Choosing entrustable professional activities for neonatology: a Delphi study.

OBJECTIVE: To assess candidate neonatology EPAs taken from separate but overlapping sets from two organizations. STUDY DESIGN: Using a Delphi process, we asked that neonatology fellowship directors (1) assess importance and scope of 19 candidate EPAs, and (2) propose additional EPAs if necessary. In round 2, we sought clarification of first round responses and evaluated proposed additional EPAs. RESULTS: Twenty program directors participated. In round 1, all EPAs were scored as important, but four were overly broad. In round 2, respondents rejected proposed subdivisions of one overly broad EPA, retaining it as originally proposed. Specification of entrustment criteria improved the scope of the three other broad EPAs. However, after specification, they were re-rated as insufficiently important and therefore rejected. Neither newly proposed EPA from round 1 was rated as sufficiently important. CONCLUSION: The Delphi process yielded 13 EPAs with which to assess capability to practice clinical neonatology.

The new 6-unit individualized curriculum for pediatric residents: the perspective of neonatology fellowship program directors.

OBJECTIVE: Starting in 2013, all pediatric residents entering fellowship must be provided six educational units whose structure is to be determined by their individual career plans. We sought to determine whether (1) neonatology fellowship program directors (PDs) consistently identify certain weaknesses among incoming fellows and (2) neonatology fellowship PDs agree on the most beneficial activities in which pediatric residents should participate to improve preparation for entry into neonatology fellowships. STUDY DESIGN: We sent a 21-question survey focused on the structure and implementation of the 6-unit curriculum to all members of the Organization of Neonatology Training Program Directors. RESULTS: Sixty-seven percent of PDs responded. Seventy-five percent cited insufficient procedural skills as the primary weakness of incoming fellows. More than 80% rated additional training in clinical neonatology, including procedural and resuscitation training, as 'beneficial' or 'highly beneficial'. In contrast, fewer than 40% of PDs gave the same positive ratings to activities broadly focused on scholarship. CONCLUSIONS: The results of the survey may help guide pediatric residency programs as they undertake development of these new curricular initiatives for individual residents entering neonatology.

Effects of an S6 strain of Mycoplasma gallisepticum inoculation before beginning of lay on the leukocytic characteristics of commercial layers.

A clinical study was conducted on commercial layers housed in biological isolation units, within which exogenous stress factors potentially affecting bird performance were minimized. This set-up was devised in order to assess how a pre-lay inoculation of S6 strain Mycoplasma gallisepticum affects the leukocytic properties of laying chickens. Previous studies have demonstrated relative decreases in lymphocyte and relative increases in heterophil percentages in birds infected with other strains of Mycoplasma gallisepticum. However, current results showed that the differential percentages of lymphocytes were decreased, whereas those of heterophils were increased, in both sham-inoculated control birds and birds inoculated with S6 Mycoplasma gallisepticum between 19 and 26 wk of age. This study clearly shows that a pre-lay inoculation of S6 Mycoplasma gallisepticum alone had no apparent effect on the leukocyte profile of commercial layers housed in biological isolation units.

Effects of an S6 strain of Mycoplasma gallisepticum challenge at onset of lay on digestive and reproductive tract characteristics in commercial layers.

Mycoplasma gallisepticum (MG), a reproductive/respiratory pathogen in poultry, has been implicated in suboptimum egg production and decreased hatchability. Commercial layer hens raised in a controlled environment were inoculated with the S6 strain of MG at 20 wk of age. The S6 inoculation had no effect on bird weight, egg production, digestive tract weight and length, or histopathologic lesion scores, although significant differences were noted in the lengths and weights of various portions of the reproductive tract. This study shows that S6MG inoculation does not detrimentally affect layer hen performance when in the absence of environmental stressors customary to a caged layer facility.

Effects of an S6 strain of Mycoplasma gallisepticum challenge before beginning of lay on various egg characteristics in commercial layers.

Mycoplasma gallisepticum (MG) is a reproductive/respiratory disease in poultry implicated in suboptimum egg production and decreased hatchability. Commercial layer hens raised in a controlled environment were inoculated with the S6 strain of MG at 10 wk of age. Egg production and selected egg and egg quality parameters were quantitated over the entire lay cycle for inoculated and control birds. The S6 inoculation had no effect on bird weight, egg production, associated egg quality parameters, or histopathologic lesion scores. This study shows that in the absence of environmental stressors a prelay S6 MG inoculation does not produce detrimental effects on layer hen performance.

Placental development in normal and compromised pregnancies-- a review.

Intrauterine growth restriction (IUGR) is a significant cause of infant mortality and morbidity. It is now clear that IUGR infants exhibit higher rates of coronary heart disease, type 2-diabetes, hypertension and stroke as adults. Therefore, fetal growth not only impacts the outcome of the perinatal period, but also impacts adult well-being. The etiologies of IUGR are numerous, but are often associated with abnormalities in placental structure and function. The process of implantation and placentation requires the production of a plethora of growth factors, cell-adhesion molecules, extracellular matrix proteins, hormones and transcription factors. Many of these exhibit altered expression within the placenta of IUGR pregnancies. However, it has been difficult to fully assess their role during the development of placental insufficiency (PI) in the human, underscoring the need for animal models. Using an ovine model of PI-IUGR we have observed changes in the expression of vascular endothelial growth factor, placental growth factor, their common receptors, as well as angiopoietin 2 and its receptor, Tie 2. We found that changes in these growth factors can be associated with both acute and chronic changes in placental vascular structure and function. These studies and others are providing needed insight into the developmental chronology of placental insufficiency.

NO and prostaglandin interactions during hemodynamic stress in the fetal ovine pulmonary circulation.

Nitric oxide (NO) and prostacyclin (PGI(2)) are potent fetal pulmonary vasodilators, but their relative roles and interactions in the regulation of the perinatal pulmonary circulation are poorly understood. We compared the separate and combined effects of nitric oxide synthase (NOS) and cyclooxygenase (COX) inhibition during acute hemodynamic stress caused by brief mechanical compression of the ductus arteriosus (DA) in chronically prepared fetal lambs. Nitro-L-arginine (L-NNA; NOS antagonist), meclofenamate (Mec; COX inhibitor), combined drugs (L-NNA-Mec), or saline (control) was infused into the left pulmonary artery (LPA) before DA compression. In controls, DA compression decreased pulmonary vascular resistance (PVR) by 43% (P < 0.01). L-NNA, but not Mec, treatment completely blocked vasodilation and caused a paradoxical increase in PVR (+31%; P < 0.05). The effects of L-NNA-Mec and L-NNA on PVR were similar. To determine if the vasodilator effect of PGI(2) is partly mediated by NO release, we studied PGI(2)-induced vasodilation before and after NOS inhibition. L-NNA treatment blocked the PGI(2)-induced rise in LPA blood flow by 73% (P < 0.001). We conclude that NO has a greater role than PGs in fetal pulmonary vasoregulation during acute hemodynamic stress and that PGI(2)-induced pulmonary vasodilation is largely mediated by NO release in the fetal lung.

Effects of chronic estrogen-receptor blockade on ovine perinatal pulmonary circulation.

Prolonged infusions of 17beta-estradiol reduce fetal pulmonary vascular resistance (PVR), but the effects of endogenous estrogens in the fetal pulmonary circulation are unknown. To test the hypothesis that endogenous estrogen promotes pulmonary vasodilation at birth, we studied the hemodynamic effects of prolonged estrogen-receptor blockade during late gestation and at birth in fetal lambs. We treated chronically prepared fetal lambs with ICI-182,780 (ICI, a specific estrogen-receptor blocker, n = 5) or 1% DMSO (CTRL, n = 5) for 7 days and then measured pulmonary hemodynamic responses to ventilation with low- and high-fraction inspired oxygen (FI(O(2))). Treatment with ICI did not change basal fetal PVR or arterial blood gas tensions. However, treatment with ICI abolished the vasodilator response to ventilation with low FI(O(2)) [change in PVR -30 +/- 6% (CTRL) vs. +10 +/- 13%, (ICI), P < 0.05] without reducing the vasodilator response to ventilation with high FI(O(2)) [change in PVR, -73 +/- 3% (CTRL) vs. -77 +/- 4%, (ICI); P = not significant]. ICI treatment reduced prostacyclin synthase (PGIS) expression by 33% (P < 0.05) without altering expression of endothelial nitric oxide synthase or cyclooxygenase-1 and -2. In situ hybridization and immunohistochemistry revealed that PGIS is predominantly expressed in the airway epithelium of late gestation fetal lambs. We conclude that prolonged estrogen-receptor blockade inhibits the pulmonary vasodilator response at birth and that this effect may be mediated by downregulation of PGIS. We speculate that estrogen exposure during late gestation prepares the pulmonary circulation for postnatal adaptation.

Role of inducible nitric oxide synthase in the pulmonary vascular response to birth-related stimuli in the ovine fetus.

To determine whether type II nitric oxide synthase (NOS II) contributes to the NO-mediated fall in pulmonary vascular resistance (PVR) at birth, we studied the effects of selective NOS II antagonists N-(3-aminomethyl) benzylacetamidine dihydrochloride (1400W) and aminoguanidine (AG) and a nonselective NOS antagonist, nitro-L-arginine (L-NA), during mechanical ventilation with low FIO(2) (<10%), high FIO(2) (100%), and inhaled NO (20 ppm) in 23 near-term fetal lambs. Intrapulmonary infusions of AG, 1400W, and L-NA increased basal PVR before delivery (P<0.05). In control animals, ventilation with low and high FIO(2) decreased PVR by 62% and 85%, respectively. Treatment with AG and 1400W attenuated the fall in PVR by 50% during ventilation with low and high FIO(2) (control versus treatment, P<0.05 for each intervention). L-NA treatment attenuated the fall in PVR during ventilation with low and high FIO(2) to a similar degree as the NOS II antagonists. To test the selectivity of the NOS II antagonists, we studied the effects of acetylcholine and inhaled NO in each study group. Acetylcholine-induced pulmonary vasodilation remained intact after treatment with selective NOS II antagonists but not after treatment with nonselective NOS blockade with L-NA. In contrast, the response to inhaled NO was similar between treatment groups. We conclude that selective NOS II inhibition is as effective as nonselective NOS blockade in attenuating pulmonary vasodilation at birth and speculate that NOS II activity contributes to NO-mediated pulmonary vasodilation at birth. We additionally speculate that stimulation of the airway epithelium by rhythmic distension and increased FIO(2) may activate NOS II release at birth.

Lung volume recruitment in lambs during high-frequency oscillatory ventilation using respiratory inductive plethysmography.

Monitoring lung volume is important in the treatment of acute hypoxemic respiratory failure. However, there are no tools available for lung volume measurement to guide ventilator management during high-frequency oscillatory ventilation (HFOV) and during dynamic changes in conventional ventilation (CV). We studied the performance of a new respiratory inductive plethysmograph (RIP) with modified software. We measured Delta changes in lung volume above end-expiratory volume (V(RIP)) during HFOV and studied whether changes in V(RIP) parallel changes in mean airway pressure. Calibration of the plethysmograph was made by serial injections of a known gas volume in six term (140 d gestation) and eight preterm (125 d gestation) lambs. Linear regression analysis of the relationship between injected gas volume and V(RIP) showed strong correlation (r(2) = 0.93-1.00 term animals, r(2) = 0.86-1.00 preterm animals). The pressure volume curves from the calibration with the injected gas volumes also correlated well with the pressure volume curves extrapolated from changes in V(RIP). Lung hysteresis was clearly demonstrated with RIP after changes in mean airway pressure during HFOV and after changes in positive end-expiratory pressure during CV. We conclude that measurements of lung volume in term and preterm lambs by use of modified RIP correlate well with changes in mean airway pressure during HFOV, with static pressure volume curves and with changes in positive end-expiratory pressure during CV. We speculate that this technique may provide clinically useful information about changes in lung volume during HFOV and CV. However, evaluation of the precision and chronic stability of RIP measurements over prolonged periods will require further studies.

Reduction of mortality in specific-pathogen-free layer chickens by a caprine serum fraction after infection with Pasteurella multocida.

Caprine serum was fractionated by size, and its proteinaceous material <8,000 Da [caprine serum fraction immunomodulator 2 (CSF-I2)] was evaluated for its ability to impart immunoresistance to specific-pathogen-free (SPF) layer chickens. The SPF layers were challenged with 18 to 30 cfu of Pasteurella multocida X-73 (serotype 1) at 5 wk of age. A high degree of mortality was apparent 24 and 48 h later (62+/-14% and 88+/-7%, respectively). Mortality observed after 48 h was minimal. Noting the rapid onset of mortality, we administered CSF-I2 (material that expressed no direct antimicrobial activity but was believed to be an immunostimulant) 1 d before challenge and coincident to time of challenge. The group of birds that received CSF-I2 (either 5 or 10 mg per administration) expressed significant reduction in mortality throughout the 1-wk study period. Reduction in mortality appeared to be dose dependent. Birds that received two administrations of 10 mg CSF-I2 had significantly fewer deaths than did the group of birds that received half that amount. No deaths were recorded through 24 h, whereas, at 48 h, the percentage mortality was 13 in CSF-I2-treated birds. This study demonstrates that one or more small molecular weight compounds isolated from caprine serum were able to reduce mortality in SPF layers infected with Pasteurella multocida.

The birth of ocular pharmacology in the 20th century.

Nineteenth century ophthalmology, characterized by significant gains in diagnostic techniques, provided the basis for great advancements in treatment during the 20th century. Drug therapy at the turn of the century was empiric, palliative, and often toxic. The development of ocular pharmacology during the 20th century provided the basis for a rational therapeutic approach to ocular disease. Foremost among the therapeutic developments were antibiotics, due to their potential to cure conditions that frequently resulted in blindness. Second, other therapeutic classes provided palliative therapy for chronic diseases, and thus decreased morbidity. For example, drugs specifically targeting many different aspects of glaucoma have had remarkable success controlling intraocular pressure and forestalling development of blindness. In addition, other new approaches provided palliative therapy for nonblinding conditions and effective adjuncts to surgical procedures. Antiallergy and anti-inflammatory drugs greatly increased patient comfort and facilitated treatment of allergic and inflammatory reactions. Local anesthetics and analgesia reduced patient discomfort during surgery. Other adjunct drugs improved surgical outcomes by reducing inflammation and infectious complications. The 21st century will undoubtedly provide novel approaches to address many of today's therapeutic dilemmas. Photodynamic therapy, growth factors, antisense technology, and genetic-based therapies all show great promise. Many of the conditions that are only treated palliatively today will be curable in the next century using many of these pharmacological advances.

Prolonged endothelin B receptor blockade causes pulmonary hypertension in the ovine fetus.

Endothelin (ET)-1 contributes to regulation of pulmonary vascular tone and structure in the normal ovine fetus and in models of perinatal pulmonary hypertension. The hemodynamic effects of ET-1 are due to activation of its receptors. The ET(A) receptor mediates vasoconstriction and smooth muscle cell proliferation, whereas the ET(B) receptor mediates vasodilation. In a lamb model of chronic intrauterine pulmonary hypertension, ET(B) receptor activity and gene expression are decreased. To determine whether prolonged ET(B) receptor blockade causes pulmonary hypertension, we studied the hemodynamic effects of selective ET(B) receptor blockade with BQ-788. Animals were treated with an infusion of either BQ-788 or vehicle for 7 days. Prolonged BQ-788 treatment increased pulmonary arterial pressure and pulmonary vascular resistance (P < 0.05). The pulmonary vasodilator response to sarafotoxin 6c, a selective ET(B) receptor agonist, was attenuated after 7 days of BQ-788 treatment, demonstrating pharmacological blockade of the ET(B) receptor. Animals treated with BQ-788 had greater right ventricular hypertrophy and muscularization of small pulmonary arteries (P < 0. 05). Lung ET-1 levels were threefold higher in the animals treated with BQ-788 (P < 0.05). We conclude that prolonged selective ET(B) receptor blockade causes severe pulmonary hypertension and pulmonary vascular remodeling in the late-gestation ovine fetus.

High-frequency oscillatory ventilation and partial liquid ventilation after acute lung injury in premature lambs with respiratory distress syndrome.

OBJECTIVE: Conventional mechanical ventilatory support (CV) contributes to lung injury in premature lambs with respiratory distress syndrome, a disease that is characterized by progressive deterioration of gas exchange and increased lung inflammation. Lung recruitment strategies, such as high-frequency oscillatory ventilation (HFOV) and partial liquid ventilation (PLV), improve gas exchange and attenuate lung inflammation when instituted immediately after birth. However, whether these recruitment strategies are effective as rescue treatment after established lung injury is unknown. To determine the separate and combined effects of HFOV and PLV when initiated after the establishment of acute lung injury in severe respiratory distress syndrome, we studied the effects of these strategies on gas exchange and histologic signs of acute lung injury in premature lambs. DESIGN: Animals were intubated, treated with surfactant and ventilated with 1.00 FIO2 for 4 hrs. After 2 hrs, animals were either continued on CV (controls) or treated with one of three strategies: HFOV; CV + PLV; or HFOV + PLV. The response to low-dose inhaled nitric oxide (5 ppm) was measured in each group at the end of the study. SETTING: An animal laboratory affiliated with University of Colorado School of Medicine. SUBJECTS: A total of 20 premature lambs at 115-118 days of gestation (term = 147 days). MEASUREMENTS AND MAIN RESULTS: In comparison with control animals, each of the rescue therapies improved PaO2 after 1 hr of treatment. The HFOV and HFOV + PLV groups had higher PaO2 than CV + PLV or CV alone (p < .05). Mean airway pressure (Paw) was lower in the PLV groups during CV or HFOV compared with their controls (p < .05). Inhaled NO improved PaO2 in all groups; however, the increase in PaO2 was greatest in the HFOV + PLV group (p < .05). Histologic examination and myeloperoxidase assay were not different between groups. CONCLUSION: We conclude that each lung recruitment strategy improved oxygenation in premature lambs with established lung injury.

Soluble beta-amyloid peptides mediate vasoactivity via activation of a pro-inflammatory pathway.

Freshly solubilized beta-amyloid (Abeta) peptides display vasoactive properties, increasing both the magnitude and the duration of endothelin-1-induced vasoconstriction. We show that Abeta vasoactivity is mediated by the stimulation of a pro-inflammatory pathway involving activation of secretory phospholipase A(2) (PLA(2)), mitogen activated protein kinase (MAPK) kinase (MEK1/2), p38 MAPK, cytosolic PLA(2), and the release of arachidonic acid. Ultimately, arachidonic acid is metabolized into proinflammatory eicosanoids via the 5-lipoxygenase and cyclooxygenase-2 (COX-2) enzymes, both of which we show to be required for A beta vasoactivity. Accordingly, p38 MAPK activity is higher in the brains of transgenic mice that overproduce A beta, and COX-2 immunoreactivity is increased in the cerebrovasculature of these transgenic animals. Taken together, our data show that freshly solubilized A beta peptides can trigger a pro-inflammatory reaction in the vasculature that can be blocked by inhibiting specific target molecules, providing the basis for novel therapeutic intervention.

Developmental changes in endothelin expression and activity in the ovine fetal lung.

Mechanisms that regulate endothelin (ET) in the perinatal lung are complex and poorly understood, especially with regard to the role of ET before and after birth. We hypothesized that the ET system is developmentally regulated and that the balance of ET(A) and ET(B) receptor activity favors vasoconstriction. To test this hypothesis, we performed a series of molecular and physiological studies in the fetal lamb, newborn lamb, and adult sheep. Lung preproET-1 mRNA levels, tissue ET peptide levels, and cellular localization of ET-1 expression were determined by Northern blot analysis, peptide assay, and immunohistochemistry in distal lung tissue from fetal lambs between 70 and 140 days (term = 145 days), newborn lambs, and ewes. Lung mRNA expression for the ET(A) and ET(B) receptors was also measured at these ages. We found that preproET-1 mRNA expression increased from 113 to 130 days gestation. Whole lung ET protein content was highest at 130 days gestation but decreased before birth in the fetal lamb lung. Immunolocalization of ET-1 protein showed expression of ET-1 in the vasculature and bronchial epithelium at all gestational ages. ET(A) receptor mRNA expression and ET(B) receptor mRNA increased from 90 to 125 and 135 days gestation. To determine changes in activity of the ET(A) and ET(B) receptors, we studied the effect of selective antagonists to the ET(A) or ET(B) receptors at 120, 130, and 140 days of fetal gestation. ET(A) receptor-mediated vasoconstriction increased from 120 to 140 days, whereas blockade of the ET(B) receptor did not change basal fetal pulmonary vascular tone at any age examined. We conclude that the ET system is developmentally regulated and that the increase in ET(A) receptor gene expression correlates with the onset of the vasodilator response to ET(A) receptor blockade. Although ET(B) receptor gene expression increases during late gestation, the balance of ET receptor activity favors vasoconstriction under basal conditions. We speculate that changes in ET receptor activity play important roles in regulation of pulmonary vascular tone in the ovine fetus.

Estradiol improves pulmonary hemodynamics and vascular remodeling in perinatal pulmonary hypertension.

Partial ligation of the ductus arteriosus (DA) in the fetal lamb causes sustained elevation of pulmonary vascular resistance (PVR) and hypertensive structural changes in small pulmonary arteries, providing an animal model for persistent pulmonary hypertension of the newborn. Based on its vasodilator and antimitogenic properties in other experimental studies, we hypothesized that estradiol (E(2)) would attenuate the pulmonary vascular structural and hemodynamic changes caused by pulmonary hypertension in utero. To test our hypothesis, we treated chronically instrumented fetal lambs (128 days, term = 147 days) with daily infusions of E(2) (10 microg; E(2) group, n = 6) or saline (control group, n = 5) after partial ligation of the DA. We measured intrauterine pulmonary and systemic artery pressures in both groups throughout the study period. After 8 days, we delivered the study animals by cesarean section to measure their hemodynamic responses to birth-related stimuli. Although pulmonary and systemic arterial pressures were not different in utero, fetal PVR immediately before ventilation was reduced in the E(2)-treated group (2.43 +/- 0.79 vs. 1.48 +/- 0.26 mmHg. ml(-1). min, control vs. E(2), P < 0.05). During the subsequent delivery study, PVR was lower in the E(2)-treated group in response to ventilation with hypoxic gas but was not different between groups with ventilation with 100% O(2). During mechanical ventilation after delivery, arterial partial O(2) pressure was higher in E(2) animals than controls (41 +/- 11 vs. 80 +/- 35 Torr, control vs. E(2), P < 0. 05). Morphometric studies of hypertensive vascular changes revealed that E(2) treatment decreased wall thickness of small pulmonary arteries (59 +/- 1 vs. 48 +/- 1%, control vs. E(2), P < 0.01). We conclude that chronic E(2) treatment in utero attenuates the pulmonary hemodynamic and histological changes caused by DA ligation in fetal lambs.

Prolonged infusions of estradiol dilate the ovine fetal pulmonary circulation.

Factors mediating both the rapid and sustained fall in pulmonary vascular resistance (PVR) at birth are incompletely understood. Acute or prolonged estrogen treatment causes vasodilation of several vascular beds in adults. Although fetal estrogen levels rise in late gestation, their effects in the fetal pulmonary circulation have not been studied. To determine whether estrogens can cause pulmonary vasodilation in the fetus, we infused 17beta-estradiol (E2) into the left pulmonary artery (LPA) of chronically catheterized fetal lambs, measured pulmonary artery pressure and LPA blood flow, and calculated PVR. Brief E2 administration (1-, 10-, and 100-microg doses) did not change baseline pulmonary hemodynamics and failed to enhance endothelium-dependent vasodilation as assessed by the dilator response to acetylcholine. However, prolonged E2 infusion (2- 8 d) caused a 2.6-fold increase in pulmonary blood flow (73+/-6 versus 188+/-44 mL/min, baseline versus E2 treatment, p<0.05), and the response was sustained for at least several hours. Treatment with the nitric oxide synthase inhibitor nitro-L-arginine (L-NA) reversed the E2-induced fall in PVR (0.15+/-0.05 versus 0.51+/-0.15 mm Hg/mL/min; before versus after L-NA, p<0.05). Endothelial nitric oxide synthase expression and endothelin-1 content were not different in E2-responders and controls, suggesting that altered expression of these mediators did not account for the increased flow. We conclude that prolonged E2 infusion causes an unusual pattern of vasodilation in the ovine fetal lung. On the basis of these observations of exogenous E2 treatment, we speculate that endogenous E2 enhances pulmonary vasodilation at birth.

Role of neuronal nitric oxide synthase in regulation of vascular and ductus arteriosus tone in the ovine fetus.

Nitric oxide (NO) is produced by NO synthase (NOS) and contributes to the regulation of vascular tone in the perinatal lung. Although the neuronal or type I NOS (NOS I) isoform has been identified in the fetal lung, it is not known whether NO produced by the NOS I isoform plays a role in fetal pulmonary vasoregulation. To study the potential contribution of NOS I in the regulation of basal fetal pulmonary vascular resistance (PVR), we studied the hemodynamic effects of a selective NOS I antagonist, 7-nitroindazole (7-NINA), and a nonselective NOS antagonist, N-nitro-L-arginine (L-NNA), in chronically prepared fetal lambs (mean age 128 +/- 3 days, term 147 days). Brief intrapulmonary infusions of 7-NINA (1 mg) increased basal PVR by 37% (P < 0.05). The maximum increase in PVR occurred within 20 min after infusion, and PVR remained elevated for up to 60 min. Treatment with 7-NINA also increased the pressure gradient between the pulmonary artery and aorta, suggesting constriction of the ductus arteriosus (DA). To test whether 7-NINA treatment selectively inhibits the NOS I isoform, we studied the effects of 7-NINA and L-NNA on acetylcholine-induced pulmonary vasodilation. The vasodilator response to acetylcholine remained intact after treatment with 7-NINA but was completely inhibited after L-NNA, suggesting minimal effects on endothelial or type III NOS after 7-NINA infusion. Western blot analysis detected NOS I protein in the fetal lung and great vessels including the DA. NOS I protein was detected in intact and endothelium-denuded vessels, suggesting that NOS I is present in the medial or adventitial layer. We conclude that 7-NINA, a selective NOS I antagonist, increases basal PVR, systemic arterial pressure, and DA tone in the late-gestation fetus and that NOS I protein is present in the fetal lung and great vessels. We speculate that NOS I may contribute to NO production in the regulation of basal vascular tone in the pulmonary and systemic circulations and the DA.