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Biomedical subjects

R M Thornton

Publications and source records attributed to R M Thornton.

18 recordsLinked to original sources
PubMed1998

Effects of electrical stimulation on edema formation in different strains of rats.

BACKGROUND AND PURPOSE: Although electrical stimulation (ES) is commonly used to curb edema formation, efficacy has been demonstrated in only one species of frog and one strain of rat. The purpose of this study was to determine whether different strains of rats respond differently to ES. SUBJECTS AND METHODS: Feet of Sprague-Dawley, Zucker-Lean, and Brown Norway rats were injured in a uniform manner. One foot served as a control, and the other foot received four 30-minute exposures to cathodal high-voltage pulsed current at amplitudes 10% less than those required to induce visible muscle activity. Each treatment period was followed by a 30-minute rest period. Limb volumes were measured before and after trauma and after each treatment and rest period. Changes from pretrauma volumes were analyzed by repeated-measures analysis of variance. RESULTS: Edema formation was curbed in Zucker-Lean and Brown Norway rats but not in Sprague-Dawley rats. CONCLUSION AND DISCUSSION: The finding that two of the three strains of rats responded to ES suggests that some strains of rats may be suitable models for the study of edema. That frogs and rats respond to high-voltage pulsed current suggests that humans might respond similarly.

Animals↗
PubMed1997

Effects of cold water immersion on edema formation after blunt injury to the hind limbs of rats.

OBJECTIVE: Despite the long history of using cryotherapy to control edema, we found no randomized, controlled studies providing evidence to substantiate this common clinical practice. The purpose of this study was to determine whether cold water immersion affects edema formation following blunt injuries in rats. DESIGN AND SETTING: The feet of 16 rats were traumatized after hind limb volumes were determined. Four 30-minute treatments of cold water immersion (12.8 degrees C to 15.6 degrees C, 55 degrees F to 60 degrees F), interspersed with four 30-minute rest periods, began immediately after trauma to one randomly selected hind limb of each rat. The limb remained in a dependent position during all treatments, rest periods, and volumetric measurements. SUBJECTS: Sixteen anesthetized Zucker Lean rats were used in the study. MEASUREMENTS: Limb volumes were measured after each treatment and rest period for a total of 4 hours. RESULTS: The volume of treated limbs was significantly smaller (p < .05) than the volume of untreated limbs after the first treatment and remained smaller throughout the experiment. CONCLUSIONS: Immersing rat limbs in 12.8 degrees C to 15.6 degrees C (55 degrees F to60 degrees F) water immediately after blunt injury was effective in curbing edema formation.

Journal Article↗
PubMed1989

Vasopressin contributes to maintenance of arterial blood pressure in dehydrated baboons.

This study primarily sought to determine whether the role of vasopressin (VP) in maintenance of arterial blood pressure is enhanced in awake, chronically instrumented baboons after 68-72 h of dehydration. This question was approached by pharmacologically blocking vasopressin V1-receptors in euhydrated and dehydrated baboons with or without a normally functioning renin-angiotensin system (RAS). VP blockade during dehydration produced a rapidly occurring (within 5 min), statistically significant (P less than 0.05) decrease in mean arterial pressure (MAP) of 5 +/- 1 mmHg in the RAS-intact condition and an identical decline in MAP (5 +/- 1 mmHg) during blockade of the RAS by captopril, an angiotensin I-converting enzyme inhibitor. At 15 min after induction of VP blockade, heart rate was elevated by 9 +/- 2 beats/min in the RAS-intact condition and by 20 +/- 5 beats/min in the RAS-blocked condition. In addition, VP blockade in the dehydrated state produced small and equal increases in hindlimb vascular conductance in RAS-intact and RAS-blocked conditions. None of these cardiovascular changes were produced by VP blockade in the euhydrated state. RAS blockade produced modest declines in MAP in both hydration states, but the fall was larger by 7 +/- 4 mmHg in the dehydrated state. Thus both VP and the RAS contribute to the maintenance of arterial blood pressure during dehydration in the conscious baboon.

Animals↗
PubMed1989

Hemodynamic effects of arginine vasopressin in rats adapted to chronic hypoxia.

Acute and chronic pulmonary and systemic hemodynamic responses to arginine vasopressin (AVP) were examined in 4-wk hypoxia-adapted and air control rats. AVP, administered intravenously as bolus injections or sustained infusions, produced major dose-dependent V1-receptor-mediated reductions in mean pulmonary arterial pressure in hypoxia-adapted rats. These effects were comparable in pentobarbital-anesthetized, thoracotomized animals and in conscious, intact rats. Chronic infusions of AVP induced a sustained reduction in mean pulmonary arterial pressure and partially prevented the development of pulmonary hypertension without changing systemic arterial pressure. AVP induced significant decreases in cardiac output in both groups; the cardiac output response was not significantly different in hypoxia-adapted and air control animals. AVP induced almost no change in MPAP in air control rats. Furthermore the systemic pressor effects of AVP were significantly blunted in hypoxia-adapted rats compared with air controls. We conclude that the pulmonary depressor and blunted systemic pressor effects of AVP observed in hypoxia-adapted rats may be related to release of a vasodilator, such as endothelium-derived relaxing factor, vasodilator prostaglandins, or atrial natriuretic peptides. Further study is needed to elucidate these mechanisms and assess the usefulness of AVP and/or its analogues in the treatment and prevention of hypoxia-induced pulmonary hypertension.

Adaptation, Physiological↗
PubMed1989

Impaired reflex response to volume expansion in NaCl-sensitive spontaneously hypertensive rats.

Abnormal baroreceptor reflex function that antedates or is a consequence of NaCl loading could contribute to the NaCl-induced exacerbation of hypertension in NaCl-sensitive spontaneously hypertensive rats (SHR-S). The current study tested the hypothesis that an impairment in cardiopulmonary baroreceptor reflex function exists in SHR-S before NaCl loading. The reflex response to volume expansion was compared in SHR-S, NaCl-resistant SHR (SHR-R), and normotensive Wistar-Kyoto (WKY) and Sprague-Dawley rats maintained on a normal NaCl diet. Conscious, free-moving SHR-S, SHR-R, WKY, and Sprague-Dawley rats were volume expanded with whole blood to 15% of blood volume within 6 minutes, and mean arterial pressure, heart rate, and lumbar sympathetic nerve activity were recorded. Heart rate and lumbar sympathetic nerve activity decreased significantly in SHR-R, WKY, and Sprague-Dawley rats after volume expansion. In contrast, in SHR-S neither heart rate after volume expansion nor lumbar sympathetic nerve activity was significantly different from levels before volume expansion. The blunted reflex response of heart rate and lumbar sympathetic nerve activity to volume expansion suggests impaired cardiopulmonary volume receptor function in SHR-S. This likely contributes to NaCl-induced hypertension in SHR-S on a high NaCl diet.

Animals↗
PubMed1988

Influence of vasoconstrictor systems on leg vasodilation during heating of dehydrated baboons.

This study, carried out in two parts, sought to determine the importance of vasopressin (VP), the renin-angiotensin system (RAS), and the sympathetic nervous system in the dehydration-produced attenuation of hindlimb (cutaneous) vasodilation during environmental heating (EH). Baboons, chronically instrumented for blood sampling and for measurement of mean iliac blood flow (MIBF), arterial pressure, and core temperature (Tc), were subjected to EH while in euhydrated and dehydrated (64-72 h of water deprivation) states. EH consisted of exposure to an elevated ambient temperature (40-42 degrees C) until Tc reached 39.5 degrees C. In part I, indexes of the above vasoconstrictor systems were measured. Base-line plasma renin activity (PRA) and VP and norepinephrine concentrations were all significantly elevated by dehydration. In addition, the increase in PRA during EH was accentuated by dehydration. In part II, the effects of blockades of the RAS, the pressor action of VP, and the innervation of the hindlimb on hindlimb vasodilation during EH were assessed. None of these blockades, singly or together, reversed the dehydration-produced attenuation of the increase in MIBF during EH. Thus we conclude that other mechanisms are responsible for the dehydration-produced attenuation of cutaneous vasodilation in baboons during EH.

Animals↗
PubMed1988

Influence of dehydration on locally mediated hindlimb vasodilation in baboons.

Previous studies indicate that the heat stress-induced cutaneous vasodilation in baboons is attenuated during dehydration by mechanisms other than the well-known neurohumoral vasoconstrictor mechanisms. Therefore, this study sought to determine whether dehydration also attenuates locally mediated maximum hindlimb blood flow and vascular conductance in baboons. Five baboons were chronically instrumented to measure arterial blood pressure and mean external iliac artery blood flow (MIBF). Hindlimb vasodilation was induced by occlusions of the external iliac artery for 2.5, 5.0, 7.5, and 10.0 min and by close-arterial injections of acetylcholine (ACh) and sodium nitroprusside (NP) in graded doses. These vasodilatory stimuli were applied in euhydrated and dehydrated states, the latter being produced by water deprivation for 64-68 h. Maximum MIBF and iliac vascular conductance (IVC) after arterial occlusion were reduced by 67-70% during dehydration. Also, maximum MIBF and IVC produced by ACh in the dehydrated state were 46-52% lower than in the euhydrated state. A similar reduction in the responses to NP occurred during dehydration. It is concluded that the maximum hindlimb blood flow and vascular conductance produced by local, nonneurohumoral mechanisms are attenuated in the baboon during dehydration.

Acetylcholine↗
PubMed1988

Enhanced cold pressor response in spontaneously hypertensive rats on high-NaCl diet.

This study sought to determine whether spontaneously hypertensive rats (SHR) on a high-NaCl diet have an enhanced pressor response to acute cold exposure and to define the peripheral mechanisms involved in the enhanced pressor response. SHR and normotensive Wistar-Kyoto (WKY) rats that had been on 1 and 8% NaCl diets for 3 wk were subjected to cold exposure. After a 30-min control period, animals were exposed to cold (6 +/- 2 degrees C) for 90 min. Mean arterial pressure (MAP), heart rate (HR), and lumbar sympathetic nerve activity (LSNA) were measured continuously. In a separate group of SHR on 1 and 8% NaCl diets, an arginine vasopressin (AVP) V1 receptor antagonist (10 micrograms/kg iv) was given before cold exposure, and MAP was measured throughout cold exposure. Plasma AVP was measured before and during cold exposure in a separate group of SHR. During cold exposure, there was a significant increase (P less than 0.05) in MAP (25 mmHg) in SHR on the 8% NaCl diet only. In contrast, HR and LSNA increased similarly during cold exposure in both SHR and WKY on the two diets. AVP was similar in both SHR groups (7.1 pg/ml for 1% vs. 6.1 pg/ml for 8%) before cold exposure, but during cold exposure it increased in the 8% NaCl SHR only, reaching 17.6 pg/ml at 90 min. The AVP V1 antagonist completely abolished the cold stress-induced rise in MAP in SHR. Thus SHR on a high-NaCl diet have an enhanced pressor response to acute cold exposure compared with SHR on a normal NaCl diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Atrial natriuretic peptide lowers pulmonary arterial pressure in hypoxia-adapted rats.

To test the hypothesis that atrial natriuretic peptide (ANP) has a direct vasodilator effect on the pulmonary vasculature that is enhanced in hypoxia-induced pulmonary hypertension in the rat, we determined the effects of ANP on mean pulmonary (MPAP) and systemic arterial pressure (MSAP) in intact conscious Sprague-Dawley rats exposed to 10% O2 or room air for 4 wk. Catheters were placed in the pulmonary artery through the right jugular vein by means of a closed-chest technique. MPAP and MSAP were monitored before and after intravenous injections of graded doses of ANP. ANP produced dose-related decreases in MPAP that were greater in the hypoxic group than in air controls. There were no significant between-group differences in the systemic depressor responses to ANP or in the ANP-induced reduction in cardiac output. ANP lowered MPAP significantly in isolated perfused lungs from both hypoxia-adapted and air control rats, and this effect was significantly greater in the hypoxic than the air control lungs. These data indicate that ANP lowers pulmonary arterial pressure in rats with hypoxia-induced pulmonary hypertension, mainly by a direct vasodilator effect on the pulmonary vasculature.

Animals↗
PubMed1986

Attenuation of hindlimb vasodilation in heat-stressed baboons during dehydration.

The influence of dehydration on hindlimb vasodilation during environmental heating (EH) was examined in eight unanesthetized chronically instrumented baboons. Mean iliac blood flow (MIBF), arterial blood pressure, and core temperature (Tc) were measured during EH of baboons in euhydrated and dehydrated states. EH consisted of acute exposure to high ambient temperatures (39-44 degrees C) until Tc reached 39.5 degrees C. Dehydration was produced by 68-72 h of fluid deprivation, which caused increases in plasma osmolality [291 +/- 1 (SE) to 338 +/- 6 mosmol/kg H2O] and sodium concentration (143 +/- 2 to 163 +/- 3 meq/l) and a 16% fall in plasma volume. The primary influence of dehydration was attenuation of the progressive rise in MIBF and iliac conductance (IC) during EH. Absolute MIBF and IC levels at Tc = 39.5 degrees C during EH were 44 and 52%, respectively, lower in the dehydrated state. Also, the MIBF-Tc and IC-Tc linear regression coefficients during EH were lower by 33 and 43%, respectively, in the dehydrated state. Since limb skeletal muscle blood flow does not increase during EH, we conclude that dehydration attenuates the heat stress-induced rise in skin blood flow in baboons, an influence that is similar to what occurs in humans.

Animals↗
PubMed1984

Oxygen storage capacity and tolerance of submergence of a non-aquatic reptile and an aquatic reptile.

The oxygen storage capacities and the tolerance to submergence of an aquatic snake, Natrix sipedon, and a non-aquatic snake, Crotalus viridis, were determined and compared. C. viridis was found to have a larger oxygen storage capacity, hemoglobin content and blood volume than N. Sipedon. The submergence time for C. viridis was 30.13 min which was less than the estimated time for submergence based on the oxygen storage capacity. N. sipedon exceeded its estimated dive time of 24.00 min and remained submerged for 65.57 min without signs of stress. During submergence, the heart rate of N. sipedon fell to 9% (5 beats/min) of the resting rate, while the heart rate of C. viridis fell to only 75% (27 beats/min) of the resting rate during this activity. These data indicate that N. sipedon responds to submergence via a typical diving reflex and extends its oxygen stores beyond that expected of a non-diver such as C. viridis.

Animals↗
PubMed1983

Pure red cell aplasia obscured by a diagnosis of carcinoma.

Three cases of pure red cell aplasia (PRCA) associated with carcinoma, previously considered a rare paraneoplastic syndrome, are reported. Two cases responded to steroid therapy. In two the diagnosis of PRCA was obscured by the carcinoma until bone marrow examination revealed the true cause of the anemia. These three cases once again support routine bone marrow examination to determine the cause of anemia, regardless of other medical problems.

Aged↗
PubMed1973

New photoresponses of phycomyces.

The influence of light on asexual fruiting and mycelial growth of Phycomyces blakesleeanus Burgeff was studied by means of fruiting body counts and size measurements in cultures on solid media under varied incubation conditions. Five types of photoresponses were shown by ATCC Strain 8743a: (a) photoinduction of giant sporangiophores; (b) interference by light with an endogenous system that otherwise induces fruiting when the mycelium approaches the rim of the Petri dish; (c) inhibition of mycelial growth rates by light; (d) inhibition of dwarf sporangiophore induction by light; and (e) postponement by light of death in clones maintained by serial transfer at low temperature. A second strain, designated G5, showed responses comparable to (a), (b), and (d). The magnitudes of the responses were greatly affected by temperature of incubation and available nitrogen (asparagine) supply. The photoinduction of giant sporangiophores could be demonstrated with light of wavelengths between 380 and 480 nanometers but not with 520 nanometers or above. At 480 nanometers, light doses as small as 40 ergs per square centimeter were effective in inducing giant sporangiophores in strain 8743a.

Journal Article↗
PubMed1972

Alternative fruiting pathways in phycomyces.

Developmental distinctions between giant and dwarf fruiting bodies of Phycomyces blakesleeanus (Burgeff) were studied by means of size measurements and growth analyses. Histograms of fruiting body lengths showed a bimodal distribution, with peaks around 0.3 millimeter (dwarfs) and 30 millimeters (giants). Individual cultures contain both giants and dwarfs. Differences between giants and dwarfs appear in the first phase of development; the apex of the giant is tapered, whereas the dwarf apex is dome-shaped. Probable cytological distinctions at this stage are cited in discussion. The dwarfs terminate enlargement upon expansion of the sporangium, thus lacking the subsequent phase of rapid elongation (stage IV) that contributes 90% of the length in the case of giants. It was concluded that P. blakesleeanus maintains two developmental patterns for asexual fruiting, with dwarfs and giants differing radically in growth regulation.

Journal Article↗
PubMed1969

Crystalloids of phycomyces sporangiophores: nature and photosensitive accumulation.

Crystalloids accumulate in the vacuoles of the giant sporangiophores of Phycomyces blakesleeanus Burgeff during growth. On the basis of solubility in alkaline solutions, cytochemical staining reactions, trypsin sensitivity, optical absorption and response in the Lowry protein test, the crystalloids have been judged to consist principally of an acidic protein. In assays by Lowry test and by reference to optical absorption at 280 mmu, dark-grown sporangiophores were consistently found to contain from 2 to 4 times as much crystalloid material as light-grown counterparts. Concurrent assays of soluble phenolic materials revealed no significant effect of culture illumination, while carotene content of sporangiophores and mycelium was found to be raised from 2 to 4-fold by illumination during growth.

Journal Article↗
PubMed1967

Transient effects of light on auxin transport in the Avena coleoptile.

The transport of indole-3-acetic acid-1-(14)C (IAA) through 4 mm segments of etiolated Avena coleoptiles was studied as a function of time by applying IAA in apical agar blocks and measuring the basal IAA export rate at 5-minute intervals. The transport velocity found in this way is at least 15 mm/hour at 26 degrees . Following a 30-minute equilibration period, the export rate is nearly constant for at least 50 minutes at physiological donor concentrations. Exposure to about 3 x 10(5) ergs/cm(2) blue light for 15 minutes leads to a transient reduction in the export. The export rate reaches a minimum about 25 minutes after the onset of illumination, then rises to reach a maximum by 35 minutes, and subsequently declines again. The result is a net export depression during the first 80 minutes, amounting to some 12 to 17%. Its timing closely matches the timing of the light growth response elicited by the same light dosage.At higher IAA concentrations (0.5 and 1.8 mg/l), the export rate reaches a peak about 60 minutes after the initial application of auxin, and thereafter declines rapidly. Light increases this decline in export rate, without causing peaks and troughs, and even at 0.25 mg/l IAA the transient changes in export appear to be superimposed on a gradual decline in export rate after illumination. Blue light is effective in all these phenomena; the red far-red system appears to exert no effect. The results are discussed in relation to the mechanism of action of light both in the light growth response and in phototropism.

Journal Article↗