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J Pharmacol Exp Ther. 2008 Oct;327(1):154-60. doi: 10.1124/jpet.108.140079. Epub 2008 Jul 1.

The effects of herkinorin, the first mu-selective ligand from a salvinorin A-derived scaffold, in a neuroendocrine biomarker assay in nonhuman primates.

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  • 1The Rockefeller University, Box 171, 1230 York Ave., New York, NY 10065, USA.


Herkinorin is the first mu-opioid receptor-selective ligand from the salvinorin A diterpenoid scaffold. Herkinorin has relative mu > kappa > delta binding selectivity, and it can act as an agonist at both mu- and kappa-receptors, in vitro. These studies were the first in vivo evaluation of the effects of herkinorin in nonhuman primates, using prolactin release, a neuroendocrine biomarker assay that is responsive to both mu- and kappa-agonists, as well as to compounds with limited ability to cross the blood-brain barrier. In cumulative dosing studies (0.01-0.32 mg/kg i.v.), herkinorin produced only small effects in gonadally intact males (n = 4), but a more robust effect in females (n = 4). Time course studies with herkinorin (0.32 mg/kg) confirmed this greater effectiveness in females and revealed a fast onset after i.v. administration (e.g., by 5-15 min). Antagonism experiments with different doses of nalmefene (0.01 and 0.1 mg/kg) caused dose-dependent and complete prevention of the effect of herkinorin in females. This is consistent with a principal mu-agonist effect of herkinorin, with likely partial contribution by kappa-agonist effects. The peripherally selective antagonist quaternary naltrexone (1 mg/kg s.c.) caused approximately 70% reduction in the peak effect of herkinorin (0.32 mg/kg) in females, indicating that this effect of herkinorin is prominently mediated outside the blood-brain barrier.

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