A neuropeptide
β-endorphin (1-26) is a neuropeptide found in rat hippocampus, brain stem, and pituitary. It is also present in the human hypothalamus, where it comprises approximately 13.1% of total β-endorphin. β-endorphin (1-26) is an opioid receptor agonist that inhibits potassium-induced norepinephrine (NE) release in rat cortical slices (IC50 = 2.5 nM). It reverses inhibition of potassium-induced NE release from rat cortical slices induced by the opioid antagonists naloxone , CTOP, norbinaltorphimine (nor-BNI), and naltrindole . In vivo, β-endorphin (1-26) (10 μg, i.c.v.) induces transient bradycardia in anesthetized rats. Intracerebroventricular administration of β-endorphin (1-26) increases the latency to tail withdrawal in response to thermal stimulation in mice with a median antinociceptive dose (AD50) of 1.57 μg per animal.
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