System Xc- Antiporter Inhibitors: Azo-Linked Amino-Naphthyl-Sulfonate Analogues of Sulfasalazine.

The cystine/glutamate antiporter system Xc- (SXc-) mediates the exchange of intracellular L-glutamate (L-Glu) with extracellular L-cystine (L-Cys2). Both the import of L-Cys2 and the export of L-Glu take on added significance in CNS cells, especially astrocytes. When the relative activity of SXc- overwhelms the regulatory capacity of the EAATs, the efflux of L-Glu through the antiporter can be significant enough to trigger excitotoxic pathology, as is thought to occur in glioblastoma. This has prompted considerable interest in the pharmacological specificity of SXc- and the development of inhibitors. The present study explores a series of analogues that are structurally related to sulfasalazine, a widely employed inhibitor of SXc-. We identify a number of novel aryl-substituted amino-naphthylsulfonate analogues that inhibit SXc- more potently than sulfasalazine. Interestingly, the inhibitors switch from a competitive to noncompetitive mechanism with increased length and lipophilic substitutions, a structure-activity relationship that was previously observed with aryl-substituted isoxazole. These results suggest that the two classes of inhibitors may interact with some of the same domains on the antiporter protein and that the substrate and inhibitor binding sites may be in close proximity to one another. Molecular modeling is used to explore this possibility.

Circadian and circaseptan (about-weekly) aspects of immigrant Indians' blood pressure and heart rate in California, USA.

Time structurally (chronomically) interpreted half-hourly monitoring of blood pressure (BP) and heart rate (HR) for at least 7 days and preferably for 17 days is recommended, separately for a diagnosis of BP disorders and when necessary again for the same or longer spans for treatment, whenever a positive diagnosis of a disorder is made. In this study, 30 clinically healthy subjects underwent 7-day monitoring and provided a series of findings, including the detection of Circadian Hyper-Amplitude-Tension (CHAT), that is blood pressure overswinging, which carries a high risk of hard cardiovascular events. The results specifically bear upon south-east Asian-Indian immigrants. They show that cardiovascular disease risk increases with age, with a positive family history of hypertension and/or other cardiovascular diseases and even with the duration of stay in the USA. A relation to body mass index is also shown. Such monitoring for prehabilitation may eventually reduce the need for rehabilitation.

Magnesium modulation of glucose-induced insulin secretion by the perfused rat pancreas.

Increasing levels of magnesium were found to cause a marked depression of glucosestimulated insulin secretion at fixed calcium levels, particularly at levels which bracketed the concentration of ultrafiltrable magnesium found in normal rat plasma (1.3 meq/l), i.e., increasing magnesium from 0.6 to 1.2 meq/l depressed secretion, and increasing magnesium from 1.2 to 2.4 meq/l resulted in a further depression. Paradoxically, when magnesium was omitted from the perfusing medium, insulin secretion was also depressed. The data strongly suggest that the calcium/magnesium ratio is a primary regulator of the insulin secretory process, since a relatively slight alteration of the physiologic ratio of calcium to magnesium (approximately 2.5) results in a marked alteration of total insulin secretion. In addition, small amounts of magnesium are necessary for optimum secretion, possibly reflecting the requirement for magnesium in several enzymatic processes. Thus, magnesium may play an important role in the regulation of insulin secretion by altering the sensitivity of the beta cells of the Islets of Langerhans to glucose.

Ethanol-insulin interrelationships in the rat studied in vitro and in vivo: evidence for direct ethanol inhibition of biphasic glucose-induced insulin secretion.

The effect of ethanol (ETOH) on glucose-stimulated insulin secretion was studied using: (1) an in vitro isolated pancreas perfusion system, and (2) an in vivo preparation utilizing unrestrained, unanesthetized rats with indwelling jugular and aortic catheters. ETOH exposure in vitro resulted in a decrease in glucose-stimulated insulin secretion from the perfused rat pancreas. Second phase secretion (min 30-60) was inhibited at low ETOH exposure (100 mg/dl) and both first (min 2-8) and second phase secretion were inhibited at higher ETOH levels (1000 mg/dl). This indicates that second phase secretion of insulin from the pancreas is more sensitive to the acute effects of ETOH than is first phase secretion. ETOH preinfusion of 4 hr in vivo resulted in an approximate 20 mg/dl decrease in plasma glucose concentrations with little or no alteration in plasma insulin levels. One hour ETOH preinfusion produced a modest 8 mg/dl fall in plasma glucose. Intravenous glucose tolerance tests following low level ETOH infusion of 4 hr resulted in an enhancement in the insulin response with no change in glucose removal. This enhancement was not observed at higher ETOH levels or after high-level, short (1 hr) ETOH preinfusion. The data suggest that stimulus-induced insulin secretion may be enhanced by an ETOH metabolite if the ETOH exposure is prolonged and at a low level. Higher ETOH concentration appears to directly block this enhancement. Due to response similarities the rat model may be of considerable value to study the effects of ETOH on stimulus-induced insulin secretion in human subjects.

Chronic centrifugation (hypergravity) disrupts the circadian system of the rat.

The present study was conducted to evaluate the response of rat deep body temperature (DBT) and gross locomotor activity (LMA) circadian rhythms to acute hypergravity onset and adaptation to chronic (14 day) hypergravity exposure over three gravity intensities (1.25, 1.5, and 2 G). Centrifugation of unanesthetized naive animals resulted in a dramatic acute decrease in DBT (-1.45, -2.40, and -3.09 degrees C for the 1.25, 1.5, and 2.0 G groups, respectively). LMA was suppressed for the duration of centrifugation (vs. control period); the percent decrease for each group on days 12-14, respectively, was 1.0 G, -15.2%, P = not significant; 1.25 G, -26.9%, P < 0.02; 1.5 G, -44.5%, P < 0.01; and 2.0 G, -63.1%, P < 0.002. The time required for DBT and LMA circadian rhythmic adaptation and stabilization to hypergravity onset increased from 1.25 to 2.0 G in all circadian metrics except daily means. Periodicity analysis detected the phenomenon of circadian rhythm splitting, which has not been reported previously in response to chronic hypergravity exposure. Our analysis documents the disruptive and dose-dependent effects of hypergravity on circadian rhythmicity and the time course of adaptation to 14-day chronic centrifugation exposure.

Leg intramuscular pressures during locomotion in humans.

To assess the usefulness of intramuscular pressure (IMP) measurement for studying muscle function during gait, IMP was recorded in the soleus and tibialis anterior muscles of 10 volunteers during treadmill walking and running by using transducer-tipped catheters. Soleus IMP exhibited single peaks during late-stance phase of walking [181 +/- 69 (SE) mmHg] and running (269 +/- 95 mmHg). Tibialis anterior IMP showed a biphasic response, with the largest peak (90 +/- 15 mmHg during walking and 151 +/- 25 mmHg during running) occurring shortly after heel strike. IMP magnitude increased with gait speed in both muscles. Linear regression of soleus IMP against ankle joint torque obtained by a dynamometer produced linear relationships (n = 2, r = 0.97 for both). Application of these relationships to IMP data yielded estimated peak soleus moment contributions of 0.95-1.65 N . m/kg during walking, and 1.43-2.70 N . m/kg during running. Phasic elevations of IMP during exercise are probably generated by local muscle tissue deformations due to muscle force development. Thus profiles of IMP provide a direct, reproducible index of muscle function during locomotion in humans.

Effect of acute intravenous administration of delta-9-tetrahydrocannabinol on the episodic secretion of immunoassayable growth hormone in the rat.

Blood samples from unrestrained, unanesthetized, male rats (300-350 g) were obtained every 15 min. for 9 consecutive hrs. (1000-1900 h). Each rat received, intravenously, a vehicle injection (controls) or a 2.0 mg/kg dose of delta-9-tetrahydrocannabinol (THC) at 1300 h to determine the effect of this drug on the spontaneous episodic secretion of plasma immunoassayable rat growth hormone (rGH). Acute administration of THC suppressed the secretion of rGH, as is evident from mean plasma level (p less than .01), peak height (p less than .02), and integrated peak amplitude (p less than .02) analyses. Episodic secretion was inhibited in all animals (n = 7) receiving THC. Although further investigation is needed to define clearly the physiological mechanisms involved in this response, these data indicate that THC can inhibit the hypothalamic-pituitary control of normal episodic growth hormone secretion in the rat.

Circadian performance of suprachiasmatic nuclei (SCN)-lesioned antelope ground squirrels in a desert enclosure.

Circadian activity parameters of 53 white-tailed antelope ground squirrels, Ammospermophilus leucurus, were measured to determine the role of the suprachiasmatic nuclei (SCN) pacemaker in their health and survival. Wheel-running activity was monitored in the laboratory with 44 individuals to document the presence of free-running circadian rhythms and ability to entrain to light-dark cycles. Twenty-two individuals were returned to the desert site of origin, including 12 intact control animals and 10 animals whose circadian timing had been disrupted by SCN-lesioning. Time of activity was recorded continuously for 15 days in a large outdoor enclosure by a motion detector, a microchip transponder detector, and video surveillance. An unplanned nighttime attack by a feral cat resulted in the death of 60% of the SCN-lesioned animals and 29% of the control animals in the enclosure. Surface activity of SCN-lesioned animals at the food cache occurred both in daytime and at night, ranging from 16.0% nighttime activity for one partially lesioned individual to 52.1% for one completely lesioned animal. Controls were strongly day-active, with nighttime surface trips constituting only 0-1.3% of all excursions to the cache. Nine wild free-ranging individuals, including one with a radiotransmitter collar, were exclusively day-active. One of the functions of the SCN in mammals may be to reduce activity of animals during times that are unfavorable for activity.

Circadian rhythms and athletic performance.

Daily or circadian rhythmical oscillations occur in several physiological and behavioral functions that contribute to athletic performance. These functions include resting levels of sensory motor, perceptual, and cognitive performance and several neuromuscular, behavioral, cardiovascular, and metabolic variables. In addition, circadian rhythms have been reported in many indices of aerobic capacity, in certain physiological variables at different exercise levels, and, in a few studies, in actual athletic performance proficiency. Circadian rhythmicity in components of athletic performance can be modulated by workload, psychological stressors, motivation, "morningness/eveningness" differences, social interaction, lighting, sleep disturbances, the "postlunch dip" phenomenon, altitude, dietary constituents, gender, and age. These rhythms can significantly influence performance depending upon the time of day at which the athletic endeavor takes place. Disturbance of circadian rhythmicity resulting from transmeridian flight across several time zones can result in fatigue, malaise, sleep disturbance, gastrointestinal problems, and performance deterioration in susceptible individuals (circadian dysrhythmia or "jet-lag"). Factors influencing the degree of impairment and duration of readaptation include direction of flight, rhythm synchronizer intensity, dietary constituents and timing of meals, and individual factors such as morningness/eveningness, personality traits, and motivation. It is the intent of the authors to increase awareness of circadian rhythmic influences upon physiology and performance and to provide a scientific data base for the human circadian system so that coaches and athletes can make reasonable decisions to reduce the negative impact of jet-lag and facilitate readaptation following transmeridian travel.

Determination of total and ultrafilterable calcium and magnesium in normal equine serum.

Total and ultrafilterable calcium (Ca) and magnesium (Mg) values were determined for Shetland pony stallions, stallions, and pregnant and diestrous mares, using a simple, inexpensive, quick procedure to obtain an ultrafiltrate of serum. There was no significant difference between horses and ponies, between stallions and mares, or between pregnant and nonpregnant mares. The percentage of total serum Ca that was ultrafilterable was 63.4+/-1.7 for horses and 64.8+/-2.2 for ponies. The percentage of total serum Mg that was ultrafilterable was 75.6+/-1.5 for horses and 77.0+/-1.7 for ponies. Total serum Ca was 12.56+/-0.26 mg/dl for horses and 12.43+/-0.32 mg/dl for ponies. Total serum Mg was 2.18+/-0.29 mg/dl for horses and 2.49+/-0.60 mg/dl for ponies. This technique can be coupled with specific assays for ionized forms of the cations or with ion electrodes to obtain values for protein-bound, ionized, or complexed and chelated Ca and Mg in equine serum.

Pineal physiology in microgravity: relation to rat gonadal function aboard Cosmos 1887.

For the first time pineal glands obtained from 5 male rats flown aboard an orbiting satellite (Soviet Biosatellite #1887) were analyzed for their melatonin, serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), and calcium content. In addition, plasma 5-HT and 5-HIAA were measured. These parameters were compared to indicators of gonadal function: plasma testosterone concentration and spermatogonia development. Plasma melatonin was low at the time of euthanasia (lights on) and was not different among the experimental groups (flight animals, synchronous controls, and vivarium controls). Pineal calcium of flight animals was not different from ground controls. However, pineal 5-HT and 5-HIAA in the flight group were significantly higher than those in ground controls (p less than 0.05). These findings suggest a possible increase in pineal 5-HT turnover in flight animals which may result in increased melatonin secretion. Since melatonin is known to possess antigonadal properties, the alteration of pineal 5-HT turnover and its expected effects on melatonin secretion may, in part, explain the lower plasma testosterone levels (p less than 0.001) and 4-11% fewer spermatogonia cells (p less than 0.02) observed in flight animals.

A review of human physiological and performance changes associated with desynchronosis of biological rhythms.

This review discusses the effects, in the aerospace environment, of alterations in approximately 24-h periodicities (circadian rhythms) upon physiological and psychological functions and possible therapies for desynchronosis induced by such alterations. The consequences of circadian rhythm alteration resulting from shift work, transmeridian flight, or altered day lengths are known as desynchronosis, dysrhythmia, dyschrony, jet lag, or jet syndrome. Considerable attention is focused on the ability to operate jet aircraft and manned space vehicles. The importance of environmental cues, such as light-dark cycles, which influence physiological and psychological rhythms is discussed. A section on mathematical models is presented to enable selection and verification of appropriate preventive and corrective measures and to better understand the problem of dysrhythmia.

New findings regarding light intensity and its effects as a zeitgeber in the Sprague-Dawley rat.

Circadian rhythmicities are oscillations of physiological cycles designed to create temporal organization. Circadian rhythms ensure that physiological mechanisms are expressed in proper relationship to each other and the 24 hour day. Light is the main zeitgeber ("time giver") for biological clocks. The daily variations in light intensity from dawn to dusk, and seasonally due to the rotation of the earth, act upon organisms to give them photoperiodic information. This entrainment allows them to vary biologically to prepare for reproduction, hibernation, migration and the daily adaptations necessary for survival. In most mammals, the suprachiasmatic nucleus of the anterior hypothalamus has been implicated as the central diving mechanism of circadian rhythmicity. The photic input from the retina, via the retino-hypothalamic tract, and modulation from the pineal gland help regulate the clock. In this study we investigated the effects of low light intensity on the circadian system of the Sprague-Dawley rat. A series of light intensity experiments were conducted to determine if a light level of 0.1 Lux will maintain entrained circadian rhythms of feeding, drinking, and locomotor activity.

Insulin action and binding in adipocytes exposed to endotoxin in vitro and in vivo.

We investigated in vitro and in vivo effects of endotoxin on glucose oxidation and insulin binding in rat adipocytes. Exposure of adipocytes to endotoxin (500 micrograms/ml) in vitro resulted in 48% increase in basal glucose oxidation after 30 minutes, 63% and 65% increase after 90 and 150 minutes, respectively. Adipocytes from rats injected 6 hours previously with endotoxin IV (2 mg/100 gm) also showed elevated (42%) basal glucose oxidation. Both the absolute levels of stimulation and sensitivity to insulin stimulation were less than in control cells. A tendency for higher insulin binding affinity at low ambient insulin concentrations was noted. At higher insulin concentrations this difference disappeared. Our results demonstrate an insulin-like effect of endotoxin, as well as perturbation by endotoxin of insulin action at the cellular level. Changes in receptor affinity are also suggested, implying that the insulin receptor may be a site for modulation of target cell sensitivity in endotoxemia.

Alterations in insulin action by endotoxin in vitro.

Fat cells isolated from epididymal fat pads of Sprague-Dawley rats were exposed to E coli endotoxin in vitro, and after washing the ensuing alterations in glucose oxidation and antilipolysis were studied. Although endotoxin (500 microgram/ml) exhibited an insulin-like effect on basal glucose oxidation, it diminished insulin stimulation of glucose oxidation, seemingly inducing an insulin-resistant state. On the other hand, identical doses of insulin elicited significantly greater antilipolytic effects in endotoxin-treated cells, than in untreated cells. Thus, endotoxin exposure (in a range of 0.05-200 microgram/0.5 ml cell suspension) rendered adipocytes more sensitive to the antilipolytic effect of insulin. Results of this study indicate that the different physiologic actions of insulin on adipocytes are not affected in a uniform manner by endotoxin exposure in vitro.

Shiftwork and safety in aviation.

For airline pilots, sleep deprivation and circadian desynchronization due to rapidly rotating shift schedules, rapid time zone changes, and unorganized sleep/wake cycles can result in severe performance decrements. Twelve case histories of accidents in which pilot scheduling might have been a factor are reviewed, and suggestions for the chronohygiene of pilot scheduling are made.

Effects of housing density on mouse physiology and behavior in the NASA Animal Enclosure Module simulators.

Space flight studies using the Animal Enclosure Module (AEM) make it possible to investigate the role of microgravity on animal physiology and behavior. In this study, we compared the health and well-being of mice housed at different densities in AEM simulators (AEMS), to vivarium shoebox (control) cages (VSBC). A stress assessment battery (SAB) of measures was developed to evaluate mouse health and well-being, and to determine if any of the population sizes resulted in a stressful environment. The SAB was based, in part, on recommendations of a NASA Workshop on Rodent Cage Sizing. It includes: 1) General assessment of appearance, 2) Behavioral assessment (video), 3) Food and water consumption, 4) Body weight changes, 5) Thymus, adrenal, spleen, heart and kidney weights, 6) Plasma corticosterone concentration, 7) Total plasma protein concentration, 8) Total blood leukocyte count, 9) Differential leukocyte count: neutrophil/lymphocyte ratio; eosinophil count, 10) Gastric histology.