Open versus laparoscopic appendicectomy: a critical review.

BACKGROUND: The benefit of laparoscopic appendicectomy remains unclear. We have analysed available randomised studies comparing laparoscopic and open appendicectomy regarding their clinical pitfalls and statistical relevance. METHODS: Thirty eight studies were analysed in terms of the following aspects: A. clinical problems (e.g., expertise of the surgeons, pre- and postoperative antibiotic treatment, definition of complications, blinding of outcomes) and B. statistical problems (e.g., definition of primary and secondary outcomes, power and sample size, statistical methods, confidence intervals, comparability of groups and studies). RESULTS: Most of the studies have clinical and statistical pitfalls. The most important pitfalls are the uncertain expertise of the operating surgeons, blinding, and the exploratory nature of the studies. Our analysis aims at giving useful information for the appraisal of existing studies and the conduct of further studies. It also gives some preliminary results. CONCLUSIONS: More than twenty years after Semm performed the first laparoscopic appendicectomy, it is necessary to clarify the superiority of laparoscopic or open appendectomy with well-defined, carefully designed randomised studies.

Significant growth inhibition of orthotopic pancreatic ductal adenocarcinoma by CpG oligonucleotides in immunodeficient mice.

BACKGROUND/AIMS: The high rate of local recurrence after radical resection of pancreatic ductal adenocarcinoma fosters intensive efforts to develop new approaches for adjuvant treatment. Antisense and modified oligodeoxynucleotides (ODNs) have demonstrated significant tumour growth inhibitory effects in preclinical systems. Our aim was to evaluate the possible therapeutic potential of ODNs containing unmethylated deoxycytidyl-deoxyguanosine dinucleotides (CpG motifs). METHODOLOGY: For in vitro analysis, [(3)H]thymidine incorporation for DNA synthesis, colorimetric cell vitality assay (EZ4U assay), and DNA fragmentation assay (JAM-[(3)H]thymidine incorporation assay) to test for apoptosis were performed. In vivo testing was done on an orthotopic pancreatic xenotransplantation model using severe combined immunodeficient (SCID) beige and nude mice. RESULTS: No significant differential effect of either control ODN or CpG-1826 ODN with regard to tumour cell proliferation or induction of apoptosis was observed in vitro. In vivo, ODN-1826 proved to have a significant inhibitory effect (up to 40% reduction of tumour weight) when compared with tumour-bearing animals treated with saline or control ODN. This was accompanied by sevenfold increase in splenomegaly and moderate hepatomegaly. The reduction of tumour weight by ODN-1826 was only slightly more pronounced in nude compared with SCID beige mice. CONCLUSION: CpG-1826 induces significant growth-inhibitory effects on orthotopic xenotransplanted pancreatic tumours in highly immunodeficient mice, which might be explained by innate immunity mechanisms and possibly a complex interaction of tumour and stroma cells.

Comparative investigation of alloplastic materials for hernia repair with improved methodology.

BACKGROUND: A variety of alloplastic materials are used for hernia repair. We discuss the long-term stability and possible shrinkage of these materials. In the past, measurement of pore sizes was used to study the physical properties of alloplastic meshes. The aim of this study was to evaluate the measurement of pore sizes with regard to its correlation to possible mesh alteration. METHODS: The water absorption of different polypropylene (PP) and polyester (PE) mesh materials under defined conditions was studied. For shrinkage studies, meshes were stored in formaldehyde, distilled water, saline solution, trypsin solution, urea solution, and hydrogen peroxide. The measurement of the relation between material and pore was evaluated to investigate the potential shrinking and enlargement processes. This material-pore index (MPI) before as well as 1, 7, and 14 days after incubation was measured. RESULTS: In comparison to measuring single pore sizes, MPI determination is the more efficient method to evaluate the possible shrinking or enlargement processes of alloplastic materials. With this technique, incorrect determination of pore sizes due to the dynamic textile structure of meshes and to shrinkage or enlargement, is excluded. All tested alloplastic materials showed an insignificant increase in water absorption under the condition of rehydration up to 0.4%. We did not observe variances in the material in shrinking or enlargement. CONCLUSIONS: MPI was found to be more reliable than measuring single pores to investigate possible external influences on polymer materials. Biomaterials such as PP and PE proved to be absolutely inert under various in vitro conditions.

Precoating of alloplastic materials with living human fibroblasts--a feasibility study.

BACKGROUND: The use of alloplastic materials such as polypropylene and polyester has reduced the recurrence of abdominal wall hernias. Concomitantly, new problems have arisen such as inflammatory response against the implanted material and the development of enteric fistulas in case of direct contact of the bowel to polypropylene and polyester. A precoating of the PP with collagen and other absorbable materials seems to reduce the incidence of adhesions and fistulas. The aim of this study was to show the technical feasibility of a precoating of polypropylene with living human fibroblasts and to investigate the growth properties of the cells under these conditions in vitro. METHODS: The textile structure of three different alloplastic materials is described (SurgiPro), TycoHealthcare; Parietene3 PP1510, Dallhausen; VIPRO II, Ethicon Endosurgery). Enhanced Green Fluorescence Protein (EGFP) transduced human foreskin fibroblasts (KiF5) were seeded onto these different alloplastic materials. Proliferation was analyzed by FACS analysis of Ki67 expression. The coating process of the whole mesh area was observed over time with UV-light microscopy, immunostaining, and scanning electron microscopy (SEM). The expression of collagen type I and III was investigated by immunostaining. RESULTS: The three alloplastic materials used were knitted fabrics with different textile structures. KiF5 colonized the entire alloplastic material within 4-6 weeks. Cells were proliferating, as detected by Ki67 expression. SEM showed surface ruffles and long cellular extensions, indicating an active cell metabolism. Light microscopy and SEM suggested that the cells modify the apolar surface by deposition of extracellular matrix components before colonization. CONCLUSION: Our study shows the feasibility of precoating of polypropylene meshes with living human fibroblasts and opens the possibility for clinical use in the future.

Neoquadruple induction with antithymocyte globulin/azathioprine/cyclosporine/prednisolone in simultaneous pancreas and kidney transplant recipients: 8.5-year results.

Ten years ago therapy with antithymocyte globulin or OKT3, azathioprine, cyclosporine, and prednisolone was the most common induction treatment for simultaneous pancreas/ kidney (SPK) recipients. Although immunosuppression was started after surgery, there was a high incidence of acute rejection episodes. In 1995, we modified the application of antithymocyte globulin and prednisolone by starting prior to reperfusion. Between 1995 and 1996, 30 patients underwent a first SPK. Prior to reperfusion, antithymocyte globulin (4-6 mg/kg body weight) and 250 mg prednisolone were administered. Intraoperatively, another 250 mg prednisolone were administered as well as intravenous azathroprine 3 mg/kg. After surgery up to 10 doses of antithymocyte globulin were administered and cyclosporine trough levels targeted to 200 to 250 ng/mL. Prednisolone was reduced gradually. After a median period of 8.5 years (range: 7.8-9.5 years) patient, pancreas, and kidney graft survival were 93.3%, 70%, and 76.7%, respectively. Sixteen acute rejection episodes were diagnosed in 11 patients (36.7%), who were treated with prednisolone bolus (n = 4), prednisolone with OKT3 (n = 8), prednisolone with antithymocyte globulin (n = 1), cyclosporine to tacrolimus conversion (n = 2), or plasmapheresis (n = 1). Two recipients died after SPK due to severe infection or carcinoma with functioning grafts. Seven further pancreas grafts were lost. Five kidney losses were observed besides the two recipients who died with functioning grafts. While previous protocols yielded a rejection incidence after SPK between 50% and 80%, we observed 60% of patients with no rejection episode during an 8.5-year median follow-up.

Single-shot antithymocyte globuline and daclizumab induction in simultaneous pancreas and kidney transplant recipient: three-year results.

Since 1996, preoperative single-shot dose antithymocyte globuline (ATG) with prednisolone (PRD), mycophenolate mofetile (MMF), and tacrolimus (TAC) is the favorite induction therapy in our center. In a series of 25 first simultaneous pancreas and kidney transplant (SPK) recipients, 5 doses of daclizumab were administered in addition to standard induction. Here we present our 3-year experience. Immunosuppression was started prior to reperfusion consisting of daclizumab (1 mg/kg body weight [bw]), ATG (4-6 mg/kg bw) and 250 mg PRD. After surgery, PRD was reduced gradually, TAC trough levels were between 8-15 ng/mL, MMF was given twice daily (2-3 g/d) as well as 4 further doses dacilzumab every 14 days. After 3 years, patient, pancreas, and kidney graft survival rates are 100%, 84%, and 92%, respectively. Four pancreas grafts were lost (chronic allograft dysfunction, n = 2; recurrent abdominal infection, n = 1; acute rejection [AR] without treatment, n = 1). Both patients suffering from severe infection and untreated AR lost their kidney graft too. During the first 3 months after SPK, 3 AR episodes were observed in 2 patients (8%). After a 3-year period, 8 AR episodes occurred in 7 recipients (28%). AR was treated using PRD (n = 5) or ATG (n = 1). In 1 case, immunosuppression was switched from TAC to sirolimus successfully. Overall, 8 AR episodes occurred in 7 patients (28%) during the first 3 years after SPK. One severe infection led to graft lost 13 months after SPK. In this series, the combination of ATG and daclizumab prevented AR episodes, successfully providing considerable 3-year survival rates.

Donors with a maximum body weight of 50 kg for simultaneous pancreas-kidney transplantation.

INTRODUCTION: Pediatric donors are rarely used for simultaneous pancreas-kidney transplantation (SPK). But the age of the donors may be less important than the body weight (BW). Therefore we retrospectively analyzed our data on SPK donors with a maximum BW of 50 kg. METHODS: Between June 1994 and December 2003, 22 patients received SPK transplants from cadaveric donors with a maximum BW of 50 kg (range, 25-50 kg; median, 42.4 kg). The median donor-recipient weight ratio was 0.61 (range, 0.47-0.91). RESULTS: Two kidney grafts (9.1%) displayed delayed graft function (2 and 9 dialyses). One patient needed insulin for 2 days (<20 IU/d), and the other patient for 1 month at a maximum of 7 IU/d. Four pancreas grafts (18.2%) were lost owing to graft thrombosis. One-year survival for patients was 95.5%; for kidneys, 86.4%; and for the pancreas, 72.7%. After a median observation period of 78 months, 6 acute rejection episodes were observed in 5 patients (22.7%). Five acute rejections were treated successfully, but 1 patient lost both organs. Two patients died of severe infections, at 3 months and 3 years, respectively, after SPK. Four kidney and 3 pancreas grafts developed chronic allograft dysfunction. CONCLUSIONS: Our results show that 1-year graft function in this series was less than the results reported to the International Pancreas Transplant Registry. The Main reason for early pancreas loss was graft thrombosis (18.2%). After a median observation period of 78 months, pancreas graft survival was 59.1%.

Single-shot antithymocyte globulin (ATG) induction for pancreas/kidney transplantation: ATG-Fresenius versus Thymoglobulin.

Single-shot antithymocyte globulin (ATG) prior to reperfusion followed by tacrolimus (TAC), mycophenolate mofetil (MMF), and prednisolone (PRD) is an established induction therapy in simultaneous pancreas kidney transplant (SPK) recipients. We retrospectively analyzed 6-month data from 105 patients who received their first SPK. From January 1996 to December 2000, ATG-Fresenius was used. Since January 2001, Thymoglobulin has been administered. In the first group, 58 patients were treated with ATG-Fresenius (4-6 mg/kg body weight). In the second group, 47 patients received Thymoglobulin (1.5-2.5 mg/kg body weight). HLA-mismatch was comparable. After an observation period of 6 months, patients, kidney, and pancreas graft survival is 98.3%, 96.6%, and 93.1% in group I and 97.9%, 97.9%, and 85.1% in group II, respectively. In each group, one death with functioning graft (DWFG) was observed. Twenty (34.5%) acute rejection episodes (AR) were observed (18 patients) in group I. They were treated with steroids (n = 16) or steroids/OKT3 (n = 4). One kidney graft failure was observed due to rejection and one due to DWFG. Four pancreas grafts were lost (thrombosis, n = 2; AR, n = 1; DWFG, n = 1). In group II, 15 AR (31.9%) were seen in 12 patients and were treated with steroids (n = 12), steroids/ATG (n = 1), or steroids/OKT3 (n = 2). Seven pancreas (thrombosis, n = 5; rejection, n = 1; DWFG, n = 1) and one kidney (DWFG, n = 1) graft losses occurred. These data clearly establish that single-shot ATG prior to reperfusion, followed by TAC, MMF, and PRD results in a low incidence of AR (34.5% in group I and 31.9% in group II) after SPK. Only 6.9% (group I) and 6.4% (group II) of the patients received antibodies for rejection treatment.

[Combined pancreas kidney transplantation after isolated kidney transplantation]. / Die kombinierte Pankreas-Nieren-Transplantation als Re-Transplantation nach isolierter Nierentransplantation.

Simultaneous pancreas kidney transplantation (SPK) is an established therapy for type 1 diabetics with end stage or preterminal renal disease. SPK is superior to isolated kidney transplantation (KTX) in diabetic patients. Even pancreas-re-transplantations are more common in these patients now, mostly after SPK. But Experience with SPK after KTX is rare. Between 1994 and 2003 six Re-SPK 4.5 to 8.5 years after KTX were performed in our department. Average age of the recipients was 40.5 years. They had been suffering from diabetes for an average of 29.3 years. Four recipients were on dialysis again, whereas two had preterminal renal insufficiency. Pancreas transplants were drained through the bladder (n = 1) or into the small intestine (n = 5) with systemic venous anastomosis. After a median observation period of 28 months (8 to 99 months) all six recipients are insulin free. One patient lost his kidney graft due to severe acute rejection. Therefore kidney graft survival is 83 %. Four acute rejections (66 %) were observed in 4 patients. Only one rejection was treated successfully by steroids. Two rejections could be stopped with antibodies. 3 patients had infections in the early postoperative period (sinusitis, urinary tract infection, wound infection). Even after KTX with graft failure, diabetic patients suffering from renal disease can be re-transplanted successfully with SPK.

[Open versus laparoscopic operation for perforated appendicitis--a comparative study]. / Konventionelle oder laparoskopische Operation der perforierten Appendizitis - Eine vergleichende Studie.

INTRODUCTION: Laparoscopic therapy of complicated appendicitis is still discussed controversially. This retrospective study compared the clinical results of open and laparoscopic appendectomy in a single centre. PATIENTS AND METHODS: Within a period of three years (1999 to 2001) 493 patients with suspected acute appendicitis were operated prospectively at a German district hospital (250 open appendectomies, 243 laparoscopic appendectomies). Twenty percent of the patients in every group had a complicated appendicitis (48 open, 44 laparoscopic appendectomies) and were analysed retrospectively considering demographic data, operative time, body mass index, preoperative inflammatory parameters (white blood cell count, C-reactive protein and body temperature) and postoperative complication rate. RESULTS: Both groups were comparable with regard to demographic data. One patient of the laparoscopic group needed an open operation (conversion rate 2.3 %). The body mass index of the laparoscopic group was significantly higher (26.3 vs. 24.1 kg/m(2)). Preoperative white blood cell count, C-reactive protein, body temperature as well as postoperative antibiotic therapy and analgesics requirement were comparable in both groups. There was no significant difference between the length of operative time (open 48 min, laparoscopic 53.5 min). The postoperative hospital stay was significantly shorter in the laparoscopic group (8 vs. 9 days, p = 0.032). Complication rate was significantly lower in the laparoscopic group (11.5 vs. 35 %, p = 0.014). CONCLUSION: Laparoscopic appendectomy is a safe procedure for the treatment of complicated appendicitis with a significantly decreased complication rate and shorter postoperative stay.

[Pancreas removal by external teams]. / Pankreasorganentnahme durch externe Teams.

Combined pancreas and kidney transplantation is an established procedure for terminal or preterminal, uremic, type 1 diabetics. The current procurement technique allows simultaneous recovery of liver and pancreas. One problem is the assessment of organ quality. It remains unclear how many pancreas organs must be withdrawn during back-table preparation. Between June 1994 and December 2003, 271 pancreas transplantations were performed at our transplant centre. Two hundred sixty-two (89.7%) pancreas grafts were harvested by teams which were not part of the transplant team. Twenty-one (8.0%) grafts were discharged for transplantation at the time of back-table preparation. Liposis of the graft and critical vessel situations were the main reasons for withdrawal. Two kidney grafts were not usable for transplantation, and 92% of the pancreas grafts were. This demonstrates the high standard of pancreas procurement in the Eurotransplant region.

Intraoperative radiofrequency ablation (RFA) for irresectable liver malignancies.

AIMS: To evaluate the outcome of patients who received radiofrequency ablation (RFA) at open laparotomy in patients with irresectable liver malignancies. METHODS: Twenty-six consecutive patients who underwent explorative laparotomy and were found to be irresectable or who had been assessed not suitable for either resection or percutaneous RFA received intraoperative RFA. An expandable electrode (RITA Medical systems) was used. Follow-up comprised CT-scans in 6-12 week intervals. RESULTS: Patients' age ranged from 35 to 72 years (median 61). A variety of pathologies were treated. In 26 patients, 88 hepatic lesions were treated: 32 with resection and 56 with RFA. The mean diameter was 4.0+/-2.6 cm with a maximum of 10 cm. In 22 patients with hepatic metastases (18 colorectal, one leiomyosarcoma, one endometrium carcinoma, one renal cell carcinoma, one malignant phaeochromocytoma) 74 lesions (median 3.4 per patient) were treated (25 by resection, 49 by RFA). Eleven patients received simultaneous resection and RFA: resection of anatomical segments in six and atypical resection in seven patients. Procedure related complication rate was 19.2%. The mean follow-up was 14.6+/-9.2 months (2-36 months). Three patients developed recurrence at the site of previous RFA indicating incomplete ablation. The overall local control rate after one year was 92 and 90.9% for patients with colorectal liver metastases, respectively. Seventeen patients (65.4%) suffered from tumour progress. In 14 patients (53.9%) tumour occurred at new hepatic localisations and in five patients extrahepatic tumour relapse was diagnosed. Twelve patients have died so far (median survival 18 months, range 4-27). Nineteen patients had either completed a follow-up of at least 12 months or died within this period, resulting in an one year survival rate of 79% (80% for liver metastases). CONCLUSION: Intraoperative RFA is a valuable tool in liver surgery which extends the surgical spectrum in cases of irresectable malignancies.

Multiple and synergistic deregulations of apoptosis-controlling genes in pancreatic carcinoma cells.

Inability to die by apoptosis is one of the reasons for the deregulated growth of tumour cells and the frequently observed failure of chemotherapy. In this study we thought to identify the common and functionally important characteristics responsible for the apoptosis resistance of pancreatic tumour cells. We analysed cell surface expression level of death receptors CD95 and TRAIL-R1-4 as well as the expression profile of sixteen apoptosis-relevant proteins in five pancreatic carcinoma cell lines Capan1, Colo357, PancTuI, Panc89 and Panc1. These data were evaluated in the context of sensitivity towards anti-CD95 and TRAIL-mediated apoptosis. Here we report that except for resistant Panc1 cells, which only marginally expressed CD95, all other cell lines showed comparable levels of CD95 and TRAIL receptors irrespectively of their apoptotic phenotype. Interestingly, we found that the elevated expression of FLIP, Bcl-x(L) and IAP in parallel with a downregulation of FADD and Bid was common for the resistant cell lines. Consequently, stable overexpression of XIAP, Bcl-x(L) or dominant negative FADD in sensitive cells significantly reduced the death receptor mediated apoptosis while the overexpression of Bid rendered the resistant cells sensitive.

[Minimally invasive video-assisted thyroid resection (MIVAT)--a well accepted operative procedure]. / Die minimalinvasive video-assistierte Schilddrüsenresektion (MIVAT)--ein Verfahren mit hoher Patientenakzeptanz.

INTRODUCTION: We report on our results of MIVAT operations. METHOD: Nineteen Patients including 15 females and 4 males were operated with MIVAT, corresponding to 11 % of all patients undergoing an operation for benign goitre in our hospital. A single node of the thyroid gland within 30 mm and enlargement of a thyroid lobe up to 25 ml were the selection criteria. The median age was 34 years (range 16-61). We performed 2 thyroidectomies, 6 Hartley-Dunhill resections, 9 hemihyroidectomies and 2 enucleations. Eighteen patients (95 %) were followed-up postoperatively. The median follow-up period was 8 months (range 1 -21). RESULTS: The median operation time was 83 min (range 60-124). The median preoperative thyroid gland volume was 25 ml (range 10-54) measured by ultrasound. The resected thyroid tissue ranged from 12 to 51 g (median 29 g). A statistical significant difference (P = 0.04 paired t-test) between the preoperative and postoperative estimated serum-calcium levels (2.31 vs. 2.25 mM) was observed. But both parameters were inside the physiological range. Paresis of the recurrent laryngeal nerve was not observed. 89 % of the patients rated the postoperative cosmetic result as very good and all patients would prefer this operation procedure once again. CONCLUSION: The MIVAT procedure is a safe operation also in small groups with excellent cosmetic results postoperatively and a high acceptance by the patients.

Meckel's diverticulum: a disease associated with a colored clinical picture.

Meckel's diverticulum is reported in only 1 or 2% of the population. In most cases, it is free of clinical symptoms. The diagnostic modalities are effective in only 60-70% of all cases. The diagnostic laparoscopy is a safe and effective method for patients suffering from unclear abdominal pain with the option of a definitive surgical therapy. We describe the case of a 10-year-old girl with recurrent abdominal pain caused by a chronic subileus due to a Meckel's diverticulum in combination with a fibrous cord from the base of diverticulum to the mesenterial root. Both were resected in a laparoscopic technique.

The influence of the cytosolic oncotic pressure on the permeability of the mitochondrial outer membrane for ADP: implications for the kinetic properties of mitochondrial creatine kinase and for ADP channelling into the intermembrane space.

Cytosolic proteins as components of the physiological mitochondrial environment were substituted by dextrans added to media normally used for incubation of isolated mitochondria. Under these conditions the volume of the intermembrane space decreases and the contact sites between the both mitochondrial membranes increase drastically. These morphological changes are accompanied by a reduced permeability of the mitochondrial outer compartment for adenine nucleotides as it was shown by extensive kinetic studies of mitochondrial enzymes (oxidative phosphorylation, mi-creatine kinase, mi-adenylate kinase). The decreased permeability of the mitochondrial outer membrane causes increased rate dependent concentration gradients in the micromolar range for adenine nucleotides between the intermembrane space and the extramitochondrial space. Although all metabolites crossing the outer membrane exhibit the same concentration gradients, considerable compartmentations are detectable for ADP only due to its low extramitochondrial concentration. The consequences of ADP-compartmentation in the mitochondrial intermembrane space for ADP-channelling into the mitochondria are discussed.

Effect of macromolecules on the regulation of the mitochondrial outer membrane pore and the activity of adenylate kinase in the inter-membrane space.

Macromolecules as components of the physiological mitochondrial environment were substituted by dextrans of different molecular weight. The addition of 10% dextran (molecular weights varying between 20 and 500 kDa) affected neither basic mitochondrial parameters (state 4 and state 3 respiration) nor kinetic properties of soluble kinases. A significant increase by 10% dextran was however observed of the voltage sensitivity of isolated porin when reconstituted in planar bilayers. The pores adapted the low conducting state already at a voltage of 10 mV. This effect of the macromolecules may explain the higher diffusion resistance of adenine nucleotides across the outer membrane as observed in different experiments: (i) the Michaelis constant of adenylate kinase in the inter-membrane space increased, in contrast to the soluble enzyme, from 118 +/- 10 microM to 193 +/- 20 microM ADP, (ii) in the presence of competing external pyruvate kinase, the mitochondrial utilization of ADP, produced by adenylate kinase in the inter-membrane space, was improved 3-fold suggesting a reduced ADP diffusion out of the outer mitochondrial compartment. The influence of the various dextrans correlated with the increase in molecular weight of the dextrans. The effect on the kinetic constants was dependent on the dextran concentration in terms of weight and not of molarity. The oncotic pressure and viscosity of dextran solutions with different molecular weight showed a comparable dependence. In general, the data indicate that the outer membrane pore responds to an increased oncotic pressure by reducing adenine nucleotide permeability. This suggests the physiological existence of a third adenine nucleotide compartment between the two envelope membranes which may be important especially at high metabolic fluxes.

Effect of macromolecules on the structure of the mitochondrial inter-membrane space and the regulation of hexokinase.

Macromolecules as components of the physiological mitochondrial environment were substituted by addition of 10% dextran 70. This led to a significant reduction of the space between the two envelope and the crista membranes and to an increase of contact sites as observed by freeze-fracture analysis. The preferential binding of hexokinase in these sites was employed to further analyze the dextran effect: (i) desorption of the enzyme by digitonin treatment was found to be significantly reduced in the presence of dextran although liberation of adenylate kinase and monoamine oxidase were not affected, (ii) the affinity of isolated hexokinase isozyme I to liver mitochondria was increased by dextran. Generally the binding of hexokinase to intact mitochondria (also control mitochondria) followed a co-operative mechanism and led to an activation. Cooperativity and activation were not observed when the contact formation was suppressed by dinitrophenol or glycerol. The binding of hexokinase to the isolated outer membrane resembled that of mitochondria in the absence of contacts (i.e., no cooperativity and activation). Conversely to the observation in intact mitochondria, dextran rather reduced the affinity of hexokinase to the isolated outer membrane. Kinetic analyses of the dextran effect served to explain the function of contact site specific hexokinase binding. We observed that dextran improved the hexokinase dependent stimulation of the oxidative phosphorylation (state 3 respiration), while the activity of the enzyme with internal or external ATP remained unaffected. The results suggest three things: (i) that contact sites are probably more frequent in the intact cell than in vitro in the absence of macromolecules, (ii) that the contact preference of hexokinase serves rather the ADP supply of the translocator than the ATP transfer to the enzyme and (iii) that the total cellular hexokinase activity may be regulated by specific binding of the enzyme to the contact sites, either because of a different pore structure or because of additional components exclusively exposed in these sites.