Animals Breathed Room Air Research Articles

Activation of Astrocytes in the Persistence of Post-hypoxic Respiratory Augmentation.

Acute hypoxia increases ventilation. After cessation of hypoxia loading, ventilation decreases but remains above the pre-exposure baseline level for a time. However, the mechanism of this post-hypoxic persistent respiratory augmentation (PHRA), which is a short-term potentiation of breathing, has not been elucidated. We aimed to test the hypothesis that astrocytes are involved in PHRA. To this end, we investigated hypoxic ventilatory responses by whole-body plethysmography in unanesthetized adult mice. The animals breathed room air, hypoxic gas mixture (7% O2, 93% N2) for 2min, and again room air for 10min before and after i.p. administration of low (100mg/kg) and high (300mg/kg) doses of arundic acid (AA), an astrocyte inhibitor. AA suppressed PHRA, with the high dose decreasing ventilation below the pre-hypoxic level. Further, we investigated the role of the astrocytic TRPA1 channel, a putative ventilatory hypoxia sensor, in PHRA using astrocyte-specific Trpa1 knockout (asTrpa1−/−) and floxed Trpa1 (Trpa1f/f) mice. In both Trpa1f/f and asTrpa1−/− mice, PHRA was noticeable, indicating that the astrocyte TRPA1 channel was not directly involved in PHRA. Taken together, these results indicate that astrocytes mediate the PHRA by mechanisms other than TRPA1 channels that are engaged in hypoxia sensing.

Astrocytes mediate the post‐hypoxic persistent respiratory augmentation

Acute hypoxia increases ventilation. After brief hypoxic exposure, switchback of inspired gas to room air is accompanied by short-term potentiation of breathing, i.e., ventilation remains elevated above the baseline level. Short-term potentiation of breathing has been thought to play a stabilizing role in control of breathing, e.g., prevention of periodic breathing. However, the mechanism of this potentiation is unclear. We aimed to test the hypothesis that astrocytes mediate this potentiation, i.e., post-hypoxic persistent respiratory augmentation (PHRA), and performed a series of in vitro and in vivo experiments. In vitro, isolated brainstem-spinal cord preparations of neonatal rats were superfused with artificial cerebrospinal fluid (aCSF) without or with arundic acid (500 µM), an inhibitory modulator of astrocytic function. Both groups were sequentially superfused with oxygenated (95% O2, 5% CO2) and hypoxic (95% N2, 5% CO2) aCSF for 5 min, and again with oxygenated aCSF for 17 min. Hypoxia universally increased the respiratory burst rate. Without arundic acid, the burst rate transiently decreased with reoxygenation, and then recovered to and remained at the pre-hypoxic level until the end of the post-hypoxic observation. Contrarily, the burst rate steadily decreased throughout the post-hypoxic phase with arundic acid, declining below the pre-hypoxic level. In vivo, the hypoxic ventilatory response was investigated by whole-body plethysmography in unanesthetized adult mice. The animals breathed room air, hypoxic gas (7% O2, 93% N2) for 2 min, and again room air for 10 min before and after i.p. administration of low (100 mg/kg) and high (300 mg/kg) doses of arundic acid. Minute ventilation in the post-hypoxic recovery was maintained above the pre-hypoxic level without arundic acid. However, it was suppressed with arundic acid. Notably with high dose arundic acid, it decreased below the pre-hypoxic level. Finally, we investigated the significance of the astrocytic TRPA1 channel, which is a ventilatory hypoxic sensor, in the PHRA using astrocyte-specific Trpa1 knockout (asTrpa1-/-) and floxed Trpa1 (Trpa1f/f) mice. Although the PHRA was observed in both Trpa1f/f and as Trpa1-/- mice, it was weaker in asTrpa1-/- as compared to Trpa1f/f mice. This observation indicates that the astrocytic TRPA1 channel plays a role in the PHRA but this by itself is not sufficient, suggesting the existence of additional key factors. These in vitro and in vivo experimental findings collectively demonstrate that astrocytes mediate the PHRA partially through the TRPA1 channel.

The Effect of Carbogen Breathing on 18F-FDG Uptake in Non-Small-Cell Lung Cancer.

It has been reported that 18F-FDG uptake is higher in hypoxic cancer cells than in well-oxygenated cells. We demonstrated that 18F-FDG uptake in lung cancer would be affected by high concentration oxygen breathing. Methods. Overnight fasted non-small-cell lung cancer A549 subcutaneous (s.c.) xenografts bearing mice (n = 10) underwent 18F-FDG micro-PET scans, animals breathed room air on day 1, and same animals breathed carbogen (95% O2 + 5% CO2) on the subsequent day. In separated studies, autoradiography and immunohistochemical staining visualization of frozen section of A549 s.c. tumors were applied, and to compare between carbogen-breathing mice and those with air breathing, a combination of 18F-FDG and hypoxia marker pimonidazole was injected 1 h before animal sacrifice, and 18F-FDG accumulation was compared with pimonidazole binding and glucose transporter 1 (GLUT-1) expression. Results. PET studies revealed that tumor 18F-FDG uptake was significantly decreased in carbogen-breathing mice than those with air breathing (P < 0.05). Ex vivo studies confirmed that carbogen breathing significantly decreased hypoxic fraction detected by pimonidazole staining, referring to GLUT-1 expression, and significantly decreased 18F-FDG accumulation in tumors. Conclusions. High concentration of O2 breathing during 18F-FDG uptake phase significantly decreases 18F-FDG uptake in non-small-cell lung cancer A549 xenografts growing in mice.

Intermittent hypoxia increases melanoma metastasis to the lung in a mouse model of sleep apnea

Obstructive sleep apnea (OSA) has recently been associated with an increased risk of cancer incidence and mortality in humans. Experimental data in mice have also shown that intermittent hypoxia similar to that observed in OSA patients enhances tumor growth. The aim of this study was to test the hypothesis that intermittent hypoxia mimicking OSA enhances lung metastasis. A total of 75 C57BL/6J male mice (10-week-old) were subjected to either spontaneous or induced melanoma lung metastasis. Normoxic animals breathed room air and intermittent hypoxic animals were subjected to cycles of 20s of 5% O2 followed by 40s of room air for 6h/day. Spontaneous and induced lung metastases were studied after subcutaneous and intravenous injection of B16F10 melanoma cells, respectively. Compared with normoxia, intermittent hypoxia induced a significant increase in melanoma lung metastasis. These animal model results suggest that intermittent hypoxia could contribute to cancer metastasis in patients with OSA.

Effects of inhalation of different concentrations of sevoflurane on pulmonary inflammatory response in rats

Objective To investigate the effects of inhalation of different concentrations of sevoflurane on pulmonary inflammatory response in rats. Methods One hundred and twenty adult Wistar rats of both sexes weighing 200-250 g were randomly divided into 4 groups: Ⅰ control group breathing room air (group C, n = 12);Ⅱ oxygen group breathing 40% O2(group O, n = 36);Ⅲ and Ⅳ sevoflurane groups breathing 1.5% and 3.0% sevoflurane in 40% O2 respectively (group S1, S2, n = 36). Group Ⅱ was further divided into 3 subgroups according to the duration of 40% O2 inhalation 4 h, 8 h and 10 h. Group Ⅲ and Ⅳ were further divided into 3 subgroups ( n = 12 each) breathing sevoflurane for 4 h, 8 h and 8 h followed by 2 h O2 (40%) inhalation. The animals were sacrificed at the end of O2 or/and sevoflurane inhalation. Broncho-alveolar lavage was performed in 6 animals in each subgroup. The TNF-α concentration in broncho-alveolar lavage fluid was determined. The TNF-α mRNA expression and MPO activity in the lung tissue were measured in the other 6 animals in each subgroup. Results Inhalation of 1.5% or 3.0% sevoflurane for 4 or 8 h did not induce inflammatory response in the lung as compared with animals breathing room air or 40% O2 . Conclusion Exposure to sevoflurane does not induce pulmonary inflammatory response in rats breathing spontaneously. Key words: Inflammation; Lung; Anesthesia,inhalation; sevoflurane

The impact of inspired oxygen concentration on tissue oxygenation during progressive haemorrhage

Standard resuscitation practice for shock states mandates use of high flow, high concentration oxygen. However, this may induce microvascular constriction and potentially impair regional oxygen delivery. We thus investigated the impact of varying inspired oxygen concentrations in a rat model of progressive haemorrhage. Tissue oxygen tension (the balance between local O2 supply and demand) was measured in four different organ beds (liver, renal cortex, muscle, bladder), with concurrent assessment of cardiorespiratory function and organ perfusion in a spontaneously breathing, anaesthetised rat model. 10% aliquots of circulating blood volume were removed at 15 min intervals until death. Different oxygen fractions in the gas mixture (0.15-1.0) were administered following 20% blood removal. A control group consisted of normovolaemic animals breathing varying oxygen fractions. Survival times following progressive haemorrhage were similar in animals breathing room air (98 +/- 10 min), 60% O2 (102 +/- 6 min) or 100% O2 (90 +/- 4 min), but significantly worse in those breathing 15% O2 (52 +/- 8 min, P < 0.01). Significant derangements of blood pressure, aortic blood flow and lactataemia were observed in both hypoxaemic and hyperoxaemic groups compared to normoxaemic animals. Breathing 100% O2 increased arterial PO2 sevenfold and tPO2 approximately threefold over baseline values during normovolaemia and mild haemorrhage (20% blood volume removal). However, with progressive haemorrhage, and despite maintained PaO2 values, tissue PO2 fell in line with the decrease in global oxygen delivery. Hypoxaemia and hyperoxaemia both compromised haemodynamics and biochemical markers of organ perfusion during severe, progressive haemorrhage. This may carry implications for resuscitation practice.

Serotonin, gasping, autoresuscitation, and SIDS—a contrarian view

in their study in the Journal of Applied Physiology , Erikson and Sposato ([4][1]) induced anoxic apnea in neonatal Pet -1 knockout (KO) and wild-type mice at postnatal day (P) 4.5 and P9 and examined the subsequent quality of gasping and autoresuscitation while the animals breathed room air. Pet-1

Pulmonary vasodilator responses to sodium nitrite are mediated by an allopurinol-sensitive mechanism in the rat

Recent studies show that pulmonary vasodilator responses to nitrite are enhanced by hypoxia. However, the mechanism by which nitrite is converted to vasoactive nitric oxide (NO) is uncertain. In the present study, intravenous injections of sodium nitrite decreased pulmonary and systemic arterial pressures and increased cardiac output. The decreases in pulmonary arterial pressure were enhanced when tone in the pulmonary vascular bed was increased with U-46619. Under elevated tone conditions, decreases in pulmonary and systemic arterial pressures in response to nitrite were attenuated by allopurinol in a dose that did not alter responses to the NO donors, sodium nitroprusside and diethylamine/NO, suggesting that xanthine oxidoreductase is the major enzyme-reducing nitrite to NO. Ventilation with a 10% O(2) gas mixture increased pulmonary arterial pressure, and the response to hypoxia was enhanced by N(G)-nitro-l-arginine methyl ester and not altered by allopurinol. This suggests that NO formed by the endothelium and not from the reduction of plasma nitrite modulates the hypoxic pulmonary vasoconstrictor response. Although intravenous injections of sodium nitrite reversed pulmonary hypertensive responses to U-46619, hypoxia, and N(G)-nitro-l-arginine methyl ester, the pulmonary vasodilator response to nitrite was not altered by ventilation with 10% O(2) when baseline pulmonary arterial pressure was increased to similar values in animals breathing room air or the hypoxic gas. These data provide evidence that xanthine oxidoreductase is the major enzyme-reducing nitrite to vasoactive NO, and that this mechanism is not modified by hypoxia.

Sodium and Water Homeostasis During Chronic Intermittent Hypoxia in Female Rats

Chronic intermittent hypoxia (CIH) is a widely used model for the repetitive bouts of hypoxia that occur during sleep apnea. Using this model we have demonstrated an elevation in blood pressure and disturbances in sodium and water homeostasis in male rats exposed to CIH. These previous findings indicate that the elevation of blood pressure is associated with sodium and water retention. We have also observed that female rats are protected against the elevation in blood pressure during exposure to CIH. To determine if the blunted blood pressure response to CIH in females was associated with diminished sodium and water retention, we evaluated sodium and water homeostasis in female rats exposed to CIH. Female Sprague-Dawley rats (n=9) were placed in metabolic cages in enclosed chambers and exposed to 7 days of room air (control), 7 days of CIH, and 7 days of room air (recovery). CIH is defined as continuous cycles of 3 minutes of room air (21% O2) and 3 minutes of 10% O2 for 8 hours (Hypoxia: 8 am to 4 pm). During the remaining 16 hours (No-Hypoxia: 4 pm to 8 am) the animals breathed room air. Water intake, urine volume, sodium intake, and urine sodium concentration were measured during the Hypoxia and No-Hypoxia periods of the day for the 21 days of the experiment. We observed no significant differences in sodium and water balances between control, CIH, and recovery periods. These results are in contrast to our previous observations of sodium and water retention in males exposed to CIH during the No-Hypoxia period of the day. We conclude that females maintain sodium and water balance during CIH which may contribute to the associated blunted elevation in blood pressure.

P0936 INTESTINAL PLATELET-ACTIVATING FACTOR ACETYLHYDROLASE ACTIVITY IN A NEONATAL PIGLET MODEL OF NECROTISING ENTEROCOLITIS.

Introduction: We recently reported a model of necrotising enterocolitis (NEC) in the neonatal piglet using hypoxia (H) and endotoxin (lipopolysaccharide, LPS), which both induce endogenous release of platelet-activating factor (PAF). Intestinal lesions produced in this model are ameliorated by a prophylactic PAF-antagonist, suggesting a role for PAF in the pathogenesis of NEC.1 PAF is rapidly degraded in-vivo by the specific enzyme PAF-acetylhydrolase (PAF-AH). The aim of this study was to determine PAF-acetylhydrolase activity throughout the intestine in this model of NEC. Methods: 9 anaesthetised neonatal piglets were studied: controls n=2; hypoxia + low dose LPS [H+LLPS] n=3; and hypoxia + high dose LPS [H+HLPS] n=4. Control animals breathed room air; H+LLPS animals received a combination of 10% O2 (for 45 minutes) and LPS (2 mg/kg); and the H+HLPS animals received 10% O2 and LPS (4 mg/kg). The experiment was terminated after 360 minutes and samples of intestine were snap-frozen and stored at −80 degrees C. Cytosolic PAF-AH activity was determined in the duodenum, jejunum, proximal ileum, distal ileum, caecum and colon with a colourmetric assay using 2-Thio-PAF as a substrate. Results: In control animals PAF-AH activity was lowest in the duodenum and increased along the intestine to a maximum in the ileum (between 5 and 7 fold) and was decreased in the colon. A similar pattern of enzyme activity was observed in both insult groups. In the H+LLPS animals there was no statistically significant change in the mean PAF-AH activity in any region when compared with controls. However, in the H+HLPS animals the mean PAF-AH activity was significantly increased (between 3.5 and 11 fold) in all regions when compared with controls (p < 0.05). Conclusion: In all groups PAF-AH activity increases between 5 and 7 fold from the duodenum to the distal ileum before decreasing in the colon. In addition, hypoxia and high dose LPS resulted in a significant rise in PAF-AH activity from the baseline levels seen in controls. In our model, these insults cause intestinal damage typical of NEC. The rise in PAF-AH activity may be in response to a rise in PAF in these areas.

Enhanced S-nitroso-albumin formation from inhaled NO during ischemia/reperfusion.

In the present study, we investigated whether inhaled nitric oxide (NO) was transported by plasma proteins, such as S-nitroso-albumin (SNO-Alb), in the feline circulation and whether this molecule delivers NO to the periphery under conditions of stress, specifically ischemia/reperfusion (I/R). A flow probe was interposed between the femoral and superior mesenteric artery for blood flow measurements, and a branch of the superior mesenteric vein was cannulated for arterial-venous sampling. In animals breathing room air, SNO-Alb was below detection level in arterial or venous blood. NO inhalation resulted in a significant arterial-venous gradient for SNO-Alb. Concomitant with this loss of SNO-Alb across the intestinal vasculature was an increase in nitrite (NO2-). However, this release of NO was not sufficient to alter intestinal blood flow. I/R during NO inhalation caused a very large increase in arterial SNO-Alb that permitted a 5-fold increase in SNO-Alb consumption and significant generation of NO2- within the postischemic intestinal vasculature. The increased SNO-Alb consumption was sufficient to dramatically improve intestinal blood flow. The very large burst of arterial SNO-Alb during I/R was completely blocked by the administration of superoxide dismutase, suggesting that oxidative stress contributed to the increased SNO-Alb formation. Our data suggest that inhaled NO can increase nitrosothiol production and these molecules may be a functional NO delivery system during cardiovascular disease.

Noninvasive in vivo oximetric imaging by radiofrequency FT EPR.

A novel method, called relaxo-oximetry, for rapid spatially resolved in vivo measurements of oxygen concentration using time-domain radiofrequency (RF) electron paramagnetic resonance (EPR) is described. Time-domain data from triaryl methyl (TAM)-based single-electron contrast agents were processed by systematic deletion of the initial time points to arrive at T2*-weighted discrimination of signal amplitudes. In experiments involving phantoms, the line widths [ approximately (T2*)(-1)] increased as a function of oxygen, and the slope (line width/pO(2)) was the same for both absorption- and magnitude-mode line shapes. Line widths derived from T2* weighting and the computed pO(2) values agreed favorably with the measured ones from phantoms of known oxygen tension. In vivo relaxo-oximetry was performed on C3H mice, and it was found that the liver was more hypoxic than the kidneys. For tumors, 2D oxygen maps were generated while the animal breathed room air or Carbogen(R) (95% O(2)/5% CO(2)). Carbogen(R) enhanced oxygen concentration within the tumor, and the pO(2) histograms showed considerable heterogeneity. Clark electrode oxygen measurements on organs and tumors were in good agreement with tissue oxygen measurements done by relaxo-oximetry. Thus, from a single spatial image data set, pO(2) measurements can be done noninvasively by relaxo-oximetry, and 3D imaging can be performed in less than 3 min.

Effects of different exposures of hyperbaric oxygen on ligament healing in rats

Hyperbaric oxygen (HBO) is a method of augmenting, intermittently, oxygen availability to tissues. We examined the effect of three different HBO exposures on the healing of experimentally induced ligament lacerations in the right hind limb of 44 male Wistar rats. Animals were divided into four groups after ligament injury: (a) control group, animals breathed room air at 1 ATA (atmosphere absolute) in a hyperbaric chamber for 60 min; (b) HBO treatment at 1.5 ATA for 30 min once a day, (c) HBO treatment at 2 ATA for 30 min once a day, (d) 2 ATA for 60 min once a day. At 14 days post-ligament injury, we compared the ligaments of the four treatment groups for gross appearance, histology and expression of pro-α(I) mRNA by northern hybridization. Our results indicate that HBO was effective in promoting ligament healing compared to control ( p<0.01). Of these three exposures, HBO at 2 ATA for 60 min was the most effective, resulting in enhanced extra-cellular matrix deposition as measured by collagen synthesis.

Improvement of tumor response by manipulation of tumor oxygenation during photodynamic therapy.

Photodynamic therapy (PDT) requires molecular oxygen during light irradiation to generate reactive oxygen species. Tumor hypoxia, either preexisting or induced by PDT, can severely hamper the effectiveness of PDT. Lowering the light irradiation dose rate or fractionating a light dose may improve cell kill of PDT-induced hypoxic cells but will have no effect on preexisting hypoxic cells. In this study hyperoxygenation technique was used during PDT to overcome hypoxia. C3H mice with transplanted mammary carcinoma tumors were injected with 12.5 mg/kg Photofrin and irradiated with 630 nm laser light 24 h later. Tumor oxygenation was manipulated by subjecting the animals to 3 atp (atmospheric pressure) hyperbaric oxygen or normobaric oxygen during PDT light irradiation. The results show a significant improvement in tumor response when PDT was delivered during hyperoxygenation. With hyperoxygenation up to 80% of treated tumors showed no regrowth after 60 days. In comparison, when animals breathed room air, only 20% of treated tumors did not regrow. To explore the effect of hyperoxygenation on tumor oxygenation, tumor partial oxygen pressure was measured with microelectrodes positioned in preexisting hypoxic regions before and during the PDT. The results show that hyperoxygenation may oxygenate preexisting hypoxic cells and compensate for oxygen depletion induced by PDT light irradiation. In conclusion, hyperoxygenation may provide effective ways to improve PDT efficiency by oxygenating both preexisting and treatment-induced cell hypoxia.

Targeted deletion of the neutral endopeptidase gene alters ventilatory responses to acute hypoxia in mice.

Neutral endopeptidase (NEP) is one of the major endopeptidases responsible for the inactivation of substance P in the carotid body, a neurotransmitter shown to be important in the transduction of hypoxic stimuli. Ventilatory responses to acute hypoxia were measured by indirect plethysmography in unanesthetized, unrestrained wild-type mice and in mice in which the NEP gene was deleted (NEP -/-). Ventilation was measured while the animals breathed room air: 12% O(2) in N(2) and 8% O(2) in N(2). Deletion of the NEP gene caused marked alterations in both the magnitude and composition of the hypoxic ventilatory response to both 8% O(2) in N(2) and 12% O(2) in N(2), compared with the wild-type mice (C57BL/6J) on the same genetic background as the NEP -/- mice. Treatment of C57BL/6J mice with thiorphan, a NEP inhibitor, resulted in a greater ventilatory response to 8% O(2) because of a significantly greater shortening of expiratory time. The results of these studies demonstrate that NEP plays an important role in modifying the expression of the ventilatory response to acute hypoxia.

Antioxidants attenuate chronic hypoxic pulmonary hypertension.

Because chronic hypoxia increases the production of oxygen radicals, we hypothesized that antioxidants attenuate chronic hypoxic pulmonary hypertension. In part 1, we examined the temporal progress in chronic hypoxic pulmonary hypertension in 46 Wistar rats exposed to hypoxia from 0-3 weeks. In part 2, we tested whether antioxidants attenuated chronic hypoxic pulmonary hypertension in 82 rats divided into 10 groups: control, fullerenol-1, U-83836E, dimethylthiourea-1, dimethylthiourea-2, hypoxia, hypoxia + fullerenol-1, hypoxia + U83836E, hypoxia + dimethylthiourea-1, and hypoxia + dimethylthiourea-2. Control animals breathed room air and were injected intraperitoneally with saline for 2 weeks. Fullerenol-1, U-83836E, and dimethylthiourea are antioxidants and were administered intraperitoneally for 2 weeks, except that dimethylthiourea was given either on days 3, 5, and 7 (dimethylthiourea-1), or on days 8, 10, and 12 (dimethylthiourea-2). Hypoxic animals were placed into a hypobaric chamber with a barometric pressure of 380 Torr for 2 weeks. Hypoxia + antioxidant groups were administered antioxidants during hypoxic exposure. We observed a gradual increase in pulmonary artery pressure, the weight ratio of right ventricle to left ventricle plus septum, and hematocrit during the 3 weeks of chronic hypoxia. These hypoxia-induced alterations were significantly attenuated by U-83836E and dimethylthiourea, but not by fullerenol-1. Neither the temporal alterations nor the antioxidant effects can be explained by the change in either tracheal neutral endopeptidase activity or the lung or plasma substance P level, perhaps because of the time lag in sampling. These results indicate that oxygen radicals play an important role in the development of chronic hypoxic pulmonary hypertension.

Capsaicin pretreatment attenuates chronic hypoxic pulmonary hypertension

Capsaicin pretreatment was used to deplete tachykinins in order to study the role of tachykinins in chronic hypoxia-induced pulmonary hypertension. Forty three young Wistar rats weighing 235 ± 4 g were randomly divided into four groups: control ( n = 10); capsaicin pretreatment ( n = 10); intermittent chronic hypoxia ( n = 10); and capsaicin pretreatment + intermittent chronic hypoxia ( n = 13). Control animals breathed room air. Rats in the capsaicin pretreatment groups were given capsaicin via subcutaneous injection over a three-day period. Hypobaric hypoxia was intermittently applied by placing animals into a hypobaric chamber with a barometric pressure of 380 Torr for two weeks. In the capsaicin pretreatment + intermittent chronic hypoxia group, rats were exposed to intermittent hypoxia for two weeks immediately after the last dose of capsaicin. Subsequently, pulmonary vascular function, as well as substance P (a tachykinin) level and neutral endopeptidase (NEP, the major degradation enzyme for tachykinins) activity in the lungs were measured. Chronic hypoxia caused significant increases in pulmonary artery pressure, right ventricle/(left ventricle + septum) weight ratio, hematocrit, and lung substance P level, as well as a significant decrease in lung NEP activity. All these chronic hypoxia-induced changes were significantly lessened by capsaicin pretreatment. Capsaicin pretreatment alone did not induce any significant alteration in vascular function. These results suggest that the chronic hypoxia causes an increase in lung tachykinin levels which, in turn, enhance the development of pulmonary hypertension.

Effects of epinephrine on the cardiorespiratory response to hypoxia in sedated newborn piglets with intact and denervated carotid bodies.

In order to evaluate the effects of epinephrine on the cardiorespiratory response to hypoxia in the neonate, 35 sedated, spontaneously breathing newborn piglets (mean +/- SD, age 5 +/- 0.8 days; weight 1.6 +/- 0.3 kg) with intact (ICB) or denervated (DCB) carotid bodies were studied before and during an infusion of saline or epinephrine (2.2 +/- 1.0 microgram/kg/min, i.v.). Cardiorespiratory measurements were performed while the animals breathed room air and after 10 min of hypoxia (FiO2 0.10) during saline or epinephrine infusion. During epinephrine infusion, the ICB animals had a sustained increase in minute ventilation during hypoxia while the control group showed a biphasic ventilatory response with depression during sustained hypoxia. After the chemodenervation, the ventilatory response to hypoxia was completely blunted in saline and epinephrine animals. In the ICB and DCB animals, the arterial blood pressure decreased significantly with hypoxia during epinephrine infusion, while cardiac output increased significantly in all ICB and DCB saline animals. The oxygen consumption (VO2) decreased significantly after 10 min of hypoxia in all groups except in the ICB epinephrine animals, in whom the VO2 did not change with hypoxia. In conclusion, the administration of epinephrine to newborn piglets reverses the depressed ventilatory response to hypoxia and this effect requires the activity of the peripheral chemoreceptors.

The nature of increased blood‐cerebrospinal fluid barrier exchange during CO2 inhalation in newborn and adult rats

Exposure of newborn (2-day-old) and adult rats to increasing levels of inspired carbon dioxide (5-15% CO2) resulted in increased steady-state cerebrospinal fluid/plasma ratios for a wide range of different-sized, lipid-insoluble permeability markers (molecular radius ranged from 0.43 nm for L-glucose to 5.3 nm for immunoglobulin G). In control animals breathing room air and animals exposed to an elevated level of inspired CO2, steady-state CSF/plasma ratios for all permeability markers were proportional to their free diffusion coefficient. Steady-state CSF/plasma ratios in newborn animals were significantly higher than in adult animals, and at all ages the ratios for animals exposed to CO2 were higher than the ratios in control animals. In contrast to the increased steady-state CSF/plasma ratios in animals exposed to elevated levels of inspired CO2, there was no significant difference in short-term (10 min after i.v. injection) CSF/plasma ratios for [14C]L-glucose between 10- to 20-day-old control rats and rats of similar age exposed to 10% inspired CO2. Steady-state experiments confirmed that CSF/plasma ratios for [14C]L-glucose in 20-day-old rats exposed to 10% inspired CO2 were raised significantly (twice those measured in control animals breathing room air). The lack of effect of raised CO2 on short-term CSF/plasma ratios indicates that the significant increases in steady-state CSF/plasma ratios, in animals exposed to elevated levels of inspired CO2, are not due to a general increase in the permeability of the blood-CSF or blood-brain barriers; they are likely to be accounted for by CO2-induced reductions in the rate of CSF secretion.

Pre- and postnatal effects of chronic maternal hypoxia on substance-P immunoreactivity in rabbit brainstem regions.

The effect of chronic maternal hypoxia on substance-P immunoreactivity (SPI) was examined in brainstem regions of fetal (gestational day E-28), neonatal (postnatal days 3, 7, 14, 21), and adult rabbits. Time-dated pregnant rabbit does were housed in environmental chambers at gestational day E-10. Between E-14 and E-28, the pregnant does were separated into two groups. Group 1, the control group, breathed 21% O2/79% N2 and group 2 the hypoxia-exposed group, breathed 12-14% O2/86-88% N2. Sacrifice occurred at various days depending on the experimental paradigm. On gestational day E-28, 6 pregnant animals were delivered by hysterotomy and the pups were immediately sacrificed. On and after gestational day E-28, the remaining 12 pregnant animals breathed room air. These animals delivered spontaneously between E-30 and E-32 and the pups remained with their mothers until sacrifice. On postnatal days 3, 7, 14, and 21, SPI was measured by radioimmunoassay in the colliculi (fetal animals), superior and inferior colliculi (postnatal analysis), pons and medulla (both groups). In both prenatally normoxia- and hypoxia-exposed animals, SPI was highest in the medulla, intermediate in the pons and lowest in the colliculi. SPI increased with development. Chronic maternal hypoxia did not alter the caudal-rostral profile nor did it alter the maturational increase in SPI. However, chronic maternal hypoxia increased SPI in prenatal animals and decreased SPI in postnatal animals at 14 and 21 days of life but not in postnatal 3- and 7-day-old animals. These data support the concept that regional differences exist in basal SPI within the brainstem of fetal and neonatal animals, and that maternal hypoxia has both immediate and long-term effects on brainstem SPI.