Opioids Flashcards
what are the therapeutic uses of opioids in animals?
analgesia
sedation
calming and euphoria
immobilization and chemical restraint
diarrhea, inhibition of gastrointestinal motility
antitussive (decrease cough)
adjunctive use for general anesthesia
increased locomotor activity
what is opium composed of?
many alkaloids
morphine
codeine
papaverine
thebaine
what are endogenous opioids?
naturally occurring opioid peptides that interact with opioid receptors
what are the endogenous opioids?
Leu-enkephalin
Met-enkephalin
dynorphin A
beta-Endorphin
what are the opioid receptors?
Mu: Mu1 and Mu2
Delta: delta 1 and delta 2
Kappa: K1, K2, K3
what are the receptor actions of the delta opioid receptor?
analgesia (spinal and supraspinal)
increase appetite
immunomodulation
what are the receptor actions of the kappa opioid receptor?
analgesia
decrease gastrointestinal motility and secretions
increase appetite
sedation
diuresis
miosis/mydriasis
nausea/vomiting or antiemetic
what is an agonist in opioids?
a chemical that binds to the receptor and activates it
what is a mixed agonist/antagonist in opioids?
depends on the conditions: can be either agonist or antagonist
what is an antagonist in opioids?
binds to the receptor to block or dampen a biological response
what are some opioid agonists?
morphine
codeine
etorphine
methadone
what are some opioid mixed agonists/antagonists?
buprenorphine
butorphanol
what are some opioid antagonists?
naloxone
naltrexone
where do opioid agonists have effects?
CNS and peripheral
what are the CNS effects of morphine (and most opioid agonists)?
analgesia
sedation/excitation
respiratory suppression
cough suppression
nausea/vomiting
convulsions
thermoregulatory changes
how do opioids exert their primary analgesic effects?
bind to spinal and supraspinal receptors
what is the mechanism for spinal analgesia with opioids?
binds to G protein coupled receptor in the dorsal horn of the spinal cord
inhibits adenylyl cyclase
activates receptor linked potassium channels: hyperpolarizes neuron
inhibits voltage gated calcium channels: decreases excitatory neurotransmitter release
antagonizes substance P
what opioid receptors are in the dorsal horn and dorsal root ganglion?
presynaptic mu, delta, and kappa in dorsal horn
postsynaptic mu in dorsal root ganglion
how does supraspinal opioid analgesia work?
opioid receptors in periaqueductal grey region activate to inhibit GABA interneurons
inhibition activates enkephalin-releasing neurons in medullary pain inhibitory pathways that inhibit dorsal horn nociceptors through release of serotonin
other brain regions have activated opioid receptors, which decrease level of pain perception (decrease anxiety and increase well-being)
what fibers are impacted by systemic opioid administration?
pain transmission neurons, primarily C fibers: dull aching pain
A delta fibers are minimally affected
what fibers do epidural opioids impact?
both C and A delta fibers
what species experience excitement with opioids?
horses
pigs
cats
what species experience sedation with opioids?
human
primates
dogs
what mediates respiratory depression with opioids?
mu receptor
dose dependent