing spare receptors to elicit maximum response, and the maximum response is reduced by the irreversible antagonist.”*

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