Local venous responses to endotoxin in humans

BACKGROUND

Septic shock is characterized by arterial and venous dilatation and decreased responsiveness to vasoconstrictors. We have developed a method to explore the effects and mechanisms of action of administration of endotoxin into a blood vessel in vivo.

METHODS AND RESULTS

Endotoxin was instilled into a dorsal hand vein for 1 hour and then removed. A dose-response curve to norepinephrine was constructed before and 1, 2, 3, and 4 hours after endotoxin. In a separate study, dose-response curves to norepinephrine were constructed in two separate veins on the same hand, only one of which received endotoxin. Sympathetic-mediated venoconstrictor responses were also studied. Cyclooxygenase inhibitors, nitric oxide synthase inhibitors, and hydrocortisone were used to explore the mechanisms of the effects seen. Endotoxin caused a rightward shift in the dose-response curve to norepinephrine. The effect was greatest at 1 hour (maximal constriction: before endotoxin, 87 +/- 4%; after endotoxin, 52 +/- 8%; occlusion n = 4; P < .05) and returned to normal by 4 hours. In addition, deep-breath venoconstrictor responses were abolished in the endotoxin-treated vein. Instillation of endotoxin daily for 3 days resulted in the development of tolerance (maximal constriction to norepinephrine after endotoxin; day 1, 39 +/- 6%; day 2, 67 +/- 7%; day 3, 85 +/- 7%). Cyclooxygenase and/or nitric oxide synthase inhibitors did not alter the response to endotoxin, whereas prior administration of hydrocortisone abolished the effects.

CONCLUSIONS

Instillation of endotoxin caused a glucocorticoid-inhibitable hyporesponsiveness to the constrictor effects of norepinephrine and abolished sympathetically induced and drug-induced venoconstriction. This acute response does not appear to be mediated by nitric oxide or prostanoids. Direct vascular tolerance to endotoxin occurs on repeated administration.

Characterization of hepatic nitric oxide synthase: identification as the cytokine-inducible form primarily regulated by oxidants

Induction of hepatic nitric oxide synthase (NOS) by tumor necrosis factor-alpha (TNF alpha), interleukin-1 beta (IL-1 beta), interferon-gamma (IFN gamma), interleukin-6 (IL-6), and lipopolysaccharide was assessed as activity and immunoreactive protein. Hepatic NOS activity was cytosolic and had cofactor requirements consistent with inducible nitric oxide synthase (NOS2). NOS induction by TNF alpha was dose dependent from concentrations of 0.06 to 60 nM and was increased 2-3-fold by IFN gamma. NOS induction was reflective of total TNF alpha binding to hepatocyte receptors. Hepatocyte TNF alpha binding fit a biphasic curve with high affinity (K(d) = 1.4 nM, Bmax = 3157 sites) and low affinity (K(d) = 157 nM, Bmax = 204,948 sites) elements. NOS2 activity was induced by lipopolysaccharide, IL-1 beta, TNF alpha, and IFN gamma but not by IL-6. All cytokine stimuli were inhibited by antioxidants. Oxygen radical generation was directly measured as dichlorofluoroscein fluorescence in isolated mitochondria. Mitochondria from TNF alpha-treated hepatocytes generated more oxygen radicals than did controls. Antioxidants reduced mitochondrial generation of oxygen radicals. Activation of the transcription factor nuclear factor-kappa B by TNF alpha, IFN gamma, and IL-1 beta was assessed by gel shift analysis. Cytokine treatment increased nuclear factor-kappa B binding, and the addition of antioxidants or rotenone inhibited cytokine activation. Taken together, these data suggest that oxygen radicals, possibly generated by mitochondria, play a major role in NOS2 induction by cytokines.

Distress and radiological investigations of the urinary tract in children

The distress associated with radiological investigations may be related to the information and style of parental explanation given to the child and the parents own coping style. In a questionnaire survey we assessed distress in relation to investigations of the urinary tract using the Groningen Distress Rating Scale and the Utrecht Coping List. We found the micturating cystourethrogram (MCUG) to be significantly more distressing than radionuclide investigations. MCUG distress was adversely correlated with passive and palliative parental coping styles. Results suggested that cognitive coping styles modelled by the parents ameliorated distress on dimercaptosuccinic acid scintigraphy.

CONCLUSION

The high level of MCUG associated distress and presence of traumatised children in the MCUG sample, along with the potential for parental contribution to distress reduction, suggests that both children and parents would benefit from more active preparation programmes prior to MCUG testing.

Gastric intramural pH in mechanically ventilated patients

BACKGROUND

The hypothesis that gastric intramural pH (pHi) is predictive of outcome in haemodynamically stable, mechanically ventilated patients was tested in 25 patients on assisted mechanical ventilation for respiratory failure.

METHODS

Simultaneous samples of arterial blood and gastric juice were obtained from patients on assist control, synchronised intermittent and pressure control ventilation during the first 48 hours of mechanical ventilation. Gastric pHi was calculated from the equation: pHi= 6.1 + log HCO3/(gastric PCO2 X 0.03). The outcome was survival or death due to respiratory or circulatory failure within 45 days of admission.

RESULTS

Gastric pHi proved to be a better predictor of outcome than all presently utilised parameters. Although all patients included in this study were haemodynamically stable and were similar for all laboratory indices, the only variable capable of accurately predicting outcome was gastric pHi. Patients with a normal arterial pH but a gastric intramural pH of less than 7.25 had an observed mortality of 66%. Standard severity of illness scores grossly underestimated mortality rates. The sensitivity and specificity of a gastric pHi value of less than 7.25 in predicting death were 86% and 83%, respectively. A receiver operator curve for all variables exaggerates the superiority of gastric pHi as a predictor of outcome.

CONCLUSION

Low gastric pHi, a marker of gastrointestinal ischaemia, may occur in the presence of normal haemodynamics and may be used to predict severity of illness and mortality accurately.

Isolated reduction in single-breath diffusion capacity in young, healthy, asymptomatic women

The clinical significance of an isolated reduction in the carbon monoxide diffusing capacity (DLCO) in nonsmoking, asymptomatic individuals is not known. Whether a reduced DLCO despite otherwise normal pulmonary function tests warrants further investigation remains unanswered. In this article, the authors describe five healthy, asymptomatic, young women who had isolated, reduced DLCO and subsequent follow-up examinations over a span of 6 years. This case series lends support to the contention that an isolated low DLCO in asymptomatic subjects is not clinically significant and does not necessitate additional medical inquiry.

Vasodilatation to arachidonic acid in humans. An insight into endogenous prostanoids and effects of aspirin

BACKGROUND

Human endothelial and vascular smooth muscle cells synthesize prostanoids. Several of these have been implicated in the physiological and pathophysiological regulation of vascular tone; however, there is no direct evidence that human blood vessels synthesize sufficient prostanoid to alter vessel tone.

METHODS AND RESULTS

We explored the effects of local infusions of arachidonic acid on the tone of preconstricted superficial hand veins in healthy volunteers. Aspirin was used to assess the contribution of prostanoids to the responses seen. Local infusion of arachidonic acid produced a dose-dependent dilatation of preconstricted veins. This was abolished by local infusion of aspirin. Oral aspirin was also effective: a high (anti-inflammatory) dose of aspirin (1 g) taken 2 hours before the experiment blocked the arachidonic acid-induced venodilatation; however, a low (cardioprotective) dose of aspirin (75 mg) did not. Unlike the responses to arachidonic acid, responses to glyceryltrinitrate and bradykinin were unaltered by aspirin (1 g). Ex vivo platelet aggregation was inhibited by aspirin in both high and low doses. Aspirin (1 g) inhibited arachidonic acid-induced venodilatation for up to 5 days. The time course was similar for vascular and platelet effects.

CONCLUSIONS

The present findings demonstrate that local generation of prostanoids in a human vessel in vivo alters vascular tone. The predominant prostanoid synthesized is a dilator and its synthesis can be blocked by an anti-inflammatory but not a cardioprotective dose of aspirin. The results suggest that selective inhibition of platelet aggregation by oral aspirin might be a function of dose rather than the interval between doses.

A comparison of the efficacy and tolerability of moclobemide given as a single daily dose or in three divided doses per day for the treatment of patients with a major depressive episode (DSM-III-R)

This was a prospective, double-blind, randomized, multicenter trial comparing moclobemide once daily (OD) with three times daily (TDS) dosing. The duration of the study was 6 weeks with the initial dose of moclobemide being 450 mg/day (either 450 mg in the morning or 150 mg three times daily). Placebo tablets were used to ensure that the study was double blind. After 2 weeks, the dose could be increased to 600 mg/day if tolerability was acceptable and efficacy was judged insufficient by the investigator. Patients were assessed at baseline and at days 3, 7, 14, 21, 28, and 42. Efficacy was primarily judged on the Hamilton Rating Scale for Depression (HAM-D) (17item). Patients had to score at least 17 to enter the study. Safety and tolerability were judged on reported adverse events, safety parameters, premature withdrawals, and a physicians' global tolerability rating. There were also three secondary efficacy parameters--the Hamilton Rating Scale for Anxiety, Visual Analogue Scales for pain and irritability, and physicians' Clinical Global Impression (CGI). A total of 130 evaluable patients were required to detect a difference of more than 20% (alpha = 0.05 and beta = 0.8) between groups. A total of 189 patients entered the study, and the standard analysis comprised 145 patients. The efficacies between the two dosing regimens as determined by the HAM-D score and from the CGI were found not to differ significantly. For the standard analysis population, there was a reduction in mean HAM-D of 73.8 and 72.9% for the OD and TDS groups, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Vascular and hormonal responses to arginine: provision of substrate for nitric oxide or non-specific effect?

1. The vascular and hormonal effects of L- and D-arginine were compared in healthy subjects and in patients with insulin-dependent diabetes mellitus or untreated essential hypertension. 2. Infusion of L- or D-arginine (40 mumol/l) in the forearm vascular bed, sufficient to increase the local concentration approximately 20-fold, had no effect on blood flow or the vasodilator response to acetylcholine (30 and 100 nmol/min) in patients with insulin-dependent diabetes (n = 7) or essential hypertension (n = 7), or in age- and sex-matched control subjects (n = 7 in both groups). 3. Systemic infusion of 10 g of L-arginine (n = 5) or D-arginine (n = 3) increased plasma concentration of arginine approximately 20-fold without altering supine or erect haemodynamics. Increases in plasma insulin, prolactin and glucagon were seen with both enantiomers. The stereopurity of arginine was confirmed in a cell-culture assay system. 4. We conclude that, in healthy subjects and patients with essential hypertension or insulin-dependent diabetes, synthesis of nitric oxide within the vasculature is not limited by substrate availability. At high concentrations of arginine, non-stereospecific effects, including alterations in hormone concentration, occur. It remains to be determined whether these non-stereospecific hormonal changes might contribute to certain haemodynamic effects of arginine.

Measuring forearm blood flow and interpreting the responses to drugs and mediators

Venous occlusion plethysmography has been widely used to study forearm blood flow. The principle of the technique is straightforward: the rate of swelling of the forearm during occlusion of venous return is used to assess the rate of arterial inflow. Provided that perfusion pressure (arterial blood pressure) remains constant, changes in flow reflect changes in smooth muscle tone in small arteries and arterioles. Local infusion into the brachial artery allows assessment of the direct effect of drugs on vascular tone and has been used to probe the roles of endogenous mediators. The technique is at its most powerful when dose-response relationships to different drugs or mediators within a single study are being compared but can also be used for comparison of responses to drugs between healthy control subjects and patient populations. However, when responses between groups are being compared, it is important to take into account the starting conditions of baseline blood flow and pressure. This article describes venous occlusion plethysmography, discusses the presentation and analysis of data (dose of drug or concentration? forearm blood flow or resistance?), and highlights certain potential problems and limitations of the technique as a means of studying disease states.

Relative potency and arteriovenous selectivity of nitrovasodilators on human blood vessels: an insight into the targeting of nitric oxide delivery

The arteriovenous potency of sodium nitroprusside (SNP), linsidomine (SIN-1) and S-nitrosoglutathione (GSNO) was determined in human capacitance (veins) and resistance (arterioles) vessels in vitro and in vivo and compared with the venoselective nitrovasodilator nitroglycerin (GTN). Concentration-response curves were constructed to GTN, SNP, GSNO and SIN-1 (0.001-10 microM) in preconstricted human saphenous vein and to GTN, GSNO and SIN-1 (0.001-10 microM) in omental resistance vessels. In vivo the dilator responses of the dorsal hand vein and the forearm resistance bed were recorded during local infusions of GTN, SNP, GSNO and SIN-1 (1 pmol/min to 160 nmol/min). SNP and SIN-1 had similar arteriovenous profiles to that of GTN. SNP was equipotent with GTN in arterioles and veins but SIN-1 was 10-fold less potent than GTN in vitro and 100-fold less potent in vivo; the potency of SIN-1 was increased after incubation of saphenous vein with superoxide dismutase. GSNO was equipotent with GTN in arterioles but 10-fold less potent in veins in vitro and in vivo. These results demonstrate that most nitrovasodilators are venoselective irrespective of their mechanism of biotransformation to nitric oxide (NO) and suggests that NO itself might be venoselective in vivo. Endogenous carrier molecules, including glutathione, could alter the vascular profile of NO with physiological and therapeutic implications.

Defective repair of O6-methylguanine-DNA in primary Sjögren's syndrome patients predisposed to lymphoma

OBJECTIVE

To investigate a role for mutation in the aetiogenesis of autoimmune disease by examining levels of repairing enzyme for the promutagenic DNA base lesion, O6-methylguanine, in lymphocyte extracts from patients with autoimmune diseases. We included primary Sjögrens syndrome (PSS) patients because of the additional relevance of their being at increased risk (> 40-fold) of developing lymphoma.

METHODS

Lymphocytes were prepared from patients with PSS (n = 22) (12 with parotid gland enlargement, an indicator of extensive lymphoproliferation), rheumatoid arthritis (n = 12), primary biliary cirrhosis (n = 11), osteoarthritis (n = 12), and healthy individuals (n = 11). MGMT amounts were determined in lymphocyte extracts by direct enzyme assay and expressed in relation to total extract DNA, protein, or cell number.

RESULTS

We found no defect in the repairing methyltransferase enzyme between any of the groups, except in PSS patients at increased risk of developing lymphoma (those with enlarged parotid glands): p < 0.0001 and p = 0.0056, compared with healthy controls and PSS patients without parotid gland swelling, respectively.

CONCLUSIONS

Our findings implicate persistence of O6-methylguanine-DNA in the aetiology of lymphoma associated with PSS, and raise the possibility that an alternative repair process for O6-methylguanine-DNA, nucleotide excision repair, might be defective in autoimmune disease.

Spinal aspergillus abscess in a patient with bronchocentric granulomatosis

Aspergillus fumigatus hyphae is often found in the lung tissue of patients with bronchocentric granulomatosis (BCG). This organism is believed to be one agent responsible for inciting the hypersensitivity response and subsequent development of the characteristic pathology that defines BCG. The definitive etiology of this disease, however, remains conjectural. Corticosteroids represent the mainstay of therapy. The fungi recovered from patients with BCG are considered noninvasive; thus, the risk of fungal invasion secondary to steroid-induced immunosuppression is believed to be negligible. However, we report a case of spinal aspergillus abscess that developed in a patient with BCG subsequent to steroid therapy. This case also highlights the necessity for aggressive medical and neurosurgical intervention to avert the development of neurological sequelae.