Zones of atrial vulnerability. Relationships to basic cycle length

BACKGROUND

Bradycardia is commonly found in individuals at risk for paroxysmal atrial fibrillation (AF). However, a clear relationship between lengthening of basic cyclic length (BCL) and AF has not been demonstrated.

METHODS AND RESULTS

In 20 open-chest dogs, atrial refractoriness, AF vulnerability, and atrial activation times (ACTs) were determined in sinus rhythm and at BCLs of 400, 300, and 200 ms, and the findings at the same coupling intervals and stimulus strengths were compared. As BCL increased, AFV zone lengthened, and its outer limit occurred later in diastole. The outer limit of the AF vulnerability zone for a BCL was its relative refractory period; the inner limit, however, was not its effective refractory period. A border zone, defined by the inner limit of the AF vulnerability zone and the effective refractory period for a BCL, decreased as BCL lengthened, offsetting the increase in the AF vulnerability zone. The border zone was characterized by paradoxical stimulus current strength propagation relations and features suggesting supernormal conduction. ACT also increased with BCL lengthening. When AF induced by rapid atrial burst pacing was contrasted with AF induced by an extrastimulus, it tended to have a more disorganized pattern and lasted longer.

CONCLUSIONS

Lengthening of BCL increases the AF vulnerability zone, extending its outer limit later in diastole and comprising an increasing component of the total duration of the relative refractory period. Very short BCLs create conditions that also favor AF vulnerability.

Regional expression and subcellular localization of the tyrosine-specific phosphatase SH-PTP2 in the adult human nervous system

The protein tyrosine phosphatase SH-PTP2 has been implicated in a variety of cell signaling cascades, including those mediating neuronal survival. We therefore investigated the expression of SH-PTP2 in the adult human nervous system using Western blotting, immunohistochemistry and immunoelectron microscopy. SH-PTP2 immunoreactivity was noted only in neurons, but was not restricted to a specific neuronal type or location. Immunohistochemistry showed perikaryal staining, whereas Western blotting and ultrastructural analysis suggested that SH-PTP2 is present in axons as well. While immunohistochemistry showed a Nissl-like pattern in large motor neurons, immunoelectron microscopy demonstrated a diffuse pattern of cytoplasmic staining, without apparent preferential localization. The presence of the SH2 domain-containing tyrosine-specific phosphatase SH-PTP2 in diverse neurons in the adult nervous system suggests that SH-PTP2 may play a role in a broad spectrum of neuronal responses.

Cicaprost and the type IV phosphodiesterase inhibitor, rolipram, synergize in suppression of tumor necrosis factor-alpha synthesis

Suppression of tumor necrosis factor-alpha (TNF) synthesis is one major target in pharmacological immunomodulation. We now showed the synergistic suppressive effect of the specific type IV phosphodiesterase inhibitor, rolipram, and of the stable prostacyclin analogue, cicaprost, on TNF synthesis. This effect was seen with lipopolysaccharide and Staphylococcus epidermidis as stimuli in human peripheral blood mononuclear cells and in whole blood. Lipopolysaccharide-induced TNF synthesis by mononuclear cells decreased from 3.4 ng/ml to 1.5 ng/ml in the presence of 100 nM rolipram and to 0.7 ng/ml in the presence of 10 nM cicaprost. The combination of both agents suppressed TNF synthesis more than 10-fold, to 0.3 ng/ml. Synergistic suppression was also demonstrated for TNF mRNA.

An alternative role for the src-homology-domain-containing phosphotyrosine phosphatase (SH-PTP2) in regulating epidermal-growth-factor-dependent cell growth

The association of the src homology 2 (SH2) domain-containing tyrosine phosphatase (SH-PTP2) with the activated epidermal growth factor (EGF) and platelet-derived growth factor receptors, as well as the insulin receptor substrate 1 and growth-factor-receptor-bound protein 2 and its intrinsic tyrosine phosphatase activity suggests an important role for this phosphatase in signal transduction. Previous studies have shown a positive role for SH-PTP2 in growth-factor-mediated cell signaling. We show here that SH-PTP2 can also function to negatively regulate EGF-mediated signal transduction in the human glioma cell line SNB19. We demonstrate this by showing that, in SNB19 cells, which lack the ability to proliferate in response to EGF but retain the ability to bind EGF and also activate the EGF receptor as well as allow for the association of SH-PTP2 with the phosphorylated receptor, stable overexpression of an interfering SH-PTP2 mutant can restore the ability of these cells to proliferate in response to EGF.

Radioimmunoassays for cyclic AMP cross-react with phosphodiesterase inhibitors and buffer components

We addressed the issue of cross-reactivity of several commonly used phosphodiesterase inhibitors with radioimmunoassays for cyclic AMP, after we had observed a considerably high cross-reactivity with a noncommercial antibody. Theophylline, pentoxifylline, penthydroxifylline (BL 194), albifylline (HWA 138), torbafylline (HWA 448), A 80 2715, isobutyl methylxanthine, and the nonmethylxanthines amrinone and rolipram were dissolved in supplemented and boiled cell culture medium (RPMI 1640). These samples were assayed for apparent cyclic AMP in two different, commercially available radioimmunoassay kits (based on polyclonal antibodies), applying the nonacetylated protocol. Cross-reactivity was dose-dependent and nonlinear. Samples containing theophylline and amrinone exhibited the strongest cross-reactivity in assay A (NEN/DuPont): 3.0 +/- 0.5(-nM) and 2.4 +/- 1.1 (-nM) apparent cyclic AMP +/- SD at 1-nM spike, respectively. With the more sensitive assay B (Amersham), higher concentrations of apparent cyclic AMP were detected: from 7.9 +/- 0.4 nM (for albifylline) to 3.5 +/- 0.1 nM (for rolipram). Values were calculated from standard curves set up in the respective assay buffer, where culture medium controls resulted in 1.8 +/- 0.3 nM and 3.1 +/- 0.1 nM for assay A and B, respectively. The culture medium interference increased with rising cyclic AMP concentrations. Although comparatively low, this degree of cross-reactivity is relevant for in vitro experiments. Phosphodiesterase inhibitors are commonly administered at millimolar concentrations, and resulting cyclic AMP levels are often in the nanomolar range. Neglecting these findings may lead to falsely high readouts of cyclic AMP concentrations.

The specific type IV phosphodiesterase inhibitor rolipram differentially regulates the proinflammatory mediators TNF-alpha and nitric oxide

We compared the effect of the specific type IV phosphodiesterase inhibitor rolipram on intracellular cAMP concentration, nitric oxide (NO) and tumour necrosis factor-alpha (TNF) formation in the murine macrophage cell line RAW 264.7. We found a dose-dependent increase of nitrite accumulation in LPS-stimulated macrophages from 17.5 to 25.1 microM nitrite with rolipram, whereas TNF synthesis was suppressed to less than 30% of control. This was accompanied by an increase from 7.4 to a maximum of 10.5 nM cAMP in RAW cells incubated with rolipram. These results were confirmed with the stable cAMP analogue (S)-p-adenosine 3',5'-cyclic phosphorothioate [(S)-p-cAMPS]. These findings demonstrate that elevation of cAMP in RAW 264.7 cells by rolipram decreases TNF synthesis and increases NO formation.

Enhanced tumor necrosis factor suppression and cyclic adenosine monophosphate accumulation by combination of phosphodiesterase inhibitors and prostanoids

We investigated cooperative effects of phosphodiesterase (PDE) inhibitors and prostanoids on cyclic adenosine monophosphate (cAMP) accumulation and tumor necrosis factor (TNF)-alpha synthesis in human peripheral blood mononuclear cells (PBMC). PDE inhibitors alone induced only a small increase in cAMP levels in lipopolysaccharide (LPS)-stimulated PBMC. Cicaprost (a stable analogue of prostacyclin) and pentoxifylline added simultaneously to LPS-stimulated PBMC (2.0 x 10(6)/ml) induced a rapid increase of cAMP to a level of 100 nM that peaked within 10 min and remained at a plateau for up to 4 h. Thus combined prostanoids and PDE inhibitors enhanced cAMP accumulation. TNF-alpha suppression in the presence of pentoxifylline and prostanoids exceeded that of either drug alone. The potency of different PDE inhibitors (theophylline, pentoxifylline, penthydroxifylline, albifylline, torbafylline, A 80 2715, amrinone and rolipram) to increase cAMP levels in combination with cicaprost was evaluated after 1 h of incubation. The dose-dependent increase of cAMP for all PDE inhibitors tested in this combined stimulation provided a useful tool for evaluating the potency of PDE inhibitors on cAMP accumulation. The effective concentration of PDE inhibitors, which raised cAMP levels to 300% of control, (EC300), correlated with the IC50 for TNF-alpha suppression (r = 0.930, p = 0.007, with theophylline excluded from the analysis). Interestingly, by contrast, the specific type IV PDE inhibitor rolipram caused only a moderate rise of accumulated cAMP in the same cells. Our data support cAMP as an essential mediator for TNF-alpha suppression by PDE inhibitors. Furthermore, an enhanced inhibiting effect on TNF-alpha production may prove therapeutically advantageous. It may occur in inflammatory and infectious diseases in vivo, since high levels of endogenous prostaglandins are liberated in these conditions.

Amrinone suppresses the synthesis of tumor necrosis factor-alpha in human mononuclear cells

Tumor necrosis factor-alpha (TNF) exerts a wide spectrum of biological activities and contributes to the pathophysiology of septic shock. Elevated circulating levels of TNF have also been reported in patients with severe chronic heart failure. We studied the effect of amrinone, a class III cyclic nucleotide phosphodiesterase inhibitor used in the treatment of acute heart failure, on the synthesis of TNF in vitro. Peripheral blood mononuclear cells from healthy volunteers or cells of a permanent monoblast cell line were stimulated for 20 h with bacterial lipopolysaccharide and different doses of amrinone. TNF production is suppressed in a dose-dependent manner to a minimum of 9% of controls with 1000 microM of amrinone, reaching half-maximal inhibition at 80 microM amrinone. This effect appears to be mediated via cAMP, which accumulated nearly twofold in the presence of amrinone. Suppression of TNF synthesis by therapeutically administered phosphodiesterase inhibitors such as amrinone may contribute to their beneficial effect in the treatment of heart failure.

LAPAROSCOPIC SURGERY

The speed of adoption and popularity of laparoscopic cholecystectomy is without precedence in modern surgical history. This has resulted in therapeutic and diagnostic laparoscopy being attempted in almost every field of surgery to substitute open surgical procedures. The list is endless. It will take time to evaluate the safety and advantages of many of these procedures as reports of controlled studies and long term follow up results are awaited. While certain procedures like gall bladder surgery and appendicectomy will establish their many fold advantages over open surgery, many other procedures like repair of hernias, radical resection of bowel for malignancy etc may fail to do so once the initial enthusiasm wanes away. Any way the concept of minimally invasive surgery is going to be a dominant factor in the surgery of this decade and one should prepare to face this fascinating challenge. Further developments in laparoscopic instruments, optical system and video imaging techniques will add to the progress and safety of laparoscopic surgical procedures in the days ahead.

Cross-linking of the beta-glucan receptor on human monocytes results in interleukin-1 receptor antagonist but not interleukin-1 production

The beta-glucan receptor, found on monocytes and neutrophils, binds glucose polymers derived from fungi. Ligands for the receptor have various immunomodulatory effects, including increased microbicidal killing activity. We have investigated the effect of beta-glucans on the production of interleukin-1 (IL-1) and its naturally occurring inhibitor, the IL-1 receptor antagonist (IL-1Ra). Particulate beta-glucan induced IL-1Ra production from human peripheral blood mononuclear cells (PBMC) but did not stimulate IL-1 beta synthesis or gene expression in these same cells. Monomeric (soluble) beta-glucan did not induce IL-1Ra production. However, when preincubated with PBMC, monomeric beta-glucan significantly (P < .01) reduced particulate beta-glucan induction of IL-1Ra by 40%, suggesting that crosslinking of beta-glucan receptors is required for induction of IL-1Ra. In support of this, monomeric beta-glucan immobilized on plastic surfaces stimulated IL-1Ra production. Vitamin D3, which increases the functional capacity of beta-glucan receptors, increased IL-1Ra production induced by particulate beta-glucan, whereas dexamethasone suppressed IL-1Ra synthesis. Because of their differential effects on cytokine production, beta-glucans may be used to therapeutic advantage in the diseases in which IL-1 is implicated.

Prostacyclin analogs suppress the synthesis of tumor necrosis factor-alpha in LPS-stimulated human peripheral blood mononuclear cells

Recent reports have shown that prostaglandin E2 (PGE2) is able to suppress lipopolysaccharide (LPS)-stimulated production of tumor necrosis factor-alpha (TNF-alpha). In the present study we compared PGE2 with prostacyclin (PGI2) analogs in their potency to influence LPS-stimulated production of interleukin-1 beta (IL-1 beta) and TNF-alpha by human mononuclear cells (MNC). Our results show, that the stable analogs of PGI2, iloprost and cicaprost, markedly suppress TNF-alpha synthesis in LPS-stimulated MNC without effect on IL-1 beta production. Although there was no significant difference in maximal suppression of TNF-alpha, iloprost and cicaprost reached suppression to 50% of control at 20-fold lower concentrations than PGE2. The ID50 for iloprost and cicaprost were 8 nM and 5 nM, respectively, compared to 125 nM for PGE2. Moreover, the prostacyclin analogs as well as PGE2 suppressed LPS-induced production of TNF-alpha in Mono Mac 6 cells, a permanent human cell line with characteristics of mature monocytes. Suppression of TNF-alpha synthesis by cicaprost and PGE2 is probably mediated by an increased intracellular cAMP formation. We were able to show elevated cAMP levels with 1 microM and 10 microM of PGE2 and cicaprost in this system. The suppression of TNF-alpha synthesis may add to the beneficial effects of iloprost reported in animal models of acute respiratory distress syndrome (ARDS) and may offer a therapeutic approach in TNF-alpha mediated pathologic processes.

Nitric oxide-releasing agents enhance cytokine-induced tumor necrosis factor synthesis in human mononuclear cells

In septic shock tumor necrosis factor (TNF) leads to increased nitric oxide (NO) production by induction of NO synthase. An inverse regulatory effect, the influence of NO on cytokine synthesis, has rarely been investigated. The present study assessed the influence of NO-releasing agents on TNF production from interleukin-1 alpha (IL-1 alpha)-stimulated human peripheral blood mononuclear cells (PBMC). 3-Morpholino-sydnonimine (SIN-1) enhanced IL-1 alpha-induced TNF synthesis to a maximum of 272% (mean of n = 5 donors), with 100% set as TNF production by stimulation with IL-1 alpha alone. This finding was confirmed using another NO-donor, i.e., sodium nitroprusside (SNP). The effect was specific for TNF compared to the uninfluenced synthesis of IL-1 beta. Kinetic analysis showed the most pronounced increase in TNF synthesis when SIN-1 was added during the first 60 min after IL-1 alpha addition. These data reveal an enhancing effect of NO on cytokine-induced TNF synthesis. It may contribute to the regulation of TNF synthesis in pathological processes such as microbicidal activity, tumor cell lysis or endothelium-mediated hypotension.

A dual-mode thickness-shear quartz pressure sensor

The development of a dual-mode thickness-shear quartz pressure sensor to meet the demanding performance requirements of oil-field applications is discussed. The objective was to develop a sensor with an operating pressure range of 0-103.42 MPa (0.15 000 lb/in(2)), a temperature range of -10 to +175 degrees C, a pressure calibration accuracy of 6894.8 Pa (1 lb/in(2)), and resolution of 68.95 Pa (0.01 lb/in(2)) with 1-s counter gate time. Doubly rotated cuts with piezoelectric coupling to both the C-modes of vibration were investigated. A theoretical study and general design considerations in the development of such sensors are described. Experimental results were obtained for two sensor designs: one uses a cylindrical design with the SBTC-cut, and the other, called SPA, is a special resonator design vibrating around 5 MHz without any activity dips. Pressure sensitivity of approximately 145 Hz/MPa (1 Hz/lb/in(2)) at 175 degrees C is obtained. Laboratory evaluation of the static and dynamic performances is discussed for the prototypes based on the SPA design.

Genetics of leaf blight resistance in wheat

Studies on the genetics of leaf blight caused byAlternaria triticina using generation mean analysis revealed that additive components played a major role, but that dominance components also contributed significantly in controlling the variability for leaf blight resistance in wheat crosses. Furthermore, the additive x additive type of epistasis was predominant in the first three crosses, whereas in the fourth cross additive x dominance (j) and dominance x dominance (1) components of epistasis were most significant. Because of this it may be desirable to follow a simple recurrent selection scheme for higher tolerance, to isolate resistant plants from the segregating populations derived from crosses of parents of diverse origin following the pedigree method of breeding. CPAN-1887 was very tolerant to leaf blight in the present study and should be utilized in hybridization programs to develop leaf-blight-resistant varieties.

Cyclic nucleotides differentially regulate the synthesis of tumour necrosis factor-alpha and interleukin-1 beta by human mononuclear cells

Recent reports have shown that phosphodiesterase (PDE) inhibitors suppress production of tumour necrosis factor-alpha (TNF-alpha) in mouse macrophages. In the present study we show that theophylline, pentoxifylline and 3-isobutyl-1-methylxanthine markedly suppress the lipopolysaccharide (LPS)-induced synthesis of TNF-alpha (also) in human mononuclear cells. This effect is selective for TNF-alpha since up to several-fold higher concentrations of these PDE inhibitors do not affect production of interleukin-1 beta (IL-1 beta) in the same system. The observed effect of PDE inhibitors appears to be mediated by accumulation of cAMP since (i) addition of PDE inhibitors increases cAMP while cGMP levels are only marginally elevated; (ii) raising cAMP by another mechanism (enhanced formation induced by prostaglandin E2; PGE2) leads to a similar suppression of TNF-alpha production; and (iii) raising cGMP by activating the soluble guanylate cyclase by 3-morpholinosydnonimine (SIN 1) does not inhibit TNF-alpha synthesis. However, SIN 1 suppressed the synthesis of IL-1 beta. Selective suppression of TNF-alpha synthesis by PDE inhibitors may contribute to their beneficial effects in animal models of septic shock or lung injury and may thus have clinical implications.

Noncardiac side-effects of long-term oral amiodarone in the elderly

Amiodarone is a powerful anti-arrhythmic drug. However, its use is somewhat limited by side-effects. No study examining side-effects specifically in elderly patients exists. We have reviewed noncardiac side-effects in 61 elderly patients on long-term oral amiodarone treatment (follow-up 3-66 months). The most troublesome side-effect was hypothyroidism (nine patients, 15%). No cases of frank hyperthyroidism were seen. Elevation of aspartate transaminase (AST) was common (16 patients, 26%), but generally mild and transient. Photosensitivity occurred in six patients (10%). Corneal deposits were common but gave rise to symptoms in only one patient. Two patients reported tremor. Hypothyroidism appeared to be more common and photosensitivity less common than in previously reported series in younger adults. Possible reasons for this are discussed. It is our policy to continue to prescribe amiodarone to elderly patients, regulate monitoring for adverse effects is however mandatory.

Does radiolabelled diphosphonate retention reflect bone metabolism in the elderly?

The 24-h whole-body retention of diphosphonates (WBR), a useful measure of bone metabolism in young subjects, was measured in 27 elderly subjects (19 from home and eight in-patients). WBR rose with increasing age (r = 0.55, P less than 0.01) and was negatively correlated with renal function (r = -0.60, P less than 0.01). In five subjects given vitamin D, WBR did not fall. The measurement of WBR in the elderly has to be assessed in the light of an accurate assessment of renal function and so is rarely clinically useful.

Transurethral resection of the prostate with local anesthesia in 100 patients

We performed transurethral resections of the prostate in 100 patients under local anesthesia supplemented when appropriate by intravenous medication. In the first part of the study (40 patients) local anesthesia was infiltrated into the prostate transurethrally only, while in the second part (60 patients) infiltration was performed transurethrally and perineally. Prostate sizes ranged from 5 to 50 gm., and pain control was excellent in the majority of the patients, especially when perineal infiltration was added to the procedure. Of the patients 98 per cent said they would do it again, no patient required conversion to general anesthesia and there were no significant complications relating to the anesthesia. Local anesthesia with intravenous supplementation can be performed successfully in the majority of the patients with small to moderately sized prostate glands.

Boom town mental health

Population surveys were conducted, examining nonpsychotic psychiatric symptoms, life events, and problems in community living in Primrose, a community experiencing rapid growth in anticipation of the construction of a heavy oil extraction plant, and in Wolf Creek, a stable rural town. Psychiatric symptom levels were lower in the boom town than in Wolf Creek, but the Primrose symptom levels were comparable to those in Saskatchewan. More life events were experienced by Primrose residents who, despite lower symptom levels, had seen their physician more often for minor illnesses. The complaints about living in the town of Primrose matched those of boom town residents from elsewhere. There was no evidence to support the popular view that living in a boom town creates more nonpsychotic psychiatric symptomatology. The higher proportion of the boom town population using physician services for minor illnesses, the higher level of life events reported, and the high frequency of reported problems for families living in the boom town support suggestions that stress is associated with these conditions.

Treatment of urinary incontinence with an artificial sphincter: further experience with the AS791/792 device

Artificial sphincter models AS791 and AS792 were used to treat 36 male and 7 female patients with urinary incontinence. Satisfactory results were obtained in 72 per cent of the patients. Of 100 surgical procedures performed to achieve these results 61 were planned procedures (initial implantation and delayed activation) and 39 were revisions required to improve continence, change mechanically failing devices or remove eroded sphincters. From our study 3 major problems with the artificial sphincter are apparent: 1) stress incontinence, which was present in 55 per cent of the patients with bulbous urethral sphincter compared to 21 per cent with sphincters located at the bladder neck, 2) erosions, which appear to be related to balloon pressure used and location of the artificial sphincter (there seems to be a higher incidence of erosions when the bulbous urethral site is used with balloon pressure greater than 80 cm. water) and 3) mechanical failures of the device, which accounted for 41 per cent of the unplanned operations in our series. These 3 major problems are reviewed, the possible etiology of persistent stress incontinence is discussed and possible ways to avoid these complications are suggested.

A spirohydantoin derivative of dimethoxytetrahydronaphthalene: an experimental anticonvulsant

A 2-spirohydantoin of 6,7-dimethoxytetrahydronaphthalene was synthesized and purified. The compound, showing structural similarities to both phenytoin and dopamine, was found to decrease spontaneous motor activity of mice and to exert a pronounced protective effect against convulsive seizures induced by pentylenetetrazol (Metrazol).

Hyperammonemia in a boy with obstructive ureterocele and proteus infection

We report on a boy with ureteroceles that obstructed the bladder outlet and ureters, who presented with sepsis and hyperammonemia despite normal liver function. The hyperammonemia was most likely caused by excessive absorption of ammonia produced by Proteus mirabilis in the obstructed urinary tract.

Pharmacokinetics of meptazinol after single and multiple oral administration to elderly patients

Oral administration of meptazinol (200 mg Meptid) to male and female geriatric patients (greater than 70 years) resulted in rapid absorption, with peak drug concentrations at 0.5 to 3 h after dosage. Subsequent elimination also proceeded rapidly with a half-life of 3.39 h (+/- 0.26 SEM) after a single dose and 4.97 h (+/- 0.80 SEM) after 13 consecutive 6-h doses. These values were not statistically different. There was no accumulation of meptazinol above that expected from the single-dose kinetics. Plasma protein binding of meptazinol was 33.8% (+/- 0.74 SEM). No sex difference was apparent in any of the pharmacokinetic parameters determined. Comparison of these results with those obtained in an earlier study in young volunteers showed that although the half-life of meptazinol was somewhat longer than the value of 2 h seen in the young, peak plasma concentrations after single and multiple dosing were similar for both age groups, implying that clearance remained largely unaltered. It was concluded that there was no pharmacokinetic basis for recommending a reduction in dosage when treating elderly patients with oral meptazinol.

Diazepam therapy in eclampsia

The single drug therapy of diazepam can be introduced to effectively control convulsions in eclampsia. This treatment will have particular application in rural obstetrics where eclampsia is seen in severe form. The dose schedule of diazepam, as described in this study, shows the therapy to have a stabilizing effect on hypertension and pulse rate. It causes neither respiratory depression nor oliguria. Diazepam is an effective muscle relaxant. Its depressive effect on the newborn is in no way inferior to that of lytic cocktail therapy. The drug is readily available at low cost, even in the remote rural areas, and can be easily administered by any doctor or midwife.