Nalmefene causes greater hypothalamic-pituitary-adrenal axis activation than naloxone in normal volunteers: implications for the treatment of alcoholism

Among other actions, opioid antagonists modulate the control endogenous opioids exert on the hypothalamic-pituitary-adrenal (HPA) axis. Naloxone, nalmefene, and naltrexone are the opioid antagonists approved for use in man and are primarily mu-opioid selective. Naltrexone and nalmefene have been demonstrated to be useful in the treatment of alcoholism. Compared with naloxone, nalmefene has a longer half-life, is more potent at the mu-receptor, and has a higher affinity for kappa- and delta-opioid receptors. We conducted an inpatient study comparing the effects of 10 and 30 mg doses of intravenous naloxone and nalmefene in normal, nonsubstance nor alcohol-abusing, volunteers. Significant increases in ACTH and cortisol were observed after both antagonists, without an apparent dose-response relationship; however, both doses of nalmefene resulted in greater HPA axis activation than either dose of naloxone (ACTH: p <0.005). These results indicate that kappa- and delta-opioids may play important roles in the regulation of the HPA axis; nalmefene may be useful as both a probe to explore the HPA axis physiology and as a pharmacotherapeutic agent.

A matter of methods: perspectives on the role of the British general practitioner in the care of people with HIV/AIDS

This paper is a critique of, and a comment on, the debate about the role of British general practitioners (GPs) in HIV care. We argue that (1) this debate is conducted around arguments which leave significant aspects of GPs' contribution undocumented and unnoticed, and that (2) research has contributed to this omission. The paper reviews the history of the debate about GPs' involvement in HIV care and argues that social research using structured survey methods has reinforced the continuing negative image of GP care. The paper draws on an ethnographic research project in Lothian (Scotland) which found that many people with HIV strongly valued their ongoing personal relationship with their GP. People with HIV also valued the hospital-based outreach system which provided reliable and high quality care, but sometimes experienced the associated interprofessional information sharing and discussion as invasive and controlling. Their GP relationship was valued because it was outside this hospital-based system of care. The paper concludes by suggesting that future developments in GP care should build on this positive aspect of the GP-patient relationship.

Self-recorded stress levels for general practitioners before and after forming an out-of-hours primary care centre

The Nottingham Stress-Arousal Checklist (SACL) was used to compare stress and arousal levels within a group of 36 Scottish general practitioners (GPs) before and after an out-of-hours primary care centre opened in 1995. Overall, GPs reported significantly lower stress and higher arousal scores with the new service.

Differential hepatic and renal cholesterol levels in diabetes-prone BHE/cdb rats fed menhaden oil or beef tallow

A series of experiments were conducted to determine whether the feeding of beef tallow compared with menhaden oil would affect renal cortex membrane composition, Na,K-ATPase activity, renal cholesterol uptake, and plasma lipoprotein cholesterol profile. BHE/cdb rats were used because they carry a genetic trait for non-insulin-dependent diabetes mellitus and are prone to develop diabetic nephropathy. Beef tallow feeding resulted in an increase in HDL cholesterol and an increase in Na,K-ATPase activity. The different fats also affected the arachidonic acid content of the membrane but not the membrane cholesterol content. These diet effects may explain why the development of renal disease in beef tallow-fed rats is delayed when compared with rats fed an equivalent amount of menhaden oil.

A population based survey of women's experience of the menopause

OBJECTIVES

To describe the prevalence of, and degree of distress caused by, 15 symptoms commonly attributed to the menopause among a random sample of women aged 45 to 54, selected from the total population of a geographically defined area.

DESIGN

Postal questionnaire survey.

SETTING

Grampian Health Board area.

PARTICIPANTS

Eight thousand women, aged 45 to 54, randomly selected from the Grampian Community Health Index.

MAIN OUTCOME MEASURES

Self-reported symptoms, including depression, and use of hormone replacement therapy (HRT) among women of differing menopausal status.

RESULTS

The response rate was 78%; 57% of respondents had experienced one or more of the 15 symptoms listed, but only 22% had found such symptoms a problem. Women's experience of classic vasomotor and atrophic symptoms varied according to menopausal status but experience of general somatic and psychological symptoms did not. Users of HRT and women whose menopause was iatrogenic found more symptoms a problem.

CONCLUSIONS

Symptoms attributed to the menopause are common among women in the age group studied but often are not perceived as a problem. Among nonusers of HRT, only vasomotor and atrophic symptoms vary with menopausal status. Other somatic and psychological symptoms experienced by middle-aged women cannot be regarded as part of the same "menopausal syndrome'.

Diabetes mellitus induced by low-dose interleukin-2

Interleukin-2 (IL-2) is a potent immunomodulator that has been associated with the clinical development of autoimmune disorders. However, diabetes mellitus has not been reported in patients treated with single-agent IL-2. We conducted a clinical trial of a protracted daily schedule of subcutaneously administered low-dose IL-2. A patient with advanced colorectal cancer, treated with 1.5 x 10(6) international units of IL-2 daily, developed insulin-requiring diabetes during therapy. Hyperglycemia improved during treatment interruption and recurred with reinstitution of IL-2. The diabetes in this patient developed in the context of T cell and natural killer cell expansion, and the presence of islet cell autoantibodies was documented. We postulate that, in this patient, IL-2 reversed the anergy of autoreactive T cells that had escaped clonal deletion. It is possible that prolonged daily exposure to immunomodulatory doses of IL-2 will result in the development of autoimmune phenomena not observed with other schedules of administration.

Daily subcutaneous injection of low-dose interleukin 2 expands natural killer cells in vivo without significant toxicity

We aimed to determine the toxicity and immunological effects of daily s.c. administered low-dose interleukin (IL) 2. Adult cancer patients received a single daily s.c. injection of IL-2 as outpatients for 90 consecutive days. Cohorts of four to nine patients were treated at escalating IL-2 dose levels until the maximum tolerated dose (MTD) was defined. Peripheral blood mononuclear cell phenotyping, IL-2 serum levels, and the presence of anti-IL-2 antibodies were investigated. Thirty-eight patients were treated at seven IL-2 dose levels ranging from 0.4 to 1.75 million International Units (mIU)/m2 daily. The MTD was 1.25 mIU/m2, with constitutional side effects, vomiting, and hyperglycemia dose limiting. Severe toxicity did not occur at or below the MTD, although mild local skin reaction and mild constitutional side effects were common. Objective tumor regressions were not observed during this Phase I trial. Low-dose IL-2 resulted in natural killer (NK) cell (CD3(-) CD56(+)) expansion at all dose levels. This effect was dose dependent (P < 0.01), ranging from a 154 to 530% increase over baseline. Peak NK levels were achieved at 6-8 weeks and sustained through 12 weeks of therapy. As predicted by in vitro studies of IL-2 receptor structure-activity relationships, the subset of NK cells that constitutively express high-affinity IL-2 receptors (CD3(-)CD56(bright+)) showed more profound dose-dependent expansion, with increases ranging from 368 to 2763% (P = 0.015). NK expansion occurred at peak IL-2 levels <10 pM (2.3 IU/ml). Three patients developed nonneutralizing anti-IL-2 antibodies. Thus, we concluded that selective expansion of NK cells may be achieved in vivo with daily s.c. injections of low-dose IL-2 with minimal toxicity.

Incidence and severity of injuries resulting from amateur boxing in Ireland

OBJECTIVE

To determine the incidence, pattern, and severity of injuries resulting from participation in amateur boxing.

DESIGN

A prospective 5-month survey of injuries which occurred during competitive amateur boxing and training.

SETTING

Amateur boxing competitions held in Dublin between November 1992 and March 1993, and the six largest amateur boxing clubs in Dublin.

PARTICIPANTS

All the competitors in the tournaments and the > 16 year old members of the boxing clubs.

INTERVENTIONS

Participation in competitive amateur bouts and/or boxing training.

MAIN OUTCOME MEASURES

Incidence, pattern, and severity of injuries sustained in competition and training.

RESULTS

The incidence of injuries in competition was 0.92 injuries per man-hour of play (or 0.7 injuries per boxer per year), while the incidence in training was 0.69 injuries per boxer per year. Cerebral injuries were reported only in competition, most of these being mild concussion. Hand, wrist and facial injuries were related to direct impact and occurred more frequently in competition than training, while injuries to other body parts were predominantly chronic and training-associated. Shoulder and knee injuries were the most debilitating injuries seen.

CONCLUSIONS

The yearly risk of injury resulting from participation in amateur boxing is relatively low when compared with other sports. Cerebral injuries, which occur almost exclusively in competition, are predominantly mild concussions.

Evaluating the workload of practice nurses: a study

In 1990 and 1991, 67 practice nurses with a total of 12,725 consultations took part in a before and after study of health board attached and practice-employed nurse workload. The intervention of the New General Practitioner Contract (DoH 1989) and other primary care changes in April 1990 provided an opportunity to examine the process of care, and identify and changes in workload or differences in working patterns of attached and practice-employed nurses, as a result of these modifications. Practice-employed nurses initiated more of their own appointments following implementation of the New Contract and saw fewer GP referrals. Routing treatment room work had decreased for both groups of nurses in the second year. Both groups of nurses had also increased their level of therapeutic listening in the second year, but practice-employed nurses reported higher levels of therapeutic listening than their attached colleagues during both recording periods.

Psychological response to cervical screening

BACKGROUND

Few studies have examined the psychological costs of cervical screening, despite expressed concern over possible negative sequelae.

METHODS

Seventy-five women with mild or moderately dyskaryotic smears, under cytological surveillance, 75 women referred for colposcopy after a first-ever abnormal smear showing severe dyskaryosis, and 75 controls with recent negative cytology were interviewed at home, and their psychological adjustment was assessed.

RESULTS

Levels of distress were higher among women with an abnormal smear than among controls with a recent negative smear. Anxiety (Hospital Anxiety and Depression Scale range 0-21, "normal" range 0-7) was highest among those referred for colposcopy (mean 8.12, controls 5.88, P < 0.001); afterward, distress fell (mean 6.61, P < 0.001) but more problems of social adjustment were evident (surveillance vs controls, P < 0.01). High anxiety was associated with social maladjustment (colposcopy, P < 0.001; surveillance, P < 0.01) and negative feelings about the self (P < 0.05). Current anxiety was unrelated to knowledge about abnormal smears, but in the surveillance group was related to satisfaction with the explanation provided (P < 0.05).

CONCLUSION

A positive cervical smear may by psychologically traumatic for a significant minority of women, irrespective of management strategy.

Scottish neonatal intensive care units; a study of staff and parental attitudes

The study takes a three stage approach to review Scottish unit policies, staff views and parents experiences of visiting and involvement with their low birthweight infant (1,750 gm or less) in a sample of Scottish neonatal intensive care units (NICUs). The study indicated that while most units had 'liberal' views regarding parental and family visiting some staff views were not in line with their unit policy and retained reservations about family visiting. Many parents reported visiting daily despite considerable 'social' and real costs. Unit differences emerged regarding the degree of parental involvement as measured by tasks carried out.

Manometric rhinometry: a new method of measuring nasal volume

A new method of measuring the volume of the air space in the nose and sinuses is presented. We have called this method "manometric rhinometry." By closing off the nose anteriorly and posteriorly a closed space is created. A volume of air is then removed and the resultant pressure change is recorded. The original volume is calculated from the pressure change. Twenty adults have been investigated using this method. The volume recorded ranged from 78 to 198 ml (average: 138 ml). Test-retest analysis showed a correlation coefficient of 0.98. In addition, 24 children aged 4 to 12 years were examined. Their volumes were 43 to 198 ml. Test-retest analysis gave a correlation coefficient of 0.94. The significance of these findings is discussed.

Development of the brachial spinal cord in the marsupial Macropus eugenii (tammar wallaby)

The development of the brachial spinal cord was studied in the marsupial Macropus eugenii (tammar wallaby) on postnatal days 1-34. On day 1 the spinal cord was histologically immature, with a deep central canal, proliferating neuroepithelium and roof and floor plates. The lateral motor column had formed, and forelimb muscles contained primary myotubes. The spinal cord gradually attained a mature appearance between days 1-34. The results confirm the suitability of the wallaby spinal cord for studies of early mammalian development.

Plasma, platelet and erythrocyte glutathione peroxidases as risk factors in ischaemic heart disease in man

1. Plasma, platelet and erythrocyte glutathione peroxidase activities and serum lipid concentrations were measured in patients with ischaemic heart disease and matched control subjects. 2. Mean plasma and platelet glutathione peroxidase activities were significantly lower in the patients with ischaemic heart disease. Erythrocyte glutathione peroxidase activities and serum lipid concentrations were similar in patients with ischaemic heart disease and control subjects. 3. No correlations between plasma, platelet and erythrocyte glutathione peroxidase activities were observed. 4. The combination of plasma and platelet glutathione peroxidase activities provided an 86% discrimination between patients with ischaemic heart disease and matched control subjects. 5. Our data suggest that plasma and platelet glutathione peroxidases may be significant risk factors for ischaemic heart disease. Plasma glutathione peroxidase is a previously unrecognized risk factor.

Fiscal and clinical evaluation of patient care. A case management model for the future

The cost of healthcare within the United States continues to climb as does the number of individuals who have limited access to the healthcare system. By the year 2000, healthcare costs are predicted to comprise 15% of the gross national product. Over the last 10 years, the number of Americans who do not have financial protection from medical costs has risen dramatically. Presently, an estimated 35 million individuals have no insurance or other coverage.

Immunoblotting of transferrin in the identification of cerebrospinal fluid otorrhoea and rhinorrhoea

Cerebrospinal rhinorrhoea is potentially serious due to the risk from infection. In patients presenting with a nasal discharge of clear fluid it is important to identify the nature of the fluid. Cerebrospinal fluid is readily identified by the presence of asialo-transferrin (tau protein). A method is presented for the identification of tau protein based upon agarose electrophoresis, followed by transfer onto cellulose nitrate membrane and immunochemical detection of transferrin. The method is reliable, sensitive and simple, and requires only basic electrophoresis apparatus.

Intracellular expression of Kluyveromyces lactis toxin gamma subunit mimics treatment with exogenous toxin and distinguishes two classes of toxin-resistant mutant

The Kluyveromyces lactis toxin is a heterotrimeric protein which irreversibly arrests proliferation of sensitive Saccharomyces cerevisiae cells in the G1 phase of the cell cycle. By expressing the gamma subunit of the toxin in sensitive yeast cells from a conditional promoter, it was previously demonstrated that it alone is required for inhibition (Tokunaga et al. (1989). Nucleic Acids Res. 17, 3435-3446). Here we show that, like native exogenous toxin, intracellular gamma subunit expression promotes a striking arrest of sensitive cells in G1. However, unlike the G1 arrest caused by native toxin, that induced by the gamma subunit alone does not result in reduced cellular viability and is fully and rapidly reversible, suggesting that the G1 arrest and the irreversibility of action may reflect different aspects of the toxin's interaction with sensitive cells. We have selected a large number of S. cerevisiae mutants which are highly resistant to the toxin in order to study its mode of action in more detail. Complementation analysis demonstrated that all but one of the mutants were recessive and these defined four separate genes. Members of two complementation groups concurrently acquired resistance to intracellular gamma subunit expression, suggesting that they contain a modified toxin target site. The other two genes appear to be required for entry of the gamma subunit into the sensitive cells since these mutants, while refractory to exogenous toxin, were fully sensitive to intracellular gamma subunit expression.

The effect of ice packs upon nasal mucosal blood flow

The effect on nasal mucosal blood flow of ice packs on the forehead and ice packs within the mouth was investigated in 16 healthy subjects. The laser Doppler flowmeter was used to record changes in blood flow to the inferior turbinate, as measured by change in the flux. Ice packs within the mouth produced a significant decrease in nasal mucosal blood flow (p less than 0.05). The average fall was 23% (SEM 5.9) compared with the control measurements. No significant change was recorded following the application of ice packs to the forehead. The results of this study question the scientific rationale behind the use of forehead ice packs in clinical practice.

Lyme Disease in a Young Girl

In brief: An 11 1/2-year-old girl had a seven-month history of bilateral knee pain and swelling; her x-rays and bone scan were normal. She had been treated unsuccessfully with rest and physical therapy before being referred to a sports medicine clinic. Laboratory studies demonstrated a positive titer for Lyme disease. She was treated with tetracycline and had an uneventful recovery.

The Sheehan total knee arthroplasty. A retrospective review

Sixty Sheehan total knee arthroplasties (TKA) in 44 patients were reviewed 3.5 years following surgery. Patient mobility was improved, but only 29 knees were completely free of pain. In 18 knees there was a complaint of pain localized to the patellofemoral joint, and in five knees the pain was severe enough to require further surgery. Complications included three knees with presumed deep infection and three knees with tibial stud fractures. Aseptic loosening did not occur, although sinkage of the tibial component was observed. Revision arthroplasty was not successful mainly because of poor residual bone stock. Salvage surgery included three successful arthrodeses. The high incidence of patellofemoral problems and violation of bone stock make the current surface replacements attractive alternatives for TKA.

Sulfur Vulcanization with Two Plateaus—Formation of an Inhibitor during Vulcanization?

Efficient sulfur vulcanizing systems based on thiazolesulfenamide accelerators derived from secondary amines show unusual and complex vulcanization kinetics in NR. This feature does not appear to have been reported previously. Depending on the nature and purity of the accelerator, the ratio of accelerator to sulfur, the cure temperature, the type of rubber being used, and the presence of other additives, two distinct periods of crosslinking may be evident, separated by a more or less well-defined plateau. This plateau is longer and more distinct if the accelerator is pure, its ratio to sulfur is high, the cure temperature is low, and there are no other additives present. Sulfenamide accelerators derived from both primary and secondary amines may give rise to this behavior in rubbers other than NR. The observed behavior has been shown to be due to the formation, during the first cure period, of an extractable crosslinking inhibitor. The structure of this inhibitor is still in doubt, but the present balance of evidence favors it being an aminodithiobenzothiazole [Structure (1)] or a dithiobisdialkylamine [Structure (2)] or a polythio variant of those structures.

The Prairie State Games: Organization of Medical Care

In brief: The finals of the Prairie State Games, an Olympic-style sports festival, annually attract nearly 3,000 Illinois amateur athletes, who sustain an average of 265 injuries per year. Although most of the injuries are orthopedic, a moderate number of heat-related problems occur. Most injuries are associated with soccer, wrestling, and basketball. A medical director who is a physician coordinates the efforts of the more than 30 volunteer physicians and 60 athletic trainers who constitute the medical corps. This article describes the guidelines for providing medical care at this large-scale athletic event.

Fractures of the distal radius. Intermediate and end results in relation to radiologic parameters

The purpose of this study was to quantify the functional impairment following distal radial fractures and to identify the factors affecting prognosis. One hundred fifteen patients were assessed six months and two years following initial injury. On final assessment, subjectively, 56% had good, 39% had fair, and 5% had poor results. Median grip strength improved from 51% to 78%, range of movement from 87% to 94%, and wrist torque from 93% to 100%. Redisplacement occurred in 59%; only 33% clinically and 19% radiologically had perfect cosmetic results. Radial malunion was important functionally. Only when the dorsal angle exceeded 20 degrees or the radial angle fell below 10 degrees with a 30 degrees mean was there reduction in grip strength (p = 0.05). Comminution and intraarticular involvement predisposed to a median loss of movement of 15% and 11%, respectively (p = less than 0.05). Patients requiring physiotherapy formed a poor prognostic group. A combination of factors is responsible for poor results. Attention should be directed toward early and adequate rehabilitation of the injured hand and wrist.

Distance Race Injuries: An Analysis of Runners' Perceptions

In brief: This report examines the type and frequency of self-reported injuries that occurred at the Chicago Distance Classic, a 20km race held each year in July. Questionnaires were sent to the nearly 5,000 entrants. The runners were asked about their medical history and if they had suffered injuries or illnesses from the race. Most entrants had been running two to five years. More than half stretched regularly before and after running. The knee was most often injured (10%), and the foot was second. Most orthopedic, knee, and foot injuries occurred to beginners, and most entrants were between ages 31 and 40. Many of the entrants said they were affected by the heat; 31 said they suffered severely from the heat.

Clobetasol propionate versus fluocinonide creams in psoriasis and eczema

A double-blind, parallel comparison was made of the short-term efficacy and safety of three times daily regimens of 0.05% clobetasol propionate cream and 0.05% fluocinonide cream in 114 adolescent and adult patients with psoriasis and 113 with eczema. After 2 weeks of topical applications, patients were assessed according to (1) investigators' overall judgment of clinical response, (2) degree of severity of specific signs and symptoms, and (3) patients' evaluation of improvement. In all three response categories in psoriasis, and in two of three in eczema, clobetasol was statistically significantly superior to fluocinonide (p less than 0.05-p less than 0.001). Healing commenced more rapidly with clobetasol and there was no indication of tachyphylaxis. In contrast, the healing rate with fluocinonide slowed noticeably after the first week, and there was a greater tendency to relapse following fluocinonide treatment. Both regimens were safe: drug-related side effects were generally mild and occurred most commonly with fluocinonide therapy in eczema patients. Overall, drug-related effects occurred in 4% of patients receiving clobetasol and 12% receiving fluocinonide (p less than 0.05). Transient morning plasma cortisol reductions below 5 micrograms/dl occurred in 6% of clobetasol-treated patients, reverting to normal within 1 week of the end of treatment.

An altered beta-adrenoreceptor-mediated modulation of noradrenaline-induced vasoconstriction in spontaneously hypertensive rat mesenteric arteries

Pressor responses to bolus injections of noradrenaline (NA) were analysed, in the isolated perfused spontaneously hypertensive (SHR) rat mesenteric arterial bed, in an attempt to investigate the beta-adrenoreceptor-mediated modulation of catecholamine-induced vasoconstriction. NA-induced responses were potentiated in the presence of timolol (10(-7) M) and suppressed by (-)isoprenaline (10(-4) M), indicating the presence of a vasodilator beta-adrenoreceptor population. The suppressant effect of (-)isoprenaline (10(-4) M) was antagonised by timolol (10(-7) M). Lower doses of (-)isoprenaline (10(-7) M - 10(-5) M) potentiated the NA-induced pressor responses, while (+)isoprenaline (10(-5) M - 10(-4) M) suppressed the NA-induced responses. It is concluded that although a vasodilator beta-adrenoreceptor population exists in the SHR mesenteric vasculature, its vasodilator function is compromised when compared to that found in normotensive rats.

Temperature Effects on the Stability of Intermediates and Crosslinks in Sulfur Vulcanization

The dependence of the physical properties of sulfur vulcanizates of diene rubbers on network structure is reviewed and the influence of degree of crosslinking, crosslink structure, and main-chain modification are discussed. In polyisoprenes, these are determined, in practice, by the balance between three competing types of reaction: the conversion of polysulfidic pendent groups into polysulfidic crosslinks; the desulfuration of polysulfidic pendent groups and crosslinks, eventually to the corresponding monosulfides, with recirculation of the removed sulfur into the crosslinking pathway; thermal decomposition of di- and polysulfidic pendent groups and crosslinks with the formation of cyclic sulfide, conjugated diene and triene, and cis, trans-isomerized groups in the rubber chains. At temperatures above about 160°C, the thermal breakdown of monosulfide crosslinks and pendent groups has to be considered. Zinc accelerator-thiolate complexes play a central role in controlling the balance between the various reactions because they promote the primary sulfuration of the rubber to form polysulfidic pendent groups and the conversion of these to crosslinks; they are the agents which desulfurate both pendent groups and crosslinks; they catalyze polysulfide exchange reactions; and in some cases they promote the decomposition of crosslinks. Other factors which affect the balance between these reactions are the temperature and the structure of the main rubber chain in the immediate vicinity of the crosslink. The latter is, in turn, at least partly controlled by the structure and concentration of zinc accelerator-thiolate complexes. The vulcanization of polybutadiene rubbers deviates substantially from this reaction pattern, evidently because the bulk of the accelerator becomes irreversibly bound to the rubber at an early stage. This denudes the vulcanizing system of zinc accelerator-thiolate complexes and, therefore, prevents desulfuration from occurring. The crosslinks thus remain di- and polysulfidic and are apparently less prone to decomposition than in the case of the polyisoprene rubbers, since cyclic sulfides and conjugated hydrocarbon groupings seem not to be prominent products. The removal of accelerator leaves the system unresponsive to zinc and gives it the characteristics of unaccelerated vulcanization with the result that vicinal crosslinking and crosslinks with saturated chain junctions become important products.

What is, must be best: a research note on conservative or deferential responses to antenatal care provision

During a study of innovations in antenatal care it was found that overall levels of satisfaction with care were high. Pregnant women appeared to assume that whatever arrangements they had experienced were the best arrangements possible and to be negative about innovations until they had experienced them. This response, which may be due to conservatism or deference, is examined in relation to aspects of general practice and hospital care, and its implications for the evaluation of health care are discussed.

Beta-adrenoreceptor-mediated modulation of vasoconstriction in rat isolated perfused mesenteric arteries

Pressor responses to bolus injections of noradrenaline (NA) were studied, in the isolated perfused rat mesenteric arterial bed, in the presence of beta-adrenoreceptor agonists and antagonists, in an attempt to identify a possible beta-adrenoreceptor mediated modulation of catecholamine-induced vasoconstrictor effects. NA-induced responses were potentiated in the presence of timolol and (-)propranolol and suppressed in the presence of (-)isoprenaline; (+)isoprenaline was less effective against the NA-induced responses. Timolol attenuated the effects of (-)isoprenaline on NA-induced responses but not those of the stereoisomer (+)isoprenaline. It is concluded that the NA-induced pressor effect in the rat mesenteric vasculature is the net result of vasoconstrictor alpha- and vasodilator beta-adrenoreceptor activation and that the interaction of the two opposing adrenoreceptor-mediated effects represents a 'physiological antagonism'.