Biallelic variants in genes previously associated with dominant inheritance: CACNA1A, RET and SLC20A2.

A subset of families with co-dominant or recessive inheritance has been described in several genes previously associated with dominant inheritance. Those recessive families displayed similar, more severe, or even completely different phenotypes to their dominant counterparts. We report the first patients harboring homozygous disease-related variants in three genes that were previously associated with dominant inheritance: a loss-of-function variant in the CACNA1A gene and two missense variants in the RET and SLC20A2 genes, respectively. All patients presented with a more severe clinical phenotype than the corresponding typical dominant form. We suggest that co-dominant or recessive inheritance for these three genes could explain the phenotypic differences from those documented in their cognate dominant phenotypes. Our results reinforce that geneticists should be aware of the possible different forms of inheritance in genes when WES variant interpretation is performed. We also evidence the need to refine phenotypes and inheritance patterns associated with genes in order to avoid failures during WES analysis and thus, raising the WES diagnostic capacity in the benefit of patients.

Protein metabolism in clinically stable adult cystic fibrosis patients with abnormal glucose tolerance.

Cystic fibrosis (CF) patients are reported to experience chronic protein catabolism. Since diabetes or impaired glucose tolerance (IGT) is common in CF, we hypothesized that their protein catabolic state is related to reduced insulin secretion or reduced insulin action. A total of 12 clinically stable adult CF patients with abnormal glucose tolerance and 12 age-, sex-, and lean body mass-matched healthy control subjects underwent protein turnover studies using L-[1-(13)C]leucine, L-[(15)N]phenylalanine, and L-[(2)H(4)]tyrosine, with and without exogenous insulin infusion. In the baseline fasting state, protein metabolism was entirely normal in CF patients, with no evidence of increased protein catabolism. In contrast, striking abnormalities were seen in CF patients when insulin was infused, since they did not experience normal suppression of the appearance rates of leucine, phenylalanine, or tyrosine (indexes of protein breakdown). At an insulin concentration of 45 +/- 2 microU/ml, normal control subjects suppressed the leucine appearance rate by 19 +/- 5% (P < 0.01), ketoisocaproate appearance rate by 10 +/- 3% (P = 0.03), tyrosine appearance rate by 11 +/- 2% (P = 0.03), and phenylalanine appearance rate by 6 +/- 3% (P = 0.07). Phenylalanine conversion to tyrosine decreased by 22 +/- 7% (P = 0.03). At a similar insulin concentration of 44 +/- 3 microU/ml, normal suppression of amino acid appearance did not occur in CF. The leucine appearance rate decreased by 4 +/- 2% (P = 0.65), ketoisocaproate appearance rate by 1 +/- 2% (P = 0.94), tyrosine appearance rate by 0 +/- 6% (P = 0.56), phenylalanine appearance rate by 5 +/- 6% (P = 0.34), and phenylalanine conversion to tyrosine by 5 +/- 6% (P = 0.95). Poor suppression of the amino acid appearance rate in CF was not related to previously documented glucose tolerance status (IGT or CF-related diabetes without fasting hyperglycemia), fasting insulin levels, the acute insulin response, insulin sensitivity, cytokine or counterregulatory hormone levels, resting energy expenditure, caloric intake, pulmonary function, or clinical status. Protein synthesis was not significantly affected by insulin infusion in either normal control subjects or CF patients. In conclusion, clinically stable adult CF patients have normal indexes of protein breakdown and synthesis in the fasting state. In contrast, elevation of plasma insulin to physiological postprandial levels fails to normally suppress indexes of protein breakdown. It is therefore likely that inability to spare protein during the postprandial state is the cause of protein catabolism in these patients.

Insulin and glucose excursion following premeal insulin lispro or repaglinide in cystic fibrosis-related diabetes.

OBJECTIVE: Insulin and glucose levels in response to premeal insulin lispro or repaglinide were evaluated in adult patients with cystic fibrosis-related diabetes (CFRD) without fasting hyperglycemia. RESEARCH DESIGN AND METHODS: Seven patients with CFRD were fed 1,000-kcal liquid mixed meals. Three study conditions were administered in random order on separate mornings: 1) no premeal diabetes medication, 2) insulin lispro, 0.1 unit/kg body wt premeal and 3) repaglinide 1 mg premeal. Glucose and insulin levels were measured every 20 min for 5 h. RESULTS: Fasting insulin and glucose levels were normal in patients with CFRD, but the peak glucose level was elevated. Insulin lispro significantly decreased the peak glucose level (P = 0.0004) and the 2-h (P = 0.001) and 5-h (P < 0.0001) glucose area under the curve (AUC). Repaglinide significantly decreased the 5-h glucose AUC (P = 0.03). Neither drug completely normalized cystic fibrosis glucose excursion at the doses used for this study. Insulin lispro significantly increased the 5-h insulin AUC (P = 0.04). CONCLUSIONS: In response to subcutaneous insulin lispro, postprandial glucose excursion was significantly diminished and insulin secretion was enhanced compared with a control meal in which no medication was given to patients with CFRD. The oral agent repaglinide resulted in lesser corrections in these parameters. Neither drug completely normalized glucose or insulin levels, suggesting that the doses chosen for this study were suboptimal. Placebo-controlled longitudinal studies comparing the effectiveness of repaglinide and insulin on glucose metabolic control as well as overall nutrition and body weight are needed to help determine optimal medical treatment of CFRD.

Differential effects of ascending neurons containing dopamine and noradrenaline in the control of spontaneous activity and of evoked responses in the rat prefrontal cortex.

The medial prefrontal cortex receives converging projections from the mediodorsal thalamic nucleus, dopaminergic cells from the ventral tegmental area dn noradrenergic cells from the locus coeruleus. Stimulation of the ventral tegmental area inhibits the spontaneous activity of prefrontal cortical neurons and blocks the excitatory response evoked by stimulation of the mediodorsal thalamic nucleus (10 Hz). The aim of the present study was to compare the influence of dopaminergic and noradrenergic afferents on the spontaneous and evoked activity of medial prefrontal cortical neurons. In ketamine-anaesthetized rats, repetitive stimulation (20 Hz, 10 s) of the locus coeruleus produced a long-lasting post-stimulus inhibition (mean duration: 45 s) of the spontaneous activity of 56% of the tested cells. This effect was decreased markedly following selective destruction of the ascending noradrenergic pathways (local 6-hydroxy-dopamine injection) or depletion of cortical catecholamines by alpha-methyl-para-tyrosine pretreatment, suggesting that these inhibitory responses are mediated by noradrenergic neurons. The excitatory response to mediodorsal thalamus nucleus stimulation (10 Hz) could still be evoked during the post-stimulus inhibitory period induced by locus coeruleus stimulation (20 Hz, 10 s) resulting in the enhancement of signal-to-noise ratio. On the other hand, a population of prefrontal cortex neurons (26%) was found to be reproducibly activated by noxious tail pinch. This evoked response was still present during the post-stimulus inhibitory period induced by locus coeruleus stimulation but was completely suppressed during stimulation of the ventral tegmental area (10 Hz). In conclusion, these results indicate that the dopaminergic and noradrenergic systems exert a completely distinct control of information transfer in the medial prefrontal cortex.

Randomized, controlled trial of low-dose inhaled nitric oxide in the treatment of term and near-term infants with respiratory failure and pulmonary hypertension.

UNLABELLED: Recent reports indicate that inhaled nitric oxide (iNO) causes selective pulmonary vasodilation, increases arterial oxygen tension, and may decrease the use of extracorporeal membrane oxygenation (ECMO) in infants with persistent pulmonary hypertension of the newborn (PPHN). Despite these reports, the optimal dose and timing of iNO administration in PPHN remains unclear. OBJECTIVES: To test the hypotheses that in PPHN 1) iNO at 2 parts per million (ppm) is effective at acutely increasing oxygenation as measured by oxygenation index (OI); 2) early use of 2 ppm of iNO is more effective than control (0 ppm) in preventing clinical deterioration and need for iNO at 20 ppm; and 3) for those infants who fail the initial treatment protocol (0 or 2 ppm) iNO at 20 ppm is effective at acutely decreasing OI. STUDY DESIGN: A randomized, controlled trial of iNO in 3 nurseries in a single metropolitan area. Thirty-eight children, average gestational age of 37.3 weeks and average age <1 day were enrolled. Thirty-five of 38 infants had echocardiographic evidence of pulmonary hypertension. On enrollment, median OI in the control group, iNO at 0 ppm, (n = 23) was 33.1, compared with 36.9 in the 2-ppm iNO group (n = 15). RESULTS: Initial treatment with iNO at 2 ppm for an average of 1 hour was not associated with a significant decrease in OI. Twenty of 23 (87%) control patients and 14 of 15 (92%) of the low-dose iNO group demonstrated clinical deterioration and were treated with iNO at 20 ppm. In the control group, treatment with iNO at 20 ppm decreased the median OI from 42.6 to 23.8, whereas in the 2-ppm iNO group with a change in iNO from 2 to 20 ppm, the median OI did not change (42.6 to 42.0). Five of 15 patients in the low-dose nitric oxide group required ECMO and 2 died, compared with 7 of 23 requiring ECMO and 5 deaths in the control group. CONCLUSION: In infants with PPHN, iNO 1): at 2 ppm does not acutely improve oxygenation or prevent clinical deterioration, but does attenuate the rate of clinical deterioration; and 2) at 20 ppm acutely improves oxygenation in infants initially treated with 0 ppm, but not in infants previously treated with iNO at 2 ppm. Initial treatment with a subtherapeutic dose of iNO may diminish the clinical response to 20 ppm of iNO and have adverse clinical sequelae.

Risk of death in cystic fibrosis patients with severely compromised lung function.

BACKGROUND: Lung disease accounts for most of the mortality in patients with cystic fibrosis (CF). Lung transplantation is an option for patients severely impaired, being recommended when life expectancy is estimated to be <2 years. Our objectives were to evaluate in our patient population the validity of currently accepted criteria for low life expectancy and to identify other potentially useful criteria. METHODS: Data were retrieved from CF patients followed up at our center who reached and kept an FEV1 <30% predicted. A life table was created and stratified according to characteristics believed to be of importance. In addition, the rate of decline in percent predicted FEV1 was analyzed. These characteristics were evaluated as predictors of risk of death. RESULTS: The median survival was 3.9 years (95% confidence interval, 2.88 to 4.12 years), with no significant differences according to gender, nutritional status, presence of diabetes, or decade in which the patient was cared for. Only by age was there a significant difference in the median survival (p<0.05). By proportional hazards regression, only the rate of decline in percent predicted FEV1 was a significant predictor of the risk of death, with a borderline effect from younger age (p=0.06). CONCLUSION: In our patient population, a cutoff value of FEV1 of < 30% predicted is not a reliable predictor of high risk of death within 2 years. The yearly rate of decline of percent predicted FEV1 is a better parameter to identify those patients at high risk for death.

Clinical significance of the recovery of Aspergillus species from the respiratory secretions of cystic fibrosis patients.

The frequent recovery of Aspergillus species from the respiratory tract secretions of cystic fibrosis (CF) patients is well recognized, and the presence of the fungus in the airways may trigger an inflammatory response that can manifest as the clinical entity known as allergic bronchopulmonary aspergillosis (ABPA). In our CF patient population we studied the clinical characteristics of those who had Aspergillus sp. recovered from their respiratory tract secretions (n = 45) and compared them with the characteristics seen, during the same time period, in those patients who were culture negative for Aspergillus sp. (n = 167). There were no differences in peripheral blood eosinophil count (P = 0.9) or serum immunoglobulin E levels (P = 0.61). By logistic regression analysis there seemed to be an increased risk for more advanced lung disease, both radiographically (defined by a Brasfield chest radiograph score < 18) and by lung function parameters in those who were culture positive. However, after appropriate adjustment, almost all the increased risk was associated with age and gender, but not with the presence of Aspergillus sp. in respiratory secretions. Additionally, increasing age was strongly correlated with the risk of Aspergillus sp. being cultured from respiratory secretions (P = 0.0025). The presence of Aspergillus sp. in respiratory secretions was not associated with two indicators of atopy in our CF patient population. We do not have evidence that the culture of Aspergillus sp. from CF respiratory secretions is independently associated with an increased risk for more advanced lung disease.

Glycemic response to dietary supplements in cystic fibrosis is dependent on the carbohydrate content of the formula.

BACKGROUND: Enteral formula feedings are frequently prescribed to cystic fibrosis (CF) patients to boost caloric intake. A substantial number of these patients are glucose intolerant and have severe respiratory compromise. METHODS: To determine the effect of the carbohydrate content on glucose tolerance and respiratory function in glucose-intolerant CF patients with poor lung function, we examined the response to bolus feedings of five dietary supplements; a high-fat formula developed in our Clinical Research Center (CRC), Pulmocare, a high-carbohydrate formula developed in our CRC, Ensure Plus, and sugar-free Scandishake. RESULTS: Glucose excursion in response to the formulas with the lowest carbohydrate content was significantly less than that found in response to formulas with higher carbohydrate content. Insulin levels were also markedly lower in response to the low-carbohydrate high-fat formulas. Glucose excursion, expressed as a percent of the response to the CRC high-fat formula, was 111% +/- 12% for Pulmocare (p = NS), 202% +/- 34% for Ensure Plus (p < 01), 227% +/- 37% for CRC high carbohydrate (p = .001), and 357% +/- 33% for sugar-free Scandishake (p < .001). CO2 production, O2 consumption, minute ventilation, and respiratory rate increased modestly but not significantly in response to all formulas. No significant differences were found between the formulas in regards to these parameters. There were no subjective complaints of dyspnea during any of the five studies. CONCLUSION: The carbohydrate content of liquid dietary supplements appears to be an important determinant of hyperglycemia in glucose-intolerant adult CF patients.

[Pelvic presentation, always cesarean?]. / Presentación pélvica, siempre cesárea?

During one year, 104 term products were in fetal presentation. Cesarean was done in 75%, and most frequent indications were, deflexionated head (24.2%); previous section 24.2%; head hyperextension 12.8%. Section was done only in 14.4% of product with the requisites for vaginal delivery. There were two neonate al deaths among the ones by vaginal via; one due to major congenital malformations. Corrected neonatal mortality was 34.4 for 1000 alive products. Severe perinatal asphyxia was in 0.76% in vaginal birth and in 0.38% of cesarean products; and difference was not statistically significant. Maternal morbidity was 20.3% in cesarean and 0% for vaginal delivery. In the cases with pelvic presentation, well selected for vaginal delivery, fetal morbidity was not significantly increased, and maternal morbidity decreases importantly. In selected patients and with well trained physicians for this purpose, vaginal delivery is a good option.

Systematic review with meta-analysis: the declining risk of colorectal cancer in ulcerative colitis.

BACKGROUND: Patients with ulcerative colitis (UC) have an increased risk of developing colorectal cancer (CRC); however, the magnitude of this effect is open to debate. AIM: To assess the risk of CRC in UC patients by systematic review and meta-analysis. METHODS: A systematic literature search was performed up to November 2013. We selected studies describing the incidence and prevalence of CRC in patients with UC. Articles were assessed for quality using the Newcastle-Ottawa Scale. Cumulative incidence and incidence rates of CRC were combined and analysed using the generic inverse variance method. Sub-analyses were performed to identify factors associated with an increased risk of developing CRC. RESULTS: A total of 81 studies (181 923 patients) met the inclusion criteria. The incidence rate of CRC in patients with UC was 1.58 per 1000 patient-years (py) [95% confidence interval (CI), 1.39­1.76]. Results were heterogeneous (I2 = 81­89%). The incidence rate was 4.02/1000 py (95%CI = 2.74­5.31) in studies that only included patients with extensive colitis, and 1.24/1000 py (95%CI = 1.01­1.47) in population-based studies. The incidence rate was 0.91/1000 py (95%CI = 0.61­1.2) in the first decade of disease, 4.07/1000 py (95%CI = 2.58­5.56) in the second, and 4.55/1000 py (95%CI = 2.64­6.46) in the third. The incidence rate decreased from 4.29/1000 py in the studies published in the 1950s to 1.21/1000 py in studies published in the last decade. CONCLUSIONS: The risk of patients with ulcerative colitis developing colorectal cancer has decreased steadily over the last six decades, but the extent and duration of the disease increase this risk.

Oncogenic osteomalacia: loss of hypophosphatemia might be the key to avoid misdiagnosis.

Diagnosing oncogenic osteomalacia is still a challenge. The disorder is characterized by osteomalacia caused by renal phosphate wasting and low serum concentration of 1,25-dihydroxyvitamin D3 occurring in the presence of a tumor that produces high levels of fibroblast growth factor 23. However, it is possible that the disease is much more misdiagnosed than rare. We present the case of a 42-year-old man with a long-term history of undiagnosed progressive muscle weakness. His laboratory results mainly showed low serum phosphate. Surgical removal of a nasal hemangiopericytoma that had been diagnosed five years earlier, brought him to a symptom-free condition. Even though knowing the underlying etiology would explain his osteomalacia, the patient sought medical help from countless physicians for five consecutive years, and only after adequate treatment a rewarding outcome was achieved.

Pre-transplant risk factors affecting outcome in Hurler syndrome.

Allogeneic transplantation remains the standard of care for patients with Hurler syndrome. As enzyme replacement therapy (ERT) has become available, controversy has emerged in regards to whether the use of enzyme in the peri-transplant period is appropriate. An analysis was performed on 74 patients with Hurler syndrome transplanted at the University of Minnesota between 1990 and 2003, before our use of ERT associated with transplant, with the intention of determining if patients at higher risk during the transplant can be identified based on evaluations and events before transplantation. Age, the presence of hydrocephalus, a history of cardiovascular issues or upper airway obstruction before transplant was not associated with significant differences in survival. In contrast, patients who had a history of lower airway disease, including reactive airway disease or bronchiolitis, or a history of pneumonia, had a significantly inferior outcome based on OS. The risk for serious respiratory complications was also assessed by evaluating the incidence of intubation. Overall, 31% of these patients were intubated. The risk of intubation was higher in older patients and in those with a history of lower airway disease. These findings have implications for the care of patients with high-risk features.

Oncogenic osteomalacia: loss of hypophosphatemia might be the key to avoid misdiagnosis / Osteomalacia oncogênica: a perda de fosfatemia pode ser a chave para evitar o diagnóstico incorreto

Diagnosing oncogenic osteomalacia is still a challenge. The disorder is characterized by osteomalacia caused by renal phosphate wasting and low serum concentration of 1,25-dihydroxyvitamin D3 occurring in the presence of a tumor that produces high levels of fibroblast growth factor 23. However, it is possible that the disease is much more misdiagnosed than rare. We present the case of a 42-year-old man with a long-term history of undiagnosed progressive muscle weakness. His laboratory results mainly showed low serum phosphate. Surgical removal of a nasal hemangiopericytoma that had been diagnosed five years earlier, brought him to a symptom-free condition. Even though knowing the underlying etiology would explain his osteomalacia, the patient sought medical help from countless physicians for five consecutive years, and only after adequate treatment a rewarding outcome was achieved. Arq Bras Endocrinol Metab. 2012;56(8):570-3.

A osteomalacia oncogênica é um diagnóstico clínico desafiador, caracterizado pela perda renal de fosfato e baixos níveis de 1,25-di-hidroxivitamina D3, ocorrendo na presença de um tumor produtor de altos níveis de fator de crescimento de fibroblasto 23. No entanto, é possível que se trate muito mais de uma falha de diagnóstico clínico do que propriamente uma doença rara. Os autores relatam o caso de um homem de 42 anos com histórico de fraqueza muscular progressiva por cinco anos e restrição à cadeira de rodas, sem diagnóstico. Seus exames laboratoriais evidenciavam baixos níveis de fósforo. A remoção cirúrgica de um hemangiopericitoma detectado previamente em cavidade nasal levou à resolução completa dos sintomas. Os autores enfatizam que, mesmo com a etiologia já evidenciada, o paciente consultou diversos clínicos no decorrer dos cinco anos até que fossem instituídos o diagnóstico e o tratamento adequados. Arq Bras Endocrinol Metab. 2012;56(8):570-3.

Long-term effects of aerosolised rhDNase on pulmonary disease progression in patients with cystic fibrosis.

BACKGROUND: After multiple studies, including clinical trials, suggested some mild clinical benefits from the use of rhDNase by patients with cystic fibrosis, a widespread acceptance of the drug has followed. However, long-term effects, specifically on lung disease progression, have not been demonstrated. Experience with the use of this drug in a single cystic fibrosis centre is presented and compared with the trends seen in the patient population of the centre before the introduction of the drug. METHODS: Patients with cystic fibrosis routinely followed at the University of Minnesota Cystic Fibrosis Center and prescribed rhDNase for at least two years were included in this retrospective study. Data on spirometric parameters (FEV1 and FEV1/FVC), allometric index, and admissions to hospital were retrieved from the centre's database for the two years preceding the prescription of rhDNase and the two years that followed. Trends in pulmonary function and allometric index were analysed by mixed linear modelling, and hospital admission rates for both periods were calculated and compared. RESULTS: One hundred and ninety patients met the inclusion criteria for the study. In the two years preceding the prescription of rhDNase the trends noted were those of a mild decline in FEV1, a stable FEV1/FVC, and a mild improvement in allometric index. In the two years that followed the prescription of rhDNase a mild decline in all these parameters occurred which was a significant change from the previous period (all p < 0.009). There was no difference between females and males in the trends experienced after the start of rhDNase. By logistic regression analysis only the presence of malnutrition at the time of prescription was associated with a positive trend after the introduction of rhDNase. No significant change in the hospital admission rates occurred, with rates of 0.52 (0.16) and 0.56 (0.21) admissions/patient/year for the periods before and after the prescription of rhDNase, respectively. CONCLUSIONS: The introduction of rhDNase to the regimen of patients with cystic fibrosis cared for at this centre has not been followed by a positive trend in lung function and nutritional parameters. There are some differences between this patient population and those who participated in previous studies which may help to explain the contrasting findings of this study. However, it is also possible that factors other than mucus clearance need to be improved to achieve a favourable response in disease progression. Patients on this treatment should be followed closely and the benefit judged on an individual basis. More studies are needed to define better the specific indications and use of this form of treatment.

Trends in pulmonary function in patients with cystic fibrosis correlate with the degree of glucose intolerance at baseline.

In patients with cystic fibrosis, CF-related diabetes mellitus (CFRD) has been associated with increased morbidity and mortality. Whether glucose intolerance is also associated with poor outcomes is unclear. To better define these relationships we prospectively followed a group of 152 patients with CF without diabetes for 4 yr. Patients were classified as having normal glucose tolerance (NGT), impaired glucose tolerance (IGT), or CFRD without fasting hyperglycemia (CFRD-No FH). FEV(1), FVC, and body mass index (BMI) were measured at baseline and quarterly. At baseline 45% of the patients had NGT, 38.8% had IGT, and 15.8% had CFRD-No FH. FEV(1), FVC, and BMI at baseline were comparable among these groups (all p > 0.1). After 4 yr an overall decline in FEV(1) and FVC occurred, with no change in BMI. The rates of decline for FEV(1) and FVC correlated with the glucose tolerance groups, with the highest rates of decline occurring among the CFRD-No FH group. In addition, patients in the lowest quartile for insulin production at baseline experienced the highest rates of pulmonary function decline over time, suggesting a relationship between insulin deficiency and clinical deterioration. We conclude that the degree of glucose intolerance is a strong determinant of future lung function decline in patients with CF.

PCR ribotyping and endonuclease subtyping in the epidemiology of Burkholderia cepacia infection.

Because of conflicting data about hospital-based transmission of Burkholderia (Pseudomonas) cepacia, an important respiratory pathogen in cystic fibrosis (CF), we compared strains found in sputum, lung, or blood of 29 CF patients in our center from 1988 to 1994, studying the relationship between strain and hospital exposure of incident and that of prevalent cases. Exposure was defined as a concurrent hospital stay between a prevalent and an incident case. B. cepacia strains were determined by polymerase chain reaction (PCR) ribotyping and endonuclease subtyping. The 16S to 23S spacer regions of the bacterial ribosomal RNA (rRNA) genes were amplified by PCR, and the product-size patterns used to type each B. cepacia isolate. Endonuclease digestion of the PCR products provided length polymorphisms for subtyping. There were 17 incident events during the period from 1988 to 1994, 16 of which involved a single ribotype. These 16 ribotypes could be divided into five subtypes by endonuclease mapping. Four patients grew B. cepacia from the blood, with the organism being the same strain as found in the lung in each case. Case controls were obtained to evaluate risk factors for B. cepacia acquisition. Concurrent hospitalization with a prevalent case significantly increased the risk of acquisition. There was no association between length of hospitalization, length of exposure, or FEV1 and the risk of B. cepacia acquisition.

NO causes perinatal pulmonary vasodilation through K+-channel activation and intracellular Ca2+ release.

Evidence suggests that nitric oxide (NO) causes perinatal pulmonary vasodilation through K+-channel activation. We hypothesized that this effect worked through cGMP-dependent kinase-mediated activation of Ca2+-activated K+ channel that requires release of intracellular Ca2+ from a ryanodine-sensitive store. We studied the effects of 1) K+-channel blockade with tetraethylammonium, 4-aminopyridine, a voltage-dependent K+-channel blocker, or glibenclamide, an ATP-sensitive K+-channel blocker; 2) cyclic nucleotide-sensitive kinase blockade with either KT-5823, a guanylate-sensitive kinase blocker, or H-89, an adenylate-sensitive kinase blocker; and 3) blockade of intracellular Ca2+ release with ryanodine on NO-induced pulmonary vasodilation in acutely prepared late-gestation fetal lambs. N-nitro-L-arginine, a competitive inhibitor of endothelium-derived NO synthase, was infused into the left pulmonary artery, and tracheotomy was placed. The animals were ventilated with 100% oxygen for 20 min, followed by ventilation with 100% oxygen and inhaled NO at 20 parts/million (ppm) for 20 min. This represents the control period. In separate protocols, the animals received an intrapulmonary infusion of the different blockers and were ventilated as above. Tetraethylammonium (n = 6 animals) and KT-5823 (n = 4 animals) attenuated the response, whereas ryanodine (n = 5 animals) blocked NO-induced perinatal pulmonary vasodilation. 4-Aminopyridine (n = 5 animals), glibenclamide (n = 5 animals), and H-89 (n = 4 animals) did not affect NO-induced pulmonary vasodilation. We conclude that NO causes perinatal pulmonary vasodilation through cGMP-dependent kinase-mediated activation of Ca2+-activated K+ channels and release of Ca2+ from ryanodine-sensitive stores.