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We investigated the mechanism for the augmentation of the calcitonin gene-related peptide (CGRP)-induced elevation of skin temperature in ovariectomized (OVX) rats. I.v. injection of alphaCGRP (10 micro g/kg) elevated skin temperature of the hind paws. The elevation was significantly greater in OVX rats than in sham-operated rats and was inhibited by pretreatment with human CGRP(8-37) (100-1000 micro g/kg i.v.), a CGRP receptor antagonist, in a dose-dependent manner. In addition, ovariectomy not only potentiated vasorelaxation due to alphaCGRP but increased the number of CGRP receptors in mesenteric arteries. Further, the plasma concentration of endogenous CGRP was significantly lower in OVX rats. These results suggest that the low concentration of plasma CGRP due to ovarian hormone deficiency may induce the increase in the number of CGRP receptors due to up-regulation. Therefore, the increased number of CGRP receptors may be responsible for potentiation of exogenous alphaCGRP-induced elevation of skin temperature in OVX rats. The mechanism underlying the hot flashes observed in menopausal women may also involve, in part, the up-regulation of CGRP receptors following ovarian hormone deficiency.

The effects of a Japanese herbal medicine, Keishi-bukuryo-gan, and 17beta-estradiol on calcitonin gene-related peptide (CGRP)-induced elevation of skin temperature were investigated in ovariectomized (OVX) rats. Ovariectomy not only potentiated CGRP-induced elevation of skin temperature and arterial vasorelaxation but also induced a lower concentration of endogenous CGRP in plasma and up-regulation of arterial CGRP receptors, suggesting that lowered CGRP in plasma due to ovarian hormone deficiency increases the number of CGRP receptors and consequently amplifies the stimulatory effects of CGRP to elevate skin temperature. Oral Keishi-bukuryo-gan (100-1000 mg/kg, once a day for 7 days) restored a series of CGRP-related responses observed in OVX rats by normalizing plasma CGRP levels in a dose-dependent manner as effectively as s.c. injection. 17Beta-estradiol (0.010 mg/kg, once a day for 7 days). However, Keishi-bukuryo-gan did not affect the lower concentration of plasma estradiol and the decreased uterine weight due to ovariectomy, although the hormone replacement of 17beta-estradiol restored them. These results suggest that Keishi-bukuryo-gan, which does not confer estrogen activity on plasma, may be useful for the treatment of hot flashes in patients for whom estrogen replacement therapy is contraindicated, as well as menopausal women.