Basal tail skin temperature elevation and augmented response to calcitonin gene-related peptide in ovariectomized rats

Menopause review: Emerging treatments for menopausal symptoms

Vasomotor symptoms (VMS) affect 2 out of 3 women during menopause and are highly disruptive and intolerable. They exert a negative impact on a woman's physical and mental well-being and are considered a high clinical priority requiring effective treatment. Although hormone therapy remains the gold-standard treatment for hot flushes, it is associated with several side effects and contraindications. Furthermore, alternative treatments for VMS are currently less efficacious and have limited availability; therefore, a new medication to treat VMS would benefit millions of women worldwide. Neurokinin 3 receptor (NK3R) antagonists have recently been developed as novel therapeutic agents for the amelioration of VMS through their action on NK3 receptors within the hypothalamus and consequent regulation of the thermoregulatory centre. So far, three NK3R antagonists have been studied in menopausal women, which have demonstrated significant reductions in VMS frequency and severity and have shown their ability to transform patients' quality of life.

Long-term oral administration of a novel estrogen receptor beta agonist enhances memory and alleviates drug-induced vasodilation in young ovariectomized mice

Development of estrogen therapies targeting the β (ERβ) but not α (ERα) estrogen receptor is critically needed for the treatment of negative menopausal symptoms, as ERα activation increases health risks like cancer. Here, we determined the effects of long-term oral treatment with EGX358, a novel highly selective ERβ agonist, on memory, vasodilation, and affect in young ovariectomized mice. Mice were orally gavaged daily for 9 weeks with vehicle, 17β-estradiol (E₂), the ERβ agonist diarylpropionitrile (DPN), or EGX358 at doses that enhance memory when delivered acutely. Tail skin temperature was recorded as a proxy for vasodilation following injection of vehicle or senktide, a tachykinin receptor 3 agonist used to model hot flashes. Anxiety-like behavior was assessed in the open field (OF) and elevated plus maze (EPM), and depression-like behavior was measured in the tail suspension (TST) and forced swim tests (FST). Finally, memory was assessed in object recognition (OR) and object placement (OP) tasks. E₂, DPN, and EGX358 reduced senktide-mediated increases in tail skin temperature compared to vehicle. All three treatments also enhanced memory in the OR and OP tasks, whereas vehicle did not. Although E₂ increased time spent in the center of the OF, no other treatment effects were observed in the OF, EPM, TST, or FST. These data suggest that long-term ERβ activation can reduce hot flash-like symptoms and enhance spatial and object recognition memories in ovariectomized mice. Thus, the highly selective ERβ agonist EGX358 may be a promising avenue for reducing menopause-related hot flashes and memory dysfunction.

The neuroendocrinology of the preoptic area in menopause: Symptoms and therapeutic strategies

The preoptic area of the hypothalamus is the central hub of thermoregulation in mammals, coordinating autonomic heat-effector pathways in response to sensory information from the ambient and internal environment. This aims to maintain temperature homeostasis at a predetermined thermoregulatory set-point. However, hormonal and neuronal changes during the menopause, including estrogen deficiency, disrupt these normal thermoregulatory responses. This results in abnormal activation of heat dissipation effectors, manifesting clinically as hot flush symptoms. Neurokinin B (NKB) signaling via the neurokinin-3 receptor (NK3R) within the preoptic area is thought to play an important role in the pathophysiology of hot flushes. Therefore attenuation of the NKB/NK3R signaling pathway has garnered much interest as a novel therapeutic target for the amelioration of menopausal hot flushes. Recent clinical trials have demonstrated that NK3R antagonists can produce rapid and sustained improvements in hot flush frequency, severity, and quality of life, without the need for estrogen exposure. Therefore NK3R antagonists are fast emerging as a safe and efficacious alternative to hormone replacement therapy, the current gold standard of treatment.

Is calcitonin gene-related peptide a modulator of menopausal vasomotor symptoms?

PURPOSE

Calcitonin gene-related peptide (CGRP) is a neuropeptide widely distributed in the central and peripheral nervous systems, which is known as a potent vasodilator. Postmenopausal women who experience hot flushes have high levels of plasma CGRP, suggesting its involvement in menopausal vasomotor symptoms.

METHODS

In this review, we describe the biochemical aspects of CGRP and its effects associated with deficiencies of sexual hormones on skin temperature, vasodilatation, and sweating as well as the possible peripheral and central mechanisms involved in these events.

RESULTS

Several studies have shown that the effects of CGRP on increasing skin temperature and inducing vasodilatation are potentiated by a deficiency of sex hormones, a common condition of postmenopausal women. Additionally, the medial preoptic area of the hypothalamus, involved in thermoregulation, contains over 25-fold more CGRP-immunoreactive cells in female rodents compared with male rodents, reinforcing the role of female sex hormones on the action of CGRP. Some studies suggest that ovarian hormone deficiency decreases circulating endogenous CGRP, inducing an upregulation of CGRP receptors. Consequently, the high CGRP receptor density, especially in blood vessels, amplifies the stimulatory effects of this neuropeptide to raise skin temperature in postmenopausal women during hot flushes.

CONCLUSIONS

The duration of the perception of each hot flush in a woman is brief, while local reddening after intradermal administration of α-CGRP persists for 1 to 6 h. This contrast remains unclear.

Neurokinin 3 Receptor Antagonism: A Novel Treatment for Menopausal Hot Flushes

Menopause is associated with significant symptomatic burden, with approximately two-thirds of postmenopausal women suffering from vasomotor symptoms, hot flushes, and night sweats. The mainstay of treatment for hot flushes continues to be hormone replacement therapy. However, as hormone replacement therapy is contraindicated in some cases, alternative, efficacious treatment options are also required. Hot flushes are thought to arise as a result of significant changes in the neuroendocrine circuitry underpinning the reproductive axis during menopause. This includes reduced circulating ovarian oestrogens, hypersecretion of gonadotropins, and increased expression of kisspeptin and neurokinin B (NKB) within the infundibular nucleus of the hypothalamus. In recent years, NKB, predominantly acting via the neurokinin 3 receptor (NK3R), has emerged as an important player in the development of menopausal hot flushes. Antagonism of NK3R has garnered much interest as a novel therapeutic target to help ameliorate hot flush symptoms. Improvements in hot flush frequency, severity, and quality of life have been demonstrated in a number of clinical trials using novel NK3R antagonists in postmenopausal women. Within this review, we will explore the growing body of evidence supporting antagonism of NK3R as a potentially promising treatment for menopausal hot flushes.

Menopausal Hot Flashes: A Concise Review

Hot flashes (HFs), defined as transient sensations of heat, sweating, flushing, anxiety, and chills lasting for 1-5 min, constitute one of the most common symptoms of menopause among women though only a few seek treatment for these. The basis of HFs lies in abnormal hypothalamic thermoregulatory control resulting in abnormal vasodilatory response to minor elevations of core body temperature. Recent data suggest an important role for calcitonin gene-related peptide, hypothalamic kisspeptin, neurokinin B and dynorphin signal system, serotonin, norepinephrine in causation of HFs in addition to estrogen deficiency which plays a cardinal role. The mainstay of treatment includes hormonal replacement therapy, selective serotonin, and norepinephrine reuptake inhibitors in addition to lifestyle modification. In this review, we address common issues related to menopause HFs and suggest a stepwise approach to their management.

Role of calcitonin gene-related peptide in energy metabolism

PURPOSE

Calcitonin gene-related peptide (CGRP) is a neuropeptide produced by alternative tissue-specific splicing of the primary transcript of the CALC genes. CGRP is widely distributed in the central and peripheral nervous system, as well as in several organs and tissues. The presence of CGRP in the liver and brown and white adipose tissue suggests an effect of this neuropeptide on regulation of energy homeostasis.

METHODS

In this review, we summarize the current knowledge of the effect of CGRP on the control of energy metabolism, primarily focusing on food intake, thermoregulation and lipid metabolism in adipose tissue, liver and muscle.

RESULTS

CGRP induces anorexia, stimulating anorexigenic neuropeptide and/or inhibiting orexigenic neuropeptide expression, through cAMP/PKA pathway activation. CGRP also induces energy expenditure, increasing the skin temperature and brown adipose tissue thermogenesis. It has been also suggested that information related to peripheral lipid stores may be conveyed to the brain via CGRP-sensory innervation from adipose tissue. More recently, it was demonstrated that mice lacking αCGRP are protected from obesity induced by high-fat diet and that CGRP regulates the content of lipid in liver, muscle and adipose tissue.

CONCLUSIONS

It is unclear the receptor responsible by CGRP effects, as well as whether this neuropeptide acts directly or indirectly in liver, muscle and adipose tissue.

Effects of Aqueous Extracts of Cynanchum wilfordii in Rat Models for Postmenopausal Hot Flush

Menopausal hot flushes (HFs), which manifest as a transient increase in skin temperature, occur most frequently in postmenopausal women, and sometimes negatively influence daily life. We investigated the effect of an aqueous extract of Cynanchum wilfordii (CWW) in a rat model of menopausal HFs, where tail skin temperature (TST) is increased after the rapid estrogen decline induced by ovariectomy. Ten-week-old female rats were ovariectomized and treated with CWW for 1 week. We measured TST and rectal temperatures (RT) and investigated serum estradiol. The TST in ovariectomized (OVX) rats was significantly elevated after ovariectomy compared with control rats, whereas the RT in OVX rats was not elevated. Administration of CWW (200 mg/kg/d for 7 days, p.o.) significantly improved the skin temperature increase in OVX rats. The lower level of serum estradiol in OVX rats was significantly increased by supplying E2, but it was not affected by CWW. The present study indicates a need for future research involving treatment with high concentrations of C. wilfordii and measurement over 24 h.

Modulation of body temperature and LH secretion by hypothalamic KNDy (kisspeptin, neurokinin B and dynorphin) neurons: a novel hypothesis on the mechanism of hot flushes

Despite affecting millions of individuals, the etiology of hot flushes remains unknown. Here we review the physiology of hot flushes, CNS pathways regulating heat-dissipation effectors, and effects of estrogen on thermoregulation in animal models. Based on the marked changes in hypothalamic kisspeptin, neurokinin B and dynorphin (KNDy) neurons in postmenopausal women, we hypothesize that KNDy neurons play a role in the mechanism of flushes. In the rat, KNDy neurons project to preoptic thermoregulatory areas that express the neurokinin 3 receptor (NK3R), the primary receptor for NKB. Furthermore, activation of NK₃R in the median preoptic nucleus, part of the heat-defense pathway, reduces body temperature. Finally, ablation of KNDy neurons reduces cutaneous vasodilatation and partially blocks the effects of estrogen on thermoregulation. These data suggest that arcuate KNDy neurons relay estrogen signals to preoptic structures regulating heat-dissipation effectors, supporting the hypothesis that KNDy neurons participate in the generation of flushes.

[Effects of estrogen and keishibukuryogan on hot flash-like symptoms induced by yohimbine in ovariectomized rats]

Hot flash (HF) is the most common phenomenon in climacteric symptoms which often develop concomitantly with a decrease in estrogen in postmenopausal women. The onset mechanism of the hot flash is complicated and remains unclear. To date, some animal models of postmenopausal HF have been devised, but they are not fully available because of the difficulty in producing them. It is thought that hyperactivity of the central α-adrenergic system with a decrease in estrogen participates in the onset of postmenopausal HF. Therefore, in the present study, we examined whether a HF model could be easily produced by administering yohimbine (YOH), a presynaptic α₂-adrenoceptor antagonist which promotes norepinephrine release, to female rats. HF-like symptoms such as a rise in tail skin temperature and a fall in rectal temperature were shown in the rats who received YOH (3 mg/kg) subcutaneously seven days after the ovariectomy (OVX). Such symptoms following YOH administration were observed in sham rats as well, but were much more clearly noted in OVX rats. We next examined the effects of various drugs, which are clinically effective against postmenopausal HF, on HF-like symptoms in YOH-treated OVX rats: clonidine, a presynaptic α₂-adrenoceptor agonist which inhibits norepinephrine release; β-estradiol as an estrogen; and Keishibukuryogan, a Kampo medicine. These drugs inhibited HF-like symptoms in YOH-treated OVX rats. These results suggest that the activity of the α-adrenergic system is enhanced with a decrease in estrogen in OVX rats whereby YOH causes HF-like symptoms more conspicuously than in sham rats. Therefore, it is thought that YOH-treated OVX rats will be a novel and simple model of postmenopausal HF.

Ambient temperature and 17β-estradiol modify Fos immunoreactivity in the median preoptic nucleus, a putative regulator of skin vasomotion

Estrogen has pronounced effects on thermoregulation, but the anatomic sites of integration between the reproductive and thermoregulatory axes are unknown. In this study, we tested whether estradiol-17β (E(2)) treatment would alter the activity of thermoregulatory brain regions responding to mild changes in ambient temperature (T(AMBIENT)). Core and tail skin temperatures were recorded at the ambient temperatures of 20, 24, or 31 C in ovariectomized (OVX) rats with and without E(2). Neuronal activity was evaluated by counting the number of Fos-immunoreactive cells in the brains of rats killed 90 min after exposure to one of the three ambient temperatures. Of 14 brain areas examined, the median preoptic nucleus (MnPO) was the only site that exhibited increased Fos immunoreactivity at the high T(AMBIENT) of 31 C. At 24 C, OVX rats exhibited increased numbers of MnPO Fos-immunoreactive cells, compared with OVX + E(2) rats. Interestingly, tail skin vasomotion and MnPO Fos expression were affected in a similar manner by T(AMBIENT) and E(2) treatment. In the arcuate nucleus and anteroventral periventricular nucleus (AVPV), Fos immunoreactivity was highest at the low T(AMBIENT) of 20 C, with inhibitory (arcuate nucleus) and stimulatory (AVPV) effects of E(2). No other areas responded to both T(AMBIENT) and E(2) treatment. These results implicate the MnPO, the arcuate nucleus, and the AVPV as sites of integration between the reproductive and thermoregulatory axes. Combined with studies showing the importance of MnPO neurons in heat-defense pathways, the MnPO emerges as a likely site for E(2) modulation of thermoregulatory vasomotion.

Effects of estradiol on the thermoneutral zone and core temperature in ovariectomized rats

Hot flushes represent a disorder of central thermoregulation characterized by the episodic activation of heat loss mechanisms. Although flushes are associated with estrogen withdrawal, there is little understanding of the effects of estrogen on thermoregulation in any species. It has been proposed that hormone withdrawal increases the sensitivity of hypothalamic neural pathways that control heat dissipation effectors. If so, we predicted that ovariectomized rats without estradiol treatment would activate tail skin vasodilatation (a major heat loss effector) at lower ambient temperatures and thereby lower the thermoneutral zone. The thermoneutral zone, defined as the range of ambient temperatures in which thermoregulation is achieved only by sensible (dry) heat loss, was evaluated based on properties of skin vasomotion. Core and tail skin temperatures were recorded in ovariectomized rats (with and without estradiol-17beta) exposed to ambient temperatures from 13 to 34 C in an environmental chamber. Rats without estradiol exhibited increased skin vasodilatation and a shift in the thermoneutral zone to lower ambient temperatures. Moreover, the ambient temperature threshold for skin vasodilatation was significantly lower in rats without estradiol treatment. At most ambient temperatures, average core temperature was unaffected by estradiol. However, at ambient temperatures of 32.5 C and above, untreated ovariectomized rats exhibited higher core temperatures compared with estradiol-treated rats. Thus, estradiol-17beta treatment enhanced the maintenance of core temperature during heat exposure. These findings support the hypothesis that estrogen withdrawal increases the sensitivity of thermoregulatory neural pathways and modifies the activation of heat loss mechanisms.

Significance of measured elevation of skin temperature induced by calcitonin gene-related peptide in anaesthetized rats

To assess whether peripheral changes related to skin temperature rise were induced by ovarian hormone deficiency, we investigated the effects of anaesthesia on calcitonin gene-related peptide (CGRP)- or luteinizing hormone-releasing hormone (LH-RH)-induced elevation of skin temperature in female rats. CGRP was used as an inducer of peripherally-mediated elevation of skin temperature, whereas LH-RH was used as an inducer of centrally-mediated elevation of skin temperature. Intravenous (i.v.) but not intracerebroventricular injection of CGRP (10 μg kg−1) or intracerebroventricular but not intravenous injection of LH-RH (10 μg/rat) elevated the skin temperature of unanaesthetized rats restrained in a Ballman's cage. The elevation with LH-RH was completely inhibited by urethane anaesthesia, whereas the elevation with CGRP was not. These results suggested that changes in skin temperature measured under anaesthesia reflected a peripherally rather than a centrally mediated mechanism. The CGRP (1.0–30 μg kg−1, i.v.)-induced elevation of skin temperature was potentiated in ovariectomized rats and inhibited by pretreatment with a CGRP receptor antagonist CGRP8–37 (1000 μg kg−1, i.v.), suggesting that the potentiation may participate in peripheral factors such as a postsynaptic hypersensitivity to CGRP following ovarian hormone deficiency. Thus, measurement of skin temperature in the anaesthetized rat was a useful procedure to seek the peripheral mechanism of potentiation of skin temperature induced by CGRP, thought to be closely related to menopausal hot flashes.

Calcitonin gene-related peptide alters the firing rates of hypothalamic temperature sensitive and insensitive neurons

Background

Transient hyperthermic shifts in body temperature have been linked to the endogenous hormone calcitonin gene-related peptide (CGRP), which can increase sympathetic activation and metabolic heat production. Recent studies have demonstrated that these centrally mediated responses may result from CGRP dependent changes in the activity of thermoregulatory neurons in the preoptic and anterior regions of the hypothalamus (POAH).

Results

Using a tissue slice preparation, we recorded the single-unit activity of POAH neurons from the adult male rat, in response to temperature and CGRP (10 μM). Based on the slope of firing rate as a function of temperature, neurons were classified as either warm sensitive or temperature insensitive. All warm sensitive neurons responded to CGRP with a significant decrease in firing rate. While CGRP did not alter the firing rates of some temperature insensitive neurons, responsive neurons showed an increase in firing rate.

Conclusion

With respect to current models of thermoregulatory control, these CGRP dependent changes in firing rate would result in hyperthermia. This suggests that both warm sensitive and temperature insensitive neurons in the POAH may play a role in producing this hyperthermic shift in temperature.

Skin temperature rise induced by calcitonin gene-related peptide in gonadotropin-releasing hormone analogue-treated female rats and alleviation by Keishi-bukuryo-gan, a Japanese herbal medicine

The effects of Keishi-bukuryo-gan on calcitonin gene-related peptide (CGRP)-induced elevation of skin temperature were investigated in gonadotropin-releasing hormone (GnRH) analogue-treated female rats. Leupline (1.0 mg/kg) as the GnRH analogue was subcutaneously (s.c.) injected into female rats. After Keishi-bukuryo-gan (100-1,000 mg/kg, p.o.) or 17beta-estradiol (0.010 mg/kg, s.c.) was administered to GnRH analogue-treated rats for 14 days, CGRP-induced skin temperature elevation, concentration of plasma 17beta-estradiol and pituitary gonadotropin (luteinizing hormone; LH, and follicle stimulating hormone; FSH) were measured. In addition, effects of 17beta-estradiol and Keishi-bukuryo-gan on the proliferation of estrogen-dependent human breast cancer (MCF-7) cells were investigated under in vitro conditions. GnRH analogue significantly lowered the concentrations of plasma 17beta-estradiol and pituitary gonadotropins. Tissue weights of the ovaries and uterus were also decreased by the analogue. Under the condition of estrogen deficiency, intravenous (i.v.) injection of exogenous CGRP (10 microg/kg) elevated the skin temperature of the hind paws more significantly than it did in sham-treated control rats. Estrogen supplementation inhibited this elevation of skin temperature with restoration of both the lowered plasma estrogen level and the decreased uterine weight in GnRH analogue-treated rats. On the other hand, Keishi-bukuryo-gan inhibited the elevation of skin temperature in a dose-dependent manner without restoring the plasma estrogen level and uterine weight. In addition, in an in vitro study, MCF-7 cells proliferated in a dose-dependent manner by the addition of 17beta-estradiol (10(-13)-10(-8) M) to the medium. However, Keishi-bukuryo-gan (10(-6)-10(-4) mg/ml) did not activate the MCF-7 cell proliferation. These results suggest that Keishi-bukuryo-gan, which does not exhibit estrogen activity, may be useful for the treatment of hot flashes in women who are undergoing medical ovariectomy with a GnRH analogue.

Involvement of calcitonin gene-related peptide in elevation of skin temperature in castrated male rats

OBJECTIVES

To assess the involvement of calcitonin gene-related peptide (CGRP) in the occurrence of hot flashes in men after castration for treatment of prostate cancer, we investigated the effects of CGRP on skin temperature in surgically and medically castrated male rats.

METHODS

Changes in skin temperature of the hind paws after intravenous injection of 10 microg/kg of CGRP and CGRP family peptides (adrenomedullin and amylin) were measured at 5-minute intervals for 120 minutes, 3 weeks after bilateral orchiectomy or 2 weeks after subcutaneous injection of a gonadotropin-releasing hormone analogue (1.0 mg/kg Leuplin) in male rats. Antagonism with CGRP8-37 (1000 microg/kg intravenously), a CGRP1 receptor antagonist, to the CGRP-induced response was examined by injecting it 10 minutes before injection of CGRP. The effect of testosterone replacement on castration was evaluated in each castrated rat by the administration of testosterone (1.0 mg/kg subcutaneously once a day) for 14 days before the day of the temperature analysis.

RESULTS

CGRP, but not adrenomedullin and amylin, elevated the skin temperature in surgical or medical castration-induced testosterone-deficient rats more than in the sham-treated rats. The difference was statistically significant. The CGRP-induced potentiation in the castrated rats was inhibited by pretreating with CGRP8-37 or by supplying testosterone.

CONCLUSIONS

CGRP is the most potent peptide in a family that elevates the skin temperature in male rats. The elevation of the skin temperature was more affected by the testosterone deficiency resulting from castration. These results suggest that CGRP is involved in the mechanism underlying hot flashes in men.

Menopausal hot flash and calciotonin gene-related peptide; effect of Keishi-bukuryo-gan, a kampo medicine, related to plasma calciotonin gene-related peptide level

OBJECTIVES

The purpose of this study is to investigate relationship of menopausal hot flash and calcitonin gene-related peptide (CGRP). Furthermore, this study evaluated the effect of the Japanese herbal (kampo) medicine Keishi-bukuryo-gan from the aspect of CGRP regulation.

METHODS

Plasma CGRP and vasoactive intestinal peptide (VIP) levels were measured during hot flash and CGRP reactivity was studied by cold load test in subjects with/without hot flashes. The effect of Keishi-bukuryo-gan was assessed in comparison with plasma CGRP level.

RESULTS

Only plasma CGRP but not VIP significantly elevated at the occurrence of hot flash (P=0.002). Stress by cold load significantly enhanced the over-secretion of CGRP in subjects with flash compared with those without flash (P=0.003) 3 min after the load. Keishi-bukuryo-gan decreased plasma CGRP level in subjects with hot flash.

CONCLUSIONS

CGRP but not VIP was mainly related to the occurrence of hot flash. Keishi-bukuryo-gan, Japanese herbal medicine, improves hot flash possibly affecting plasma CGRP level.

Effects of the vasoactive neuropeptides calcitonin gene-related peptide, substance P and vasoactive intestinal polypeptide on skin temperature in ovariectomized rats

The effects of three vasoactive neuropeptides, calcitonin gene-related peptide (CGRP), substance P (SP) and vasoactive intestinal polypeptide (VIP), on vasodilation and skin temperature were investigated in ovariectomized (OVX) and sham-operated control rats. CGRP (0.01-1 nmol), VIP (0.01-10 nmol) and SP (0.1-100 nmol) produced vasodilation in PGF(2 alpha) (10 microM)-induced contraction of mesenteric vascular beds isolated from OVX and sham-operated rats in a dose-dependent manner. Intravenous injection of CGRP (1-10 microg/kg), VIP (10-50 microg/kg) and SP (10-50 microg/kg) elevated the skin temperature in OVX and sham-operated rats in a dose-dependent manner. CGRP had the greatest effect on both parameters, followed by VIP, with the smallest effect in SP. These parallel increases of vasodilation and skin temperature with CGRP were significantly greater in OVX rats than in sham-operated rats. However, no significant differences were observed in VIP- or SP-induced vasodilation and skin temperature increases between OVX and sham-operated rats. These results suggest not only that CGRP is closely related to the elevation of skin temperature but also that CGRP-induced responses are more affected by ovarian hormone deficiency.

Biphasic effects of orchidectomy on calcitonin gene-related peptide synthesis and release

We hypothesize that the decline of male gonadal hormones may play a role in age-related decrease of calcitonin gene-related peptide (CGRP) synthesis and release. Orchidectomized rats were raised with or without testosterone replacement and CGRP levels in serum and some tissues as well as the perfusate from the isolated mesenteric arterial bed (MAB) were measured at 1, 2 and 4 months after orchidectomy. CGRP levels of serum and tissues, and CGRP release from MAB were significantly elevated after 1 month and decreased after 4 months in orchidectomized rats. The changes were restored by testosterone replacement. Our results indicate that the age-related decline of testosterone might contribute to the age-related decrease of CGRP synthesis and release.

Effects of estrogen on thermoregulatory tail vasomotion and heat-escape behavior in freely moving female rats

Effects of estrogen on thermoregulatory vasomotion and heat-escape behavior were investigated in ovariectomized female rats supplemented with estrogen (replaced estrogen rats) or control saline (low estrogen rats). First, we measured tail temperature of freely moving rats at ambient temperatures (T(a)) between 13 and 31 degrees C. Tail temperature of the low estrogen rats was higher than that of the replaced estrogen rats at T(a) between 19 and 25 degrees C, indicating that the low estrogen rats exhibit more skin vasodilation than the replaced estrogen rats. There was no significant difference in oxygen consumption and core temperature between the two groups. Second, we analyzed heat-escape behaviors in a hot chamber where rats could obtain cold air by moving in and out of a reward area. The low estrogen rats kept T(a) at a lower level than did the replaced estrogen rats. These results imply that the lack of estrogen facilitates heat dissipation both by skin vasodilation and by heat-escape behavior. Ovariectomized rats may mimic climacteric hot flushes not only for autonomic skin vasomotor activity but also for thermoregulatory behavior.

Effects of progesterone on the elevation of tail skin temperature in ovariectomized rats

We examined the effects of progesterone on the elevation of tail skin temperature (TST) in ovariectomized rats and compared them with those of estradiol. Progesterone showed only insignificant effects on the TST elevation, whereas estradiol showed complete inhibition. The TST elevation induced by ovariectomy is caused by estradiol deficiency, but progesterone plays little or no role.

Elevation of tail skin temperature in ovariectomized rats in relation to menopausal hot flushes

Menopausal hot flushes (HFs), which manifest as an increase in skin temperature, most frequently occur after menopause and cease with the passage of time. We designed this study to elucidate the characteristics of the elevation of tail skin temperature (TST) in ovariectomized (OVX) rats, which is relevant to human symptoms of HFs. First, we measured TST and rectal temperature (RT) and investigated the time course of their changes up to 20 wk after ovariectomy. The TST in OVX rats (28.4 +/- 0.3 degrees C) was significantly (P = 0.0035) elevated from 2 to 7 wk after the ovariectomy compared with that in sham-operated (Sham) rats (27.0 +/- 0.2 degrees C), whereas the RT in OVX rats was elevated from 8 to 20 wk. We next examined the therapeutic effects of estradiol (E(2)) on the elevation of the TST by continuous subcutaneous infusion. E(2) treatment (1.0 microg/day) completely (P = 0.0232) inhibited the elevation of the TST (28.4 +/- 0.3 degrees C for Sham rats, 29.3 +/- 0.3 degrees C for OVX rats, 28.2 +/- 0.4 degrees C for OVX + E(2) 1.0 microg/day rats). These results demonstrated that the elevation of TST in OVX rats was exhibited soon after the estrogen removal and diminished with time and that it was normalized with continuous E(2) replacement. These characteristics are similar to the symptoms of menopausal HFs in women.