Off-pump coronary artery bypass surgery for critical left main stem disease: safety, efficacy and outcome.

OBJECTIVES: To determine whether patients with critical left main stem (LMS) coronary artery disease can undergo off-pump coronary artery bypass (OPCAB) surgery safely and successfully. METHODS: From May 1996 to March 2000 data for patients with critical (> or =50%) LMS stenosis who underwent conventional coronary artery bypass surgery with cardiopulmonary bypass (CCAB) or without (OPCAB) were collected prospectively using the Patient Analysis & Tracking System. A reusable pressure stabilizer, intra-coronary shunts and a single posterior pericardial stitch exposure technique were used in all OPCAB cases. Non-randomized, retrospective data analysis included demographic and preoperative risk factors, operative details, clinical outcome and early follow-up. RESULTS: During the study period 387 patients with LMS stenosis underwent surgery (OPCAB n=75, CCAB n=312). Groups were similar in terms of preoperative and intraoperative variables although CCAB patients received significantly more grafts per patient (3.1+/-0.73 vs. 2.6+/-0.76, P< or =0.001). Mortality was similar in both groups (OPCAB 1.3% vs. CCAB 2.6%). OPCAB patients when compared to CCAB patients had a lower requirement for postoperative inotropes (12.0% vs. 38.1%, P=0.0001), temporary postoperative pacing (2.7% vs. 10.1%, P=0.02), and blood product transfusion (6.7% vs. 31.4%, P<0.0001), a lower incidence of postoperative chest infection (0% vs. 6.7%, P=0.02) and a slightly reduced postoperative length of stay (7.9+/-5.46 vs. 8.3+/-5.11 days, P=0.01). At 24 months follow-up, CCAB and OPCAB actuarial survival was 94.1+/-1.7% and 97.7+/-2.3%, respectively. CONCLUSIONS: OPCAB surgery is safe and effective in patients with critical LMS disease.

The role of antibodies in dysfunction of pig-to-baboon pulmonary transplants.

OBJECTIVE: Pulmonary transplantation has become the preferred treatment for end-stage lung disease, but application of the procedure is limited because of a paucity of donors. One way to solve donor limitations is to use animal organs as a donor source or xenotransplantation. The current barrier to pulmonary xenotransplantation is the rapid failure of the pulmonary xenograft. Although antibodies are known to play a role in heart and kidney xenograft rejection, their involvement in lung dysfunction is less defined. This project was designed to define the role of antibodies in pulmonary graft rejection in a pig-to-baboon model. METHODS: Orthotopic transgenic swine left lung transplants were performed in baboons depleted of antibodies by one of three techniques before transplantation: (1) ex vivo swine kidney perfusion, (2) total immunoglobulin-depleting column perfusion, and (3) ex vivo swine lung perfusion. Results were compared with those of transgenic swine lung transplants in unmodified baboons. RESULTS: All three techniques of antibody removal resulted in depletion of xenoreactive antibodies. Only pretransplantation lung perfusion improved pulmonary xenograft function compared with lung transplantation in unmodified baboons. CONCLUSIONS: The pathogenesis of pulmonary injury in a swine-to-primate transplant model is different from that in renal and cardiac xenografts. Depletion of antibodies alone does not have a beneficial effect and may actually be detrimental.

Human complement regulatory proteins protect swine lungs from xenogeneic injury.

BACKGROUND: Pulmonary xenotransplantation is not possible because of hyperacute lung injury, the pathogenesis of which is unknown. This study evaluates complement-dependent pathways of pulmonary injury during heterologous perfusion of swine lungs. METHODS: Lungs from unmodified swine and swine expressing human decay-accelerating factor and human CD59 (hDAF/hCD59 swine) were perfused with either human plasma or baboon blood. Pulmonary vascular resistance and static pulmonary compliance were measured serially, and swine lung tissue were examined by light microscopy. Complement activation was assessed by serial measurements of baboon plasma C3a-desArg concentrations. RESULTS: Perfusion of unmodified swine lungs with human plasma and baboon blood resulted in hyperacute lung injury within minutes of perfusion. However, function was preserved in swine lungs expressing human decay-accelerating factor and human CD59. In both study groups, xenogeneic perfusion with baboon blood resulted in at least a sevenfold increase in plasma C3a-desArg levels suggesting transient activation of complement. CONCLUSIONS: Lungs from swine expressing human decay-accelerating factor and human CD59 were resistant to injury during perfusion with human plasma and baboon blood, indicating that complement mediated some of the features of xenogeneic acute lung injury.

Complement-mediated pulmonary xenograft injury: studies in swine-to-primate orthotopic single lung transplant models.

BACKGROUND: The pathogenesis of acute pulmonary xenograft injury has not yet been determined. The present study evaluates the role of complement in mediating pulmonary xenograft dysfunction by using cobra venom factor (CVF) to deplete recipient complement and transgenic swine, which express human regulators of complement activation (human decay-accelerating factor [hDAF] and hCD59). METHODS: Fifteen orthotopic lung transplants were performed as follows: group I, swine-to-swine (n=5); group II, unmodified swine-to-baboon (n=3); group III, unmodified swine-to-(CVF treated) baboon (n=3); and group IV, hCD59/hDAF swine-to-baboon (n=4). Left pulmonary artery flow and pulmonary vascular resistance were measured at 30-min intervals. Serial lung biopsies were examined by light microscopy and immunofluorescence. The activation of complement was quantified by measurement of baboon plasma CH50 and C4 functional activity. RESULTS: Group II xenotransplants ceased functioning within 30 min of reperfusion. Histopathologic ab normalities included erythrocyte/platelet aggregates and hemorrhagic pulmonary edema. Groups I and IV showed excellent function throughout. hDAF/hCD59 lungs (group IV) showed trace venular fibrin plugs and moderate loss of alveolar architecture. Pretreatment with CVF (group III) was ineffective in preventing xenograft injury. CONCLUSIONS: These results characterize the fundamental features of discordant pulmonary xenotransplantation. Correction of the known defects in the regulation of heterologous complement activation was partially effective in preventing pulmonary xenograft dysfunction, suggesting that complement mediates, in part, some of the features of acute lung injury after discordant lung xenotransplantation.

Total respiratory support from swine lungs in primate recipients.

UNLABELLED: The use of nonhuman lung donors, such as swine, has the potential to provide an unlimited supply of organs. However, hyperacute rejection has prevented pulmonary xenotransplantation. OBJECTIVE: Our aim was to test the hypothesis that immunodepletion by pretransplantation swine lung perfusion will prevent hyperacute swine-to-primate pulmonary xenograft rejection and allow for a functional swine pulmonary xenograft. METHODS: Seven baboons underwent left pneumonectomy followed by orthotopic transplantation of the swine left lung. Four baboons received immunodepletion by perfusion with swine lungs before transplantation, and three received no treatment before transplantation. RESULTS: After transplantation, pulmonary xenografts from immunodepleted baboons had a low pulmonary vascular resistance and a high pulmonary blood flow compared with control animals, which had a high pulmonary vascular resistance and a low pulmonary blood flow. After 60 minutes of reperfusion, three of four immunodepleted animals also tolerated complete occlusion of the right pulmonary artery, with the baboon relying completely on the swine pulmonary xenograft for respiratory function for 11 hours. Pathologic analysis of peripheral lung biopsy specimens taken from control lungs displayed alveolar disruption and hemorrhage within small vessels, whereas swine lungs transplanted into immunodepleted baboons displayed little histologic evidence of injury. Furthermore, pulmonary xenografts transplanted into immunodepleted baboons demonstrated excellent respiratory function and adequate hemodynamics during occlusion of the right pulmonary artery. CONCLUSION: Hyperacute pulmonary xenograft rejection can be prevented by pretransplantation swine lung perfusion. Swine pulmonary xenografts can provide complete respiratory support in primates when rejection is prevented.

Swine lungs expressing human complement-regulatory proteins are protected against acute pulmonary dysfunction in a human plasma perfusion model.

UNLABELLED: Pulmonary transplantation is currently limited by the number of suitable cadaver donor lungs. For this reason, pulmonary xenotransplantation is currently being investigated. OBJECTIVE: Our goal was to assess the role of complement in pulmonary xenograft dysfunction. METHODS: The pulmonary function of swine expressing human decay accelerating factor and human CD59 (n = 6) was compared with that of the lungs from nontransgenic (control) swine (n = 6) during perfusion with human plasma. RESULTS: After 2 hours of perfusion, the pulmonary vascular resistance was 1624 +/- 408 dynes.sec.cm-5 in control lungs and 908 +/- 68 dynes.sec.cm-5 in transgenic lungs (p < 0.05). Control lungs had a venous oxygen tension of 271 +/- 23 mm Hg with a ratio of venous oxygen tension to inspired oxygen fraction of 452 +/- 38 at 2 hours of perfusion; transgenic lungs had a venous oxygen tension of 398 +/- 11 mm Hg and a ratio of venous oxygen tension to inspired oxygen fraction of 663 +/- 18 (p < 0.05). Control lungs showed a decrease of 79.8% +/- 3.7% in static pulmonary compliance by 2 hours, versus a 12.0% +/- 8.1% decrease by the transgenic lungs (p < 0.05). The control lungs also developed 561.7 +/- 196.2 ml of airway edema over 2 hours, in contrast to 6.5 +/- 1.7 ml in transgenic lungs (p < 0.05). CONCLUSION: Lungs from swine expressing human decay accelerating factor and human CD59 functioned better than nontransgenic swine lungs when perfused with human plasma. These results suggest that complement activation is involved in producing acute pulmonary xenograft dysfunction and demonstrate that lungs from swine expressing human decay accelerating factor and human CD59 are protected against pulmonary injury when perfused with human plasma.

The novel UGT1 gene complex links bilirubin, xenobiotics, and therapeutic drug metabolism by encoding UDP-glucuronosyltransferase isozymes with a common carboxyl terminus.

The UDP-glucuronosyltransferase system (transferase) plays an important role in the pharmacokinetics of clearance of endogenous metabolites, therapeutic drugs, and xenobiotics. The human bilirubin and phenol transferases are encoded by the same gene complex which we designate UGT1. The gene arrangement indicates there are 6 exon 1s each with a promoter and each of which can predictably undergo differential splicing to the 4 common exons (2 through 5) to generate possibly 6 different mRNAs. The entire unique amino acid terminus of each isoform is encoded by an exon 1, and the common carboxyl terminus is encoded by the 4 common exons. Evidence supports the existence of other exon 1s upstream of the currently described locus. The 13-bp deletion in exon 2 represents the most common defect, to date, in the Crigler-Najjar, Type I individuals. Different point mutations in the 4 common exons and in exon 1 of UGT1A, however, also account for defective bilirubin transferase activity. The gene arrangement, in conjunction with the toxicity data from the Gunn rat, leads to the prediction that detoxification of bilirubin, xenobiotics, and therapeutic drugs is linked to the UGT1 locus. The Crigler-Najjar syndromes are uncommon, but the Gilbert individuals are commonly represented in 6% of the population. It is expected that, similar to the deleterious mutations in the common region of the UGT1 locus in Crigler-Najjar, Type I individuals, there is a range of moderate to intermediate deleterious mutations in this region of the gene of at least some Gilbert's individuals. Linkages, therefore, at this locus could signal that these individuals are at risk for certain drug toxicities and/or idiosyncratic drug reactions.

Lung Transplantation in patients with systemic diseases: an eleven-year experience at Papworth Hospital.

BACKGROUND: The presence of a systemic disease has traditionally been considered a contraindication to lung transplantation. METHODS: We present a retrospective review of 19 patients undergoing lung transplantation for end-stage pulmonary disease associated with a systemic illness since 1984. There were 11 male and 8 female patients, aged from 23 to 59 years (median 43 years) with end-stage pulmonary involvement by sarcoidosis (11 patients), Langerhan's cell histiocytosis (three patients), systemic vasculitis (four patients: three with systemic lupus erythrematosis, one with Churg-Strauss), and common variable immunodeficiency (one patient). Ten patients received a heart-lung transplant, and eight patients received a single lung transplant. One patient underwent single lung transplantation after an earlier heart-lung transplant. RESULTS: The 30-day mortality was 5.3%. Nine patients died overall. Two of these had systemic lupus erythrematosis with anticardiolipin antibodies and died from complications of their underlying vasculitis. The mean 1- and 2-year actuarial survivals for all patients were 71% (standard error +/- 10.8%) and 64% (standard error +/- 11.9%), respectively. All patients surviving longer than 3 months achieved an improvement in functional status to New York Heart Association class I or II, and a significant increase occurred in mean forced expiratory volume in 1 second and forced vital capacity. Disease recurrence without clinical significance occurred in two patients with sarcoidosis. Of the nine patients who died, seven had autopsies and none showed evidence of disease recurrence in the lungs. CONCLUSIONS: Patients with systemic diseases can be considered for lung transplantation and each case should be judged on its individual merits. However, patients with systemic lupus erythrematosis (particularly when associated with anticardiolipin antibodies) should probably not be offered lung transplantation because they are likely to develop further complications of their underlying vasculitis.

Cardiac transplantation: a review.

Cardiac transplantation is currently a highly successful treatment for selected patients with end-stage cardiac failure. The long-term results are limited by the development of coronary artery vasculopathy, infection and malignancy. The activity of transplantation programmes worldwide is severely limited by the availability of donor organs. Further refinements of immunosuppressive agents are likely to result in improved prevention of both acute and chronic rejection. The donor pool is unlikely to be significantly extended as a result of measures to increase donor organ supply. Alternative methods to allograft transplantation need further investigation to increase the number of therapeutic options available for those patients with end-stage heart failure.

Altered coding for a strictly conserved di-glycine in the major bilirubin UDP-glucuronosyltransferase of a Crigler-Najjar type I patient.

The characterization (Ritter, J.K., Chen, F., Sheen, Y. Y., Tran, H.M., Kimura, S., Yeatman, M.T., and Owens, I. S. (1992) J. Biol. Chem. 267, 3257-3261) of the single-copy UGT1 gene complex locus encoding both bilirubin and phenol UDP-glucuronosyltransferases (transferase) has been critical to the determination of genetic defects in Crigler-Najjar patients. The complex (UGT1A-UGT1M) codes for at least two bilirubin, three bilirubin-like, and eight phenol transferase isozymes. In the 5' region, a minimum of 13 different exons 1, each with an upstream promoter, are arrayed in series with 4 common exons in the 3' region of the locus. Each exon 1 encodes the amino terminus of a transferase, and the common exons encode the common carboxyl terminus of each isoform. Although a deleterious mutation in a common exon inactivates the entire locus, a deleterious mutation in an exon 1, as we report here for the UGT1A gene in a Crigler-Najjar Type I patient, affects the amino terminus of that single isoform. Recessively inherited mutant alleles for the predominant bilirubin isozyme, the HUG-Br1 protein, substituted Arg for Gly at codon 276 (G276R) in exon 1 of UGT1A abolishing a conserved di-glycine. The mutant HUG-Br1-G276R protein expressed in COS-1 cells had no detectable bilirubin glucuronidating activity at either pH 7.6 or 6.4. Although each of the bilirubin-type isozymes contains a conserved peptide between residues 270 and 288, all UDP-glucuronosyltransferases contain a di-glycine at approximately position 276-277, making it strictly conserved. Structure-function relationship was studied by site-directed mutations of the HUG-Br1 cDNA; G276A, G276Q, G276E, G276I, and P270G mutants were inactive, and V2751- and P285G-altered transferases expressed normal activity. Conservation of residues between the related baculoviral ecdysone UDP-glucosyltransferase and the UDP-glucuronosyltransferases confirms the critical role of the Gly-276 as well as other residues.

A single axillary crease incision for wide local excision and axillary clearance in breast cancer.

Wide local excision and axillary clearance or sampling has become the standard surgical treatment for many breast cancers. We describe a single incision that allows good access to the primary tumour and the axilla, lies parallel to Kraissl's lines of the skin and gives good cosmetic results.

Nocturnal orthopaedic operating: can we let sleeping orthopaedic surgeons lie?

A 12-month retrospective study of emergency orthopaedic operations in a district general hospital was performed. There were 962 emergency admissions of whom 272 (17.7%) underwent emergency operation. The largest group consisted of those undergoing operation for femoral neck fractures (37.6% of the total). Despite 58.8% of the patients presenting to the accident and emergency (A&E) department between 0800 and 1700 hours, the majority (66.2%) were operated on 'out-of-hours'. Those patients undergoing emergency operation out-of-hours were allocated to one of three categories (emergency, urgent, or scheduled) depending on the nature and severity of their presenting condition. In the authors' opinion, 81.9% of the patients could have been appropriately classified as scheduled cases and that all out-of-hours operating in this group of patients could have been deferred until the following morning. This would have reduced the number of orthopaedic operations performed out-of-hours from 182 to 33. The operating time at night would have been reduced from 126.9 h to 15.8 h. The implications of this study are important in view of the currently proposed changes in the hours worked by surgical trainees, the CEPOD findings, and the Government's proposals outlined in Achieving a Balance.

A phenylalanine codon deletion at the UGT1 gene complex locus of a Crigler-Najjar type I patient generates a pH-sensitive bilirubin UDP-glucuronosyltransferase.

The characterization (Ritter, J. K., Chen, F., Sheen, Y. Y., Tran, H. M., Kimura, S., Yeatman, M. T., and Owens, I. S. (1992) J. Biol. Chem. 267, 3257-3261) of the single-copy UGT1 gene complex encoding both bilirubin and phenol UDP-glucuronosyltransferases (transferase) has been critical to the determination of genetic defects in Crigler-Najjar Type I patients. The complex (UGT1A-UGT1G) codes for at least two bilirubin, three bilirubin-like, and two phenol transferases. Seven different exons 1, each with an upstream promoter and each encoding the amino terminus of an isoform, are arrayed in series with four common exons (encoding seven identical carboxyl termini) in the 3'-region of the locus. Predictably, a critical mutation in a common exon inactivates the entire locus. A deleterious mutation in an exon 1, as we report here for the UGT1A gene in a Crigler-Najjar Type I patient, predictably affects the amino terminus of that single isoform. The code for the predominant bilirubin isozyme, the HUG-Br1 protein, is missing the phenylalanine codon at position 170 in exon 1 of UGT1A, abolishing a conserved diphenylalanine. We demonstrate that, at the pH (7.6) routinely used for bilirubin glucuronidation studies, both the HUG-Br1 protein and human liver microsomes have approximately one-third the activity seen at the major pH optimum of 6.4 and at low ionic strength. The altered isozyme with nearly normal activity at pH 7.6 is inactive at pH 6.4, a result consistent with the definition of a pH-sensitive mutant. The Km value for bilirubin using the wild-type protein is approximately 2.5 microM at both pH 6.4 and 7.6 and that for the mutant is 5.0 microns at pH 7.6. The structure of the wild-type enzyme compared to that of the mutant indicates that hydrophobic properties at the active center are critical for metabolizing the lipophile-like substrate. The low ion/pH requirements for bilirubin glucuronidation may signal the basis for the distribution of these isozymes to an organelle (endoplasmic reticulum) that can establish compatible conditions/compartments for each catalysis.

'Correctable undetected visual acuity deficit' in patients aged 65 and over attending an accident and emergency department.

The rate of occurrence of correctable undetected visual acuity deficit (CUVAD) in a population of patients aged 65 and over was investigated, using a pinhole screening method, to compare the sociodemographic and optical eye care habits of patients with or without a functionally significant CUVAD. Of 136 patients 46 (34%) were found to have a functionally significant CUVAD in one or both eyes which was not significantly associated with optician or general practitioner contact, age, sex, social class, living situation, or number of medications. Half the patients with significant CUVAD had not attended for 2 years mainly because of financial considerations. Three quarters attended of their own volition; only one in seven were prompted by opticians' postal invitations. It was concluded that a significant degree of CUVAD could be detected using a simple procedure which can be carried out by general practitioners as part of their general elderly health screen.

Identification of a genetic alteration in the code for bilirubin UDP-glucuronosyltransferase in the UGT1 gene complex of a Crigler-Najjar type I patient.

Patients with Crigler-Najjar syndrome (CN) type I inherit an autosomal recessive trait for hyperbilirubinemia, which is characterized by the total absence of bilirubin UDP-glucuronosyltransferase (transferase) activity. The recent identification of two bilirubin transferase isoforms with identical carboxyl termini (Ritter, J. K., J. M. Crawford, and I. S. Owens. 1991. J. Biol. Chem. 266:1043-1047) led to the discovery of a unique locus, UGT1, which encodes a family of UDP-glucuronosyltransferase isozymes, including the two bilirubin forms (Ritter, J. K., F. Chen, Y. Y. Sheen, H. M. Tran, S. Kimura, M. T. Yeatman, and I. S. Owens. 1992. J. Biol. Chem. 267:3257-3261). The UGT1 locus features a complex of six overlapping transcriptional units encoding transferases, each of which shares the four most 3' exons (2, 3, 4, and 5) specifying the 3' half of the transferase coding regions (condons 289-533) and the entire 3' untranslated region of each mRNA. This gene model predicts that a single critical mutation in any of these four "common" exons may inactivate the entire family of encoded transferases. In agreement with this prediction, we show here that in the first CN type I individual analyzed (patient F.B.), a 13-bp deletion has occurred in exon 2. Analysis of product generated by the polymerase chain reaction and genomic DNA demonstrated that F.B. is homozygous for the defective allele (UGT1*FB), and that the consanguineous parents are both heterozygotic at this locus. The mutation is predicted to result in the synthesis of severely truncated bilirubin transferase isozymes that are lacking a highly conserved sequence in the carboxyl-terminus and the characteristic membrane (endoplasmic reticulum)-anchoring segment of the protein molecule.

A novel complex locus UGT1 encodes human bilirubin, phenol, and other UDP-glucuronosyltransferase isozymes with identical carboxyl termini.

Two human liver UDP-glucuronosyltransferase (transferase) cDNAs, HUG-Br1 and HUG-Br2, were previously isolated (Ritter, J. K., Crawford, J. M., and Owens, I. S. (1991) J. Biol. Chem. 266, 1043-1047), and each was shown to encode a bilirubin transferase isozyme which catalyzes the formation of all physiological conjugates of bilirubin IX alpha following expression in COS-1 cells. Sequence data showed that the cDNAs contained identical 3' ends (1469 base pairs in length) to each other and to that of the human phenol transferase cDNA, HLUG P1 (Harding, D., Fournel-Gigleux, S., Jackson, M. R., and Burchell, B. (1988) Proc. Natl. Acad. Sci. U.S.A. 85, 8381-8385). Here we report that the two corresponding bilirubin transferases and the phenol transferase are encoded by a novel locus, UGT1, which is also predicted to encode three other bilirubin transferase-like isozymes all having identical carboxyl termini. The transcriptional arrangement utilizes six nested promoter elements, each of which is positioned upstream of a unique exon 1. Each exon 1 encodes the NH2-terminal domain (286 amino acids) and confers the substrate specificity of the isoform. The 3' end of the locus contains 4 common exons which encode the identical carboxyl termini (246 amino acids). It is predicted that six nested primary transcripts are synthesized and that each exon 1 is differentially spliced to the 4 common exons to produce six unique, mature mRNAs. Although the gene organization is present as a single copy, it provides the flexibility of independent regulation of each isoform which is known to occur in the case of bilirubin and phenol transferase activities. With an understanding of the gene structure, lethal, as well as the nonlethal defects, associated with bilirubin transferase activity can now be determined.

Empyema thoracis: a review of a 4 1/2 year experience of cases requiring surgical treatment.

During the period January 1985 to June 1989, 53 cases of empyema thoracis were treated surgically at Papworth hospital regional cardio-thoracic centre. Of these, 47 patients underwent thoracotomy and decortication as their primary surgical treatment. The remaining six patients were treated by rib resection. Prior to surgical referral 20 of these had undergone previous tube drainage for a mean period of 18 days (range 7-42 days). The principle cause of empyema was broncho-pulmonary infection. In 57% of cases no organisms were isolated from pleural debris or fluid. In the remainder, a variety of organisms were encountered. Early surgical drainage and freeing of the underlying lung met with good results and no deaths in the uncomplicated group. The median duration of postoperative chest drainage for the whole group was 7 days (mean 12 days) and median postoperative in-hospital stay was 13 days (mean 20 days). This is in stark contrast to the duration of hospitalization of patients prior to surgical referral (mean 103.6 days). There were five deaths. All occurred in patients with severe debilitating associated illnesses. In these patients initial drainage of the empyema space with a tube or by rib resection may have allowed recovery prior to more major surgery.

Mannitol and reperfusion-induced arrhythmias: possible mechanisms of action in the isolated rat heart.

Mannitol has been shown to exert a dose-dependent, antiarrhythmic effect in the rat heart during reperfusion following a brief period of regional myocardial ischemia. Isolated perfused rat hearts were used to determine whether this protective effect is direct (ie, operative during reperfusion) or indirect (ie, due to an action during ischemia). Hearts (12 in each group) were subjected to 5, 10, 20, 30 or 40 mins of regional ischemia which was induced by ligation of the left anterior descending coronary artery. Upon reperfusion 25%, 100%, 83%, 33% and 17%, respectively, of the hearts fibrillated and 8%, 92%, 58%, 17% and 17% remained in irreversible fibrillation for the duration of the reperfusion period. Addition of mannitol (50 mM, the optimal antiarrhythmic dose) to the perfusion fluid throughout the experiment (early administration) caused a shift of this 'bell-shaped' time-vulnerability curve to the right such that the highest incidence of arrhythmias occurred after 20 mins rather than 10 mins of ischemia. Similar shifts were seen in other indices of electrical instability. Regional ischemia caused a 40 to 45% reduction in coronary flow in all groups of hearts, with no significant difference between the control and the mannitol-treated series. Heart rate fell by a mean of 10 to 15% in all control hearts and by a similar extent in mannitol-treated hearts. In additional studies, mannitol (50 mM) was administered 2 mins before reperfusion and throughout the reperfusion period (late administration studies). In the mannitol-free control group 100% of the hearts exhibited fibrillation and 92% remained in fibrillation for the duration of the reperfusion period.(ABSTRACT TRUNCATED AT 250 WORDS)