Meta-analysis of long-term survival after elective endovascular or open repair of abdominal aortic aneurysm.

BACKGROUND: Endovascular aneurysm repair (EVAR) has become the preferred strategy for elective repair of abdominal aortic aneurysm (AAA) for many patients. However, the superiority of the endovascular procedure has recently been challenged by reports of impaired long-term survival in patients who underwent EVAR. A systematic review of long-term survival following AAA repair was therefore undertaken. METHODS: A systematic review was performed according to PRISMA guidelines. Articles reporting short- and/or long-term mortality of EVAR and open surgical repair (OSR) of AAA were identified. Pooled overall survival estimates (hazard ratios (HRs) with corresponding 95 per cent c.i. for EVAR versus OSR) were calculated using a random-effects model. Possible confounding owing to age differences between patients receiving EVAR or OSR was addressed by estimating relative survival. RESULTS: Some 53 studies were identified. The 30-day mortality rate was lower for EVAR compared with OSR: 1·16 (95 per cent c.i. 0·92 to 1·39) versus 3·27 (2·71 to 3·83) per cent. Long-term survival rates were similar for EVAR versus OSR (HRs 1·01, 1·00 and 0·98 for 3, 5 and 10 years respectively; P = 0·721, P = 0·912 and P = 0·777). Correction of age inequality by means of relative survival analysis showed equal long-term survival: 0·94, 0·91 and 0·76 at 3, 5 and 10 years for EVAR, and 0·96, 0·91 and 0·76 respectively for OSR. CONCLUSION: Long-term overall survival rates were similar for EVAR and OSR. Available data do not allow extension beyond the 10-year survival window or analysis of specific subgroups.

The Consequences of Real Life Practice of Early Abdominal Aortic Aneurysm Repair: A Cost-Benefit Analysis.

BACKGROUND: The reported 54 mm median intervention diameter for endovascular aneurysm repair (EVAR) in the Vascular Quality Initiative and European data from the Pharmaceutical Aneurysm Stabilisation Trial (PHAST) implies that in real life the majority of abdominal aortic aneurysm (AAA) repairs occur at diameters smaller than the consensus intervention threshold of 55 mm. This study explores the potential consequences of this practice. METHODS: The differences between real life AAA repair and consensus based intervention threshold were explored in reported data from vascular quality initiatives and PHAST. The subsequent consequences of advancement of endovascular aneurysm repair (EVAR) were estimated using a multistate model based on life tables for the EVAR Medicare population. RESULTS: There appears an approximate 5 mm difference in AAA diameter between real life practice and consensus intervention threshold. Assuming a 2.5 mm annual growth rate, this results in an approximately 2 year advancement of AAA repair. According to the model used, early repair reduces overall small aneurysm patient mortality by 2.3%, it results in 21.9% more EVAR procedures, more EVAR related deaths, and 42.3% and 36.8% more open and endovascular re-interventions, respectively. Cost-benefit estimates imply 482 fewer AAA related deaths, but 140 extra EVAR related deaths for a population of more than 30,000 AAA patients, and a 300 million USD increase in health costs for the 8 year observation period in the Medicare population. CONCLUSIONS: In the real life situation a large proportion of EVAR procedures appear to occur before reaching the consensus threshold. Although this reduces mortality, it comes at a cost of approximately 1 million USD per prevented rupture related death.

Succinate Accumulation and Ischemia-Reperfusion Injury: Of Mice but Not Men, a Study in Renal Ischemia-Reperfusion.

A recent seminal paper implicated ischemia-related succinate accumulation followed by succinate-driven reactive oxygen species formation as a key driver of ischemia-reperfusion injury. Although the data show that the mechanism is universal for all organs tested (kidney, liver, heart, and brain), a remaining question is to what extent these observations in mice translate to humans. We showed in this study that succinate accumulation is not a universal event during ischemia and does not occur during renal graft procurement; in fact, tissue succinate content progressively decreased with increasing graft ischemia time (p < 0.007). Contrasting responses were also found with respect to mitochondrial susceptibility toward ischemia and reperfusion, with rodent mitochondria robustly resistant toward warm ischemia but human and pig mitochondria highly susceptible to warm ischemia (p < 0.05). These observations suggest that succinate-driven reactive oxygen formation does not occur in the context of kidney transplantation. Moreover, absent allantoin release from the reperfused grafts suggests minimal oxidative stress during clinical reperfusion.

Randomized clinical trial of mast cell inhibition in patients with a medium-sized abdominal aortic aneurysm.

BACKGROUND: Abdominal aortic aneurysm (AAA) is thought to develop as a result of inflammatory processes in the aortic wall. In particular, mast cells are believed to play a central role. The AORTA trial was undertaken to investigate whether the mast cell inhibitor, pemirolast, could retard the growth of medium-sized AAAs. In preclinical and clinical trials, pemirolast has been shown to inhibit antigen-induced allergic reactions. METHODS: Inclusion criteria for the trial were patients with an AAA of 39-49 mm in diameter on ultrasound imaging. Among exclusion criteria were previous aortic surgery, diabetes mellitus, and severe concomitant disease with a life expectancy of less than 2 years. Included patients were treated with 10, 25 or 40 mg pemirolast, or matching placebo for 52 weeks. The primary endpoint was change in aortic diameter as measured from leading edge adventitia at the anterior wall to leading edge adventitia at the posterior wall in systole. All ultrasound scans were read in a central imaging laboratory. RESULTS: Some 326 patients (mean age 70·8 years; 88·0 per cent men) were included in the trial. The overall mean growth rate was 2·42 mm during the 12-month study. There was no statistically significant difference in growth between patients receiving placebo and those in the three dose groups of pemirolast. Similarly, there were no differences in adverse events. CONCLUSION: Treatment with pemirolast did not retard the growth of medium-sized AAAs. REGISTRATION NUMBER: NCT01354184 (https://www.clinicaltrials.gov).

Editor's Choice - Pharmaceutical Management of Small Abdominal Aortic Aneurysms: A Systematic Review of the Clinical Evidence.

BACKGROUND: Management of abdominal aortic aneurysms (AAAs) relies on surgical repair of larger AAAs. Consequently medical interventions inhibiting AAA progression could greatly reduce the need for surgical repair. A spectrum of pharmaceutical strategies has been reported, albeit conclusions often appear contradictory. Given the longstanding interest in pharmaceutical AAA stabilization, a systematic review of the available literature is relevant. OBJECTIVES: The aim is to provide an up to date systematic review of the available data on pharmaceutical therapies for stabilizing or impeding AAA growth. METHODS: A search using Pubmed, Embase, Web of science, Cochrane, CINAHL, Academic Search Premier, and Science Direct identified 27 eligible papers that studied the clinical effect of the pharmaceutical therapy on AAA diameter growth. RESULTS: This review shows that there is currently no pharmaceutical strategy that reduces AAA growth. Most studies are of poor methodological quality. Initial promising reports are often not confirmed in subsequent larger studies, raising the possibility of selective reporting. CONCLUSION: There is currently no pharmaceutical means that halts AAA growth.

The collagen cross-linking enzyme lysyl oxidase is associated with the healing of human atherosclerotic lesions.

BACKGROUND: Acute clinical complications of atherosclerosis such as myocardial infarction (MI) and ischaemic stroke are usually caused by thrombus formation on the ruptured plaque surface. Collagen, the main structural protein of the fibrous cap, provides mechanical strength to the atherosclerotic plaque. The integrity of the fibrous cap depends on collagen fibre cross-linking, a process controlled by the enzyme lysyl oxidase (LOX). METHODS AND RESULTS: We studied atherosclerotic plaques from human carotid endarterectomies. LOX was strongly expressed in atherosclerotic lesions and detected in the regions with ongoing fibrogenesis. Higher LOX levels were associated with a more stable phenotype of the plaque. In the studied population, LOX mRNA levels in carotid plaques predicted the risk for future MI. Within the lesion, LOX mRNA levels correlated positively with levels of osteoprotegerin (OPG) and negatively with markers of immune activation. The amount of LOX-mediated collagen cross-links in plaques correlated positively also with serum levels of OPG. CONCLUSIONS: Lysyl oxidase may contribute to the healing of atherosclerotic lesions and to the prevention of its lethal complications. Mediators of inflammation may control LOX expression in plaques and hence plaque stability.

The impact of human papillomavirus genotype on colposcopic appearance: a cross-sectional analysis.

OBJECTIVE: To study colposcopic performance in diagnosing high-grade cervical intraepithelial neoplasia or cervical cancer (CIN2+ and CIN3+) using colposcopic characteristics and high-risk human papillomavirus (hrHPV) genotyping. DESIGN: Cross-sectional multicentre study. SETTING: Two colposcopy clinics in The Netherlands and Spain. POPULATION: Six hundred and ten women aged 17 years and older referred for colposcopy because of abnormal cytology. METHODS: A cervical smear was obtained. Colposcopists identified the worst lesion, graded their impression and scored the colposcopic characteristics of the lesions. Up to four biopsies were collected, including one biopsy from visually normal tissue. MAIN OUTCOME MEASURES: CIN2+ and CIN3+, positive for HPV16 or other high-risk HPV types (non-16 hrHPV-positive). RESULTS: The mean age in HPV16-positive CIN2+ women was 35.1 years compared with 39.1 years in women with other hrHPV types (P = 0.002). Sensitivity for colposcopy to detect CIN2+ was 87.9% (95%CI 83.2-91.5), using colposcopic cut-off of 'any abnormality'. The remaining CIN2+ were found by a biopsy from visually normal tissue or endocervical curettage (ECC). Detection of CIN2+ by lesion-targeted biopsies was not different between HPV16-positive women [119/135; 88.1% (95%CI 81.2-92.9)] and non-16 hrHPV-positive women [100/115; 87.0% (95%CI 79.1-92.3); P = 0.776]. In multivariate analysis, 'acetowhitening' [odds ratio (OR) 1.91, 95%CI 1.56-3.17], 'time of appearance' (OR 1.95, 95%CI 1.21-3.15) and 'lesion >25% of visible cervix' (OR 2.25, 95%CI 1.44-3.51) were associated with CIN2+. CONCLUSIONS: In this population following European screening practice, HPV16-related CIN2+ lesions were detected at younger age and showed similar colposcopic impression as non-16 hrHPV high-grade lesions. There was no relationship between any of the colposcopic characteristics and HPV16 status.

Cardiospecific sevoflurane treatment quenches inflammation but does not attenuate myocardial cell damage markers: a proof-of-concept study in patients undergoing mitral valve repair.

BACKGROUND: Inflammation is considered a key mediator of complications after cardiac surgery. Sevoflurane has been shown to quench inflammation and to provide cardioprotection in preclinical studies. Clinical studies using sevoflurane confirm this effect on inflammation but do not consistently show clinical benefits. This paradox may indicate that the contribution of inflammation to postoperative sequalae is less than commonly thought or that systemic doses are too low in their local concentration. To test the latter, we evaluated the effects of intramyocardial sevoflurane delivery. METHODS: Selective myocardial sevoflurane delivery was performed during aortic cross-clamping in patients undergoing valve surgery (n=11). Results were compared with a control group not receiving sevoflurane (n=10). A reference group (n=5) was added to evaluate the effects of systemic sevoflurane delivery. Paired arterial and myocardial venous blood samples were collected at various time points post-reperfusion. Inflammatory mediators and myocardial cell damage were studied. RESULTS: Intramyocardial delivery was superior to systemic delivery in attenuation of interleukin-6 and interleukin-8 (-44% and -25%, respectively; both P=0.001). Myocardial and systemic sevoflurane delivery effectively suppressed surgery-related inflammatory responses including postoperative C-reactive protein levels when compared with controls [63 (47-99) (P=0.01) and 58 (56-81) (P=0.04) compared with 107 (79-144) mg litre(-1)]. Sevoflurane treatment did not reduce postoperative troponin T, creatine kinase, and creatine kinase-MB values. CONCLUSIONS: This proof-of-concept study suggests that intramyocardial delivery compared with the systemic delivery of sevoflurane more strongly attenuates the systemic inflammatory response after cardiopulmonary bypass without reducing postoperative markers of myocardial cell damage. CLINICAL TRIAL REGISTRATION: Nederlands Trial Register NTR2089.

An association between chronic obstructive pulmonary disease and abdominal aortic aneurysm beyond smoking: results from a case-control study.

OBJECTIVES: It is currently unclear whether the parallels between abdominal aortic aneurysms (AAAs) and chronic obstructive pulmonary disease (COPD) are explained by common risk factors alone, such as cigarette smoking, or by a predetermined cause. Given the persistent controversy with regard to the association between AAA and COPD, we studied this association in depth. METHODS: We conducted a case-control study comparing patients with a small AAA (maximum infrarenal diameter 35-50 mm, n = 221) with controls diagnosed with peripheral artery disease (PAD, n = 87). The controls were matched to the cases for lifetime cigarette smoking. Pulmonary function was measured by spirometry, and all subjects completed a questionnaire on medical history and smoking habits (current, former and never smokers). RESULTS: Aneurysm patients were similar to controls with respect to gender (p = 0.71), lifetime cigarette smoking (39 vs. 34 pack years, p = 0.23) and history of cardiovascular disease (45% vs. 55%, p = 0.12). Aneurysm patients had more airway obstruction (forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) (0.69 ± 0.12 vs. 0.78 ± 0.11, p < 0.001)), which was most pronounced in never smokers (0.73 ± 0.07 vs. 0.86 ± 0.07, p < 0.001). COPD was more prevalent in aneurysm patients (44%; 98/221) than in controls (20%; 17/87) (adjusted odds ratio (OR) 3.0; 95% confidence interval (95%CI) 1.6-5.5, p < 0.001). In particular, a major proportion of AAA patients was newly diagnosed with COPD; only 40 of 98 patients (41%) with COPD (mild, moderate or severe/very severe) were known before with obstructive pulmonary defects and received treatment. CONCLUSIONS: This study confirms an association between AAA and COPD and shows that this association is independent from smoking. Findings also demonstrate that COPD is under-diagnosed in AAA patients.

Donor brain death predisposes human kidney grafts to a proinflammatory reaction after transplantation.

Donor brain death has profound effects on post-transplantation graft function and survival. We hypothesized that changes initiated in the donor influence the graft's response to ischemia and reperfusion. In this study, human brain dead donor kidney grafts were compared to living and cardiac dead donor kidney grafts. Pretransplant biopsies of brain dead donor kidneys contained notably more infiltrating T lymphocytes and macrophages. To assess whether the different donor conditions result in a different response to reperfusion, local cytokine release from the reperfused kidney was studied by measurement of paired arterial and renal venous blood samples. Reperfusion of kidneys from brain dead donors was associated with the instantaneous release of inflammatory cytokines, such as G-CSF, IL-6, IL-9, IL-16 and MCP-1. In contrast, kidneys from living and cardiac dead donors showed a more modest cytokine response with release of IL-6 and small amounts of MCP-1. In conclusion, this study shows that donor brain death initiates an inflammatory state of the graft with T lymphocyte and macrophage infiltration and massive inflammatory cytokine release upon reperfusion. These observations suggest that brain dead donors require a novel approach for donor pretreatment aimed at preventing this inflammatory response to increase graft survival.

Systematic approach towards reliable estimation of abdominal aortic aneurysm size by ultrasound imaging and CT.

BACKGROUND: The management of abdominal aortic aneurysm (AAA) is fully dictated by AAA size, but there are no uniform measurement guidelines, and systematic differences exist between ultrasound- and CT-based size estimation. The aim of this study was to devise a uniform ultrasound acquisition and measurement protocol, and to test whether harmonization of ultrasound and CT readings is feasible. METHODS: A literature review was undertaken to evaluate evidence for ultrasound-based measurement of AAA. A protocol for measuring AAA was then developed, and intraobserver and interobserver reproducibility was tested. Finally, agreement between ultrasound readings and CT-based AAA diameters was evaluated. This was an observational study of patients with a small AAA who participated in two pharmaceutical intervention trials. RESULTS: Based on a literature review, an ultrasound acquisition and reading protocol was devised. Evaluation of the protocol showed an intraobserver repeatability of 1.6 mm (2s.d.) and an interobserver intraclass correlation coefficient (ICC) of 0.97. Comparison of protocolled ultrasound readings and local CT readings indicated a good correlation (r = 0.81), but a systematic +4.1-mm difference for CT. Harmonized size readings for ultrasound imaging and CT increased the correlation (r = 0.91) and reduced the systematic difference to +1.8 mm by CT. Interobserver reproducibility of protocolized CT measurements showed an ICC of 0.94 for the inner-to-inner method and 0.96 for the outer-to-outer method. CONCLUSION: The absence of harmonized size acquisition and reading guidelines results in overtreatment and undertreatment of patients with AAA. This can be avoided by the implementation of standardized ultrasound acquisition and a harmonized reading protocol for ultrasound- and CT-based readings.

A systematic review of implementation of established recommended secondary prevention measures in patients with PAOD.

OBJECTIVE: Since patients with peripheral arterial occlusive disease (PAOD) are at high-risk for cardiovascular morbidity and mortality, preventive measures aimed to reduce cardiovascular adverse events are advocated in the current guidelines. We conducted a systematic review to assess the implementation of secondary prevention (SP) measures in PAOD patients. METHODS: PubMed, Cochrane Library, EMBASE and Web of Science databases were searched to perform a systematic review of the literature from 1999 till June 2008 on SP for PAOD patients. Assessment of study quality was done following the Cochrane Library review system. The record outcomes were antiplatelet agents, heart rate lowering agents, blood pressure lowering agents, lipid lowering agents, glucose lowering agents, smoking cessation and walking exercise. RESULTS: From a total of 2137 identified studies, 83 observational studies met the inclusion criteria, of which 24 were included in the systematic review comprising 34 157 patients. These patients suffered from coronary artery disease (n=3516, 41%), myocardial infraction (n=2647, 38%), angina pectoris (n=1790, 31%), congestive heart failure (n=2052, 14%), diabetes mellitus (n=10 690, 31%),hypertension (n=20 823, 73%) and hyperlipidaemia (n=15 067, 64%). Contrary to what the guidelines prescribe, antiplatelet agents, heart rate lowering agents, blood pressure lowering agents and lipid lowering agents were prescribed in 63%, 34%, 46% and 45% of the patients, respectively. Glucose lowering agents were prescribed in 81% and smoking cessation in 39% of the patients. CONCLUSION: The majority of patients suffering from PAOD do not receive the entire approach of SP measures as suggested by the current guidelines. To our knowledge, the cause of this undertreatment is multifactorial: patient, physician or health-care-related.

Early renal ischemia-reperfusion injury in humans is dominated by IL-6 release from the allograft.

The pathophysiology of ischemia/reperfusion (I/R) injury is complex, and current knowledge of I/R injury in humans is incomplete. In the present study, human living-donor kidney transplantation was used as a highly reproducible model to systematically study various processes potentially involved in early I/R injury. Unique, direct measurements of arteriovenous concentration differences over the kidney revealed massive release of interleukin (IL)-6 in the first 30 minutes of graft reperfusion and a modest release of IL-8. Among the assessed markers of oxidative and nitrosative stress, only 15(S)-8-iso-PGF(2alpha) was released. When assessing cell activation, release of prothrombin factor 1 + 2 indicated thrombocyte activation, whereas there was no release of markers for endothelial activation or neutrophil activation. Common complement activation complex sC5b-9 was not released into the bloodstream, but was released into urine rapidly after reperfusion. To investigate whether IL-6 plays a modulating role in I/R injury, a mouse experiment of renal I/R injury was performed. Neutralizing anti-IL-6 antibody treatment considerably worsened kidney function. In conclusion, this study shows that renal I/R in humans is dominated by local IL-6 release. Neutralization of IL-6 in mice resulted in a significant aggravation of renal I/R injury.

Extracellular matrix components and regulators in the airway smooth muscle in asthma.

There is an intimate relationship between the extracellular matrix (ECM) and smooth muscle cells within the airways. Few studies have comprehensively assessed the composition of different ECM components and its regulators within the airway smooth muscle (ASM) in asthma. With the aid of image analysis, the fractional areas of total collagen and elastic fibres were quantified within the ASM of 35 subjects with fatal asthma (FA) and compared with 10 nonfatal asthma (NFA) patients and 22 nonasthmatic control cases. Expression of collagen I and III, fibronectin, versican, matrix metalloproteinase (MMP)-1, -2, -9 and -12 and tissue inhibitor of metalloproteinase-1 and -2 was quantified within the ASM in 22 FA and 10 control cases. In the large airways of FA cases, the fractional area of elastic fibres within the ASM was increased compared with NFA and controls. Similarly, fibronectin, MMP-9 and MMP-12 were increased within the ASM in large airways of FA cases compared with controls. Elastic fibres were increased in small airways in FA only in comparison with NFA cases. There is altered extracellular matrix composition and a degradative environment within the airway smooth muscle in fatal asthma patients, which may have important consequences for the mechanical and synthetic functions of airway smooth muscle.

Intramuscular or combined intramuscular/intra-arterial administration of bone marrow mononuclear cells: a clinical trial in patients with advanced limb ischemia.

AIM: Recent evidence indicates that bone marrow mononuclear cells (BMC) promote collateral vessel formation in patients with severe peripheral arterial disease (PAD). However, aspects concerning optimal administration mode, durability and long-term safety require consideration. Combined intra-arterial (IA) plus intramuscular (IM) BMC delivery may be more effective than exclusive intramuscular injections. The aim of this study was to evaluate feasibility, safety and effect of exclusive IM versus combined IM+IA delivery of autologous BMC in patients who were not candidates for surgical or endovascular treatment. METHODS: Twenty-seven patients were treated with either combined IA+IM (N=12) or sole IM (N=15) administration of autologous BMC. Efficacy was assessed after 1, 6 and 12 months. Limb salvage, pain-free walking distance, ankle-brachial pressure index (ABI) and pain scores were evaluated. RESULTS: There were no adverse reactions related to injection of the cells. Three patients died within the first year of follow-up due to non-procedure related causes. Two patients in the IA+IM group required limb amputation because of ongoing critical ischemia versus 7 patients in the IM group (P=0.17). BMC treatment in the remaining patients resulted in a significant and sustained (>12 months) improvement. Pain-free walking distance improved from 81+/-56 meters at baseline to 257+/-126 meters at t=6 months (P=0.0002). Mean ABI increased 23% after 6 months (P=0.01) and pain score reduced for up to 50% as shown by Brief Pain Inventory (P=0.001). CONCLUSION: Both IM and combined IM/IA delivery of autologous BMC are safe, and result in relevant and sustained improvement in a considerable proportion of patients with severe PAD who are not amenable for conventional treatment.

Myostatin mediates abdominal aortic atherosclerosis progression by inducing vascular smooth muscle cell dysfunction and monocyte recruitment.

Myostatin (Mstn) is a skeletal muscle growth inhibitor involved in metabolic disorders and heart fibrosis. In this study we sought to verify whether Mstn is also operative in atherosclerosis of abdominal aorta. In human specimens, Mstn expression was almost absent in normal vessels, became detectable in the media of non-progressive lesions and increased with the severity of the damage. In progressive atherosclerotic lesions, Mstn was present in the media, neointima, plaque shoulder and in infiltrating macrophages. Mstn co-localized with α-smooth muscle actin (α-SMA) staining and with some CD45+ cells, indicating Mstn expression in VSMCs and bloodstream-derived leukocytes. In vitro, Mstn was tested in VSMCs and monocytes. In A7r5 VSMCs, Mstn downregulated proliferation and Smoothelin mRNA, induced cytoskeletal rearrangement, increased migratory rate and MCP-1/CCR2 expression. In monocytes (THP-1 cells and human monocytes), Mstn acted as a chemoattractant and increased the MCP-1-dependent chemotaxis, F-actin, α-SMA, MCP-1 and CCR2 expression; in turn, MCP-1 increased Mstn mRNA. Mstn induced JNK phosphorylation both in VSMCs and monocytes. Our results indicate that Mstn is overexpressed in abdominal aortic wall deterioration, affects VSMCs and monocyte biology and sustains a chronic inflammatory milieu. These findings propose to consider Mstn as a new playmaker in atherosclerosis progression.

Nuclear magnetic resonance and detection of human breast tumor.

Malignant, benign, and normal breast tissues corrected for fat appeared to have similar nuclear magnetic proton spin-lattice relaxation times, contrary to previously published reports. However, due to a lower fat content, benign and malignant tumors relaxed more slowly than the surrounding normal tissue. This provides a possibility for locating them (but not for discriminating between them) in a breast by the nuclear magnetic resonance imaging technique zeugmatography.

Gonadal receptors. I. Evidence for irreversibility in the binding of human chorionic gonadotropin and human luteinizing hormone.

The binding of human chorionic gonadotropin and human luteinizing hormone to particulate receptors of rat testes has generally been assumed to follow an equilibrium model similar to that proposed for many enzyme systems. Our work shows that equilibrium dissociation constant (Kd) and number of hormone binding sites (Bmax) are highly sensitive to changes in hormone and/or receptor concentration and to treatment received by tissue or receptor preparation prior to the assay. The results of binding assays obtained using receptor preparation pretreated with hormone (labeled as well as unlabeled) indicated that the binding reaction between hormone and receptor was irreversible and that pretreatment of the tissue with hormone greatly alters the number of high affinity gonadotropin binding sites in the testicular homogenate. Data from studies involving increasing receptor concentrations revealed that increasing the mass of particulate receptors in the binding assays leads to higher Kd as well as Bmax values. These findings are incompatible with a binding model based upon occupancy of receptor sites and the state of equilibrium implied. The incompatibilities are analyzed and an alternate model advanced (Bhalla, V.K., Trowbridge, C.G., Chen, C.J.H., Lindeman, J.G. and Rojas, F.J. (1979) Biochim. Biophys. Acta 584, 436--453).

Gonadal receptors. II. Effects of time and reaction volume upon the binding of human chorionic gonadotropin and human luteinizing hormone to particulate receptors.

The effect of reaction volume upon the binding of gonadotropins by particulate receptors was studied. Two experimental approaches were used: one involved increasing the reaction volume of the binding assay (i.e. diluting the hormone and receptor concentrations and will be referred to as buffer coincubation studies) and the other involved incubating the testicular homogenate in various buffer volumes prior to the binding assay (buffer preincubation stidies). The results showed that the number of hormone binding sites inferred from Scatchard analysis was inversely related to the reaction volume in the coincubation as well as in the preincubation studies. Time-dependent dissociation of receptors from the intact testis was demonstrated by perifusion studies and the loss of receptors from intact testis correlated with the appearance of soluble factors (Bhalla, V.K., Haskell, J., Grier, H. and Mahesh, V.B. (1976) J. Biol. Chem. 251, 4947--4957) in the eluate obtained. The results obtained along with those presented in the preceding manuscript (Chen, C.J.H., Lindeman, J.G., Trowbridge, C.G. and Bhalla, V.K. (1979) Biochim. Biophys. Acta 284, 407--435) question the validity of the rapid equilibrium model which assumes reversible hormone occupancy of a fixed number of receptor sites. An alternate binding model is proposed herein and its implications are discussed.