PT  - JOURNAL ARTICLE
AU  - M. J. Kreek
AU  - J. Schluger
AU  - L. Borg
AU  - M. Gunduz
AU  - A. Ho
TI  - Dynorphin A<sub>1–13</sub> Causes Elevation of Serum Levels of Prolactin Through an Opioid Receptor Mechanism in Humans: Gender Differences and Implications for Modulation of Dopaminergic Tone in the Treatment of Addictions
DP  - 1999 Jan 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 260--269
VI  - 288
IP  - 1
4099  - http://jpet.aspetjournals.org/content/288/1/260.short
4100  - http://jpet.aspetjournals.org/content/288/1/260.full
SO  - J Pharmacol Exp Ther1999 Jan 01; 288
AB  - Dynorphin peptides act preferentially at κ- as well as μ- and δ-opioid receptors. This study was conducted to determine whether dynorphin peptides act to lower dopaminergic tone in the tuberoinfundibular system, resulting in elevated serum prolactin levels and, if so, whether such an effect is mediated by the opioid receptors. Dose-related increases in serum prolactin levels were observed after dynorphin A1–13 was administered i.v. in doses of 120 and 500 μg/kg to healthy human volunteers with no history of drug or alcohol abuse. Studies were then conducted to determine whether this effect is opioid receptor mediated and, if so, whether at κ- or μ types. Pretreatment with the opioid antagonist nalmefene (30 mg i.v.), which has high affinity at both μ- and κ-opioid receptors, caused a greater attenuation in dynorphin A1–13-stimulated increases in serum prolactin levels than pretreatment with similarly high doses of naloxone, an antagonist with lower affinity for both μ- and κ-opioid receptors. These results suggest dynorphin A1–13 lowers tuberoinfundibular dopaminergic tone through action at κ- and possibly μ-opioid receptors. Female subjects were significantly more responsive to the prolactin effects of dynorphin than were male subjects. Dynorphin gene expression, dynorphin peptides, and κ-opioid receptor gene expression and binding have been shown to be altered in response to cocaine administration. Also, both dynorphin peptides and synthetic κ-opioid agonists have been shown to lower dopamine levels in the nucleus accumbens and to attenuate cocaine-induced surges in dopamine levels. Thus, a dynorphin–like compound capable of reaching critical mesolimbic-mesocortical and nigrostriatal dopaminergic systems may be effective in the management of cocaine addiction. The American Society for Pharmacology and Experimental Therapeutics