David C. Kem

Primary Aldosteronism: Diagnosis, Localization, and Treatment

New diagnostic techniques have enhanced the detection of primary aldosteronism. However, the response of blood pressure after operation in unilateral and bilateral adrenal disease is different. We have compared four localizing techniques--adrenal venography, adrenal isotopic scanning, a modified adrenal venous sampling for steroid measurements, and the anomalous postural decrease in plasma aldosterone concentration--in 51 patients with primary aldosteronism, all of whom had undergone operative confirmation. Adrenalectomy resulted in normal blood pressure in 59%, improvement in 25%, and no change in 16%. Correct localization of the lesion was obtained in 47% by the adrenal isotopic scan, in 66% by adrenal venography, and in 91% by the modified adrenal venous hormone technique despite four false-positives. Of the 26 patients with an anomalous postural decrease in plasma aldosterone, 88% had a unilateral lesion.

Racial differences in pressure, volume and renin interrelationships in essential hypertension.

SUMMARY The interrelationships of arterial pressure, plasma volume (PV), and plasma renin activity were studied in 152 consecutive male patients with uncomplicated essential hypertension. Of these, 22 (17 white and 5 black) subjects had normal plasma volumes and because of tbe small number were not included in the analysis of results. Tbe remaining 130 (35 black and 95 white) patients were classified as having either expanded or contracted plasma volume. A higher percentage of black (43%) than white (21%) subjects were volume expanded (PV > 19 ml/cm) and a lower percentage of blacks (57%) than whites (79%) were volume contracted (PV < 17 ml/cm). There was no significant difference in mean arterial pressure and plasma renin activity between tbe volume expanded and contracted black patients. In contrast, the white patients with contracted plasma volume had significantly higher arterial pressures (p < 0.05) and plasma renin activity (p < 0.001) than those with expanded plasma volume. More blacks than whites had low plasma reoin activity and did not manifest the inverse relationship of plasma renin activity to plasma volume as did the whites. These data conflnn and extend previous observations that the relationship between plasma volume and plasma renin activity (PRA) in the male patient with essential hypertension seems to differ between the black and white race. Efforts to explain tbe low PRA in black patients might be best directed toward those patients with suppressed PRA and with contracted intravascular volume.

Circadian Rhythm of Plasma Aldosterone Concentration in Patients with Primary Aldosteronism

Plasma aldosterone, cortisol, and renin activity were measured in nine recumbent patients with hyperaldosteronism, including seven with adenomas, one with idiopathic hyperplasia, and one with glucocorticoid suppressible hyperplasia. All had peak values of plasma aldosterone concentration from 3 a.m. to noon and lowest values at 6 p.m. or midnight. This rhythm was similar to the circadian pattern of plasma cortisol in the same patients. When these data were normalized to eliminate the wide variation in ranges of plasma aldosterone and cortisol between individuals, there was an excellent correlation (r = + 0.87, P < 0.005) between the two hormones. In contrast, plasma aldosterone concentrations did not correlate with plasma renin activity before or after normalization of data. Short term suppression of ACTH by administration of dexamethasone eliminated the circadian variation of plasma aldosterone in both patients with hyperplasia and in four of five patients with adenomas, while it markedly altered the rhythm in the fifth. Similar doses of dexamethasone were administered to four normal subjects and did not flatten the circadian rhythm of plasma aldosterone. These data suggest that patients with primary aldosteronism have a circadian rhythm of plasma aldosterone mediated by changes in ACTH.

Autoimmune Basis for Postural Tachycardia Syndrome

Background Patients with postural tachycardia syndrome (POTS) have exaggerated orthostatic tachycardia often following a viral illness, suggesting autoimmunity may play a pathophysiological role in POTS. We tested the hypothesis that they harbor functional autoantibodies to adrenergic receptors (AR). Methods and Results Fourteen POTS patients (7 each from 2 institutions) and 10 healthy subjects were examined for α1AR autoantibody‐mediated contractility using a perfused rat cremaster arteriole assay. A receptor‐transfected cell‐based assay was used to detect the presence of β1AR and β2AR autoantibodies. Data were normalized and expressed as a percentage of baseline. The sera of all 14 POTS patients demonstrated significant arteriolar contractile activity (69±3% compared to 91±1% of baseline for healthy controls, P<0.001) when coexisting β2AR dilative activity was blocked; and this was suppressed by α1AR blockade with prazosin. POTS sera acted as a partial α1AR antagonist significantly shifting phenylephrine contractility curves to the right. All POTS sera increased β1AR activation (130±3% of baseline, P<0.01) and a subset had increased β2AR activity versus healthy subjects. POTS sera shifted isoproterenol cAMP response curves to the left, consistent with enhanced β1AR and β2AR agonist activity. Autoantibody‐positive POTS sera demonstrated specific binding to β1AR, β2AR, and α1AR in transfected cells. Conclusions POTS patients have elevated α1AR autoantibodies exerting a partial peripheral antagonist effect resulting in a compensatory sympathoneural activation of α1AR for vasoconstriction and concurrent βAR‐mediated tachycardia. Coexisting β1AR and β2AR agonistic autoantibodies facilitate this tachycardia. These findings may explain the increased standing plasma norepinephrine and excessive tachycardia observed in many POTS patients.

Proteasome inhibition during myocardial infarction

The ubiquitin-proteasome system (UPS) plays a central role in protein degradation and regulates a variety of critical cellular processes. During recent years, the cardiac UPS has become increasingly recognized as a key regulator of cardiac function under both physiological and pathological conditions. Numerous studies have demonstrated that altered UPS function is involved in the pathogenesis of cardiac disease including myocardial ischaemia or infarction. The expression and activity of the E3 ubiquitin ligases, which confer substrate specificity in the UPS pathway, affect the apoptosis and severity of disease in myocardial ischaemia and reperfusion. Although impaired proteasome function is commonly associated with myocardial ischaemic injury, recent evidence also supports a cardioprotective role for proteasome inhibitors in myocardial ischaemia. We will review these studies and data, discuss controversies regarding the UPS alterations and use of proteasome inhibitors in myocardial ischaemia, and attempt to identify strategies that may enhance their clinical application.

Early myocardial dysfunction in streptozotocin-induced diabetic mice: a study using in vivo magnetic resonance imaging (MRI)

BackgroundDiabetes is associated with a cardiomyopathy that is independent of coronary artery disease or hypertension. In the present study we used in vivo magnetic resonance imaging (MRI) and echocardiographic techniques to examine and characterize early changes in myocardial function in a mouse model of type 1 diabetes.MethodsDiabetes was induced in 8-week old C57BL/6 mice with two intraperitoneal injections of streptozotocin. The blood glucose levels were maintained at 19–25 mmol/l using intermittent low dosages of long acting insulin glargine. MRI and echocardiography were performed at 4 weeks of diabetes (age of 12 weeks) in diabetic mice and age-matched controls.ResultsAfter 4 weeks of hyperglycemia one marker of mitochondrial function, NADH oxidase activity, was decreased to 50% of control animals. MRI studies of diabetic mice at 4 weeks demonstrated significant deficits in myocardial morphology and functionality including: a decreased left ventricular (LV) wall thickness, an increased LV end-systolic diameter and volume, a diminished LV ejection fraction and cardiac output, a decreased LV circumferential shortening, and decreased LV peak ejection and filling rates. M-mode echocardiographic and Doppler flow studies of diabetic mice at 4 weeks showed a decreased wall thickening and increased E/A ratio, supporting both systolic and diastolic dysfunction.ConclusionOur study demonstrates that MRI interrogation can identify the onset of diabetic cardiomyopathy in mice with its impaired functional capacity and altered morphology. The MRI technique will lend itself to repetitive study of early changes in cardiac function in small animal models of diabetic cardiomyopathy.

Consequences of unlocking the cardiac myosin molecule in human myocarditis and cardiomyopathies.

Myocarditis, often initiated by viral infection, may progress to autoimmune inflammatory heart disease, dilated cardiomyopathy and heart failure. Although cardiac myosin is a dominant autoantigen in animal models of myocarditis and is released from the heart during viral myocarditis, the characterization, role and significance of anti-cardiac myosin autoantibodies is poorly defined. In our study, we define the human cardiac myosin epitopes in human myocarditis and cardiomyopathies and establish a mechanism to explain how anti-cardiac myosin autoantibodies may contribute to heart disease. We show that autoantibodies to cardiac myosin in sera from myocarditis and dilated cardiomyopathies in humans targeted primarily epitopes in the S2 hinge region of cardiac myosin. In addition, anti-cardiac myosin antibodies in sera or purified IgG from myocarditis and cardiomyopathy targeted the beta-adrenergic receptor and induced antibody-mediated cAMP-dependent protein kinase A (PKA) cell signaling activity in heart cells. Antibody-mediated PKA activity in sera was abrogated by absorption with anti-human IgG. Antibody-mediated cell signaling of PKA was blocked by antigen-specific inhibition by human cardiac myosin or the beta-adrenergic receptor but not the alpha adrenergic receptor or bovine serum albumin. Propranolol, a beta blocker and inhibitor of the beta-adrenergic receptor pathway also blocked the antibody-mediated signaling of the beta-adrenergic receptor and PKA. The data suggest that IgG antibody against human cardiac myosin reacts with the beta-adrenergic receptor and triggers PKA signaling in heart cells. In summary, we have identified a new class of crossreactive autoantibodies against human cardiac myosin and the beta-adrenergic receptor in the heart. In addition, we have defined disease specific peptide epitopes in the human cardiac myosin rod S2 region in human myocarditis and cardiomyopathy as well as a mechanistic role of autoantibody in the pathogenesis of disease.

Tumor necrosis factor alpha, rapid ventricular tachyarrhythmias, and infarct size in canine models of myocardial infarction.

Etanercept (2 mg/kg), a TNFα sequestrant, was administered 24 hours and 1 hour before LAD coronary artery ligation to examine the role of TNFα on lethal ventricular tachyarrhythmias and myocardial necrosis. Dogs treated with etanercept had decreased very rapid (>360 bpm) ventricular triplets (6 ± 1/h, n = 8) 2 to 24 hours following coronary artery ligation compared with saline (21 ± 6/h, n = 10, P < 0.05). This was concordant with 8-fold salvage of β-adrenergic receptor kinase 1 (βARK) activity compared with control (33.8 ± 7.2% versus 4.3 ± 2.2% of unoperated control tissue, P < 0.01, n = 5). Salvage of βARK occurred without change in the thickness of the epicardial tissue overlying the infarct. In dogs pretreated with etanercept before a 2-hour occlusion/4-hour reperfusion of the LAD coronary artery, infarct mass decreased by 61% (% area at risk) and 55% (% left ventricular mass) in the etanercept group (n = 8) compared with saline (n = 9, P < 0.05). This was concordant with an etanercept-mediated six-fold decrease in leukocyte accumulation within ischemically injured myocardium. TNFα antagonism decreases malignant ventricular tachyarrhythmias and may relate to partial protection of normal βARK-mediated desensitization of β-adrenergic receptors. TNFα sequestration also decreases infarct size in an occlusion/reperfusion model of myocardial ischemia.

Captopril stimulation of differential renins in renovascular hypertension.

Twenty-six patients being evaluated for renovascular hypertension were studied to assess the diagnostic value of enhancing the differential between renal venous renins (PRA) by a single 25 mg oral dose of converting enzyme inhibitor (CEI, captopril). Antihypertensive medications were not discontinued prior to the study, and renal venous effluent was sampled before and 30 minutes after CEI. Eight patients without stenosis who did not have surgery had post-CEI ratios of less than 3.0. The other 18 patients had operative intervention, with 14 subsequently having improved blood pressure control. Of these 14, seven patients with unilateral stenosis, four patients with bilateral stenosis, and one patient without overt stenosis but with other evidence of reduced renal blood flow had 30-minute PRA ratios of 3.0 or greater. Five of these 14 patients had prestimulation ratios of less than 1.5 and might not be considered operative candidates by conventional criteria. Four other patients unimproved by surgery had post-CEI ratios of less than 3.0 despite a baseline ratio of greater than 1.5 in two of four. Only two patients with post-CEI ratios of less than 3.0 were improved with surgery. We conclude that a 30-minute post-CEI renal venous ratio of 3.0 or greater enhances the probability that patients with renovascular disease, and hypertension will respond to surgical intervention with improved blood pressure control.

Proteasome inhibition 1 h following ischemia protects GRK2 and prevents malignant ventricular tachyarrhythmias and SCD in a model of myocardial infarction.

Arrhythmia-prone epicardial border zone (EBZ) tissues demonstrate decreased G protein-coupled receptor kinase-2 (GRK2) activity and increased sensitivity to isoproterenol 6-24 h after coronary artery ligation in the dog. We previously demonstrated that the ischemia-mediated decrease in GRK2 in cardiac ischemic tissue was largely blocked by proteasome blockade initiated 1 h before the onset of ischemia, and this was associated with significant cardioprotection against malignant ventricular tachyarrhythmias. For application to clinical circumstances, it is desirable to determine whether a clinical window exists following the onset of ischemia for such a protective effect. The treatment of six dogs with the selective proteasome inhibitor bortezomib 1 h after the surgical induction of left coronary artery ischemia provided 80% (EBZ) and 42% (infarct) protection (by immunoblot) against the loss of GRK2 at 24 h. There was no significant increase of heat shock protein 70(72) in the EBZ of bortezomib-treated animals compared with control. There was a striking absence of rapid (>300 beats/min) and very rapid (>360 beats/min) ventricular triplets that is highly predictive of sudden cardiac deaths (SCDs) during electrocardiogram monitoring of the first 24 h in the bortezomib-treated animals in contrast with nontreated infarcted animals. There were no SCDs in the 6 treated animals (0%) and five SCDs in the 14 control animals (36%). Assay of whole blood proteasome activity demonstrated the expected decrease over the 24-h observation period. These data support the concept that proteasome inhibition within a window of time following myocardial infarction may be of use in suppressing malignant tachyarrhythmias and SCD.