Morphometric analysis of hypoxia-induced synaptic activity in intrapulmonary neuroepithelial bodies

Summary A morphometric analysis has demonstrated ultrastructural changes induced by hypoxia in the epithelial cells and the intracorpuscular nerve endings of the presumed chemoreceptive intrapulmonary neuroepithelial bodies (NEB) of neonatal rabbits.Acute hypoxia stimulates an exocytosis of epithelial dense-core vesicles (DCV) at the level of the morphologically afferent or sensory (type 1 a) intracorpuscular nerve endings of the NEB. Assuming the epithelial cells to be chemoreceptive, this phenomenon could represent a transduction of sensory stimuli.In the morphologically efferent or motor (type 2 and type 1 b) intracorpuscular nerve endings of the NEB, acute hypoxia causes a depletion of synaptic vesicles and an increase in the amount of membrane-bounded cisternae and multivesicular bodies, suggestive of an enhanced synaptic activity of these nerve endings. It is proposed that the chemoreceptor cells could thus in turn be modulated centrifugally by their efferent-like intracorpuscular nerve endings.It has been proposed in our earlier studies that the NEB probably are intrapulmonary chemoreceptors with local secretory activities, reacting to the composition of the inhaled air. By the release of serotonin and peptide substances they may produce a local vasoconstriction in hypoxically aerated lung areas, enabling an intrapulmonary regulation of the V/Q ratio. The present study provides evidence that, in addition to this local effect, NEB could generate centripetal nerve impulses via exocytosis of epithelial DCV at the afferent-like intracorpuscular nerve endings. At the same time they could be modulated by the CNS via their efferent-like intracorpuscular nerve endings.With respect to their innervation, numerous similarities appear to exist morphologically and functionally between the carotid body and the intrapulmonary NEB.     

Intrapulmonary neuro-epithelial bodies in newborn rabbits

Summary Neonatal rabbit neuro-epithelial bodies (NEB) were investigated under various experimental conditions with light microscopy, microspectrography, morphometry and electron microscopy. (1) Hypoxia causes a decreased amine fluorescence intensity and an increased secretory exocytosis of dense core vesicles (DCV). Otherwise the NEB appear structurally normal. (2) Hypercapnia also produces a decreased fluorescence and an increased exocytosis; ultrastructurally, however, the dense core of DCV fragmentizes. (3) Hyperoxia does not appear to affect significantly either fluorescence or exocytosis. (4) The uptake of biogenic amines such as 5-HTP and L-DOPA was demonstrated by fluorometry and electron microscopy. (5) Reserpine, on the other hand, provokes an amine depletion with a decrease of the NEB fluorescence and an ultrastructural palor of the DCV. (6) Intratracheally administered nicotine is accompanied by a decreased fluorescence and a distinct exocytosis of fragmented DCV.The reaction of NEB to hypoxia and hypercapnia suggests that these corpuscles could be intrapulmonary chemoreceptors (in addition to the classically known central and peripheral chemoreceptors), inducing a reflex reaction through the liberation of DCV at the corpuscular sensible nerve endings and via the CNS. In addition, they may subserve a local intrapulmonary effect by modulating directly the hypoxic and hypercapnic pulmonary vasoconstriction and thus the V/Q ratio. Acknowledgment. This study was supported by a grant from The Council for Tobacco Research, U.S.A., and the Nationaal Fonds voor Wetenschappelijk Onderzoek, Belgium. We thank M.R. Van Hamme, R. Renwart and K. Armee for technical, G. Pison and St. Ons for photographical and N. Tyberghien and G. Verbeeck for secretarial assistanceMartin Deleersnyder (deceased May 11, 1976) was Candidate of the Nationaal Fonds voor Wetenschappelijk Onderzoek, Belgium     

Immunohistochemical localization of serotonin in intrapulmonary neuro-epithelial bodies

Summary A recently developed immunohistochemical technique for serotonin (Steinbusch et al. 1978) was used in the present investigation to study the occurrence of this indoleamine in the granulated epithelial cells of neuroepithelial bodies (NEB). Lungs from neonatal rabbits and pigs exhibit immunoreactive cell groups identical in morphology and their preferential location (i.e., at bronchiolar bifurcations) to the recently described intrapulmonary NEB. Moreover, in the trachea and lung of rabbits isolated immunoreactive cells, presumably of Kultschitsky type, were found in the lining respiratory mucosa. Such single cells were also frequently observed in the bronchial epithelium of pig lungs. It is concluded that the corpuscular cells, being modulated by the central nervous system, probably represent intrapulmonary neuro(chemo-)receptors with local secretory activities, one of the substances released being serotonin and reacting to the oxygen composition of the inhaled air. It is proposed that the cells of Kultschitsky type exert a more local effect upon the airways. Send offprint requests to: Katholieke Universiteit te Leuven, School of Medicine, Laboratory of Histopathology, B-3000 Leuven, Belgium     

Effects of unilateral vagal stimulation on intrapulmonary neuroepithelial bodies

We studied the influence of unilateral vagal stimulation on intrapulmonary neuroepithelial bodies (NEB) in rabbits. The left vagus nerve was cut and electrically stimulated for 10 min. Animals were killed and the lungs studied with fluorescence and electron microscopy. Intensity of formaldehyde-induced fluorescence, which reflects the serotonin content in NEB, was higher on the stimulated side than on the nonstimulated side (118 +/- 7 vs. 100%, n = 8, P less than 0.001). The latter difference was found to correlate with the stimulus amplitude (r = 0.9, P less than 0.05). Ultrastructurally a decrease in the number of exocytotic dense-cored vesicle (DCV) profiles at the level of the NEB basal epithelial cell membrane was found on the stimulated side (0.32 +/- 0.10 vs. 0.45 +/- 0.16 DCV/micron of basal epithelial cell membrane, n = 8, P less than 0.05). Section of the left vagus nerve without electrical stimulation affected neither the fluorescence intensity nor the number of exocytotic DCV profiles. In animals with supranodosal or infranodosal chronic vagotomy the observed effects of unilateral vagal stimulation were no longer present. We conclude that 1) vagal stimulation increases the serotonin content of NEB; 2) it decreases the number of exocytotic DCV profiles; 3) this effect depends on the amplitude of the stimulus; 4) it is obtained through efferent vagal fibers; 5) these results are the opposite of the effects seen after exposing normal NEB to acute hypoxia; and 6) these physiological experiments corroborate a vagal innervation of NEB, which may play an important role in modulating the sensitivity and reaction of NEB to various stimuli.     

Ultrastructural localization of serotonin in the intrapulmonary neuroepithelial bodies of neonatal rabbits by use of immunoelectron microscopy

Summary The ultrastructural localization of serotonin in neuroepithelial bodies (NEB) of neonatal rabbits was examined by use of the recently developed immunogold-staining method. In the granulated epithelial cells of NEB serotoninimmunoreactive material could be demonstrated only in dense-cored vesicles (DCV) of the first type. No immunoreactivity was observed in DCV of the second type. The present findings support the previously made suggestion that the corpuscular NEB cells contain two distinctive DCV types which react differently with the immunogold-staining procedure for identifying serotonin. NEB, known as intrapulmonary sources of serotonin (and peptide substances), may play a prominent role in lung physiology.     

The aetiology of hypoxaemia in chickens selected for rapid growth

In comparison to other classes of chickens, broilers selected for rapid growth tend to be hypoxaemic, and many develop congestive heart failure (CHF). In order to explain the physiological mechanisms associated with hypoxaemia in fast-growing broiler chickens (Gallus gallus), this study examined several basic physiological parameters including the blood gas profile in arterial [left atrial (LA)] and mixed venous [right atrial (RA)] blood, systemic oxygen extraction ratio, and intrapulmonary shunt fraction. These parameters were further studied in the context of blood flow in the pulmonary circulation, structural characteristics of the lungs, and cardiac function [measured as cardiac index (CI)]. Overall, broilers had lower arterial and mixed venous blood pO(2) levels and higher pCO(2) levels compared to leghorns. The cardiac index was lower in fast-growing and CHF broilers compared to leghorn chickens or feed-restricted broilers. Systemic oxygen extraction ratio (ER) and intrapulmonary shunt fraction were significantly higher in fast-growing broilers and birds with CHF (all P<0.01). Lungs of all broilers, but not leghorns, contained ectopic, irregular nodular formations located within air spaces. Broilers with clinical signs of hypoxaemia revealed the highest number of these formations in their lung. Taken together, the present findings indicate that key factors associated with the development of hypoxaemia in fast-growing broilers include: (1) high demand for oxygen as evidenced by high oxygen ER; (2) inadequate cardiac output (CO) to fulfill the higher oxygen demands, leading to severe depletion of O(2) in mixed venous blood; and (3) elevated intrapulmonary shunt fraction and possibly dead space associated with specific pathological and anatomical characteristics within the lung.     

Postnatal maturation of neuroepithelial bodies and carotid body innervation: A quantitative investigation in the rabbit

The intrapulmonary airways contain oxygen-sensitive chemoreceptors which may be analogous to the arterial chemoreceptors: the neuroepithelial bodies (NEB). While the NEB are prominent in the neonatal lung, physiological studies indicate that the carotid bodies are still relatively inactive at birth. This points to an unequal degree of development of both during the early neonatal period. As a reflexogenic chemoreceptor function depends on a well-developed innervation, we undertook a comparative investigation of the development of the NEB and the carotid body glomus cell innervation. Two morphological aspects of the innervation of NEB and carotid body glomus cells were quantified in rabbits of different age groups. The total sectional area of intracorpuscular and intraglomerular nerve endings per NEB or glomus cell group, respectively, was measured and the area percentage of mitochondria and synaptic vesicles was determined. In the NEB, no significant difference in total sectional area of the nerve endings between the age groups was observed, while in the carotid body there was a significant increase in the adult age group. In addition, the area percentage of mitochondria and synaptic vesicles of the nerve endings did not change significantly with age in the NEB, while in the carotid body these increased and decreased, respectively, with age. These observations point to a shift from morphologically efferent nerve endings, rich in synaptic vesicles, to morphologically afferent nerve endings, rich in mitochondria. Our interpretation of these findings is that, at birth, the NEB innervation is more mature than the carotid body glomus cell innervation and that the latter matures at a later time than the former. These findings support the theory that the NEB may act as complementary chemoreceptors to the carotid body during the early postnatal period.     

Effect of hyperoxia on the rate of restoration of blood composition after blood loss]

Regeneration of the peripheral red blood was considerably retarded in the anemic rabbits (blood letting of 2% of body weight) after a 5-hour exposure to the hyperoxiconditions (98% of oxygen in the inhaled air, 2 ata).     

Effects of moderate hypoxia on fetal electrocortical activity, eye movements, and breathing activity in sheep

Isocapnic hypoxaemia (delta PaO2 = -8.0 +/- 0.5 mmHg; delta CaO2 = -2.86 +/- 0.20 ml/dl) was produced in fetal sheep by having the ewe breathe for one hour a gas mixture (v/v) of 10.5% O2 and 1.5% CO2 in N2. Mean fetal heart rate, blood pressure, and incidence of low voltage electrocortical activity were not affected. However, the incidence of rapid-eye-movements and breathing activity was reduced by about 40%. Breathing movements during hypoxaemia had a mean inspiratory time, breath interval, and tracheal pressure amplitude which did not differ significantly from those during control experiments in which the ewe breathed air from the plastic bag. These observations suggest that hypoxia decreases the incidence of breathing movements but does not affect the amplitude or pattern of breathing activity and that it may reduce the incidence of eye movements and breathing activity through a common mechanism.     

Distribution and frequency of neuro-epithelial bodies in post-natal rabbit lung: Quantitative study with monoclonal antibody against serotonin

Summary The distribution, frequency and size of neuroepithelial bodies (NEB) were studied in lungs of rabbits during different stages of development (27-day fetus, newborn, 6, 11, 21, 28 and 56 days postnatally). NEB were visualized by immunostaining with monoclonal antibody against serotonin. Detailed quantitiation of NEB was performed by use of camera lucida drawings of immunostained serial sections from the same anatomical region, i.e. the lower lobe of the left lung. The total number of NEB was counted and expressed per epithelial length of airway, surface area and volume. The size of NEB defined as surface area as well as the position of NEB in relation to the airway bifurcations was assessed in airways of different sizes. The overall number and size of NEB were found to increase during the immediate perinatal period followed by a sharp decline at 56 days of age. The number of NEB peaked at 6 days postnatally (mean 175.5 NEB/mm³ of airway epithelium) and declined significantly (3.0 NEB/mm³) at 56 days of postnatal age. The size of NEB reached its maximum at 11 days (mean surface area 659.54 m², with the largest NEB measuring 1839.98 m²). By 56 days of age, NEB became significantly smaller (mean surface area 177.29 m²) consisting of small clusters of cells situated deep within the airway epithelium. At all ages, about half of all NEB (mean 47.6%) were localized within the small peripheral airways with up to 63.9% located at airway bifurcations. These findings indicate that the functional activity of NEB may be confined predominantly to the perinatal period. The postulated functions of NEB include those of intrapulmonary hypoxia-sensitive chemoreceptors and/or endocrine-paracrine activity in the lung. Such function(s) may be important during adaptation to extrauterine life as well as for growth and development of the lung.     

Temperature depression while aerating moist soils and the resultant effect on maize seedling growth

Summary Moist soil surfaces were aerated with air at relative humidities from 4 to 100%, flowing at rates from 0.07 to 3.5 liters per min. Evaporation occurred and resulted in measureable depressions of soil temperature when the aerating air was less than 100% saturated with water vapor and flowing at rates above 0.1 liter per min. Growth of young maize seedlings was markedly affected by depressed soil temperatures when the aerating air was at 30% relative humidity and flowing at 3.0 liters per min. Growth was affected even though the soil containers were submerged in constant temperature water baths to help maintain the uniformity of soil temperature. In containers similar to those used in this study, plant growth would be affected by aerating soils with air that is less than saturated with water vapor and is flowing at rates as low as 0.5 to 1.0 liter per min. On the other hand, plant growth would probably not be affected when aerated even with very dry air flowing at rates below about 0.1 liter per min.     

Sarafotoxin expression in the bronchopulmonary tract: immunohistochemical occurrence and colocalization with endothelins

The immunohistochemical occurrence of sarafotoxin (SRTX), a snake venom peptide under strong evolutionary control, was investigated in the pulmonary diffuse neuroendocrine system (PDNES) of newborn cats and rats. By applying the avidin-biotin-peroxidase complex method on serial lung sections, we have demonstrated its distribution and colocalization with different endothelin (ET) isoforms. A light microscopic study revealed apparent immunostaining for SRTX in neuronal components and smooth muscle tissue and in neuroepithelial bodies (NEB), while isolated neuroendocrine cells (NEC) remain unlabelled. Comparison of the SRTX reactivity pattern with that of different ET peptides on adjacent lung sections showed colocalization of SRTX-b with ET-3 in NEB, intrapulmonary ganglion cells and nerve fibres, on the one hand, and with ET-1 in airway and vascular smooth muscle cells, on the other. These findings, in addition to the remarkable functional and structural similarities between SRTX and ET peptides, suggest a common evolutionary origin and biological significance of sarafotoxin and endothelins. Moreover, this is the first time that a toxic peptide has been demonstrated in the PDNES.     

The distribution of monoamines in the tel-, di-and mesencephalon of Xenopus laevis tadpoles,with special reference to the hypothalamo-hypophysial system

Summary In an attempt to further our knowledge about the structure and function of the recently identified intrapulmonary Neuro-epithelial Bodies (NEB's) (Lauweryns et al., 1972a, 1972b), lungs of 84 neonatal rabbits and 6 neonatal mice were studied along four different lines of investigation. Several routine and silver staining methods, Falck's fluorescent amine technic and histochemical and electron microscopical techniques were performed.1. In order to test the probable chemoreceptor function of the NEB's, animals were exposed to hypoxia. Under such circumstances, the corpuscular cells of the NEB's secrete their dense-cored, serotonin-containing vesicles at their basal vascular pole. 2. After reserpine pretreatment, the NEB's of otherwise normal animals reveal a distinct amine depletion, the corpuscular cells exhibiting a decreased yellow fluorescence and ultrastructurally a clearing up of their dense-cored vesicles. 3. Studied on serial sections with the electron microscope, various types of morphologically afferent-like and efferent-like nerve endings, making contact as well with the corpuscular cells as amongst themselves have been detailed. 4. Cytochemically the corpuscular cells react positively with alpha-glycerophosphate dehydrogenase, acetylcholinesterase and Solcia's lead hematoxylin stain for endocrine cells producing polypeptides and amines.It is proposed that the NEB's provide an intrapulmonary, hypoxia-sensitive neuro(chemo-) receptor system in addition to the well established central and peripheral (e.g. carotid body) chemoreceptors. They contain and secrete serotonin and probably also related amines or peptides, which could influence the pulmonary vasoconstrictor response. According to classic morphologic criteria, they possess a dual innervation, both afferent and efferent.Various other possible functions of the NEB's in normal and diseased lungs are briefly proposed.This study has been supported by a grant from The Council for Tobacco Research — U.S.A. and the Nationaal Fonds voor Wetenschappelijk Onderzoek — Belgium. We thank P. Theunynck for performing some of the histochemical studies, B. Van Rijkel, B. Emanuel and R. Renwart for technical, G. Pison and St. Ons for photographical and N. Tyberghien for secretarial assistance.     

急性低氧与间断低氧适应对家兔局部血流分布的影响

本实验目的在于探讨急性低氧和间断低氧适应对局部血流分布的影响。我们将26只家兔分为急性低氧,低氧适应和常氧对照三组。在麻醉状态下用放射性标记的蟾蜍红细胞分别测定左心室、双侧肾、双侧肾上腺的血流量;并分区测定了大脑皮质、海马、丘脑下部、脑干的局部脑血流。吸入10％低氧混合气1小时后,急性低氧组脑局部、左心室、肾上腺的血流显著高于对照。经2周间断低氧适应后,低氧适应组脑局部(脑干除外)、左心室、肾上腺的血流下降。两组动物低氧时的肾血流变化不明显。结果提示,2周间断低氧适应能改变局部血流分布,血流的再分布有利于改善机体的抗低氧能力。     

Effect of exposure to 15% oxygen on breathing patterns and oxygen saturation in infants: interventional study

Objective: To assess the response of healthy infants to airway hypoxia (15% oxygen in nitrogen). Design: Interventional study. Settings: Infants’ homes and paediatric ward. Subjects: 34 healthy infants (20 boys) born at term; mean age at study 3.1 months. 13 of the infants had siblings whose deaths had been ascribed to the sudden infant death syndrome. Intervention: Respiratory variables were measured in room air (pre-challenge), while infants were exposed to 15% oxygen (challenge), and after infants were returned to room air (post-challenge). Main outcome measures: Baseline oxygen saturation as measured by pulse oximetry, frequency of isolated and periodic apnoea, and frequency of desaturation (oxygen saturation ⩽80% for ⩾4 s). Exposure to 15% oxygen was terminated if oxygen saturation fell to ⩽80% for ⩾1 min. Results: Mean duration of exposure to 15% oxygen was 6.3 (SD 2.9) hours. Baseline oxygen saturation fell from a median of 97.6% (range 94.0% to 100%) in room air to 92.8% (84.7% to 100%) in 15% oxygen. There was no correlation between baseline oxygen saturation in room air and the extent of the fall in baseline oxygen saturation on exposure to 15% oxygen. During exposure to 15% oxygen there was a reduction in the proportion of time spent in regular breathing pattern and a 3.5-fold increase in the proportion of time spent in periodic apnoea (P<0.001). There was an increase in the frequency of desaturation from 0 episodes per hour (range 0 to 0.2) to 0.4 episodes per hour (0 to 35) (P<0.001). In 4 infants exposure to hypoxic conditions was ended early because of prolonged and severe falls in oxygen saturation. Conclusions: A proportion of infants had episodes of prolonged (⩽80% for ⩾1 min) or recurrent shorter (⩽80% for ⩾4 s) desaturation, or both, when exposed to airway hypoxia. The quality and quantity of this response was unpredictable. These findings may explain why some infants with airway hypoxia caused by respiratory infection develop more severe hypoxaemia than others. Exposure to airway hypoxia similar to that experienced during air travel or on holiday at high altitude may be harmful to some infants.

Key messages

• A reduction in inspired oxygen concentration to 15% can induce severe prolonged hypoxaemia in a small proportion of infants
• Prediction of which infants will become hypoxaemic does not appear possible from analysing oxygenation or the respiratory pattern of infants breathing room air at sea level
• The way in which an infant responds to airway hypoxia may contribute to understanding the relation between respiratory infections, hypoxaemic episodes, and the sudden infant death syndrome
• Airline travel and holidays at high altitude may result in hypoxaemia in a small proportion of infants

     

Hypoxic initiation of pulmonary hypertension is mediated by serotonin secretion from neuroepithelial bodies in chemodenervated dogs

The purpose of this study was to investigate the stimulatory effect of hypoxia on the secretion of serotonin by neuroepithelial bodies (NEB) as well as to determine the relation between its level and changes in pulmonary arterial pressure (PAP) and also to determinate the effect of serotonin antagonists (pizotifen and methysergide) on the responses of pulmonary and systemic arterial pressures. The experiments were carried out in peripheral chemoreceptor-denervated dogs anesthetized with Na penthabarbital (30 mg/kg i.v.). On the breathing of normoxic and hypoxic (7% O2-93% N2) gas mixtures and on the injection of KCN (80 microg/kg i.v.), PAP, systemic arterial blood pressure (BP), tidal volume (VT), respiratory frequency (f/min), ventilation minute volume (VE) were determined. Also PAP and BP were recorded before and after the injection of pizotifen (0.5 mg/kg i.v.) and methysergide (1 mg/kg i.v.) during normoxic or hypoxic gas mixture breathing. At the end of each experimantal phase, serotonin level, PaO2, PaCO2 and pHa values in blood samples obtained from left ventricle and femoral artery were determined. On the breathing of the hypoxic gas mixture of the chemodenervated dogs, VT, VE and BP significantly decreased (P < 0.001, P < 0.001, P < 0.01). The mean value of PAP and serotonin levels (ventricular and femoral) were found significantly increased when compared with the corresponding normoxic values (P < 0.001, P < 0.05). On the other hand, injection of KCN produced no significant changes in PAP, serotonin levels, BP and respiratory parameters. After the injection of pizotifen, PAP was significantly increased in hypoxia (P < 0.01). After the injection of methysergide, the response of PAP was completely abolished during the breathing of hypoxic gas mixture. The finding of the abolition of response of PAP to hypoxia after the injection of methysergide indicates that serotonin release from NEB may be responsible for the elevation of PAP in hypoxic hypoxia.     

Intrapulmonary shunting and pulmonary gas exchange during normoxic and hypoxic exercise in healthy humans.

Exercise-induced intrapulmonary arteriovenous shunting, as detected by saline contrast echocardiography, has been demonstrated in healthy humans. We have previously suggested that increases in both pulmonary pressures and blood flow associated with exercise are responsible for opening these intrapulmonary arteriovenous pathways. In the present study, we hypothesized that, although cardiac output and pulmonary pressures would be higher in hypoxia, the potent pulmonary vasoconstrictor effect of hypoxia would actually attenuate exercise-induced intrapulmonary shunting. Using saline contrast echocardiography, we examined nine healthy men during incremental (65 W + 30 W/2 min) cycle exercise to exhaustion in normoxia and hypoxia (fraction of inspired O(2) = 0.12). Contrast injections were made into a peripheral vein at rest and during exercise and recovery (3-5 min postexercise) with pulmonary gas exchange measured simultaneously. At rest, no subject demonstrated intrapulmonary shunting in normoxia [arterial Po(2) (Pa(O(2))) = 98 +/- 10 Torr], whereas in hypoxia (Pa(O(2)) = 47 +/- 5 Torr), intrapulmonary shunting developed in 3/9 subjects. During exercise, approximately 90% (8/9) of the subjects shunted during normoxia, whereas all subjects shunted during hypoxia. Four of the nine subjects shunted at a lower workload in hypoxia. Furthermore, all subjects continued to shunt at 3 min, and five subjects shunted at 5 min postexercise in hypoxia. Hypoxia has acute effects by inducing intrapulmonary arteriovenous shunt pathways at rest and during exercise and has long-term effects by maintaining patency of these vessels during recovery. Whether oxygen tension specifically regulates these novel pathways or opens them indirectly via effects on the conventional pulmonary vasculature remains unclear.     

Quantitation of pulmonary neuroepithelial bodies in pre- and postnatal rabbits

Summary The size, density and total number of neuroepithelial bodies (NEB) in the lungs of late fetal, neonatal, and mature rabbits were determined using fluorescence microscopy. In this study lungs from 27-, 29-, 30-, and 31-day fetuses; neonates of ages 2, 7, and 30 days; and 4- and 7(+)-month-old rabbits, were used. The total number of NEB in the entire lung of rabbits from each age group was estimated based on measurements of collapsed lung volume, average NEB diameter, and NEB density (number/mm²). Average NEB diameter increased between 27 and 29 days gestation, then remained constant at 42–44 m between 29 days gestation and two days post-partum. Thereafter the diameter was significantly reduced in the 7-day group (33.7 m) and further reduced in the 4-month group (20.3 m). NEB density was initially high in 27-day fetuses (3.87/mm²), decreased significantly by 30 days gestation, increased to a high level by 2 days post-partum, then fell steadily, reaching the lowest level in the adult (0.15/mm²). This steady decrease in density was paralleled by a large increase in lung volume. The estimated total number of NEB in the lung was constant in all age groups except for a significant drop at 30 and 31 days gestation. These data indicate that the total number of NEB is maintained into adulthood; however, the density and average diameter of NEB decreases rapidly after 2 days postpartum. A sharp decrease in both total number and density observed under fluorescence microscopy at 30 and 31 days gestation suggests a change in NEB cellular activity just prior to birth.     

Effect of hypoxic breathing on cutaneous temperature recovery in man

Effect of hypoxia (12% O₂) on skin temperature recovery was studied on healthy young men. Forty male volunteers free of any respiratory disorder were randomly selected to participate in the study. Skin temperature, peripheral blood flow, heart rate and end expiratoryPO₂ andPCO₂ were measured. During hyoxic ventilation the peripheral blood flow was reduced and a corresponding drop in skin temperature occurred. This was partly due to hyperventilation associated with hypoxic ventilation. The recovery of skin temperature after cooling the hand for 2 min in cold water (10–12° C) took 5.5±0.1 min during normal air breathing; during hypoxic ventilation even after 9.1±0.3 min when the skin temperature recovery curve plateaued, the skin temperature remained about 2° C below control. The results of the present investigation indicate that hypoxia interferes with the normal functioning of the thermoregulatory mechanism in man. Hyperventilation associated with hypoxic ventilation is also partly responsible for incomplete recovery of skin temperature.     

Expression of functional purinergic receptors in pulmonary neuroepithelial bodies and their role in hypoxia chemotransmission

Adenine nucleotides act through specific cell surface receptors to invoke a variety of biological responses. Here we show that cells of neuroepithelial bodies (NEB), presumed O2 airway sensors in neonatal hamster lung, express functional P2X receptors (P2X-R). Positive immunostaining was detected in NEB cells using double-label immunohistochemistry with antibodies against P2X2 and P2X3 receptor subunits, which co-localized with serotonin (5-HT), a marker of NEB cells. For electrophysiological characterization of P2X2-R in NEB cells, fresh neonatal hamster lung slice preparation was used. Under whole-cell patch clamp, perfusion with ATP induced a concentration-dependent, non-desensitizing inward current (EC50=12 microM). Perfusion with alpha,beta-methylene ATP also induced a slow-desensitizing inward current (EC50=8.2 microM). Suramin (IC50 ca. 43 microM) and TNP-ATP (IC50 ca. 8 microM) blocked the currents evoked by both ATP and alpha,beta-methylene ATP. Using carbon fiber amperometry we observed that hypoxia and ATP induced 5-HT release from NEB cells and that this release was blocked by suramin. These data suggest that functional P2X2/3 heteromeric receptors are expressed in NEB cells. The possible function of these purinoreceptors in NEB cells could include modulation of hypoxia chemotransmission.