Adult liver transplantation: UCL experience

OBJECTIVE

To evaluate the impact of standardized operative and peri-operative care on the outcome of liver transplantation in a single center series of 395 adult patients.

METHOD AND MATERIAL

Between February 1984 and December 31, 1998, 451 orthotopic liver transplantations were performed in 395 adult patients (> or = 15 years) at the University Hospitals St-Luc in Brussels. Morbidity and mortality of the periods 1984-1990 (Gr I--174 pat.) and 1991-1998 were compared (Gr II--221 pat.). During the second period anti-infectious chemotherapy and perioperative care were standardized and surgical technique changed from classical orthotopic liver transplantation with recipients' vena cava resection (and use of veno-venous bypass) towards liver implantation with preservation of the vena cava (without use of bypass). Immunosuppression was cyclosporine based from 1984 up to 1996 and tacrolimus based during the years 1997 and 1998. Immunosuppression was alleviated during the second period due to change from quadruple to triple and even double therapy and due to the introduction of low steroid dosing and of steroid withdrawal, once stable graft function was obtained. Indications for liver grafting were chronic liver disease (284 pat--71.9%), hepatobiliary tumor (52 pat--13.2%), acute liver failure (40 pat--10.1%) and metabolic disease (19 pat--4.8%). Regrafting was necessary because of graft dysfunction (21 pat), technical failure (12 pat), immunological failure (18 pat) and recurrent viral allograft disease (5 pat); three of these patients were regrafted at another institution. Follow-up was complete for all patients with a minimum of 9 months.

RESULTS

Actuarial 1, 5 and 10 years survival rates for the whole group were 77.9%, 65.7% and 58.3%. These survival rates were respectively 77.3%, 69.7%, 62.5% and 73.2%, 59.6% 51.4% for benign chronic liver disease and acute liver failure; those for malignant liver disease were 80.6%, 44.3% and 36.7%. Early (< 3 months) and late (> 3 months) posttransplant mortalities were. 14.4% (57 pat) and 21.2% (84 pat). Early mortality lowered from 20% in Gr I to 9.4% in Gr II (p < 0.02); this was due to a significant reduction during the second period of bacterial (99/174 pat.--56.9% vs 82/221 pat.--37.1%), fungal (14 pat.--8% vs 7 pat.--3.2%) and viral (87 pat.--50% vs 49 pat.--22.2%) infections (p < 0.05) as well as of perioperative bleeding (92 pat.--52.9% vs 39 pat.--17.6%--p < 0.001). Late mortality remained almost identical throughout the two periods as lethal outcome was mainly caused by recurrent allograft diseases, cardiovascular and tumor problems. Morbidity in these series was important considering that almost, half of the patients had a technical complication, mostly related to bleeding (131 pat--33.2%) and biliary problems (66 pat--16.7%). Retransplantation index was 1.1 (54 pat.--14%). Early retransplantation mortality was 24%; it lowered, although not yet significantly, during the second period (8/25 pat.--32% vs. 5/29 pat.--17.2%).

CONCLUSION

Despite a marked improvement of results, liver transplantation remains a major medical and surgical undertaking. Standardization of operative and perioperative care, less haemorraghic surgery and less aggressive immunosuppression are the keys for further improvement.

Traumatic anterior lens dislocation: a case report

A 45-year-old man presented to the emergency department complaining of decreased vision and pain in the left eye after blunt trauma to the eye. On evaluation, the vision was limited to detecting hand motions, and the intraocular pressure was 37 mmHg. Secondary acute angle-closure glaucoma, with pupillary block due to anterior dislocation of the lens, was diagnosed. The intraocular pressure remained elevated after medical therapy, and the patient underwent intracapsular cataract extraction and anterior vitrectomy. The possibility of elevated intraocular pressure due to lens dislocation or other types of secondary glaucoma should be considered after blunt ocular trauma.

Shock response induced in rat brain and spleen during primary infection with Trichinella spiralis larvae

An infection approach was adopted for examining consequential heat shock (HS) or stress response in brain and spleen tissues from Wistar rats. Stress in this system was due to interactions with the infecting helminth, Trichinella spiralis, or its body-dwelling larval stages, or products thereof. It was argued that in the infection model used, elements effecting stress in the brain would differ from those in the spleen. HS responses were measured by quantitation of 4 levels of HS proteins (HSP25, HSP60, HSP70 and HSP90) with time, in infected and uninfected rat tissues using an assay depending on immunoblotting specifically to detect the separate HSPs and image analysis to measure HSP content. In brain and spleen tissue from uninfected rats, a continuous expression of the above HSPs was observed at levels which hardly varied throughout the experiment. In contrast, HSP25, HSP60 and HSP70 levels in infected rat tissues varied and apparently depended on 'infection cycle'-related events. Thus, an enhanced expression of HSP25 and HSP60 and of these plus HSP70 was observed at certain, yet different, time-points during infection in rat spleen and rat brain, respectively. Interestingly, HSP90 expression in spleen tissue from infected rats versus controls, was significantly reduced throughout the experiment suggesting some important (as yet undefined) role for HSP90 in the infection cycle. These studies seem to have provided evidence for the occurrence of soluble factors causing altered HSP expression at both sides of the blood-brain barrier in rats with a primary T. spiralis infection.

Instructional set and physiological response to CO2 inhalation

OBJECTIVE

Previous studies have suggested that manipulations in patient instructions before inhalation of carbon dioxide (CO2) may blunt its anxiogenic effects. The authors examined the effects of a range of instructional types on panic rates and physiological responses to CO2 inhalation.

METHOD

Thirty-seven patients with panic disorder and 16 normal subjects were exposed to CO2 inhalation under one of three instructional conditions: 1) reassurance (reiterated safety assurances), 2) control dial (patients were instructed on using an operative dial to reduce the concentration of CO2 in the breathing canopy), and 3) basic instructions (standard information). Perceived breathlessness was measured with the Borg Scale of Respiratory Exertion.

RESULTS

Manipulation of instructional sets did not affect panic rates among patients. The reassurance condition, however, produced a significant reduction in perceived breathlessness.

CONCLUSIONS

CO2-induced panic is a robust biological effect that occurs independent of cognitive set changes, such as illusion of control or reassurance of safety. Conclusions drawn from this study are bolstered by the fact that it is methodologically rigorous: it had a large number of subjects, used random assignment to one of three instructions, included a full array of both subjective and biological measures, and included independent ratings.

Synthesis and biological evaluation of C-terminal hydroxamide analogues of bombesin

Bombesin pseudo-peptide analogues containing a hydroxamide function on the C-terminal part of the molecule, e.g. H-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOBzl 1 and H-D-Phe-Gln-Trp-Ala-Val-Gly-His-Leu-NHOH 2 were synthesized. These compounds were tested for their ability to recognize the bombesin receptor on rat pancreatic acini and on 3T3 cells, to stimulate (i) amylase secretion from rat pancreatic acini and (ii) accumulation of tritiated thymidine in 3T3 cells. Compounds 1 and 2 were able to recognize bombesin receptors on both models with high affinity (Ki = 7 +/- 2 and 5.8 +/- 0.9 nM on rat pancreatic acini, and Ki = 4.1 +/- 1.2 and 7.7 +/- 1.9 nM on 3T3 cells, respectively). Interestingly, compound 1 behaved as a potent agonist in stimulating amylase secretion from rat pancreatic acini and is able to stimulate thymidine accumulation in 3T3 cells, while compound 2 was able to potently antagonize bombesin-stimulated amylase secretion (Ki = 22 +/- 5 nM) in rat pancreatic acini and had no proper effect on 3T3 cells; however, it was able to inhibit bombesin-stimulated thymidine accumulation in 3T3 cells with high potency (Ki = 1.6 +/- 0.6 nM).

The interleukin-1 type 2 receptor gene displays immediate early gene responsiveness in glucocorticoid-stimulated human epidermal keratinocytes

Human epidermal keratinocytes (HEKs) in primary culture (P2-P4) were used to study glucocorticoid (GC)-mediated transcription of the genes encoding the constitutively expressed interleukin-1 type 1 receptor (IL-1R1) and the inducible interleukin-1 type 2 receptor (IL-1R2). Utilizing Northern dot blot analysis and a quantitative reverse transcription-polymerase chain reaction protocol for IL-1R1 and IL-1R2, dexamethasone and, in particular, the budesonide epimer R were shown to effectively and rapidly induce transcription from the IL-IR2 gene when compared with IL-1R1 or beta-actin RNA message levels in the same sample. Southern blot analysis of newly generated IL-1R2 reverse transcription-polymerase chain reaction products using end-labeled IL-1R2 intron probes suggested that GC enhancement of IL-1R2 expression was regulated primarily at the level of de novo transcription. GC-induced IL-1R2 gene transcription displayed features characteristic of a classical immediate early gene response, including a signal transduction function, a relatively low basal abundance, a rapid, transient induction, cycloheximide superinduction, actinomycin D suppression, and a rapid decay of IL-1R2 RNA message. Parallel time course kinetic analysis of IL-1R2 RNA message levels with Western immunoblotting revealed tight coupling of de novo IL-IR2 gene transcription with translation of the IL-1R2 RNA message; a newly synthesized ( approximately 46-kDa) IL-1R2 protein was detected in the HEK growth medium as early as 1 h after budesonide epimer R treatment. These data indicate that different GC compounds can variably up-regulate the IL-1R2 response in HEKs through transcription-mediated mechanisms and, for the first time, suggest that a gene encoding a soluble cytokine receptor can respond like an immediate early gene.

Syntheses and biological activities of potent bombesin receptor antagonists

Bombesin receptor antagonists are potential therapeutic agents due to their ability to act as inhibitors of cellular proliferation. On the basis of our hypothesis concerning the mechanism of action of gastrin associating an activating enzyme to the receptor and on the results reported in the literature, we have synthesized bombesin analogs which have been modified in the C-terminal part. Potent bombesin receptor antagonists were obtained by replacement of Leu-13 with a statyl residue or with a residue bearing an hydroxyl group in place of the carbonyl function of Leu-13. Several inhibitors were able to recognize the bombesin receptor on rat pancreatic acini and antagonized bombesin stimulated amylase secretion in the nanomolar range. These compounds were also able to recognize the bombesin receptor and to inhibit [3H] thymidine incorporation in 3T3 cells with the same potency.

Complications of emergency intubation with and without paralysis

Expert and definitive airway management is fundamental to the practice of emergency medicine. In critically ill patients, rapid sedation and paralysis, also known as rapid-sequence intubation, is used to facilitate endotracheal intubation in order to minimize aspiration, airway trauma, and other complications of airway management. An alternative method of emergent endotracheal intubation, intubation minus paralysis, is performed without the use of neuromuscular blocking agents. The present study compared complications of these two techniques in the emergency setting. Sixty-seven intubations minus paralysis were prospectively compared with 166 rapid-sequence intubations. Complications were greater in number and severity in the nonparalyzed group and included aspiration (15%), airway trauma (28%), and death (3%). None of these difficulties were observed in the rapid-sequence group (P < .0001). These results show that rapid-sequence intubation when compared with intubation minus paralysis significantly reduces complications of emergency airway management and should be made available to emergency physicians trained in its use.

Heterotopic pregnancy: discovery of ectopic pregnancy after elective abortion

We report a case of combined intrauterine and tubal pregnancy in a 23-year-old woman. The patient came to the emergency department complaining of lower abdominal pain after having had an elective abortion 2 weeks earlier. Her physician had done pelvic ultrasonography, noting an intrauterine pregnancy before the abortion. Our working diagnosis in the emergency department was retained products of conception versus postabortion endometritis. Pelvic ultrasonography in the emergency department revealed an ectopic pregnancy without evidence of retained products of conception, and the patient had a right salpingotomy with removal of the ectopic fetus without complications.

Pulmonary hypertension in patients with myelofibrosis secondary to myeloproliferative diseases

We examined the clinical characteristics of six patients with myelofibrosis secondary to myeloproliferative diseases whose clinical courses were complicated by pulmonary hypertension to determine possible causal links between the two disorders. Six patients (four male, two female), with diagnoses of myeloproliferative disease, myelofibrosis (one with polycythemia vera, three with agnogenic myeloid metaplasia, one with unclassified myeloproliferative syndrome, one with essential thrombocytosis), and pulmonary hypertension are presented. Measurement of the pulmonary artery pressure was performed by Doppler echocardiography in all patients and by right sided heart catheterization in four patients. The range of resting pulmonary artery systolic pressure was 35 to 47 mmHg above the mean right atrium by echocardiography. One patient had autopsy evidence of pulmonary myeloid metaplasia and interstitial fibrosis; another had acute leukemic infiltration of the lung parenchyma. All patients had thrombocytosis; symptomatology in one patient with marked thrombocytosis improved with plateletpheresis. Two patients suffered systemic thrombosis. All patients had severe hepatomegaly. Two patients had evidence of left ventricular dysfunction. The interval between the development of dyspnea and death was less than seven months in five of the patients. A causal link between pulmonary hypertension and myelofibrosis secondary to myeloproliferative diseases is suggested for each patient. Hematopoietic infiltration of the pulmonary parenchyma, portal hypertension, thrombocytosis, hypercoagulability, and left ventricular failure may account in part for the development of pulmonary hypertension in these patients. Patients with myelofibrosis and dyspnea should have Doppler echocardiography to evaluate pulmonary artery pressures.

Pulmonary hypertension in patients with myelofibrosis secondary to myeloproliferative diseases

We examined the clinical characteristics of six patients with myelofibrosis secondary to myeloproliferative diseases whose clinical courses were complicated by pulmonary hypertension to determine possible causal links between the two disorders. Six patients (four male, two female), with diagnoses of myeloproliferative disease, myelofibrosis (one with polycythemia vera, three with agnogenic myeloid metaplasia, one with unclassified myeloproliferative syndrome, one with essential thrombocytosis), and pulmonary hypertension are presented. Measurement of the pulmonary artery pressure was performed by Doppler echocardiography in all patients and by right sided heart catheterization in four patients. The range of resting pulmonary artery systolic pressure was 35 to 47 mmHg above the mean right atrium by echocardiography. One patient had autopsy evidence of pulmonary myeloid metaplasia and interstitial fibrosis; another had acute leukemic infiltration of the lung parenchyma. All patients had thrombocytosis; symptomatology in one patient with marked thrombocytosis improved with plateletpheresis. Two patients suffered systemic thrombosis. All patients had severe hepatomegaly. Two patients had evidence of left ventricular dysfunction. The interval between the development of dyspnea and death was less than seven months in five of the patients. A causal link between pulmonary hypertension and myelofibrosis secondary to myeloproliferative diseases is suggested for each patient. Hematopoietic infiltration of the pulmonary parenchyma, portal hypertension, thrombocytosis, hypercoagulability, and left ventricular failure may account in part for the development of pulmonary hypertension in these patients. Patients with myelofibrosis and dyspnea should have Doppler echocardiography to evaluate pulmonary artery pressures.

Influence of parasitization by Trichinella spiralis on the levels of heat shock proteins in rat liver and muscle

To examine levels of heat shock proteins (HSPs) in host responses to helminth infection, rats were infected with Trichinella spiralis. The kinetics of HSP25, HSP60, HSP70 and HSP90 production in the liver and muscle of infected rats was compared with that of non-infected controls. HSPs were detected using electrophoretic analysis of fixed amounts of proteins (0.02 mg) and then blotting and incubation of membranes with polyclonal anti-HSP25 antibody, or monoclonal antibody against HSP60, or HSP70 or HSP90. Quantitation of blotted separated polypeptides reactive with the specific anti-HSP antibodies was achieved using an image analyser. Enhancement of HSP25 production was observed in the liver of infected rats, whereas muscle from the same rats exhibited enhanced production of HSP25 and HSP60 one day after infection only. These data indicate that HSPs levels can be used successfully to measure stress injury brought about by helminth infection in organs and tissues of the host.

Glicentin and oxyntomodulin modulate both the phosphoinositide and cyclic adenosine monophosphate signaling pathways in gastric myocytes

We have investigated the transduction pathways mediating the contractile effect of two glucagon-containing peptides, glicentin (GLIC) and oxyntomodulin (OXM), on smooth muscle cells isolated from rabbit antrum. Low concentrations of GLIC induced a biphasic and rapid (first phase at 5-8 sec) Ins(1,4,5)P3 production. By comparison, higher concentrations of OXM or OXM(19-37) were required to obtain biphasic time-courses of Ins(1,4,5)P3 production. In a Ca2+ free medium, the first phase of Ins(1,4,5)P3 production induced by GLIC or OXM was maintained, while the second phase disappeared. In saponin-permeabilized cells, all three peptides induced cell contraction with similar efficacies and potencies. Exogenous Ins(1,4,5)P3 mimicked the contractile effect of the peptides and heparin, which inhibits the Ins(1,4,5)P3 binding to its receptor, prevented contraction stimulated by each effector. We conclude that a Ca2+ mobilization from the intracellular stores is essential in the contractile effects of GLIC and OXM. Using the fluo-3 probe, a [Ca2+]i increase was observed in the presence of GLIC, OXM, or OXM(19-37). The three peptides reduced by 30-40% the cAMP content of cells stimulated by forskolin. This effect was pertussis toxin sensitive as demonstrated with OXM(19-37). Our data constitute important clues for the existence in smooth muscle cells of receptor(s) specific for the GLIC/OXM hormones, coupled via G protein(s) to both Ca2+ and cAMP pathways.

Identification of the receptor subtype involved in the analgesic effect of neurotensin

The neuropeptide neurotensin (NT) elicits hypothermic and naloxone-insensitive analgesic responses after brain injection. Recent pharmacological evidence obtained with NT agonists and antagonists suggests that these effects are mediated by a receptor distinct from the initially cloned high-affinity NT receptor (NTR1). The recent cloning of a second NT receptor (NTR2) prompted us to evaluate its role in NT-induced analgesia. Intracerebroventricular injections in mice of two different antisense oligodeoxynucleotides from the NTR2 markedly decreased NTR2 mRNA and protein and reduced NT-induced analgesia. This effect was specific, because NTR1 levels were unaffected, and sense or scramble oligodeoxynucleotides had no effect. Structure-activity studies revealed a close correlation between the analgesic potency of NT analogs and their affinity for the NTR2 and disclosed potent and selective agonists of this receptor. These data confirm that NTR1 is involved in the NT-elicited turning behavior and demonstrate that the NTR2 mediates NT-induced analgesia.

JMV1155: a novel inhibitor of glycine-extended progastrin-mediated growth of a human colon cancer in vivo

BACKGROUND

Glycine-extended progastrin (G-17-Gly), the immediate biosynthetic precursor to gastrin (G-17), stimulates growth of some gastrointestinal cancers in vitro. The purpose of this study was twofold: to evaluate the effects of G-17-Gly on a human colon cancer (DLD-1) in vivo and to determine whether the novel gastrin-receptor antagonist, JMV1155, inhibits G-17-Gly-mediated growth.

METHODS

DLD-1 cells (2 x 10(6)) were injected subcutaneously (s.c.) at a single site in athymic nude mice. Mice were randomized to four groups (n = 6/group) to receive injections, s.c., tid of either saline (control), G-17-Gly, JMV1155, or G-17-Gly + JMV1155 for 28 days. Tumors were measured biweekly until sacrifice at which time tumors were weighed and analyzed for DNA and protein content.

RESULTS

JMV1155 significantly inhibited G-17-Gly-stimulated growth of DLD-1 tumors by 14 days of treatment, producing a 56% decrease in tumor size by 28 days. JMV1155 also significantly decreased G-17-Gly-mediated increases in tumor weight (by 64%), DNA content (by 61%), and protein content (by 65%).

CONCLUSIONS

We have demonstrated, for the first time, that the novel gastrin-receptor antagonist, JMV1155, blocks G-17-Gly-induced growth of a transplanted human colon cancer in vivo. Hormonally based therapy with JMV1155 potentially could be employed for some patients with colon carcinoma.

Chemical reactivity in matrix-assisted laser desorption/ionization mass spectrometry

During the control of a multistep organic synthesis on a soluble polymer (PEG) by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry, a chemical reactivity was encountered when the matrix was acidic, for the samples where the amino moiety of the anchored compounds was protected as a Schiff base. Such imine hydrolysis was proven to be solely mediated by the acidic matrix during analyses since the expected protected structures were detected when the experiments were duplicated with a non-acidic matrix. Even if MALDI mass spectrometry was found to be more convenient than electrospray ionization mass spectrometry for the monitoring of liquid phase organic syntheses, the chemical reactivity imparted by the use of a matrix must be taken into account to avoid erroneous spectra interpretations. Copyright 1999 John Wiley & Sons, Ltd.

Long-term graft survival is improved in cadaveric renal retransplantation by flow cytometric crossmatching

BACKGROUND

Cadaveric renal retransplantation is associated with a higher risk of early graft failure than primary grafts. A large proportion of those graft losses is likely attributable to donor-directed HLA class I antibodies, detectable by flow cytometry cross-matching but not by conventional crossmatching techniques.

METHODS

Long-term graft survival in a group of 106 recipients of consecutive cadaveric renal regrafts between 1990 and 1997, in whom a negative flow T-cell IgG crossmatch was required for transplantation, was compared with two other groups of cadaveric transplant recipients. The first group consisted of 174 cadaveric regrafts transplanted between 1985 and 1995 using only a negative anti-human globulin (AHG) T-cell IgG crossmatch. The second group was primary cadaveric transplants done concurrently with the flow group (1990 to 1997) using only the AHG T-cell IgG crossmatch.

RESULTS

The long-term (7 year) graft survival rate of flow crossmatch-selected regraft recipients (68%; n= 106) was significantly improved over that of regraft recipients who were selected for transplantation by only the AHG crossmatch technique (45%; n=174; log-rank=0.001; censored for patients dying with a functioning graft). Graft outcome for the flow cross-matched regraft recipients was not significantly different from that of primary cadaveric patients (72%; n=889; log-rank=0.2; censored for patients dying with a functioning graft). Finally, a positive B-cell IgG flow cytometric crossmatch had no influence on long-term regraft outcome.

CONCLUSIONS

The use of the flow T-cell IgG cross-match as the exclusion criterion for cadaveric renal retransplantation yields an improved long-term graft outcome over that obtained when only the AHG cross-match is used and has improved survival of regraft recipients to the level of our primary cadaveric renal transplant population.

Transplantation rate of the blood group B waiting list is increased by using A2 and A2B kidneys

BACKGROUND

We have increased the transplantation rate for blood group B cadaveric waiting list candidates by transplanting them with A2 and A2B kidneys.

METHODS

Since 1991, five of the seven renal transplant programs in our organ procurement organization service area have preferentially transplanted blood group A2 and A2B cadaveric kidneys to B blood group waiting list candidates with histories of low anti-A isoagglutinin titers.

RESULTS

Between 1991 and 1997, these five centers performed transplantations on 71 patients from the B cadaveric waiting list. Of those 71 patients, 29% (21 of 71) underwent transplantation with either A2 (n=18) or A2B (n=3) cadaveric kidneys. In 1997 alone, 48% (11 of 23) of the B patient transplant recipients received A2 or A2B kidneys.

CONCLUSIONS

Transplantation of A2 and A2B kidneys into B waiting list patients has successfully increased access of B patients to kidneys. Such an allocation algorithm implemented nationally may similarly increase the transplantation rate of B waiting list candidates.

Symptomatic venous hypertension because of occult iliofemoral deep vein thrombosis: a report of two cases

Two 25-year-old males with symptomatic venous hypertension (venous claudication, n = 1; swollen leg, n = 1) were evaluated for iliofemoral venous occlusive disease. One patient had a common femoral vein/external iliac vein occlusion with no history of deep vein thrombosis or trauma. The second patient had an acute deep vein thrombosis superimposed on a chronic external iliac vein stenosis. No source of extrinsic venous compression was identified in either patient. Venous reconstruction with vein bypass (patient no. 1) and vein patch angioplasty (patient no. 2) led to resolution of their hypertensive symptoms. Intraoperative examination of the involved vein segments revealed chronic changes consistent with a prior occult deep vein thrombosis in both patients. Occult iliofemoral deep vein thrombosis in young healthy males is rarely seen. The acute deep vein thrombosis may manifest minimal or no symptoms but it can lead to chronic venous occlusive disease and serious post-phlebitic morbidity. In this context, these two cases are discussed with a review of the pertinent literature.

Proteolysis of cell adhesion molecules by serine proteases: a role in long term potentiation?

Tissue plasminogen activator (tPA), a serine protease endogenous to hippocampal neurons, is shown to recognize a highly conserved sequence in the extracellular domain of cell adhesion molecules (CAMs). When added to brain homogenates, tPA generated a CAM fragment similar in size to that produced in hippocampal slices by brief periods of NMDA receptor stimulation. The serine protease inhibitor 4-(2-Aminoethyl)-benzenesulfonyl fluoride blocked the effects of tPA with an approximately 50% suppression at 250 microM. The inhibitor at this concentration had no evident effect on synaptic responses but caused long term potentiation to decay back to baseline over a 1 h period. These results suggest that extracellular breakdown of cell adhesion molecules initiated by NMDA receptors and mediated by serine proteases contributes to the formation of stable potentiation.