Cerebrospinal fluid biogenic amines depletion and brain atrophy in adult patients with phenylketonuria.

Biogenic amines synthesis in phenylketonuria (PKU) patients with high phenylalanine (Phe) concentration is thought to be impaired due to inhibition of tyrosine and tryptophan hydroxylases and competition with amino acids at the blood-brain barrier. Dopamine and serotonin deficits might explain brain damage and progressive neuropsychiatric impairment in adult PKU patients. Ten early treated adult PKU patients (mean age 38.2 years) and 15 age-matched controls entered the study. Plasma and cerebrospinal fluid (CSF) Phe, 5-hydroxyindoleacetic acid (5-HIAA), 5-hydroxytryptophan (5-HTP), 3,4-dihydroxy-l-phenylalanine (l-DOPA) and homovanillic acid (HVA) were analyzed. Voxel-based morphometry statistical nonparametric mapping was used to test the age-corrected correlation between gray matter atrophy and CSF biogenic amines levels. 5-HIAA and 5-HTP were significantly reduced in PKU patients compared to controls. Significant negative correlations were found between CSF 5-HIAA, HVA, and 5-HTP and Phe levels. A decrease in 5-HIAA and 5-HTP concentrations correlated with precuneus and frontal atrophy, respectively. Lower HVA levels correlated with occipital atrophy. Biogenic amines deficits correlate with specific brain atrophy patterns in adult PKU patients, in line with serotonin and dopamine projections. These findings may support a more rigorous Phe control in adult PKU to prevent neurotransmitter depletion and accelerated brain damage due to aging.

Dorsal raphe serotonin neurons in mice: immature hyperexcitability transitions to adult state during first three postnatal weeks suggesting sensitive period for environmental perturbation.

Trauma during early life is a major risk factor for the development of anxiety disorders and suggests that the developing brain may be particularly sensitive to perturbation. Increased vulnerability most likely involves altering neural circuits involved in emotional regulation. The role of serotonin in emotional regulation is well established, but little is known about the postnatal development of the raphe where serotonin is made. Using whole-cell patch-clamp recording and immunohistochemistry, we tested whether serotonin circuitry in the dorsal and median raphe was functionally mature during the first 3 postnatal weeks in mice. Serotonin neurons at postnatal day 4 (P4) were hyperexcitable. The increased excitability was due to depolarized resting membrane potential, increased resistance, increased firing rate, lack of 5-HT1A autoreceptor response, and lack of GABA synaptic activity. Over the next 2 weeks, membrane resistance decreased and resting membrane potential hyperpolarized due in part to potassium current activation. The 5-HT1A autoreceptor-mediated inhibition did not develop until P21. The frequency of spontaneous inhibitory and excitatory events increased as neurons extended and refined their dendritic arbor. Serotonin colocalized with vGlut3 at P4 as in adulthood, suggesting enhanced release of glutamate alongside enhanced serotonin release. Because serotonin affects circuit development in other brain regions, altering the developmental trajectory of serotonin neuron excitability and release could have many downstream consequences. We conclude that serotonin neuron structure and function change substantially during the first 3 weeks of life during which external stressors could potentially alter circuit formation.

Serotonergic neuron regulation informed by in vivo single-cell transcriptomics.

Despite the recognized importance of the dorsal raphe (DR) serotonergic (5-HT) nuclei in the pathophysiology of depression and anxiety, the molecular components/putative drug targets expressed by these neurons are poorly characterized. Utilizing the promoter of an ETS domain transcription factor that is a stable marker of 5-HT neurons (Pet-1) to drive 5-HT neuronal expression of YFP, we identified 5-HT neurons in live acute slices. We isolated RNA from single 5-HT neurons in the ventromedial and lateral wings of the DR and performed single-cell RNA-Seq analysis identifying >500 G-protein coupled receptors (GPCRs) including receptors for classical transmitters, lipid signals, and peptides as well as dozens of orphan-GPCRs. Using these data to inform our selection of receptors to assess, we found that oxytocin and lysophosphatidic acid 1 receptors are translated and active in costimulating, with the α1-adrenergic receptor, the firing of DR 5-HT neurons, while the effects of histamine are inhibitory and exerted at H3 histamine receptors. The inhibitory histamine response provides evidence for tonic in vivo histamine inhibition of 5-HT neurons. This study illustrates that unbiased single-cell transcriptomics coupled with functional analyses provides novel insights into how neurons and neuronal systems are regulated.

Targeting activation of specific NF-κB subunits prevents stress-dependent atherothrombotic gene expression.

Psychosocial stress has been shown to be a contributing factor in the development of atherosclerosis. Although the underlying mechanisms have not been elucidated entirely, it has been shown previously that the transcription factor nuclear factor-κB (NF-κB) is an important component of stress-activated signaling pathway. In this study, we aimed to decipher the mechanisms of stress-induced NF-κB-mediated gene expression, using an in vitro and in vivo model of psychosocial stress. Induction of stress led to NF-κB-dependent expression of proinflammatory (tissue factor, intracellular adhesive molecule 1 [ICAM-1]) and protective genes (manganese superoxide dismutase [MnSOD]) via p50, p65 or cRel. Selective inhibition of the different subunits and the respective kinases showed that inhibition of cRel leads to the reduction of atherosclerotic lesions in apolipoprotein(-/-) (ApoE(-/-)) mice via suppression of proinflammatory gene expression. This observation may therefore provide a possible explanation for ineffectiveness of antioxidant therapies and suggests that selective targeting of cRel activation may provide a novel approach for the treatment of stress-related inflammatory vascular disease.

Neonatal rearing conditions distinctly shape locus coeruleus neuronal activity, dendritic arborization, and sensitivity to corticotrophin-releasing factor.

Early life events influence vulnerability to psychiatric illness. This has been modelled in rats and it has been demonstrated that different durations of maternal separation shape adult endocrine and behavioural stress reactivity. One system through which maternal separation may act is the locus coeruleus (LC)-norepinephrine system that regulates emotional arousal. Here we demonstrate that different durations of maternal separation have distinct effects on LC physiology and dendritic morphology. Rat pups were separated from the dam for 15 min/d (HMS-15) or 180 min/d (HMS-180) from post-natal days 2-14. Others were either undisturbed (HMS-0) or were vendor-purchased controls. LC characteristics were compared at age 22-35 d using whole-cell recordings in vitro. Cells were filled with biocytin for morphological analysis. LC neurons of HMS-180 rats were tonically activated compared to HMS-15 and control rats, with firing rates that were 2-fold higher than these groups. Corticotrophin-releasing factor (CRF) application did not further activate LC neurons of HMS-180 rats but increased LC firing rate in HMS-0 and control rats. LC neurons of HMS-15 rats were resistant to excitation by CRF. Maternal separation also affected LC dendritic morphology. LC dendrites of HMS-15 rats exhibited less branching and decreased total dendritic length, an effect that could decrease the probability of contacting limbic afferents that terminate in the pericoerulear region. This effect may provide a structural basis for an attenuated magnitude of emotional arousal. Together, these results demonstrate long-term consequences of early life events on the LC-norepinephrine system that may shape adult behaviour.

Lower plasma cholesterol, LDL-cholesterol and LDL-lipoprotein subclasses in adult phenylketonuria (PKU) patients compared to healthy controls: results of NMR metabolomics investigation.

BACKGROUND: Phenylketonuria (PKU; OMIM#261600) is a rare metabolic disorder caused by mutations in the phenylalanine hydroxylase (PAH) gene resulting in high phenylalanine (Phe) in blood and brain. If not treated early this results in intellectual disability, behavioral and psychiatric problems, microcephaly, motor deficits, eczematous rash, autism, seizures, and developmental problems. There is a controversial discussion of whether patients with PKU have an additional risk for atherosclerosis due to interference of Phe with cholesterol synthesis and LDL-cholesterol regulation. Since cholesterol also plays a role in membrane structure and myelination, better insight into the clinical significance of the impact of Phe on lipoprotein metabolism is desirable. In 22 treated PKU patients (mean age 38.7 years) and 14 healthy controls (mean age 35.2 years), we investigated plasma with NMR spectroscopy and quantified 105 lipoprotein parameters (including lipoprotein subclasses) and 24 low molecular weight parameters. Analysis was performed on a 600 MHz Bruker AVANCE IVDr spectrometer as previously described. RESULTS: Concurrent plasma Phe in PKU patients showed a wide range with a mean of 899 µmol/L (50-1318 µmol/L). Total cholesterol and LDL-cholesterol were significantly lower in PKU patients versus controls: 179.4 versus 200.9 mg/dL (p < 0.02) and 79.5 versus 104.1 mg/dL (p < 0.0038), respectively. PKU patients also had lower levels of 22 LDL subclasses with the greatest differences in LDL2 Apo-B, LDL2 Particle Number, LDL2-phospholipids, and LDL2-cholesterol (p < 0.0001). There was a slight negative correlation of total cholesterol and LDL-cholesterol with concurrent Phe level. VLDL5-free cholesterol, VLDL5-cholesterol, VLDL5-phospholipids, and VLDL4-free cholesterol showed a significant (p < 0.05) negative correlation with concurrent Phe level. There was no difference in HDL and their subclasses between PKU patients and controls. Tyrosine, glutamine, and creatinine were significantly lower in PKU patients compared to controls, while citric and glutamic acids were significantly higher. CONCLUSIONS: Using NMR spectroscopy, a unique lipoprotein profile in PKU patients can be demonstrated which mimics a non-atherogenic profile as seen in patients treated by statins.

Exogenous cytochrome C restores myocardial cytochrome oxidase activity into the late phase of sepsis.

Mitochondrial dysfunction is thought to play a role in the pathogenesis of a variety of disease states, including sepsis. An acquired defect in oxidative phosphorylation potentially causes sepsis-induced organ dysfunction. Cytochrome oxidase (CcOX), the terminal oxidase of the respiratory chain, is competitively inhibited early in sepsis and progresses, becoming noncompetitive during the late phase. We have previously demonstrated that exogenous cytochrome c can overcome myocardial CcOX competitive inhibition and improve cardiac function during murine sepsis at the 24-h point. Here, we evaluate the effect of exogenous cytochrome c on CcOX activity and survival in mice at the later time points. Exogenous cytochrome c (800 microg) or saline was intravenously injected 24 h after cecal ligation and puncture (CLP) or sham operation. Steady-state mitochondrial cytochrome c levels and heme c content increased significantly 48 h post-CLP and remained elevated at 72 h in cytochrome c-injected mice compared with saline injection. Cecal ligation and puncture inhibited CcOX at 48 h in saline-injected mice. However, cytochrome c injection abrogated this inhibition and restored CcOX kinetic activity to sham values at 48 h. Survival after CLP to 96 h after cytochrome c injection approached 50% compared with only 15% after saline injection. Thus, a single injection of exogenous cytochrome c 24 h post-CLP repletes mitochondrial substrate levels for up to 72 h, restores myocardial COX activity, and significantly improves survival.

Customized reconstruction with the free anterolateral thigh perforator flap.

From April of 2003 through September of 2006, 70 free anterolateral thigh (ALT) flaps were transferred for reconstructing soft-tissue defects. The overall success rate was 96%. Among 70 free ALT flaps, 11 were elevated as cutaneous ALT septocutaneous vessel flaps. Fifty-seven were harvested as cutaneous ALT myocutaneous "true" perforator flaps. Two flaps were used as fasciocutaneous perforator flaps based on independent skin vessels. Fifty-four ALT flaps were used for lower extremity reconstruction, 11 flaps were used for upper extremity reconstruction, 3 flaps were used for trunk reconstruction, and 1 flap was used for head and neck reconstruction. Total flap failure occurred in 3 patients (4.28% of the flaps), and partial failure occurred in 5 patients (7.14% of the flaps). The three flaps that failed completely were reconstructed with a free radial forearm flap, a latissimus dorsi flap and skin grafting, respectively. Among the five flaps that failed partially, three were reconstructed with skin grafting, one with a sural flap, and one with primary closure. The free ALT flap has become the workhorse for covering defects in most clinical situations in our center. It is a reliable flap with consistent anatomy and a long, constant pedicle diameter. Its versatility, in which thickness and volume can be adjusted, leads to a perfect match for customized reconstruction of complex defects.

Developmental effects of serotonin 1A autoreceptors on anxiety and social behavior.

The serotonin 1A receptor (5-HT1A) has a major role in modulating the effects of serotonin on mood and behavior. Previous studies have shown that knockout of 5-HT1A selectively in the raphe leads to higher levels of anxiety during adulthood. However, it remains unclear whether this phenotype is due to variation in receptor levels specifically during development or throughout life. To test the hypothesis that developmental sensitivity may underlie the effects of 5-HT1A on anxiety, we used an inducible transgenic system to selectively suppress 5-HT1A levels in serotonergic raphe neurons from post-natal days (P) 14 to P30, with a maximal reduction of 40% at P21 and return to regular levels by P30. This developmental decrease in receptor levels has long-lasting consequences, increasing anxiety and decreasing social investigation in adulthood. In addition, post-natal knockdown of autoreceptors leads to long-term increases in the excitability of serotonergic neurons, which may represent a mechanism underlying the effects of post-natal receptor variation on behavior later in life. Finally, we also examined the interplay between receptor variation and juvenile exposure to stress (applied from P14 to P21). Similar to receptor knockdown, juvenile exposure to stress led to increased anxiety phenotypes but did not exacerbate 5-HT1A knockdown-mediated anxiety levels. This work indicates that the effects of 5-HT1A autoreceptors on anxiety and social behaviors are developmentally mediated and suggests that natural variations in the expression of 5-HT1A may act during development to influence individual anxiety levels and contribute to susceptibility to anxiety disorders.

Effects of chronic sleep fragmentation on wake-active neurons and the hypercapnic arousal response.

STUDY OBJECTIVES: Delayed hypercapnic arousals may occur in obstructive sleep apnea. The impaired arousal response is expected to promote more pronounced oxyhemoglobin desaturations. We hypothesized that long-term sleep fragmentation (SF) results in injury to or dysfunction of wake-active neurons that manifests, in part, as a delayed hypercapnic arousal response. DESIGN: Adult male mice were implanted for behavioral state recordings and randomly assigned to 4 weeks of either orbital platform SF (SF4wk, 30 events/h) or control conditions (Ct4wk) prior to behavioral, histological, and locus coeruleus (LC) whole cell electrophysiological evaluations. MEASUREMENTS AND RESULTS: SF was successfully achieved across the 4 week study, as evidenced by a persistently increased arousal index, P < 0.01 and shortened sleep bouts, P < 0.05, while total sleep/wake times and plasma corticosterone levels were unaffected. A multiple sleep latency test performed at the onset of the dark period showed a reduced latency to sleep in SF4wk mice (P < 0.05). The hypercapnic arousal latency was increased, Ct4wk 64 ± 5 sec vs. SF4wk 154 ± 6 sec, P < 0.001, and remained elevated after a 2 week recovery (101 ± 4 sec, P < 0.001). C-fos activation in noradrenergic, orexinergic, histaminergic, and cholinergic wake-active neurons was reduced in response to hypercapnia (P < 0.05-0.001). Catecholaminergic and orexinergic projections into the cingulate cortex were also reduced in SF4wk (P < 0.01). In addition, SF4wk resulted in impaired LC neuron excitability (P < 0.01). CONCLUSIONS: Four weeks of sleep fragmentation (SF4wk) impairs arousal responses to hypercapnia, reduces wake neuron projections and locus coeruleus neuronal excitability, supporting the concepts that some effects of sleep fragmentation may contribute to impaired arousal responses in sleep apnea, which may not reverse immediately with therapy.

Subcutaneous application of levothyroxine as successful treatment option in a patient with malabsorption.

BACKGROUND: Hypothyroidism can usually be treated effectively by oral levothyroxine supplementation. There are, however, some rare circumstances, when oral levothyroxine application is not sufficient, for example malabsorption, interactions with food or other medications, or various gastrointestinal diseases. CASE REPORT: We present a 42 year old woman with refractory and severe symptomatic hypothyroidism after subtotal thyroidectomy in spite of high dose oral levothyroxine supplementation. By stepwise increasing oral levothyroxine dosage up to 2200 micrograms plus 80 micrograms of thyronine, no sufficient substitution could be achieved. After suspicion of enteral malabsorption due to a pathological D-Xylose-test, subcutaneous levothyroxine supplementation was started. Finally, a sustained euthyroid state could be achieved. CONCLUSIONS: For selected patients who do not respond to oral treatment subcutaneous application of levothyroxine can be a suitable and effective therapy.

Effectiveness of a low-calorie weight loss program in moderately and severely obese patients.

AIMS: To compare effectiveness of a 1-year weight loss program in moderately and severely obese patients. METHODS: The study sample included 311 obese patients participating in a weight loss program, which comprised a 12-week weight reduction phase (low-calorie formula diet) and a 40-week weight maintenance phase. Body weight and glucose and lipid values were determined at the beginning of the program as well as after the weight reduction and the weight maintenance phase. Participants were analyzed according to their BMI class at baseline (30-34.9 kg/m²; 35-39.9 kg/m²; 40-44.9 kg/m²; 45-49.9 kg/m²; ≥50 kg/m²). Furthermore, moderately obese patients (BMI < 40 kg/m²) were compared to severely obese participants (BMI ≥ 40 kg/m²). RESULTS: Out of 311 participants, 217 individuals completed the program. Their mean baseline BMI was 41.8 ± 0.5 kg/m². Average weight loss was 17.9 ± 0.6%, resulting in a BMI of 34.3 ± 0.4 kg/m² after 1 year (p < 0.001). Overall weight loss was not significantly different in moderately and severely obese participants. Yet, severely obese participants achieved greater weight loss during the weight maintenance phase than moderately obese participants (-3.1 ± 0.7% vs. -1.2 ± 0.6%; p = 0.04). Improvements in lipid profiles and glucose metabolism were found throughout all BMI classes. CONCLUSION: 1-year weight loss intervention improves body weight as well as lipid and glucose metabolism not only in moderately, but also in severely obese individuals.

Orexins/hypocretins act in the posterior paraventricular thalamic nucleus during repeated stress to regulate facilitation to novel stress.

Orexins/hypocretins heavily innervate the posterior division of the paraventricular nucleus of the thalamus (pPVT), which expresses both orexin receptor types. The pPVT is important for adaptations to repeated stress, particularly the ability to facilitate to novel stress after repeated stress exposure. Here, we examined how orexins acting in the pPVT regulate facilitation of hypothalamic-pituitary-adrenal (HPA) responses to novel restraint after 4 d of repeated swim stress. Blockade of orexin receptors in the pPVT with SB334867 before novel restraint did not change the facilitated HPA response. However, blockade of orexin receptors before each of four daily swim exposures prevented the facilitated ACTH and facilitated hypothalamic c-Fos response to restraint as well as the repeated swim stress-induced increase in CRH mRNA in the paraventricular hypothalamus. These results suggest that orexin actions in the pPVT during the 4 d of swim, but not during restraint, are necessary for the facilitated HPA response to heterotypic restraint. Exposure to the fourth swim produced a shift in orexin1 receptors from membrane to cytosolic fractions. OrexinA also changed the firing patterns of pPVT cells to be more responsive in repeatedly swim stressed rats compared with nonstressed rats. Together, the results suggest that orexin actions in the pPVT, mediated by orexin1 receptors, are important for the ability to adapt to repeated stress.

The presynaptic component of the serotonergic system is required for clozapine's efficacy.

Clozapine, by virtue of its absence of extrapyramidal side effects and greater efficacy, revolutionized the treatment of schizophrenia, although the mechanisms underlying this exceptional activity remain controversial. Combining an unbiased cheminformatics and physical screening approach, we evaluated clozapine's activity at >2350 distinct molecular targets. Clozapine, and the closely related atypical antipsychotic drug olanzapine, interacted potently with a unique spectrum of molecular targets. This distinct pattern, which was not shared with the typical antipsychotic drug haloperidol, suggested that the serotonergic neuronal system was a key determinant of clozapine's actions. To test this hypothesis, we used pet1(-/-) mice, which are deficient in serotonergic presynaptic markers. We discovered that the antipsychotic-like properties of the atypical antipsychotic drugs clozapine and olanzapine were abolished in a pharmacological model that mimics NMDA-receptor hypofunction in pet1(-/-) mice, whereas haloperidol's efficacy was unaffected. These results show that clozapine's ability to normalize NMDA-receptor hypofunction, which is characteristic of schizophrenia, depends on an intact presynaptic serotonergic neuronal system.

Mitochondrial resuscitation with exogenous cytochrome c in the septic heart.

OBJECTIVE: Mitochondrial dysfunction may play a role in the pathogenesis of sepsis-induced organ dysfunction. Respiratory-chain deficiencies that occur in sepsis, however, have never been shown to cause organ failure or to be reversible. Cytochrome oxidase uses electrons donated by its substrate, cytochrome c, to reduce oxygen to H2O. In the septic heart, cytochrome oxidase is competitively inhibited. We hypothesized that cytochrome oxidase inhibition coupled with reduced substrate availability is a reversible cause of sepsis-associated myocardial depression. DESIGN: Prospective observational study aimed to overcome myocardial cytochrome oxidase inhibition with excess cytochrome c and improve cardiac function. SETTING: University hospital-based laboratory. SUBJECTS: Seventy-five C57Bl6 male mice. INTERVENTIONS: Mice underwent cecal ligation and double puncture, sham operation, or no operation. Exogenous cytochrome c or an equal volume of saline was intravenously injected at the 24-hr time point. All animals were evaluated 30 mins after injection. MEASUREMENTS AND MAIN RESULTS: Exogenous cytochrome c readily repleted cardiac mitochondria with supranormal levels of substrate (>1.6 times baseline), restored heme c content, and increased cytochrome oxidase kinetic activity. This increased left ventricular pressure and increased pressure development during isovolumic contraction (dP/dtmax) and relaxation (dP/dtmin) by >45% compared with saline injection. CONCLUSION: Impaired oxidative phosphorylation is a cause of sepsis-associated myocardial depression, and mitochondrial resuscitation with exogenous cytochrome c overcomes cytochrome oxidase inhibition and improves cardiac function.

Evidence of myocardial hibernation in the septic heart.

OBJECTIVE: Myocardial hibernation is an adaptive response to ischemia and hypoxia. Hibernating cardiomyocytes are reversibly hypocontractile and demonstrate characteristic metabolic and ultrastructural changes. These include a switch in primary substrate utilization from fatty acids to glucose, up-regulation of the myocardial specific glucose transporters (GLUT1 and GLUT4), and glycogen deposition within and between cardiomyocytes. We hypothesized that myocardial hibernation may underlie sepsis-associated myocardial depression. DESIGN: Prospective observational study aimed at identifying the characteristic changes of hibernation in the septic heart. SETTING: University hospital-based laboratory. SUBJECTS: Forty-three C57Bl6 male mice. INTERVENTIONS: Mice underwent cecal ligation and double puncture, sham operation, or no operation and were evaluated 48 hrs after the procedure. MEASUREMENTS AND MAIN RESULTS: Using novel, clinically relevant technology such as magnetic resonance imaging, positron emission tomography, and single photon emission computed tomography imaging, we found septic mice to have diminished cardiac performance, increased myocardial glucose uptake, increased steady-state levels of myocardial GLUT4, and increased deposits of glycogen, recapitulating the changes during hibernation. Importantly, these changes occurred in the setting of preserved arterial oxygen tension and myocardial perfusion. CONCLUSIONS: Sepsis-associated cardiac dysfunction may reflect hibernation. Furthermore, such down-regulation of cellular function may underlie sepsis-induced dysfunction in other organ systems.

Chronic hypoxemia increases myocardial cytochrome oxidase.

OBJECTIVE: Cyanotic patients have potentially decreased tissue oxygen tension. Cytochrome oxidase catalyzes the reduction of oxygen and is integral to adenosine triphosphate production. Cytochrome oxidase subunit I, the active site, is encoded by mitochondrial DNA. Using a newborn swine model of chronic hypoxemia, we evaluated ventricular cytochrome oxidase subunit I mRNA and protein expression and assessed cytochrome oxidase activity. METHODS: Thirty-two newborn piglets underwent thoracotomy and placement of a pulmonary artery-to-left atrium shunt or sham operation. Two weeks later, partial pressure of arterial oxygen, hematocrit, and left ventricular shortening fraction values were compared with baseline values. Northern blot hybridization and protein immunoblotting for ventricular cytochrome oxidase subunit I were performed. Cytochrome oxidase kinetic activity was measured. Heme a,a3 content and turnover number were determined. Significance was assessed with a t test. RESULTS: Baseline partial pressure of arterial oxygen and hematocrit values were similar. Hypoxemic piglets had a lower partial pressure of arterial oxygen of 38 +/- 10 mm Hg (P < .001) and higher hematocrit value of 31.4% +/- 2.9% (P < .001) compared with a partial pressure of arterial oxygen of 140 +/- 47 mm Hg and hematocrit value of 24.6% +/- 3.9% after the sham operation. Baseline and postprocedure left ventricular shortening fraction were similar within and between groups. Chronic hypoxemia increased right ventricular and left ventricular cytochrome oxidase I mRNA and protein by more than 1.4-fold. Cytochrome oxidase activity increased significantly in hypoxemia by 2.5-fold compared with that seen after the sham operation. Heme a,a3 content and turnover number increased by 1.5-fold during hypoxemia. CONCLUSIONS: Chronic hypoxemia increases cytochrome oxidase I message, protein expression, and activity. The increase in kinetics was due to increased enzyme content and catalytic activity. This is a possible adaptive mechanism that might preserve organ function during chronic hypoxemia.