Hypoxic Animal Research Articles

Transcriptomics and metabolomics study in mouse kidney of the molecular mechanism underlying energy metabolism response to hypoxic stress in highland areas.

Exposure to hypoxia disrupts energy metabolism and induces inflammation. However, the pathways and mechanisms underlying energy metabolism disorders caused by hypoxic conditions remain unclear. In the present study, a hypoxic animal model was created and transcriptomic and non-targeted metabolomics techniques were applied to further investigate the pathways and mechanisms of hypoxia exposure that disrupt energy metabolism. Transcriptome results showed that 3,007 genes were significantly differentially expressed under hypoxic exposure, and Gene Ontology annotation analysis and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analysis showed that the differentially expressed genes (DEGs) were mainly involved in energy metabolism and were significantly enriched in the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) pathway. The DEGs IDH3A, SUCLA2, and MDH2 in the TCA cycle and the DEGs NDUFA3, NDUFS7, UQCRC1, CYC1 and UQCRFS1 in the OXPHOS pathway were validated using mRNA and protein expression, and the results showed downregulation. The results of non-targeted metabolomics showed that 365 significant differential metabolites were identified under plateau hypoxia stress. KEGG enrichment analysis showed that the differential metabolites were mainly enriched in metabolic processes, such as energy, nucleotide and amino acid metabolism. Hypoxia exposure disrupted the TCA cycle and reduced the synthesis of amino acids and nucleotides by decreasing the concentration of cis-aconitate, α-ketoglutarate, NADH, NADPH and that of most amino acids, purines, and pyrimidines. Bioinformatics analysis was used to identify inflammatory genes related to hypoxia exposure and some of them were selected for verification. It was shown that the mRNA and protein expression levels of IL1B, IL12B, S100A8 and S100A9 in kidney tissues were upregulated under hypoxic exposure. The results suggest that hypoxia exposure inhibits the TCA cycle and the OXPHOS signalling pathway by inhibiting IDH3A, SUCLA2, MDH2, NDUFFA3, NDUFS7, UQCRC1, CYC1 and UQCRFS1, thereby suppressing energy metabolism, inducing amino acid and nucleotide deficiency and promoting inflammation, ultimately leading to kidney damage.

Irisin Was Decreased By Hypoxic Exercise Which Related To Hypoxia-induced Muscle Atrophy

PURPOSE: Irisin has been identified as a pro-myogenic factor for ameliorating muscle atrophy, but whether it plays some role in hypoxia-induced muscle atrophy was not investigated. METHODS: 11-13 weeks old male C57BL/6 J mice were placed in a hypobaric hypoxic animal chamber with a simulated height of 5300 m and 11.6% O2 partial pressure. Mice in the control group were raised in the normoxic environment (at an altitude of 399 m). The body composition and grip strength were detected during hypoxic stimulation. After 4 weeks, the mice were subjected to a single treadmill exhaustive exercise to detect the muscle fatigue strength, and blood was taken from the heart immediately after the acute exercise programme, the gastrocnemius (Gas) muscle of the mouse was isolated, and the plasma irisin and irisin-related proteins in the Gas muscle were detected. RESULTS: 4 weeks of hypoxic treatment significantly reduced the body weight (26.47 ± 2.22 vs 21.26 ± 1.98, P < 0.01) and Gas muscle weight (0.076 ± 0.006 vs 0.061 ± 0.007, P < 0.005 ) of the mice, the grip (45.82 ± 11.83 vs 30.75 ± 4.62, P < 0.01) and fatigue strength (101.5 ± 48.74 vs 41 ± 20.31, P < 0.01) were also significantly reduced. Hypoxic exercise significantly increased the expression of HIF-1α in Gas muscle (0.45 ± 0.087 vs 0.94 ± 0.36, P < 0.05), meanwhile decreasing the expression of FNDC5 (1.55 ± 0.44 vs 0.85 ± 0.21, P < 0.05) in Gas muscle and irisin in plasma (14.66 ± 1.15 vs 12.44 ± 1.61, P < 0.01) compared with the normoxic exercise group. However, both FNDC5 and ADAM10 (splicing FNDC5 to irisin) mRNA expression were not changed in Gas muscle. And PGC-1α expression was not affected by hypoxic exercise both in protein and mRNA levels. CONCLUSIONS: Our research indicated that FNDC5/irisin was reduced in hypoxic exercise which may due to muscle atrophy induced by hypoxia.

Hypoxia Acclimation Protects against Heart Failure Postacute Myocardial Infarction via Fundc1-Mediated Mitophagy.

Mitochondrial dysfunction is the main cause of heart failure (HF) postacute myocardial infarction (AMI). Hypoxia acclimation (HA) reduces efficiently the area of AMI caused by ischemia and/or reperfusion and delays HF. Here, we examined whether HA improves mitochondrial structure and function through the hypoxic autophagy receptor FUNDC1 to prevent HF post-AMI. Male adult mice were acclimated in a low-pressure hypoxic animal chamber (11% oxygen (O2)) for 8 h/day for 28 days, and then, an induced HF post-AMI model via left anterior descending (LAD) artery ligation was structured to explore the efficacy and mechanism of HA. Our results showed that HA exposure can improve cardiac structure and function in mice with HF post-AMI and protected myocardial mitochondrial morphology and function. Further studies showed that HA increased the expression of Fundc1 protein and its associated mitophagy protein LC3 in myocardial tissue after infarction. We then established a cellular model of oxygen glucose deprivation (OGD) in vitro, and knockdown of FUNDC1 attenuated the protective effect of HA exposed on cardiomyocyte mitochondria and increased cardiomyocyte apoptosis. In conclusion, the protective effect of HA on HF post-AMI is achieved by regulating Fundc1-mediated mitophagy in myocardial tissue. FUNDC1-mediated mitophagy could be a promising strategy to treat cardiovascular diseases, including HF.

Classical complement pathway inhibition reduces brain damage in a hypoxic ischemic encephalopathy animal model.

Perinatal hypoxic ischemic encephalopathy (HIE) remains a major contributor of infant death and long-term disability worldwide. The role played by the complement system in this ischemia-reperfusion injury remains poorly understood. In order to better understand the role of complement activation and other modifiable mechanisms of injury in HIE, we tested the dual-targeting anti-inflammatory peptide, RLS-0071 in an animal model of HIE. Using the well-established HIE rat pup model we measured the effects of RLS-0071 during the acute stages of the brain injury and on long-term neurocognitive outcomes. Rat pups subject to hypoxia-ischemia insult received one of 4 interventions including normothermia, hypothermia and RLS-0071 with and without hypothermia. We measured histopathological effects, brain C1q levels and neuroimaging at day 1 and 21 after the injury. A subset of animals was followed into adolescence and evaluated for neurocognitive function. On histological evaluation, RLS-0071 showed neuronal protection in combination with hypothermia (P = 0.048) in addition to reducing C1q levels in the brain at 1hr (P = 0.01) and at 8 hr in combination with hypothermia (P = 0.005). MRI neuroimaging demonstrated that RLS-0071 in combination with hypothermia reduced lesion volume at 24 hours (P<0.05) as well as decreased T2 signal at day 21 in combination with hypothermia (P<0.01). RLS-0071 alone or in combination with hypothermia improved both short-term and long-term memory. These findings suggest that modulation by RLS-0071 can potentially decrease brain damage resulting from HIE.

PiRNA-63076 contributes to pulmonary arterial smooth muscle cell proliferation through acyl-CoA dehydrogenase.

Piwi‐interacting RNAs (piRNAs) are thought to be germline‐specific and to be involved in maintaining genome stability during development. Recently, piRNA expression has been identified in somatic cells in diverse organisms. However, the roles of piRNAs in pulmonary arterial smooth muscle cell (PASMC) proliferation and the molecular mechanism underlying the hypoxia‐regulated pathological process of pulmonary hypertension are not well understood. Using hypoxic animal models, cell and molecular biology, we obtained the first evidence that the expression of piRNA‐63076 was up‐regulated in hypoxia and was positively correlated with cell proliferation. Subsequently, we showed that acyl‐CoA dehydrogenase (Acadm), which is negatively regulated by piRNA‐63076 and interacts with Piwi proteins, was involved in hypoxic PASMC proliferation. Finally, Acadm inhibition under hypoxia was partly attributed to DNA methylation of the Acadm promoter region mediated by piRNA‐63076. Overall, these findings represent invaluable resources for better understanding the role of epigenetics in pulmonary hypertension associated with piRNAs.

Assessing the association between hypoxia during craniofacial development and oral clefts.

ObjectivesTo evaluate the association between hypoxia during embryo development and oral clefts in an animal model, and to evaluate the association between polymorphisms in the HIF-1A gene with oral clefts in human families.Material and MethodsThe study with the animal model used zebrafish embryos at 8 hours post-fertilization submitted to 30% and 50% hypoxia for 24 hours. At 5 days post-fertilization, the larvae were fixed. The cartilage structures were stained to evaluate craniofacial phenotypes. The family-based association study included 148 Brazilian nuclear families with oral clefts. The association between the genetic polymorphisms rs2301113 and rs2057482 in HIF-1A with oral clefts was tested. We used real time PCR genotyping approach. ANOVA with Tukey's post-test was used to compare means. The transmission/disequilibrium test was used to analyze the distortion of the inheritance of alleles from parents to their affected offspring.ResultsFor the hypoxic animal model, the anterior portion of the ethmoid plate presented a gap in the anterior edge, forming a cleft. The hypoxia level was associated with the severity of the phenotype (p<0.0001). For the families, there was no under-transmitted allele among the affected progeny (p>0.05).ConclusionHypoxia is involved in the oral cleft etiology, however, polymorphisms in HIF-1A are not associated with oral clefts in humans.

Effect of panax notoginseng saponins on pulmonary artery pathology of pulmonary hypertension rats

Objective To observe the effect of panax notoginseng saponins on pulmonary artery pathology in chronic hypoxic pulmonary hypertensionp (HPH) rats models, discuss the role and possible mechanisms of panax notoginseng saponins in prevention of chronic hypoxic pulmonary hypertension. Methods Forty male Sprague-Dawley (SD) rats were randomly divided into four groups (n=10). Group C: control group; Group H: rats were treated with hypoxia only; Group HC: rats were treated with hypoxia and captopril; and Group HP: rats were treated with hypoxia and panax notoginseng saponins. To observe the effect of panax notoginseng saponins prophylactic treatment in chronic hypoxic pulmonary hypertension rats, after the establishment of the model of hypoxic rat animal pulmonary hypertension models, transthoracic direct pulmonary artery intubation was measured in rat pulmonary arterial systolic pressure and mean pulmonary artery pressure, at the end of separation and cut for pulmonary artery to observe the pathological changes of pulmonary artery, results were recorded and statistically analyzed. Results ⑴Transthoracic direct pulmonary artery intubation was measured in rat pulmonary arterial systolic pressure and mean pulmonary artery pressure: pulmonary artery systolic pressure (PASP) and mean pulmonary arterial pressure (MPAP) were significantly higher in Group H than in Group C (P<0.05), Group HP was no significant difference relative to Group C. ⑵Pathological section shew that the primary pathological change of group H is vascular intimal hyperplasia and the proliferation of smooth muscle cells, medial hypertrophy, extracellular matrix increased, thickening of the vessel wall and the vascular stenos. Conclusions Panax notoginseng saponins inhibit the formation of chronic hypoxic pulmonary hypertension and pulmonary vascular remodeling in rats, and have the effect of prevention and treatment of pulmonary hypertension. Key words: SANCHINOSIDE/PD; Hypertension, pulmonary/DT/PA; Pulmonary artery/PA; Anoxia

Protective effects of diltiazem against vascular endothelial cell injury induced by angiotensin-II and hypoxia

To provide pharmacological data for future clinical studies, this study investigated the protective effects of diltiazem on vascular endothelial cell (VEC) injury induced by angiotensin-II (AngII), hypoxia, and a combination of both treatments. The concentration of intracellular free calcium and the mitochondrial membrane potential in VEC were assessed as indicators of cell injury. An in vivo hypoxic animal model was used to test the protective effect of diltiazem on vascular endothelial tissues. Our study showed that AngII and hypoxia decreased the mitochondrial membrane potential in VEC, which was significantly inhibited by diltiazem. Diltiazem protected against VEC injury induced by the increased concentration of intracellular free calcium, which was associated with AngII and hypoxia. Diltiazem reduced the apoptosis of rat VEC under a sustained hypoxic condition. In addition, it reduced AngII and endothelin I levels in rat vascular endothelial tissues. Our study confirmed that AngII and hypoxia induced VEC injury by regulating the levels of mitochondrial membrane potential and intracellular free calcium. Diltiazem, a calcium channel blocker, protected VEC from AngII- and hypoxia-induced injury.

Applications of azo-based probes for imaging retinal hypoxia.

We report the design and synthesis of an activatable molecular imaging probe to detect hypoxia in mouse models of retinal vascular diseases. Hypoxia of the retina has been associated with the initiation and progression of blinding retinal vascular diseases including age-related macular degeneration, diabetic retinopathy, and retinopathy of prematurity. In vivo retinal imaging of hypoxia may be useful for early detection and timely treatment of retinal diseases. To achieve this goal, we synthesized HYPOX-3, a near-infrared (NIR) imaging agent coupled to a dark quencher, Black Hole Quencher 3 (BHQ3), which has been previously reported to contain a hypoxia-sensitive cleavable azo-bond. HYPOX-3 was cleaved in hypoxic retinal cell culture and animal models, enabling detection of hypoxia with high signal-to-noise ratios without acute toxicity. HYPOX-3 fluorescences in hypoxic cells and tissues and was undetectable under normoxia. These imaging agents are promising candidates for imaging retinal hypoxia in preclinical disease models and patients.

MRNA expression of Follistatin and follistatin-like 3, bone morphogenetic protein-4 antagonists in lung tissues of hypoxic mice

To observe the expression changes of Follistatin (FSN) and follistatin-like 3 (FSRP) mRNA, both of bone morphogenetic protein-4(BMP4) antagonists, in mice lung tissue under different hypoxic time and its relation with BMP4. Thirty BMP4+/+ C57BL/6J wild type mice were randomly divided into normoxic control group, and 4 groups including 1 day, 3 days, 7 days and 21 days under hypoxic condition. The hypoxic animal model was established by exposing the mice to hypoxic condition for different time. The expressing level of FSN and FSRP mRNA in lung tissues were measured by Quantitative Real-Time PCR. FSN and FSRP mRNA increased in hypoxic 1 day group as (28.0 ± 9.4) and (2.0 ± 0.4), in hypoxic 3 day group, FSN mRNA increased by (6.3 ± 3.2) and FSRP mRNA by (1.67 ± 0.7) (P < 0. 05). Compared with the normoxic group (1.77 ± 0.36) and (1.22 ± 0.15) (P < 0. 01), FSN and FSRP mRNA up-regulated in hypoxic 7 day group. The positive degree of FSN and FSRP mRNA in hypoxic 21 day group were (1.04 ± 0.27) and (0.85 ± 0.10) (P < 0. 05). In normoxic 1 day group, FSN mRNA of lung tissues of BMP4+/- C57BL/6J mice was (0.95 ± 0.05); FSRP mRNA was (1.11 ± 0.03) (P < 0. 05). In BMP4+/- C57BL/6J mice lung tissues, FSN mRNA were (1.10 ± 0.40) (P < 0. 05); FSRP mRNA were (0.85 ± 0.18). The expression of FSN and FSRP mRNA in hypoxic 1;3;7 day mice lung tissues increased obviously, and FSN may play an important role in the hypoxic pulmonary hypertension through BMP4.

A New Technique for Collection of Cerebrospinal Fluid in Rat Pups.

BACKGROUNDNeuroprotective strategies to prevent or decrease brain injury in hypoxic ischemic newborns are one of the main research lines in neonatology. Animal models have been used to assess the efficiency of new therapeutic strategies. Brain damage biomarkers in cerebrospinal fluid (CSF) are frequently used to evaluate the outcome at the bedside. Despite the importance of this approach in clinical practice, there are many difficulties in using it in small animals. The aim of this paper was to describe a new technique for collecting CSF in rat pups. Furthermore the reference values of S100β protein levels, commonly used in common clinical practice, were analyzed in animals between 7 to 12 days.METHODS42 Wistar rat pups aged 7 to 12 days were used. CSF was obtained by direct puncture of the cisterna magna with a 24-gauge needle. S100β protein levels were determined with enzyme-linked immunosorbent assay (ELISA).RESULTSCSF was successfully obtained in 96% of the cases, with an average amount of 21.28 μl (5–40 μl). Normal values for S100β were described. HI animals presented higher S100β values than controls.CONCLUSIONSA simple, reproducible technique for CSF collection in rat pups has been described. This new method will allow study of brain injury biomarkers in newborn hypoxic ischemic animal models.

A simple mechanical device reduces subglottic injury in ventilated animals

To test whether a simple inexpensive device that dynamically minimizes endotracheal cuff pressure throughout the respiratory cycle reduces endotracheal cuff pressure-related subglottic injury. Hypoxic animal model with one control and one experimental group. Twelve S. scrofa domesticus piglets (14-16 kg) were intubated with standard endotracheal tubes and maintained in a hypoxic state to accelerate airway injury. Animals in the control group (n = 6) were ventilated with a constant pressure of 20 cm H₂O in the endotracheal tube cuff. Animals in the experimental group (n = 6) were ventilated using a custom-designed circuit that altered the pressure in the endotracheal tube cuff in synchrony with the ventilatory cycle. Larynges were harvested at the end of the experiment and examined histologically to determine the degree of airway injury induced by the endotracheal cuff. Animals in the experimental group suffered significantly less airway damage than those in the control group. The differences were seen primarily in the subglottis (aggregate damage score 6.5 vs. 12, P <0.05), where the experimental endotracheal tube cuff exerted the least pressure. There was no difference in damage to the glottic or supraglottic structures. A simple, reliable, and inexpensive means of modulating endotracheal tube cuff pressure with the ventilatory cycle led to a substantial decrease in airway injury in our animal model. Such reduction in cuff pressure may prove important for humans, particularly those in intensive care units who tend to have underlying conditions predisposing them to tracheal damage from the endotracheal tube cuff.

Altered glucose metabolism and preserved energy charge and neuronal structures in the brain of mouse intermittently exposed to hypoxia

The key for an animal to survive prolonged hypoxia is to avoid rapid decline in ATP levels in vital organs such as the brain. This can be well achieved by a very few of hypoxia-tolerant animals such as freshwater turtles and newborn animals, since these animals can substantially suppress their metabolic levels by coordinated regulation of ATP-producing and ATP-demanding pathways. However, most animals, especially adult mammals, can only tolerate a short period of hypoxia since they are unable to maintain constant ATP levels and energy charge in vital organs during prolonged hypoxic exposure. Here, we described a special mouse model, in which a hypoxia intolerant adult mouse gradually built up an ability to survive prolonged hypoxia after intermittent hypoxic exposures. This increased ability was accompanied by reductions in body temperature and O2 consumption as well as transient variations in blood pCO2, pO2 and pH. The glucose and energy metabolism in the brain of the mouse altered similarly to those reported in the brain of hypoxic turtles. Activities of phosphofructokinase and pyruvate kinase, the two rate-limiting enzymes controlling the rate of glycolysis decreased to baseline levels after a short period of increase. In contrast, the activity of complex I, the major enzyme complex controlling oxidative phosphorylation, was kept inhibited. These alterations in the ATP-producing pathway suggest the occurrence of reverse Pasteur effect, indicating that the animal had entered a hypometabolic state favoring maintenance of ATP level and energy charge in hypoxic conditions. In supporting this idea, the ATP levels and energy charge as well as neuronal structures in the brain were well preserved. This study provides evidence for a possibility that a hypoxic intolerant animal can build up an ability to survive prolonged hypoxia through regulation of its glucose and energy metabolism after an appropriate hypoxic training, which deserves further investigation.

S96 Novel biomarkers in idiopathic pulmonary arterial hypertension

BackgroundCirculatingosteopontin levels predict survival in right heart failure and lung tissue expression is increased in hypoxic animal models of pulmonary hypertension. Growth differentiation factor (GDF)-15 and red cell distribution width...

Doppler echocardiographic assessment of left ventricular diastolic function in chronic hypoxic rats.

Little information is available on the mechanism of diastolic left ventricular (LV) dysfunction in patients with chronic respiratory disease complicated by hypoxia. The purpose of this study was to investigate how chronic hypoxia impairs LV diastolic function in an hypoxic animal model. Thirty-six male Wistar rats 8 weeks old were assigned to normoxia (N), chronic hypoxia (CH), and re-normoxia (RN) groups, 12 rats per group. The N group rats were kept in ambient air for 8 weeks, while the CH group was kept hypoxic for 8 weeks. After 8 weeks of hypoxia the RN group rats were kept for a further 8 weeks in ambient air. LV systolic and diastolic functions, as well as right ventricular (RV) function, were analyzed using Doppler echocardiography;we also measured the hematocrit, and weighed the LV and RV. Hematocrit, RV weight/body weight, and RV weight/LV weight were higher in the CH group than in the other 2 groups. However, most of these parameters returned to normoxia levels after re-normoxia. In the CH group, LV dimension and area were smaller than in the other 2 groups. LV systolic function was preserved in all groups;however, in the CH group, mitral flow showed a restrictive pattern, while pulmonary flow demonstrated a pulmonary hypertensive pattern with prolonged RV ejection time. In conclusion, chronic hypoxia induced pulmonary hypertension and RV hypertrophy. Although LV systolic function was preserved, diastolic function was impaired in hypoxia. Ventricular interaction may impair LV diastolic function.

Haemodynamic effects of intracoronary pyruvate in patients with congestive heart failure: an open study

Pyruvate, as an intermediate in the Krebs cycle, is an important source of energy for myocardium and improves contractility of normal, hypoxic, and postischaemic animal myocardium. We investigated the effect of intracoronary pyruvate in patients with congestive heart failure. Haemodynamic measurements were done in eight patients with dilated cardiomyopathy after two 15 min infusions of pyruvate into the left main coronary artery and after saline washout of pyruvate. There were no significant differences between the two pyruvate concentrations. Application of pyruvate resulted in a 23% increase in cardiac index (p<0.05), a 38% increase in stroke-volume index (p<0.05), and a 36% decrease in pulmonary capillary wedge pressure (p<0.05). Heart rate decreased significantly by 11%. Mean aortic pressure and systemic vascular resistance did not change. Most of the effects of pyruvate were reversed 15 min after the infusion stopped. Pyruvate has the profile of a favourable inotropic substance. Other modes of administration need to be studied.

Nautilus and the art of metabolic maintenance

THE cephalopod mollusc Nautilus is often called a living fossil because its multichambered shell resembles that of extinct forms from the early Palaeozoic era. Living at depths of 100–300 m, the animals not only encounter zones of low oxygen concentration, but also exploit them for refuge or feeding1,2. Despite some modest recruitment of anaerobic sources of energy, Nautilus is able to survive severe bouts of hypoxia, mainly through its prodigious capacity for aerobic metabolic rate suppression. Here we show that the hypometabolic, hypoxic animal conserves energy further by means of prolonged ventilatory and circulatory pauses, during which time the blood, having a comparatively high oxygen affinity, is apparently loaded at the venous side, across the superficially located and voluminous vena cava. Under these highly arrested conditions, a significant fraction of the animal's aerobic metabolic rate can be accounted for by a slow 'metering out' of the O2 store contained in the shell, indicating that the buoyancy chambers of Nautilus may occasionally subserve the role of a 'SCUBA tank'. The internal shell morphology and siphuncular arrangement seen in the fossilized remains of ammonites suggest that similar processes may have occurred.

The absence of effect of chemical sympathectomy on ventricular hypertrophy induced by hypoxia in young rabbits.

Young rabbits, eight at a time, were exposed to 203 and 208 h (groups I and II) and 283 and 298 h (groups III and IV) of hypoxia (O2 at 70 to 80 mmHg), at atmospheric pressure. The animals were injected ip with 25 mg X kg-1 on the first day, and with 50 mg X kg-1 on the second day and every 48 h thereafter of guanethidine (G) or 6-hydroxydopamine (6-OHDA) (O), or an equivalent volume of saline (H = hypoxic controls, or N = normoxic controls). This regime of treatment abolished, in normoxic and hypoxic animals alike, the effect of sympathetic nerve stimulation on the pupil at voltages which produced maximum dilatation in control animals. Injection of atenolol reduced heart rate by 32% in control animals, but had no effect in the guanethidine treated animals, and a very small effect in the 6-OHDA treated group. The animals in each group were litter mates of those in the other groups. In the first series the dry weight of the hypoxic right ventricles increased, relative to the normoxic controls, by 38.8% (H), 40.5% (G) and 40.9% (O). There was no left ventricular hypertrophy in the hypoxic animals, but there was a small, but not statistically significant, rise in the haematocrit (Hct). In the second series the right ventricular hypertrophy was greater (+98% (H), +89% (G) and +102% (O]. There was also a significant left ventricular hypertrophy (+38% (H), +40.3% (G) and +41% (O] and a highly significant increase in haematocrit in all the hypoxic groups. The right atria were only slightly hypertrophied in the first series, but greatly hypertrophied in the second series (+103%, H), an effect attenuated by the treatment (+34%, G, and +39%, O). When each treated hypoxic animal was compared with its untreated hypoxic littermate (n = 12), the mean treated/untreated ratio for the right ventricular dry weight was 0.991 +/- 0.022 for the guanethidine group (n = 11) and 1.023 +/- 0.043 for the 6-hydroxydopamine (n = 11). Such identity of the extent of the hypertrophy in all the hypoxic groups, irrespective of the duration of hypoxia, implies that the hypertrophy was not conditional upon sympathetic activity.

1563 CEREBRAL AUTOREGULTION IN NEONATAL PUPPIES

In an attempt to document autoregulation of cerebral blood flow in the hyperoxic and hypoxic newborn animal, cerebral blood flow was measured in 6 hyperoxic (HE) and 4 hypoxic (H) neonatal puppies aged 2-13 days using the radioactive microsphere reference organ technique. In the HE group arterial oxygen tension was maintained above 250 torr with 100% O2 throughout all periods. In the H group arterial oxygen tension was maintained at 47.5 torr ± 7.6 SEM by continuous administration of 12% O2. Following control measurements (period I), puppies were made hypotensive (period II) by withdrawing 15-25 ml/kg of blood in the HE group and 20-32 ml/kg in the H group. In the HE group during period II, mean blood pressure fell 20.5% ± 2.8 (p=0.016) and cardiac output decreased 20.9% ± 5.7 (p = 0.016) while cerebral blood flow was unchanged (31.37 ± 3.76 and 32.69 ± 5.90 ml/100g/min in periods I and II respectively). When hypoxic animals were made hypotensive, mean blood pressure fell 18.6% ± 4.7 and cardiac output decreased by 47.9% ± 10.9 while cerebral blood flow was unchanged (38.66 ± 4.64 and 45.2 ± 4.00 ml/100g/min in period I and II respectively). The fraction of cardiac output to the cerebrum increased from 2.8% ± 0.4 to 3.8% ± 0.8 in the HE animals (p < 0.05) and from 2.5% ± 0.5 to 6.3% ± 1.1 in the H group (p < 0.05) during hypotension. Thus, in the presence of decreased mean blood pressure and cardiac output in both hyperoxic and hypoxic neonatal puppies, cerebral blood flow is maintained, demonstrating the presence of cerebral autoregulation.

Effects of simulated altitude on O 2 transport in dogs

The effects of exposure to simulated altitude on skeletal muscle and on the cardiocirculatory system have been studied on awake, conscious, dogs (16–39 kg) at rest and during moderate treadmill exercise at 15% incline. Measurements were obtained in Denver at a pb of 635 mm Hg and after 3 weeks of continuous exposure to a pb of 435 mm Hg using a hypobaric chamber. At both levels of pb the dogs showed marked panting, associated with pulmonary hyperventilation and low Pa CO 2 's (28 mm Hg at 635 and 17 mm Hg at 435 mm Hg). Resting V ̈ O 2 s were high (12.4 and 11.4 ml/min · kg) reflecting the high respiratory outputs. [Hb] and Hct increased significantly after 3 weeks at 435 mm Hg with a 4 mm Hg decrease in P 50. Q̈, HR, SV and systemic blood pressures were normal in both normoxic and hypoxic animals, at rest as well as during exercise. Arterial and mixed venous P O 2 's decreased in the hypoxic dogs (82 to 56 and 42 to 36 mm Hg, respectively) but arterial 0 2 content, arterial-venous 0 2 content difference and systemic 0 2 transport remained unchanged. Capillary density in the sternothyroid muscle doubled (617 to 1245 cap/mm2) after 3 weeks at a pb of 435, whereas the average muscle fiber diameter decreased about 30%. Calculations indicate that the P O 2 , in the ‘lethal corner’ of the muscle fiber is relatively higher in the hypoxic animal because of the decrease in fiber size and intercapillary distances.