Sumping's Up: A Multidisciplinary Educational Initiative on Gastric Drainage Tubes

BACKGROUND

Nasogastric tube placement is widely taught, and tube maintenance relies on astute nursing care with adherence to both institutional and evidence-based recommendations. However, precise adherence to current recommendations relies on knowledge base regarding the identification of malfunctioning gastric drainage tubes. Troubleshooting skills are crucial in maintaining patient safety and recognizing malfunction.

METHOD

Educational sessions on nasogastric and orogastric decompression tube management, led by a surgical intensive care fellow at a level 1 trauma center, were offered to critical care nurses. A presession and postsession survey evaluated the nurses' subjective and objective knowledge and comfort with naso/orogastric decompression tube management.

RESULTS

Ninety-seven critical care RNs participated. For all questions, the proportion of correct answers significantly increased from presession survey to postsession survey (p < .001). Ninety-seven percent of all participants found the session to be very helpful.

CONCLUSION

Physician-led educational sessions on naso/orogastric decompression tube management were well-received and improved subjective and objective measurements of nurses' knowledge and comfort level with gastric decompression tubes. [J Contin Educ Nurs. 2020;51(10):484-488.].

The danger zone: Injuries and conditions associated with immediately fatal motorcycle crashes in the state of Michigan

BACKGROUND

Immediately fatal motorcycle crashes have not been well characterized. This study catalogues injuries sustained in fatal motorcycle crashes and assesses the impact of crash conditions on injury patterns.

METHODS

Autopsy records from the office of the medical examiner of Kent County, MI and publicly available traffic reports were queried for information pertaining to motorcyclists declared dead on-scene between January 1, 2007, and December 31, 2016.

RESULTS

A total of 71 autopsies of on-scene motorcycle crash fatalities were identified. The two most prevalent injuries were traumatic brain injury (TBI) (85%) and rib fractures (79%). The majority of fatalities occurred in daylight hours (54.3%) and in a 55 mph speed limit zone (63.8%).

CONCLUSIONS

This study provides a catalogue of the injuries sustained in immediately fatal motorcycle crashes and the associated conditions. Advocacy efforts that highlight the risks associated with motorcycle riding and that promote safe riding practices are warranted.

Inhibition of PAF-lnduced Systemic Responses in the Rat, Guinea Pig, Dog and Primate by the Receptor Antagonist SRI 63-441

Systemic administration of synthetic PAF produces a number of dose-dependent circulatory effects in a variety of species. We have evaluated a novel PAF antagonist, SRI 63-441, for its ability to inhibit PAF-induced effects in the rat, guinea pig, dog and primate. In the rat, a 100 ng kg-1 i.v. PAF challenge produced a (mean ± 1 S.D.) 39 ± 5% decrease in carotid blood pressure. Prior injection of SRI 63-441 inhibited this hypotensive response in a dose-dependent manner, with an ED50 of 0.15 mg kg-1 i.v. In the guinea pig, PAF at 100 ng kg-1 elicited a 50 ± 8% increase in hematocrit and a 50 ± 11% elevation in bronchial resistance. The ED50 values for inhibition by SRI 63-441 of these two physiological parameters were 0.012 mg kg-1 and 0.035 mg kg-1 i.a., respectively. Dogs challenged with 1.5 μg kg-1 PAF i.v. exhibited 28.7 ±6.5% increase in hematocrit 10 min after injection. The ED50 value for SRI 63-441 inhibition of hemoconcentration in the dog was 0.18 mg kg-1 i.v. In the primate model of PAF-induced hemoconcentration, controls responded to 3.5 pg kg-1 i.v. PAF with a 30 ± 6% increase in hematocrit. Using the primates in a cross-over design, the ED50 OF SRI 63-441 WAS 0.11 MG KG 1 i.v. At this ED50 value, the ratio of nmol kg-1 PAF used versus nmol kg-1 antagonist is ∼1:25. The effectiveness of SRI 63-441 in these models suggest potential clinical applications in disease states involving hyperpermeability and pulmonary dysfunction.

Significance of R1 resection margin in colon cancer resections in the modern era

AIM

Circumferential resection margin involvement (R1) in rectal cancer is a predictive factor for poor prognosis. The aim of this study was to confirm the prognostic significance of R1 in colon cancer resection and to establish whether the introduction of laparoscopic colorectal surgery influenced this.

METHOD

Prospectively collected data on a patient pathway data manager for sequential patients with colon cancer treated at our specialist unit from January 2005 to December 2010 were analysed. There were 1110 colonic resections (elective 865; emergency 245). A circumferential resection margin involvement of < 1 mm was considered positive.

RESULTS

The total R1 rate was 13.3% (elective 10.4%; emergency 23.6%; P < 0.001). Other statistically significant risk factors for an R1 resection included tumour perforation (P < 0.001), poorly differentiated carcinoma (P < 0.001), T4 tumour (P < 0.001), vascular invasion (P < 0.001), lymph node metastasis (P < 0.001), distant metastasis (P < 0.001) and palliative resection (P < 0.001). Over half of the elective resections were undertaken laparoscopically (486/865; 56.2%). When compared with elective open resection (379/865; 43.8%), the R1 rate was similar (P = 0.491) with similar disease-free survival (DFS) and overall survival (OS). The overall relapse rate was 18.9% in R0 and 55.5% in R1 resections (P < 0.001). Kaplan-Meier survival analysis showed significant improvements in DFS and OS in R0 over R1 patients.

CONCLUSION

The R1 margin in colon cancer resection is an important marker for advanced disease and a prognostic factor for DFS and OS. The introduction of laparoscopic surgery has not influenced the outcome in our unit despite a complex case mix.

An algorithm for the management of bile leak following laparoscopic cholecystectomy

INTRODUCTION

The management of bile leaks following laparoscopic cholecystectomy has evolved with increased experience of ERCP and laparoscopy. The purpose of this study was to determine the impact of a minimally invasive management protocol.

PATIENTS AND METHODS

Twenty-four patients with a bile leak following laparoscopic cholecystectomy were recorded consecutively between 1993 and 2003. Between 1993-1998, 10 patients were managed on a case-by-case basis. Between 1998-2003, 14 patients were managed according to a minimally invasive protocol utilising ERC/biliary stenting and re-laparoscopy if indicated.

RESULTS

Bile leaks presented as bile in a drain left in situ post laparoscopic cholecystectomy (8/10 versus 10/14) or biliary peritonitis (2/10 versus 4/14). Prior to 1998, neither ERC nor laparoscopy were utilised routinely. During this period, 4/10 patients recovered with conservative management and 6/10 (60%) underwent laparotomy. There was one postoperative death and median hospital stay post laparoscopic cholecystectomy was 10 days (range, 5-30 days). In the protocol era, ERC +/- stenting was performed in 11/14 (P = 0.01 versus pre-protocol) with the main indication being a persistent bile leak. Re-laparoscopy was necessary in 5/14 (P = 0.05 versus preprotocol). No laparotomies were performed (P < 0.01 versus pre-protocol) and there were no postoperative deaths. Median hospital stay was 11 days (range, 5-55 days).

CONCLUSIONS

The introduction of a minimally invasive protocol utilising ERC and re-laparoscopy offers an effective modern algorithm for the management of bile leaks after laparoscopic cholecystectomy.

Heavy rectal bleeding secondary to the passage of a rectal leiomyoma per anus

Leiomyoma of the rectum is rare and this is the first case reported where such a tumour has passed per rectum, resulting in heavy bleeding. The management of the acute surgical problem as well as rectal leiomyoma per se is discussed.

Four gland parathyroidectomy without reimplantation in patients with chronic renal failure

BACKGROUND

The optimal surgical management of patients in end stage chronic renal failure with secondary hyperparathyroidism is controversial. One approach advocated is four gland parathyroidectomy without reimplantation. The aim of this study was to review the medium term results of this procedure.

METHODS

Fifty four consecutive patients with end stage chronic renal failure and secondary hyperparathyroidism who had a four gland parathyroidectomy without reimplantation were studied. The procedure was performed by a single surgeon with a median (range) follow up of 29 (0-70) months.

RESULTS

Most patients (76%) developed postoperative hypocalcaemia but this was easily treated and doses of long term drugs necessary to prevent this were low. Pre-operative bone symptoms, hypercalcaemia, hyperphosphataemia, and an increased alkaline phosphatase were improved or resolved in most patients. Thirteen (24%) patients had an undetectable postoperative parathyroid hormone (PTH), (6 of 12 (50%) with a functioning renal transplant and 7 of 42 (17%) who required dialysis, p = 0.02). Median (range) postoperative PTH values in these groups were 0.1 (0.1-31) compared with 1.0 (0.1-24) pmol/l (p = 0.085) respectively. The remaining 41 of 54 (76%) patients had residual PTH secretion and postoperative hyperparathyroidism was identified in eight (15%) patients with only two requiring neck re-exploration.

CONCLUSION

Four gland parathyroidectomy without reimplantation produced good medium term biochemical and clinical results. Most patients had minor residual PTH secretion that may contribute to this and mitigate concerns regarding adynamic bone disease. Endogenous PTH secretion is only completely lost in a few patients but occurs more often in those with a functioning renal transplant. Bone densitometry is required to investigate the long term impact of this procedure.

Prospective study of routine contrast radiology after total gastrectomy (Br J Surg 2004; 91: 1015-1019)

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The impact of cyclosporine dose reduction with or without the addition of rapamycin on functional, molecular, and histological markers of chronic allograft nephropathy

BACKGROUND

Overexposure to cyclosporine is a risk factor for chronic allograft nephropathy (CAN) and dose reduction has been advocated. The purpose of this study was to determine the impact of adding the non-nephrotoxic immunosuppressant, rapamycin, after cyclosporine dose reduction in renal-allograft recipients with CAN.

METHODS

Thirty-one patients with biopsy-confirmed CAN were prospectively randomized to receive a 40% cyclosporine dose reduction with (rapamycin, n=16) or without (control, n=15) the addition of rapamycin 2 mg/day. Renal function and side-effect parameters were assessed. Patients had renal allograft biopsies taken at recruitment and after 6 months. Glomeruli were isolated from these and underwent total mRNA extraction followed by RT-PCR-ELISA to assess transforming growth factor-beta1, collagen III, TIMP-1, TIMP-2, and matrix metalloproteinase-2 expression. Samples were also stained with Sirius red and the percentage interstitial volume fraction quantified by computerized histomorphometric analysis. Data are presented as mean (+/-SD).

RESULTS

Patient characteristics and cyclosporine trough levels after dose reduction (rapamycin 68 [+/-21] vs. control 56 [+/-19] ng/mL, P=NS) were similar in both groups. Rapamycin patients had a significant fall in Cr-51 radioisotope glomerular filtration rate (31.6 [+/-8.9] to 27.3 [+/-8.6] mL/min, P<0.01) that was not significant in controls (29.5 [+/-10.4] to 27.0 [+/-8.0] mL/min, P=NS). Transforming growth factor-beta1 expression fell over time in control but remained constant in rapamycin patients. Conversely collagen III expression increased over the 6-month follow-up in rapamycin patients but not in controls. Both had comparable increases in TIMP-1 and matrix metalloproteinase-2 but only rapamycin patients developed a significant increase in TIMP-2. Sirius red-stained interstitial volume fraction fell over the study in controls (15.3-11.2%, P=0.06) but not in rapamycin patients (16.2-16.3%, P=NS).

CONCLUSION

Rapamycin (2 mg/day) did not improve functional, molecular, or histological outcome in patients with CAN after cyclosporine dose reduction. Further studies involving larger numbers of patients are necessary to confirm these findings.

Total parathyroidectomy in patients with chronic renal failure

Background

Total parathyroidectomy without reimplantation has been advocated as a treatment for hyperparathyroidism in patients with end-stage chronic renal failure. However, there are concerns that a lack of endogenous parathyroid hormone (PTH) can result in hypocalcaemia and adynamic bone disease. The aim of this study was to identify whether this is a significant clinical problem.

Methods

A review of 56 (51 four-gland and five three-gland) histologically confirmed parathyroidectomies performed by the same surgeon between 1994 and 1999 was performed. Mean(s.d.) follow-up was 30(22) months.

Results

Patients could be divided into three groups on the basis of a postoperative serum PTH concentration that was either undetectable (less than 0·1 pmol l−1), less than the upper limit of normal (7·6 pmol l−1 or less) or raised (more than 7·6 pmol l−1). Demographics, mean number of glands excised and histology were similar in each group. Patients with a raised serum level of PTH had a mean(s.d.) value of 54·1(73·3) pmol l−1. Three-gland parathyroidectomy occurred in three patients, raising the possibility of ectopic glands. Two patients had neck re-exploration after four-gland parathyroidectomy; an adenoma and an ectopic gland were identified. One patient had a parathyroid adenocarcinoma.

Conclusion

Total parathyroidectomy may leave residual functional parathyroid tissue that is not visualized at surgery. However, in patients who had no functional parathyroid tissue after operation there was little clinical or biochemical evidence of an increased incidence of hypocalcaemia or bone disease.

A case-control comparison of the results of renal transplantation from heart-beating and non-heart-beating donors

INTRODUCTION

The decline in heart-beating brainstem dead organ donors has necessitated the search for other organ sources. In the field of renal transplantation one alternative source currently available, but little used, is that of kidneys from non-heart-beating donors (NHBD). Reticence to use NHBD kidneys is in part due to concerns over the effect that warm ischemic may have subsequent graft function. Presented here are the results of the NHBD renal transplants at the Leicester transplant unit, and compared with matched heart-beating donor transplants as a case control analysis.

METHODS

In order to analyze any differences in graft performance between the two organ sources, the confounding effect of other variables known to influence the outcome of renal transplantation was minimized by matching NHBD and HBD transplants for the following criteria: donor age and sex, first or re-transplant, anastomosis and cold times, tissue match and PRA sensitisation. Transplant performance was assessed primarily by graft survival, the statistical evaluation of which was by log rank analysis of Kaplan-Meier curves.

RESULTS

72 NHBD and 192 HBD transplants were performed over an eight year period. Of the 192 HBD transplants, 105 matched one or more of the NHBD by the criteria outlined above, and thus constituted the control group for comparison. There was no significant difference in overall graft survival between the two groups. The 5 year survival for the NHBD was 73% compared with 65% for HBD kidneys. When death with a functioning graft is treated as censored data, then these figures become 75% and 81% respectively, again without statistical significance.

CONCLUSION

NHBD kidneys are a valuable additional source of organs for transplantation, with long-term survival, comparable to transplants from HBD.

Bilateral absence of the superior vena cava

Congenital anomalies of the superior vena cava are rare and often coexist with other cardiac abnormalities. In this report, we present a case of absent bilateral superior vena cava with no associated cardiac anomaly. Blood from the arms, head, and upper torso returned to the right atrium through the azygos vein and the inferior vena cava, mimicking chronic superior vena cava obstruction.

Rapamycin in transplantation: a review of the evidence

Rapamycin in transplantation: A review of the evidence. The calcineurin inhibitors have been the mainstays of immunosuppression for solid organ transplantation over the last two decades, but nephrotoxicity limits their therapeutic benefit. Rapamycin is a new drug with both immunosuppressant and antiproliferative properties that has a unique mechanism of action distinct from that of the calcineurin inhibitors. It has a role as a maintenance immunosuppressant either alone or in combination with a calcineurin inhibitor and can also be used to treat refractory acute rejection. Theoretical evidence suggests that it may limit the development and progression of chronic rejection in transplant recipients, but this has yet to be confirmed. This review examines the current in vitro animal and human work underlying the use of rapamycin and, in addition, comments on the pharmacokinetics and side-effect profile of this promising new agent.

Workload generated by a living donor programme for renal transplantation

BACKGROUND

The ethical and medical implications of live kidney donation result in a comprehensive work-up process. The aim of this study was to determine the magnitude of the workload and the yield of renal transplants generated by a live donor programme.

METHODS

Referrals to the Leicester live donor programme over the five-year period 1994-1998 were retrospectively assessed. These were initiated by nephrology referral and subsequently investigated in a stepwise manner. Patients were counselled and baseline tests performed prior to consultant surgeon review and assessment of donor renal function/anatomy.

RESULTS

One hundred and fifty referrals consisting of 150 recipients with 269 potential donors were originally made. This resulted in 32/120 (27%) related and 3/30 (10%) unrelated recipients (P=0.06) and 32/220 (15%) related and 3/49 (6%) unrelated donors proceeding to live donor transplantation, with a mean work-up time (+/-SD) of 9 (+/-7) months. One hundred and fifteen recipients (77%) and 234 (87%) donors failed to proceed at various stages of assessment, for a variety of immunological, medical and social reasons. A large number of expensive immunological investigations were required for potential donors, the majority of which did not proceed to transplantation. However as a result of performing these in the early stages of assessment the number of more invasive tests is kept to a minimum.

CONCLUSIONS

There is a relatively low yield of transplants from live donor referrals, particularly those between unrelated individuals. The vast majority of referrals fail to proceed for legitimate reasons, but as a result, create a significant workload with notable staffing and financial implications.

Release of platelet-activating factor from ischemic-reperfused rabbit heart

This study shows that platelet-activating factor (PAF) is released in significant amounts (10.9 +/- 12.8 ng/min) during the initial reperfusion of the ischemic-isolated rabbit heart. When reperfusion was performed in the presence of autologous rabbit platelets, the electrical and mechanical alterations characteristic of this phase were significantly worsened. These alterations were antagonized by pretreatment of rabbit platelets with a PAF receptor antagonist (SDZ 63-675), suggesting a contribution of PAF released during reperfusion in the cardiac dysfunction. To discriminate whether the effect of PAF was platelet dependent, infusion of PAF (10-40 ng) was performed in nonischemic rabbit hearts perfused with or without autologous platelets. Although the effect of PAF per se was minimal, in the presence of platelets PAF induced a biphasic effect characterized by a transient positive inotropism followed by a dose-dependent decrease in coronary flow, negative inotropism, reduction of action potential duration, and conduction arrhythmias. These effects were abolished by pretreatment of platelets with SDZ 63-675, suggesting a PAF receptor-mediated platelet activation. In addition, a relative contribution of histamine, thromboxanes, and leukotrienes released from activated platelets was inferred by experiments performed with pyrilamine and cimetidine, imidazole, and FPL 55712, respectively.

Effects of combined receptor antagonists of leukotriene D4 (LTD4) and platelet-activating factor (PAF) on rhesus airway responses to LTD4, PAF and antigen

Rhesus monkeys with IgE-mediated asthmatic-type responses to Ascaris suum antigen were pretreated with a combination of 2 receptor antagonists to leukotriene D4 (LTD4) and platelet-activating factor (PAF). This combination of anti-LTD4 and anti-PAF was shown to inhibit airway responses to either LTD4 or PAF in separate experiments in these Ascaris airway-reactive animals. When the same combination of LTD4 and PAF receptor antagonists was used to pretreat the same animal prior to aerosol challenge with Ascaris antigen we could not demonstrate inhibition of the antigen-induced airway response. Thus, combined receptor blockade for LTD4 and PAF did not alter IgE-mediated acute airway responses to antigen in this species. We review the current status of rhesus asthma and LTD4 and PAF receptor antagonist activity in this model.

Biological effects of the orally active platelet activating factor receptor antagonist SDZ 64-412

SDZ 64-412 is a trimethoxyphenylethylphenyl imidazo[2,1-a] isoquinoline molecule that displays marked in vitro inhibition of platelet activating factor (PAF)-induced human platelet aggregation (IC50 = 60 nM) but is without inhibition (at 100 microM) of epinephrine-, ADP- or collagen-induced aggregation. SDZ 64-412 antagonized receptor binding of radiolabeled PAF to human platelet membranes with an IC50 = 60 nM. In the rat, SDZ 64-412 inhibited 100 ng kg-1 PAF-induced hypotension when given i.v. (ED50 = 0.23 mg kg-1) or p.o. (ED50 = 13 mg kg-1). In the guinea pig, SDZ 64-412 inhibited 50 ng kg-1 PAF-induced bronchoconstriction (ED50 = 4.2 mg kg-1 p.o.) and hemoconcentration (ED50 = 5.0 mg kg-1 p.o.). SDZ 64-412 exhibited oral activity in the dog against 1.5 micrograms kg-1 PAF-induced hypotension (ED50 = 5.1 mg kg-1 p.o.) and hemoconcentration (ED50 = 4.9 mg kg-1) and 3.5 micrograms kg-1 PAF-induced hemoconcentration in the cebus primate (ED50 = 12.8 mg kg-1 p.o.). SDZ 64-412 protected in a dose-dependent manner against PAF-induced lethality (LD75 = 75 micrograms kg-1 i.v.) in mice, where 20 mg kg-1 p.o. improved survival from 25 +/- 4% to 77 +/- 8%. SDZ 64-412 afforded complete protection against endotoxin-induced lethality (LD90 = 7.5 mg kg-1 endotoxin i.v.) where the ED50 was 45 mg kg-1 twice predose.(ABSTRACT TRUNCATED AT 250 WORDS)

Evaluation of the effect of a platelet activating factor antagonist on platelet activating factor and Ascaris antigen-induced airway responses in rhesus monkeys

An acute airway response to aerosolized platelet activating factor (PAF) can be induced in certain rhesus monkeys. This PAF airway response is completely inhibited by the PAF antagonist, SRI 63-441, in normal monkeys. After the completion of these studies showing inhibition of the PAF airway response, we evaluated whether the PAF antagonist could inhibit three types of acute IgE-mediated airway responses to Ascaris suum (A) in rhesus monkeys. The A aerosol test protocols used the following: a single A aerosol challenge system; a threshold dose of A challenge system, which consists of increasing A aerosol exposure until an airway response occurs; and two sequential A challenges in which the response to the second A challenge always occurs if there is a response to the first A challenge. When SRI 63-441 was tested as a potential antagonist of the A airway response in any of these three systems, no inhibition was shown.

Inhibition by SRI 63-072 and SRI 63-119 of PAF-acether and immune complex effects in the guinea pig

We have examined two PAF-acether receptor antagonists, SRI 63-072 and SRI 63-119, for their ability to inhibit PAF-acether and immune complex effects in the guinea pig. Both compounds exhibited dose-dependent inhibition of bronchoconstriction and hemoconcentration induced by 0.1 micrograms kg-1 PAF-acether, where the ED50 values of SRI 63-072 were 0.3/0.4 mg kg-1 i.a. and 0.14/0.17 mg kg-1 i.a. for SRI 63-119 for each response, respectively. The d and 1 chiral forms of both antagonists were equipotent towards inhibition of hemoconcentration and bronchoconstriction, suggesting a lack of enantiomeric selectively. SRI 63-072 was further evaluated for its ability to inhibit dermal extravasation in the reverse passive Arthus reaction. Guinea pigs given 125I-BSA i.v as antigen and anti-BSA antibodies by intradermal injection exhibited plasma leakage that was dose- and time-dependent relative to the antibody amount. SRI 63-072 exhibited 46% maximal inhibition of dermal plasma leakage when injected in the skin (100 micrograms site-1 i.d.) with the antibody but less than 10% inhibition when administered intra-arterially (3.0 mg kg-1 i.a.) with the antigen. Therefore, these antagonists effectively inhibit systemic effects of PAF-acether and are partially effective towards inhibition of the dermal extravasation induced by immune complexes. Furthermore, unlike the enantiomeric differences between R and S PAF-acether, the chiral molecules of 63-119 and 63-072 effectively antagonized hemoconcentration and bronchoconstriction induced by PAF-acether.

Release of platelet-activating factor from rabbit heart perfused in vitro by sera with transplantation alloantibodies

During "hyperacute rejection" of rabbit heart perfused with transplantation alloantibodies, platelet activating factor (PAF) was released into the coronary effluent, which appeared to have physicochemical and functional properties similar to the 1-octadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (synthetic PAF) and to PAF obtained from IgE-sensitized rabbit basophils. The release of PAF was associated with an early tachycardia, followed by increasing bradycardia and conduction arrhythmias, as well as decrease of coronary flow and of amplitude of electrogram. The heart stopped beating within 30 min. The release of PAF as well as the "rejection" required the presence of fresh rabbit serum as a source of complement. The PAF receptor antagonist SRI 63-072 in a dose of 0.6 mg, reversed by 70% the reduction of coronary flow within 2-4 min after its addition to the perfusate; ED50 was 0.4 mg. Bradycardia and arrhythmia were reduced; however, the normal electrical activity was only occasionally restored. The cessation of heart action was delayed up to 50 min after the beginning of perfusion with transplantation alloantibodies and complement, but it was not prevented. These results suggest that PAF is released during "rejection" of the heart perfused in vitro with serum containing transplantation alloantibodies in the absence of inflammatory cells and that this mediator is at least in part responsible for the deterioration of cardiac function.

In vitro and in vivo pharmacological profiles of the PAF receptor antagonist SRI 63-675

We have examined a recently developed PAF antagonist SRI 63-675 (dimethyl-tetrahydrofuran-methoxyphosphinyloxy-ethylquinolinium ) for its ability to inhibit several major PAF-induced physiological responses. The compound was a potent inhibitor of PAF-induced platelet aggregation in platelet rich plasma obtained from humans, guinea pigs, and rabbits, with IC50 values of 3.43, 0.25, and 0.97 microM, respectively. SRI 63-675 did not inhibit ADP, collagen nor epinephrine-induced human platelet aggregation. The IC50 for inhibition of PAF receptor binding to human platelets was 0.37 microM. In the rat SRI 63-675 inhibited 0.1 microgram kg-1 i.v. PAF-induced hypotension, with an ED50 of 32 micrograms kg-1 i.v. Using the same PAF challenge in the guinea pig, SRI 63-675 inhibited the hemoconcentration (ED50 = 17 micrograms kg-1 i.v.) and bronchoconstriction (ED50 = 24 micrograms kg-1 i.v.) responses. In the primate, the ED50 was 28 micrograms kg-1 i.v. against 3.5 micrograms kg-1 PAF-induced hemoconcentration. The ratio (1:6) in the primate of PAF used (6.3 nmol kg-1) to antagonist at the ED50 (40.7 nmol kg-1) indicates exceptional potency of SRI 63-675 in this species. The inhibition by SRI 63-675 of the major PAF-induced effects in the rat, guinea pig and primate suggests a common receptor may be involved in the expression of these PAF responses.

Platelet-activating factor antagonists

Over the past decade platelet-activating factor has achieved the status of an important inflammatory mediator. The scientific enthusiasm and number of research investigators, publications, and meetings recently devoted to PAF suggest that this mediator will be the subject of continued study in the foreseeable future. The potential for the presence and involvement of PAF in human disease is easily concluded from the reports described in this review. Both the need for low concentrations for cellular response and the rapid biological clearance mechanisms have made the proof of the involvement of PAF in human disease difficult. The discovery of PAF receptor antagonists and structure-activity relationships of such antagonists (159) will make this determination possible in the near future. The current PAF antagonists may be considered as first generation agents, since the most potent antagonist is still less than 1/100th as potent as PAF is as an agonist. The wide diversity of clinical applications from asthma to septic shock may also require antagonists with selective attributes such as delivery route (oral vs intravenous vs topical) or biological half-life (prolonged vs short). PAF may prove to be the key mediator of several poorly understood disease syndromes such as hyperacute organ transplant rejection, ischemic bowel necrosis (160), and adult respiratory distress syndrome. We must wait for clinical results to draw further conclusions.

Biological properties of the antagonist SRI 63-441 in the PAF and endotoxin models of hypotension in the rat and dog

Intravenous administration of platelet-activating factor (PAF) produces dose-dependent hypotension in several species. We have evaluated a recently developed PAF antagonist, SRI 63-441, for its ability to inhibit the hypotensive effect of PAF in the rat and dog. In the rat, 100 ng/kg PAF produced a 38.6 +/- 5.1% decrease in carotid mean arterial pressure (MAP), followed by a 3.2 +/- 0.7 min recovery period for MAP to return to baseline values. SRI 63-441 reduced the hypotension response in the rat, where the ED50 values for inhibition of MAP were 0.16 mg/kg i.v. and 0.19 mg/kg i.v. for the recovery period. Dogs challenged with 1.5 micrograms/kg PAF i.v. demonstrated a 52 +/- 8% decrease in MAP that persisted for at least 15 min. The ED50 for inhibition of MAP by SRI 63-441 was 0.20 mg/kg i.v. Following injection of tritium-labeled SRI 63-441, 56.8 +/- 2.4% of the dose was recovered in the urine and 43.2 +/- 8.9% in the feces in the rats while in dogs 38.7 +/- 5.6% and 60.9 +/- 23.5% of the dose was excreted in the urine and feces, respectively. In the rat model of endotoxin-induced hypotension, SRI 63-441 given 1 min after a 5 mg/kg endotoxin challenge (which produced a 52 +/- 7% decrease in MAP), reversed the systemic effects, with an ED50 of 0.18 mg/kg i.v. The ED50 for reversal 6 min after endotoxin injection was 0.01 mg/kg. These results of inhibition and reversal by SRI 63-441 strongly implicate PAF as a pivotal mediator of hypotension and shock.

Inhibition of PAF-induced systemic responses in the rat, guinea pig, dog and primate by the receptor antagonist SRI 63-441

Systemic administration of synthetic PAF produces a number of dose-dependent circulatory effects in a variety of species. We have evaluated a novel PAF antagonist, SRI 63-441, for its ability to inhibit PAF-induced effects in the rat, guinea pig, dog and primate. In the rat, a 100 ng kg-1 i.v. PAF challenge produced a (mean +/- 1 S.D.) 39 +/- 5% decrease in carotid blood pressure. Prior injection of SRI 63-441 inhibited this hypotensive response in a dose-dependent manner, with an ED50 of 0.15 mg kg-1 i.v. In the guinea pig, PAF at 100 ng kg-1 elicited a 50 +/- 8% increase in hematocrit and a 50 +/- 11% elevation in bronchial resistance. The ED50 values for inhibition by SRI 63-441 of these two physiological parameters were 0.012 mg kg-1 and 0.035 mg kg-1 i.a., respectively. Dogs challenged with 1.5 micrograms kg-1 PAF i.v. exhibited 28.7 +/- 6.5% increase in hematocrit 10 min after injection. The ED50 value for SRI 63-441 inhibition of hemoconcentration in the dog was 0.18 mg kg-1 i.v. In the primate model of PAF-induced hemoconcentration, controls responded to 3.5 micrograms kg-1 i.v. PAF with a 30 +/- 6% increase in hematocrit. Using the primates in a cross-over design, the ED50 of SRI 63-441 was 0.11 mg kg-1 i.v. At this ED50 value, the ratio of nmol kg-1 PAF used versus nmol kg-1 antagonist is approximately 1:25. The effectiveness of SRI 63-441 in these models suggest potential clinical applications in disease states involving hyperpermeability and pulmonary dysfunction.

Inhibition and reversal of endotoxin-, aggregated IgG- and paf-induced hypotension in the rat by SRI 63-072, a paf receptor antagonist

Platelet activating factor (paf) given intravenously produces systemic hypotension in the rat. Similar effects can be induced using endotoxin or heat-aggregated IgG challenges, which are thought to involve endogenous paf release. Extending this concept, we have examined the ability of the paf antagonist SRI 63-072 to inhibit or reverse systemic hypotension induced with paf, heat-aggregated IgG or endotoxin 0111-B4 in rats. At 100 ng kg-1 paf, there occurred a 38.6 +/- 5.1% decrease in carotid mean arterial pressure (MAP) followed by a 3.2 +/- 0.7 min recovery period (RP) to return to normal pressure values. The ED50 of SRI 63-072 was 0.16 mg kg-1 i.v. (MAP) and 0.25 mg kg-1 (RP) when given 1-5 min before the paf challenge. Endotoxin (15 mg kg-1 i.v.) produced a hypotensive response (54 +/- 8% decrease in MAP) and a corresponding 80% decrease in mesenteric artery blood flow. When given 2-8 min after endotoxin, 1.0 mg kg-1 i.v. SRI 63-072 totally restored blood pressure and artery blood flow. SRI 63-072 similarly reversed heat-aggregated IgG (10 mg kg-1) induced reduction of MAP, with an ED50 of 0.05 mg kg-1 i.v. The observations that SRI 63-072 can inhibit or reverse systemic vascular effects produced from paf and other provocators of endogenous paf release strongly implicates paf as a common final mediator of hypotension and shock. As SRI 63-072 is a competitive receptor antagonist, the hypotensive effects of these provocators appear to be mediated by vascular receptors for paf.

Suppression of rat carotid lesion development by the calcium channel blocker PN 200-110

Balloon catheter damage of the rat carotid artery endothelium results in an extensive and reproducible neointimal lesion composed of smooth muscle cells and connective matrix. The authors have examined two calcium channel blockers, PN 200-110 and PY 108-068, for their ability to inhibit neointimal lesion development in the rat carotid model. When given subcutaneously (1.0 mg/kg day) both compounds produced rapidly acting and long-lasting hypotension, reducing blood pressure 25-29%. At this dose given daily, PN 200-110 reduced lesion cross-sectional area by 44%, compared with only 25% seen by PY 108-068, which suggests that the antiatherosclerotic effect may not be related to lowering of blood pressure. Furthermore, PN 200-110 did not reduce the extent of platelet deposition (compared with controls) occurring at the denuded vessel surface 1 hour or 24 hours after balloon catheterization, which indicates that the inhibition of lesion development may not reflect an antiplatelet mechanism. The observed inhibition by PN 200-110 may relate to mitogen responses of the smooth muscle cell in the vessel wall (migration and proliferation) involved in lesion progression after endothelial damage.

Vascular responses of platelet-activating factor in the Cebus apella primate and inhibitory profiles of antagonists SRI 63-072 and SRI 63-119

We have evaluated several effects of intravenous administration of synthetic platelet-activating factor (PAF) in the non-human primate Cebus apella. Parameters measured were hemoconcentration (monitored by changes in hematocrit), thrombocytopenia (platelet counts), leukopenia (loss of buffy coat), bronchoconstriction (increased airway resistance to fixed airway ventilation), thromboxane A2 production (radioimmunoassay to thromboxane B2) and in vitro aggregation responses of platelets in platelet-rich plasma. Cebus platelets were refractory to PAF-induced aggregation (up to 50 microM) and there was no evidence of thrombocytopenia, elevated thromboxane B2 levels, loss of buffy coat or bronchoconstriction following systemic PAF injection. Animals exhibited reproducible but varying sensitivities to PAF-induced hemoconcentration, where 3.5-30 micrograms/kg PAF (6.6-57 nmol/kg) was required to produce 28-32% increased hematocrit range for the colony. Hemoconcentration induced by PAF in baboons and rhesus occurred at similar doses, suggesting comparable sensitivity. Prior administration of PAF receptor antagonists SRI 63-072 or SRI 63-119 at 3 mg/kg inhibited cebus hemoconcentration responses to 3.5 micrograms/kg PAF by 96% and 100%, respectively. The ED50 values were 0.95 and 0.60 mg/kg, respectively. These results suggest that the cebus exhibits a reproducible hemoconcentration effect to PAF and that these vascular responses can be inhibited by a PAF receptor antagonist.

Evidence for distinct systemic extravasation effects of platelet activating factor, leukotrienes B4, C4, D4 and histamine in the guinea pig

The relative potencies of platelet-activating factor (PAF), leukotrienes B4 (LTB4), C4 (LTC4), D4 (LTD4) and histamine to induce hemoconcentration (HC) were evaluated in the guinea pig. The maximal hematocrit increase (MHI) from PAF, LTD4 and histamine occurred 5-7 min after i.v. injection, whereas the MHI of LTC4 occurred 13-15 min after injection. LTB4 (2.97-5.95 nmol kg-1) did not produce HC. The magnitude of PAF-induced MHI was 2-fold that of LTC4 or LTD4, regardless of the dose of leukotrienes used. The doses (nmol kg-1) needed to produce 30% HC were: 0.14-PAF, 0.71-LTD4 and 3.37-LTC4 and 2,400 histamine. The HC effects of LTD4 were markedly reduced by prior administration of FPL-55712. However, neither LTC4 or LTD4 HC effects were significantly reduced by prior i.v. injection of CV-3988 (3.4 mg kg-1), a competitive receptor antagonist to PAF which is 98% effective in abolishing HC response to 0.14 nmol kg-1 PAF. Diphenhydramine abolished histamine-induced hemoconcentration but was without effect on PAF or LTD4. These results suggest that the responses of PAF, leukotrienes and histamine differ in their potency and may involve separate vascular recognition sites related to acute increases in vascular permeability.

Evidence for a direct effect on vascular permeability of platelet-activating factor induced hemoconcentration in the guinea pig

The ability of synthetic platelet-activating factor (PAF) given intravenously to produce loss (extravasation) of protein rich plasma (resulting in hemoconcentration) has been examined using guinea pigs. Hemoconcentration induced by PAF was not prevented by prior administration of inhibitors of thromboxane synthetase (7-(3-pyridyl)heptanoic acid, UK-37,248-01), PGI2, aspirin, indomethacin or antiserum induced thrombocytopenia. Calcium channel blockers (nifedipine, verapamil, diethylamino octyltrimethoxybenzoate, diltiazem), antihistamines (pyrilamine, cimetidine, diphenhydramine), or the elevator of cAMP IBMX were ineffective in blocking PAF-induced hemoconcentration. In contrast, CV-3988, reported to be a specific antagonist to PAF, was 98% inhibitory of PAF extravasation when given i.a. at 3.5 mg/kg. The ED50 was 0.14 mg/kg I.A. and 15 mg/kg p.o. against 75 ng/kg PAF. These data suggest that PAF-induced hemoconcentration involves receptor mediated alterations of vascular permeability that are inhibited by a specific PAF antagonist.

Effect of platelet activating factor on endothelial permeability to plasma macromolecules

We have examined the effect of intrajugular administration of platelet activating factor (PAF-C16) on vascular permeability in the guinea pig. To examine the loss of selective endothelial permeability, the extravasative effect of PAF was assessed by monitoring hemoconcentration and the plasma loss of 125I-albumin (6.7 nm), 125I-low density lipoproteins (22.0 nm) or 125I-very low density lipoproteins (62.1 nm). Extravasation was dose-dependent and began 1 min after PAF administration, continuing for 5-7 min. During extravasation, there was no evidence for selective plasma retention of any of the labeled plasma tracers, as measured by plasma radioactivity. These results suggest that PAF-induced extravasation is dose-dependent, with increases in vascular permeability sufficient to permit similar plasma efflux rates of albumin, low density lipoproteins and very low density lipoproteins.

Evaluation of dose and route effects of platelet activating factor-induced extravasation in the guinea pig

Platelet-activating factor (PAF) is a naturally occurring lipid that is reported to induce vessel hyperpermeability leading to loss of protein-rich plasma (extravasation). We have quantitated the systemic extravasation effects of synthetic PAF in the guinea pig by monitoring increases in hematocrit. When given intravenously (10-170 ng/kg), PAF produced dose-dependent increases in hematocrit, with maximal hemoconcentration developing in 5-7 min. In leukopenic animals the expected hematocrit increase was reduced by 57%. PAF given intra-arterially produced the dose-dependent changes in hematocrit similar to the intravenous effects of PAF. However, PAF given intraperitoneally (10-2500 micrograms/kg) was 800-1100-fold less effective than the other routes and hemoconcentration continued for 30-45 min until a maximal hematocrit was observed. These results show that PAF may markedly influence extravasation of plasma in a dose and route-dependent manner.

The biological properties of aspartame. V. Effects on a variety of physiological parameters related to inflammation and metabolism

Aspartame (APM), L-aspartyl-L-phenylalanine methyl ester, is a low calorie sweetening agent 180 times sweeter than sucrose. As part of a series of studies designed to determine the potential effects of ingestion of excesses of APM on a wide spectrum of physiological processes, experiments were conducted in which high multiples (mg/kg basis) of the projected maximum daily human intake (20 mg/kg) were administered intragastrically to laboratory rats. Doses up to 16 times the maximum intake had no effect on inflammation parameters including carrageenin-induced paw edema, connective tissue formation and adjuvant arthritis. APM, likewise, showed no antihistamine activity in vitro. Even higher multiples (up to 103 times) of the maximum intake had no effect on various parameters of carbohydrate and lipid metabolism. These results indicate that APM ingested in great excess would not be expected to significantly impair inflammatory processes nor influence carbohydrate and lipid metabolism.