ArticleSex steroid hormones exert biphasic effects on cytosolic magnesium ions in cerebral vascular smooth muscle cells: possible relationships to migraine frequency in premenstrual syndromes and stroke incidence
Introduction
It has been established that changes in the serum and blood cell concentration of magnesium are probably related to the stages of the menstrual cycle in normal women. It was reported, as early as 1970, that a decrease of serum total magnesium is seen in the ovulatory phase 17, 25. Further studies showed that total serum Mg concentrations were higher during menses, were lower during the ovulatory phase in plasma, and exhibited an increase during the luteal phase in plasma [18], polymorphonuclear neutrophils and lymphocytes [21]. Recently, serum Mg2+ and Ca2+ concentrations in healthy women of reproductive age in conjunction with their hormone profiles have been examined [39]. The latter investigators found that these women showed recurring changes in serum levels of Mg2+ and total Mg, and alterations in the ratio of Ca2+ to Mg2+ as serum levels of estrogen, testosterone, and progesterone rose and fell. Both total Mg and Mg2+ were comparatively elevated following low serum levels of estrogen and testosterone; high, physiologic levels of estrogen in the menstrual cycle were associated with reduced serum levels of Mg2+ and total Mg. When the progesterone level peaked, the Ca2+/Mg2+ ratio was significantly increased [39]. Studies with menopausal women demonstrated that the serum levels of Mg2+ and total Mg varied inversely with the estrogen concentration [40], while studies with men demonstrated that the ion levels appeared to be under the control of progesterone [41].
Considering the modulation by Mg2+ of neural excitability, plasma membrane stability and vascular contraction 5, 9, 10, 32, Abraham hypothesized that Mg2+ deficiency might account for many of the cyclical symptoms of premenstrual syndromes [1]. Altura proposed in 1985 that changes in brain Mg2+ might be important in etiology and amelioration of migraine headache [4]. Jain et al. [27] found decreased total Mg levels in cerebrospinal fluid of migraine patients in comparison to asymptomatic controls. By using 31P-nuclear magnetic resonance (NMR) spectroscopy, reduction of intracellular Mg2+ content was revealed in the brain cortex of migraine patients during an attack [48]. Facchinetti et al. reported that total intracellular Mg levels of lymphocytes and polymorphonucleated cells, in patients with menstrual migraine, were reduced compared to controls [22]. Oral Mg treatment of these patients resulted in significant increases of total Mg in lymphocytes and polymorphonucleated cells [22]. Recently, it has been demonstrated that a deficiency in serum ionized Mg2+ levels and an elevated serum Ca2+/Mg2+ ratio are associated with the onset of migraine, cluster and tension headaches in female subjects 34, 35. Clinical trials indicate that these headaches are relieved in most women after i.v. administration of Mg2+ 34, 35. These studies support the hypothesis that a lower migraine threshold could be related to Mg2+ deficiency. In addition, migraine has been found to occur far more frequently in women who have had preeclampsia than in those who have not before the 34th week of pregnancy [38]. The higher incidence of migraine among those women prone to hypomagnesemia 9, 34, 35, and the influence of low extracellular magnesium ions ([Mg2+]o) on vascular tone, prostanoids and thrombogenesis, support the premise that Mg2+ deficiency is involved in the pathogenesis of migraine and eclampsia 4, 5, 11.
It has been reported that Mg2+ and sex hormones exert important effects on cerebral vascular smooth muscle. For example, low [Mg2+]o levels result in constriction and spasm of intact and isolated cerebral vessels, reduced cerebral cortical blood flow 6, 8 and concomitant Mg2+ depletion of cerebral vascular smooth muscle cells 33, 58. Female sex hormones have been shown to alter blood flow and vascular smooth muscle reactivity by different mechanisms 2, 3, 12, 16, 19, 24, 31. The interrelationships between Mg2+ and sex hormones may be the underlying basis or trigger for modulating changes in cerebral vascular wall tone and reactivity, which are associated with the premenstrual syndrome, including that found in migraine and eclampsia. However, whether sex steroid hormones can directly modulate levels of intracellular free magnesium ions ([Mg2+]i) is not known. This may be quite important in view of a very recent ongoing NIH clinical trial in which administration of estrogenic hormones appears to increase the risk of the women under study for stroke [42]. This becomes quite important in light of recent findings on stroke patients in whom serum levels of Mg2+, but not total Mg, were found to be reduced early after both ischemic and hemorrhagic stroke [14]. The present study was designed to determine whether sex steroid hormones can alter, directly, [Mg2+]i levels of cerebral vascular smooth muscle cells.
Section snippets
General procedures
Experiments were carried out on single cultured smooth muscle cells of canine cerebral basilar arteries obtained from pentobarbital sodium-anesthetized (40 mg/Kg, i.v.) male mongrel dogs (25–36 kg). Male animals were used to avoid any additional influence of female sex/gonadotrophin hormones. The procedure employed to isolate arterial smooth muscle cells and the use of digital imaging microscopy with the fluorescent indicator, mag-fura-2, is similar to that reported 13, 56, 57. Briefly,
Results
The range of [Mg2+]i concentrations for resting, basal levels in cultured canine single cerebral smooth muscle cells, measured by use of the fluorescent indicator mag-fura-2/AM and digital imaging microscopy, was from 579 to 796 μM. Exposure of these cultured cells to 10 pg/ml estrogen for 10 min failed to interfere with levels of [Mg2+]i, although the concentrations of [Mg2+]i are cyclical during the period of measurement (Table 1, Fig. 1). When the concentration of estrogen in the medium
Discussion
The present study demonstrates three new findings. First, estrogen directly affects the resting [Mg2+]i levels of single primary cultured cerebral vascular smooth muscle cells, as exemplified by a concentration-dependent reduction of [Mg2+]i levels. Second, progesterone exerts biphasic effects on [Mg2+]i levels of the cultured cells, depending upon the concentration used in the study. Treatment of the vascular smooth muscle cells with low doses of progesterone resulted in an elevation in [Mg2+]i
Acknowledgements
We are grateful to Drs. O. Muneyyirci-Delale and V.L. Nacharaju for helpful discussions and the gifts of pure estrogen, progesterone and testosterone employed in our studies. This work was supported in part by NIH Grant AA-08674.
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