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Abstract
Hot flashes are among the most common complaints of perimenopausal women. Despite the high prevalence of the phenomenon ,the background to the development of hot flashes is still not completely understood, through a hypothesized central mechanism ,involving norepinephrine and luteinizing hormone-releasing hormone (LH-RH) secretion is widely accepted. We studied the influence of sex steroid deficiency and hormone replacement therapy on the biomechanical properties of musculocutaneous arterioles ,to see whether a peripheral mechanism also exists in the development of hot flashes. Fifty adult ,nulliparous, non-pregnant female Sprague-Dawley rats received pharmacological ovariectomy ,and estradiol ,medroxyprogesterone ,or both hormones. After 12 weeks the saphenous artery was isolated by microdissection. Norepinephrine-induced tone (active tangential strain) was measured as a function of intraluminal pressure in an organ bath. The norepinephrine-induced arterial tone was significantly different between the control group and the ovariectomized animals in the range of 80-150 mmHg intraluminal pressure (p < 0.05). Also ,significant differences were found between the ovariectomized group and the animals receiving estradiol monotherapy (p < 0.01 between 80 and 170 mmHg ,and p < 0.05 between 180 and 200 mmHg intraluminal pressure). Neither medroxyprogesterone monotherapy nor combined hormone replacement therapy induced significant changes in the norepinephrine-induced vascular tone. The absence of sex steroids leads to decreased reactivity to norepinephrine in small musculocutaneous arteries ,while chronic estradiol replacement therapy restores the impaired responsiveness of the vessels. Our data raise the possibility that in addition to the central mechanism ,a previously unknown peripheral background mechanism for perimenopausal hot flashes may exist.