Effect of fluid replacement with green tea on body fluid balance and renal responses under mild thermal hypohydration: a randomized crossover study.

PURPOSE: Maintaining an appropriate hydration level by ingesting fluid in a hot environment is a measure to prevent heat-related illness. Caffeine-containing beverages, including green tea (GT), have been avoided as inappropriate rehydration beverages to prevent heat-related illness because caffeine has been assumed to exert diuretic/natriuretic action. However, the influence of caffeine intake on urine output in dehydrated individuals is not well documented. The aim of the present study was to examine the effect of fluid replacement with GT on body fluid balance and renal water and electrolyte handling in mildly dehydrated individuals. METHODS: Subjects were dehydrated by performing three bouts of stepping exercise for 20 min separated by 10 min of rest. They were asked to ingest an amount of water (H2O), GT, or caffeinated H2O (20 mg/100 ml; Caf-H2O) that was equal to the volume of fluid loss during the dehydration protocol; fluid balance was measured for 2 h after fluid ingestion. RESULTS: The dehydration protocol induced hypohydration by ~ 10 g/kg body weight (~ 1% of body weight). Fluid balance 2 h after fluid ingestion was significantly less negative in all trials, and the fluid retention ratio was 52.2 ± 4.2% with H2O, 51.0 ± 5.0% with GT, and 47.9 ± 6.2% with Caf-H2O; those values did not differ among the trials. After rehydration, urine output, urine osmolality, and urinary excretions of osmotically active substances, sodium, potassium and chloride were not different among the trials. CONCLUSION: The data indicate that ingestion of GT or an equivalent caffeine amount does not worsen the hydration level 2 h after ingestion and can be effective in reducing the negative fluid balance for acute recovery from mild hypohydration. TRIAL REGISTRATION: ISRCTN53057185; retrospectively registered.

Endogenous Androgens Diminish Food Intake and Activation of Orexin A Neurons in Response to Reduced Glucose Availability in Male Rats.

Sex steroids modify feeding behavior and body weight regulation, and androgen reportedly augments food intake and body weight gain. To elucidate the role of endogenous androgens in the feeding regulation induced by reduced glucose availability, we examined the effect of gonadectomy (orchiectomy) on food intake and orexin A neuron's activity in the lateral hypothalamic/perifornical area (LH/PFA) in response to reduced glucose availability (glucoprivation) induced by 2-deoxy-d-glucose (2DG) administration in male rats. Rats (7W) were bilaterally orchiectomized (ORX group) or sham operated (Sham group). Seventeen days after the surgery, food intake response to 2DG (400 mg/kg, i.v.) was measured for 4 h after the infusion. The same experiment was performed for the immunohistochemical examination of c-Fos-expressing orexin A neurons in the LH/PFA and c-Fos expression in the arcuate nucleus (Arc). Food intake induced by glucoprivation was greater in the ORX group than the Sham group, and the glucoprivation-induced food intake was inversely correlated with plasma testosterone concentration. Glucoprivation stimulated c-Fos expression of the orexin A neurons at the LH/PFA and c-Fos expression in the dorsomedial Arc. The number and percentage of c-Fos-expressing orexin A neurons in the LH/PFA and c-Fos expression in the dorsomedial Arc were significantly higher in the ORX group than the Sham group. This indicates that endogenous androgen, possibly testosterone, diminishes the food intake induced by reduced glucose availability, possibly via the attenuated activity of orexin A neuron in the LH/PFA and neurons in the dorsomedial Arc.

Estradiol replacement improves high-fat diet-induced insulin resistance in ovariectomized rats.

The role of 17ß-estradiol (E2) in high-fat diet (HFD)-induced alteration of the protein kinase B (Akt) signaling pathway in ovariectomized (OVX) rats is unclear. Therefore, we examined whether chronic estrogen replacement restores HFD-induced impairment in insulin sensitivity by its effects concomitant with alterations in the Akt isoform 2 (Akt2) and Akt substrate of 160 kDa (AS160) phosphorylation in muscles of OVX rats. Nine-week-old female Wistar rats underwent ovariectomy under anesthesia; after 4 weeks, subcutaneous implantation of either E2 or placebo (PL) pellets was performed, and HFD feeding was initiated. Intravenous glucose tolerance tests were performed to assess insulin sensitivity. Following insulin injection into rats' portal vein, the liver and gastrocnemius muscle were dissected for insulin signaling analysis. We observed that HFD increased energy intake and body weight in the PL group; however, it was temporarily decreased in the E2 group. Adipose tissue accumulation was larger in HFD-fed rats than in normal chow diet (NCD)-fed rats in the PL group; however, this difference was not observed in the E2 group. HFD reduced insulin sensitivity in the PL group only. In vivo insulin stimulation increased Akt2 phosphorylation in the muscles of NCD-fed rats in both groups. In contrast, HFD affected insulin-stimulated phosphorylation of Akt2 and AS160 in the muscles of rats in the PL group but not in the E2 group. Our data suggest that E2 replacement improves HFD-induced insulin resistance, and this effect is accompanied by the alterations in the Akt2 and AS160 phosphorylation in insulin-stimulated muscles of OVX rats.

Estradiol Replacement Improves High-Fat Diet-Induced Obesity by Suppressing the Action of Ghrelin in Ovariectomized Rats.

This study aims to investigate the effects of estradiol replacement on the orexigenic action of ghrelin in ovariectomized (OVX) obese rats fed with a high-fat diet (HFD). Four weeks after OVX at 9 weeks of age, Wistar rats were subcutaneously implanted with either 17ß-estradiol (E2) or placebo (Pla) pellets and started on HFD feeding. After 4 weeks, growth hormone-releasing peptide (GHRP)-6, a growth hormone secretagogue receptor (GHSR) agonist injected intraperitoneally, induced changes in HFD intake, and c-Fos-positive neurons in the hypothalamic arcuate nucleus (ARC) were measured in both groups. The ghrelin protein and mRNA levels, as well as GHSR protein in stomach, were analyzed by Western blotting and real-time PCR. HFD increased energy intake and body weight in the Pla group, while it temporarily reduced these in the E2 group. GHRP-6 enhanced HFD intake and activated neurons in the ARC only in the Pla group. Furthermore, gastric ghrelin and GHSR protein levels were lower in the E2 group than in the Pla group, but plasma acyl ghrelin levels were similar in both groups. Our results suggest that E2 replacement improves obesity by inhibiting the orexigenic action of ghrelin via downregulation of ghrelin and its receptor in stomach in HFD-fed OVX rats.

Fluoxetine Mimics the Anorectic Action of Estrogen and Its Regulation of Circadian Feeding in Ovariectomized Female Rats.

Our previous study demonstrated that chronic estrogen replacement in ovariectomized rats reduces food intake and augments c-Fos expression in the suprachiasmatic nucleus (SCN), specifically during the light phase. Here, we hypothesized that serotonergic neurons in the central nervous system (CNS), which have anorectic action and play a role in regulating circadian rhythm, mediate the light phase-specific anorectic action of estrogen, and that selective serotonin reuptake inhibitors (SSRIs) mimic the hypophagic action of estrogen. Female Wistar rats were ovariectomized and treated with estradiol (E2) or cholesterol by subcutaneously implanting a silicon capsule containing E2 or cholesterol. Then, half of the cholesterol-treated rats were injected with the SSRI fluoxetine (5 mg/kg) (FLX group), while the remaining rats in the cholesterol-treated group (CON group) and all those in the E2 group were injected with saline subcutaneously twice daily at the onsets of the light and dark phases. Both E2 and FLX reduced food intake during the light phase but not the dark phase, and reduced body weight gain. In addition, both E2 and FLX augmented the c-Fos expression in the SCN, specifically during the light phase. These data indicate that FLX exerts estrogen-like antiobesity and hypophagic actions by modifying circadian feeding patterns, and suggest that estrogen regulates circadian feeding rhythm via serotonergic neurons in the CNS.

Endurance running exercise is an effective alternative to estradiol replacement for restoring hyperglycemia through TBC1D1/GLUT4 pathway in skeletal muscle of ovariectomized rats.

Menopause is a risk factor for impaired glucose metabolism. Alternative treatment of estrogen for postmenopausal women is required. The present study was designed to investigate the effects of 5-week endurance running exercise (Ex) by treadmill on hyperglycemia and signal pathway components mediating glucose transport in ovariectomized (OVX) placebo-treated rats, compared with 4-week 17ß-estradiol (E2) replacement or pair-feeding (PF) to the E2 group. Ex improved the hyperglycemia and insulin resistance index in OVX rats as much as E2 or PF did. However, Ex had no effect on body weight gain in the OVX rats. Moreover, Ex enhanced the levels of GLUT4 and phospho-TBC1D1 proteins in the gastrocnemius of the OVX rats, but E2 or PF did not. Instead, the E2 increased the Akt2/AS160 expression and activation in the OVX rats. This study suggests that endurance Ex training restored hyperglycemia through the TBC1D1/GLUT4 pathway in muscle by an alternative mechanism to E2 replacement.

The effect of menstrual cycle phase on foot skin temperature during mild local cooling in young women.

Japanese women can experience a sensation of cold feet in daily life. It is possible that this sensation of coldness in feet may be associated with female hormones, but to date the effect of menstrual cycle phase on the skin temperature (Tsk) of the foot during local cooling is unknown. We therefore examined Tsk and partial cutaneous blood flow in the foot during the follicular (F) and luteal (L) phases of the menstrual cycle in women experiencing local cooling. Tsk was measured in the toes and the dorsum of the left foot using infrared thermography, while cutaneous blood flow was evaluated in the big toe of the left foot using laser Doppler flowmetry (LDF), both at 28 °C. Mild local cooling (24.7 °C) was then applied for 30 min to the right foot. During cooling of the right foot, no significant differences in Tsk were observed between the F and L phases in either the toes of the left foot or the dorsum of the left foot of all subjects. However, cutaneous blood flow determined by LDF in the big toe of the left foot was greater in the F phase than in the L phase. These results suggest that the menstrual cycle phase did not affect Tsk in the foot, but it did affect cutaneous blood flow in the big toe during mild local cooling.

Estrogen replacement enhances insulin-induced AS160 activation and improves insulin sensitivity in ovariectomized rats.

Menopause predisposes women to impaired glucose metabolism, but the role of estrogen remains unclear. In this study, we examined the effects of chronic estrogen replacement on whole body insulin sensitivity and insulin signaling in ovariectomized rats. Female Wistar rats aged 9 wk were ovariectomized under anesthesia. After 4 wk, pellets containing either 17ß-estradiol (E2) or placebo (Pla) were subcutaneously implanted in the rats. After 4 wk of treatment, the intra-abdominal fat accumulation was greater in the Pla group than that in the E2 group. Hyperinsulinemic-euglycemic clamp analysis and intravenous glucose tolerance test revealed that insulin sensitivity was significantly lower in the Pla group than in the E2 group. In addition, Western blotting showed that in vivo insulin stimulation increased protein kinase B (Akt) phosphorylation to a similar degree in the gastrocnemius and liver of both groups, but phosphorylated Akt2 Ser474 was enhanced in the muscle of the E2 group compared with the Pla group. Moreover, insulin-stimulated phosphorylation of Akt substrate of 160 kDa (AS160) Thr642 was observed only in the E2 group, resulting in the difference between the two groups. Additionally, AS160 protein and mRNA levels were higher in muscle of the E2 group than the Pla group. In contrast, E2 replacement had no effect on glucose transporter 4 protein levels in muscle and glycogen synthase kinase-3ß in muscle and liver. These results suggest that estrogen replacement improves insulin sensitivity by activating the Akt2/AS160 pathway in the insulin-stimulated muscle of ovariectomized rats.

Blood pressure predicts endothelial function and the effects of ethinyl estradiol exposure in young women.

Hypertension, obesity, and endothelial function predict cardiovascular disease in women, and these factors are interrelated. We hypothesized that hypertension and obesity are associated with endothelial dysfunction in young women and that short-term ethinyl estradiol exposure mitigates this dysfunction. We examined flow-mediated dilation (FMD) responses before and during 7 days of oral ethinyl estradiol (30 µg/day) in 19 women (25 ± 5, 18-35 yr). We divided our sample into two groups based on two criteria: blood pressure and obesity. Women were divided into normal blood pressure (NBP; mean arterial pressure range: 78-91 mmHg, n = 7) and high blood pressure (HBP; mean arterial pressure range: 95-113 mmHg, n = 9) groups. We also stratified our subjects by body composition (lean: 18-31%, n = 8; obese: 38-59%, n = 9). We evaluated brachial FMD after two distinct shear stress stimuli: occlusion alone and occlusion with ischemic handgrip exercise. Obesity was unrelated to both FMD responses. Before ethinyl estradiol administration, the HBP group had blunted ischemic exercise responses relative to the NBP group (8.0 ± 3.5 vs. 12.3 ± 3.2%, respectively, P = 0.05). However, during ethinyl estradiol administration, ischemic exercise responses increased in the HBP group (12.8 ± 6.1%, P = 0.04) but decreased in the NBP group (5.6 ± 2.4%, P = 0.01). Standard FMD did not reveal differences between groups. In summary, 1) moderate HBP predicted endothelial impairment, 2) ethinyl estradiol administration had divergent effects on FMD in women with NBP versus HBP, and 3) enhanced FMD (ischemic handgrip exercise) revealed differences in endothelial function, whereas standard FMD (occlusion alone) did not. NEW & NOTEWORTHY We are the first to show that mild hypertension is a stronger predictor of endothelial dysfunction than obesity in healthy women without overt cardiovascular dysfunction. Importantly, the standard 5-min flow-mediated vasodilation stimulus did not detect endothelial dysfunction in our healthy population; only an enhanced ischemic handgrip exercise shear stress stimulus detected endothelial impairment. Estradiol administration increased flow-mediated dilation in women with high blood pressure, so it may be a therapeutic intervention to improve endothelial function.

Estrogen replacement attenuates stress-induced pressor responses through vasorelaxation via ß2-adrenoceptors in peripheral arteries of ovariectomized rats.

We examined whether chronic estrogen replacement has an inhibitory effect on stress-induced pressor responses via activation of ß2-adrenoceptor (AR) in peripheral arteries of ovariectomized rats. Female Wistar rats aged 9 wk were ovariectomized. After 4 wk, pellets containing either 17ß-estradiol (E2) or placebo (Pla) were subcutaneously implanted into the rats. After 4 wk of treatment, rats underwent cage-switch stress, and, in a separate experiment, a subset received an infusion of isoproterenol (ISO) with or without pretreatment with the ß1-AR blocker atenolol or the ß2-AR blocker butoxamine. In addition, the isolated mesenteric artery was used to assess the concentration-related relaxing responses to ISO and the ß1- or ß2-AR mRNA level. The cage-switch stress-induced pressor response was significantly attenuated in the E2-treated group compared with the Pla-treated group. Pretreatment with atenolol reduced blood pressure responses in both groups. However, butoxamine enhanced the pressor response only in the E2-treated group, resulting in no difference between the two groups. In addition, the intravenous ISO-induced depressor response was significantly enhanced in the E2-treated group compared with the Pla-treated group. Furthermore, the difference in the depressor response was abolished by pretreatment with butoxamine but not by atenolol. In the isolated mesenteric artery, butoxamine caused a rightward shift in ISO-induced concentration-related relaxation in the E2-treated group. The ß2-AR mRNA level in the mesenteric artery was higher in the E2-treated group than in the Pla-treated group. These results suggest that estrogen replacement attenuated the stress-induced pressor response probably by suppressing vasoconstriction via activation of ß2-ARs in peripheral arteries of ovariectomized rats. NEW & NOTEWORTHY In this study, we show, for the first time, that estrogen replacement has an inhibitory effect on the psychological stress-induced pressor response through vasorelaxation via ß2-adrenoceptors, probably due to overexpression of ß2-adrenoceptor mRNA, in peripheral arteries of ovariectomized rats.

S-equol Exerts Estradiol-Like Anorectic Action with Minimal Stimulation of Estrogen Receptor-α in Ovariectomized Rats.

Chronic estrogen replacement in ovariectomized rats attenuates food intake and enhances c-Fos expression in the suprachiasmatic nucleus (SCN), specifically during the light phase. S-equol, a metabolite of daidzein, has a strong affinity for estrogen receptor (ER)-ß and exerts estrogenic activity. The purpose of the present study was to elucidate whether S-equol exerts an estrogen-like anorectic effect by modifying the regulation of the circadian feeding rhythm in ovariectomized rats. Ovariectomized female Wistar rats were divided into an estradiol (E2)-replaced group and cholesterol (vehicle; Veh)-treated group. These animals were fed either a standard diet or an S-equol-containing diet for 13 days. Then, the brain, uterus, and pituitary gland were collected along with blood samples. In the rats fed the standard diet, E2 replacement attenuated food intake (P < 0.001) and enhanced c-Fos expression in the SCN (P < 0.01) during the light phase. Dietary S-equol supplementation reduced food intake (P < 0.01) and increased c-Fos expression in the SCN (P < 0.01) in the Veh-treated rats but not in the E2-replaced rats during the light phase. Dietary S-equol did not alter ER-α expression in the medial preoptic area or the arcuate nucleus, nor did dietary S-equol affect pituitary gland weight or endometrial epithelial layer thickness. By contrast, E2 replacement not only markedly decreased ER-α expression in these brain areas (P < 0.001) but also increased both the pituitary gland weight (P < 0.001) and the endometrial epithelial layer thickness (P < 0.001). Thus, dietary S-equol acts as an anorectic by modifying the diurnal feeding pattern in a manner similar to E2 in ovariectomized rats; however, the mechanism of action is not likely to be mediated by ER-α. The data suggest a possibility that dietary S-equol could be an alternative to hormone replacement therapy for the prevention of hyperphagia and obesity with a lower risk of adverse effects induced by ER-α stimulation.

Effects of estrogen replacement on stress-induced cardiovascular responses via renin-angiotensin system in ovariectomized rats.

The purpose of this study was to determine whether chronic estrogen replacement in ovariectomized rats inhibits the pressor response to psychological stress by attenuating the activation of the renin-angiotensin system. Female Wistar rats aged 9 wk were ovariectomized. After 4 wk, the rats were randomly assigned to be implanted subcutaneously with pellets containing either 17ß-estradiol (E2) or placebo (Pla). After 4 wk of treatment, the rats underwent cage-switch stress and, in a separate experiment, a subset received an infusion of angiotensin II. The cage-switch stress rapidly elevated blood pressure (BP) and heart rate (HR) as measured by radiotelemetry in both groups. However, the BP and HR responses to the stress were significantly attenuated in the E2 group compared with the Pla group. An angiotensin II type 1 receptor blocker, losartan, given in drinking water, abolished the difference in the pressor response to stress between the two groups. Moreover, the stress-induced elevation in plasma renin activity and angiotensin II concentration was significant in the Pla group, but not in the E2 group. In addition, the expression of renin mRNA in the kidney was lower in the E2 group relative to the Pla group. Finally, we found that intravenous angiotensin II infusion increased BP and decreased HR to a similar degree in both groups. These results suggest that the inhibitory effects of estrogen on psychological stress-induced activation of the renin-angiotensin system could be at least partially responsible for the suppression of the pressor responses to psychological stress seen in estrogen-replaced ovariectomized rats.

Target intensity and interval walking training in water to enhance physical fitness in middle-aged and older women: a randomised controlled study.

PURPOSE: To determine the target intensity for fast walking during interval walking training (IWT) in water for middle-aged and older people to enhance physical fitness. METHODS: Thirty-one women [59 ± 5 (SD) years old] were randomly divided into two groups: IWT on land (LG, N = 15) and in water (WG, N = 16). All subjects were instructed to perform ≥ 6 sets of fast and slow walking for 3 min each in a day, ≥ 4 days week(-1), for 8 weeks, at an intensity 35% higher than the oxygen consumption rate at the gas exchange threshold (VO2GET), with a subjective feeling of 16-18 points of the Borg scale during fast walking in each condition. Before and after IWT, we measured VO2GET, peak aerobic capacity (VO2peak) by graded walking and cycling tests on land and isometric knee extension (F EXT) and flexion (F FLX) forces. RESULTS: Before IWT, the VO2GET for walking in water was 14% higher and the heart rate (HR) at a given VO2 was ~10 beats min(-1) lower (P=0.001) than on land. During IWT, subjects in both groups performed IWT for ~4 days week(-1)(P > 0.9) with a 14% higher fast walking intensity in WG than in LG (P < 0.05). After IWT, the VO2peak and VO2GET for cycling, F EXT and F FLX increased more in WG than in LG (all, P < 0.05). CONCLUSION: Walking in water elevated VO2GET and decreased HR at a given exercise intensity in middle-aged and older women, which enabled them to perform exercise at a higher metabolic rate than on land due to improved subjective feelings, which, for these subjects, resulted in greater gains in physical fitness.

Involvement of orexin-A neurons but not melanin-concentrating hormone neurons in the short-term regulation of food intake in rats.

In order to elucidate the involvement of melanin-concentrating hormone (MCH) and orexin-A (ORX-A) neurons of the perifornical/lateral hypothalamic areas (PF/LH) in the regulation of food intake induced by acutely reduced glucose availability, we examined the food intake response and c-Fos expression in the MCH and ORX-A neurons in the PF/LH during 2-deoxy-D-glucose (2DG)-induced glucoprivation (400 mg/kg; i.v.) and systemic insulin-induced hypoglycemia (5 U/kg; s.c.) in male Wistar rats. The administration of both 2DG and insulin stimulated food intake and induced c-Fos expression in the ORX-A neurons corresponding to food intake, but not in the MCH neurons. These data indicate that ORX-A neurons, but not MCH neurons, play a role in the short-term regulation of food intake, and that the input signals for the neurons containing MCH and ORX-A are different, and these neurons play different roles in the regulation of feeding behavior.

Mn-citrate and Mn-HIDA: intermediate-affinity chelates for manganese-enhanced MRI.

In this study we investigated two manganese chelates in order to improve the image enhancement of manganese-enhanced MRI and decrease the toxicity of free manganese ions. Since both MnCl2 and a low-affinity chelate were associated with a slow continuous decrease of cardiac functions, we investigated intermediate-affinity chelates: manganese N-(2-hydroxyethyl)iminodiacetic acid (Mn-HIDA) and Mn-citrate. The T1 relaxivity values for Mn-citrate (4.4 m m⁻¹ s⁻¹) and Mn-HIDA (3.3 m m⁻¹ s⁻¹) in artificial cerebrospinal fluid (CSF) were almost constant in a concentration range from 0.5 to 5 m m at 37 °C and 4.7 T. In human plasma, the relaxivity values increased when the concentrations of these Mn chelates were decreased, suggesting the presence of free Mn²âº bound with serum albumin. Mn-HIDA and Mn-citrate demonstrated a tendency for better contractility when employed with an isolated perfused frog heart, compared with MnCl2. Only minimal changes were demonstrated after a venous infusion of 100 m m Mn-citrate or Mn-HIDA (8.3 µmol kg⁻¹ min⁻¹) in rats and a constant heart rate, arterial pressure and sympathetic nerve activity were maintained, even after breaking the blood-brain barrier (BBB). Mn-citrate and Mn-HIDA could not cross the intact BBB and appeared in the CSF, and then diffused into the brain parenchyma through the ependymal layer. The responses in the supraoptic nucleus induced by the hypertonic stimulation were detectable. Therefore, Mn-citrate and Mn-HIDA appear to be better choices for maintaining the vital conditions of experimental animals, and they may improve the reproducibility of manganese-enhanced MRI of the small nuclei in the hypothalamus and thalamus.

Chronic oestrogen replacement in ovariectomised rats attenuates food intake and augments c-Fos expression in the suprachiasmatic nucleus specifically during the light phase.

Oestrogen replacement in ovariectomised (OVX) rats has been reported to attenuate food intake, especially during the light phase. To gain better insight into the central mechanism of oestrogen-induced reduction of food intake, we examined the effect of chronic oestrogen replacement in OVX rats on c-Fos expression in the suprachiasmatic nucleus (SCN) and on food intake during the light and dark phases. Eight-week-old female rats were ovariectomised and implanted with either an oestradiol (E2) or a vehicle pellet (Veh) subcutaneously. The animals were housed in an environment with a 12 h light-12 h dark cycle with the lights on at 07.00 hours. The amount of spontaneous food intake relative to each animal's body weight was significantly less for the E2 group than for the Veh group during the light phase, but there were no differences shown between these groups during the dark phase. There were no differences shown in the number of c-Fos-immunoreactive cells in the SCN in the E2 group compared with the Veh group during the early dark phase (22.00 hours; Zeitgeber time 15.00 (ZT15)), but the number was significantly higher than in the Veh group during the early light phase (10.00 hours; ZT3). This finding suggests that chronic oestrogen replacement chronically enhances SCN activity, specifically during the light phase. The oestrogen-induced enhancement of SCN activity during the light phase is possibly involved in the light phase-specific attenuation of food intake by oestrogen replacement in OVX rats.

Mn-bicine: a low affinity chelate for manganese ion enhanced MRI.

The toxicity of free Mn(2+) is a bottleneck for the in vivo application of manganese ion enhanced MRI. To reduce free Mn(2+) concentration ([Mn(2+) ]), a low affinity chelate reagent: N,N-bis(2-hydroxyethyl)glycine (bicine) was used. Considering the conditional association constant of Mn-bicine at pH 7.4 (10(2.9) M(-1) ), (i) a 100 mM Mn-bicine solution should contain about 10 mM of free manganese ion, but (ii) free manganese will make up 3/4 of the final plasma concentration (0.5 mM) with an intravenous infusion of 100 mM Mn-bicine. The T(1) relaxivity of Mn-bicine in a 5 mM Mn-bicine solution was estimated as 5 mM(-1) sec(-1) at 24°C, 7 T in a pH range of 6.8-7.5. Mn-bicine demonstrated a tendency for better contractility when employed with an isolated perfused frog heart, compared with MnCl(2) . A venous infusion of 100 mM Mn-bicine (8.3 µmol kg(-1) min(-1) ) showed a minimal decrease and maintained a constant heart rate level and arterial pressure in rats, while rats infused with 100 mM of MnCl(2) showed a significant suppression of the hemodynamic functions. Thus, Mn-bicine appears to be a better choice for maintaining the vital conditions of experimental animals, and may improve the reproducibility of manganese ion enhanced MRI.

Lateral diffusion of manganese in the rat brain determined by T(1) relaxation time measured by (1)H MRI.

In order to optimize manganese ion-enhanced MRI in thalamic and hypothalamic nuclei, we analyzed the diffusion of manganese in the brain followed by the intra-cerebroventricular application of manganese-bicine (Mn-bicine). T(1)-weighted MRI intensities, with 9-pixel ROIs in the hypothalamus perpendicular to the third ventricle, were measured during continuous infusion of Mn-bicine solution in the lateral cerebroventricle. Using a relationship between the image intensity of T(1)-weighted MRI and T(1) relaxation time, the image intensity was converted into the concentration of manganese. Assuming a simple diffusion process, the apparent diffusion coefficient (D (ap)) of manganese (4.2 × 10(-5) mm(2) s(-1)) is much lower than that of water (6 × 10(-4) mm(2) s(-1)), and the D (ap) tended to decrease when the distance from the third ventricle increased. These results suggest (1) the Mn(2+) ion is trapped by neural cells during diffusion and (2) the manganese efflux is discharged from the brain via veins.

Plasma hyperosmolality elevates the internal temperature threshold for active thermoregulatory vasodilation during heat stress in humans.

Plasma hyperosmolality delays the response in skin blood flow to heat stress by elevating the internal temperature threshold for cutaneous vasodilation. This elevation could be because of a delayed onset of cutaneous active vasodilation and/or to persistent cutaneous active vasoconstriction. Seven healthy men were infused with either hypertonic (3% NaCl) or isotonic (0.9% NaCl) saline and passively heated by immersing their lower legs in 42 degrees C water for 60 min (room temperature, 28 degrees C; relative humidity, 40%). Skin blood flow was monitored via laser-Doppler flowmetry at sites pretreated with bretylium tosylate (BT) to block sympathetic vasoconstriction selectively and at adjacent control sites. Plasma osmolality was increased by approximately 13 mosmol/kgH(2)O following hypertonic saline infusion and was unchanged following isotonic saline infusion. The esophageal temperature (T(es)) threshold for cutaneous vasodilation at untreated sites was significantly elevated in the hyperosmotic state (37.73 +/- 0.11 degrees C) relative to the isosmotic state (36.63 +/- 0.12 degrees C, P < 0.001). A similar elevation of the T(es) threshold for cutaneous vasodilation was observed between osmotic conditions at the BT-treated sites (37.74 +/- 0.18 vs. 36.67 +/- 0.07 degrees C, P < 0.001) as well as sweating. These results suggest that the hyperosmotically induced elevation of the internal temperature threshold for cutaneous vasodilation is due primarily to an elevation in the internal temperature threshold for the onset of active vasodilation, and not to an enhancement of vasoconstrictor activity.

Involvement of central angiotensin II type 1 receptors in LPS-induced systemic vasopressin release and blood pressure regulation in rats.

The purpose of this study was to evaluate the involvement of central angiotensin II (ANG II) and ANG II type 1 (AT(1)) receptors in systemic release of arginine vasopressin (AVP) and blood pressure regulation during endotoxemia. LPS (150 microg/kg) was injected intravenously 30 min after intracerebroventricular (icv) losartan (50 microg), an AT(1) receptor antagonist, or subcutaneous (sc) captopril (50 mg/kg), an angiotensin-converting enzyme inhibitor. Rats with icv and sc saline injections served as control. LPS administration increased plasma AVP concentration from 2.1 +/- 0.2 to 15.2 +/- 2.5 pg/ml (60 min after LPS injection) without significant changes in plasma osmolality or hematocrit. LPS-induced AVP secretion was significantly attenuated by pretreatment with icv losartan (2.3 +/- 0.5 to 3.7 +/- 0.5 pg/ml) but was not attenuated after peripheral captopril treatment (2.2 +/- 0.6 to 17.6 +/- 4.2 pg/ml). LPS administration significantly decreased systolic blood pressure (SBP) by 22.7 +/- 5.4 mmHg after intravenous LPS injection in icv losartan-treated rats, while SBP remained unchanged in vehicle-treated or sc captopril-treated rats by intravenous LPS. These results indicate that central AT(1) receptors, not responsive to peripheral ANG II, play an important role in systemic AVP secretion and maintenance of blood pressure during endotoxemia.