Alarmin-activated B cells accelerate atherosclerosis after myocardial infarction via plasma cell-immunoglobulin dependent mechanisms

Introduction

Myocardial infarction (MI) accelerates atherosclerosis and for years greatly increases the risk of recurrent cardiovascular events, such as stroke and MI. B cell-derived autoantibodies produced in response to MI also persist for years.

Purpose

We investigated the role of B cells in adaptive immune responses to MI.

Methods

We used an apolipoprotein-E-deficient (ApoE−/−) mouse model of MI-accelerated atherosclerosis to assess the importance of B cells using loss and gain of function approaches. In loss of function experiment, after inducing an MI we depleted B cells using an anti-CD20 antibody. Gain of function experiments involve transfers of purified MI-B cells from different donor mice, isolated one week after MI, into atherosclerotic ApoE−/− mice.

Results

Depletion of B cells in MI mice prevented immunoglobulin G accumulation in plaques and MI-induced acceleration of atherosclerosis. Adoptive transfer of wildtype MI-B cells into atherosclerotic ApoE−/− mice greatly increased IgG accumulation in plaque and accelerated atherosclerosis in recipient mice. Cytokines that promote humoral immunity were also greatly increased in B cells activated by MI. These cells formed germinal centres within the spleen where they differentiated into antibody-producing plasma cells. Transfer of MI-B cells deficient in Blimp-1, the transcriptional repressor that drives their terminal differentiation to antibody-producing plasma cells failed to accelerate atherosclerosis in recipient mice. Alarmins released from infarcted heart were responsible for activation of B cells via toll-like receptors; transfer of MI-B cells deficient in MyD88, the canonical adaptor protein for inflammatory signaling downstream of toll-like receptors, prevented acceleration of atherosclerosis in recipient mice.

Conclusion

Our data implicate early B cell activation and autoantibodies as a central cause for accelerated atherosclerosis post MI and identifies novel therapeutic strategies towards preventing recurrent cardiovascular events such as MI and stroke.

Funding Acknowledgement

Type of funding source: Public grant(s) – National budget only. Main funding source(s): National Health and Medical Research Council of Australia

P1625A pivotal role for cytotoxic CD8+ T cells in development of cardiac fibrosis

Background/Introduction

Pressure overload-induced cardiac fibrosis increases myocardial stiffness leading to reductions in cardiac performances and cardiac failure. CD8+ T cells have been shown to accumulate during development of fibrosis but their role has not been defined.

Purpose

We examined the role and significance of CD8+ T cells in development of cardiac fibrosis.

Methods

Trans-aortic constriction (TAC) or 2-kidney-1-clip (2K1C) procedures were used to generate pressure overload-induced cardiac fibrosis in mice. Rat anti-mouse CD8β (lyt-3) monoclonal antibody (clone YTS 156.7) was used to deplete CD8+ T cells. A mixed bone marrow chimera strategy was used to specifically delete innate receptor Natural Killer Group 2D (NKG2D) or cytotoxin perforin from CD8+ T cells.

Results

Depleting CD8+ T cells in mice subjected to TAC or 2K1C-renal hypertension attenuated left ventricular fibrosis by 93% and 84% without affecting blood pressure. In TAC mice this was associated with a 68% reduction in apoptotic cardiomyocytes, a 74% reduction in macrophage accumulation, a 65% reduction in TGF-beta positive cells and a 95% reduction in TGF-beta positive macrophages, whilst CD4+ T cells were unaffected. Cardiomyocytes in regions of developing cardiac fibrosis contained cytoplasmic DNA and expressed the NKG2D ligand, Rae-1, indicative of activation of a DNA damage response; CD8+ T cells expressed the NKG2D receptor. Deletion of the NKG2D receptor from CD8+ T cells attenuated cardiac fibrosis by 82%; deletion of cytotoxin perforin has similar effects.

Conclusion(s)

We conclude that CD8+ T cells contribute to development of cardiac fibrosis by targeting stressed/damaged cardiomyocytes via an NKG2D-Rae-1 cytotoxic mechanism inducing their apoptosis. Macrophages then accumulate in the heart in response to increased numbers of apoptotic cardiomyocytes, clearing the apoptotic cells through engulfment and increasing their expression of the pro-fibrotic factor TGF-beta1.

Acknowledgement/Funding

The National Health and Medical Research Council of Australia

Biological Psychiatry Congress 2015

<p><strong>List of Abstract Titles and authors:<br /></strong></p><p><strong>1. Psychosis: A matter of mental effort?</strong></p><p>M Borg, Y Y van der Zee, J H Hsieh, H Temmingh, D J Stein, F M Howells</p><p><strong>2.In search of an affordable, effective post-discharge intervention: A randomised control trial assessing the influence of a telephone-based intervention on readmissions for patients with severe mental illness in a developing country</strong></p><p><strong></strong>U A Botha, L Koen, M Mazinu, E Jordaan, D J H Niehaus</p><p><strong>3. The effect of early abstinence from long-term methamphetamine use on brain metabolism using 1H-magnetic resonance spectro-scopy (1H-MRS)</strong></p><p>A Burger, S Brooks, D J Stein, F M Howells</p><p><strong>4. The effect of <em>in utero exposure </em>to methamphetamine on brain metabolism in childhood using 1H-magnetic resonance spectroscopy (1H-MRS)</strong></p><p>A Burger, A Roos, M Kwiatkowski, D J Stein, K A Donald, F M Howells</p><p><strong>5. A prospective study of clinical, biological and functional aspects of outcome in first-episode psychosis: The EONKCS Study</strong></p><p><strong></strong>B Chiliza, L Asmal, R Emsley</p><p><strong>6. Stimulants as cognitive enhancers - perceptions v. evidence in a very real world</strong></p><p><strong></strong>H M Clark</p><p><strong>7. Pharmacogenomics in antipsychotic drugs</strong></p><p><strong></strong>Ilse du Plessis</p><p><strong>8. Serotonin in anxiety disorders and beyond</strong></p><p><strong></strong>Ilse du Plessis</p><p><strong>9. HIV infection results in ventral-striatal reward system hypo-activation during cue processing</strong></p><p><strong></strong>S du Plessis, M Vink, J A Joska, E Koutsilieri, A Bagadia, D J Stein, R Emsley</p><p><strong>10. Disease progression in schizophrenia: Is the illness or the treatment to blame?</strong></p><p>R Emsley, M J Sian</p><p><strong>11. Serotonin transporter variants play a role in anxiety sensitivity in South African adolescents</strong></p><p> S M J Hemmings, L I Martin, L van der Merwe, R Benecke, K Domschke, S Seedat</p><p><strong>12. Iron deficiency in two children diagnosed with multiple sclerosis: Report on whole exom sequencing</strong></p><p><strong></strong>S Janse van Rensburg, R van Toorn, J F Schoeman, A Peeters, L R Fisher, K Moremi, M J Kotze</p><p><strong>13. Benzodiazepines: Practical pharmacokinetics</strong></p><p><strong></strong>P Joubert</p><p><strong>14. What to consider when prescribing psychotropic medications</strong></p><p><strong></strong>G Lippi</p><p><strong>15. Current prescribing practices for obsessive-compulsive disorder in South Africa: Controversies and consensus</strong></p><p><strong></strong>C Lochner, L Taljaard, D J Stein</p><p><strong>16. Correlates of emotional and behavioural problems in children with preinatally acquired HIV in Cape Town, South Africa</strong></p><p><strong></strong>K-A Louw, N Phillips, JIpser, J Hoare</p><p><strong>17. The role of non-coding RNAs in fear extinction</strong></p><p><strong></strong>S Malan-Muller, L Fairbairn, W M U Daniels, M J S Dashti, E J Oakleley, M Altorfer, J Harvey, S Seedat, J Gamieldien, S M J Hemmings</p><p><strong>18. An analysis of the management og HIV-mental illness comorbidity at the psychiatric unit of the Dr George Mukhari Academic Hospital</strong></p><p><strong></strong>M L Maodi, S T Rataemane, T Kyaw</p><p><strong>19. The identification of novel genes in anxiety disorders: A gene X environment correlation and interaction study</strong></p><p><strong></strong>N W McGregor, J Dimatelis, S M J Hemmings, C J Kinnear, D J Stein, V Russel, C Lochner</p><p><strong>20. Collaborations between conventional medicine and traditional healers: Obstacles and possibilities</strong></p><p><strong></strong>G Nortje, S Seedat, O Gureje</p><p><strong>21. Thought disorder and form perception: Relationships with symptoms and cognitive function in first-episode schizophrenia</strong></p><p>M R Olivier, R Emsley</p><p><strong>22. Investigating the functional significance of genome-wide variants associated with antipsychotic treatment response</strong></p><p><strong></strong>E Ovenden, B Drogemoller, L van der Merwe, R Emsley, L Warnich</p><p><strong>23. The moral and bioethical determinants of "futility" in psychiatry</strong></p><p><strong></strong>W P Pienaar</p><p><strong>24. Single voxel proton magnetic resonance spectroscopy (1H-MRS) and volumetry of the amylgdala in social anxiety disorder in the context of early developmental trauma</strong></p><p>D Rosenstein, A T Hess, J Zwart, F Ahmed-Leitao, E Meintjies, S Seedat</p><p><strong>25. Schizoaffective disorder in an acute psychiatric unit: Profile of users and agreement with Operational Criteria (OPCRIT)</strong></p><p><strong></strong>R R Singh, U Subramaney</p><p><strong>26. The right to privacy and confidentiality: The ethics of expert diagnosis in the public media and the Oscar Pistorius trial</strong></p><p><strong></strong>C Smith</p><p><strong>27. A birth cohort study in South Africa: A psychiatric perspective</strong></p><p>D J Stein</p><p><strong>28. 'Womb Raiders': Women referred for observation in terms of the Criminal Procedures Act (CPA) charged with fetal abduction and murder</strong></p><p><strong></strong>U Subramaney</p><p><strong>29. Psycho-pharmacology of sleep wake disorders: An update</strong></p><p>R Sykes</p><p><strong>30. Refugee post-settlement in South Africa: Role of adjustment challenges and family in mental health outcomes</strong></p><p><strong></strong>L Thela, A Tomita, V Maharaj, M Mhlongo, K Jonathan</p><p><strong>31. Dstinguishing ADHD symptoms in psychotic disorders: A new insight in the adult ADHD questionnaire</strong></p><p>Y van der Zee, M Borg, J H Hsieh, H Temmingh, D J Stein, F M Howells</p><p><strong>32. Oscar Pistorius ethical dilemmas in a trial by media: Does this include psychiatric evaluation by media?</strong></p><p>M Vorster</p><p><strong>33. Genetic investigation of apetite aggression in South African former young offenders: The involvement of serotonin transporter gene</strong></p><p>K Xulu, J Somer, M Hinsberger, R Weierstall, T Elbert, S Seedat, S Hemmings</p><p><strong>34. Effects of HIV and childhood trauma on brain morphemtry and neurocognitive function</strong></p><p>G Spies, F Ahmed-Leitao, C Fennema-Notestine, M Cherner, S Seedat</p><p><strong>35. Measuring intentional behaviour normative data of a newly developed motor task battery</strong></p><p><strong></strong>S Bakelaar, J Blampain, S Seedat, J van Hoof, Y Delevoye-Turrel</p><p><strong>36. Resilience in social anxiety disorder and post-traumatic stress disorder in the context of childhood trauma</strong></p><p>M Bship, S Bakelaar, D Rosenstein, S Seedat</p><p><strong>37. The ethical dilemma of seclusion practices in psychiatry</strong></p><p>G Chiba, U Subramaney</p><p><strong>38. Physical activity and neurological soft signs in patients with schizophrenia</strong></p><p>O Esan, C Osunbote, I Oladele, S Fakunle, C Ehindero</p><p><strong>39. A retrospective study of completed suicides in the Nelson Mandela Bay Metropolitan Area from 2008 to 2013 - preliminary results</strong></p><p><strong></strong>C Grobler, J Strumpher, R Jacobs</p><p><strong>40. Serotonin transporter variants play a role in anxiety sensitivity in South African adolescents</strong></p><p><strong></strong>S M J Hemmings, L I Martin, L van der Merwe, R Benecke, K Domschke, S Seedat</p><p><strong>41. Investigation of variants within antipsychotic candidate pharmacogenes associated with treatment outcome</strong></p><p>F Higgins, B Drogmoller, G Wright, L van der Merwe, N McGregor, B Chiliza, L Asmal, L Koen, D Niehaus, R Emsley, L Warnich</p><p><strong>42. Effects of diet, smoking and alcohol consumption on disability (EDSS) in people diagnosed with multiple sclerosis</strong></p><p>S Janse van Rensburg, W Davis, D Geiger, F J Cronje, L Whati, M Kidd, M J Kotze</p><p><strong>43. The clinical utility of neuroimaging in an acute adolescnet psychiatric inpatient population</strong></p><p><strong></strong>Z Khan, A Lachman, J Harvey</p><p><strong>44. Relationships between childhood trauma (CT) and premorbid adjustment (PA) in a highly traumatised sample of patients with first-episode schizophrenia (FES</strong>)</p><p>S Kilian, J Burns, S Seedat, L Asmal, B Chiliza, S du Plessis, R Olivier, R Emsley</p><p><strong>45. Functional and cognitive outcomes using an mTOR inhibitor in an adolescent with TSC</strong></p><p>A Lachman, C van der Merwe, P Boyes, P de Vries</p><p><strong>46. Perceptions about adolescent body image and eating behaviour</strong></p><p><strong></strong>K Laxton, A B R Janse van Rensburg</p><p><strong>47. Clinical relevance of FTO rs9939609 as a determinant of cardio-metabolic risk in South African patients with major depressive disorder</strong></p><p>H K Luckhoff, M J Kotze</p><p><strong>48. Childhood abuse and neglect as predictors of deficits in verbal auditory memory in non-clinical adolescents with low anxiety proneness</strong></p><p>L Martin, K Martin, S Seedat</p><p><strong>49. The changes of pro-inflammatory cytokines in a prenatally stressed febrile seizure animal model and whether <em>Rhus chirindensis</em> may attenuate these changes</strong></p><p><strong></strong>A Mohamed, M V Mabandla, L Qulu</p><p><strong>50. Influence of TMPRSS6 A736v and HFE C282y on serum iron parameters and age of onset in patients with multiple sclerosis</strong></p><p><strong></strong>K E Moremi, M J Kotze, H K Luckhoff, L R Fisher, M Kidd, R van Toorn, S Janse van Rensburg</p><p><strong>51. Polypharmacy in pregnant women with serious mental illness</strong></p><p>E Thomas, E du Toit, L Koen, D Niehaus</p><p><strong>52. Infant attachment and maternal depression as predictors of neurodevelopmental and behavioural outcomes at follow-up</strong></p><p>J Nothling, B Laughton, S Seedat</p><p><strong>53. Differences in abuse, neglect and exposure to community violence in adolescents with and without PTSD</strong></p><p><strong></strong>J Nothling, S Suliman, L Martin, C Simmons, S Seedat</p><p><strong>54. Assessment of oxidative stress markers in children with autistic spectrum disorders in Lagos, Nigeria</strong></p><p><strong></strong>Y Oshodi, O Ojewunmi, T A Oshodi, T Ijarogbe, O F Aina, J Okpuzor, O C F E A Lesi</p><p><strong>55. Change in diagnosis and management of 'gender identity disorder' in pre-adolescent children</strong></p><p>S Pickstone-Taylor</p><p><strong>56. Brain network connectivity in women exposed to intimate partner violence</strong></p><p>A Roos, J-P Fouche, B Vythilingum, D J Stein</p><p><strong>57. Prolonged exposure treatment for PTSD in a Third-World, task-shifting, community-based environment</strong></p><p>J Rossouw, E Yadin, I Mbanga, T Jacobs, W Rossouw, D Alexander, S Seedat</p><p><strong>58. Contrasting effects of early0life stress on mitochondrial energy-related proteins in striatum and hippocampus of a rat model of attention-deficit/ hyperactivity disorder</strong></p><p><strong></strong>V Russell, J Dimatelis, J Womersley, T-L Sterley</p><p><strong>59. Attention-deficit hyperactivity disorder in adults: A South African perspective</strong></p><p>R Schoeman, M de Klerk, M Kidd</p><p><strong>60. Cognitive function in women with HIV infection and early-life stress</strong></p><p>G Spies, C Fennema-Notestine, M Cherner, S Seedat</p><p><strong>61. Changes in functional connectivity networks in bipolar disorder patients after mindfulness-based cognitic therapy</strong></p><p>J A Starke, C F Beckmann, N Horn</p><p><strong>62. Post-traumatic stress disorder, overweight and obesity: A systematic review and meta-analysis</strong></p><p><strong></strong>S Suliman, L Anthonissen, J Carr, S du Plessis, R Emsley, S M J Hemmings, C Lochner, N McGregor L van den Heuvel, S Seedat</p><p><strong>63. The brain and behaviour in a third-trimester equivalent animal model of fetal alcohol spectrum disorders</strong></p><p>P C Swart, C B Currin, J J Dimatelis, V A Russell</p><p><strong>64. Irritability Assessment Model (IAM) to monitor irritability in child and adolescent psychiatric disorders.</strong></p><p>D van der Westhuizen</p><p><strong>65. Outcome of parent-adolescent training in chilhood victimisation: Adaptive functioning, psychosocial and physiological variables</strong></p><p>D van der Westhuizen</p><p><strong>66. The effect of ketamine in the Wistar-Kyoto and Sprague Dawley rat models of depression</strong></p><p>P J van Zyl, J J Dimatelis, V A Russell</p><p><strong>67. Investigating COMT variants in anxiety sensitivity in South African adolescents</strong></p><p>L J Zass, L Martin, S Seedat, S M J Hemmings</p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p><strong><br /></strong></p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p><p> </p>

Parietal cell antibody identified by ELISA is superior to immunofluorescence, rises with age and is associated with intrinsic factor antibody

Parietal cell antibody is a marker for autoimmune gastritis. With identification of gastric H/K ATPase as its molecular target, ELISAs have been introduced. We compared performance of ELISA with immunofluorescence in a retrospective and prospective sera set and correlated the results with intrinsic factor antibody. In 138 retrospective sera selected for positivity or negativity for intrinsic factor antibody, 87 reacted with gastric H/K ATPase by Euroimm ELISA but only 62 reacted by immunofluorescencence.. Similar results were obtained with Inova ELISA with 78 positives that were also positive by Euroimm ELISA. In 161 prospective sera, 29 sera tested positive by ELISA compared to 24 by immunofluorescence. ELISA positive but immunofluoresnce negative sera are bona fide positives because a representative set of 16 sera reacted with both 95kD α and 60-90kDβ subunits of gastric H/K ATPase. ELISA values rose with age regardless of whether immunofluorescence tests were positive or negative. Of 53 sera containing antibody to intrinsic factor, 46/53 (87%) reacted to gastric H/K ATPase by ELISA. Taken together, the data indicates an enhanced detection rate by ELISA over immunofluorescence and validates it as a robust diagnostic assay for parietal cell antibody. As parietal cell antibody marks asymptomatic autoimmune gastritis that may progress to end stage gastric atrophy and haematological complications, and as autoimmune gastritis is associated with autoimmune thyroiditic and type 1 diabetes mellitus, early detection of parietal cell antibody by a sensitive ELISA will enable early follow-up of at risk subjects.

Seronegative conversion in four Neospora caninum-infected cows, with a low rate of transplacental transmission

Four Neospora-seropositive pregnant cows (prebreeding indirect fluorescent antibody (IFA) titers between 1:400 and 1:1600) were confined and observed until parturition. All cows gave birth to normal calves. Selected tissues were tested for NC by histopathology, immunohistochemical (IHC) and polymerase chain reaction (PCR). Parasite isolation was attempted in vero cell cultures. At parturition, all cows were seronegative at 1:200 and two of four cows had a titer of 1:100 when further tested. Three of four calves were not infected, as determined by negative results of precolostral serology (1:25 cut-off), histopathology, IHC and PCR. One calf was congenitally infected, as shown by the presence of a thick-walled cyst labelled by IHC in its brain, positive PCR of brain and a precolostral IFA titer of 1:100. It was concluded that NC antibody titers may drop or convert to seronegative status in chronically infected cows by the time of parturition and this finding in four of four cows indicates that this could be a common occurrence. Similarly, the finding of an infected calf with a low antibody titer indicates that precolostral serology may not be a fool-proof means of identifying calves with congenital Neospora caninum infections. These findings call into question conclusions of other studies that have estimated rates of congenital transmission of this parasite based on serological tests at calving. This study is the first confirmed report of congenital NC infection in a calf in Thailand.

Neospora caninum seroprevalence in dairy cattle in central Thailand

The seroprevalence, in dairy cattle, of antibodies to Neospora caninum, the relationship between seropositivity and age (heifer versus cow), the relationship of herd infection with herd size and the relationship of herd infection with the presence of dogs on the farm were studied. The study involved 549 cows and 82 dogs in 59 dairy herds in Nakhon Pathom, Thailand. A competitive enzyme-linked immunosorbent assay (cELISA) with NC-specific monoclonal antibody was used to detect the NC antibodies in the sera. Individual and herd seroprevalence of NC were 5.5% (30/549) and 34% (20/59), respectively. No significant relationships between NC seropositivity with the age of the cows (heifer versus cow; P > 0.05) and between herd infection and the presence of dogs on the farm (P > 0.05) were found. Herd size significantly affected herd infection (P < 0.05) with higher infection in large than small herds (> or = 21 versus < or = 20 cows). Of 12 cows with a history of abortion, one was seropositive to NC. The seroprevalence of NC antibodies in dogs was 1.2% (1/82). This is the first NC seroprevalence study in dogs in Thailand. It was concluded that Neospora infection was more common at the herd level rather than the individual level in Thailand and the presence of dogs on the farm was not related to the level of herd infection. Caution should be taken in the interpretation of serological tests from the farm dogs.

The prevalence of Enterocytozoon bieneusi in acquired immunodeficiency syndrome (AIDS) patients from the north west of England: 1992-1995

Microsporidia are increasingly being recognised as important enteric pathogens in patients with advanced human immunodeficiency virus (HIV) disease, i.e. acquired immunodeficiency syndrome (AIDS). The aims of this study were to investigate the frequency of detection of microsporidia associated with diarrhoea in patients with advanced HIV disease in the north west of England, and to determine the species involved and their prevalence. During the period from April 1992 to the end of December 1995, chronic diarrhoea in 88 patients in the late stage of HIV disease was investigated. Duodenal biopsies, duodenal aspirates or jejunal biopsies were received from 38 patients, and stool samples from 63 patients, as part of the routine investigation of possible causes of diarrhoea in these patients. Biopsies and aspirates were examined by thin-section electron microscopy (EM), and stool samples were examined by epi-fluorescence microscopy after staining with Calcofluor. Putative stool positives were confirmed by transmission electron microscopy. CD4-lymphocyte counts were available from all patients who provided samples. Nine out of 63 patients (14.3%) were found to be excreting microsporidial spores on stool examination. The species was confirmed as Enterocytozoon bieneusi. The mean CD4-lymphocyte count for this group was 37 x 10(6)/L (normal range 517-1677 x 10(6)/L). Three out of 38 biopsy specimens (7.9%) were also found to be infected with this microsporidian. The mean CD4-lymphocyte count for this group was 72 x 10(6)/L. Encephalitozoon intestinalis was not found in any samples examined. The prevalence of microsporidial infection in AIDS patients in the north west of England appears to be similar to that of patients in London, but less than that reported in studies from other developed countries.

Interaction between gabaergic and opioid pathways in the regulation of gonadotropin secretion in males

The effects of naloxone infusion given together with an infusion of LRH on gonadotropin secretion, were studied in 6 normal male volunteers before and after pretreatment with the GABA-transaminase inhibitor, valproic acid. In concordance with previous studies, naloxone infusion augmented the LRH-stimulated secretion of LH. Baseline serum LH concentrations were not significantly different after valproic acid pretreatment compared to control values. Similarly, valproic acid pretreatment failed to blunt the naloxone-augmented LRH-stimulated secretion of LH. Our data suggest that the previously reported animal studies on the central suppressive effect of GABA on endogenous LRH release is less prominent than the suppressive effect of opioidergic regulatory mechanisms in the human male.

The renin-angiotensin system in hypothyroidism of short duration

In six hypothyroid patients (2 male, 4 females, ages 22 through 59 years), plasma renin activity (PRA) and aldosterone (Aldo) were measured when the patients were euthyroid on levothyroxine therapy and one month after the therapy was stopped. Colonic mucosal potential differences were measured during the hypothyroid and euthyroid stages, and catecholamine sensitivity was determined by the blood pressure response to infused norepinephrine. Significant differences were observed in the PRA and aldosterone concentrations which were 4.1 +/- 2.5 ng/ml/h and 9.4 +/- 5.9 ng/dl, respectively in the hypothyroid stage and 6.9 +/- 2.3 ng/ml/h and 15.2 +/- 7.3 ng/dl, respectively when the patients were made euthyroid. The colonic mucosal potential differences (which reflect increased endogenous mineralocorticoid activity), became more electronegative after correction of hypothyroidism (-16.8 +/- 7.5 mV vs -32 +/- 18.2 mV; P less than 0.04) concentrations. Statistically significant decreases in norepinephrine pressor effects were observed in hypothyroid patients when compared to the euthyroid state (7.4 +/- 2.3 vs 10.9 +/- 1.9 micrograms/ng/min; P less than 0.01). It is concluded that patients with hypothyroidism have a hormonal pattern reminiscent of "low renin hypertension", and exhibit decreased sensitivity to catecholamines. Such changes are corrected when the patients become euthyroid on levothyroxine therapy.