Fludrocortisone is effective in the management of tacrolimus-induced hyperkalemia in liver transplant recipients.

Tacrolimus is the cornerstone of immunosuppression following liver transplantation (OLT). However, this agent may cause hyperkalemia by multiple mechanisms affecting potassium in the distal tubule. The purpose of this study was to evaluate the impact of fludrocortisone for the management of tacrolimus-induced hyperkalemia. Hospitalized adult OLT recipients who received fludrocortisone for tacrolimus-induced hyperkalemia were retrospectively identified. Change in serum potassium within 14 days of initiation was the primary endpoint. Secondary endpoints included serum sodium, blood urea nitrogen, serum creatinine, and tacrolimus concentrations up to 14 days after fludrocortisone initiation. Nine patients were evaluated. Outcomes were analyzed with separate repeated-measures analyses of variance. Mean daily fludrocortisone dose was 0.14 ± 0.08 mg. Serum potassium decreased significantly within the 14-day study period (P < .001). Mean potassium decreased from 5.7 ± 1 to 4.3 ± 0.5 mmol/L within 48 hours of fludrocortisone initiation (P = .002). Sodium concentrations were statistically higher (P = .024), while serum creatinine was not significantly different by day 14. Mean tacrolimus concentration at fludrocortisone initiation was 10.2 ± 5.2 and remained stable to 14 days (10.4 ± 4.7 ng/mL; P = .9). This is the first study in OLT recipients demonstrating fludrocortisone significantly decreases serum potassium in patients with stable tacrolimus concentrations. Larger prospective studies are needed to confirm these results.

Requirement for both micron- and submicron scale structure for synergistic responses of osteoblasts to substrate surface energy and topography.

OBJECTIVE: Surface roughness and surface free energy are two important factors that regulate cell responses to biomaterials. Previous studies established that titanium (Ti) substrates with micron-scale and submicron scale topographies promote osteoblast differentiation and osteogenic local factor production and that there is a synergistic response to micro-rough Ti surfaces that have retained their high surface energy via processing that limits hydrocarbon contamination. This study tested the hypothesis that the synergistic response of osteoblasts to these modified surfaces depends on both surface micro-structure and surface energy. METHODS: Ti disks were manufactured to present three different surface structures: smooth pretreatment (PT) surfaces with R(a) of 0.2 microm; acid-etched surfaces (A) with a submicron roughness R(a) of 0.83 microm; and sandblasted/acid-etched surfaces (SLA) with R(a) of 3-4 microm. Modified acid-etched (modA) and modified sandblasted/acid-etched (modSLA) Ti substrates, which have low contamination and present a hydroxylated/hydrated surface layer to retain high surface energy, were compared with regular low surface energy A and SLA surfaces. Human osteoblast-like MG63 cells were cultured on these substrates and their responses, including cell shape, growth, differentiation (alkaline phosphatase, osteocalcin), and local factor production (TGF-beta1, PGE(2), osteoprotegerin (OPG)) were analyzed (N=6 per variable). Data were normalized to cell number. RESULTS: There were no significant differences between smooth PT and A surfaces except for a small increase in OPG. Compared to A surfaces, MG63 cells produced 30% more osteocalcin on modA, and 70% more on SLA. However, growth on modSLA increased osteocalcin by more than 250%, which exceeded the sum of independent effects of surface energy and topography. Similar effects were noted when levels of latent TGF-beta1, PGE(2) and OPG were measured in the conditioned media. CONCLUSIONS: The results demonstrate a synergistic effect between high surface energy and topography of Ti substrates and show that both micron-scale and submicron scale structural features are necessary.

Long-term subclinical carrier state precedes scrapie replication and adaptation in a resistant species: analogies to bovine spongiform encephalopathy and variant Creutzfeldt-Jakob disease in humans.

Cattle infected with bovine spongiform encephalopathy (BSE) appear to be a reservoir for transmission of variant Creutzfeldt-Jakob disease (vCJD) to humans. Although just over 100 people have developed clinical vCJD, millions have probably been exposed to the infectivity by consumption of BSE-infected beef. It is currently not known whether some of these individuals will develop disease themselves or act as asymptomatic carriers of infectivity which might infect others in the future. We have studied agent persistence and adaptation after cross-species infection using a model of mice inoculated with hamster scrapie strain 263K. Although mice inoculated with hamster scrapie do not develop clinical disease after inoculation with 10 million hamster infectious doses, hamster scrapie infectivity persists in brain and spleen for the life span of the mice. In the present study, we were surprised to find a 1-year period postinfection with hamster scrapie where there was no evidence for replication of infectivity in mouse brain. In contrast, this period of inactive persistence was followed by a period of active replication of infectivity as well as adaptation of new strains of agent capable of causing disease in mice. In most mice, neither the early persistent phase nor the later replicative phase could be detected by immunoblot assay for protease-resistant prion protein (PrP). If similar asymptomatic carriers of infection arise after exposure of humans or animals to BSE, this could markedly increase the danger of additional spread of BSE or vCJD infection by contaminated blood, surgical instruments, or meat. If such subclinical carriers were negative for protease-resistant PrP, similar to our mice, then the recently proposed screening of brain, tonsils, or other tissues of animals and humans by present methods such as immunoblotting or immunohistochemistry might be too insensitive to identify these individuals.

Porphyrin and phthalocyanine antiscrapie compounds.

The transmissible spongiform encephalopathies (TSEs) are fatal, neurodegenerative diseases for which no effective treatments are available. The likelihood that a bovine form of TSE has crossed species barriers and infected humans underscores the urgent need to identify anti-TSE drugs. Certain cyclic tetrapyrroles (porphyrins and phthalocyanines) have recently been shown to inhibit the in vitro formation of PrP-res, a protease-resistant protein critical for TSE pathogenesis. We now report that treatment of TSE-infected animals with three such compounds increased survival time from 50 to 300%. The significant inhibition of TSE disease by structurally dissimilar tetrapyrroles identifies these compounds as anti-TSE drugs.

Method for the determination of 5,5-diphenylbarbituric acid and its separation from 1,3-dimethoxymethyl-5,5-diphenylbarbituric acid in plasma by high-performance liquid chromatography.

A method is described for the measurement of 5,5-diphenylbarbituric acid in plasma using high-performance liquid chromatography with UV detection. Briefly, the compounds are separated on a C18 reversed-phase column using a mobile phase of 50 mM sodium acetate (pH 4.5) and methanol. The flow-rate is 1.0 ml/min and 25 microl are injected and detected at 215 nm. The method is specific and sensitive in the range of concentrations tested, with a limit of quantification of 0.25 microg/ml. The calibration curves are linear for concentrations between 0.25 and 10 microg/ml. Intra-day and inter-day coefficients of variation are less than 8.5 and 10.5%, respectively, over the linear range. Intra-day and inter-day bias are less than 7.0 and 8.0%, respectively. A pharmacokinetic study conducted in male Beagle dogs administered 10 mg/kg of 1,3-dimethoxymethyl-5,5-diphenylbarbituric acid or 8 mg/kg of 5,5-diphenylbarbituric acid intravenously demonstrates the utility of this method.

Restraint and housing of ratites.

Large animal practitioners are called upon to assist producers to prevent and control disease and to manage flocks. The concerns that exist in traditional livestock and poultry management are also applicable to ratites. Adequate ventilation, shelter, and space allocation are the foundations of flock health. Practitioners need to know how to handle ratites in order to perform a through physical examination and collect diagnostic samples.

NASA G-133 "GoldHelox": A Project Update.

NASA G-133, also known as the "GoldHelox Project", is a fully autonomous, soft X-ray, solar telescope designed for use on board the space shuttle. Conceived, designed and built by students at Brigham Young University, it will image the sun with a spatial resolution of 2.5 arc-seconds with a temporal resolution of one second. The instrument will image X-rays with wavelengths between 171Å and 181Å coming from highly ionized Fe lines in the sun's corona. Data will consist of several hundred high resolution photographs that will help in understanding the initial phases of solar flares, and the relationship between solar flares and the physics of the coronal-chromospheric transition region. This paper briefly outlines the project's goals, gives a brief overview of the construction and operation of the instrument and addresses the unique aspects of running a predominantly undergraduate research project. It summarizes the lessons learned to date, and the current project status.

Comparison of midazolam and diazepam by the intramuscular route for the control of seizures in a mouse model of status epilepticus.

A model system is described in which sustained clonic seizures are produced by a combination of phenytoin (PHT) and pentylenetetrazol (PTZ) in the mouse, the former agent preventing the terminal tonic spasms produced by the latter. In this system, midazolam (MDL), a water-soluble benzodiazepine, was compared with diazepam (DZP), a sparingly soluble agent which is widely used to treat status epilepticus (SE) in humans. Both agents were administered intramuscularly (i.m.) in approximately equieffective doses in animals exhibiting clonic seizure activity. MDL proved to be about twice as potent as DZP. Whereas control animals convulsed for a period of approximately 90 min, those treated with DZP 0.2 and 0.4 mg/kg convulsed for 7.8 and 3.9 min, respectively; mice receiving MDL 0.1 and 0.2 mg/kg convulsed for 1.9 and 1.4 min, respectively. MDL arrested seizures substantially more rapidly than diazepam (p less than 0.05). These data suggest that MDL has sufficiently rapid anticonvulsant action to merit evaluation for control of SE in humans when a rapidly absorbed antiepileptic drug (AED) is needed and intravenous (i.v.) administration is not feasible.

Effects of calcium channel blocking agents on neostigmine-induced fasciculations.

Male Sprague-Dawley rats were anesthetized with pentobarbital and prepared for monitoring contractions of the gastrocnemius muscle evoked by stimulation of the sciatic nerve. Animals received atropine prior to a dose of neostigmine of 0.02 mg/kg i.v. The effects on contractile strength and the number of fasciculations in a 2-min period were assessed. Pretreatment with phenytoin, 20 mg/kg, reduced the number of fasciculations to 32% of control without altering contractile strength. Both nifedipine and nitrendipine, 1 mg/kg each, virtually abolished fasciculations without altering twitch strength. Verapamil, 4 and 8 mg/kg, depressed fasciculation frequency to 50% of control without affecting pre-neostigmine twitch height. The dihydropyridine calcium blocking agents did however reduce the neostigmine-induced augmentation of contraction strength. These data suggest that a calcium-mediated current at presynaptic motor endings participates in the generation of repetitive nerve terminal discharges leading to muscle fasciculations.

Spinal cord contusion in the rat: somatosensory evoked potentials as a function of graded injury.

A weight-drop technique was used to produce mild, moderate, or severe spinal cord contusive injury in rats. At 4 weeks after injury, somatosensory evoked potentials (SEPs) were recorded with silver ball electrodes placed over the somatosensory cortex of anesthetized rats to measure the response to sciatic nerve stimulation. Both SEP area and amplitude were measured and were highly correlated with each other. Both indices of the SEP correlated inversely with the height of the weight drop and directly with the degree of residual function assessed at 4 weeks after injury. Measures of residual function consisted of a motor score, inclined plane test, and a combined behavioral score based on several neurologic functions. No correlation between latency of the SEP with degrees of contusive injury was observed. The data indicate that the SEP can be used as one criterion in the assessment of the severity of a lesion in a rat model of a graded spinal cord injury.

Protection by phenytoin and calcium channel blocking agents against the toxicity of diisopropylfluorophosphate.

Pretreatment of male Swiss-Webster mice with phenytoin, 25 mg/kg, verapamil, 25 to 3.0 mg/kg, nifedipine, 0.05 to 0.1 mg/kg, nitrendipine, 0.1 mg/kg, and nimodipine, 1 to 2.5 mg/kg, elevated the LD50 of diisopropylfluorophosphate (DFP) to a significant degree. In addition, these agents enhanced the protection that can be obtained from atropine and 2-pralidoxime. The protective effects of phenytoin cannot be attributed to an anticonvulsant action, per se, since carbamazepine, phenobarbital, and diphenylbarbituric acid in anticonvulsant doses did not influence DFP lethality. The mechanism of action of phenytoin and the other effective calcium channel blockers in providing protection over and above that achieved with atropine and 2-pralidoxime appears to be due to a protective action of the former agents on central respiratory centers and peripheral nicotinic sites and may involve the movement of calcium into excitable membranes.

Diphenylbarbituric acid: its effects on neuromuscular and spinal cord function in the cat.

In studies of neuromuscular function in the cat soleus muscle, diphenylbarbituric acid (DPB; 10-80 mg/kg i.v.) depressed both the degree and the duration of posttetanic potentiation (PTP) in a dose-dependent manner. At doses of greater than 20 mg/kg, twitch strength was increased in both indirectly stimulated and directly stimulated chronically denervated preparations, indicating a direct effect of DPB on muscle. In the spinal cord, DPB (10-60 mg/kg) depressed both monosynaptic (2N) and polysynaptic discharges, with flexor and extensor reflexes being similarly affected. In addition, DPB was not selective for isolated 2N as compared with posttetanically potentiated monosynaptic responses. Thus, in its actions on neuromuscular function DPB resembles phenytoin; in the spinal cord the drug resembles phenobarbital. The data suggest that the capacity of a drug to curb high-frequency repetitive discharges is more important than curbing recruitment as exhibited by PTP of the 2N reflex.

Description and analysis of the myotonolytic effects of phenytoin in the decerebrate cat: implications for potential utility of phenytoin in spastic disorders.

Phenytoin (DPH) was evaluated for its capacity to reduce several motor manifestations of decerebrate rigidity in the cat. In doses of the order of 40 to 50 mg/kg i.v., DPH diminished the force necessary to collapse the hyperextended limbs; at about half this dose range, the drug reduced gamma-motoneuron discharges; at still lower doses the drug profoundly depressed mechanical and electromyographic responses evoked by stretch from both forelimb and hindlimb extensor muscles. Serum levels of DPH associated with substantial reduction in electrical and mechanical manifestations of the extensor hypertonus were of the same order conventionally encountered when the drug is administered to humans for acute seizure management. The data are supportive of a centrally and peripherally mediated muscle relaxing effect of the drug in states where muscle spindle involvement is a contributing factor, and may help to explain further the utility of DPH in the treatment of spasticity.

Effects of carbamazepine on muscle tone in the decerebrate cat.

Previous studies, which have demonstrated that carbamazepine (CBZ) possesses direct muscle spindle suppressant activity, suggest that CBZ may have therapeutic value in the treatment of hypertonic disorders characterized by high fusimotor drive. The effects of CBZ on motor tone in the midcollicular decerebrate cat were therefore examined. CBZ, in a concentration-dependent manner, reduced muscle tone, as measured by the force necessary to overcome hyperextension. Significant depression was first observed at a serum concentration of about 25 micrograms/ml, whereas 50% depression occurred at about 40 micrograms/ml. These effects could not be attributed to the hypotensive effect of the drug. CBZ produced little or no effect on spontaneous gamma motoneuron activity recorded in teased ventral roots of segmentally deafferented spinal cords of decerebrate animals; chlorpromazine, however, was effective in suppressing such activity. In the same preparations, CBZ reduced polysynaptic but had little effect on monosynaptic spinal reflexes evoked by dorsal root stimulation. The drug also shortened the duration of the pause in spontaneous gamma motoneuron activity after dorsal root stimulation. Serum concentrations which diminished extensor rigidity in decerebrate cats induced mild to moderate intoxication in intact unanesthetized cats. This was characterized by ataxic gait, sedation and hypotonia. These experiments indicate that CBZ may be of value alone or adjunctively in the reduction of some forms of muscle hypertonicity.

Phenytoin and chlorpromazine in the treatment of spasticity.

The efficacy of phenytoin sodium and chlorpromazine hydrochloride in the reduction of spasticity was evaluated in both open and controlled studies. In each study, the majority of patients exhibited both objective and subjective signs of improvement. Reduction of motor tone in spastic muscles, as well as improvement in functiional status, was observed. Most patients experienced greater benefit from the combination of phenytoin and chlorpromazine than from either drug alone. The use of the drugs in combination permitted decreased chlorpromazine doses and reduced unwanted side effects such as lethargy and somnolence. These drugs may exert their action by suppressing fusimotor efferent as well as afferent discharged from muscle spindles. The results suggest that the fusimotor system is an important pharmacologic target in the treatment of spasticity.

The effects of phenytoin and lidocaine on a proprioceptor of the cockroach, Blaberus discoidalis: a simple method for discriminating between inhibitors of sensory transduction and axonal conduction.

Three linearly aligned tibial tactile spines of the cockroach Blaberus discoidalis were stimulated by a mechanically driven glass probe. A "window" was cut at the base of the central spine and various concentrations of phenytoin, lidocaine and colchicine were applied. Colchicine, phenytoin and a low concentration of lidocaine selectively inhibited stimulus-evoked discharges from the central spine, while lidocaine in higher concentrations inhibited discharges from the central and distal spines. We conclude that phenytoin and colchicine suppress afferent discharges by their ability to interfere with sensory transduction, while lidocaine suppresses afferent responses by interfering with axonal conduction as well as sensory transduction.

Differential selectivity of several barbiturates on experimental seizures and neurotoxicity in the mouse.

Six barbiturates with diverse time-action characteristics--thiopental, pentobarbital, butabarbital, phenobarbital, diphenylbarbiturate, and barbital--were evaluated for "anticonvulsant" and "neurotoxic" effects. For the former, the MES test, clonic seizures induced by pentylenetetrazol, 90 mg/kg, s.c., and maximal seizures produced by pentylenetetrazol, 200 mg/kg, s.c., were employed. For the latter, we used a rotorod technique. Time to peak activity in the MES test was employed as the time for other tests. Pentobarbital required at least neurotoxic doses to produce substantial "anticonvulsant" activity, its protective index ranging from 0.79 to 0.98 in the three tests. Among the drugs tested, phenobarbital and diphenylbarbiturate exhibited the most favorable protective indices, ranging from 2.71 to 3.41 for phenobarbital and from 3.85 to 5.0 for diphenylbarbiturate. Barbital, another drug with a prolonged duration of action, exhibited a range from 0.84 to 2.81. Although a prolonged duration of action is an important characteristic for antiepileptic activity, this property does not confer per se a favorable protective index.

Carbamazepine suppression of post-tetanic potentiation at the neuromuscular junction.

The effects of carbamazepine (CBZ) on post-tetanic potentiation (PTP) were evaluated using an in vivo cat coleus neuromuscular preparation. CBZ was administered i.p. and plasma CBZ concentrations were determined by gas liquid chromatography during PTP tests over a 90-min period. CBZ produced a concentration-dependent depression of PTP. Significant depression was first noted at about 12 microgram/ml and 50% depression occurred at 20 microgram/ml; this depression was time-dependent. No effect was observed on unpotentiated, supramaximal twitches. CBZ also modified the pattern of tetanic contraction; the most predominant change was an enhancement of the initial falling phase of the tetanus. Antidromically propagated post-tetanic repetitive afterdischarges (PTR) were monitored in single isolated vertral root filaments innerving the soleus muscle. CBZ inhibited PTR without affecting conduction velocity or the capacity of the fiber to follow the high frequency (tetanic) stimulation. These results are similar to those previously reported for phenytoin. CBZ inhibits PTP in this preparation by inhibition of PTR through a presynaptic effect; possible mechanisms are discussed. These observations may contribute to the understanding of the actions of this drug in epilepsy and neuromyotonia.

The influence of heart rate on ouabain cardiotoxicity in cats with spinal cord transection.

The dose, serum level and ventricular content of ouabain needed to produce cardiotoxicity were examined in control cats, cats with transected spinal cords and cats with transected spinal cords whose heart rates were restored to control values by artificial pacing. The lethal dose of ouabain was higher in cats with transected spinal cords and not paced than it was in the control group. However, the lethal dose of ouabain in spinal-sectioned cats with ventricular pacing was no different from that in controls. However, in both groups of spinal-sectioned cats, death was associated with higher ventricular and serum levels of ouabain than in controls. The ventricular ouabain content of paced animals with transected spinal cords was higher than that of controls and lower than that of unpaced spinal cats. Thus, restoration of heart rate to control levels in spinal animals appeared to accelerate myocardial ouabain uptake. The lower myocardial ouabain content in the spinal-sectioned animals which were paced suggests that pacing sensitizes the heart to cardiotoxicity. Spinal section itself appears to decrease the sensitivity to ouabain partly through a decrease in cardiac rate and partly through a loss of neurogenic influence.