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At least 685 records · Page 38Linked to original sources
PubMed1979

Effects of chemoreceptor stimulating agents on reflex bradycardia.

Effects of carotid body chemoreceptor stimulation on reflex bradycardia were studied by injecting various pharmacological and physiological agents into the external carotid artery of rabbits. Reflex bradycardia was induced by ACh and nicotine in doses from 3 micrograms to 10 micrograms. The response to ACh was markedly potentiated by physostigmine and small doses of atropine, while it was completely blocked bymecamylamine and a large dose of atropine. The nicotine-induced bradycardia was also inhibited by mecamylamine and a large dose of atropine. After reserpinization, the responses to ACh and nicotine were depressed, but were elicited by increasing the doses. NaCN, low pH solution and high CO2 saline induced weaker bradycardiac responses which were not affected by atropine and mecamylamine, but were abolished in the reserpinized animals. The results indicate possible participation of dopamine in the chemoreceptor transmission.

Acetylcholine↗
PubMed1973

The significance of the timing of chemoreceptor impulses for their effect upon respiration.

Alveolar partial pressure of carbon dioxide (PACO2) and alveolar partial pressure of oxygen (PAO2) oscillate at the frequency of respiration and the oscillations persist into the arterial blood as oscillations of arterial partial pressure of carbon dioxide (PaCO2) and arterial partial pressure of oxygen (PaO2). Arterial chemoreceptors respond quickly enough to changes in PaCO2 and PaO2 for the arterial oscillations to give rise to oscillations in their afferent discharge at the frequency of respiration. The respiratory centre responds with short latency to afferent impulses reaching it. If a burst of impulses reaches it during an inspiration, the depth of that inspiration, is increased but if the burst arrives during expiration, the succeeding inspiration is little affected. Thus if the peaks of chemoreceptor afferent discharge coincide with inspiration, they have a greater effect on respiration than if they coincide with expiration. The phase relation between the activity of the respiratory centre and the oscillations it produces is determined, inter alia, by the frequency of respiration and the heart output. Thus it may well change in exercise.

Animals↗
PubMed1980

Intracarotidal injection of beta-adrenergic blocking agents: variations in the carotid sinus baro- and chemoreceptor activity.

The intracarotidal injection of some bet-adrenergic blocking agents (dl-acebutolol, dl-, l-, d-alprenolol, dl-bunitrolol, dl-buthoxamine, dl-, l-, d-INPEA, dl-Ko 592, dl-metoprolol, dl-oxprenolol, dl-propranolol, dl-tolamolol) in anesthetized and bivagotomized dogs reduced the arterial blood pressure and the baro- and chemoreceptor activity. These effects seem to be mediated by an interaction with central nervous, cardiovascular and respiratory structures dependent on the carotid arteries and by a direct interference of these drugs with the carotid sinus baro- and chemoreceptor structures. Moreover, these effects were not a result of the beta-adrenolytic properties of the drugs.

Adrenergic beta-Antagonists↗
PubMed1984

Influence of age on carotid body size and arterial chemoreceptor reflex effects in spontaneously hypertensive (SHR) and normotensive rats.

In normotensive Wistar rats of a random-bred strain and in spontaneously hypertensive rats (SHR) of the Okamoto-Aoki-strain, the mean systemic arterial blood pressure, the pO2, pCO2, pH-values and the base excess of the arterial blood were measured during ventilating normal air as well as hypoxic (12.6% O2 in N2) and hyperoxic (100% O2) gas mixtures. The animals were anaesthetized and breathed spontaneously; they aged 5-6, 15-20, 30-40, and 50-70 weeks. The volume of their carotid bodies was determined morphometrically. When compared with the age-matched normotensive controls at an age of 5-6 weeks the SHR already exhibited slightly but significantly elevated blood pressures but had equal carotid body size and arterial carbon dioxide tension. In contrast, hypertensive animals in the established phase of hypertension (older than 15 weeks) showed greater carotid bodies and a highly significant respiratory alkalosis when compared with the corresponding age-group of the normotensive rats. The reactions of the mean systemic arterial blood pressure and the arterial pCO2 provoked by hypoxia and hyperoxia proved to be age-dependent in both the normotensive and hypertensive animals but this influence of age was different in the two strains of rats. The data support the concept that alterations of arterial chemoreceptor structures and reflex effects found in the established phase of hypertension are the result of this disease. Furthermore they indicate that, when interpreting arterial chemoreceptor reflex effects in hypertensive humans and animals, the stage of hypertension must be taken into account.

Aging↗
PubMed1982

[Tissue chemoreceptors].

Intraarterial administration of acids or perfusion with solutions inducing acidosis in the small intestine tissue, increase the afferent impulsation in the splanchnic nerves as well as the arterial pressure in anesthetized cats. Threshold concentrations of lactic and carbonic acids don't exceed, at that, their normal contents in the blood and tissues. Similar data were obtained in perfusion of the small intestine with blood of a donor animal whose acid--alkaline balance (AAB) was altered. The tissue receptors were found to be more sensitive to the metabolic rather than respiratory acidosis, due to different alteration of of the intratissue pH. Sensitivity of the skeletal muscles' chemoreceptors proved somewhat lower as compared with the small intestine receptors. Nevertheless, the threshold shifts of the AAB parameters in the m. gastrocnemius perfusion developed within the normal range. The changes of minute volume of ventilation revealed the possibility of tissue receptors participation in the reflex control of respiration as well. The data on adequate sensitivity of the tissue receptors to terminal products of aerobic and anaerobic metabolism: carbonic and lactic acids, once more corroborate V. N. Tchernigosky's ideas of the tissue chemoreceptors as a special class of receptor structures providing the c.n.s. with necessary information on intensity of the tissue metabolism.

Acid-Base Imbalance↗
PubMed1981

Interaction of carotid chemoreceptor and pulmonary inflation reflexes in circulatory regulation in conscious dogs.

The interaction of carotid chemoreceptor and pulmonary inflation reflex control of peripheral and coronary vasoactivity and myocardial contractility was examined in conscious dogs. Stimulation of carotid chemoreceptors resulted in an increase in rate and depth of respiration, an increase in myocardial contractility, and more intense vasoconstriction in the iliac than in the mesenteric, renal, or cerebral beds. The coronary bed responded primarily with vasodilation. The increase in rate and depth of respiration stimulated pulmonary inflation reflexes, which in turn were partially responsible for the coronary vasodilation, but also attenuated the positive inotropic response and even reversed the initial peripheral vasoconstriction to a period of significant vasodilation.

Blood Pressure↗
PubMed1978

[Comparative characteristics of neuronal response in the vagus and facial nerve lobes of carp medulla oblongata to chemoreceptor stimulation].

The unit activity in the vagal lobe of medulla oblongata in response to stimulation of the mouth cavity and gills chemoreceptors with solutions of hydrochloric acid and sodium chloride was studied in immobilized carps and compared with those in the facial lobe in response to skin chemoreceptors stimulation. The firing rate in the vagal lobe is lower and the latent period is longer than in the facial lobe. The level of the chemical stimuli gradations analysis is different in two parts of the chemoreception primary centre. In the vagal lobe units responding to the impulses from both receptive fields as well as those responding selectively to stimulation either of the mouth cavity or the gills were found. Activity of a firing pattern was predominant in the vagal lobe units in response to stimulation with sodium chloride solutions.

Animals↗
PubMed1981

Effects of carotid body chemoreceptor stimulation on respiration and phrenic nerve activity in intact and vagotomized rabbits.

The effects of carotid body chemoreceptor stimulation by NaCN on respiration and phrenic nerve activity were studied in intact and vagotomized rabbits. In intact animals, an intracarotid injection of 30 micrograms of NaCN resulted in an elevation of phrenic nerve activity and a rapid onset of respiratory excitation associated with an increase in respiratory rate and the response was markedly potentiated after vagotomy. The change in respiratory rate was primarily due to a decrease in expiration time in intact animals, whereas it resulted from a pronounced decrease in inspiration time in vagotomized animals. The results suggest a suppressive effect of the vagus nerve on carotid body chemoreceptor reflex and a possible interaction of the latter input with the pneumotaxic center. An induction of a continuous increase in phrenic nerve activity accompanied by apneustic respiration by intracarotid dopamine was another evidence to support the assumption.

Animals↗
PubMed1981

Effects of carotid Body chemoreceptor stimulation by 5-HT on phrenic nerve activity and ventilation in the rabbit.

Effects of carotid body chemoreceptor stimulation by 5-hydroxytryptamine (5-HT) on the phrenic nerve activity and ventilation were studied by injecting it into the external carotid artery of the rabbits. 5-HT induced an immediate and transient increase of ventilatory rate which became more pronounced with increasing the dose, but it was accompanied by decreases in integrated phrenic nerve activity and tidal volume. The excitatory response was followed by an inhibition in 35% of the experiments. The 5-HT-induced excitation was unaffected by pretreatment with atropine and mecamylamine, but it was completely blocked by tetrodotoxin (TTX) which failed to inhibit the excitation induced by NaCN. Prior administration of atropine abolished the inhibitory effect of 5-HT and the ventilatory excitation induced by baroreceptor stimulation. It may be suggested that the excitation induced by 5-HT results from stimulation of chemoreceptor nerve endings, whereas the inhibition is probably due to its action on baroreceptor nerve endings.

Animals↗
PubMedDate not supplied

Influence of clonidine upon sympathetic component of the carotid chemoreceptor reflex.

The central influence of clonidine on the sympathetic component of carotid chemoreflex was verified in chloraloseurethane anaesthetised cats. The electrical stimulation of sinus nerve evoked only the excitatory responses in the sympathetic cardiac and renal nerve in the full range of stimulus strength. The excitatory response in the sympathetic renal nerve was completely depressed during the central cardiodepressor action of clonidine. Taking into account that the evoked excitatory responses in the sympathetic nerves were mainly the result of chemoreceptor carotid afferent fibre stimulation, it was concluded that clonidine depresses centrally carotid chemoreceptor reflex.

Animals↗
PubMed1995

Long-term modulation of inward currents in O2 chemoreceptors by chronic hypoxia and cyclic AMP in vitro.

In mammals, ventilatory acclimatization to hypoxia is associated with an enhanced chemosensitivity of the O2-sensing carotid body, resulting in an increased respiratory drive. To test whether this sensitization involves long-term modulation of ion channel function in endogenous O2 chemoreceptors, i.e., type 1 cells, we exposed cultures of dissociated rat carotid body to chronic hypoxia (6% O2) for 1-2 weeks, before monitoring the electrophysiological properties of type 1 cells using whole-cell, perforated patch recording. Chronic hypoxia augmented voltage-dependent inward Na+ and Ca2+ currents in type 1 cells, without significant changes in voltage dependence of activation or steady-state inactivation. However, after normalizing for the concomitant increase in cell size, indicated by the whole-cell capacitance, only the Na+ current density was significantly enhanced. The Na+ current was sensitive to tetrodotoxin (TTX; 0.5-1 microM) or choline substitution, whereas most of the Ca2+ current was sensitive to the L-type calcium channel blocker, nifedipine (10 microM). Several of these effects of hypoxia were mimicked qualitatively by growing normoxic cultures in the presence of agents that elevate intracellular cyclic AMP, including dibutyryl cAMP (db-cAMP; 200 microM-1 mM) and forskolin (10 microM); treatment with similar concentrations of dibutyryl cyclic GMP was ineffective. Na+ channel induction by db-cAMP was abolished by the protein synthesis inhibitor, cycloheximide (90-180 microM). In current-clamp mode, these altered chemoreceptors had typical resting potentials of approximately -55 mV, and following depolarization often fired multiple spikes that appeared to consist of both short-duration Na+ and long-duration Ca2+ components. We propose that chronic hypoxia, acting in part through cAMP-dependent pathways, increases electrical excitability and calcium mobilization in type 1 cells, and these adaptations may help enhance chemosensitivity during hypoxic acclimatization.

Action Potentials↗
PubMed1994

Deducing the organization of a transmembrane domain by disulfide cross-linking. The bacterial chemoreceptor Trg.

The transmembrane domain of chemoreceptor Trg from Escherichia coli contains four segments, two from each subunit of the homodimer. We used site-specific mutagenesis to introduce cysteines into those segments and oxidative cross-linking of cysteine pairs to identify residues that are near each other in space. Propensity for cross-linking was determined for pairs of homologously placed cysteines in the two subunits of the dimer at all 54 possible positions. Also, combinations of cysteines were identified that readily oxidized to join heterologous segments within or between monomers. These patterns of cross-linking were used to develop a model for the three-dimensional structure of the transmembrane domain in which the four transmembrane segments are helices associated in a bundle, with stronger interactions near the periplasm and weaker interactions near the cytoplasm. The striking similarity of this model to a model for the transmembrane domain of chemoreceptor Tar, derived using the same experimental strategy, strengthens the notion that a combination of comprehensive cysteine substitutions and analysis of patterns of disulfide cross-linking is sufficient to deduce a detailed three-dimensional structure for a transmembrane domain.

Bacterial Proteins↗
PubMed1993

Heart rate fall during acute hypoxemia: a measure of chemoreceptor response in fetal sheep.

The peripheral arterial chemoreceptor response to hypoxemia in the fetus is predominantly cardiovascular, invoking a fall in heart rate and a variable change in blood pressure. No quantifiable measure of chemoreceptor activity has yet been described in the intact fetus. We described the course, quantified the overall response, and defined the reproducibility of the heart rate response to acute hypoxemia in 22 late-term unanesthetized fetal sheep. Fetuses were chronically instrumented and studied between 1-6 days postoperatively. Acute hypoxemia was induced by occluding a balloon cuff around the common hypogastric artery. We performed 151 occlusions, starting at an initial saturation of 66 +/- 11%, decreasing saturation by 8-50%. Soon after balloon inflation, arterial oxygen saturation fell, followed by a decrease in heart rate. We calculated delta HR/delta sat, the fall in heart rate divided by the fall in saturation. Multiple linear regression analysis showed a sensitive chemoreflex, delta HR/delta sat averaging 2.5 +/- 1.2 bpm.%saturation-1. Initial saturation did not alter the first phase of the response (from the onset of the decrease in oxygen saturation to the onset of the decrease in oxygen saturation to the onset of the decrease in heart rate), but it did increase the overall response (delta HR/delta sat) when saturation was less than 65%. After adjusting in the lower range of initial saturations to that predicted at 65%, delta HR/delta sat was very reproducible within animals, with intra-animal variance being only 7% of inter-animal variance.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1994

Identification of peripheral chemoreceptor stimuli.

This short review considers the essential structure and stimulus-response characteristics of the carotid body chemoreceptors and attempts to relate the latter to their role in the generation of exercise hyperpnea. It shows that the arterial chemoreceptors do contribute substantially to the drive to breathe in exercising man and it suggests that this extra drive results from an increase in discharge which occurs in spite of the fact that the classical stimuli to its discharge, do not change. The possibility that in exercise the carotid body is excited by activation of its sympathetic innervation, and by raised arterial potassium, is considered. The idea that breath-by-breath oscillations of arterial blood gas tension convey accurate information about the whole body rate of carbon dioxide production is described and found wanting.

Animals↗
PubMed1994

Peripheral chemoreceptor control of exercise hyperpnea in humans.

Estimates of the proportional contribution of the peripheral chemoreceptors (i.e., the carotid bodies) to human ventilatory control during moderate exercise (i.e., below the lactate threshold, theta L) suggest that they: (a) exert no discernible influence on the initial (usually rapid) phase I component; (b) provide significant modulation of the slower, exponential phase II dynamics, therefore contributing to the tightness of arterial PCO2 regulation and the magnitude of the transient hypoxemia in this phase; and (c) account for approximately 20% of the steady-state phase III drive, which can rise to over 50% in hypoxia (PaO2 approximately 50 mm Hg). Above theta L, the carotid bodies constrain the transient fall in arterial pH by mediating much (but not all) of the compensatory hyperventilation for the metabolic acidemia. The carotid body contribution above theta L, estimated by Dejours O2 testing, is not appreciably different from subthreshold estimates, suggesting that: (a) the respiratory alkalosis in blood and cerebrospinal fluid resulting from the hyperventilation may suppress carotid chemosensitivity; (b) an artifact resulting from secondary hyperoxia-induced stimulation of central chemoreceptors may lead to underestimation of the carotid body contribution; or (c) the carotid bodies may not be entirely "silenced" by hyperoxia during a metabolic acidemia.

Carotid Body↗
PubMed1977

Effect of 5-hydroxytryptamine on the peripheral chemoreceptors in the rat.

5-Hydroxytryptamine (5-HT), in the doses of 2-5 mug/kg injected into the carotid body area, produced a significant increase in the respiratory rate and carotid sinus nerve activity. Selective ablation of the ipsilateral carotid sinus nerve abolished the respiratory stimulation produced by the drug. On the other hand, the same doses of 5-HT injected into the ascending aorta did not produce stimulation of respiration when the carotid sinus nerves were sectioned. The activity of the aortic nerves did not increase after injecting the drug into the ascending aorta or at the root of the right subclavian artery. These results indicate that 5-HT stimulates the chemoreceptors in the carotid body of the rat. The lack of responses to the injections of the drug in the aortic or subclavian region was due to the absence of chemoreceptors in these regions of the rat.

Animals↗
PubMed1996

Cardiorespiratory and renal responses to arterial chemoreceptor stimulation in early hypertension.

The peripheral arterial chemoreceptors (PAC) modify not only cardiorespiratory but also renal hemodynamic and excretory function. There is evidence that in hypertensive animals and humans the reflectoric actions of the PAC on ventilation and circulation differ from those of normotensive subjects. However, the influence of these receptors on kidney function of hypertensive subjects is poorly understood. Cardiorespiratory and renal responses to pharmacological stimulation of PAC by almitrine bismesylate during normoxia were measured in 16 normotensive (NT) and 13 age-matched borderline-hypertensive young men (BHT) undergoing water diuresis. Placebo experiments served as time controls in each subject. NT reacted to almitrine with significant rises in heart rate, minute ventilation, and filtration fraction. Renal vascular resistance tended to increase slightly. In BHT the drug caused a significant rise in heart rate and minute ventilation too, however, this reaction had a longer latency when compared to NT. In contrast to NT, filtration fraction, and renal vascular resistance decreased. Renal fractional sodium and lithium excretion did not show any clear response to almitrine in NT, but decreased in BHT. The results suggest that the weaker ventilatory response in BHT vs. NT might indicate a lower reactivity of their PAC to almitrine. The different reactions of the renal vascular bed to pharmacological chemoreceptor excitation in mild hypertensives might result from a different reactivity of the renal arterioles, whereas the enhanced proximal tubular sodium reabsorption could be due to an exaggerated increase in efferent renal nerve activity.

Adult↗
PubMed1976

Indirect evidence for arterial chemoreceptor reflex facilitation by face immersion in man.

It has been demonstrated that the usual diving bradycardia can be greatly intensified when face immersion is superimposed on a state of apneic exercise. This intensification is neither due to chemoreceptor stimulation, or to face immersion per se. It is concluded that the intensification is caused by chemoreceptor reflex facilitation, due to stimulation of trigeminal receptors in the face.

Adult↗