Endogenous Angiotensin II‐induced p44/42 Mitogen‐Activated Protein Kinase Activation Mediates Sodium Appetite but not Thirst or Neurohypophysial Secretion in Male Rats

The renin–angiotensin–aldosterone system makes a critical contribution to body fluid homeostasis, and abnormalities in this endocrine system have been implicated in certain forms of hypertension. The peptide hormone angiotensin II (AngII) regulates hydromineral homeostasis and blood pressure by acting on both peripheral and brain targets. In the brain, AngII binds to the angiotensin type 1 receptor (AT1R) to stimulate thirst, sodium appetite and both arginine vasopressin (AVP) and oxytocin (OT) secretion. The present study used an experimental model of endogenous AngII to examine the role of p44/42 mitogen‐activated protein kinase (MAPK) as a signalling mechanism to mediate these responses. Animals were given a combined treatment of furosemide and a low dose of captopril (furo/cap), comprising a diuretic and an angiotensin‐converting enzyme inhibitor, respectively, to elevate endogenous AngII levels in the brain. Furo/cap induced p44/42 MAPK activation in key brain areas that express AT1R, and this effect was reduced with either a centrally administered AT1R antagonist (irbesartan) or a p44/42 MAPK inhibitor (U0126). Additionally, furo/cap treatment elicited water and sodium intake, and irbesartan markedly reduced both of these behaviours. Central injection of U0126 markedly attenuated furo/cap‐induced sodium intake but not water intake. Furthermore, p44/42 MAPK signalling was not necessary for either furo/cap‐ or exogenous AngII‐induced AVP or OT release. Taken together, these results indicate that p44/42 MAPK is required for AngII‐induced sodium appetite but not thirst or neurohypophysial secretion. This result may allow for the discovery of more specific downstream targets of p44/42 MAPK to curb sodium appetite, known to exacerbate hypertension, at the same time as leaving thirst and neurohypophysial hormone secretion undisturbed.     

Chronic Hyponatremia Causes Neurologic and Psychologic Impairments

Hyponatremia is the most common clinical electrolyte disorder. Once thought to be asymptomatic in response to adaptation by the brain, recent evidence suggests that chronic hyponatremia may be linked to attention deficits, gait disturbances, risk of falls, and cognitive impairments. Such neurologic defects are associated with a reduction in quality of life and may be a significant cause of mortality. However, because underlying diseases such as adrenal insufficiency, heart failure, liver cirrhosis, and cancer may also affect brain function, the contribution of hyponatremia alone to neurologic manifestations and the underlying mechanisms remain unclear. Using a syndrome of inappropriate secretion of antidiuretic hormone rat model, we show here that sustained reduction of serum sodium ion concentration induced gait disturbances; facilitated the extinction of a contextual fear memory; caused cognitive impairment in a novel object recognition test; and impaired long-term potentiation at hippocampal CA3–CA1 synapses. In vivo microdialysis revealed an elevated extracellular glutamate concentration in the hippocampus of chronically hyponatremic rats. A sustained low extracellular sodium ion concentration also decreased glutamate uptake by primary astrocyte cultures, suggesting an underlying mechanism of impaired long-term potentiation. Furthermore, gait and memory performances of corrected hyponatremic rats were equivalent to those of control rats. Thus, these results suggest chronic hyponatremia in humans may cause gait disturbance and cognitive impairment, but these abnormalities are reversible and careful correction of this condition may improve quality of life and reduce mortality.     

Neonatal oxytocin manipulations have long-lasting, sexually dimorphic effects on vasopressin receptors

Developmental exposure to oxytocin (OT) or oxytocin antagonists (OTAs) has been shown to cause long-lasting and often sexually dimorphic effects on social behaviors in prairie voles (Microtus ochrogaster). Because regulation of social behavior in monogamous mammals involves central receptors for OT, arginine vasopressin (AVP), and dopamine, we examined the hypothesis that the long-lasting, developmental effects of exposure to neonatal OT or OTA might reflect changes in the expression of receptors for these peptides. On postnatal day 1, prairie voles were injected intraperitoneally with either OT (1 mg/kg), an OTA (0.1 mg/kg), saline vehicle, or were handled only. At approximately 60 days of age, vasopressin V1a receptors, OT receptors (OTR) and dopamine D2 receptor binding were quantified using receptor autoradiography in brain tissue taken from males and females. Significant treatment effects on V1a binding were found in the bed nucleus of the stria terminalis (BNST), cingulate cortex (CgCtx), mediodorsal thalamus (MdThal), medial preoptic area of the hypothalamus (MPOA), and lateral septum (LS). The CgCtx, MPOA, ventral pallidum, and LS also showed significant sex by treatment interactions on V1a binding. No significant treatment or sex differences were observed for D2 receptor binding. No significant treatment difference was observed for OTR receptor binding, and only a marginal sex difference. Changes in the neuropeptide receptor expression, especially the V1a receptor, may help to explain sexually dimorphic changes in behavior that follow comparable neonatal manipulations.     

The changes in,and relationship between,plasma nitric oxide and corticotropin‐releasing hormone in patients with major depressive disorder

There is strong evidence of roles of the hypothalamus‐pituitary‐adrenal axis and nitric oxide (NO) synthase‐NO system in depression, but the relationship between them is unknown. The aim of this study, therefore, was to elucidate whether there is any correlation between NO and corticotropin‐releasing hormone (CRH) in major depressive disorder (MDD) patients. In 16 outpatients with MDD and 18 healthy controls, the plasma amino acids citrulline (Cit) and arginine (Arg) were determined by high‐performance liquid chromatography, and CRH levels was measured by radioimmunoassay. The Cit/Arg ratio was calculated as an index of NO synthesis. Correlations between NO and CRH were examined with the Spearman test. Before treatment, no significant correlation was observed between the plasma NO level and CRH levels in MDD patients. The plasma NO levels were significantly higher in MDD patients. A significant correlation was found between NO levels and Hamilton Depression Rating Scale (HAMD) scores in MDD patients. The plasma CRH levels were significantly higher in MDD patients than in controls. After monotherapy for 2 months, the NO levels had dramatically declined but were also higher than those in the controls. This study is the first report of the absence of a significant correlation between plasma NO and CRH levels, although both levels are elevated in MDD patients. Furthermore, the strong links between the plasma NO levels and the HAMD scores, as well as the increased NO reduction after remission, suggest that NO plays a key role in depression and may be an indicator of therapeutic success.     

Arginase and α‐smooth muscle actin induction after hyperoxic exposure in a mouse model of bronchopulmonary dysplasia

The L‐arginine/NO pathway is an important regulator of pulmonary hypertension, the leading cause of mortality in patients with the chronic lung disease of prematurity, bronchopulmonary dysplasia. L‐arginine can be metabolized by NO synthase (NOS) to form L‐citrulline and NO, a potent vasodilator. Alternatively, L‐arginine can be metabolized by arginase to form urea and L‐ornithine, a precursor to collagen and proline formation important in vascular remodelling. In the current study, we hypothesized that C3H/HeN mice exposed to prolonged hyperoxia would have increased arginase expression and pulmonary vascular wall cell proliferation. C3H/HeN mice were exposed to 14 days of 85% O₂ or room air and lung homogenates analyzed by western blot for protein levels of arginase I, arginase II, endothelial NOS (eNOS), ornithine decarboxylase (ODC), ornithine aminotransferase (OAT), and α‐smooth muscle actin (α‐SMA). Hyperoxia did not change arginase I or eNOS protein levels. However, arginase II protein levels were 15‐fold greater after hyperoxia exposure than in lungs exposed to room air. Greater protein levels of ODC and OAT were found in lungs following hyperoxic exposure than in room air animals. α‐SMA protein levels were found to be 7‐fold greater in the hyperoxia exposed lungs than in room air lungs. In the hyperoxia exposed lungs there was evidence of greater pulmonary vascular wall cell proliferation by α‐SMA immunohistochemistry than in room air lungs. Taken together, these data are consistent with a more proliferative vascular phenotype, and may explain the propensity of patients with bronchopulmonary dysplasia to develop pulmonary hypertension.     

A novel Tc‐99m and fluorescence‐labeled arginine‐arginine‐leucine‐containing peptide as a multimodal tumor imaging agent in a murine tumor model

We developed a Tc‐99m and TAMRA‐labeled peptide, Tc‐99m arginine‐arginine‐leucine (RRL) peptide (TAMRA‐GHEG‐ECG‐RRL), to target tumor cells and evaluated the diagnostic performance of Tc‐99m TAMRA‐GHEG‐ECG‐RRL as a dual‐modality imaging agent for tumor in a murine model. TAMRA‐GHEG‐ECG‐RRL was synthesized using Fmoc solid‐phase peptide synthesis. Binding affinity and in vitro cellular uptake studies were performed. Gamma camera imaging, biodistribution, and ex vivo imaging studies were performed in murine models with PC‐3 tumors. Tumor tissue slides were prepared and analyzed with immunohistochemistry using confocal microscopy. After radiolabeling procedures with Tc‐99m, Tc‐99m TAMRA‐GHEG‐ECG‐RRL complexes were prepared in high yield (>96%). The K_d of Tc‐99m TAMRA‐GHEG‐ECG‐RRL determined by saturation binding was 41.7 ± 7.8 nM. Confocal microscopy images of PC‐3 cells incubated with TAMRA‐GHEG‐ECG‐RRL showed strong fluorescence in the cytoplasm. Gamma camera imaging revealed substantial uptake of Tc‐99m TAMRA‐GHEG‐ECG‐RRL in tumors. Tumor uptake was effectively blocked by the coinjection of an excess concentration of RRL. Specific uptake of Tc‐99m TAMRA‐GHEG‐ECG‐RRL was confirmed by biodistribution, ex vivo imaging, and immunohistochemistry stain studies. In conclusion, in vivo and in vitro studies revealed substantial uptake of Tc‐99m TAMRA‐GHEG‐ECG‐RRL in tumors. Tc‐99m TAMRA‐GHEG‐ECG‐RRL has potential as a dual‐modality tumor imaging agent.     

Regional and Systemic Haemodynamic Effects of Some Vasopressins: Structural Features of the Hormone which Prolong Activity

Abstract. Cardiac output and regional blood flows to myocardium, gut, uterus and kidney were determined in anaesthetised female rats by a single injection of ⁸⁶RbCl. The haemodynamic responses were measured at various time intervals up to 2 h after single I. V. injections of lysine-vasopressin and the following of its analogues: a) with extended peptide chains at the N-terminal (including “hormonogens”) N^a-glycyl-glycyl-glycyl-lysine-vasopressin, N^a-glycyl-glycyl-glycyl-arginine-vasopressin and N^a-D-valyl-lysine-vasopressin, b) “carba” modifications desamino-carba⁶-arginine-vasopressin, desamino-carba⁶-D-arginine⁸-vasopressin, desamino-carba⁶-ornithine⁸-vasopressin, desamino-dicarba-arginine-vasopressin and c) other steric alterations - desamino-D-arginine⁸-vasopressin and desamino-N-methylarginine⁸-vasopressin. Sub-pressor doses of lysine-vasopressin were followed by marked reductions in gut and uterus blood flows which reached a peak at 10 min. and had completely receded by 60 min. The presence of steric alterations in the C-terminal tripeptide of the molecule- D-arginine or N-methylarginine in sequence position 8- practically completely eliminated vascular activity. The same was true for N^a-D-valyl-lysine-vasopressin. None of the latter three analogues showed any inhibitor properties to the action of lysine-vasopressin. The two hormonogens (triglycyl N-terminal extensions) had to be given in doses 10 times greater to obtain a vasoconstrictor effect in gut and uterus equivalent in amplitude to that of lysine-vasopressin, but this effect was still present to the same degree 2 h later with the hormonogen of lysine-vasopressin, and was only starting to return to baseline values at the same time with the arginine-vasopressin hormonogen. The vascular potency of both mono-carba L-analogues was higher than that of lysine-vasopressin, and the effect was as prolonged as with the hormonogens. The dicarba analogue also showed a prolonged action, but with much reduced potency. No significant changes in renal or myocardial blood flows were observed at all. Molecular features of vasopressin smooth muscle activity were discussed, and a receptor model was proposed. It was suggested that the -S-S-, -SCH2 and -CH₂CH₂-bridges in the above analogues are not directly bound in the peptide-receptor complex and constitute the limiting factor determining complex duration, or persistence of the active peptide in the “receptor compartment”. These results provide an experimental basis for possible clinical application of triglycyl-vasopressin and carba-vasopressin in bleeding from both gut and uterus and for induction of menstruation.     

垂体后叶素在腹腔镜下卵巢囊肿剥除术中的应用研究

目的探讨经腹腔镜行卵巢囊肿剥除术中垂体后叶素的使用价值。方法回顾分析经腹腔镜卵巢囊肿剥除术120例的临床资料,随机分为观察组和对照组各60例。观察组巧克力囊肿20例、畸胎瘤20例、卵巢单纯性囊肿20例,均为单侧。对照组巧克力囊肿20例、畸胎瘤20例、卵巢单纯性囊肿20例,也均为单侧。观察组分别于卵巢囊肿剥除前在正常卵巢皮质与囊肿壁间注射垂体后叶素稀释液（浓度15%）,然后行囊肿剥除术,对照组直接剥除。比较两组手术时间、术中出血量、囊肿破裂率、术后卵巢功能。卵巢功能的判断采取术前及术后月经恢复情况及术后3、6、12个月测定的卵泡刺激素（FSH）水平。结果观察组手术时间、术中出血量、术中肿块破裂率、术后月经恢复天数明显少于对照组（P〈0.05）,术后住院天数两组差异无统计学意义（P〉0.05）;术前和术后的FSH水平在对照组存在显著差异（P〈0.05）,在观察组差异不大（P〉0.05）。结论使用垂体后叶素注射分离法在腹腔镜下卵巢囊肿剥除术中能达到易于分离、较好止血及减少卵巢功能伤害。     

Antagonists of the Vasopressin V1 Receptor and of the β1-Adrenoceptor Inhibit Cytotoxic Brain Edema in Stroke by Effects on Astrocytes – but the Mechanisms Differ

Brain edema is a serious complication in ischemic stroke because even relatively small changes in brain volume can compromise cerebral blood flow or result in compression of vital brain structures on account of the fixed volume of the rigid skull. Literature data indicate that administration of either antagonists of the V1 vasopressin (AVP) receptor or the β₁-adrenergic receptor are able to reduce edema or infarct size when administered after the onset of ischemia, a key advantage for possible clinical use. The present review discusses possible mechanisms, focusing on the role of NKCC1, an astrocytic cotransporter of Na⁺, K⁺, 2Cl^- and water and its activation by highly increased extracellular K⁺ concentrations in the development of cytotoxic cell swelling. However, it also mentions that due to a 3/2 ratio between Na⁺ release and K⁺ uptake by the Na⁺,K⁺-ATPase driving NKCC1 brain extracellular fluid can become hypertonic, which may facilitate water entry across the blood-brain barrier, essential for development of edema. It shows that brain edema does not develop until during reperfusion, which can be explained by lack of metabolic energy during ischemia. V1 antagonists are likely to protect against cytotoxic edema formation by inhibiting AVP enhancement of NKCC1-mediated uptake of ions and water, whereas β₁-adrenergic antagonists prevent edema formation because β₁-adrenergic stimulation alone is responsible for stimulation of the Na⁺,K⁺-ATPase driving NKCC1, first and foremost due to decrease in extracellular Ca²⁺ concentration. Inhibition of NKCC1 also has adverse effects, e.g. on memory and the treatment should probably be of shortest possible duration.     

Glyoxal-induced formation of advanced glycation end-products in type 1 collagen decreases both its strength and flexibility in vitro

The high plasma glucose induced in glucose metabolism disorders leads to the non-enzymatic glucose-dependent modification (glycation) of type 1 collagen, which is an essential component of bone tissue. The glycation of proteins induces the formation of advanced glycation end-products, such as carboxymethyl arginine, which is preferentially generated in glycated collagen. However, the effect of advanced glycation end-product formation on the characteristics of type 1 collagen remains unclear due to the lack of suitable in vitro experimental systems analyzing type 1 collagen. Here, we show that the glycation of type 1 collagen can be analyzed in vitro using a goldfish-scale bone model. Our study using these scales provides evidence that the advanced glycation end-product formation in type 1 collagen induced by glyoxal, the carboxymethyl arginine inducer, facilitates the crosslinking of type 1 collagen, decreasing both its strength and flexibility.