Central and peripheral haemodynamic effects of L-NAME infusion in healthy volunteers

AIMS

To evaluate the effects of the intravenous administration of the nitric oxide synthesis inhibitor N(g)nitro-L-arginine methyl ester (L-NAME) in healthy volunteers.

METHODS

L-NAME (0.25, 0.5 and 0.75 mg/kg over 8 min) was infused in 13 healthy male volunteers. Finally, subjects were infused with either L- or D-arginine.

RESULTS

L-NAME resulted in dose-dependent falls in heart rate 60 bpm (55-64 bpm) to 49 bpm (46-52 bpm) (P<0.01) and increased mean arterial pressure 77.0 mmHg (73.2-80.8 mmHg) to 90.0 mmHg (87.1-92.8 mmHg) (P<0.01). The cardiac output was significantly reduced after each L-NAME infusion, and systemic vascular resistance increased linearly over the dosage range. Cardiac stroke volume was significantly reduced only following 0.75 mg/kg/min L-NAME: from 100 ml (91.3-108.7 ml) to 83 ml (74.7-91.4 ml); P<0.01. Forearm blood flow was unchanged at any dosage. L-arginine but not D-arginine infusion reversed the haemodynamic effects of L-NAME.

CONCLUSIONS

Contrasting with the profound dose-dependent effects of L-NAME had significant effects on central haemodynamics but no discernible effects on peripheral blood flow.

Early vascular abnormalities and de novo nitrate tolerance in diabetes mellitus

OBJECTIVE

The haemodynamic consequence of altered mechanical wall properties in diabetes can impair the compliance characteristics or pulsatile function of arteries before changes in calibre or peripheral resistance become evident. We studied the sensitivity of pulsatile and steady-state haemodynamic variables in identifying vascular abnormalities and assessing arterial responsiveness to glyceryl trinitrate (GTN) in patients with diabetes, free from clinical complications of the disease.

METHODS

Radial artery pressure waveforms were recorded in 22 patients with diabetes and 22 age- and sex-matched control subjects, using a calibrated tonometer device. A computer-based assessment of the diastolic pressure decay was used to quantify changes in arterial waveform morphology in terms of pulsatile (arterial compliance) and steady-state (peripheral resistance) haemodynamics. Pressure pulse waveforms were recorded before and 3, 6 and 9 min after the administration of 300 micro g of GTN.

RESULTS

Of the pulsatile and steady-state impedance parameters, only small artery compliance was significantly different in patients, 4.7 ml/mmHg (95% CI 3.8-5.8), compared with control subjects 7.1 ml/mmHg (95% CI 5.4-8.7); (p < 0.05). In response to GTN small artery compliance increased, and systemic vascular resistance decreased significantly in control subjects; (p < 0.05) but remained unchanged in patients with diabetes.

CONCLUSIONS

Arterial waveform analysis proved more sensitive in detecting early vascular abnormalities and tracking the haemodynamic effects of GTN in patients with diabetes than changes in total peripheral resistance. The diminished responsiveness of the arterial vasculature to organic nitrates may have therapeutic implications for the treatment of cardiovascular disease in diabetes mellitus.

Anomalies of cardiac venous drainage associated with abnormalities of cardiac conduction system

The embryological development of the superior vena cava (SVC) is complex. If the left common cardinal vein fails to occlude it can, along with the left duct of Cuvier form a left SVC, which frequently drains into the coronary sinus. This may result in abnormalities in the anatomy of this structure. A persistent left SVC occurs in 0.5% of the normal population, and 3% to 4.3% of patients with congenital heart anomalies. The pacemaking tissue of the heart is derived from two sites near the progenitors of the superior vena cava. The right-sided site forms the sinoatrial node, the left-sided site is normally carried down to an area near the coronary sinus. Out of 300 patients with cardiac rhythm abnormalities, who have undergone electrophysiological studies (EPS), or permanent pacemaker insertion (PPI), we identified 12 patients with cardiac conduction abnormalities and anomalies of venous drainage. Anomalies of the coronary sinus may be associated with abnormalities of the conduction system of the heart. This may be due to the close proximity of the coronary sinus to the final position of the left-sided primitive pacemaking tissue. In our series of 300 patients, 4% had an associated left SVC, a similar incidence to that found in previous studies of congenital heart disease.

Unique case of fatal carbon monoxide poisoning in the absence of a combustible fossil fuel

A 37-year-old man died as a result of exposure to carbon monoxide within an apartment. An investigation of the apartment showed no gas appliances or gas supply to the apartment and no evidence of any combustion event to any part of the apartment or roof space. Inhalation of dichloromethane was excluded. Heating to the apartment was found to be via an electrical storage heater, the examination of which revealed that the cast-iron core and insulating material showed evidence of heat damage with significant areas devoid of carbon. This electric storage heater is hypothesized to be the source of carbon for the fatal production of carbon monoxide within the apartment.

Bacterial translocation and immunohistochemical measurement of gut immune function

AIMS

The local immune response in the small bowel mucosa might play a role in bacterial translocation (BT). The aim of this study was to quantify immune cells and secretory antibodies in the small bowel mucosa, and relate this to BT as assessed by culture of a mesenteric lymph node.

METHODS

Immunohistochemical techniques were used to measure the frequency of plasma cells and IgA and IgM positive cells in the lamina propria and semiquantitatively to assess mucosal surface IgA and IgM values in small bowel specimens obtained from 11 patients in whom positive evidence of BT had been identified in a mesenteric lymph node harvested at the time of laparotomy. These were compared with similar specimens obtained from 11 patients in whom a similar lymph node had yielded no growth.

RESULTS

BT was associated with a significantly increased median frequency of plasma cells (p < 0.01) and IgA positive cells (p < 0.05) in the lamina propria. The frequency of IgM positive cells was also higher in these patients, although this difference was not significant. In addition, semiquantitatively scored IgA and IgM concentrations at the mucosal surface were both significantly higher in the patients in whom BT had been identified (p = 0.006 and 0.016, respectively).

CONCLUSION

Higher numbers of plasma cells and higher IgA and IgM values are present in the small bowel mucosa of patients in whom BT has been shown to occur, suggesting an increased local immune response.

Nitric oxide modulation of blood vessel tone identified by arterial waveform analysis

Traditionally, nitric oxide-mediated alteration in blood vessel tone has been inferred from changes in flow in response to physical and pharmacological interventions using plethysmographic or ultrasonic techniques. We hypothesized that alteration in pulsatile arterial function may represent a more sensitive measure to detect and monitor nitric oxide-mediated modulation of arterial smooth muscle tone. Healthy male volunteers (n = 15) had radial artery pressure pulse waveforms recorded using a calibrated tonometer device. A computer-based assessment of the diastolic pressure decay was employed to quantify changes in arterial waveform morphology in terms of altered pulsatile (arterial compliance) and steady-state (peripheral resistance) haemodynamics. N(G)-nitro-L-arginine methyl ester (L-NAME), a stereospecific inhibitor of nitric oxide synthesis, was infused intravenously in incrementally increasing doses of 0.25, 0.5 and 0.75 mg/kg for 8 min each. Subjects then received either L-arginine or D-arginine (200 mg/kg over 15 min) intravenously in a blinded fashion. On a separate day, subjects had radial artery pressure pulse waveforms recorded before and after the sublingual administration of glyceryl trinitrate, an exogenous donor of nitric oxide. Cardiac output and heart rate decreased and mean arterial blood pressure increased significantly (P < 0.01 for all) in response to the incremental intravenous infusion of L-NAME. Small artery compliance decreased, whereas systemic vascular resistance increased in response to nitric oxide synthesis inhibition (P < 0.01 for both). The intravenous infusion of L-arginine restored the pulsatile and steady-state haemodynamic parameters to pre-treatment values, whereas D-arginine had no effect. Sublingual glyceryl trinitrate decreased systemic vascular resistance by 11%, whereas large artery- and small artery-compliance increased by 25% and 44% respectively. Pressure pulse contour analysis represents a sensitive and convenient technique capable of tracking changes in the pulsatile function of arteries accompanying nitric oxide-mediated alteration in arterial smooth muscle tone.

Analysis of a dimethacrylate copolymer (bis-GMA and TEGDMA) network by DSC and 13C solution and solid-state NMR spectroscopy

In this work the effect of dilution with TEGDMA on the kinetics of Bis-GMA polymerization and on the extent of polymerization or degree of conversion was studied using (a) DSC and (b) NMR. The systems with lower viscosity and lower Tg exhibited higher extent of polymerization. For Bis-GMA/TEGDMA mixtures the calculated Tg values were found to be higher than the experimental values suggesting that a dilution effect is predominant rather than intermolecular hydrogen bonding. Solid state NMR has been shown to be a convenient method for measuring the total amount of conversion in a mixed monomer system. The disappearance of the NMR solution spectrum was used to reveal overall polymerization kinetics.

Small bowel haemangioma with local lymph node involvement presenting as intussusception

Gastrointestinal haemangiomas make up 0.05% of all intestinal neoplasms. They are sometimes multiple and usually present with pain, bleeding, and obstruction. An associated haemangiomatous change in regional lymph nodes has not been reported previously. A woman of 21 years presented with abdominal pain and vomiting. Abdominal ultrasound and computed tomography scan showed a lower abdominal mass. Laparotomy revealed a small bowel tumour causing an intussusception together with enlarged mesenteric lymph nodes. Pathological examination revealed a small bowel haemangioma with mesenteric node involvement. The pathogenesis of haemangiomatous involvement of lymph nodes is discussed. Hamartomatous change is the likely cause in this patient.

Diagnosis of malignant melanoma by general practitioners and hospital specialists

The aim of this study was to audit all malignant melanomas confirmed histologically in the Scarborough Health District over six years, prompted by the continuing rise in incidence rate nationally and relatively high number of malignant melanomas excised by general practitioners (GPs) in this area. A total of 157 malignant melanomas were diagnosed (60% from females and 40% from males) over the six years; primary excisions being carried out by GPs (37%) and hospital specialists (63%). The clinical diagnosis of malignant melanoma was made in 9% of GP cases and 35% of the hospital specialist cases. However another 45.5% of GP cases, and 38% of hospital specialist cases were regarded as suspicious pigmented lesions clinically. The histological diagnosis was of superficial spreading malignant melanoma in 72% of the GP and 69% of the hospital specialist cases. Most of the GP melanomas were excised with a lateral margin of 2 mm or less (71%); around half of the hospital excisions had a margin of over 2 mm (49%). Most melanomas were 2 mm or less in depth (Breslow depth) in both the GP (81%) and hospital specialist (75%) series. Over the six year period (1993-98) the incidence of malignant melanomas has continued to rise, but Breslow depth at diagnosis has not changed significantly. It is therefore important to continue with early recognition of this condition by GPs in the first instance, reduction in its incidence being the long term goal. During five years of the study there were only 67 lesions thought clinically to be malignant melanoma (26 GP and 41 hospital specialist cases), but which proved to be benign histologically.

Pathophysiology and Treatment of Hepatitis C Infection

The pathophysiology and treatment of hepatitis C infection, formerly known as non-A, non-B hepatitis, are discussed. The worldwide prevalence is approximately 1%. The majority of patients infected with hepatitis C virus will develop chronic infection, leading to cirrhosis in a significant percentage. Transmission of hepatitis C is primarily through parenteral routes. Those who use intravenous drugs or received blood transfusions prior to 1992 comprise the major risk groups for the infection. The progression of chronic hepatitis C infection is insidious with possible progression to an inflammatory hepatitis developing within 5–10 years, cirrhosis in 10–20 years, and hepatocellular carcinoma in 20–30 years. Combination therapy with interferon alpha-2b and ribavirin is currently the treatment of choice. Therapy for hepatitis C continues to evolve with newer forms of interferon and HCV antivirals under development.

The general practitioners' view

General practitioners have patients on their lists who work in a variety of occupations, but the doctor is most unlikely to have had any training in occupational medicine. As a result, occupational causes for illness are rarely considered by GPs. Little contact occurs between occupational health physicians and GPs leading to a lack of understanding of the occupational physician's role. These two factors, when combined, may lead to patients receiving sub-optimal treatment. This could be remedied by better undergraduate and postgraduate training, and by greater professional contact.

Ultrasound-guided Tru-cut biopsy of the breast

Ultrasound-guided automated Tru-cut needle biopsy may be used as an alternative to fine needle aspiration cytology for the assessment of discrete mass lesions of the breast. This is a retrospective study of 187 biopsies, comparing the results with a final diagnosis obtained from subsequent excision or outpatient follow-up. Biopsies were performed using a spring-loaded gun under ultrasound guidance. Invasive malignancy was demonstrated in 114 biopsies, 98 of which were subjected to surgery, with no false-positives. Twelve biopsies contained 'atypical cells', pre-invasive malignancy or risk factors for invasive carcinoma, ten of which proved to be invasive malignancy on excision. Normal or benign tissue was found in 61 biopsies, but of those that proceeded to excision biopsy, 16 were invasive or in situ carcinoma. The sensitivity of the procedure for detecting significant pathology was 88.7%, and the specificity 100%. When used as part of triple assessment, the sensitivity increases to 97.9%. Ultrasound-guided Tru-cut needle biopsy is a well-tolerated and reliable procedure for providing a tissue diagnosis of malignancy before definitive treatment, and obviating the need for formal excision biopsy of lesions for which there is a low index of suspicion.

Endoscopic sclerotherapy compared with percutaneous transjugular intrahepatic portosystemic shunt after initial sclerotherapy in patients with acute variceal hemorrhage. A randomized, controlled trial

BACKGROUND

Hemorrhage from esophageal varices remains a substantial management problem. Endoscopic sclerotherapy was preferred for more than a decade, but fluoroscopically placed intrahepatic portosystemic stents have recently been used with increasing frequency.

OBJECTIVE

To compare sclerotherapy with transjugular intrahepatic portosystemic shunt (TIPS) in patients with bleeding from esophageal varices.

DESIGN

Randomized, controlled clinical trial.

SETTING

Three teaching hospitals.

PATIENTS

49 adults hospitalized with acute variceal hemorrhage from November 1991 to December 1995: 25 assigned to sclerotherapy and 24 assigned to TIPS.

INTERVENTION

Patients assigned to repeated sclerotherapy had the procedure weekly. In those assigned to TIPS, an expandable mesh stent was fluoroscopically placed between an intrahepatic portal vein and an adjacent hepatic vein.

MEASUREMENTS

Pretreatment measures included demographic and laboratory data. Postrandomization data included index hospitalization survival, duration of follow-up, successful obliteration of varices, rebleeding from varices, number of variceal rebleeding events, total days of hospitalization for variceal bleeding, blood transfusion requirements after randomization, prevalence of encephalopathy, and total health care costs.

RESULTS

Mean follow-up (+/-SE) was 567 +/- 104 days in the sclerotherapy group and 575 +/- 109 days in the TIPS group. Varices were obliterated more reliably by TIPS than by sclerotherapy (P < 0.001). Patients having TIPS were significantly less likely to rebleed from esophageal varices than patients receiving sclerotherapy (3 of 24 compared with 12 of 25; P = 0.012). No other follow-up measures differed significantly between groups. A trend toward improved survival, which was not statistically significant, was noted in the TIPS group (hazard ratio, 0.53 [95% CI, 0.18 to 1.5]).

CONCLUSIONS

In obliterating varices and reducing rebleeding events from esophageal varies, TIPS was more effective than sclerotherapy. However, TIPS did not decrease morbidity after randomization or improve health care costs. It seemed to produce better survival, but the increase in survival was not statistically significant.

Induced 1080 Bait-Shyness in Captive Brushtail Possums and Implications for Management

The probable cause of possums (Trichosurus vulpecula) becoming 'shy' towards 1080 [sodium fluoroacetate] bait, a growing problem in the control of this pest, was determined. Possums captured from North Canterbury, New Zealand, (n = 131) were offered sublethal baits (1 or 2.5 g) followed by lethal (6 g) baits 2 days later. Most possums became bait shy and the proportion becoming shy appeared to be related to the size of the initial sublethal dose. Most of a group of survivors retested after 3 months with toxic pellets were still shy. Shyness was not overcome by changing to a different mask (orange flavour, as opposed to cinnamon flavour) or toxin (brodifacoum), but changing to both a different bait base (carrot) and mask (orange) resulted in most shy possums eating a lethal quantity of bait. Possums therefore appeared to learn to recognise the bait base as the cue for avoiding poisoning. More shy possums than naive possums rejected non-dyed, non-masked, non-toxic pellets, confirming that shy possums recognised the bait base. Green dye appears to act as a secondary cue for avoiding pellets as a higher percentage of 'shy' possums than naive possums rejected dyed baits.

Effect of green lentils on colonic function, nitrogen balance, and serum lipids in healthy human subjects

Green lentils are an increasingly popular food, but their effects on human colonic function and serum lipids have been studied little. Nine healthy males aged 19-38 y consumed for 3-wk periods a controlled Western diet and the same diet supplemented with 130 g dry lentils/d [which contained 11.8 g non-starch polysaccharide (NSP)] incorporated into loaves, cakes, and soups. Protein was equilibrated with soy protein isolate and carbohydrate with soft drinks. Radioopaque markers were used to calculate mean transit time (MTT) and to correct fecal weight for infrequency of bowel movements. Feces were collected throughout the study and blood was taken on 2 d at the end of each period. Lentils increased fecal weight from 131 +/- 12 g/d (means +/- SEM) to 189 +/- 17.4 g/d (44.9%) (P < 0.005). MTT was unchanged: 46 +/- 6 h for the control diet and 43 +/- 4 h for the lentils (NS). Fecal nitrogen was increased to 2.49 +/- 0.08 g/d for lentils compared with 1.74 +/- 0.09 g/d for the control diet (P < 0.001) and urine nitrogen decreased to 15.31 +/- 0.52 g/d with the lentils compared with 15.90 +/- 0.51 g/d for the control diet (P < 0.05); nitrogen balance was unaffected. Serum lipids were unchanged by addition of lentils to the diet. Green lentils were effective in increasing fecal weight and can therefore make a valuable contribution to a healthy diet.

Intake of carbohydrate and its components--international comparisons, trends over time, and effects of changing to low-fat diets

Carbohydrate constitutes the major source of dietary energy for all peoples of the world. However, it has been difficult to make accurate determinations of intakes of carbohydrate and its constituents because of lack of individual assessments in which carbohydrate components are included. For many countries, only food balance information is available and values for total carbohydrate are often derived by difference. Available information indicates that carbohydrate consumption decreased in many industrialized nations as prosperity led to an increased consumption of fat. Fat intakes have fallen over the past two decades and carbohydrate intakes have increased, but still do not approach the 60-70%contribution of carbohydrate to total energy in developing countries. A negative image for carbohydrate has led to a reluctance to accept it as a legitimate dietary component, particularly in North America. New evidence of the beneficial effects of starch in the diet indicates that increased consumption of carbohydrate, especially in the form of starch, should be promoted in Western countries.

Chloroplast gene sequence data suggest a single origin of the predisposition for symbiotic nitrogen fixation in angiosperms

Of the approximately 380 families of angiosperms, representatives of only 10 are known to form symbiotic associations with nitrogen-fixing bacteria in root nodules. The morphologically based classification schemes proposed by taxonomists suggest that many of these 10 families of plants are only distantly related, engendering the hypothesis that the capacity to fix nitrogen evolved independently several, if not many, times. This has in turn influenced attitudes toward the likelihood of transferring genes responsible for symbiotic nitrogen fixation to crop species lacking this ability. Phylogenetic analysis of DNA sequences for the chloroplast gene rbcL indicates, however, that representatives of all 10 families with nitrogen-fixing symbioses occur together, with several families lacking this association, in a single clade. This study therefore indicates that only one lineage of closely related taxa achieved the underlying genetic architecture necessary for symbiotic nitrogen fixation in root nodules.

A high-throughput assay for cyclic nucleotide phosphodiesterases

The search for cyclic nucleotide phosphodiesterase inhibitors in large chemical and natural product libraries is limited by assay throughput. A high-throughput assay that can monitor different phosphodiesterase activities would be useful for these inhibitor searches. We have developed a sensitive phosphodiesterase assay which is based on the selective precipitation of the radiolabeled 5'-nucleotide product by zinc and barium. This assay is unique to previous precipitation methods in that it measures product formed, either GMP or AMP. The procedure was adapted to a microtiter plate format for high-throughput, making it possible to perform in excess of 960 assays per day. This method was used to determine accurate enzyme kinetic constants for three different phosphodiesterases. The results agree favorably with literature values. Using the cyclic guanosine 3',5'-monophosphate-specific phosphodiesterase, IC50 values for the inhibitors M&B 22,948 and 3-isobutyl-1-methylxanthine were also determined. Demonstration of appropriate Km and inhibitor IC50 values verifies the ability of this new assay to identify selective cyclic nucleotide phosphodiesterase inhibitors.