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Biomedical subjects

B H Natelson

Publications and source records attributed to B H Natelson.

At least 127 records · Page 7Linked 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

Methodological problems in the study of classical aversive conditioning of adrenocortical responses.

The present studies were conducted to demonstrate classical aversive conditioning of a corticosterone stress response in male rats. In the first experiment animals exposed to an odor which had previously preceded tube restraint stress had significantly higher plasma corticosterone levels than animals which were probed with a novel odor, or animals in which stress was followed, rather than preceded, by the odor. Careful consideration of corticosterone responses obtained on different days during training made it impossible to conclude unequivocally that learning had occurred. A second experiment was designed specifically to deal with the problems raised by the first, but we were again unable to show rigorously that learning had taken place. However, with data and paradigms comparable to our own, other researchers have prematurely concluded that aversive visceral conditioning can occur. It is suggested that the methodological considerations raised in the present studies could also be important for interpreting other experiments. Given the classical importance ascribed to learning components in many psychosomatic pathologies, future experiments are necessary to determine if stress responses can be classically conditioned, but they must be more rigorously designed than in the past.

Adrenal Cortex↗
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

Neurocardiology. An interdisciplinary area for the 80s.

This review focuses on the relations between neural structures and the heart in the pathogenesis of severe cardiac dysfunction (namely, cardiac arrhythmias, focal cardiac lesions, and the sudden death syndrome). After establishing the anatomic connections between the brain and the heart and then reviewing ways to assess the integrity of nerves to the heart, the clinical literature relating human brain dysfunction to cardiologic problems is reviewed. Next the experimental literature is briefly reviewed. The organization of the information is based on whether or not the heart of the experimental animal is normal as well as on the part of the nervous system involved (ie, either central or peripheral). In addition, since the effect of environmental stress on cardiac dysfunction must be modulated via the brain, the review is briefly extended to examine the role of stress in the production of severe cardiac dysfunction in people as well as animals.

Animals↗
PubMed1985

Daily feeding schedule and housing on incidence of activity-stress ulcer.

In Experiment 1 the number and size of ulcers resulting from exposure to an activity-stress procedure were inversely related to the length of the pre-stress experience with either 1 hr or 2 hr daily feeding schedules. In Experiment 2, rats housed in group cages during the pre-stress period were more vulnerable to the ulcerogenic effects of the activity-stress procedure. A pellet food or powdered food treatment condition failed to provide significant group differences. Vulnerability to stress-ulcer is discussed in terms of the disparity of the environmental conditions between the acclimation period and the activity-stress period.

Animal Feed↗
PubMed1985

Visceral predictors of cardiovascular deconditioning in late middle-aged men.

A major task for space biologists is to try to delineate methods which can be used to predict the degree of cardiovascular deconditioning that given individuals might develop while in space. Toward that end, we have studied a number of different visceral and behavioral variables in a group of late middle-aged men (55-65 years) on day 1 and day 5 of a bedrest regimen. During each 8-h study period, data were collected every 15 min. Mean arterial blood pressure and plasma cortisol and norepinephrine concentrations were significantly higher on the day 5 than on the day 1 of bedrest; heart rate, core temperature, plasma epinephrine and subjective arousal were unchanged. Pair-wise correlations between each of these variables and the time to blackout on a +3-Gz test of acceleration tolerance administered on day 9 of bedrest (mean decrease in latencies from prebedrest was 52%) revealed a significant correlation for the mean arterial blood pressure variable. Thus, these data indicate that men in this age span with relatively low resting blood pressures are at greater risk for developing clinical signs relating to their cardiovascular deconditioning than other men with higher basal blood pressures.

Acceleration↗
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↗
PubMed1984

Effects of stellectomy on cardiac rhythm disturbances induced by ouabain in guinea pigs.

The purpose of this study was first to provide further data on the role of the sympathetic nervous system in the pathogenesis of ventricular arrhythmias produced by digitalis administration and also to ascertain whether the left or right stellate ganglia had diverse effects on arrhythmogenesis. To do this, we subjected alpha-chloralose-anesthesized guinea pigs to either right, left, bilateral or sham stellectomy and then infused ouabain until death under constant ECG monitoring. Only guinea pigs with right stellectomy showed a significant change (i.e., increase) in Q-Tc interval when compared with sham-operated controls. The increased Q-Tc interval seen in the right stellectomized group did not change during ouabain infusion whereas it became significantly shorter in shams and in left and bilateral stellectomized pigs. The right stellectomized animals were sensitized to the toxic effects of ouabain whereas, conversely, left and bilateral stellectomized animals were protected. Cause of death also varied with left and bilateral stellectomized animals dying of cardiac asystole and right stellectomized animals of cardiac fibrillation. These anatomic ablation experiments 1) confirm the earlier concept based on pharmacological and neurophysiological work that the sympathetic nervous system plays an important role in the initiation of digitalis-induced arrhythmias; 2) make the point that the arrhythmic trigger works preponderantly through the left stellate; and 3) suggest that use of digitalis in patients with the long Q-T syndrome may put them at further risk of developing arrhythmias.

Animals↗