Contribution of estrogen receptors alpha and beta in the brain response to traumatic brain injury

OBJECT

Although there is evidence that estradiol has neuroprotective effects after traumatic brain injury (TBI) in female rats, it is unclear which estrogen receptor (ER) subtype, ERα or ERβ, mediates this effect. The authors therefore examined the roles of the different ERs in this effect. Here the authors used the ERα selective agonist propyl pyrazole triol (PPT) and the ERβ selective agonist diarylpropionitrile (DPN) alone and in combination in female rats to investigate this question.

METHODS

Before the ovariectomized animals were injured using the Marmarou TBI technique, they were randomly divided into the following 9 groups: control, sham, TBI, vehicle, E1 (physiological dose of 17-β estradiol), E2 (pharmacological dose of 17-β estradiol), PPT, DPN, and PPT+DPN. Levels of blood-brain barrier (BBB) disruption (5 hours) and water content (24 hours) were evaluated after TBI. In groups receiving drugs or vehicle, treatment was administered as a single dose intraperitoneally 30 minutes after induction of TBI.

RESULTS

Results showed that brain edema or brain water content after TBI was lower (p < 0.001) in the E2, PPT, DPN, and PPT+DPN groups than it was in the vehicle group. After trauma, the Evans blue dye content or BBB permeability was significantly higher in the TBI and vehicle groups (p < 0.001) than in the E2, PPT, DPN, and PPT+DPN groups. The inhibitory effects of PPT+DPN on brain water content, neurological scores, and Evans blue dye content were the highest for all groups. Although both PPT and DPN increased neurological scores after TBI, PPT appears to be more effective in increasing neurological scores.

CONCLUSIONS

Neuroprotective effects of estradiol on brain edema, BBB permeability, and neurological scores are mediated through both ERα and ERβ. This may suggest a therapeutic potential in the brain trauma for ER-specific agonists.

Effect of orally administered propylthiouracil in pregnant and lactating rats on isolated aorta contractility of their adult male offspring

BACKGROUND

The effect of propylthiouracil (PTU) administration to pregnant and lactating rats on isolated aorta contractility of their adult offspring was investigated.

MATERIAL/METHODS

Three groups of female rats were selected; in the fetal group (FG), PTU was added to their drinking water during gestation; in the neonatal group (NG), PTU was added to the mothers' drinking water for 25 days after delivery; untreated rats were controls (CG). Thyroid hormone concentrations were measured in the sera of the mothers and their adult offspring. Aortic contractility of the offspring was measured with an isometric transducer in the presence of different concentrations of potassium chloride (KCl) and phenylephrine.

RESULTS

The mothers were hypothyroid at the time of PTU cessation. Thyroid hormone levels in offspring were not significantly different from those of controls except for TSH, which was significantly (p<0.05) higher in the FG offspring. Recorded tension in FG offspring with 5, 10, 20, 40, and 60 mmol/l KCl were 0.21+/-0.02, 0.75+/-0.07, 1.07+/-0.07, 1.38+/-0.08, and 1.5+/-0.09 g/mm2, respectively, significantly (p<0.05) lower than the control values (0.43+/-0.05, 1.19+/-0.17, 1.76+/-0.23, 2.06+/-0.22, 2.5+/-0.09). Aortic contractility with 10-8, 10-7, and 10-6 mmol/l of phenylephrine in the FG offspring were 0.6+/-0.13, 1.4+/-0.15, and 1.8+/-0.15 g/mm2, significantly lower than control values (1.24+/-0.19, 2.3+/-0.25, 2.6+/-0.28). Contractility of the NG aorta did not differ significantly from controls.

CONCLUSIONS

Hypothyroidism during the fetal period has significant effects on the differentiation and development of the vascular bed (aorta), the long-term effects of which can still be observed during adulthood.

Serum nitric oxide metabolites in subjects with metabolic syndrome

OBJECTIVES

Evidence are available showing that higher nitric oxide production is associated with metabolic disorders. The aim of this study was to determine serum nitric oxide metabolites (NOx) concentration in subjects with metabolic syndrome (MetS).

DESIGN AND METHODS

In a cross-sectional study, NOx was measured in 3505 subjects, aged 20-94 years, using the Griess reaction. After excluding subjects taking medications for hypertension and dyslipidemia, data for 3148 subjects were analyzed.

RESULTS

There was a direct association between the numbers of metabolic risk factors and serum NOx values in both genders (p for trend<0.05). After multivariable adjustment, serum NOx concentration was significantly higher in subjects with MetS [(31.9 (29.4-34.6) vs. 29.8 (27.6-32.1), p<0.01) or type 2 diabetes (34.6 (31.3-38.2) vs. 30.2 (27.9-32.6), p<0.001) as compared to their corresponding controls.

CONCLUSIONS

Higher NOx concentrations in subjects with MetS and type 2 diabetes support the existing hypothesis that NO overproduction affects insulin's metabolic actions.

Possible role of carbonic anhydrase in rat pancreatic islets: enzymatic, secretory, metabolic, ionic, and electrical aspects

The presence of carbonic anhydrase (type V) was recently documented in rat and mouse pancreatic islet beta-cells by immunostaining and Western blotting. In the present study, the activity of carbonic anhydrase was measured in rat islet homogenates and shown to be about four times lower than in rat parotid cells. The pattern for the inhibitory action of acetazolamide on carbonic anhydrase activity also differed in islet and parotid cell homogenates, suggesting the presence of different isoenzymes. NaN3 inhibited carbonic anhydrase activity in islet homogenates and both D-[U-14C]glucose oxidation and glucose-stimulated insulin secretion. Acetazolamide (0.3-10.0 mM) also decreased glucose-induced insulin output but failed to affect adversely D-[U-14C]glucose oxidation, although it inhibited the conversion of D-[5-3H]glucose to [3H]OH and that of D-[U-14C]glucose to acidic metabolites. Hydrochlorothiazide (3.0-10.0 mM), which also caused a concentration-related inhibition of the secretory response, like acetazolamide (5.0-10.0 mM), decreased H(14)CO3- production from D-[U-14C]glucose (16.7 mM). Acetazolamide (5.0 mM) did not affect the activity of volume-sensitive anion channels in beta-cells but lowered intracellular pH and adversely affected both the bioelectrical response to d-glucose and its effect on the cytosolic concentration of Ca2+ in these cells. The lowering of cellular pH by acetazolamide, which could well be due to inhibition of carbonic anhydrase, might in turn account for inhibition of glycolysis. The perturbation of stimulus-secretion coupling in the beta-cells exposed to acetazolamide may thus involve impaired circulation in the pyruvate-malate shuttle, altered mitochondrial Ca2+ accumulation, and perturbation of Cl- fluxes, resulting in both decreased bioelectrical activity and insulin release.

Effect of chronic restraint stress on carbohydrate metabolism in rat

There is some evidence suggesting that stress may induce diabetes mellitus; the effects of restraint stress however need to be investigated. The present study investigates the role of chronic restraint stress on carbohydrate metabolism in male rats. The animals of the stressed group (n=8) were exposed to different restraint stressors (1 h twice daily) for 30 days. On days 1, 15 and 30, before stress exposure, the animals were weighed and fasting blood samples were obtained by tail snipping and subsequently oral glucose tolerance tests (OGTT) were carried out. Fasting plasma glucose levels on the 15th day and the plasma glucose concentrations, on the 15th and 30th days of the experiment at 15 and 60 min following OGTT, in the stressed group, were significantly higher as compared to the control group. In the stressed group, fasting plasma insulin levels on the 15th and 30th days of the experiment and the plasma insulin concentrations, on the 15th day at 15 and 60 min after performing OGTT, were significantly lower as compared to the control group. Fasting plasma corticosterone concentrations were significantly increased on the 15th day of the experiment in the stressed rats as compared to the control rats and to concentrations on the 1st day. The weights of the stressed rats on the 15th and 30th experimental days were significantly lower than the controls. In conclusion, chronic restraint stress for 30 days leads to low body weight gain in rats and impairs glucose metabolism perhaps by affecting corticosterone and insulin secretion and by inducing a degree of insulin resistance.

Behavioral and electrophysiological studies of chronic oral administration of L-type calcium channel blocker verapamil on learning and memory in rats

It has been shown that L-type voltage dependent calcium channels (VDCCs) have important role in learning and memory. In vivo and in vitro electrophysiological recordings of hippocampal neurons have demonstrated their involvement in long-term potentiation (LTP), which considers being one possible cellular mechanism underlying learning and memory. The long-term effect of VDCCs of hippocampal dentate gyrus (DG) so far on synaptic plasticity has not received much attention. In this study, the effect of chronic (60 days) oral administration of L-type calcium channel blocker verapamil on learning and memory and synaptic plasticity of hippocampal dentate gyrus in rats has been investigated. L-type calcium channel antagonist, verapamil chronically and orally at different doses (10, 20 and 50 mg/kg) was used to investigate learning and memory by passive avoidance learning. LTP in perforant-DG synapses was assessed (by either 200 or 400 Hz tetanization) in order to investigate long-term effect of verapamil on synaptic plasticity. In this case, field excitatory postsynaptic potential (fEPSP) slope and population spike (PS) amplitude were measured. Our behavioral study has shown that chronic oral treatment of verapamil has no effect on learning whereas verapamil (50 mg/kg) decreased memory retrieval. Verapamil (20 and 50 mg/kg) inhibited EPSP-LTP induction at 400 Hz but not at 200 Hz tetanization. Furthermore, only verapamil (50mg/kg) decreased PS-LTP with respect to control group. These data suggest that 400 Hz LTP is required for activation of L-type VDCCs and it seems that verapamil is more effective on L-type calcium channels of DG dendrites than their soma.

Effects of administration of oral magnesium on plasma glucose and pathological changes in the aorta and pancreas of diabetic rats

1. Magnesium deficiency has recently been proposed as a novel factor implicated in the pathogenesis of the complications of diabetes. The purpose of the present study was to determine the relationship between oral Mg supplementation and changes in plasma glucose, calcium, haemoglobin, Ca/Mg ratio, blood pressure and the histology of the pancreas and vascular system in streptozotocin-induced diabetic rats. 2. Ten days after the induction of diabetes in male Wistar rats, half the diabetic animals were divided into six groups, receiving 0, 1, 3, 10, 30 or 50 g/L MgSO4 added into the drinking water for 8 weeks. Plasma glucose and Mg were measured at days 1, 2, 3, 5, 7, 14 and 21 to find the optimum dose of Mg and the time-course of its effect. In addition, histological observations were undertaken. Eight weeks later, all animals were decapitated, the pancreas and thoracic aorta were removed carefully and immersed immediately in 10% formaldehyde for histological study. 3. To evaluate the effects of Mg on plasma glucose, calcium, haemoglobin, Mg and blood pressure, another group of animals was divided into four experimental groups, as follows: (i) non-diabetic controls received tap water for 8 weeks; (ii) acute diabetics received tap water for 10 days; (iii) chronic diabetic controls received tap water for 8 weeks; and (iv) Mg-treated chronic diabetic rats received 10 g/L MgSO4 added into the drinking water 10 days after the induction of diabetes for 8 weeks. 4. Magnesium dose dependently affects plasma glucose levels. The peak effect was reached during the first 24 h following oral administration. Administration of 10 g/L MgSO4 results in the return of normal structure in the diabetic pancreas and aorta. Moreover, this concentration of MgSO4 causes glucose, haemoglobin, calcium, the Ca/Mg ratio and blood pressure to reach normal levels. Although the Mg level increases slightly following the administration of 10 g/L MgSO4 to diabetic rats, it never reaches control levels. 5. On the basis of the results of the present study, it may be concluded that chronic Mg administration may have beneficial effects on diabetes.

Oral magnesium administration prevents vascular complications in STZ-diabetic rats

Vascular disease is one of the complicating features of diabetes mellitus. Magnesium deficiency has recently been proposed as a novel factor implicated in the pathogenesis of diabetes complications. Several studies have indicated that hypertension in diabetic patients is an independent altered reaction of blood vessels to neurotransmitters and circulating hormones. Since magnesium has been proposed to decrease vascular sensitivity to vasoconstrictor agents, the present study was designed to determine whether chronic magnesium sulfate administration could prevent vascular complications of STZ-induced diabetes in rats. The animals were divided into six groups: two groups served as controls and received tap water for 8 weeks, while in the other four groups, made diabetic with a single IV injection of 40 mg/kg STZ, two groups treated with magnesium sulfate (10 g/L) added to the drinking water, and the other two groups received tap water only. After 8 weeks, in 3 groups (control, diabetic and Mg-treated), left common carotid artery was cannulated for continuous recording of blood pressure. All animals in these groups were decapitated and blood samples were drawn for glucose, Ca and Mg measurements. In the 3 remaining groups (again divided into control, diabetic and Mg-treated), the mesenteric vascular bed was perfused according to the McGregor method, and descending thoracic aortas were used for measurement of elasticity. In diabetic rats, plasma glucose was significantly increased and plasma magnesium was significantly decreased compared to controls and Mg-treated animals. Although plasma magnesium of Mg-treated animals increased significantly, it failed to reach to the magnesium level of the control group. Ca/Mg ratio was also increased compared to the control and Mg-treated animals. Mean arterial blood pressure in diabetics was significantly higher than control and Mg-treated rats. Similarly, there was a significant difference in mean arterial blood pressure of Mg-treated rats compared to control animals. Baseline perfusion pressure of diabetic group was significantly higher than control and Mg-treated groups with intact and denuded endothelium. Magnesium sulfate treatment decreased mean perfusion pressure of mesenteric vascular bed in intact and denuded endothelium in comparison with non-treated diabetic rats. There was a significant increase in passive tension in the aorta of diabetic rats compared to control and Mg-treated rats. However, there was no significant difference between Mg-treated and control rats. From the results of this study it may be concluded that magnesium could control STZ-induced diabetes and prevent its vascular complications.

Relaxatory effect of magnesium on mesenteric vascular beds differs from normal and streptozotocin induced diabetic rats

Magnesium deficiency has recently been proposed as a novel factor implicated in the pathogenesis of diabetes complications. Previous studies have shown that magnesium decreases basal tone in normal isolated aortic rings and reduces phenylephrine-induced contraction. The mechanism of this magnesium action is not very well known. The present study was designed to determine the role of endothelium and nitric oxide in magnesium sulfate-induced vasorelaxation in diabetic rat vessels. Diabetes was induced by a single tail injection of streptozotocin. Eight weeks later, superior mesenteric arteries of control and diabetic animals were isolated and perfused according to the McGregor method. Prepared vascular beds were constricted with phenylephrine to induce 70-75% of maximal constriction. Magnesium sulfate at concentrations of 0.001 M to 0.1 M was added into the medium and perfusion pressure was then recorded. Mesenteric bed baseline perfusion pressure in intact and denuded endothelium of diabetic groups was higher than controls. In all groups, relaxant response to magnesium in mesenteric bed was attenuated after endothelium removal, but a relaxatory effect appears at high concentration. In the presence of N (omega)-nitro-L-arginine methyl ester (L-NAME), magnesium-induced relaxation was significantly suppressed in intact mesenteric bed of control animals but in diabetics, the relaxant response was slightly inhibited. From the results of this study, it can be concluded that magnesium-induced endothelium dependent and endothelium independent vasorelaxation are mediated by nitric oxide in control rats while in diabetic animals other mechanisms may be involved.