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Biomedical subjects

D G Baker

Publications and source records attributed to D G Baker.

At least 145 records · Page 8Linked to original sources
PubMed1980

Search for a cardiac nociceptor: stimulation by bradykinin of sympathetic afferent nerve endings in the heart of the cat.

1. We have examined the effect of bradykinin on impulse traffic in sympathetic afferent fibres from the heart, great vessels and pleura, and have attempted to identify cardiac nociceptors that on the basis of their functional characteristics might have a role in the initiation of cardiac pain. 2. In anaesthetized cats, we recorded afferent impulses from 'single-fibre' slips of the left 2nd--5th thoracic rami communicantes and associated chain, and selected fibres arising from endings in the heart, great vessels, pericardium and pleura. We applied bradykinin solution (0 . 1--1 . 0 microgram/ml.) locally to the site of the ending; we also injected bradykinin (0 . 3--1 . 0 microgram/kg) into the left atrium. 3. Afferent endings excited by bradykinin (159 of 191 tested) were of two types. The larger group (140) were primarily mechanoreceptors with A delta of C fibres (mean conduction velocity, 7 . 5 +/- 0 . 6 m/sec). They were very sensitive to light touch. Those located in the heart, great vessels or overlying pleura had a cardiac rhythm of discharge and were stimulated by an increase in blood pressure or cardiac volume. 4. Bradykinin increased mechanoreceptor firing from 0 . 7 +/- to 5 . 0 +/- 0 . 3 (mean +/- S.E. of mean) impulses/sec. Some endings appeared to be stimulated directly by bradykinin, others sensitized by it so that they responded more vigorously to the pulsatile mechanical stimulation associated with the cardiac cycle. 5. The smaller group of eighteen endings, of which ten were in the left ventricle, were primarily chemosensitive. Most had C fibres, a few had A delta fibres (mean conduction velocity, 2 . 3 +/- 0 . 7 m/sec). They were insensitive to light touch. With one exception they never fired with a cardiac rhythm, and even large increases in aortic or left ventricular pressure had little effect on impulse frequency. 6. Chemosensitive endings were stimulated by bradykinin, impulse activity increasing from 0 . 6 to 15 . 6 +/- 1 . 3 impulses/sec and remaining above the control level for 1-3 min. The evoked discharge, which was either continuous or occurred in irregular bursts, was not secondary to mechanical changes in the heart and great vessels. 7. Tachyphylaxis occurred when the interval between successive applications of bradykinin was 20 min or less. It was a feature of the response of both mechanosensitive and chemosensitive endings. 8. Because of their responsiveness to changes in pressure and their sensitivity to light touch, the mechanosensitive endings appear to be unlikely to subserve a primarily nociceptive function, although they may be responsible for evoking some of the components of the pseudoaffective response. By contrast, the chemosensitive endings appear well fitted to act as cardiac nociceptors.

Action Potentials↗
PubMed1980

Bradykinin stimulates afferent vagal C-fibers in intrapulmonary airways of dogs.

Bradykinin is released in the lungs in asthma and pulmonary anaphylaxis. It has negligible direct bronchoconstrictor effects in humans or dogs, but inhaled as aerosol it causes cough and reflex bronchoconstriction in asthmatics and some normal subjects. The afferent nerves responsible for these reflex effects have not been identified. We recorded vagal impulses in anesthetized dogs to determine whether lung afferents were stimulated by bradykinin. C-fiber endings in the intrapulmonary airways accessible from the systemic circulation were stimulated by bradykinin injected into the left atrium (0.5-1.0 micrograms/kg) or bronchial artery (1.5 micrograms), activity increasing 15-fold on average. C-fiber endings accessible from the pulmonary circulation were relatively insensitive to bradykinin. Bradykinin caused a small increase in firing of some rapidly adapting (irritant) receptors, but the effect appeared to be secondary to vascular changes. Bradykinin had variable effects on slowly adapting stretch receptors, but did not stimulate them directly. Thus vagally mediated sensory or reflex effects initiated by bradykinin in the lung are probably due to stimulation of "bronchial" C-fibers.

Action Potentials↗
PubMed1980

Response of mouse kidney to hyperthermia: pathology and temperature--dependence of injury.

Hyperthermia either alone or in combination with radiotherapy and chemotherapy is being used increasingly in the treatment of malignant tumors. This study was designed to evaluate the response of the mouse kidney exposed to a range of hyperthermic temperatures (41 to 45 degrees C) used to induce regression of malignant tumors. Minimal histologic evidence of renal injury occurred in the proximal tubules of the subcapsular region. More extensive damage was characterized by necrosis of tubules and glomeruli in a sharply circumscribed area that involved the lateral subcapsular area where the temperature induced was highest. The tissue histologic reaction was maximal by 24 hours. At temperatures below 41 degrees C no necrosis occurred, whereas at temperatures between 42 and 45 degrees C there was an increasing incidence of necrosis. This increase in tissue reaction above 42 to 43 degrees C is consistent with reported observations from tissue culture and in vivo skin heating experiments, and indicates that normal tissue injury may occur in the same range of temperatures shown to cause regression in malignant tumors.

Animals↗
PubMed1980

Carotid sinus nerve efferents: properties and physiological significance.

The significance of a sympathetic efferent nerve supply, vasoconstrictor to the carotid body and hence facilitatory to carotid chemoreceptors, is well understood. The significance of a second efferent pathway, whose impulses, passing down the sinus nerve, are inhibitory to the chemoreceptors, is less certain. Activity in these sinus nerve efferents is increased by injection of pressor agents, by hypoxia, by hypercapnia, by application of alkaline solutions to the ventral medulla, and by severe hypocapnia. All these stimuli appear to act centrally. Sinus nerve efferents can also be activated reflexly by stimulating ipsilateral carotid chemoreceptors. The mechanism of efferent inhibition is disputed. A purely cholinergic vasodilator role is unlikely because inhibitory effects are abolished by alpha-adrenergic antagonists. Sinus efferents probably cause release of an inhibitory transmitter, dopamine, but convincing evidence for a releasing mechanism has yet to be obtained. Stimulation of nociceptive endings in the heart has reciprocal effects on sinus nerve efferents and sympathetic efferents to the carotid body, inhibiting the former and stimulating the latter. Recent results are cited which indicate that the responses of sinus nerve efferents to changes in blood pressure are more variable than is generally believed, and that the conventional explanation of the relationship between sinus efferent activity and arterial pressure needs to be revised.

Animals↗
PubMed1979

The use of 2450 megahertz of microwave in cancer therapy; a pilot study.

Contraindications to microwave diathermy traditionally include malignant tumors. This paper describes a pilot study of tissue hyperthermia treatment (average 42.5 degrees C, 108.5 degrees F) for superficial cancers, using 2450 megahertz of microwave diathermy. Tissue temperatures were recorded for prolonged periods of time, and tumor responses to heat alone, or to heat combined with radiation therapy, were observed. Such treatments were tolerated by the patients, but were not without side effects. Preliminary results of this pilot study, as well as those of other investigators, showed that tissue hyperthermia would be a useful treatment modality for cancer therapy. The familiarity of physical therapists with microwave diathermy may be an asset to them as clinicians. Physical therapists, however, should not attempt to treat cancer patients alone. Further clinical research in the area should be conducted in the proper setting under the guidance of an oncologist.

Body Temperature↗
PubMed1979

Factors affecting the physical performance of the rat in hyperbaric environments.

Experiments were designed to partition the effect of inspired oxygen tension (PIO2), gas density (rho), and ambient pressure (P) at rest and during exercise in rats. At rest oxygen uptake (VO2) was reduced by 19.5% (P less than 0.01) in 3 ATA air and by 32.1% (P less than 0.01) in 10 ATA air from 1 ATA air control of 29.3 +/- 1.21 (SE) ml/min.kg; there was no difference in VO2 between 1, 3, and 10 ATA He mixtures containing 20% O2. During exercise, VO2 was depressed by 36.2% (P less than 0.01) in 3 ATA air from 1 ATA air value of 55.3 +/- 3.23 ml/min.kg; VO2 was unaffected in 3 ATA He containing 20% O2 as compared to that of 46.5 +/- 2.43 ml/min.kg at 1 ATA He-O2 ambient. These VO2 values were compared to that obtained from normoxic ambients for separation of effects of elevated PIO2, P, and rho on VO2 at rest and during exercise. The effect of PIO2 was deduced by comparing VO2 in normoxic and hyperoxic He and N2 at a given P and rho. The density effect was obtained by comparing the VO2 in various densities at a given P and PIO2. The P effect was obtained by comparing the VO2 in various ambient pressures at a given rho and PIO2. Summation of the effects of P, rho, and PIO2 sufficiently approximates the changes in VO2 at rest. The same procedure underestimates the actually measured VO2 in all N2 ambients.

Air Pressure↗
PubMed1979

Immunonephelometric assay for urinary total protein and albumin in mice.

A quantitative immunonephelometric assay for measuring total protein and albumin in mouse urine has been developed. Antisera to whole mouse sera or to mouse albumin was added to aliquots of urine and the antigen-antibody complexes formed were measured by laser nephelometry. Sample volumes were small (20 microliters) and the assay time was 90 minutes. The assays were sensitive to 10 mg/L and within-day and day-to-day precision studies demonstrated coefficients of variation of less than 15%. Average urinary total protein and albumin concentrations for random urine specimens in female C3H mice (age 80-150 days) were 42 and 24 mg/L respectively. Urinary total protein and albumin to creatinine ratios were also determined.

Albuminuria↗
PubMed1979

Absence of antiarrhythmic effects of helium in patients with spontaneous premature ventricular beats at rest.

Six patients with spontaneously occurring arrhythmias were studied to assess the antiarrhythmic properties of helium. The patients were divided into two subgroups breathing air, helium-oxygen (heliox), and nitrogen-oxygen (nitrox) in an alternating sequence during successive 20-min periods under continuous ECG surveillance at rest. There were no significant reductions in spontaneously occurring premature ventricular beats while breathing heliox, compared to breathing air of nitrox. Alternating the breathing gases in this manner caused no change in plasma concentration of electrolytes or in activity of serum glutamic-oxaloacetic transaminase or lactic acid dehydrogenase. We conclude that helium does not affect spontaneously occurring chronic premature ventricular beats in conscious resting man when it is breathed for a period of up to 20 min.

Adult↗
PubMed1977

Influence of a chronic environmental stress on the incidence of methylcholanthrene-induced tumors.

The influence of a chronic environmental stress, living in a 2 degrees environment, on the incidence of methylcholanthrene-induced tumors in albino female Simonsen rats, a Sprague-Dawley-derived strain, was studied. The results indicated that the metabolic rate was double for rats kept at 2 degrees, compared with those kept at 25 degrees. Exposure to 2 degrees for life, with no other treatment, reduced median life expectancy to 560 days compared with 686 days for rats kept at 25 degrees. Transfer to a 2 degrees environment after 250 days at 25 degrees reduced the incidence of spontaneous tumors, while transfer to 25 degrees after 250 days at 2 degrees increased the incidence of tumors compared to that for rats always kept at 25 degrees. Exposure to an environmental temperature of 2 degrees immediately following a carcinogenic stimulus (3-methylcholanthrene, 2 mg s.c.) significantly reduced the incidence of tumors compared to that in rats kept at 25 degrees but did not change tumor induction time. The reduced tumor incidence may have resulted from inhibition of the carcinogenic transformation by chronic stress. The survival time of rats with 3-methylcholanthrene induced tumors was not significantly less in a 2 degrees environment than it was at 25 degrees.

Animals↗
PubMed1976

Effects of head-out water immersion on cardiorespiratory responses to maximal cycling exercise.

Our objectives were to determine effects of head-out immersion (HOI), scuba breathing, and water temperature on cardiorespiratory responses to maximal aerobic work. Measurements of VO2, VE, and heart rate (HR) were obtained on seven men (27 yr, 177 cm, 67 kg) as they performed the same upright bicycling exercise to exhaustion (4-5 min) in 23 degrees C air and 30 degrees C water. Maximal oxygen uptake (VO2 max) during HOI was 3.18 liters - min-1, which was not statistically different from the mean of 3.29 liters- min-1 in air. When compressed air was breathed via scuba during HOI, VO2 max was 3.12 liters- min-1 and not significantly different from that when room air was breathed and a low-resistance valve in water was used. HOI decreased VE by 15.7 liters - min-1 and HR by 10 beats (b) - min-1. Scuba breathing further reduced VE by 22.0 liters - min-1. Similar measurements were made on four of the subjects after 18 min of HOI in water temperatures of 35,30, and 25 degrees C. Water temperature had no significant affect on VO2 max, although HR was 8 b- min-1 lower in 30 degrees C and 15 b - min-1 lower in 25 degrees C as compared to 35 degrees C water. The results show that VO2 max was not significantly changed by HOI, scuba breathing, or brief exposures to 25, 30, and 35 degrees C water, despite significant reductions that occurred for VE and HR.

Adult↗