Mechanism of action of N-acetylcysteine in the protection against the hepatotoxicity of acetaminophen in rats in vivo

N-Acetylcysteine is the drug of choice for the treatment of an acetaminophen overdose. It is thought to provide cysteine for glutathione synthesis and possibly to form an adduct directly with the toxic metabolite of acetaminophen, N-acetyl-p-benzoquinoneimine. However, these hypothese have not been tested in vivo, and other mechanisms of action such as reduction of the quinoneimine might be responsible for the clinical efficacy of N-acetylcysteine. After the administration to rats of acetaminophen (1 g/kg) intraduodenally (i.d.) and of [(35)S]-N-acetylcysteine (1.2 g/kg i.d.), the specific activity of the N-acetylcysteine adduct of acetaminophen (mercapturic acid) isolated from urine and assayed by high pressure liquid chromatography averaged 76+/-6% of the specific activity of the glutathione-acetaminophen adduct excreted in bile, indicating that virtually all N-acetylcysteine-acetaminophen originated from the metabolism of the glutathione-acetaminophen adduct rather than from a direct reaction with the toxic metabolite. N-Acetylcysteine promptly reversed the acetaminophen-induced depletion of glutathione by increasing glutathione synthesis from 0.54 to 2.69 mumol/g per h. Exogenous N-acetylcysteine did not increase the formation of the N-acetylcysteine and glutathione adducts of acetaminophen in fed rats. However, when rats were fasted before the administration of acetaminophen, thereby increasing the stress on the glutathione pool, exogenous N-acetylcysteine significantly increased the formation of the acetaminophen-glutathione adduct from 57 to 105 nmol/min per 100 g. Although the excretion of acetaminophen sulfate increased from 85+/-15 to 211+/-17 mumol/100 g per 24 h after N-acetylcysteine, kinetic simulations showed that increased sulfation does not significantly decrease formation of the toxic metabolite. Reduction of the benzoquinoneimine by N-acetylcysteine should result in the formation of N-acetylcysteine disulfides and glutathione disulfide via thiol-disulfide exchange. Acetaminophen alone depleted intracellular glutathione, and led to a progressive decrease in the biliary excretion of glutathione and glutathione disulfide. N-Acetylcysteine alone did not affect the biliary excretion of glutathione disulfide. However, when administered after acetaminophen. N-acetylcysteine produced a marked increase in the biliary excretion of glutathione disulfide from 1.2+/-0.3 nmol/min per 100 g in control animals to 5.7+/-0.8 nmol/min per 100 g. Animals treated with acetaminophen and N-acetylcysteine excreted 2.7+/-0.8 nmol/min per 100 g of N-acetylcysteine disulfides (measured by high performance liquid chromatography) compared to 0.4+/-0.1 nmol/min per 100 g in rats treated with N-acetylcysteine alone. In conclusion, exogenous N-acetylcysteine does not form significant amounts of conjugate with the reactive metabolite of acetaminophen in the rat in vivo but increases glutathione synthesis, thus providing more substrate for the detoxification of the reactive metabolite in the early phase of an acetaminophen intoxication when the critical reaction with vital macromolecules occurs.

Age-dependence of hypertensive-normotensive differences in plasma norepinephrine

We compared venous plasma norepinephrine (NE) concentrations in 191 resting, supine patients with essential hypertension and 129 normotensive controls. Among normotensives, plasma NE increased significantly with age, but among hypertensives, no age-related increase occurred, due to relatively high NE values among young hypertensives. When patients and controls less than 40 years old were considered, hypertensives showed significantly higher plasma NE than the controls (317 vs 245 pg/ml, t = 3.15, p less than 0.01); but above the age of 40 years, no significant hypertensive-normotensive difference was obtained. These results, predicted by recent literature reviews, help to resolve the persistent controversy about sympathetic neural activity in essential hypertension, since such activity appears to be abnormal mainly in young patients. The data are consistent with increased sympathetic nervous system activity in the early stages of essential hypertension.

Platelet aggregation in whole blood determined using the Ultra-Flo 100 Platelet Counter

The Ultra-Flo 100 Whole Blood Platelet Counter has proved a useful tool for measuring platelet aggregation in whole blood, the extent of aggregation being deduced from the number of single platelets that remain. The technique has allowed us to show that platelets aggregate spontaneously in citrated blood and in heparinized blood but not in whole blood collected into EDTA. The aggregation occurs during storage but its rate is enhanced by stirring and it occurs more readily when the whole blood has been exposed to plastic rather than glass. It occurs much more readily in whole blood from some individuals than from others and the process may involve adenosine diphosphate (ADP). The rate of aggregation in whole blood is enhanced by several aggregating agents including collagen, ADP and sodium arachidonate which are more usually studied in platelet-rich plasma.

Metastasizing mammary tumors. Spontaneous mammary tumors in asplenic mice heterozygous for athymia

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Absence of morphological, chromosomal and antigenic changes in the K-562 cell line growing as localized or disseminated tumours in nude mice

Transplantation of K-562 cells into adult and newborn nude mice led to the development of localized s.c. and disseminated myelosarcomas, respectively. This age-associated, changing pattern of in vivo proliferation of K-562 cells derived from a single aliquot was consistently repeated throughout sequential passages. The only variable in this experimental system was the age of the recipient mice. Not only did the mice have an identical genetic background, but also the transplanted K-562 cells were derived from a single culture passage. As shown by cytological and histological examinations, the characteristic morphology and percentage composition of the subpopulations of the K-562 cell line were preserved in successive in vitro and in vivo passages. The K-562 cells had no prevailing phenotypic traits which could be associated with the growth either in the s.c. tissue or in the viscera. Furthermore, the cells maintained the human karyotype, including their typical chromosomal abnormalities and antigenic determinants, as demonstrated by the binding of a specific antibody, throughout all passages. Our results demonstrate that heterotransplanted K-562 cells may change their behaviour in vivo without undergoing modifications associated with different types of growth. These findings would indicate that the ability of neoplastic cells to proliferate in various environments (metastases) is not the consequence of predetermined cellular characteristics but is functionally conditioned.

Early reporting of myocardial infarction: impact of an experiment in patient education

Many deaths from myocardial infarction occur before medical help is sought. A campaign was mounted in Nottingham ("Nottingham Heartwatch") to encourage early reporting. A total of 13 828 men and women aged 40 and over registered with three general practices were asked to telephone a hospital-based number if they developed chest pain lasting for more than 10 minutes. Patients from study practices reported chest pain earlier after our invitation than they had before and also earlier than patients from control practices. While accepting the advice to call early some patients from the study practices ignored our special number and telephoned their general practitioner. The calls received on the Heartwatch line yielded a lower percentage of definite and probable infarcts than the calls received by the patients' own doctors. The way in which the characteristics of the study practices might have influenced this difference is discussed since it has considerable implications for larger-scale attempts to bring patients with suspected myocardial infarction under medical care at the earliest opportunity.

Arrest and extravasation of neoplastic cells. An electron microscopy study of serial sections at sequential stages

The morphological aspects of the arrest and extravasation of malignant cells of human origin (K-562 cell line) in the lungs of athymic (nude) and asplenic-athymic (lasat) mice were studied by electron microscopy examination of serial sections. The specimens were obtained at sequential stages after the sc inoculation into newborn mice of 10(7) malignant cells. K-562 cells (10(5)) were also injected iv into control groups of nude and lasat mice to assess the influence of the route of inoculation on the in vivo behavior of K-562 cells. Our results demonstrated that K-562 cells were arrested and proliferated within the pulmonary capillaries without the participation of platelets or fibrin. The neoplastic cells extravasated by attrition and penetration of the endothelium (rather than by diapedesis) and continued to proliferate in the interstitial tissue of the lung, developing into neoplastic nodules. Following iv injection, K-562 cells induced the formation of platelet-tumor cell aggregates within the pulmonary capillaries. However, under these conditions, the neoplastic cells did not adhere to the endothelium nor did they proliferate or extravasate. These aggregates were flushed out by the circulation, restoring the permeability of the capillaries.

Rhesus diploid rabies vaccine (adsorbed), a new rabies vaccine. Results of initial clinical studies of preexposure vaccination

To meet the need for a safe, efficacious, and low-cost rabies vaccination program, the Michigan Department of Public Health developed a new rabies vaccine: rhesus diploid rabies vaccine, adsorbed (RDRV). Initial clinical studies were conducted in 534 volunteers using preexposure protocols consisting of two injections of RDRV given 1, 2, or 4 weeks apart. This new rabies vaccine induced an excellent rabies virus antibody response two to three weeks after vaccination: antibody levels were superior to those reported after duck embryo rabies vaccine and were similar to those reported with human diploid rabies vaccine. In addition, vaccination with RDRV was associated with an acceptable level of local and constitutional symptoms.

The distribution and associations of blood pressure in an adolescent population

In this report we describe the distributions of blood pressure and its associations in adolescence. Six hundred and twenty-five subjects aged 13 to 18 were drawn from three general practices in different urban and rural settings. Systolic pressures were higher and rose with age in boys (mean = 119 mm Hg) compared with girls (mean = 114 mm Hg), who showed no age association. Diastolic pressures (phase 5) were higher in girls (mean = 64 mm Hg) than in boys (mean = 60 mm Hg) and showed no association with age in either sex. Initial blood pressures were generally higher than those recorded after a further five minutes' rest in the sitting position, although diastolic pressures rose on the second reading in the older subjects. Systolic pressures of subjects from the suburban practice and in the late autumn were relatively low; diastolic pressures tended to be lower in the spring and in subjects from the rural practice. Systolic pressures were lower in the morning and this was found to be primarily related to fasting status. Individuals with a positive family history of hypertension had significantly higher blood pressures than those with a negative history. Boys who frequently played sports had lower diastolic pressures, largely accounting for the above sex difference. We conclude that although blood pressure measurement in adolescence is a difficult screening procedure it should be offered to selected groups such as those with a family history of hypertension.

In vivo regulation of hepatic glutathione synthesis: effects of food deprivation or glutathione depletion by electrophilic compounds

The increased glutathione turnover that occurs during fasting results from two mechanisms. Because of a decrease in the intrahepatic free glutathione: mixed disulfide ratio, which is apparently mediated by c-AMP, the free glutathione pool contracts and turns over more rapidly in order to maintain glutathione synthesis. In addition, glutathione consumption via the gamma-glutamyl cycle apparently is increased during fasting. Additional data indicate that an inability to stimulate further the rate of glutathione synthesis during fasting, rather than a reduction in glutathione synthesis are previously postulated, probably explains the increased susceptibility of fasted animals to tissue attack by electrophilic drug metabolites.

Relevance of lipids to heterotransplantation of human malignancies

Although the transplantation of human neoplasms in immunodeficient mice is now a well-established procedure, the majority of primary malignancies cannot be successfully maintained for long periods of time in adult athymic (nude) and asplenic-athymic (lasat) mice. Various lipids such as cholesterol, cholesterol oleate, stearic and palmitic acid esters markedly depress the RES phagocytic activity and immunocompetence of mammals. In view of the immunosuppressive properties of certain lipids and in order to graft and grow as many tumors as possible, further studies into the effects of lipids on the growth of heterotransplanted human tumors is warranted. Lipids may enhance local growth and facilitate the development of metastases rarely seen in nude and lasat mice bearing xenogeneic cancer cells. Lipids may accelerate human malignant cell proliferation in mice by both depressing further the defense of host and modifying the cancer cell membrane. The relationship of lipids to the onset and progression of 'spontaneous' tumors in humans is not known.

Toxic doses of acetaminophen suppress hepatic glutathione synthesis in rats

The effect of a toxic dose of acetaminophen on hepatic glutathione turnover was studied in fed and fasted rats. Following the administration of 1 gm per kg of acetaminophen, the fractional rate of glutathione turnover increased from 0.19 to 0.28 hr-1 in fed rats and from 0.43 to 0.50 hr-1 in rats fasted for 48 hr. The increase in the fractional rate of turnover was proportionally much less than the decrease in hepatic glutathione concentration resulting from the toxic dose of acetaminophen. Thus, the estimated hepatic synthesis of glutathione decreased from 0.86 and 1.50 mumole per gm liver . hr to 0.59 and 0.53 mumole per gm . hr in fed and fasted rats, respectively. The excretion of acetaminophen-sulphate was significantly decreased in fasted rats. The fraction of administered acetaminophen metabolized to the mercapturic acid, however, was similar in both groups. Nevertheless, all fasted animals had massive centrilobular necrosis whereas virtually no necrosis was observed in fed animals. The administration of sulfate did not protect against liver injury in fasted rats. In view of the similar synthesis of glutathione in fed and fasted rats following a toxic dose of acetaminophen, an inability to synthesize adequate quantities of glutathione or a decreased availability of sulfate cannot account for the increased susceptibility to liver injury in the fasted state. However, a toxic dose of acetaminophen depletes the hepatic glutathione to a lower nadir before glutathione is repleted by synthesis, and a greater amount of tissue arylation occurs during this brief period of critically depleted glutathione.

Adolescents' use of mental health services in a comprehensive treatment facility: age, sex and mode of entry

Data are presented from the clinical records of 185 adolescents who were admitted to the mental health service of a youth health center serving a community of military dependents. Eight and one-half per cent of the population made a first visit to the center during an eight month period. Midadolescence (ages 15-16) was the age period when patients began to refer themselves to mental health services in significant numbers. The importance of parents as referral sources decreased with age, while medical and school sources were important in all ages. The psychological morbidity in the target population was greater in midadolescence than in early and late adolescence and higher in females than in males. Females presented with more somatic and family problems, males more often with aggressive behavior problems.

Blood pressure reduction in elderly: a randomised controlled trial of methyldopa

A total of 123 out of 549 elderly residents of local authority welfare homes in Nottinghamshire were found at screening to have a standing or lying diastolic blood pressure of 100 mm Hg or more. These 123 subjects were randomly allocated to simple observation or to treatment with methyldopa. The cumulative mortality was similar in the observed and treated groups and in the normotensive group from which the subjects had been separated. Thus moderate hypertension, whether treated or not, was not a major risk predictor in the elderly population studied.

The diagnosis and management of patients admitted to hospital with acute breathlessness

The authors have studied 352 emergency medical admissions during a summer period and 355 during the winter months to identify 177 patients who had been treated for breathlessness. Multiple and rapidly changing treatments have been taken to indicate diagnostic uncertainty. Using this model, the authors have shown that there is much more uncertainty in winter than in summer and that the working diagnosis of chest infection or asthma is particularly likely to be associated with multiple treatment. It is questionable whether the stereotyped descriptions of diseases in standard text books provide an adequate basis for emergency treatment decisions and it is considered that the diagnostic value of investigations such as chest radiography needs further careful scrutiny.

Serum lipids in a teenage population: geographic, seasonal and familial factors

The lipid results of a cross-sectional study of cardiovascular disease risk factors in over 600 13-18 year olds drawn from general practices in contrasting areas are reported. Differences were noted between the 3 practices, including a significant variation in the blood group distribution. HDL cholesterol showed a marked variation between the 3 practices which was unlikely to be due solely to seasonal variation. Alcohol consumption though not an univariate correlate of HDL cholesterol was however a strong partial correlate, as were age, height, sexual maturation, adiposity and smoking. Using 6 factors in each sex, 13% of the interchild variance of HDL cholesterol in boys could be explained in a multiple linear regression analysis, and 8% in girls. Including the practice variation as a further independent variable increased the explanation in 18% in boys and 15% in girls. An intraclass correlation (sib-sib) of 0.36 was found for HDL cholesterol, suggesting a strong familial influence. The implications of these results are discussed, along with the difficulties of screening for hyperlipidaemia in this age group.