Effects of estrogen and progesterone on the neurogenic inflammatory neuropeptides: implications for gender differences in migraine

DOI: https://doi.org/10.1007/s00221- 020- 05923- 7

Abstract-Summary Neurogenic inflammation including calcitonin gene-related peptide (CGRP) and substance-P (SP) release plays a pivotal role in migraine pathogenesis.

We investigated the effects of female sex hormones estrogen and progesterone on

CGRP and SP in in-vivo and ex-vivo in rats of both sexes.

For in-vivo experiments, male, female and ovariectomized rats were separated into four groups (n = 7) as control, estrogen, progesterone and estrogen + progester- one, respectively.

In in-vivo experiments, 17β-estradiol decreased CGRP levels in males and SP

levels in ovariectomized rats.

Progesterone increased both CGRP and SP levels in females. Their combination decreased both CGRP and SP levels in males, and only SP

levels in ovariectomized rats.

In ex-vivo experiments, 17β-estradiol reduced CGRP release in males and SP

release in females in trigeminal ganglia.

While progesterone increased CGRP release in trigeminal ganglia, it reduced SP

release from hemiskulls in both sexes.

Estrogen alleviates neurogenic inflammation through modulation of CGRP and

SP release.

Extended: Progesterone increased both CGRP and SP release in female rats,

whereas estrogen may have a reducing effect.

We focused on effects of estrogen and progesterone on the basal releases of CGRP and SP, instead of the stimulated-releases, using in-vivo and ex-vivo experi- mental models using rats of both sexes, mainly for the following reasons: (1) to

2.5 Hormones

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reveal, first of all, fundamental physiological mechanisms of effects of female sex hormones fluctuations on the releases of CGRP and SP in the trigeminovascular system and plasma, (2) in this way to better understand the effects of female sex hormones fluctuations in the pathophysiology underlying gender-dependent differ- ence in migraine, (3) to fill the gap in the literature on this issue.

Our findings confirm the inhibitory effects of estrogen on the CGRP and SP

release.

Introduction In accordance with this purpose, we investigated effects of estrogen and progester- one on the release of CGRP and SP biomarkers of neurogenic inflammation under- lying migraine pain in the in-vivo as well as in the isolated rat trigeminal ganglia and meningeal trigeminal nerve terminals using ex-vivo preparations in rats of both sexes.

We focused on effects of estrogen and progesterone on the basal releases of CGRP and SP, instead of the stimulated-releases, using in-vivo and ex-vivo experi- mental models using rats of both sexes, mainly for the following reasons: (1) to reveal, first of all, fundamental physiological mechanisms of effects of female sex hormones fluctuations on the releases of CGRP and SP in the trigeminovascular system and plasma, (2) in this way to better understand the effects of female sex hormones fluctuations in the pathophysiology underlying gender-dependent differ- ence in migraine, (3) to fill the gap in the literature on this issue.

Materials and Methods To ensure whether ketamine anaesthesia that was performed shortly before collec- tion of the blood samples at the end of the experiments may affect the CGRP and SP levels, we produced additional three control groups for intact male, intact female and ovariectomized female groups that were received 10% ethanol as a vehicle (n = 7 for each group).

Isolated trigeminal ganglia and hemiskull preparations from both male and female rats were randomly divided into three groups (n = 6 both trigeminal ganglia and hemiskulls for males, n = 8 both trigeminal ganglia and hemiskulls for females in each group), respectively, as follows: estrogen, progesterone, and estrogen + progesterone.

On the sixth day of the experiments, blood collection from all rats in intact

female group were carried out at proestrus phase of the estrous cycle.

Discussion In addition to CGRP, estrogen did not change basal plasma SP levels in intact male and female rats, while decreased the SP levels in ovariectomized rats.

We found that progesterone increased both plasma basal CGRP and SP levels in intact female rats, while it did not affect them in both male and ovariectomized rats. Based on the results of the in-vivo experiments, it was observed that both estro- gen and progesterone show different effects on both the plasma CGRP and SP levels in male, female and ovariectomized rats, respectively.

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2 Mechanisms

Estrogen alleviated progesterone-induced plasma CGRP levels in intact female

rats, and reduced plasma SP levels in ovariectomized rats.

Conclusion Our findings suggested that estrogen exhibited protective effects against neurogenic inflammation underlying pathophysiology of migraine through modulating CGRP and SP release in both sexes.

Progesterone demonstrated dual effects on the neurogenic inflammation by

inducing or inhibiting CGRP and SP release in females.

Limitations of the Study We chose all female rats at the same phase (proestrus) of the estrous cycle, and did not study the other phases such as estrus, metestrus and diestrus stage.

To the proestrus stage of the estrous cycle, if the other phases were also exam- ined, the impact of each phase of the estrus cycle on these neuropeptides would be investigated more comprehensively.

In the present study, we focused on predominant markers of neurogenic inflam-

mation underlying migraine such as CGRP and SP.

Acknowledgement A machine generated summary based on the work of Cetinkaya, Ayhan; Kilinc, Erkan; Camsari, Cagri; Ogun, Muhammed Nur. 2020  in Experimental Brain Research.

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