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At least 451 records · Page 25Linked to original sources
PubMed1991

[Effect of adenosine on carotid chemoreceptor activity in the rabbit].

The response of single carotid chemoreceptor afferent fibers upon adenosine acting on the carotid body (CB) was examined in 39 urethan-anesthetized rabbits. Totally 73 units with spontaneous discharge were recorded in our experiment. The results were as follows: (1) Of 55 units, 51 showed an increase in discharge frequency from 0.76 +/- 0.10 to 1.53 +/- 0.23 imp/s. A few new units were recruited concomitantly in response to intracarotid injection of adenosine (10 micrograms/kg). (2) Adding adenosine in the doses of 0.5, 1.5, 10, 50 and 100 micrograms/kg to the perfusate passing through the isolated carotid sinus led to dose-dependent increase in the discharge from 0.51 +/- 0.06 to 0.58 +/- 0.07, 0.78 +/- 0.13, 0.96 +/- 0.15, 1.11 +/- 0.17, 1.34 +/- 0.21 and 1.38 +/- 0.18 imp/s, respectively (P less than 0.001, n = 9 units). (3) In other 9 units with spontaneous discharge rate of 1.30 +/- 0.40 imp/s, the activity was decreased to 0.56 +/- 0.19 imp/s (P less than 0.01) by intracarotid injection of dopamine (50 micrograms/kg). Intracarotid injection of adenosine to the CB pretreated with dopamine still activated the units with an increase in firing rate to 1.07 +/- 0.28 imp/s (P less than 0.01). However, the increment was less prominent as compared with that of adenosine administration before dopamine injection (P less than 0.001). From the results obtained, it is hypothesized that the exciting effect of adenosine on the CB chemoreceptor may be attributed to its action on the presynaptic component of the chemoreceptor complex in attenuating the release of inhibitory transmitter dopamine, and its direct stimulating action on the chemosensory nerve endings.

Adenosine↗
PubMed1991

The role of peripheral chemoreceptors in the rapid response of the pulmonary vasculature of the late gestation sheep fetus to changes in PaO2.

The effect of removing the input from the peripheral arterial chemoreceptors on pulmonary vascular responses to changes in PaO2 was examined in late gestation fetal sheep. Blood flow in the left pulmonary artery and driving pressure across the pulmonary vascular bed were monitored in chronically prepared fetal sheep at 126-129 days gestation. Five fetuses had carotid sinus and vagus nerves sectioned bilaterally and four were left intact. In normoxia (PaO2 ca. 23 mmHg) pulmonary vascular resistance was slightly greater and pulmonary blood flow reduced in the denervated group relative to the intact group but these differences were not significant. When made hypoxic (PaO2 ca. 14 mmHg), pulmonary blood flow fell and pulmonary vascular resistance increased in all fetuses. However, in the intact fetuses these changes were significantly more rapid. In all fetuses the vasoconstriction was prolonged after their return to normoxia. When made hyperoxic (PaO2 ca. 27 mmHg), pulmonary blood flow increased by a similar amount in all fetuses. We conclude that in the term fetus the peripheral chemoreceptors play no appreciable role in the maintenance of the high pulmonary vascular resistance in normoxia, or the fall in resistance produced by a rise in PaO2. The chemoreceptors do however initiate the rapid phase of pulmonary vasoconstriction in hypoxia.

Animals↗
PubMedDate not supplied

Are central respiratory chemoreceptors confined to ventrolateral medulla?

There is ample evidence that the ventrolateral medulla (VLM) is involved in regulation of respiration. The VLM is considered to be the site of location of the central respiratory chemoreceptors. Neither neuroanatomical nor neurophysiological coordinates of the chemoreceptor have ever been indisputably identified or verified, despite decades of research. This commentary addresses new hypotheses concerning the process of central chemoreception and recent findings calling into question the exclusivity of VLM for the chemoreceptor location and function. These findings rekindle the possibility of medullary respiratory neurons being chemosensors. Crucial issues concerning the central chemoreception remain unsettled and are open to further research.

Chemoreceptor Cells↗
PubMed1977

[Specificity of the effect of thrombin on the chemoreceptors of the frog carotid labyrinth].

Perfusion of thrombin and trypsin solutions through the frog carotid labyrinth acts on the carotid chemoreceptors and evokes reflex response of the anticoagulating system. The similarity of effects of both these agents seems to be due to similarity of their structures. Other agents acting on the frog vascular chemoreceptors: sodium chloride hypoxia, lobeline,--cause no activation of the reflex anticoagulating system. Thrombin is concluded to be the adequate and specific irritant of the vascular chemoreceptors of the frog anticoagulating system.

Animals↗
PubMed1988

Peripheral chemoreceptors and human adaptation to high altitude.

Basal hypoxic chemoreflex drive values and respiratory responses to poikilocapnic hypoxic gas mixtures (pO2 = 9.33 kPa) were determined in 142 healthy residents of various Tien-Shan and Pamir altitudes (760 m, 2800 m, 3600 m). The age of the subjects ranged from 13 to 50 years. It was found that at 760 m and 2800 m (Tien-Shan) a chemoreflex mechanism maintains 13 to 18% of the total volume of eupnoic ventilation regardless of the age of the subject studied. No decreases in ventilation were observed at 3600 m following inhalation of two tidal volumes of oxygen, suggesting alterations in the chemoreflex components of respiratory regulation. Respiratory responses to poikilocapnic hypoxia were found to be qualitatively similar at all three altitudes. It is concluded that (1) the arterial chemoreceptor activity threshold is shifted towards lower PACO2 values at 3600 m; (2) this alteration in arterial chemoreceptor activity is related either to changes in their excitability during hypocapnia and/or prolonged hypoxia, or to central inhibition of arterial chemoreceptor activity; (3) respiratory centers are responsible for the blunted ventilatory hypoxic responses.

Adaptation, Physiological↗
PubMed1988

Effects on carotid chemoreceptor resetting of pulmonary ventilation in the fetal lamb in utero.

We tested the hypothesis that postnatal resetting of the carotid chemoreceptors is initiated by, and is dependent on, the rise in arterial PO2 (PaO2) which normally occurs after birth as air breathing is established. Previous studies had indicated that this resetting takes at least 24 h. We applied a technique for ventilation of the lungs of fetal sheep in utero to 3 groups of fetuses of 140-142 days gestational age: group 1 were exposed to normocapnic hyperoxia (mean PaO2 179.9 +/- 22.2 mmHg) for 27.4 +/- 0.9 h; group 2 were exposed to normocapnic hyperoxia (mean PaO2 229.4 +/- 77.5 mmHg) for 7.0 +/- 0.3 h; group 3 were ventilated for 21.6 +/- 3.3 h with a nitrogen/CO2 mixture to maintain PaO2 and PaCO2 within the normal fetal range. At the end of the ventilation period the fetuses were delivered by caesarean section, anaesthetized, paralysed and ventilation was continued. The responses of single or few fibre carotid chemoreceptor preparations to isocapnic hypoxia were then determined. To compare their response curves quantitatively, hyperbolic curves were fitted to the data. No significant differences between any of the groups were found in the vertical or the horizontal asymptotes. There was no difference in the slope of the hyperbolic line between group 2 and group 3. However, this slope was significantly greater for Group 1 than for either group 2 or group 3. Our results show that a period of hyperoxia of 24-31 h in utero, although not a similar period of normoxic ventilation, initiates the process of carotid chemoreceptor resetting.

Animals↗
PubMed1987

Suppression of the plasma aldosterone to renin activity ratio in anaesthetized cats after pharmacological stimulation of the peripheral arterial chemoreceptors with almitrine bismesylate.

In chloralosed, non-vagotomized, spontaneously breathing cats the peripheral arterial chemoreceptors were stimulated by intravenous infusion of almitrine bismesylate (Vectarion, 0.20 mg/kg). Within 5 h after administration of the drug, a decline of both the mean systemic arterial blood pressure and the effective renal plasma flow, as well as an increase of the plasma renin activity (PRA) and the plasma aldosterone concentration (PAC) was observed. But as the PAC increase was less than that of PRA, a highly significant suppression of the PAC to PRA ratio was noted. The results indicate that not only whole body altitude hypoxia, but also stimulation of the peripheral arterial chemoreceptors in normoxic animals lowers the PAC-to-PRA ratio. It remains to be verified experimentally whether there exists a specific reflex influence of the peripheral arterial chemoreceptors on the renin-aldosterone relationship.

Aldosterone↗
PubMed1987

The link between chemoreceptor activity and voluntary salt intake in spontaneously hypertensive rats: a hypothesis.

The effect of normobaric hyperoxia on voluntary salt intake was investigated in conscious male SHR (n = 16). The animals were housed individually in metabolic cages and given free access to food, water and 2.5% NaCl-solution. The exposure of the rats to 40% oxygen in nitrogen for four days resulted in a significant enhancement of the salt intake. The present experiment further clarifies the relationship between chemoreceptor activity and salt intake. Hypobaric hypoxia as well as the pharmacological substance almitrine, both stimuli of the carotid bodies, decrease the voluntary salt intake in SHR significantly, whereas hyperoxia, characterized by lowering of the chemoreceptor activity, increases the salt intake. Our studies support the hypothesis that chemoreceptor activity has a modulating influence on salt appetite in SHR.

Animals↗
PubMed1987

Effects of denervation on baroreceptor and chemoreceptor endings in the aorta and pulmonary trunk of the domestic fowl (Gallus gallus domesticus).

Denervation experiments were carried out on twelve adult domestic fowls in order to investigate the location of the cell bodies of baroreceptor and chemoreceptor endings of the aorta and pulmonary trunk. Soon after both distal vagal ganglionectomy and midcervical vagotomy, baroreceptor and chemoreceptor endings showed distinct signs of abnormalities. These abnormal signs included many irregular and deformed clear vesicles, large membranous whorls and vacuolated mitochondria. The endings which were severely affected became greatly swollen and almost empty except for a flocculent substance and disordered filamentous material. It is suggested that the cell bodies of the majority of baroreceptor and chemoreceptor endings are not in the distal vagal ganglion and may be in the proximal vagal ganglion and/or proximal or distal glossopharyngeal ganglia. The chief cells of the aortico-pulmonary bodies were also affected after denervation when their axonal endings degenerated. The degenerative changes took the form of many expanded membrane-bound empty spaces and increased size and number of the dense-cored vesicles. It is concluded that the axonal endings exert a trophic effect upon the granular cells.

Animals↗
PubMedDate not supplied

Chemoreceptor reflexes and cardiovascular control.

Evidence is presented which indicates that in the absence of other known inputs to the nervous system and during controlled pulmonary ventilation, stimulation of the carotid body chemoreceptors causes bradycardia and selective peripheral vasoconstriction. These responses may be attenuated, however, by concomitant changes in respiration and arterial blood pressure, and by activity of higher parts of the brain stem. Stimulation of the aortic bodies in mammals in which they are functionally active, causes bradycardia or tachycardia and selective peripheral vasoconstriction. The reflex vascular effects from the peripheral arterial chemoreceptors are mediated by alpha-adrenergic sympathetic fibres. A potential mechanism exists therefore whereby the peripheral arterial chemoreceptors could contribute to the neurogenic component of hypertension.

Animals↗
PubMedDate not supplied

Augmented chemoreceptor reflex tonic drive in early human hypertension and in normotensive subjects with family background of hypertension.

The study was carried out in 30 subjects with mild primary hypertension and in 82 normotensive age-matched volunteers, 18-20 years of age. Hyperoxia test was used to withdraw the tonic chemoreceptor reflex drive. The following circulatory and respiratory effects of short lasting hyperoxia were observed in the hypertensive group and in most of the normotensive subjects yet with a family background of hypertension: a decrease in the mean arterial pressure, in total peripheral vascular resistance, and in forearm vascular resistance, and a significantly greater reduction of the resting ventilation as compared to the normotensive group. Our results suggest that the augmented arterial chemoreceptor drive is one of the mechanisms responsible for the elevated arterial blood pressure and total peripheral resistance in early human hypertension. The positive response to hyperoxia test in healthy subjects with a family background of hypertension suggests a familial occurrence of the hyperactivity of the arterial chemoreceptors.

Adolescent↗
PubMed1986

Degenerative lesions of a coronary chemoreceptor and nearby neural elements in the hearts of victims of sudden death.

A coronary chemoreceptor and its neighboring nerves and ganglia were studied by serial sections of tissue taken from the hearts of sixteen victims of sudden unexpected death. Either focal or extensive inflammatory destruction was present in the chemoreceptors of 13 of the 16 hearts, and similar abnormalities of local nerves and ganglia were present in all 16 hearts. Since an identical coronary chemoreceptor in the dog has previously been shown to be the site of origin of a powerful reflex with major influence upon the electrical activity heart, the functional significance of the neural abnormalities found in these 16 human hearts may include important distortion of cardiac rhythm, conduction or repolarization. Future studies are needed to determine the prevalence of such lesions in the hearts of other victims of sudden death and among control subjects, as well as to determine the etiology of this special neuropathology of the heart.

Adolescent↗
PubMed1979

Interaction of cardiopulmonary chemoreceptor (Bezold-Jarisch) and somatosympathetic reflexes.

Cardiopulmonary chemoreceptor (Bezold-Jarisch) and baroreceptor reflexes produce similar overall cardiovascular effects although central integrating mechanisms are not identical. In view of recent reports emphasizing the complexity of baroreceptor mechanisms, the influence of both reflexes on spontaneous sympathetic outflow as well as their interaction with the somatosympathetic reflex were compared in anesthetized cats. The chemoreflex and the baroreceptor reflex were activated by i.v. injection of veratrine and norepinephrine, respectively, and both inhibited spontaneous efferent sympathetic nerve traffic. Stimulation of somatic nerves produces a two-component reflex potential in sympathetic nerves. Activation of cardiopulmonary chemoreceptor and baroreceptor reflexes inhibited the amplitude of the initial (spinal) phase of this somasympathetic reflex slightly and greatly attenuated the secondary (supraspinal) component. These experiments demonstrate that the cardiopulmonary chemoreceptor and baroreceptor reflexes exert similar effects on the somatosympathetic reflex and that the former two reflexes may influence sympathetic mechanisms at spinal as well as supraspinal levels.

Animals↗
PubMed1981

The effect of activation of carotid body chemoreceptors on baroreceptor inhibition of sympathetic activity.

The effect of combined stimulation of peripheral chemo- and baroreceptors upon sympathetic discharge was studied in cats anesthetized with chloralose and urethan, immobilized with tricuran, and artificially ventilated. The right carotid sinus was arterially isolated, the left sinus nerve and both vago-sympathetic trunks were cut. A rise of pressure in isolated carotid sinus from 100 to 200 mm Hg produced an inhibition of sympathetic activity recorded simultaneously from the inferior cardiac and the renal nerves. For a combined chemo- and baroreceptor stimulation, the carotid sinus was perfused at a constant pressure of 100 mm Hg with venous blood bubbled with CO2.Twenty seconds after the onset of the perfusion the carotid sinus pressure was raised up to 200 mm Hg. A combination of the chemoreceptor stimulation and of the rise of sinus pressure produced only a small inhibition of sympathetic activity in both nerves compared to the effect observed without concomitant chemoreceptor activation. It was demonstrated that chemically induced stimulation of the carotid body chemoreceptors strongly influences the magnitude of the sympathetic inhibition produced by activation of the baroreceptor reflex.

Animals↗
PubMed1981

[Neuronal activity of the frog medulla oblongata in response to chemical stimulation of gustatory and cutaneous chemoreceptors].

The unit activity of medulla oblongata extracellularly recorded during stimulation of the taste receptors and skin chemoreceptors with solutions of the hydrochloric and citric acids, sodium chloride and potassium chloride, in the majority of neurons responded at least to the solutions of one acid and one salt. The number of units which responded to all the solutions was twice as high on stimulation of taste receptors than skin chemoreceptors. The chemical stimuli graduation analysis is more suitable in the case of taste receptor stimulation. The peculiarities of the primary center unit activity response to the stimulation of the receptive fields in question may be connected with different role of taste and skin chemoreceptors in adaptive behaviour.

Afferent Pathways↗
PubMed1980

[Reactions of neurons of the vagal lobe of the carp medulla oblongata to stimulation of chemoreceptors of the skin surface, oral cavity and gills].

In the experiments on immobilized carps it was found that the units of the vagal lobe of medulla oblongata respond not only to the stimulation of the mouth cavity and gills, but of skin chemoreceptors as well. The units responding selectively to skin surface stimulation are less in number than those responding to stimulation of the two other receptive fields. There are significant differences between the changes in unit activity elicited by natural alimentary stimulus (extract from the food product) and by hydrochloric acid and sodium chloride. Comparison of neuronal responses to stimulation of skin chemoreceptors in vagal and facial lobes revealed a different role in processing afferent information from skin chemoreceptors.

Animals↗
PubMedDate not supplied

Effect of osmotic stimuli on the carotid baroreceptor and chemoreceptor discharges in cats.

In 15 cats under chloralose-urethan anaesthesia carotid sinus area was arterially isolated and perfused with artificially pulsatile pressures. Solutions of NaCl, of various osmolality, mannitol, glucose and bicarbonate were locally perfused through the isolated carotid area and the single baroreceptor and chemoreceptor fibre activity was recorded with standard technique. An increase in the osmolality of the perfused fluid evoked an increase of the single baroreceptor discharge. Each pulse pressure produced more spikes of higher frequency in big A type baroreceptor fibres. Clear effects were observed during perfusion of 300 mM NCl solutions. Solutions of higher osmolility transformed rhythmical pulse pressure discharge into continuous baroreceptor firing. The excitatory effects of hyperosmolar solutions were reversible after switching to the perfusion fluids of normal osmolality. An increased activity was also observed in the single carotid chemoreceptor fibres. It is concluded that both baro- and chemoreceptors are sensitive to osmotic stimulation.

Animals↗
PubMed1980

Effects of haloperidol on chemoreceptor reflex ventilatory response in the rabbit.

In order to obtain further evidence for the modulatory role of dopamine in chemoreceptors, effects of haloperidol, a potent dopamine antagonist, on chemoreceptor reflex ventilatory response were studied in the rabbit carotid body. An injection of 30 microgram of haloperidol into the external carotid artery induced evident ventilatory excitation which became more marked and sustained at a higher dose. The response was produced by blockade inhibitory dopamine receptors since it was completely abolished in the catecholamine depleted animals. The NaCN-induced excitation of ventilation was potentiated by prior treatment of the carotid body with haloperidol, whereas the treatment blocked the induction of the postexcitatory depression of ventilation. The results indicate the negative feedback as the most possible mechanism by which dopamine exerts its suppressor effect on chemoreceptor nerve activity.

Animals↗