RT Journal Article
SR Electronic
T1 Sex-/Ovarian Steroid-Dependent Release of Endomorphin 2 from Spinal Cord
JF Journal of Pharmacology and Experimental Therapeutics
JO J Pharmacol Exp Ther
FD American Society for Pharmacology and Experimental Therapeutics
SP 635
OP 641
DO 10.1124/jpet.106.118505
VO 321
IS 2
A1 Daya S. Gupta
A1 Hans von Gizycki
A1 Alan R. Gintzler
YR 2007
UL http://jpet.aspetjournals.org/content/321/2/635.abstract
AB μ-Opioid receptor (MOR) agonists have been shown to be more potent analgesics in male than female rodents. Regulation of spinal MOR-coupled antinociception by 17β-estradiol (estrogen, E2) and progesterone (P) is also sexually dimorphic; pregnancy levels of E2/P activate MOR-coupled analgesic pathways in male but not female rats. We hypothesized that the sexual dimorphic characteristics of MOR-coupled antinociception reflects sexual dimorphism in the regulation of the release from spinal cord of the endogenous MOR agonist, endomorphin 2 (EM2). Parameters of spinal EM2 release manifesting sexual dimorphism include its 1) magnitude: in vitro basal and K+-evoked release of EM2 from spinal tissue of male rats is approximately 50% greater than that observed from spinal cord of females; 2) modulation by ovarian sex steroids: E2/P treatment significantly enhanced K+-evoked EM2 release from spinal tissue of males, but not females; and 3) enhancement by opioid receptor blockade: naloxone enhanced stimulated EM2 release from spinal tissue of both males and females, but it augmented basal release from spinal tissue of only males. Enhancement of EM2 release by naloxone reflects negative coupling of MOR to EM2 release and hence its modulation by negative feedback since only activation of MOR, not κ-or δ-opioid receptors, was able to inhibit evoked EM2 release. These data reveal that the EM2-MOR spinal analgesic system is more robust and “higher gain” in male versus female rodents. These findings could provide a mechanistic rubric for understanding the male female dichotomy in prevalence and intensity of chronic pain syndromes. The American Society for Pharmacology and Experimental Therapeutics