Acute myocardial infarctions, strokes and influenza: seasonal and pandemic effects.

The incidence of myocardial infarctions and influenza follow similar seasonal patterns. To determine if acute myocardial infarctions (AMIs) and ischaemic strokes are associated with influenza activity, we built time-series models using data from the Nationwide Inpatient Sample. In these models, we used influenza activity to predict the incidence of AMI and ischaemic stroke. We fitted national models as well as models based on four geographical regions and five age groups. Across all models, we found consistent significant associations between AMIs and influenza activity, but not between ischaemic strokes and influenza. Associations between influenza and AMI increased with age, were greatest in those aged >80 years, and were present in all geographical regions. In addition, the natural experiment provided by the second wave of the influenza pandemic in 2009 provided further evidence of the relationship between influenza and AMI, because both series peaked in the same non-winter month.

Direct and sympathetically mediated venoconstriction in essential hypertension. Enhanced responses to endothelin-1.

Endothelin-1 is a potent endothelium-derived vasoconstrictor peptide. Although circulating concentrations are not increased in essential hypertension, enhanced sensitivity to endothelin-1 has been observed in animal models of hypertension. We investigated dorsal hand vein responses to local infusion of endothelin-1 and norepinephrine in 12 patients with essential hypertension who had never received treatment and in 12 age and sex matched normotensive control subjects. The maximal venoconstriction and the geometric mean of the dose of norepinephrine that caused 50% of maximal venoconstriction were similar in hypertensive (mean +/- SE; 80 +/- 4%; 31 +/- 8 pmol/min) and normotensive subjects (87 +/- 5%, 22 +/- 9 pmol/min). In contrast, mean venoconstriction to endothelin-1 was significantly greater in hypertensive (49 +/- 5%) than in normotensive subjects (27 +/- 2%; P = 0.004). Sympathetically mediated venoconstriction elicited by deep breath was substantially potentiated by endothelin-1 in hypertensive (67 +/- 7% at 90 min) but not normotensive subjects (11 +/- 3% at 90 min; P = 0.001). Venoconstriction to endothelin-1 correlated positively with mean arterial pressure in the hypertensive subjects (r = 0.82; p = 0.001) but negatively in the normotensive subjects (r = -0.58; p = 0.047). Endothelin-1 may contribute to the reduction of venous compliance occurring in the early stages of essential hypertension and to the altered systemic hemodynamics in this condition.

Receptor-mediated regional sympathetic nerve activation by leptin.

Leptin is a peptide hormone produced by adipose tissue which acts centrally to decrease appetite and increase energy expenditure. Although leptin increases norepinephrine turnover in thermogenic tissues, the effects of leptin on directly measured sympathetic nerve activity to thermogenic and other tissues are not known. We examined the effects of intravenous leptin and vehicle on sympathetic nerve activity to brown adipose tissue, kidney, hindlimb, and adrenal gland in anesthetized Sprague-Dawley rats. Intravenous infusion of mouse leptin over 3 h (total dose 10-1,000 microg/kg) increased plasma concentrations of immunoreactive murine leptin up to 50-fold. Leptin slowly increased sympathetic nerve activity to brown adipose tissue (+286+/-64% at 1,000 microg/kg; P = 0.002). Surprisingly, leptin infusion also produced gradual increases in renal sympathetic nerve activity (+228+/-63% at 1,000 microg/kg; P = 0.0008). The effect of leptin on sympathetic nerve activity was dose dependent, with a threshold dose of 100 microg/kg. Leptin also increased sympathetic nerve activity to the hindlimb (+287+/-60%) and adrenal gland (388+/-171%). Despite the increase in overall sympathetic nerve activity, leptin did not increase arterial pressure or heart rate. Leptin did not change plasma glucose and insulin concentrations. Infusion of vehicle did not alter sympathetic nerve activity. Obese Zucker rats, known to possess a mutation in the gene for the leptin receptor, were resistant to the sympathoexcitatory effects of leptin, despite higher achieved plasma leptin concentrations. These data demonstrate that leptin increases thermogenic sympathetic nerve activity and reveal an unexpected stimulatory effect of leptin on overall sympathetic nerve traffic.

Lessons from Leptin's molecular biology: Potential therapeutic actions of recombinant leptin and leptin-related compounds.

Leptin, a peptide secreted by the white adipose tissue, circulates to the central nervous system and signals the status of body energy stores, regulating feeding behavior and energy balance. As human obesity is characterized by hyperleptinemia and leptin resistance, increasing leptin sensitivity is an attractive target for obesity treatment.

Role of oxidant stress in endothelial dysfunction produced by experimental hyperhomocyst(e)inemia in humans.

BACKGROUND: Moderate elevations in plasma homocyst(e)ine concentrations are associated with atherosclerosis and hypertension. We tested the hypothesis that experimental perturbation of homocysteine levels produces resistance and conduit vessel endothelial dysfunction and that this occurs through increased oxidant stress. METHODS AND RESULTS: Oral administration of L-methionine (100 mg/kg) was used to induce moderate hyperhomocyst(e)inemia ( approximately 25 micromol/L) in healthy human subjects. Endothelial function of forearm resistance vessels was assessed by use of forearm vasodilatation to brachial artery administration of the endothelium-dependent dilator acetylcholine. Conduit vessel endothelial function was assessed with flow-mediated dilatation of the brachial artery. Forearm resistance vessel dilatation to acetylcholine was significantly impaired 7 hours after methionine (methionine, 477+/-82%; placebo, 673+/-110%; P=0.016). Methionine did not alter vasodilatation to nitroprusside and verapamil. Flow-mediated dilatation was significantly impaired 8 hours after methionine loading (0.3+/-2.7%) compared with placebo (8. 2+/-1.6%, P=0.01). Oral administration of the antioxidant ascorbic acid (2 g) prevented methionine-induced endothelial dysfunction in both conduit and resistance vessels (P=0.03). CONCLUSIONS: Experimentally increasing plasma homocyst(e)ine concentrations by methionine loading rapidly impairs both conduit and resistance vessel endothelial function in healthy humans. Endothelial dysfunction in conduit and resistance vessels may underlie the reported associations between homocysteine and atherosclerosis and hypertension. Increased oxidant stress appears to play a pathophysiological role in the deleterious endothelial effects of homocysteine.

Impairment of endothelium-dependent vasodilation of resistance vessels in patients with obstructive sleep apnea.

BACKGROUND: Patients with obstructive sleep apnea (OSA) experience repetitive episodic hypoxemia with consequent sympathetic activation and marked blood pressure surges, each of which may impair endothelial function. We tested the hypothesis that patients with OSA have impaired endothelium-dependent vasodilation, even in the absence of overt cardiovascular disease. METHODS AND RESULTS: We studied 8 patients with OSA (age 44+/-4 years) and 9 obese control subjects (age 48+/-3 years). Patients with OSA were newly diagnosed, never treated for OSA, on no medications, and free of any other known diseases. All obese control subjects underwent complete overnight polysomnographic studies to exclude occult OSA. Resistance-vessel function was tested by use of forearm blood flow responses to intra-arterial infusions of acetylcholine (a vasodilator that stimulates endothelial release of nitric oxide), sodium nitroprusside (an exogenous nitric oxide donor), and verapamil (a calcium channel blocker). Conduit-vessel function was also evaluated by ultrasonography. Brachial artery diameter was measured under baseline conditions, during reactive hyperemia (with flow increase causing endothelium-dependent dilatation), and after sublingual administration of nitroglycerin (an endothelium-independent vasodilator). Patients with OSA had a blunted vasodilation in response to acetylcholine (P:<0.007), but responses to sodium nitroprusside and verapamil were not significantly different from those of control subjects. No significant difference in conduit-vessel dilation was evident between OSA patients and obese control subjects. CONCLUSIONS: Patients with OSA have an impairment of resistance-vessel endothelium-dependent vasodilation. This may be implicated in the pathogenesis of hypertension and heart failure in this condition.

Effect of acute and antecedent hypoglycemia on sympathetic neural activity and catecholamine responsiveness in normal rats.

Adrenergic responsiveness to acute hypoglycemia is impaired after prior episodes of hypoglycemia. Although circulating epinephrine responses are blunted, associated alterations in adrenal sympathetic nerve activity (SNA) have not been reported. We examined adrenal nerve traffic in normal conscious rats exposed to acute insulin-induced hypoglycemia compared with insulin with (clamped) euglycemia. We also examined adrenal SNA and catecholamine responses to insulin-induced hypoglycemia in normal conscious rats after two antecedent episodes of hypoglycemia (days -2 and -1) compared with prior episodes of sham treatment. Acute insulin-induced hypoglycemia increased adrenal sympathetic nerve traffic compared with insulin administration with clamped euglycemia (165 +/- 12 vs. 118 +/- 21 spikes/s [P < 0.05]; or to 138 +/- 8 vs. 114 +/- 10% of baseline [P < 0.05]). In additional experiments, 2 days of antecedent hypoglycemia (days -2 and -1) compared with sham treatment significantly enhanced baseline adrenal SNA measured immediately before subsequent acute hypoglycemia on day 0 (180 +/- 11 vs. 130 +/- 12 spikes/s, respectively; P < 0.005) and during subsequent acute hypoglycemia (229 +/- 17 vs. 171 +/- 16 spikes/s; P < 0.05). However, antecedent hypoglycemia resulted in a nonsignificant reduction in hypoglycemic responsiveness of adrenal SNA when expressed as percent increase over baseline (127 +/- 5% vs. 140 +/- 14% of baseline). Antecedent hypoglycemia, compared with sham treatment, resulted in diminished epinephrine responsiveness to subsequent hypoglycemia. Norepinephrine responses to hypoglycemia were not significantly altered by antecedent hypoglycemia. In summary, prior hypoglycemia in normal rats increased adrenal sympathetic tone, but impaired epinephrine responsiveness to acute hypoglycemia. Hence, these data raise the intriguing possibility that increased sympathetic tone resulting from antecedent hypoglycemia downregulates subsequent epinephrine responsiveness to hypoglycemia. Alternatively, it is possible that the decrease in epinephrine responsiveness after antecedent hypoglycemia could be the result of reduced adrenal sympathetic nerve responsiveness.

Endothelin receptor antagonism in patients with chronic heart failure.

OBJECTIVE: The relative importance of ETA and ETB receptors in mediating the constrictor effects of endogenous endothelin-1 in patients with chronic heart failure is not known. The primary purpose of this study was to compare the acute effects of selective ETA and ETB receptor antagonists in vivo in healthy subjects and patients with chronic heart failure. Our secondary aim was to examine more closely the effect of chronic heart failure on endothelin biosynthesis. METHODS: We studied the effects of BQ-123 (a selective ETA antagonist) and BQ-788 (a selective ETB antagonist) in ten healthy subjects and ten patients with chronic heart failure. Locally active doses of each antagonist were infused into the non-dominant brachial artery for 90 min on separate days at least 1 week apart. Changes in forearm blood flow were measured by venous occlusion plethysmography. Venous blood samples were obtained prior to antagonist infusion for assay of total endothelin, big endothelin-1 and C-terminal fragment immunoreactivity. RESULTS: BQ-123 (100 nmol/min) increased blood flow by 54+/-10% (P<0.001) and 30+/-5% (P<0.001) in controls and heart failure patients, respectively. BQ-788 (1 nmol/min) reduced blood flow by 15+/-5% (P=0. 036) and 9+/-4% (P=0.001) in controls and heart failure patients, respectively. Total endothelin immunoreactivity was non significantly greater in heart failure patients than controls (6. 8+/-1.4 vs. 4.6+/-0.5 pM; P=0.13). Big endothelin-1 (2.6+/-0.4 vs. 1. 7+/-0.1 pM; P=0.04) and C-terminal fragment immunoreactivity (2. 1+/-0.3 vs. 0.6+/-0.1 pM; P<0.0001) were each significantly greater in heart failure patients than controls. CONCLUSIONS: Selective ETA receptor antagonism caused vasodilatation in the peripheral circulation of healthy subjects and patients with chronic heart failure while selective ETB receptor antagonism caused vasoconstriction in each group. ETB receptor antagonism may therefore cause potentially deleterious vasoconstriction in chronic heart failure. Chronic heart failure is associated with a significant increase in plasma big endothelin-1 and C-terminal fragment immunoreactivity.

Effects of leptin on insulin sensitivity in normal rats.

To determine whether leptin has insulin sensitizing effects in normal rodents, we measured plasma glucose and insulin concentrations in male Sprague-Dawley rats treated with leptin or vehicle by continuous s.c. infusion for 48 h. In additional experiments, we examined the acute effect of i.v. leptin upon insulin sensitivity under conditions of clamped glycemia. Subcutaneous leptin was administered at 10.0 and 1.0 microg/h. To avoid confounding effects of differences in food intake, both leptin- and vehicle-treated rats were fasted during the 48-h period of infusion. Infusion of leptin, 10 microg/h, significantly reduced both plasma glucose and insulin. Leptin, 1.0 microg/h, also decreased plasma glucose and insulin, although the effects on insulin did not achieve statistical significance. Leptin at either dose did not alter body weight or epididymal fat mass compared with vehicle treated controls. Leptin, 10 microg/h, decreased circulating insulin-like growth factor-1 levels. No differences in GLUT-4 content in either in brown or epididymal fat were observed as a result of leptin-treatment. Leptin, 10 microg/h, significantly decreased urine osmolality, increased water intake, and reduced renal potassium excretion compared with vehicle-infused rats. In additional rats, we measured the acute effect of i.v. leptin on insulin sensitivity determined as whole body glucose utilization during hyperinsulinemic glucose clamps performed at glucose targets of 60 and 90 mg/100 ml. Glucose utilization was increased by 29% during the last 135 min of glycemia clamped at 60 mg/100 ml (P < 0.05) and by 30% during the last 135 min of glycemia clamped at 90 mg/dl (P < 0.01) in rats infused with leptin compared with vehicle. In summary, leptin increased insulin sensitivity in normal rats both under fasting conditions and in the presence of hyperinsulinemia at clamped glucose. These effects did not appear dependent on altered body weight. Leptin also altered salt and water metabolism under fasting conditions resulting in increased water intake and more dilute urine.

Sympathetic and cardiorenal actions of leptin.

Body weight is tightly regulated physiologically. The recent discovery of the peptide hormone leptin has permitted more detailed evaluation of the mechanisms responsible for control of body fat. Leptin is almost exclusively produced by adipose tissue and acts in the CNS through a specific receptor and multiple neuropeptide pathways to decrease appetite and increase energy expenditure. Leptin thus functions as the afferent component of a negative feedback mechanism to control adipose tissue mass. Increasing evidence suggests that leptin may have wider actions influencing autonomic, cardiovascular, and endocrine function. Intravenous leptin increases norepinephrine turnover and sympathetic nerve activity to thermogenic brown adipose tissue. Studies from our laboratory suggest that leptin also increases sympathetic nerve activity to kidney, hindlimb, and adrenal gland. However, systemic administration of leptin does not acutely increase arterial pressure or heart rate in anesthetized animals. Thus, longer-term exposure to hyperleptinemia may be necessary for full expression of the expected pressor effect of renal sympathoexcitation. Alternatively, leptin may have additional cardiovascular actions to oppose sympathetically mediated vasoconstriction. Leptin in high doses increases renal sodium and water excretion, apparently through a direct tubular action. In addition, leptin appears to increase systemic insulin sensitivity, even in the absence of weight loss. Although we are at an early stage of understanding, we speculate that abnormalities in the actions of leptin may have implications for the sympathetic, cardiovascular, and renal changes associated with obesity.

State-of-the-art-lecture: Obesity-induced hypertension: new concepts from the emerging biology of obesity.

offsity is associated with an increased risk of hypertension. In the past 5 years there have been dramatic advances into the genetic and neurobiological mechanisms of obesity with the discovery of leptin and novel neuropeptide pathways regulating appetite and metabolism. In this brief review, we argue that these mounting advances into the neurobiology of obesity have and will continue to provide new insights into the regulation of arterial pressure in obesity. We focus our comments on the sympathetic, vascular, and renal mechanisms of leptin and melanocortin receptor agonists and on the regulation of arterial pressure in rodent models of genetic obesity. We suggest 3 concepts. First, the effect of obesity on blood pressure may depend critically on the genetic-neurobiological mechanisms underlying the obesity. Second, obesity is not consistently associated with increased blood pressure, at least in rodent models. Third, the blood pressure response to obesity may be critically influenced by modifying alleles in the genetic background.

Interactions between the melanocortin system and leptin in control of sympathetic nerve traffic.

Leptin plays an important role in regulation of body weight through regulation of food intake and sympathetically mediated thermogenesis. The hypothalamic melanocortin system, via activation of the melanocortin-4 receptor (MC4-R), decreases appetite and weight, but its effects on sympathetic nerve activity (SNA) are unknown. In addition, it is not known whether sympathoactivation to leptin is mediated by the melanocortin system. We tested the interactions between these systems in regulation of brown adipose tissue (BAT) and renal and lumbar SNA in anesthetized Sprague-Dawley rats. Intracerebroventricular administration of the MC4-R agonist MT-II (200 to 600 pmol) produced a dose-dependent sympathoexcitation affecting BAT and renal and lumbar beds. This response was completely blocked by the MC4-R antagonist SHU9119 (30 pmol ICV). Administration of leptin (1000 microg/kg IV) slowly increased BAT SNA (baseline, 41+/-6 spikes/s; 6 hours, 196+/-28 spikes/s; P=0.001) and renal SNA (baseline, 116+/-16 spikes/s; 6 hours, 169+/-26 spikes/s; P=0.014). Intracerebroventricular administration of SHU9119 did not inhibit leptin-induced BAT sympathoexcitation (baseline, 35+/-7 spikes/s; 6 hours, 158+/-34 spikes/s; P=0.71 versus leptin alone). However, renal sympathoexcitation to leptin was completely blocked by SHU9119 (baseline, 142+/-17 spikes/s; 6 hours, 146+/-25 spikes/s; P=0.007 versus leptin alone). This study demonstrates that the hypothalamic melanocortin system can act to increase sympathetic nerve traffic to thermogenic BAT and other tissues. Our data also suggest that leptin increases renal SNA through activation of hypothalamic melanocortin receptors. In contrast, sympathoactivation to thermogenic BAT by leptin appears to be independent of the melanocortin system.

Genetic characterization of the "new" Harlan Sprague Dawley Dahl salt-sensitive rats.

In 1994, it was reported that Dahl salt-sensitive SS/Jr rats supplied by Harlan Sprague Dawley were genetically contaminated and resistant to the pressor effects of a high salt diet. Harlan Sprague Dawley subsequently developed new pedigree expansion and production colonies from their foundation colony to supply new, purportedly inbred, Harlan Sprague Dawley SS/Jr (S(HSD)). To evaluate the genetic integrity and salt sensitivity of thse new S(HSD), we performed genotyping (microsatellite DNA markers) and phenotyping (radiotelemetric arterial pressure) of 12 S(HSD), 16 "authentic" SS/Jr from the inbred colony of John Rapp (S(Rapp)), 9 Harlan Sprague Dawley salt-resistant SR/Jr (R(HSD)), and (genotyping only) 6 known "contaminated" Harlan Sprague Dawley Dahl SS/Jr (S*). In the genotyping studies, 20 of 22 markers revealed polymorphisms between S(Rapp) and S* and 18 were polymorphic between S(Rapp) and R(Rapp), but none of the 22 markers revealed polymorphisms between S(Rapp) and the new S(HSD). The phenotyping studies showed that during an ultra-low salt diet, mean arterial pressure was higher (P < .05) in both authentic S(Rapp) (129 +/- 2 mm Hg; mean +/- SE) and new S(HSD) (120 +/- 2 mm Hg) than in R(HSD) (93 +/- 1 mm Hg). A high salt diet increased mean arterial pressure in every S(HSD) and S(Rapp). Increases in mean arterial pressure after 4 weeks of a high salt diet were significantly (P < 0.05) greater in authentic S(Rapp) (+51 +/- 3 mm Hg) than in new S(HSD) (+39 +/- 3 mm Hg). In addition, salt-induced mortality was significantly greater in S(Rapp) (62.5%) than S(HSD) (8.3%) after 8 weeks (P < 0.01). S(HSD) were genotypically indistinguishable from S(Rapp), had an elevated arterial pressure on a low salt diet, and had a pressor response to salt. Thus, the new S(HSD) supplied to us had several characteristics of inbred Dahl SS/Jr and did not have evidence of the previously detected genetic contamination. However, phenotypic characteristics such as body weight, salt-induced hypertension, and mortality were significantly different in S(HSD) compared with S(Rapp). This may reflect genetic differences between these two strains or differences in environmental factors and suggests that the S(HSD) and S(Rapp) may now constitute distinct substrains of Dahl SS/Jr.

Big endothelin-3 constricts forearm resistance vessels but not hand veins in humans.

BACKGROUND: Endothelin-3 (ET-3) and its inactive precursor, big endothelin-3 (big ET-3), are both found in human plasma. We investigated whether big ET-3 is converted to ET-3 in the human forearm resistance vessels and dorsal hand veins in vivo. METHODS: In a 4-phase study, 6 subjects received 90 minute intrabrachial artery infusions of big ET-3 (50 and 100 pmol x min(-1)) and ET-3 (5 and 10 pmol x min(-1)) in random order. Forearm blood flow was measured by venous occlusion plethysmography. In a second 3-phase study, 6 subjects received 90-minute dorsal hand vein infusions of saline solution, big ET-3 (50 pmol x min(-1)) and ET-3 (5 pmol x min(-1)) in random order. In a third 2-phase study, 6 subjects received 90-minute dorsal hand vein infusions of big ET-3 (100 pmol x min(-1)) and ET-3 (10 pmol x min(-1)). In the dorsal hand vein studies, vessel diameter was measured by the Aellig technique. RESULTS: Intra-arterial ET-3 caused local forearm vasoconstriction of 20%+/-9% (P = .009) at 5 pmol x min(-1) and 20%+/-10% (P = .001) at 10 pmol x min(-1) after 90 minutes, with no difference between doses (P = .69). Intra-arterial big ET-3 also caused local forearm vasoconstriction of 22%+/-6% at 50 pmol x min(-1) (P = .004) and 18%+/-3% at 100 pmol x min(-1) (P<.0001) after 90 minutes, with no difference between doses (P = .44). There were no significant differences between the responses to intra-arterial big ET-3 and ET-3 at these doses. Local intravenous ET-3 caused a constriction of 9%+/-2% at 5 pmol x min(-1) (P = .04) and 22%+/-8% at 10 pmol x min(-1) (P = .002) after 90 minutes. Big ET-3 at 50 pmol x min(-1) and 100 pmol x min(-1) did not affect hand vein tone. All responses were slowly progressive. CONCLUSIONS: Based on vasoconstriction, measurable conversion of big ET-3 to ET-3 occurs in forearm resistance vessels but not in dorsal hand veins in vivo. An endothelin-converting enzyme, capable of converting exogenously administered big ET-3 to ET-3, appears to be present in upper limb resistance arteries but not in capacitance vessels in humans.

Endothelin as a regulator of cardiovascular function in health and disease.

The endothelins are a family of endothelium-derived peptides that possess characteristically sustained vasoconstrictor properties. Endothelin-1 appears to be the predominant member of the family generated by vascular endothelial cells. In addition to its direct vascular effects, endothelin-1 has inotropic and mitogenic properties, influences homeostasis of salt and water, alters central and peripheral sympathetic activity and stimulates the renin-angiotensin-aldosterone system. Studies with endothelin receptor antagonists have indicated that endothelin-1 probably has complex opposing vascular effects mediated through vascular smooth muscle and endothelial ET(A) and ET(B)receptors. Endogenous generation of endothelin-1 appears to contribute to maintenance of basal vascular tone and blood pressure through activation of vascular smooth muscle ET(A)receptors. At the same time, endogenous endothelin-1 acts through endothelial ET(B) receptors to stimulate formation of nitric oxide tonically and to oppose vasoconstriction. In view of the multiple cardiovascular actions of endothelin-1, there has been much interest in its contribution to the pathophysiology of hypertension. Results of most studies suggest that generation of, or sensitivity to, endothelin-1 is no greater in hypertensive than it is in normotensive subjects. Nonetheless, the deleterious vascular effects of endogenous endothelin-1 may be accentuated by reduced generation of nitric oxide caused by hypertensive endothelial dysfunction. It also appears likely that endothelin participates in the adverse cardiac and vascular remodelling of hypertension, as well as in hypertensive renal damage. Irrespective of whether vascular endothelin activity is increased in hypertension, anti-endothelin agents do produce vasodilatation and lower blood pressure in hypertensive humans. There is more persuasive evidence for increased endothelin-1 activity in secondary forms of hypertension, including pre-eclampsia and renal hypertension. Endothelin-1 also appears to play an important role in pulmonary hypertension, both primary and secondary to diseases such as chronic heart failure. The hypotensive effects of endothelin converting enzyme inhibitors and endothelin receptor antagonists should be useful in the treatment of hypertension and related diseases. Development of such agents will increase knowledge of the physiological and pathological roles of the endothelins, and should generate drugs with novel benefits.

Inhibition of nitric oxide synthesis increases blood pressure in healthy humans.

OBJECTIVE: To examine whether endogenous production of the endothelium-derived vasodilator nitric oxide influences blood pressure in healthy humans. METHODS: After preliminary pilot dose-ranging studies, 3 mg/kg NG-monomethyl-L-arginine (L-NMMA), an inhibitor of nitric oxide synthase, and saline placebo were infused intravenously over 5 min to eight healthy subjects in a two-phase, randomized, single-blind crossover study. Blood pressure and cardiac and renal function were measured. RESULTS: Compared with placebo, L-NMMA increased mean arterial pressure by 10%, decreased heart rate by 19%, decreased cardiac index by 25% and increased calculated total peripheral resistance by 46%. Effects were maximal 10-15 min after starting L-NMMA infusion. Urinary sodium and fractional sodium excretions were increased by L-NMMA, but creatinine clearance was unchanged. CONCLUSIONS: Basal generation of nitric oxide influences total peripheral resistance and blood pressure in healthy humans. The natriuresis induced by L-NMMA may be related to the increase in blood pressure, or arise from inhibition of the intrarenal actions of nitric oxide. Any decrease in nitric oxide generation, as has been postulated to occur in essential hypertension, could have substantial effects on blood pressure and tissue blood flow.

The effects of short-term passive smoke exposure on endothelium-dependent and independent vasodilation.

OBJECTIVE: There is limited information on the mechanisms mediating the deleterious effects of passive smoke exposure. Cross-sectional studies indicate that nonsmokers exposed chronically to passive smoke have impaired endothelium mediated vasodilation. We tested the hypothesis that acute exposure to sidestream (passive) smoke impairs endothelium-dependent vasodilation in healthy nonsmokers. METHODS AND RESULTS: We studied 12 healthy nonsmokers (aged 27 +/- 5 years, nine men and three women). We obtained measurements of blood pressure, heart rate, and bilateral forearm blood flow (FBF). Each individual was studied twice, following a randomized, placebo-controlled design. The effects of passive smoke were studied on one day and the effects of vehicle (room air) on a separate day. Acetylcholine (ACh) and sodium nitroprusside (SNP) were infused into the left brachial artery before and after 15 min of exposure to either passive smoke (carbon monoxide concentration between 20 and 40 p.p.m.) or vehicle (room air). The order of ACh and SNP, and smoke or vehicle, was randomized between individuals. Smoke exposure increased carboxyhemoglobin from 0.5 +/- 0.1 % to 0.8 +/- 0.1% (P= 0.002). Neither passive smoke nor vehicle changed baseline measurements of heart rate, blood pressure and forearm vascular resistance (FVR). The vasodilatory responses to ACh and SNP were very similar, both before and after exposure to passive smoke and before and after vehicle. CONCLUSION: Our data demonstrate that acute exposure to passive smoke does not alter either endothelium-dependent or independent vasodilatory responses in healthy nonsmoking individuals. Hence, impaired endothelial vasodilatory responses in nonsmokers chronically exposed to passive smoke most likely reflect chronic functional and/or structural changes in responses to cigarette smoke, rather than the acute effects of cigarette smoke toxicity on endothelial function.

Effects of obstructive sleep apnea on endothelin-1 and blood pressure.

OBJECTIVE: To evaluate blood pressure and humoral vasoconstrictor responses to recurrent episodes of obstructive sleep apnea and the effects of therapy by means of continuous positive airway pressure. PATIENTS AND METHODS: We prospectively evaluated overnight changes in hemodynamics, oxygen saturation, the apnea-hypopnea index, circulating endothelin-1, norepinephrine and plasma renin activity in 22 patients with severe obstructive sleep apnea before and after successful therapy using continuous positive airway pressure therapy (three measurements). Measurements of endothelin-1 and blood pressure were also obtained on three occasions, at similar times, in 12 healthy control subjects without sleep disturbances. RESULTS: Mean arterial pressure and endothelin-1 concentrations increased significantly after 4 h of untreated obstructive sleep apnea, and decreased after 5 h of continuous positive airway pressure. Changes in endothelin-1 levels were correlated with changes in mean arterial pressure (r = 0.44, P < 0.02) and with changes in oxygen saturation (r = 0.37, P < 0.05). Norepinephrine levels and plasma renin activity did not change significantly in patients with obstructive sleep apnea, and were not correlated with changes in blood pressure or oxygen saturation. In controls, blood pressure measurements at similar times during the night showed changes directionally opposite to that seen in obstructive sleep apnea, while endothelin-1 levels remained unchanged. CONCLUSIONS: Sleep apnea elicits increases in blood pressure and endothelin-1, with reductions in both after treatment. Vasoconstrictor and mitogenic effects of endothelin-1 may be implicated in increased cardiovascular risk in patients with obstructive sleep apnea.

Contrasting blood pressure effects of obesity in leptin-deficient ob/ob mice and agouti yellow obese mice.

OBJECTIVE: Recent advances in understanding the neuroendocrine pathways regulating appetite, metabolism and body weight afford an opportunity to explore further the mechanisms by which obesity influences arterial pressure. ob/ob(Lep(ob)/Lep(ob)) mice have a mutation in the ob gene and are leptin-deficient. Leptin possesses pressor actions and has been shown to increase arterial pressure when infused chronically or over-expressed transgenically. In contrast, agouti yellow obese(Ay) mice have overexpression of an agouti peptide that blocks melanocortin receptors. Stimulation of melanocortin receptors by alpha-melanocyte-stimulating hormone decreases arterial pressure. DESIGN AND METHODS: This study measured arterial pressure in leptin-deficient ob/ob mice, agouti yellow obese mice and their lean controls to test the hypothesis that the effects of obesity on arterial pressure are importantly influenced by the genetic and neuroendocrine mechanisms causing the obesity. We measured arterial pressure directly in conscious ob/ob mice (n = 14), agouti yellow obese mice (n = 6) and the same number of lean littermates. RESULTS: Body weight was nearly twice as high in ob/ob mice as in their lean controls, but mean arterial pressure was significantly lower in ob/ob mice (92+/-3 mmHg) compared with their lean controls (106+/-2 mmHg; P = 0.00017). In contrast, mean arterial pressure was significantly higher in agouti yellow obese mice (124+/-3 mmHg) than in their lean controls (99+/-1 mmHg; P = 0.000002) despite the fact that the agouti mice had milder obesity. CONCLUSIONS: This study prompts three conclusions: (1) leptin-deficient ob/ob mice and agouti yellow obese mice have contrasting blood pressure responses to obesity, (2) obesity does not invariably increase arterial pressure in mice, and (3) the arterial pressure response to obesity may depend critically on the underlying genetic and neuroendocrine mechanisms.

Effect of vitamin E on resistance vessel endothelial dysfunction induced by methionine.

We tested if vitamin E, a fat-soluble antioxidant, prevents resistance vessel endothelial dysfunction caused by methionine-induced hyperhomocysteinemia in humans. Moderate elevations in plasma homocysteine concentrations are associated with atherosclerosis and hypertension. Homocysteine causes endothelial dysfunction possibly through several mechanisms. No previous study has tested if a fat-soluble antioxidant can prevent endothelial dysfunction caused by experimental hyperhomocysteinemia. Ten healthy subjects participated in a 2 x 2 factorial, double-blind crossover study, receiving L-methionine (100 mg/kg at -6 hours) or vehicle, with and without vitamin E (1,200 IU at -13 hours). Endothelial function of forearm resistance vessels was assessed using forearm blood flow responses to brachial artery administration of endothelium-dependent and endothelium-independent agents. Forearm resistance vessel dilatation to acetylcholine was significantly impaired 7 hours after methionine (placebo, 583 +/- 87% vs methionine 30 +/- 68%; p <0.05). Dilatation to bradykinin was also impaired (placebo, 509 +/- 54% vs methionine 289 +/- 48%; p <0.05). Methionine did not alter vasodilatation to the endothelium-independent vasodilators, nitroprusside, and verapamil. Methionine-induced impairment of resistance vessel dilatation to acetylcholine and bradykinin (p <0.05 vs placebo) was prevented by administration of vitamin E (acetylcholine, p = 0.004; bradykinin, p = 0.004; both vs methionine alone). Experimentally increasing plasma homocysteine concentrations by oral methionine rapidly impairs resistance vessel endothelial function in healthy humans and this effect is reversed with administration of the fat-soluble antioxidant, vitamin E.