Catecholamine content of the carotid body in cats ventilated with 8 - 40% oxygen.

The content of catecholamines in the carotid body varies directly with inspired oxygen concentration in the range between 8 and 40% oxygen. The decrease in content during hypoxia is mediated mainly through an efferent neural pathway in the carotid sinus nerve.     

Regulation of Tyrosine Hydroxylase Gene Expression in the Rat Carotid Body by Hypoxia

The activity (Vmax) of tyrosine hydroxylase (TH; EC 1.14.16.2), the rate limiting enzyme in the synthesis of catecholamines, is increased in carotid body, superior cervical ganglion, and the adrenal medulla during hypoxia (i.e., reduced PaO2). The present study was undertaken to determine if the increase in TH activity in these tissues during hypoxia is regulated at the level of TH mRNA. Adult rats were exposed to hypoxia (10% O2) or room air for periods lasting from 1 to 48 h. The carotid bodies, superior cervical ganglia, and adrenals were removed and processed for in situ hybridization using 35S-labeled oligonucleotide probes. The concentration of TH mRNA was increased by hypoxia at all time points in carotid body type I cells, but not in cells of either superior cervical ganglion or adrenal medulla. The increase in TH mRNA in carotid body during hypoxia did not require innervation of the carotid body or intact adrenal glands. In addition, hypercapnia, another physiological stimulus of carotid body activity, failed to induce an increase in TH mRNA in type I cells. Our findings suggest that hypoxia stimulates TH gene expression in the carotid body by a mechanism that is intrinsic to type I cells.     

The Carotid Body: A Pathologist's View

A review of the literature on the histogenesis and function of the carotid body suggests that the results and the original interpretations of embryological, histological and histochemical investigations have not provided a convincing explanation of the origin of this structure. That the carotid body is developed from mesoderm and is a sensory organ (chemoreceptor) seems unlikely because of: morphological similarities between some of the carotid body tumours and certain tumours of peripheral nerves; certain electron microscopic similarities between the cells of carotid body and adrenal medulla; chromatographic demonstration of catecholamines in the human carotid bodies; and contradictory results of both animal experiments and clinical observations concerning function of this structure.It is concluded that the carotid body arises from ectoderm and should probably be classified as a gland of internal secretion, related to the adrenal medulla and other paraganglia.     

Loss of histochemically demonstrable catecholamines in the glomus cells of the carotid body after alpha-methyl-para-tyrosine treatment.

A statistically significant decrease in the intensity of catecholamine fluorescence of some carotid body glomus cells was observed after inhibition of the enzyme tyrosine hydroxylase by injection of 80 mg/kg alpha-methyl-paratyrosine. The intensity of the formaldehyde-induced fluorescence was measured in individual glomus cells. The maximum decrease in the intensity was observed 4 to 6 hr after the alpha-methyltyrosine injection. This suggests a rapid turnover in the catecholamines of the carotid body.     

Evidence for histamine as a transmitter in rat carotid body sensor cells

Carotid bodies harboring sensor cells for oxygen have a strategic location at the bifurcation of the carotid artery, which supplies the brain. Upon arterial hypoxia they transmit signals to the respiratory center, which increases the frequency of breathing. Dopamine is considered as the predominant transmitter of the rat carotid body sensor cells. Here we show that the rat carotid body sensor cells are the first cell type known to have the complete apparatus to synthesize, store and release both dopamine and histamine. The tyrosine hydroxylase positive dopaminergic sensor cells of juvenile rats express the histamine biosynthesis enzyme, histidine decarboxylase. Moreover, the sensor cells have not only vesicular monoamine transporter 1 (VMAT1) transporting catecholamines but also VMAT2, which is highly specific for histamine. Additionally, we found that these cells possess components of the neuroendocrine exocytosis apparatus, synaptosome-associated protein of 25 kDa (SNAP 25) and syntaxin1. The amount of histamine determined in the rat carotid body (164 pmol/carotid body) is more than 10-fold higher compared with that of dopamine. As a main effect, hypoxia significantly increased histamine release from isolated rat carotid bodies as it has been shown for dopamine. Finally, RT-PCR experiments indicate the presence of histamine receptors H1, H2 and H3 in the carotid body. Our data suggest that histamine is synthesized, stored and released upon hypoxia by dopaminergic sensor cells of the rat carotid body.     

The effect of nerve tissue growth factor on the structural-functional state of the sympathetic neurons after cutting their axons]

Under study was the influence of the nerve growth factor on morpho-functional and cytometrical characteristics of sympathetic neurons after cutting their axons. The work was carried out in albino rats which were subjected to dissection of the external and internal carotid nerves of the cranial cervical ganglion. This operation resulted in death of about 50% of the neurons of the node in question, in 30 and 60% in reduction of the intensity of fluorescence of the neuron body catecholamines within 7 and 14 days. The cause of these changes might be the cessation of entrance of the nerve growth factor from target tissues by means of retrograde transport. After 6-10 exogenous administrations of the latter (10-20 mkg/g of the body weight) 14 days after operation the amount of neurons in the cranial cervical ganglion did not practically differ from that in the group of intact rats. Seven and fourteen days later specific luminescence of the neuron body catecholamines was 24-22% greater than the values found in the operated animals given the isotonic solution of sodium chloride. Parallel stimulation of the formation of a powerful network of collateral branches by injured axons was performed resulting in more considerable (3-fold) increase of the ganglion mass than in the operated animals (2-fold) not treated with a neuro-growth protein. The newly formed fibers had not only an intercellular but also subcapsular arrangement which spoke of higher reparative--regenerative potencies of the neuron.     

Plasma catecholamines: Arterial-venous differences and the influence of body temperature

Using sensitive radio-enzymatic assays, levels of plasma total catecholamines and norepinephrine in rats change dramatically with changes in body temperature. The decrease in plasma catecholamines induced by warming the animal is reflected in an apparent arterio-venous difference when arterial blood is obtained at room temperature and tail sampling is aided by heat induced vasodilation. Combined blockade of extraneuronal and neuronal uptake reduces this arterio-venous difference. Blood samples obtained from the decapitated trunk of the rat contain similar levels of plasma catecholamines as those obtained from indwelling carotid catheters. Blood levels of dopamine-betahydroxylase were similar whether obtained by venous sampling during heat-induced vasodilation, decapitation or indwelling arterial cannula.     

重组鼠IL-1β和／或慢性缺氧刺激对大鼠颈动脉体中TH表达的影响

目的：观察慢性低压性缺氧和／或重组鼠白介素-1β（traiL-1β）刺激对大鼠颈动脉体（carotidbody,CB）中酪氨酸羟化酶（ty．rosinehydroxylase,TH）表达的影响。方法：雄性SD大鼠分为8组,分别为缺氧刺激0、1、2、3周组和缺氧0、1、2、3周的同时伴rmlL-1β刺激组。对CB进行免疫组化染色,并用westernblot法对TH进行半定量分析。结果：相对于缺氧0周组,缺氧1周、缺氧2周和缺氧3周组大鼠CB中TH的含量明显增加。相对于正常大鼠,rmlL-1β刺激引起大鼠CB中TH表达量增加。相对于单纯给予缺氧1周和缺氧2周,缺氧1周和缺氧2周同时给予mlL-1β刺激后引起大鼠CB中TH表达量的增加。结论：慢性缺氧和rmlL-1β刺激均可致颈动脉体TH上调,慢性缺氧伴rmlL-1β刺激比单纯缺氧刺激可引起TH更显著的增加。这个结果提示慢性缺氧或促炎性细胞因子tL-1β刺激不仅能够分剐促进颈动脉体中儿茶酚胺类物质的合成。而且IL-1β刺激可以促进慢性缺氧时颈动脉体中儿茶酚胺类物质的合成。这说明促炎性细胞因子可能对大鼠颈动脉体的慢性缺氧感受发挥调节作用。     

Regulation of chemoreceptor sensitivity in the carotid body: the role of presynaptic sensory nerves

Several neural and vascular mechanisms regulate the sensitivity of carotid body chemoreceptors to hypoxia, hypercapnia, and acidosis. Factors that control blood flow and oxygen delivery in the carotid body along with those that augment or diminish catecholamine release from glomus cells can have major effects on chemoreceptor function. In addition, the sensory nerves themselves may participate in the regulation of chemoreceptor sensitivity. A portion of the carotid body's sensory nerves are presynaptic to glomus cells. In response to stimulation, the sensory nerve terminals exhibit ultrastructural changes that resemble changes associated with increased release of transmitter from motor nerves: 1) the number of small (synaptic) vesicles decreases; and 2) coated vesicles and coated regions of cisternal membrane increase in number during stimulation. If sensory nerves of the carotid body release a neurotransmitters, sensory nerve activity could influence glomus cell secretion of catecholamines or other substances tha modify chemoreceptor sensitivity. Such an effect could be produced in the carotid body by hypoxia and other conditions that stimulate the sensory nerves or it could result from antidromic activity evoked in the sensory nerves by primary afferent depolarization of their terminals in the CNS.     

Ultrastructural changes in the rat carotid body in severe haemorrhagia

Summary Rat carotid bodies were studied electron microscopically after short-term severe hypovolaemia, which is known to induce a marked chemoreceptor activation in the carotid body. Altogether 84 nerve-endings in the hypovolaemic rats' carotid bodies and 91 nerve-endings in the control carotid bodies were investigated. An increased accumulation of the glomus cell granular vesicles near the synaptic specializations of the nerve-endings was observed after hypovolaemia. Moreover, a statistically significant increase in the contacts between the nerve-ending synaptic specializations and the glomus cell granular vesicles was observed after hypovolaemia. A suggestion was made that the glomus cells might act as modulating, probably inhibitory, interneurones, whose catecholamines are responsible for the inhibition.The authors are greatly indebted to lecturer Pekka Korkala Ph.L. from the Department of Psychology for his skilful statistical analysis of the results.     

Biogenic Amine-Stimulated Cyclic Adenosine-3'',5''-Monophosphate Formation in the Rat Carotid Body

The subcutaneous injection of isoprenaline, salbutamol, histamine, and adrenaline to rats, which were subsequently killed by microwave irradiation, resulted in a rapid increase in the cyclic AMP content of the carotid body. On the other hand, noradrenaline, dopamine, adenosine, and 5-hydroxytryptamine, at doses at least 100 times greater than that of isoprenaline, did not significantly alter the cyclic nucleotide content in vivo. The response to isoprenaline was dose related, with an ED50 of 15 micrograms X kg-1, and reached a peak level 1-1.5 min after injection. Incubation of intact carotid bodies with isoprenaline (10(-5) M) in vitro also resulted in a 10-fold increase in cyclic AMP content. The in vivo response to isoprenaline could be blocked stereo-selectively by propranolol, and ICI 118.551, a beta 2-selective antagonist, blocks the isoprenaline-elicited increase in cyclic AMP completely at a dose of 30 micrograms X kg-1; whereas betaxolol, a beta 1-selective antagonist, was ineffective, even at a dose of 300 micrograms X kg-1. Hypoxia (5% oxygen in 95% N2) did not result in a significant increase in the cyclic AMP content, nor did it significantly alter the isoprenaline-stimulated increase in the cyclic AMP content of the rat carotid body. These results suggest that some catecholamines may stimulate cyclic AMP formation by interacting with a beta 2-adrenoceptor in the rat carotid body.     

Histochemically demonstrable catecholamines in sympathetic ganglia and carotid body of spontaneously hypertensive and normotensive rats

Summary The catecholamine content and morphology of the superior cervical and the hypogastric ganglion and the carotid body were studied in Spontaneously Hypertensive Rats (SHR) before (at the age of 6 weeks) and after (at the age of 20 weeks) becoming hypertensive, with Wistar Kyoto (WKY) rats as controls. The study was performed by formaldehyde-induced fluorescence method combined with quantitative microfluorimetry of catecholamines.At the age of 6 weeks the only significant difference observed between the rat strains was a greater number of small intensely fluorescent (SIF) cells in the superior cervical ganglion of SHR. At the age of 20 weeks the fluorescence intensity was higher in the principal neurons of the superior cervical ganglion and in glomus cells of the carotid body of SHR compared to WKY. The volumes of superior cervical ganglion and carotid body were larger in 20-week-old SHR compared to WKY. In the hypogastric ganglion differences were not found between SHR and WKY rats. The present results show differences in the superior cervical ganglion and in the carotid body of adult SHR compared to controls. These differences develop during the time period when the SHR become hypertensive, and might be functionally significant in the regulation or maintenance of the increased blood pressure in SHR rats.     

Histochemically demonstrable increase in the catecholamine content of the carotid body in adult rats treated with methylprednisolone or hydrocortisone

Synopsis Carotid bodies of adult albino rats were examined using the formaldehyde-induced fluorescence (FIF) method for the demonstration of fluorogenic monaomines and staining with I% Toluidine Blue for morphological observations.In the carotid body of normal controls, most glomus (principal or type I) cells exhibited a FIF presumably due to catecholamines. The intensity of the fluorescence was weak in most cells, while some glomus cells were non-fluorescent and others exhibited a moderate or intense FIF. The sustentacular (satellite, supporting or type II) cells were essentially non-fluorescent.One week after the administration of a single intraperitoneal injection of the long-acting glucocorticoid 6-methylprednisolone sypionate (400 mg/kg) or after seven intraperitoneal injections of the water-soluble glucocorticoid hydrocortisone sodium succinate (40 mg/kg daily for a week), a distinct increase was observed in the FIF of the glomus cells. No non-fluorescent glomus cells were observed after treatment with either glucocorticoid, and the intensity of most fluorescent glomus cells was moderate or intense.It is concluded that glucocorticoids cause an increased storage of catecholamines in the glomus cells of the carotid body of the adult rat, an observation of interest in view of the fact that such changes due to glucocorticoids have as yet been reported only in catecholamine-storing cells of newborn rats.     

Function of the rat carotid body chemoreceptors in ageing

Some age-related deficits in the ventilatory responses have been attributed to a decline in the functionality of the carotid body (CB) arterial chemoreceptors, but a systematic study of the CB function in ageing is lacking. In rats aged 3-24 months, we have performed quantitative morphometry on specific chemoreceptor tissue, assessed the function of chemoreceptor cells by measuring the content, synthesis and release of catecholamines (a chemoreceptor cell neurotransmitter) in normoxia and hypoxia, and determined the functional activity of the intact organ by measuring chemosensory activity in the carotid sinus nerve (CSN) in normoxia, hypoxia and hypercapnic acidosis. We found that with age CBs enlarge, but at the same time there is a concomitant decrease in the percentage of chemoreceptor tissue. CB content and turnover time for their catecholamines increase with age. Hypoxic stimulation of chemoreceptor cells elicits a smaller release of catecholamines in rats after 12 months of age, but a non-specific depolarizing stimulus elicits a comparable release at all ages. In parallel, there was a marked decrease in the responsiveness to hypoxia, but not to an acidic-hypercapnic stimulus, assessed as chemosensory activity in the CSN. We conclude that in aged mammals chemoreceptor cells become hypofunctional, leading to a decreased peripheral drive of ventilation.     

Histochemically demonstrable catecholamines in sympathetic ganglia and carotid body of spontaneously hypertensive and normotensive rats

The catecholamine content and morphology of the superior cervical and the hypogastric ganglion and the carotid body were studied in Spontaneously Hypertensive Rats (SHR) before (at the age of 6 weeks) and after (at the age of 20 weeks) becoming hypertensive, with Wistar Kyoto (WKY) rats as controls. The study was performed by formaldehyde-induced fluorescence method combined with quantitative microfluorimetry of catecholamines. At the age of 6 weeks the only significant difference observed between the rat strains was a greater number of small intensely fluorescent (SIF) cells in the superior cervical ganglion of SHR. At the age of 20 weeks the fluorescence intensity was higher in the principal neurons of the superior cervical ganglion and in glomus cells of the carotid body of SHR compared to WKY. The volumes of superior cervical ganglion and carotid body were larger in 20-week-old SHR compared to WKY. In the hypogastric ganglion differences were not found between SHR and WKY rats. The present results show differences in the superior cervical ganglion and in the carotid body of adult SHR compared to controls. These differences develop during the time period when the SHR become hypertensive, and might be functionally significant in the regulation or maintenance of the increased blood pressure in SHR rats.     

Loss of histochemically demonstrable catecholamines in the glomus cells of the carotid body after α-methyl-para-tyrosine treatment

Summary A statistically significant decrease in the intensity of catecholamine fluorescence of some carotid body glomus cells was observed after inhibition of the enzyme tyrosine hydroxylase by injection of 80 mg/kg -methyl-paratyrosine. The intensity of the formaldehyde-induced fluorescence was measured in individual glomus cells. The maximum decrease in the intensity was observed 4 to 6h after the -methyltyrosine injection. This suggests a rapid turnover in the catecholamines of the carotid body.     

Adenine nucleotides in the carotid body

Summary Remarkably large amounts of adenine nucleotides are identified in type I-cells of the carotid body by fluorescence microscopy (labelling with quinacrine) and electron microscopy (uranaffin reaction). At the fine-structural level the matrix material of specific granules displays enhanced electron density after fixation with uranium ions. It is suggested that ATP is stored within specific granules in addition to catecholamines and proteins. Adenine nucleotides should be considered as one of the secretion products of the chief cells in the carotid body, being capable locally of influencing vascular flow and/or chemoreceptor terminals.Histochemical analysis of the activities leading to a splitting of adenine nucleotides shows a high reactivity with ATP or ADP as substrates. Reaction products are confined to the entire vascular bed of the carotid body. Using AMP or -glycerophosphate as substrate, practically no phosphohydrolytic activity could be detected within the carotid body. Thus, the phosphatases are adequate to remove ATP and ADP, but not to form adenosine.This study was supported by a grant from the Deutsche Forschungsgemeinschaft, Nr. Bo 525/3     

ELECTRON MICROSCOPIC RADIOAUTOGRAPHIC STUDIES OF THE CAROTID BODY FOLLOWING INJECTIONS OF LABELED BIOGENIC AMINE PRECURSORS

Adult Syrian hamsters were given a subcutaneous injection of reserpine 3 days before an intraperitoneal injection of ³H-3,4 dihydroxyphenylalanine or ³H-5, hydroxytryptophan and the carotid bodies were subsequently prepared for electron microscopic radioautography. Other Syrian hamsters were given a subcutaneous injection of reserpine and the carotid bodies were subjected to a sensitive cytochemical test for the detection of unsubstituted amines. These studies were made to determine whether the labeled amine precursors were incorporated into the cells and to see whether the parenchymal cells were affected by reserpine treatment. Material from hamsters treated first with reserpine and subsequently injected with ³H-3,4 dihydroxyphenylalanine or ³H-5, hydroxytryptophan exhibited reduced grains of silver over the cells which were associated mainly with the dense cores of the cytoplasmic granules. These studies offer evidence that the granules of the carotid body incorporate catecholamine and indolamine precursors. Material from hamsters incubated for the presence of unsubstituted amines gave a positive reaction (opaque cytoplasmic granules) for catecholamines but not for indolamines. The latter substances may not be present in quantities sufficient to register a positive reaction in the cytochemical test. The opaque granules, indicative of the presence of catecholamines, decreased in density after reserpine treatment. 5 days after one reserpine injection the granules had regained opacity and were comparable to those seen in the control cells.     

Biochemical studies on the release of catecholamines from the rat carotid body in vitro

The effects of hypoxia and carbachol on the release of newly synthesized catecholamines from superfused rat carotid bodies have been examined. Hypoxic superfusion medium was found to evoke catecholamine release which was dependent on the extracellular calcium concentration and was reduced by nitrendipine and atropine. Superfusion with the muscarinic agonist, carbachol, stimulated catecholamine release independently of the oxygen tension of the medium. The effect of carbachol on catecholamine release was abolished by atropine, suggesting that it was mediated by activation of cholinergic receptors of the muscarinic type. Both hypoxia and carbachol stimulated the release of 45Ca from carotid bodies prelabelled with 45Ca. The release of 45Ca with either stimulus was reduced by atropine and nitrendipine. These results suggest that although extracellular calcium plays an important role in the exocytotic secretory process of the carotid body, the mobilization of intracellular calcium pools may also contribute to the secretory response.     

Sympathetic innervation of the pulmonary artery,ascending aorta,and coronar glomera of the rabbit

Summary Adrenergic nerve fibres were demonstrated in the connective tissue of the rabbit coronar glomera by means of the formaldehyde-induced fluorescence technique for catecholamines. This type of innervation is similar to the adrenergic nerve supply to the rabbit and cat carotid body. Adrenergic fibres terminate subendothelially and only a few can be traced to type I cells in the glomera coronaria. The sympathetic innervation of the ascending aorta is exceedingly sparse in contrast to the pulmonary trunk, while vasa vasorum of the ascending aorta exhibit a dense sympathetic innervation.