Estrogen reduces efficacy of mu- but Not kappa-opioid agonist inhibition in response to uterine cervical distension.
Sandner-Kiesling A, Eisenach JC. Estrogen reduces efficacy of mu- but Not kappa-opioid agonist inhibition in response to uterine cervical distension. Anesthesiology. 2002 Feb; 96(2):375-9.