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Biomedical subjects

W N Tapp

Publications and source records attributed to W N Tapp.

At least 55 records · Page 3Linked to original sources
PubMed1987

Adrenal, thyroid, and testicular hormone rhythms in male golden hamsters on long and short days.

Plasma concentrations of adrenal, thyroid, and testicular hormones were measured at 4-h intervals around the clock in male hamsters on long (14:10-h light-dark cycle) and short (10:14-h light-dark cycle) days. Plasma corticosterone, cortisol, thyroxine (T4), triiodothyronine (T3), and testosterone rhythms were present on long days. The only one of these hormones to have a significant rhythm on short days was cortisol, but even its amplitude was suppressed compared with the cortisol rhythm on long days. Short days also lowered mean plasma levels of cortisol, T4, T3, and testosterone. Finally, short days raised the ratio of corticosterone to cortisol and lowered the ratio of T4 to T3. Both ratios had significant rhythms on long days but not on short days. Because of the many interactions among adrenal, thyroid, and testicular hormone axes, it is unclear whether the primary effect of short days is on one of these endocrine systems or on another factor that has separate effects on each of the hormone rhythms that was measured. Nonetheless, it is clear that a major effect of short day lengths in hamsters is to suppress hormone rhythms. Explanations of photoperiodic effects that depend on endocrine mediation should take this into account.

Adrenal Cortex Hormones↗
PubMed1987

The effect of chronic digitalis therapy on the course of heart failure and on endocrine function in cardiomyopathic hamsters.

Eleven month old cardiomyopathic hamsters, which have enlarged hearts and anasarca, were given access to either an ethanol vehicle or an ethanol-digoxin solution in addition to a second water bottle. In comparison to controls, treated hamsters survived and showed significant amelioration of the pathological syndrome of heart failure. Thus, in this model of advanced congestive failure, digoxin has a clear-cut beneficial effect.

Animals↗
PubMed1986

Life extension in heart disease: an animal model.

In an experimental study to investigate the effect of constant light on longevity in heart disease male hamsters with inherited heart disease were housed in pairs in either constant light or 12 h light and 12 h dark cycles. All hamsters had free access to food and water. Constant light slowed the progress of heart failure, made the hamsters more likely to survive the early stages of failure, and extended their lives. This observation may open new avenues for the treatment of human beings with heart disease.

Animals↗
PubMed1986

Feeding cycles in smokers, exsmokers and nonsmokers.

Smokers, exsmokers and nonsmokers showed 50 to 150 minute cycles of consummatory behavior (eating and drinking) that appear to reflect a biological rhythm of oral drive. Smokers and exsmokers had significantly shorter cycles, i.e., more frequent consummatory peaks, than nonsmokers. If a greater frequency of consummatory peaks contributes to heightened oral drive in smokers, it may constitute a physiological factor underlying the initiation or maintenance of compulsive smoking and the degree of difficulty in quitting smoking and remaining abstinent.

Activity Cycles↗
PubMed1986

Use of motor performance tests to differentiate aging effects from disease effects.

The present study has demonstrated that behavioral testing can provide non-invasive methods for monitoring the time-courses of aging and disease processes. Performance on two of our tests changed linearly with increasing age in both cardiomyopathic and healthy hamsters, but these changes occurred at an earlier age in the CM hamsters than in healthy control hamsters. In addition, healthy hamsters showed age-related changes in performance on some tests, while sick CM hamsters did not show parallel changes. These results indicate that disease can modify the rate of change in some markers of aging, and thus they suggest that disease might be able to modify the aging process. However, such a preliminary hypothesis requires much further work. Performance on another behavioral test was shown to be stable throughout much of the lifespan of healthy hamsters, and yet disease in CM hamsters was clearly able to affect it. Thus it was possible to find some tests which discriminated between aging and disease effects, but only because the time-course of the disease we were studying was well defined. Most importantly, these results have suggested a way of thinking about the problem of disease in aging studies that may be more fruitful than others previously used. Examining the changes over time in both healthy subjects (putatively disease-free) and those with disease should allow one to determine which age-related changes are dependent on the presence of organic disease and to separate these from the changes which might inevitably occur solely from increasing age.

Aging↗
PubMed1985

Elevated plasma vasopressin in cardiomyopathic hamsters.

Hamsters of the BIO 14.6 strain characteristically develop cardiomyopathy as they age, and hamsters of this strain have overt signs of heart failure by 11 months of age. Plasma levels of the posterior pituitary hormone arginine-vasopressin (AVP) were found to be elevated (approximately 2-fold) in 11 month old BIO 14.6 hamsters, compared to age-matched hamsters of a control strain. AVP appeared inappropriately elevated in these animals, since they were neither hyperosmotic nor markedly hypotensive. The elevated levels of AVP observed in these animals appears to contribute to vasomotor tone, since intravenous administration of a specific antagonist of the vasoconstrictor action of AVP [d(CH2)5Ome(TYR)AVP] elicited a fall in arterial pressure (9 +/- 2 mm Hg, n = 6, p less than 0.05). The AVP antagonist had no effect on arterial pressure in hamsters of a control strain, and vehicle administration had no effect on arterial pressure in either strain. These data indicate that inappropriately elevated levels of AVP contribute to the cardiovascular state of myopathic hamsters. Since elevated plasma AVP has been noted in human congestive heart failure, these results suggest that AVP may contribute to the cardiovascular status during congestive heart failure.

Age Factors↗
PubMed1985

Plasma cortisol and corticosterone concentrations in the golden hamster, (Mesocricetus auratus).

Because some recent studies of hamster adrenocortical function have depended on older studies that may have been inadequate or misinterpreted, the present study re-examined plasma corticosterone and cortisol concentrations in hamsters under several conditions to determine which plasma glucocorticoid predominated in this animal. Sensitive radioimmunoassays were used to measure separately the two glucocorticoids in the basal condition, after adrenocorticotropin (ACTH) treatment, after acute stress, and after chronic stress. In the basal condition, corticosterone concentrations were 3-4 times higher than those of cortisol. After stimulation, this difference disappeared, but rarely were any hamster's cortisol levels higher than their corticosterone levels. Both ACTH and acute stress elevated plasma corticosterone and cortisol concentrations, but only plasma cortisol concentrations were elevated following chronic stress. The dissociation between cortisol and corticosterone concentrations after chronic stress suggests that the two glucocorticoid hormones in the hamster may be regulated independently. The data also indicate that both corticosterone and cortisol should be measured when assessing adrenocortical function in the hamster.

Adrenocorticotropic Hormone↗
PubMed1985

Variable threshold R wave detector: use in automated ECG processing.

Reliable R wave detection is difficult under many commonly found conditions of varying baseline and changing morphology such as varying R wave amplitude and reduced R/T ratio. An instrument has been developed which overcomes many of these problems. The device employs a variable detection threshold which is based on the amplitude of the last occurring R wave. For large R wave amplitudes, the threshold is raised, thus providing good noise immunity. For low R wave amplitudes, the threshold is lowered, thus providing continued detection. An R wave filter de-emphasizes noise as well as P and T waves, and an adjustable refractory period following R wave detection prevents false detection during this period. The variable threshold R wave detector has been used to process ECG in a heart rate study in nearly 100 diabetic patients as well as in healthy controls. The detector provides much improved automatic R wave detection over fixed level detectors and can be constructed with parts costing under 100 dollars.

Animals↗
PubMed1984

Plasma cortisol and appetitively motivated arousal in monkeys.

A disagreement exists in the literature as to whether plasma glucocorticoids are a sensitive index of emotional arousal. In order to provide further data on this subject, arousal in adult male rhesus monkeys was produced by classical appetitive conditioning done once every 48 hr. Monkeys showed significantly more aroused behavior during CS+ sessions than during CS- sessions. Concurrent with these behavioral changes, appetitive conditioning suppressed the increase in plasma cortisol that took place in control conditions. This dissociation between cortisol and arousal provides additional data for the conclusion that plasma glucocorticoids are an insensitive index of arousal. The fact that glucocorticoids decrease dramatically under similar experimental conditions in rats suggests that hormonal regulatory mechanisms for this rodent species may differ from that for primates.

Animals↗
PubMed1984

Ultradian glucocorticoid rhythms in monkeys and rats continue during stress.

Previously we showed that rhesus monkeys have ultradian cortisol rhythms with periods of about 90 min that persist during the infusion of large amounts of adrenocorticotropin. The experiments reported here showed that rats exhibit ultradian corticosterone rhythms with a similar period (median period 61 min). However, rat ultradian corticosterone rhythms were distorted by large slow trends that had to be removed before the rhythm could be adequately assessed. The need for sophisticated trend removal suggests that physiological variables that have been described as exhibiting episodic fluctuations (e.g., human cortisol) may actually be periodic and ultradian. The ultradian glucocorticoid rhythm persisted during stress both in monkeys (median period 80 min) and rats (median period 52 min). However, the glucocorticoid stress response appeared to produce large slow trends in both monkeys and rats, indicating that environmental influences may introduce slow trends that make raw data difficult to evaluate. More importantly, the fact that ultradian glucocorticoid rhythms persist during stress provides further evidence of limits on the classical concept that glucocorticoid secretion is tightly and inseparably linked to hormonal events in the hypothalamic-pituitary unit.

Adrenal Glands↗
PubMed1983

Stress-induced heart failure.

Stress produced heart failure in cardiomyopathic hamsters (CMHs) with subclinical heart disease. CMHs exhibited a variety of peripheral manifestations of heart failure including subcutaneous edema, fluid in the abdominal and thoracic cavities, and increased organ weight. In contrast, stress did not produce heart failure in healthy hamsters. These data indicate that the presence of covert heart disease can dramatically alter the pathogenic consequences of stress.

Animals↗
PubMed1983

Role of luminal acidity in the pathogenesis of stress-induced gastroduodenal disease.

Infusion of progressively more acidic fluids into the stomachs of rats stressed by immobilization had disparate effects on gastric erosive disease despite their producing a stepwise fall in venous pH. At the highest concentration infused, disease was exacerbated. However, at lower concentrations, disease was ameliorated. The acidity of the infusate altered the incidence but not the magnitude of the duodenal disease that accompanies stress. When bicarbonate was given parenterally, systemic pH was normalized but gastric disease still developed. Thus the level of mucosal pH does not reliably predict whether or not gastric disease will develop. When a series of progressively more basic fluids was infused into the stomachs of stressed rats, gastric disease was lessened in only those rats infused with the highest concentration of bicarbonate. Increasing the pH of the infusate in a stepwise fashion produced a stepwise diminution of duodenal disease incidence with no effect on duodenal disease severity. When the stressed rat's mucosa was stimulated to secret acid by the parenteral injection of secretagogues, gastric disease severity was the same as in control animals given saline. Although secretagogue infusion did not affect the incidence of stress-induced duodenal disease, it significantly exacerbated the magnitude of the elicited disease. These experiments suggest that luminal acid plays a negligible role in the onset of stress-induced gastric disease but may be important in determining the severity of the gastric disease once it has begun. Conversely the amount of luminal acid correlates with the incidence of stress-induced duodenal disease but does not seem to play a role in determining the severity of the duodenal disease after it has begun.

Animals↗
PubMed1981

Phase shifting circadian rhythms produces retrograde amnesia.

Phase shifting circadian rhythms in rats shortly after passive avoidance training impaired their performance on retention tests. The amnesia was not due to simple performance deficits accompanying the "jet leg" effects of phase shifting or to differences in lighting or circadian phase at training and at testing. Amnesia was associated with specific rhythm reentrainment patterns. These data indicate that disrupting circadian organization can produce retrograde amnesia in rats.

Amnesia↗
PubMed1981

Ultradian rhythm of plasma norepinephrine in rats.

This study examined the possibility that laboratory rats exhibit ultradian plasma catecholamine rhythms. Four rats were prepared with chronic venous cannulas. After recovery, blood was sampled every 15 min for 8 h. Spectrum analysis revealed ultradian norepinephrine rhythms with spectral peaks around 80-90 min and around 40 min. However, no reliable ultradian rhythms were found for epinephrine. Ultradian norepinephrine rhythms appeared to be synchronized across three of the four rats, suggesting that the rhythm can be synchronized by some environmental stimulus. Thus, rats exhibit ultradian norepinephrine rhythms similar to those found in humans and in rhesus monkeys, indicating (a) that laboratory rats can be used to study the biological mechanisms of ultradian rhythms and (b) that ultradian oscillations of sympathetic function are a common property of mammalian systems.

Animals↗