Kappa Receptor Effects — FRCA Primary MCQ

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ModeratePharmacology - AnalgesicsKappa Receptor EffectsFRCA Primary

Which combination of effects is most characteristic of activation of the kappa opioid receptor?

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Correct answer: E — Analgesia, sedation and dysphoria

Explanation lettering: B = shown as A · D = shown as B · E = shown as D · A = shown as E

Kappa (KOP) receptors are Gi/Go-coupled; agonism closes N-type calcium channels and opens potassium channels, producing antinociception (predominantly spinal) accompanied by sedation, dysphoria and psychotomimesis, plus water diuresis through inhibition of antidiuretic hormone release — hence A. D describes the classic mu (MOP) profile: euphoria, reward, physical dependence and clinically important respiratory depression; kappa agonism causes little respiratory depression and is aversive rather than rewarding, which is why it is not abused. B is wrong because no opioid receptor causes respiratory stimulation or alertness. C fails because opioids cause miosis, not mydriasis, and kappa agonism produces diuresis rather than antidiuresis. E is reversed: opioid agonism reduces propulsive gut motility, causing constipation.

Reference: Zhou/Ko et al. The role of kappa-opioid receptor activation in mediating antinociception and addiction. Acta Pharmacologica Sinica, 2010 (review; adverse effects section). https://pubmed.ncbi.nlm.nih.gov/20729876/