Deficiency of female sex hormones augments PGE2 and CGRP levels within midbrain periaqueductal gray

The midbrain periaqueductal gray (PAG) is a substantial component of the descending modulatory network to control on nociceptive transmission and autonomic functions. Also, accumulated evidence has suggested that the PAG plays a crucial role in regulating migraine headache, a neurovascular disorder. The purpose of this study was to employ ELISA methods to examine the levels of prostaglandin E2 (PGE2) and calcitonin-gene related peptide (CGRP) in the PAG of rats who received ovariectomy and subsequent hormone replacement with 17β-estradiol, progesterone, or the combination of 17β-estradiol and progesterone. In addition, using Western blot analysis we examined expression of subtypes of PGE2 receptor in the PAG of rats with different conditions of female sex hormones. Results of our study demonstrated that lack of female sex hormones significantly increased the levels of PGE2 and CGRP in the dorsolateral PAG (P < 0.05) as well as expression of PGE2 EP3 receptors (P < 0.05). Furthermore, a liner relationship was observed between PGE2 and CGRP in the PAG (r = 092, P < 0.01). Also, inhibiting EP3 receptors by chronic administration of L-798106 (EP3 antagonist) into the lateral ventricles significantly attenuated expression of CGRP in the PAG of ovariectomized animals (P < 0.05 vs. vehicle control). Overall, our findings for the first time show that (1) circulating 17β-estradiol and/or progesterone influences the levels of PGE2 and CGRP in the PAG; (2) a lower level of 17β-estradiol and/or progesterone augments PGE2 and its EP3 receptor; and (3) PGE2 plays a role in regulating expression of CGRP in the PAG.