MRI­based neoadjuvant therapy indication in middle and low rectal cancer.

OBJECTIVE: The aim of this study was to evaluate the indication of neoadjuvant therapy in patients with middle and low rectal cancer based on MRI examination. BACKGROUND: In spite of noticeable advances in the diagnosis of rectal cancer, the optimal treatment remains highly debated. Current guidelines advise the use of neoadjuvant therapy in UICC stage II patients or higher. However, in clinical praxis, there is gradual implementation of new criterions and variables used in rectal cancer stage evaluation, the fact of which influences the treatment choice. The most important emerging variables taken currently into account are the distance from mesorectal fascia, circumferential resection margin, extramural venous invasion and intersphincteric plane, all of which can be evaluated using the MRI examination. METHODS: The accuracy of MRI staging was compared with definite histopathological results from resected tumors. Patient data were prospectively collected between the years 2013 and 2018 at 3rd Surgical Clinic, Faculty of Medicine, Comenius University in Bratislava, Slovakia. Data from 101 patients were gathered and divided into two groups, according to the localization of tumor within rectum, while 9 patients were excluded from the study because of benign lesion diagnosis based upon final histopathologic evaluation. RESULTS: In 92 evaluated patients, no significant change was noted between MRI and histopathological T-staging. However, in N-staging, significant differences were noted between preoperative MRI staging and postoperative histopathological staging. CONCLUSION: The results of this study demonstrate inefficient preoperative lymph node staging, suggesting overtreatment of rectal cancer patients. Although the use of neoadjuvant therapy has led to great advances in modern cancer treatment, it is connected with a number of side effects and therefore should be indicated only for patients who can benefit from this treatment (Tab. 1, Fig. 3, Ref. 16).

Insight into the incidence of acute aortic dissection in the German region of Berlin and Brandenburg.

BACKGROUND: Stanford acute type A aortic dissection (ATAAD) is a potentially lethal condition. Epidemiology studies show a statistical incidence in Europe of approximately 2-16 cases/100,000 inhabitants/year. In Germany, the estimated incidence (here subsumed under "thoracic aortic dissection" with 4.63 cases/100,000 inhabitants/year) is mainly extracted from medical death certificates by the German Federal Statistical Office. The prehospital incidence of ATAAD deaths is largely unknown. Since patients often die in the pre-hospital setting, the incidence of ATAAD is therefore likely to be higher than current estimates. MATERIAL AND METHODS: For the period from 2010 to 2014, we retrospectively analyzed all in-hospital ATAAD data from two of the largest cardiac surgical centers that treat ATAAD in the Berlin-Brandenburg region. In addition, autopsy reports of all forensic medicine institutes and of one large pathological provider in the region were analyzed to identify additional non-hospitalized ATAAD patients. Based on these findings, the regional incidence of ATAAD was calculated. RESULTS: In addition to in-hospital ATAAD patients (n=405), we identified additional 145 lethal ATAAD cases among 14,201 autopsy reports. The total of 550 ATAAD cases led to an estimated incidence of 11.9 cases/100,000 inhabitants/year for the whole Berlin-Brandenburg region. Arterial hypertension, pre-existing aortic dilatation, and hereditary connective tissue disorder were found in, respectively, 62.7%, 10%, and 1.8% of patients. CONCLUSION: ATAAD is more frequent than previously reported. Our results show that when patients who die outside of cardiac surgery centers are included, the incidence of ATAAD significantly exceeds the rate reported by the Federal Statistical Office.

Early versus delayed laparoscopic cholecystectomy in treatment of acute cholecystitis.

BACKGROUND: Acute cholecystitis is one of the most frequent diseases occurring in the developed countries of the world. Since the advent of laparoscopic cholecystectomy there has been a lack of agreement regarding the timing of the operation in the treatment of acute cholecystitis. METHODS: From September 2012 to January 2015 we carried out a prospective randomized trial at the IIIrd Surgical Department of University Hospital Milosrdní bratia in Bratislava. The aim of the trial was to compare the two basic approaches of the treatment of acute cholecystitis. During our trial, 62 patients with acute cholecystitis were admitted to the surgery department and 31 patients were treated with an early laparoscopic cholecystectomy within 72 hours after the appearance of the symptoms. Other 31 patients were primarily treated with antibiotics and subsequently underwent a delayed cholecystectomy after 6-8 weeks. RESULTS: Our results suggest several advantages of the early laparoscopic cholecystectomy such as shorter operation time, lower conversion rate, shorter length of hospital stay, shorter postoperative convalescence and lower cost of hospitalization. CONCLUSION: According to these results we believe that immediate laparoscopic cholecystectomy (within 24 hours from the patient's admission to hospital) should become a preferred method of treatment of the patients with acute cholecystitis (Tab. 1, Fig. 2, Ref. 17).

Blood transfusion during versus after cardiopulmonary bypass is associated with postoperative morbidity in neonates undergoing cardiac surgery.

INTRODUCTION: Cardiac surgery on neonates for the correction of congenital heart defects is usually associated with the transfusion of packed red blood cells (PRBCs) into the cardiopulmonary bypass (CPB) circuit. We hypothesised that such transfusions of stored PRBCs directly into the arterial system may increase postoperative morbidity when compared to intravenous transfusion. PATIENTS AND METHODS: In this retrospective cohort study, data from 122 consecutive neonates who received transfusions of PRBCs in the course of corrective surgery for congenital heart defects were analysed. Group assignment was according to the timing of the first transfusion: during CPB (On-CPB) or after weaning from CPB (Post-CPB). Chi Square and rank sum tests were applied to compare clinical characteristics. Times until extubation and release from the intensive care unit were analysed by Kaplan-Meier curves and by multivariate Cox regression. RESULTS: Transfusion of PRBCs during CPB was associated with greater 48 hour blood loss (mean±standard deviation, 86±125 versus 32±16 mL/kg, p<0.001), longer duration of mechanical ventilation (214±268 versus 99±75 h, p<0.001) and longer stay on the intensive care unit (10.9±12.1 versus 5.3±3.5 days, p<0.001). However, the groups also differed in many characteristics, such as bodyweight, complexity of surgery or preoperative haemoglobin concentration, which may also affect outcome. Yet, multivariate analyses confirmed an independent association of transfusion On-CPB with an adverse clinical outcome. CONCLUSIONS: Our results are consistent with the hypothesis that the transfusion of PRBCs during CPB may increase postoperative morbidity. However, due to the limitations of this retrospective analysis, further studies are needed to confirm a causal relationship between the timing of the transfusion and the clinical outcome and to elucidate putative mechanisms of such an association.

Transcranial Doppler sound detection of cerebral microembolism during transapical aortic valve implantation.

OBJECTIVE: Transapical aortic valve implantation (TAVI) is a new method that might reduce the surgical risk of conventional surgical aortic valve replacement in very high-risk patients. Increased downstream microembolization is expected in transapical aortic valve implantation. However, whether it usually occurs, how often, and its clinical relevance are not known. We report the results of ultrasound microembolic signal detection in the middle cerebral artery during the procedure. METHODS: Fifty patients (mean age: 80 ± 5 years; mean EuroSCORE: 36 ± 13 %) underwent transapical aortic valve implantation. Intraoperative transcranial Doppler (TCD) sound examination of both middle cerebral arteries (MCA) was used to identify high-intensity transient signals (HITS) and microembolic signals (MES) during seven phases of the procedure. Pre- and postoperative computed tomography of the brain and clinical neurological examinations were performed preoperatively and daily during the first postoperative week. RESULTS: During the procedure, HITS [right MCA: 435 ± 922 (range 9-5765); left MCA: 471 ± 996 (range 24-6432)] and MES [right MCA: 78 ± 172 (range 1-955); left MCA: 62 ± 190 (range 2-1553)] were detected in all patients. Most of the MES were recorded during valvuloplasty [right MCA: 3 ± 5.6 (range 0-31); left MCA: 2 ± 4.9 (range 0-30)] and positioning of the prosthetic valve in the aortic position [right MCA: 6 ± 5 (range 0-22); left MCA: 2 ± 6.9 (range 0-38)]. Postoperatively, there were no clinical signs of new cerebral embolism. CONCLUSIONS: Cerebral microemboli were detected by intraoperative transcranial Doppler sound examinations in all patients during transapical aortic valve implantation. Most of the signals were detected during balloon valvuloplasty and delivery of the prosthetic valve.

Mast cells promote lung vascular remodelling in pulmonary hypertension.

Left heart disease (LHD) frequently causes lung vascular remodelling and pulmonary hypertension (PH). Yet pharmacological treatment for PH in LHD is lacking and its pathophysiological basis remains obscure. We aimed to identify candidate mechanisms of PH in LHD and to test their relevance and therapeutic potential. In rats, LHD was induced by supracoronary aortic banding. Whole genome microarray analyses were performed, candidate genes were confirmed by RT-PCR and Western blots and functional relevance was tested in vivo by genetic and pharmacological strategies. In lungs of LHD rats, mast cell activation was the most prominently upregulated gene ontology cluster. Mast cell gene upregulation was confirmed at RNA and protein levels and remodelled vessels showed perivascular mast cell accumulations. In LHD rats treated with the mast cell stabiliser ketotifen, or in mast cell deficient Ws/Ws rats, PH and vascular remodelling were largely attenuated. Both strategies also reduced PH and vascular remodelling in monocrotaline-induced pulmonary arterial hypertension, suggesting that the role of mast cells extends to non-cardiogenic PH. In PH of different aetiologies, mast cells accumulate around pulmonary blood vessels and contribute to vascular remodelling and PH. Mast cells and mast cell-derived mediators may present promising targets for the treatment of PH.

Estimating the efficiency of medical diagnostic systems.

Lack of standardization in estimating the quality of diagnostic systems provides many possibilities in developing new methodologies. The paper deals with general method for determination of effectiveness of diagnostic systems in non-invasive diagnostics of thyroid. The result of presented methodology is a single number, which clearly depicts the quality of such a system with no need for further analysis. Together with the general design of such a system an overview of characteristics of a diagnostic system is described.

[Coronary artery bypass grafting in patients with highly impaired ventricular function. Long-term outcome]. / Koronarbypassoperation bei hochgradig eingeschränkter Ventrikelfunktion - Langzeitergebnisse.

BACKGROUND AND OBJECTIVE: Left ventricular function is the most important predictor of survival in patients with coronary artery disease. It is also an important indicator for hospital mortality after operation for end-stage coronary artery disease. In our study we investigated, how preoperative ventricular dysfunction influences long term survival after coronary bypass surgery. PATIENTS AND METHODS: Between 4/1986 and 12/2000, 1751 patients (1440 men/311 women) with left ventricular ejection fraction (LVEF) 10-30% underwent coronary bypass grafting (CABG) at the Deutsches Herzzentrum Berlin. The age of the patients was calculated to an average of 59,2 years. The prime criterion for CABG was ischemia ("hibernating myocardium") diagnosed by myocardial scintigraphy, echocardiography and in some cases with magnetic resonance imaging and positron emission tomography. RESULTS: Operative mortality for the group was 7,1%. The actuarial survival rate was 87,6% after 2 years, 76,0% after 5, and 53,3% after 9. 455 had LVEF 10-20%, in these actuarial survival was 79,8% after 2 years, 63,0% after 5 and 45,7% after 9 years. CONCLUSION: We conclude that CABG can be used successfully to improve life expectancy of patients with end-stage coronary artery disease. CABG leads to acceptable prognosis for these high-risk patients when the myocardium is preoperatively identified as being viable.

Predictors of survival 1 hour after implantation of an intra-aortic balloon pump in cardiac surgery.

From July 1996 to March 2000, 391 patients with intraoperative cardiac low-output syndrome who underwent surgery with heart-lung bypass and had an intra-aortic balloon pump (IABP) implanted were analyzed in a prospective study. Of these 391 patients, 153 (39%) were operated on in an emergency situation, and 238 (61%) patients had elective surgeries. The perioperative mortality was 34% (133 patients). Clinical parameters were analyzed 1 hour after IABP support began. Statistical multivariate analysis showed that patients with an adrenaline requirement higher than 0.5 microg/kg/min, a left atrial pressure higher than 15 mmHg, output of less than 100 mL/hour, and mixed venous saturation (SvQ2) of less than 60% had poor outcomes. Using this data, we developed an IABP score to predict survival early after IABP implantation in cardiac surgery. We conclude that the success or failure of perioperative IABP support can be predicted early after implantation of the balloon pump. In patients with low-output syndrome despite IABP support, implantation of a ventricular assist system should be considered.

Evaluation of post-cardiopulmonary bypass coagulation disorders by differential diagnosis with a multichannel modified thromboelastogram: a pilot investigation.

We assessed a modified multichannel thromboelastogram for differentiation of the causes of coagulopathy after cardiopulmonary bypass and its suitability as a therapy guide. Thirty adult patients undergoing surgery with cardiopulmonary bypass, who revealed a coagulopathy as observed by a prolonged activated clotting time of >150 sec after the application of protamine, were enrolled. Therapy was based on the results obtained by the computerized four-channel thromboelastogram with baseline, heparinase (2 IU/mL), heparinase/abciximab (5 microg/mL), and heparinase/fresh frozen plasma (25%) channels. The mean activated clotting time before therapy was 162.2+/-7.8 sec. Based on differential diagnosis with the modified multichannel thromboelastogram, two patients received protamine (30 mg), five desmopressin (0.4 microg/kg), 19 patients three units of fresh frozen plasma, two patients platelet transfusions, and two patients both protamine (30 mg) and three units of fresh frozen plasma. After therapy, there was a significant (p < .01) decrease of the activated clotting time to a mean value of 127+/-8.3 sec. Therapy based on the synoptic modified multichannel thromboelastogram analysis provides a guide for effective therapy of coagulopathy. However, elaboration is desirable, and larger clinical trials are necessary for a final evaluation of the protocol.

Assessment of the resonance thromboelastograph CS-3 for differentiation of coagulation disorders: a pilot in vitro investigation of simulated post-cardiopulmonary bypass coagulopathies.

Resonance thromboelastography (RTG), a further development of the thromboelastogram (TEG), has been designed for improved differentiation of the effect of the plasmatic coagulation factors (increasing F-leg) and platelets (decreasing P-leg) on clot formation. It is based on the effect of clot elasticity on the resonance of a swinging wire. We assessed the RTG for its ability to differentiate coagulation disorders that frequently occur after cardiac surgery. The RTG was performed with a CS-3 Analyzer. Samples from 10 healthy volunteers were investigated after the following preparations: (1) baseline values, (2) dilution to a hematocrit of 30% and 20% with either hydroxyl ethyl starch (HES) 10% or plasma; (3) addition of 0.25, 0.5, and 1.0 IU/mL porcine heparin with and without heparinase; and (4) addition of 1.0, 3.0, 4.0, and 5.0 microg/mL of the antiplatelet agent abciximab (ReoPro). Increasing concentrations of abciximab led to a slower decrease or in the case of higher concentrations, to a persistent elevation of the platelet leg of the RTG. Dilution of the hematocrit with plasma had no effect on the fibrin and platelet leg; whereas, dilution with HES 10% led to an inhibition of the fibrin and platelet leg. Dilution of the plasmatic coagulation factors resulted in an inhibition of both the fibrin and the platelet leg. The addition of 0.25 and 0.5 IU/mL of heparin led to an increased coagulation time and inhibition of the fibrin and platelet legs. These effects were eliminated by the addition of heparinase. The RTG enables the evaluation of platelet function under the condition of a nonimpaired plasma coagulation system. Depletion of plasma coagulation factors and the administration of small amounts of heparin do not enable the distinction between residual effects of an anticoagulant, coagulation factor deficiency, or impaired platelet function. However, the heparin effects can be eliminated by the addition of heparinase. Further improvement may be achieved using a modified RTG by adding plasma coagulation factors in one channel for an improved evaluation of platelet function, even under the condition of a loss of procoagulants.

Transcranial detection of microembolic signals in patients with a novel nonpulsatile implantable LVAD.

Mechanical ventricular assist devices (VAD) have become an accepted therapy for the support of patients in severe heart failure. With the devices presently available, the incidence of thromboembolic complications is high. Since November 1998, we have used the DeBakey VAD (MicroMed, Inc., Woodlands, TX). To detect the effect of this VAD on the appearance of microthrombi or bubbles from cavitation, we measured Microembolic Signals (MES) with transcranial Doppler in patients after the implantation of the DeBakey VAD. Transcranial Doppler studies were performed with the MULTI-DOP X4 device with two 2 MHz probes (for the left and right middle cranial arteries [MCA]) in five patients preoperatively and during 10 weeks after VAD implantation. Both MCAs were monitored simultaneously for 60 minutes in 10 sessions in each patient. The detection and analysis of MES was performed in accordance with the technique and criteria described by the international consensus group. No MES were noted during the study period in four patients. In one patient with preoperatively noted MES the prevalence of MES postoperatively was 50%. The high speed rotating impeller of the DeBakey VAD did not produce any detectable microthrombi or bubbles from cavitation effects.

Anticoagulation during cardiopulmonary bypass in patients with heparin-induced thrombocytopenia type II and renal impairment using heparin and the platelet glycoprotein IIb-IIIa antagonist tirofiban.

BACKGROUND: Patients with heparin-induced thrombocytopenia type II require an alternative to standard heparin anticoagulation. However, in patients with renal impairment, anticoagulation during cardiopulmonary bypass with agents such as danaparoid sodium or r-hirudin are associated with hemorrhage. Anticoagulation with unfractionated heparins combined with prostacyclin, a potent platelet aggregation inhibitor, is associated with severe hypotension. The authors investigated a new concept using unfractionated heparins after platelet inhibition with the short-acting platelet glycoprotein IIb-IIIa antagonist tirofiban. METHODS: Ten patients with heparin-induced thrombocytopenia type II and renal impairment were enrolled in the investigation. All had heparin-induced thrombocytopenia type II antibodies present as proved by the heparin-induced platelet aggregation assay, the heparin-platelet factor 4 enzyme-linked immunosorbent assay, or both. In all patients, preoperative anticoagulation to an activated partial thromboplastin time of 40-60 s was performed with r-hirudin. Anticoagulation during cardiopulmonary bypass was achieved with a bolus of 400 IU/kg unfractionated heparins after a bolus of tirofiban 10 microg/kg followed by an infusion of tirofiban at a rate of 0.15 microg x kg(-1) x min(-1) until 1 h before conclusion of cardiopulmonary bypass. Additional unfractionated heparins were only administered if activated clotting time decreased below 480 s. Coagulation was monitored by a abciximab-modified TEG and the adenosine diphosphate-stimulated (20 microm) platelet aggregometry. D-dimer concentrations, as a marker of venous thromboembolism, were measured before and 12, 24, and 48 h after surgery. Postoperative antithrombotic therapy was started immediately with r-hirudin to anticoagulation to an activated partial thromboplastin time of 40-60 s. RESULTS: The postoperative blood loss ranged from 110 to 520 ml. No patient needed reexploration. In no patient was there clinical evidence of thrombosis or embolism in the postoperative period or of a critical increase of the D-dimer concentrations, suggesting venous thromboembolism. Transfusion of platelets was necessary in only two patients. CONCLUSIONS: The protocol is easy to perform and no increased postoperative bleeding and no thromboembolic complications occurred. The combination of unfractionated heparins and tirofiban may be an alternative to other anticoagulation strategies in patients with heparin-induced thrombocytopenia.

A quick anti-Xa-activity-based whole blood coagulation assay for monitoring unfractionated heparin during cardiopulmonary bypass: a pilot investigation.

UNLABELLED: We developed a quick and easy method to perform anti-Xa-activity-based whole blood assay and assessed its reliability for online monitoring of unfractionated heparins (UFHs) during cardiopulmonary bypass. Seventy-five microliters of a mixture of 1:3 large- and small-range Heptest reagent were transferred into blank cartridges of the ACT II device. The plastic flags for clot detection and stirring the sample and reagent were inserted and overlaid with 75 microL of Recalmix for recalcification. One-hundred fifty microliters of citrated whole blood were added and measurements performed. In vitro, the linearity of the test over a range of 1-8 IU/mL UFH, as well as the influence of variations in hematocrit (60%, 30%, and 20%), plasma coagulation factors (50%, 30%, and 20%) and platelets (100, 50, and 20 x 10(3)/microL) on the test results were assessed. In vivo measurements performed during cardiopulmonary bypass were compared with the chromogenic assay. The test revealed linearity to concentrations of 6 IU/mL of UFH and was not significantly influenced by the variations in the in vitro set-up despite a prolongation in samples with a hematocrit of 60%. In vivo, the correlation to the chromogenic test was R: = 0.90. The ACT II anti-Xa-UFH assay performed in whole blood was reliable when used over a wide range of conditions that could be encountered clinically. Although the test is useful for point-of-care monitoring, the necessity of individual calibrations and pipetting in the operation room requires further automation before its use in clinical practice. IMPLICATIONS: The ACT II anti-Xa-unfractionated heparin assay allows for reliable monitoring of large concentrations of UFH over a wide range of hematocrit, platelet, and coagulation factor levels. Further evaluation of this point-of-care device is indicated.

Isolation and culture of highly enriched populations of Leydig cells from guinea-pig (Cavia porcellus) testes.

Leydig cells were isolated from adult male guinea-pig testes using a multi-step procedure involving enzymatic dissociation and Percoll-gradient centrifugation. The following description is the first account of a successful isolation of adolescent guinea-pig Leydig cells. The enriched Leydig-cell preparation routinely isolated from six intact testicles yielded approximately 5.0 x 10(6) +/- 0.7 x 10(6) (+/- SEM) Leydig cells with a viability of 98.0 +/- 0.4% as determined using the trypan-blue exclusion method. The purity of the isolated cell population as assessed by 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) staining averaged 82.5 +/- 0.8%. Under light microscopy, guinea-pig Leydig cells were polyhedral in shape with a large prominent nucleus and a distinct nucleolus. The acidophilic cytoplasm contained numerous lipid-filled vesicles. Ultrastructurally, guinea-pig Leydig cells displayed an eccentrically located ovoid nucleus with dark-staining peripheral heterochromatin. Large quantities of mitochondria, smooth endoplasmic reticulum and particulate-laden lipid droplets were also evident. The steroidogenic potential of the isolated Leydig cells was verified using a maximally stimulating dose of ovine LH (100 ng ml-1) and human CG (200 mIU ml-1). Leydig cells incubated in a shaking (120 cycles min-1) water bath for 3 h at 37 degrees C in capped polypropylene microcentrifuge tubes produced 233 +/- 21 ng and 223 +/- 18 ng testosterone per 1 x 10(6) cells when maximally stimulated with oLH or hCG, respectively. The inclusion of low (1-5 microM) levels of sodium ascorbate during culture enhanced significantly Leydig-cell viability vs. control values.

Elevated concentrations of ascorbate and normoxia suppress testosterone production in cultured guinea pig Leydig cells.

In recent years, several metabolic roles have been proposed for vitamin C. Recent information suggests a strong causal relationship between high endogenous levels of ascorbic acid and changes in normal reproductive biology. Using highly enriched populations of guinea pig Leydig cells, we have found that elevated levels (50 to 500 microM) of ascorbate significantly (P < 0.01) depressed testosterone production in a dose-dependent manner while low levels (0 to 10 microM) were without effect. Leydig cells incubated under hypoxic (3% oxygen) culture conditions produced significantly (P < 0.01) more testosterone than similar cells cultured under normoxic (19% oxygen) conditions. The results of this study suggest that high concentrations of ascorbate and normoxic culture conditions suppress testosterone production in isolated Leydig cells. Thus, it would seem that there exists a delicate balance between normal metabolic requirements for vitamin C and excessive ascorbate levels that might alter normal gonadal reproductive events.

Determination of oxytocin in biological samples by isocratic high-performance liquid chromatography with coulometric detection using C18 solid-phase extraction and polyclonal antibody-based immunoaffinity column purification.

A specific high-performance liquid chromatographic (HPLC) method is described for the reliable quantitation of oxytocin using culture media supernatants. The procedure employs solid-phase extraction, antibody-based immunoaffinity purification and isocratic HPLC with dual channel coulometric detection (ED). The lower limit of detection for this cyclic nonapeptide was 40 pg (40 fmol). Due to its relative simplicity, specificity and precision, the HPLC-ED of oxytocin is an accurate and attractive alternative to many existing quantitative methods.

The antioxidant defense system of isolated guinea pig Leydig cells.

Utilization of highly enriched preparations of steroidogenic Leydig cells have proven invaluable for studying the direct effects of various hormones and agents on Leydig cell function in vitro. However, recent work indicates that isolated Leydig cells are often subjected to oxygen (O2) toxicity when cultured at ambient (19%) oxygen concentrations. Because intracellular antioxidants play an important role in protecting cells against oxygen toxicity, we have investigated the intracellular antioxidant defense system of isolated Leydig cells. The cellular levels of several antioxidants including catalase, glucose-6-phosphate dehydrogenase (G-6-PDH), superoxide dismutase (SOD) of the Cu/Zn & Mn variety, glutathione peroxidase, glutathione reductase and total glutathione were quantitated using enriched populations of Leydig cells isolated from adult male guinea pig testes. Compared to whole testicular homogenates, Leydig cells contained significantly (P < 0.01) less G-6-PDH, total SOD, glutathione reductase and total glutathione, but significantly (P < 0.001) more glutathione peroxidase. Compared to hepatic values previously reported in the guinea pig, Leydig cells contain nearly 400 times less catalase, about 14 times less glutathione peroxidase and almost 11 times less glutathione reductase. Since G-6-PDH and glutathione reductase are both necessary to regenerate reduced glutathione (GSH) which couples with glutathione peroxidase to breakdown hydrogen peroxide (H2O2) under normal conditions, it is plausible that the oxygen toxicity observed in isolated Leydig cells is due to the intracellular accumulation of H2O2.(ABSTRACT TRUNCATED AT 250 WORDS)