Opiates neurotransmitters interacting with

P-Endorphin. A peptide corresponding to the 31 C-terminal amino acids of P-LPH was first discovered in camel pituitary tissue (10). This substance is P-endorphin, which exerts a potent analgesic effect by binding to cell surface receptors in the central nervous system. The sequence of P-endorphin is well conserved across species for the first 25 N-terminal amino acids. Opiates derived from plant sources, eg, heroin, morphine, opium, etc, exert their actions by interacting with the P-endorphin receptor. On a molar basis, this peptide has approximately five times the potency of morphine. Both P-endorphin and ACTH ate cosecreted from the pituitary gland. Whereas the physiologic importance of P-endorphin release into the systemic circulation is not certain, this molecule clearly has been shown to be an important neurotransmitter within the central nervous system. Endorphin has been invaluable as a research tool, but has not been clinically useful due to the avadabihty of plant-derived opiates. 

Morphine is the prototype for the class of natural and synthetic opioid analgesics and its toxicity stems mainly from its extensive effect on the central nervous system (CNS), principally that of a descending depression. Opioids interact with stereospecific and saturable binding sites mostly located in the CNS. Interaction with the opioid receptors mimics the actions of endogenous enkephalins and endorphins. Morphine is a pure opiate agonist and exerts its activity primarily on the mu receptor. Activity also appears to involve an alteration in the release of neurotransmitters, such as the inhibition of acetylcholine, norepinepherine, and dopamine. These actions result in the therapeutic effects of analgesia, sedation, euphoria, and decreased gastrointestinal motility however, in toxic amounts they can lead to... 

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