Noreen F. Rossi

Regulation of blood pressure and salt homeostasis by endothelin.

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

The role of hypoxia-inducible factor-1α, aquaporin-4, and matrix metalloproteinase-9 in blood-brain barrier disruption and brain edema after traumatic brain injury

OBJECT The present study investigated the role of hypoxia-inducible factor-1α (HIF-1α), aquaporin-4 (AQP-4), and matrix metalloproteinase-9 (MMP-9) in blood-brain barrier (BBB) permeability alterations and brain edema formation in a rodent traumatic brain injury (TBI) model. METHODS The brains of adult male Sprague-Dawley rats (400-425 g) were injured using the Marmarou closed-head force impact model. Anti-AQP-4 antibody, minocycline (an inhibitor of MMP-9), or 2-methoxyestradiol (2ME2, an inhibitor of HIF-1α), was administered intravenously 30 minutes after injury. The rats were killed 24 hours after injury and their brains were examined for protein expression, BBB permeability, and brain edema. Expression of HIF-1α, AQP-4, and MMP-9 as well as expression of the vascular basal lamina protein (laminin) and tight junction proteins (zona occludens-1 and occludin) was determined by Western blotting. Blood-brain barrier disruption was assessed by FITC-dextran extravasation, and brain edema was measured by the brain water content. RESULTS Significant (p < 0.05) edema and BBB extravasations were observed following TBI induction. Compared with sham-operated controls, the injured animals were found to have significantly (p < 0.05) enhanced expression of HIF-1α, AQP-4, and MMP-9, in addition to reduced amounts (p < 0.05) of laminin and tight junction proteins. Edema was significantly (p < 0.01) decreased after inhibition of AQP-4, MMP-9, or HIF-1α. While BBB permeability was significantly (p < 0.01) ameliorated after inhibition of either HIF-1α or MMP-9, it was not affected following inhibition of AQP-4. Inhibition of MMP reversed the loss of laminin (p < 0.01). Finally, while inhibition of HIF-1α significantly (p < 0.05) suppressed the expression of AQP-4 and MMP-9, such inhibition significantly (p < 0.05) increased the expression of laminin and tight junction proteins. CONCLUSIONS The data support the notion that HIF-1α plays a role in brain edema formation and BBB disruption via a molecular pathway cascade involving AQP-4 and MMP-9. Pharmacological blockade of this pathway in patients with TBI may provide a novel therapeutic strategy.

Syndrome of inappropriate antidiuretic hormone secretion in children following spinal fusion

OBJECTIVES a) To determine if antidiuretic hormone (ADH) is elevated in patients undergoing spinal fusion, especially in those who have clinical evidence of syndrome of inappropriate antidiuretic hormone (SIADH); b) to evaluate the relationship between ADH secretion and the secretion of atrial natriuretic peptide (ANP). SETTING Tertiary care pediatric intensive care unit (ICU) in a university hospital. DESIGN A prospective cross-sectional, observational study with factorial design. PATIENTS Thirty patients > or = 10 yrs of age undergoing spinal fusion admitted to the ICU for postoperative care. INTERVENTIONS Patients underwent anterior, posterior, or both anterior/posterior spinal fusion. Blood was collected for serial measurements of ADH, ANP and serum electrolyte levels. Heart rate, blood pressure and central venous pressure were measured. MEASUREMENTS AND MAIN RESULTS Thirty children were studied. Nineteen had idiopathic scoliosis, nine had neuromuscular scoliosis, one had Marfans disease, and one had congenital scoliosis. Ten (33%) children met clinical criteria of SIADH. There was no difference in duration of surgery, blood loss, volume of iv fluid administration pre- and intraoperatively, or type of scoliosis between those who developed SIADH and those who did not. Hemodynamic variables were similar in both groups. ADH levels increased in both groups immediately postoperatively and at 6 hrs after surgery, but were much more elevated in those patients with SIADH. Patients with SIADH also had significantly higher ADH levels preoperatively. In relation to serum osmolality, ADH was considerably higher in those with SIADH compared with those who did not. Although ANP values tended to be higher in the group with SIADH, this did not reach statistical significance. CONCLUSION SIADH occurs in a subset of children who undergo spinal fusion. The diagnosis of SIADH can be made easily using clinical parameters which are well-defined. In the face of SIADH, continued volume expansion may be harmful, and should therefore be avoided.

Effect of endothelin‐3 on vasopressin release in vitro and water excretion in vivo in Long‐Evans rats.

1. The endothlins (ETs) are a family of homologous peptides originally isolated and purified from cultured porcine endothelial cells. Although initial studies focused on the ETs as potent vasoconstrictor substances, recent findings support a role for ET in vasopressin (AVP) secretion and action. We used cultured explants of the hypothalamo‐neurohypophysial complex (HNC) to examine the effects of ET‐3 on AVP release. 2. ET‐3 produced a significant and concentration‐dependent rise in AVP release from the explants of Long‐Evans rats at 48 h, independent of medium osmolality. AVP release during two sequential control periods did not differ, and osmotically stimulated AVP release was comparable to that exhibited by HNC explants from Sprague‐Dawley rats. ET‐3 (1 nM) induced a 3‐fold rise in AVP that was completely blocked by rabbit antiET serum, which did not alter basal AVP secretion. 3. Clearance experiments were performed in anaesthetized water‐loaded rats given a non‐pressor dose of ET‐3 (0.40 nmol (kg body weight)‐1 intravenously). The means of body weight, arterial blood pressure, plasma Na+ concentrations, and plasma osmolalities did not differ between the first and second periods nor among the groups. Despite no changes in renal plasma flow and inulin clearance, free water clearance significantly increased in the ET‐treated group. This response could not be attributed to changes in osmolal clearances or Na+ reabsorption. The concurrent administration of antiET serum not only blocked this effect, but was associated with the free water clearance falling significantly below the pretreatment level. 4. Taken together, our in vivo and in vitro findings support the hypothesis that ET‐3 stimulates AVP secretion. Furthermore, our data are consistent with the site of action of ET‐3 residing within the blood‐brain barrier, though an independent effect by a higher concentration of ET at neural loci outside the barrier cannot be totally excluded. Finally, the subpressor dose of ET‐3 amplifies free water excretion independent of systemic and renal haemodynamics, Na+ excretion, osmolal clearance, or circulating AVP levels.

Maternal protein restriction leads to hyperresponsiveness to stress and salt-sensitive hypertension in male offspring

Low birth weight humans often exhibit hypertension during adulthood. Studying the offspring of rat dams fed a maternal low-protein diet is one model frequently used to study the mechanisms of low birth weight-related hypertension. It remains unclear whether this model replicates key clinical findings of hypertension and increased blood pressure responsiveness to stress or high-salt diet. We measured blood pressure via radiotelemetry in 13-wk-old male offspring of maternal normal- and low-protein dams. Neither group exhibited hypertension at baseline; however, 1 h of restraint was accompanied by a significantly greater blood pressure response in low-protein compared with normal-protein offspring. To enhance the effect of a high-salt diet on blood pressure, normal- and low-protein offspring underwent right uninephrectomy, while controls underwent sham surgery. After 5 weeks on a high-salt diet (4% NaCl), mean arterial pressure in the Low-Protein+Sham offspring was elevated by 6 +/- 2 mmHg (P < 0.05 vs. baseline), while it remained unchanged in the normal-protein offspring. In the two uninephrectomized groups, blood pressure increased further, but was of similar magnitude. Glomerular filtration rate in the low-protein uninephrectomized offspring was 50% less than that in normal-protein offspring with intact kidneys. These data indicate that, while male low-protein offspring are not hypertensive during young adulthood, their blood pressure is hyperresponsive to restraint stress and is salt sensitive, and their glomerular filtration rate is more sensitive to hypertension-causing insults. Collectively, these may predispose for the development of hypertension later in life.

Short-Term Hypothyroidism and Vasopressin Gene Expression in the Rat

Hypothyroidism is associated with abnormalities in renal water handling, which include a delay in excretion of an acute water load, decreased urinary concentrating ability, and increased urine volume. In the present study, we investigated the role of vasopressin in aminotriazole-induced hypothyroidism by measuring vasopressin concentration in the plasma and pituitary along with vasopressin mRNA levels in the hypothalamus. After 5 weeks of aminotriazole treatment, L-thyroxine levels were significantly lower in the experimental animals (122 +/- 8 v 26 +/- 1 nmol/L [9.5 +/- 0.6 v 2.0 +/- 0.1 micrograms/dL]; P less than 0.001). Serum sodium (148 +/- 0.5 v 144 +/- 1.2 mmol/L [mEq/L]; P less than 0.01), and plasma osmolality (311 +/- 2.5 v 304 +/- 1.8 mmol/kg [mOsm/kg] H2O; P less than 0.05) were also lower in the experimental animals. There were no differences in plasma (1.9 +/- 0.4 v 1.5 +/- 0.2 pg/mL) or pituitary (1.5 +/- 0.4 v 1.5 +/- 0.2 microgram/pituitary) vasopressin levels. In addition, steady-state vasopressin mRNA levels were not different between the two groups (1,286 +/- 210 v 1,093 +/- 138 pg/hypothalamus). One week of L-thyroxine replacement resulted in significant increases in serum thyroxine levels without changes in the other variables measured. These results indicate that short-term hypothyroidism, which has been shown to exert substantial effects on renal function, causes only a modest central alteration in the plasma vasopressin-osmolality relationship, which occurs in the absence of detectable changes in vasopressin synthesis.

Neuronal nitric oxide synthase within paraventricular nucleus: blood pressure and baroreflex in two-kidney, one-clip hypertensive rats.

The renin–angiotensin system is activated in the early phase of two‐kidney, one‐clip (2K‐1C) hypertension. The paraventricular nucleus (PVN) integrates inputs regulating sympathetic outflow. The PVN receives inputs from plasma angiotensin II via projections from circumventricular organs and from renal afferent nerves transmitted via the nucleus tractus solitarii. Nitric oxide within the PVN may exert a sympathoinhibitory effect. These studies tested whether decreasing endogenous nitric oxide by introducing dominant negative (DN) constructs for neuronal nitric oxide synthase (nNOS) into PVN chronically augments hypertension and/or modulates baroreflex function. Male 6‐week‐old Sprague–Dawley rats underwent sham surgery or right renal artery clipping and placement of radiotelemetry transmitters. One week later, the PVN was injected bilaterally with 250 nl artificial cerebrospinal fluid containing 250 ng μl−1 of RSV β‐galactosidase (β‐Gal), cytomegalovirus (CMV) wild‐type (WT nNOS), or respiratory syncytial virus (RSV) haeme domain or RSV haemeRedF (DN nNOS). Haemodynamics were monitored for 5 weeks. Then left renal nerve electrodes were placed, and 2 days later the rats underwent baroreflex testing in the conscious state. The rise in mean arterial pressure (MAP) was significantly potentiated in the DN nNOS 2K‐1C group beyond 15 days after PVN injection. By day 35, MAP in the 2K‐1C groups was 152 ± 6.3 (β‐Gal), 155.1 ± 6.6 (WT nNOS) and 179 ± 5.4 mmHg (DN nNOS; P < 0.01 versus all other groups). Sham‐clipped rats remained normotensive. All groups displayed progressive bradycardia over time that was attenuated in the DN nNOS 2K‐1C group. Baroreflex curves shifted to higher pressures, and baroreflex sensitivity of heart rate was diminished to a similar extent in all groups of 2K‐1C rats. The baroreflex response of renal sympathetic nerve activity was preserved. The PVN tissue from DN nNOS rats had decreased dimerization of nNOS and generation of total nitric oxide. These findings indicate that chronic interference of nNOS dimerization required for generation of nitric oxide within the PVN potentiates the increase of blood pressure by modulating the sympathoexcitation that accompanies renovascular hypertension.

Arsenic intoxication associated with tubulointerstitial nephritis

Arsenic poisoning is an often unrecognized cause of renal insufficiency. We report a case of tubulointerstitial nephritis associated with an elevated urinary arsenic concentration. Removal of the putative source of arsenic resulted in symptomatic improvement, resolution of abnormal abdominal radiographs, and stabilization of renal function. This case emphasizes the importance of heavy metal screening in patients with multisystem complaints and tubulointerstitial nephritis.

Substantial cardiac parasympathetic activity exists during heavy dynamic exercise in dogs

We investigated the extent of functional parasympathetic and sympathetic activity to the heart at rest and during mild to heavy dynamic exercise in conscious dogs. The animals were chronically instrumented to monitor mean arterial pressure (MAP), heart rate (HR), and terminal aortic blood flow (TAQ) and trained to run on a motor-driven treadmill. MAP, HR, and TAQ were monitored at rest and during steady-state dynamic exercise ranging from mild [3.2 kilometers per hour (kph), 0% grade] to heavy exercise (8 kph, 15% grade). Experiments were performed before and after blocking the effects of either the parasympathetic nerves (atropine 0.2 mg/kg iv) or sympathetic nerves (atenolol 2.0 mg/kg iv) to the heart. In addition, blood samples were taken at rest and at steady state during exercise, and plasma levels of vasopressin and renin activity were assessed. At rest and during all levels of exercise, muscarinic cholinergic receptor blockade caused a marked increase in HR over control (saline treated) levels with little effect on MAP or TAQ. β-Adrenergic receptor blockade had no significant effect on HR at rest and during mild exercise. At moderate to heavy workloads, β-receptor blockade significantly reduced MAP, HR, and TAQ and increased plasma vasopressin levels. We conclude that, even during heavy dynamic exercise, significant functional parasympathetic tone to the heart exists. Thus, over a wide range of exercise workloads, HR is under the tonic control of both sympathetic and parasympathetic nerves.

Differential effects of endothelin receptor A and B antagonism on cerebral hypoperfusion following traumatic brain injury

OBJECTIVES Our laboratory has previously shown that endothelin 1 (ET-1), a powerful vasoconstrictor, and its receptors, A (ETrA) and B (ETrB), are up-regulated following trauma. This up-regulation coincides temporally with enhanced vasoreactivity in cerebral cortical microvessels, which leads to a state of chronic hypoperfusion for up to 48 hours following traumatic brain injury (TBI). However, the direct contribution of either receptor up-regulation to decreased cerebral blood flow (CBF) after closed head trauma has not been determined. Furthermore, how ET-1 blockade may affect histological outcome following TBI has not been explored. Therefore, the effects of ETrA and B antagonism on TBI induced hypoperfusion of CBF and cell injury in sensorimotor cortex (smCx) and hippocampus (Hipp) were assessed by arterial spin labeling magnetic resonance imaging and Fluoro-Jade staining, respectively. METHODS Adult male rats were given intracerebroventricular injections of ETrA (BQ123) or ETrB antagonist (BQ788) before being subjected to TBI using a closed head acceleration impact model. Following TBI, CBF was measured and histological examination of cell integrity was carried out. RESULTS ETrA blockade ameliorated TBI induced hypoperfusion in smCx and Hipp at 4 and 24 hours after TBI and caused a mild hyperemia in both centers by 48 hours after injury. Furthermore, ETrA antagonism reduced the extent of Fluoro-Jade labeled cells within smCx and Hipp as compared with TBI only. ETrB blockade had little effect on TBI induced hypoperfusion and did not change the extent of cell injury following TBI. DISCUSSION These results suggest that decreased CBF following TBI may be caused by ETrA, but not ETrB, up-regulation. Furthermore, these results suggest that TBI induced hypoperfusion may contribute to poor neurologic outcome following TBI. In this work, we provide a rationale for studying the clinical relevancy of use of ETrA antagonists following TBI.