Prone positioning decreases cardiac output and increases systemic vascular resistance in neonates

OBJECTIVE

To evaluate the cardiovascular response to short-term prone positioning in neonates.

STUDY DESIGN

In this prospective study, we continuously monitored heart rate (HR), stroke volume (SV) and cardiac output (CO) by electrical velocimetry in hemodynamically stable neonates in each of the following positions for 10 min: supine, prone and back-to-supine position. Skin blood flow (SBF) was also continuously assessed on the forehead or foot using Laser Doppler technology. Systemic vascular resistance (SVR) index was calculated as mean blood pressure (BP)/CO. Data were analyzed using repeated measures analysis of variance.

RESULTS

Thirty neonates (gestational age: 35±4 weeks; postmenstrual age: 36±3 weeks) were enrolled. HR did not change in response to positioning. However, in prone position, SV, CO and SBF decreased and SVR index increased from 1.5±0.3 to 1.3±0.3 ml kg(-1) (mean ±s.d., P<0.01), 206±44 to 180±41 ml kg(-1) min(-1) (P<0.01), 0.54±0.30 to 0.44±0.29 perfusion units (P<0.01) and 0.25±0.06 to 0.30±0.07 mm Hg ml(-1) kg(-1) min(-1) (P<0.01), respectively. After placing the infants back-to-supine position, SV, CO, SBF and SVR index returned to baseline. The above pattern of cardiovascular changes was consistent in vast majority of the studied neonates.

CONCLUSIONS

Short-term prone positioning is associated with decreased SV, CO and SBF and increased calculated SVR index.

Does targeted neonatal echocardiography affect hemodynamics and cerebral oxygenation in extremely preterm infants?

OBJECTIVE

To investigate the effect of targeted neonatal echocardiography (TnEcho) on heart rate, arterial oxygen saturation (SPO2), cerebral regional oxygen saturation (CrSO2) and cerebral fractional oxygen extraction (CFOE) in extremely preterm infants during the first 3 postnatal days.

STUDY DESIGN

s a nested study in a prospective observational study, we acquired continuous data on heart rate, SPO2, CrSO2 and CFOE. Data averaged for the duration of TnEcho study were compared with the data collected during a baseline period immediately before the start of echocardiography. The duration of the baseline and study periods was the same. TnEcho evaluation included assessment of preload, afterload, contractility, left and right ventricular output, patent ductus arteriosus and foramen ovale.

RESULT

We analyzed 138 data pairs before and during TnEcho in 22 extremely preterm infants (gestational age 25.9 ± 1.2 weeks; range 23 to 27). There was no significant difference in heart rate between baseline and TnEcho period. There was a statistical, but clinically negligible, difference between baseline and TnEcho in SPO2 (median (quartile) 91.4% (88.9, 94.2) vs 91.3% (88.9, 94), P = 0.048), CrSO2 (76.8% (70.7, 81.5) vs 74.9% (69.5, 80.1), P<0.0001) and CFOE (15.8% (9.8, 23.6) vs 17.5% (11.3, 24.7), P<0.0001). The changes in the parameters monitored were similar in preterm infants who developed peri/intraventricular hemorrhage and in those who did not.

CONCLUSION

Although there were statistically significant changes in SPO2, CrSO2 and CFOE, the alterations were minimal and unlikely of clinical relevance. Thus, cerebral hemodynamics and systemic and cerebral oxygenation are not perturbed during TnEcho and the procedure is well tolerated by the extremely preterm infants during the postnatal transitional period.

Effects of low oxygen saturation limits on the ductus arteriosus in extremely low birth weight infants

OBJECTIVE

Postnatal increase in oxygen promotes constriction of the patent ductus arteriosus (PDA). According to the findings of prospective observational studies, the clinical practice of targeting lower fractional oxygen saturation between 70 and 90% has been associated with a reduced incidence of severe retinopathy of prematurity (ROP) without affecting survival or neurodevelopmental disability at 1 year of age. Our objective was to investigate the impact of the use of a lower oxygen saturation target range on the incidence of early hemodynamically significant PDA (hsPDA) and the need for ductal ligation in extremely low birth weight (ELBW, <1000 g) infants.

STUDY DESIGN

In this retrospective study, we analyzed data from 263 ELBW infants managed 4 years before (episode I: target oxygen saturation 89 to 94%) and after (episode II: target oxygen saturation 83 to 89%) implementation of the use of lower oxygen saturation limits in two neonatal intensive care units. Infants with a birth weight of 1000 to 1500 g were managed with the same oxygen saturation target range (89 to 94%) during both episodes, and they served as controls. Parametric and nonparametric tests were used as appropriate and multivariate logistic regression models were used to correct for confounders.

RESULTS

There was an increase in the incidence of hsPDA (63.2 vs 74.8%, P=0.043), without an increase in the need for surgical ligation (24.2 vs 29.9%, P=0.3) after implementation of the lower oxygen saturation target range policy. After adjusting for confounders, there was an increase in the odds of having an hsPDA (odds ratio (OR) 1.77, 95% confidence interval (CI) (1.03 to 3.06), P=0.04) but the odds for ductal ligation did not change in episode II (OR 1.25, 95% CI (0.70 to 2.25), P=0.4). The incidence of ROP > or = stage III (50.7 vs 15.7%; P<0.0001) and the need for laser ablation (33.8% vs 8.7%; P<0.0001) were significantly reduced. There was no change in the incidence of hsPDA or ductal ligation in the control group.

CONCLUSION

Targeting lower oxygen saturation limits to minimize periods of hyperoxemia in ELBW infants reduced the incidence of severe ROP and the need for laser ablation. The incidence of early hsPDA was increased; however, final closure rate and the incidence of surgical ligation of the ductus arteriosus were not affected.

Meningitis in a newborn infant with urosepsis, negative blood cultures and initially normal cerebrospinal fluid findings

This case presentation supports the observation that initial cerebrospinal fluid findings can be normal in newborn infants with sepsis syndrome who then develop evidence for meningeal involvement. Therefore, if initial lumbar puncture results are negative, a repeat lumbar puncture is recommended to look for meningitis in newborns that are critically ill with sepsis syndrome.

Echocardiography and the neonatologist

Pediatric echocardiography as performed and interpreted by pediatric cardiologists provides details of cardiac structure and function as well as hemodynamic data. Functional echocardiography, in contrast to echocardiography as performed by the cardiologist, is the bedside use of cardiac ultrasound to follow functional and hemodynamic changes longitudinally. Data reflecting cardiac function and systemic and pulmonary blood flow in critically ill preterm and term neonates can be monitored using this method. Functional echocardiography is being developed and driven by neonatologists as an extension of their clinical skills. A wealth of hemodynamic information can be derived from functional echocardiography used for the sick neonate, which provides clinical information different from the assumed underlying physiology. Lack of access to appropriate training programs and interdisciplinary politics is limiting the use of this potentially valuable clinical information. Without the use of functional echocardiography, clinicians are left to speculate as to the underlying pathophysiology of circulatory compromise, and the assumptions they make often are incorrect. For functional echocardiography to fulfill its clinical potential, it needs to be available at any time and at short notice in the neonatal intensive care unit (NICU). Because most NICUs do not have external diagnostic services to provide longitudinal hemodynamic follow-up assessment at the bedside, neonatologists should be able to develop appropriate echocardiographic skills in close collaboration with their cardiologist colleagues.

Limits of viability: definition of the gray zone

INTRODUCTION

As survival and long-term morbidity of very preterm infants have improved over the past decade, the limits of infant viability, the level of maturity below which survival and/or acceptable neurodevelopmental outcome are extremely unlikely, have also decreased.

STUDY DESIGN

In an effort to define the current limits of infant viability, the data in the literature on survival and long-term neurodevelopmental outcome in very preterm neonates have been reviewed.

RESULT

The gestational age and birth weight below which infants are too immature to survive, and thus provision of intensive care is unreasonable, appears to be at <23 weeks and <500 g, respectively. Infants born at > or =25 weeks' gestation and with a birth weight of > or =600 g are mature enough to warrant initiation of intensive care, as the majority of these patients survive, and at least 50% do so without severe long-term disabilities. Finally, for infants born between 23(0/7) and 24(6/7) weeks' gestation and with a birth weight of 500 to 599 g, survival and outcome are extremely uncertain. For these infants born in the so-called 'gray zone' of infant viability, the line between patient autonomy and medical futility is blurred, and medical decision-making becomes even more complex and needs to embrace careful consideration of several factors. These factors include appraisal of prenatal data and the information obtained during consultations with the parents before delivery; evaluation of the patient's gestational age, birth weight and clinical condition upon delivery; ongoing reassessment of the patient's response to resuscitation and intensive care and continued involvement of the parents in the decision-making process after delivery.

CONCLUSION

Based on these findings an algorithm is offered for consideration for neonatologists managing infants born in the 'gray zone' of infant viability. However, caution must be exercised when one considers incorporating this guideline into clinical practice because the algorithm is based on the analysis of the findings in the literature and the authors' experience rather than direct evidence.

Concurrent use of indomethacin and dexamethasone increases the risk of spontaneous intestinal perforation in very low birth weight neonates

BACKGROUND

Dexamethasone or indomethacin predisposes very low birth weight (VLBW) neonates to spontaneous intestinal perforation (SIP). However, no study has specifically investigated the role of the concurrent use of indomethacin and dexamethasone in SIP.

OBJECTIVE

To test whether the concurrent use of indomethacin and dexamethasone increases the risk of SIP.

METHODS

In this single center, retrospective, 2:1 matched, case-control study, the odds of SIP were assessed using univariate and multivariate logistic regression analysis in < or =14-day old VLBW infants.

RESULTS

Sixteen VLBW infants with SIP were matched to 32 controls by birth weight. After adjusting for clinically relevant variables, patients who received > or =3 doses of indomethacin for ductal closure or intraventricular hemorrhage prophylaxis and > or =3 doses of low-dose dexamethasone (0.3 mg/kg cumulative dose over 3 days) for refractory hypotension during the first postnatal week, were 9.6 times more likely to develop SIP [95% CI 1.22, 75.71].

CONCLUSIONS

The combined use of indomethacin and dexamethasone increases the risk of SIP in VLBW neonates.

Management of hypotension and low systemic blood flow in the very low birth weight neonate during the first postnatal week

Systemic hypotension during the first postnatal week is associated with increased mortality and morbidity in the very low birth weight (VLBW) neonate. Hypotension is generally defined as blood pressure below the fifth percentile of the gestational- and postnatal-age dependent blood pressure norms. Recent studies indicate that in most VLBW neonates, cerebral blood flow autoregulation is indeed lost when blood pressure reaches the fifth percentile. Treatment of the circulatory compromise should address the primary pathogenic factor(s) of the condition (hypovolemia, myocardial compromise, failure of vasoregulation or a combination of factors). Recent findings also suggest that vasopressor resistance can be treated with a brief course of low-dose hydrocortisone. However, due to the short- and potential long-term side effects of early hydrocortisone treatment, its use should be restricted to neonates with vasopressor-resistant hypotension. Finally, concomitant administration of hydrocortisone with indomethacin should be avoided due to the increased incidence of gastrointestinal perforations.

Use of high-frequency jet ventilation in neonates with hypoxemia refractory to high-frequency oscillatory ventilation

OBJECTIVE

To describe the response to high-frequency jet ventilation in infants with hypoxemic respiratory failure unresponsive to high-frequency oscillatory ventilation.

METHODS

This was a retrospective analysis of chart records on demographics, ventilator settings, blood gas analysis and calculated oxygenation index prior to and during the first 7 days of high-frequency jet ventilation in ten consecutive infants.

RESULTS

Before the initiation of high-frequency jet ventilation, the ventilatory mean airway pressure (MAP; cmH2O), fraction of inspired oxygen (FiO2) and oxygenation index on high-frequency oscillatory ventilation were 14.3 +/- 1.3, 0.97 +/- 0.02 and 29 +/- 5, respectively. Three hours after the initiation of high-frequency jet ventilation, the oxygenation index improved to 18 +/- 4 (p < 0.001) and the improvement was sustained during the study period. By 6 h of high-frequency jet ventilation, the FiO2 decreased to 0.62 +/- 0.09 (p < 0.01) and, by 1-3 h of ventilation, the MAP decreased to 10.9 +/- 1.3 (p < 0.01). The improvement in FiO2 persisted for 7 days while, although the MAP remained lower throughout the study, the improvement in MAP failed to reach statistical significance after 72 h. No significant changes in pH, pCO2, or pO2 before or during high-frequency jet ventilation were noted.

CONCLUSION

High-frequency jet ventilation improves hypoxemic respiratory failure unresponsive to high-frequency oscillatory ventilation in infants. These findings suggest that not all high-frequency ventilatory devices yield the same clinical results.

Cardiovascular effects of hydrocortisone in preterm infants with pressor-resistant hypotension

OBJECTIVE

To study the cardiovascular effects of hydrocortisone in preterm infants with hypotension unresponsive to volume and pressor administration.

STUDY DESIGN

Retrospective review of the cardiovascular response to 23 courses of hydrocortisone administration during the first day of treatment in 21 preterm infants (gestational age: 26.9 +/- 3.9 weeks; postnatal age: 11.3 +/- 13.1 days). Hydrocortisone (2 mg/kg/d in 16 patients and 3-6 mg/kg/d in 5 patients) was administered when dopamine (22.2 +/- 11 microg/kg/min, range: 8-60) alone (n = 16) or in combination with dobutamine (8.4 +/- 4.9 microg/kg/min, range: 5-20, n = 7) and/or epinephrine (0.38 +/- 0.56 microg/kg/min, range: 0.01-1.2, n = 4) failed to normalize blood pressure.

RESULTS

Mean blood pressure increased from 29.3 +/- 4.1 to 34.1 +/- 5.2, 38.0 +/- 8.0, and 41.8 +/- 6.6 mm Hg by 2, 4, and 6 hours of hydrocortisone administration, respectively, and remained stable thereafter. Urine output increased despite a decrease in fluid administration during the first day of hydrocortisone treatment. The dose of dopamine and the number of patients receiving dobutamine and/or epinephrine also decreased during the same period. Eighteen of the 21 patients survived.

CONCLUSIONS

Preterm infants with volume- and pressor-resistant hypotension respond to hydrocortisone with rapid normalization of the cardiovascular status and sustained decreases in volume and pressor requirement.

Controversies in the diagnosis and management of hypotension in the newborn infant

Although close to half of the newborns admitted to neonatal intensive care units receive treatment for "hypotension," the normal physiologic blood pressure range ensuring appropriate organ perfusion in the neonate is unknown. Thus, the decision to treat hypotension in the newborn is based on statistically defined gestational and postnatal age-dependent normative blood pressure values and physicians' beliefs rather than on data bearing physiologic reference. Dopamine is the most widely used sympathomimetic amine in the treatment of neonatal hypotension, and it is more effective than dobutamine in raising blood pressure. Volume administration is less effective in the immediate postnatal period, and its extensive use is associated with significant untoward effects, especially in preterm infants. During the course of their disease, some of the sickest hypotensive newborns become unresponsive to volume and pressor administration. This phenomenon is caused by the desensitization of the cardiovascular system to catecholamines by the critical illness and relative or absolute adrenal insufficiency. The findings that steroids rapidly up-regulate cardiovascular adrenergic receptor expression and serve as hormone substitution in cases of adrenal insufficiency explain their effectiveness in stabilizing the cardiovascular status and decreasing the requirement for pressor support in the critically ill newborn with volume-and pressor-resistant hypotension. Finally, despite recent advances in our understanding of the pathophysiology and management of neonatal hypotension, there are few data on the impact of the treatment on organ blood flow and tissue perfusion and on neonatal morbidity and mortality.

Circulatory support of the sick preterm infant

In the majority of preterm infants, especially during the immediate postnatal period, hypotension is primarily caused by abnormal peripheral vasoregulation and/or myocardial dysfunction and not by absolute hypovolemia. Therefore, aggressive volume resuscitation is not warranted and is potentially harmful. Volume support should be limited to 10-20 ml/kg of isotonic saline administration and, if sustained normalization of the blood pressure cannot be achieved, early initiation of cardiovascular pharmacological support is recommended. However, in preterm infants who present with an identifiable volume loss, the kind of fluid lost should first be replaced. Due to its beneficial cardiovascular and renal actions, dopamine is the drug of choice in the treatment of neonatal hypotension. Dobutamine may be added if myocardial dysfunction persists or develops during dopamine treatment. In some critically ill preterm infants, escalation of dopamine therapy or addition of epinephrine is necessary yet not always effective indicating the development of pressor resistant hypotension. Downregulation of cardiovascular adrenergic receptors and some degree of adrenal insufficiency may explain this phenomenon. In these patients, a brief course of steroid treatment may be successful in stabilizing the cardiovascular status and decreasing the requirement for pressor/inotrope support. However, well-designed randomized and controlled clinical trials are needed in the future to determine the effectiveness and potential short- and long-term side effects of steroid administration in preterm infants with pressor-resistant hypotension. In summary, management of the critically ill hypotensive preterm infant remains challenging and requires a better understanding of the pathophysiology of neonatal shock and improvements in our ability to evaluate cardiac output, organ blood flow, and tissue perfusion at the bedside.

Developmental regulation of the inhibitory effect of dopamine on prolactin release in the preterm neonate

The secretion and release of prolactin from the anterior pituitary is under the tonic inhibitory control of endogenous dopamine produced in the central nervous system. Exogenous dopamine inhibits prolactin secretion by reaching the pituitary via the portal circulation, and the hypolactotropic effect of dopamine infusion has been documented in all age groups in humans. However, the maturation of lactotroph sensitivity to dopaminergic inhibition has not been studied. Therefore, we followed the changes in serum prolactin concentrations before, during, and after dopamine infusion in 19 sick preterm infants with a mean gestational age of 30.6+/-0.6 weeks during the first 3 days of life, and examined the relationship of the hypolactotropic effect of dopamine to gestational age and birth weight in this patient population. As expected, dopamine therapy resulted in a decrease in mean serum prolactin from 89.4+/-9.5 to 58.6+/-9.1 microg/l (p < 0.05) with a return of the serum prolactin concentration to the pretreatment level 2-6 h after discontinuation of drug administration (98.3+/-11.7 microg/l, p < 0.05). However, simple regression analysis of the individual data revealed that the magnitude of the dopamine-induced decrease in serum prolactin was significantly influenced by gestational age (p = 0.006) and birthweight (p = 0.037). Thus, our findings provide evidence for the maturation of pituitary lactotroph sensitivity to dopaminergic inhibition in the preterm human neonate.

Developmental changes in erythrocyte Na(+),K(+)-ATPase subunit abundance and enzyme activity in neonates

AIM

To study the relation between erythrocyte Na(+),K(+)-ATPase subunit isoform composition, Na(+),K(+)-ATPase activity, and cation pump function in preterm and term neonates.

DESIGN

Erythrocyte Na(+),K(+)-ATPase subunit isoform abundance, Na(+),K(+)-ATPase activity, and cation pump function were studied in blood samples obtained from 56 preterm neonates of 28-32 weeks gestation (group 1), 58 preterm neonates of 33-36 weeks gestation (group 2), and 122 term neonates (group 3) during the first two postnatal days.

RESULTS

alpha(1) isoform abundance was higher and beta(2) isoform abundance was lower in group 1 than in group 3 (p = 0.0002). alpha(2) and beta(1) isoform abundance did not change with maturation and there was no evidence for the presence of the alpha(3) isoform. Gestational age was inversely related to Na(+), K(+)-ATPase activity (p = 0.0001) and directly related to intracellular Na(+) concentration (p = 0.0025).

CONCLUSIONS

Expression of the alpha(1) and beta(2) Na(+),K(+)-ATPase subunit isoforms is developmentally regulated. The increased abundance of alpha(1) isoforms of immature neonates translates to increased ATPase activity. The lower intracellular Na(+) concentration of immature neonates suggests that their erythrocyte Na(+),K(+)-ATPase cation pump function may also be increased.

Neonatal lupus erythematosus with microvascular hemolysis

A female, term newborn born to a mother with a history of idiopathic thrombocytopenic purpura and antinuclear antibodies, single-stranded A antibody, and IgM anticardiolipin antibodies presented with immune thrombocytopenia, disseminated intravascular coagulation (DIC), microangiopathic hemolytic anemia, and a characteristic lupus rash in the periorbital areas. She responded to combined treatment with dexamethasone and intravenous immunoglobulin (IVIG). At age 9 months, she was readmitted with severe thrombocytopenia, DIC, and microangiopathic hemolytic anemia. She again responded to IVIG. This suggests that microangiopathic hemolysis can be a presenting symptom in neonatal lupus erythematosus and that reoccurrence of the microangiopathic hemolysis may occur even after the disappearance of lupus antibodies.

Changes in oxygenation with inhaled nitric oxide in severe bronchopulmonary dysplasia

BACKGROUND

Severe bronchopulmonary dysplasia (BPD), which is associated with high mortality and morbidity, is thought to be the result of mechanical, inflammatory, and oxidant injury to the immature lung, and includes the development of pulmonary hypertension with vascular remodeling.

METHODS

A phase II pilot study was conducted to determine the effect of inhaled nitric oxide (iNO) on oxygenation in severe BPD. This was an open-labeled, noncontrolled trial to evaluate safety and determine appropriate dosing for a future randomized controlled trial. Infants were eligible for enrollment if they were >/=4 weeks of age and ventilator dependent with a mean airway pressure of >/=10 cm H2O and an FIO2 of >/=0.45. Study infants received iNO (20 ppm) for 72 hours, and FIO2 was adjusted to maintain oxygen saturations of >92%. Infants who had a >/=15% reduction in FIO2 after 72 hours received prolonged treatment with low-dose iNO, weaning by 20% every 3 days as tolerated.

FINDINGS

Sixteen preterm infants (23-29 weeks of gestation), age 1 to 7 months, were enrolled. Eleven of 16 infants had a significant increase in PaO2 after 1 hour of iNO (median change, 24 mm Hg; range, -15 to 59 mm Hg; P <.01), but there was no significant change in PaCO2. After 72 hours of iNO, 11 infants had >/=15% reduction in FIO2, and 7 of the 11 had >/=35% reduction (P <. 01). Among the 11 infants who responded to iNO after 72 hours, 10 had a sustained improvement in oxygenation throughout their course of treatment (duration, 8-90 days), and ventilator support could also be decreased. No adverse effects from iNO (increased methemoglobin, bleeding, or increased plasma 3-nitrotyrosine) were observed. Four of the 11 infants (36%) who responded to iNO ultimately weaned off mechanical ventilation and 4 died, whereas all the infants who failed to respond to iNO either died or continue to require mechanical ventilation.

INTERPRETATION

We conclude that the use of low-dose iNO may improve oxygenation in some infants with severe BPD, allowing decreased FIO2 and ventilator support without evidence of adverse effects. Randomized clinical trials of low-dose iNO for BPD are warranted.

Regional hemodynamic effects of dopamine in the sick preterm neonate

OBJECTIVE

To study the effects of dopamine on renal, mesenteric, and cerebral blood flow in sick preterm neonates.

STUDY DESIGN

The pulsatility index was used to assess the dopamine-induced changes in renal, mesenteric, and cerebral blood flow by means of color Doppler ultrasonography in 23 nonhypotensive preterm neonates (birth weight: 981 +/- 314 g; postnatal age: <2 days). Dopamine was given at a dose of 6.1 +/- 3.0 microgram/kg per minute to combat oliguria, impaired peripheral perfusion, or both. Blood flow velocity measurements were made before and during dopamine administration, with each patient serving as his or her own control subject.

RESULTS

Dopamine significantly increased blood pressure and urine output. Dopamine decreased the pulsatility index in the renal artery (2.98 +/- 1.18 vs 1.68 +/- 0.45; P <.05) while the pulsatility index in the superior mesenteric and medial cerebral artery was not affected. Thus renal blood flow increased while mesenteric and cerebral blood flow remained unchanged during dopamine treatment. The increase in renal blood flow was independent of the blood pressure changes.

CONCLUSIONS

These findings suggest a functionally mature renal, but not mesenteric, vasodilatory dopaminergic response in the preterm neonate. The observations also indicate the lack of an effect of low- to medium-dose dopamine on cerebral hemodynamics in the nonhypotensive preterm neonate.

The p15 matrix protein of moloney murine leukemia virus is a phosphotyrosine protein

Retroviruses have been etiologically implicated with leukemia in humans and animals. Understanding the virus life cycle, the proteins and enzymes involved in its replication, is essential for developing potent anti-viral drugs. Phosphorylation of retroviral proteins may alter their shape in such a way as to increase or inhibit their biological activities and thus influence the replication and pathogenic potential of the retroviruses. In our previous work, we demonstrated that non-cytotoxic doses of tyrphostins (protein tyrosine kinase blockers) inhibit moloney murine leukemia virus (Mo-MuLV) replication in acutely and chronically infected cells. In an attempt to understand their mode of action as anti-MoMuLV drugs, we examined the possibility that a viral protein is phosphorylated in tyrosine. Indeed, in our present work, we show that the p15 matrix protein (MA) of Mo-MuLV is a phosphotyrosine protein and is the only viral protein which is phosphorylated on tyrosine. Moreover, treatment of Mo-MuLV/NIH/3T3 chronically infected cells with tyrphostin AG-555 specifically inhibits the synthesis of p15 and other viral proteins but does not affect the synthesis of cellular proteins. Our results suggest that tyrosine phosphorylation of p15 MA protein may play a pivotal role in Mo-MuLV replication.

DNA binding properties of the zinc-bound and zinc-free HIV nucleocapsid protein: supercoiled DNA unwinding and DNA-protein cleavable complex formation

The HIV nucleocapsid (NC) protein contains, as those of other retroviruses, two Cys-His arrays which function as zinc finger binding domains. The nucleic acid binding properties of retroviral NC have been previously demonstrated. In this study, we characterized the DNA binding ability of the zinc-bound and zinc-free forms of HIV NC. We found that in addition to binding single-stranded DNA, both forms bind and unwind supercoiled plasmid DNA. The binding ability of the zinc-bound form was higher than the zinc-free form. In addition we showed the formation of NC protein-DNA cleavable complex which is the result of a presumably covalent bond formed between the protein and the phosphate moiety of the DNA backbone. The NC unwinding activity and the protein-DNA cleavable complex formation resembles the first step of the relaxing mechanism of DNA topoisomerase. Our results shed light on the possibility of a novel physiological function for the HIV NC protein in the viral life cycle.

Effects of low-dose dopamine infusion on cardiovascular and renal functions, cerebral blood flow, and plasma catecholamine levels in sick preterm neonates

Effects of 2 and 4 micrograms/kg/min dopamine infusion on cardiovascular and renal functions, cerebral blood flow (CBF) and plasma catecholamine levels were studied in sick preterm neonates during the first four days of life. Preterm infants were found to have an enhanced responsiveness to the pressor effects of dopamine during this period. Comparison of the renal effects of 2 and 4 micrograms/kg/min dopamine in 61 preterm infants indicate that 2 micrograms/kg/min dopamine induces maximum diuresis and natriuresis during the first day of life provided that systemic blood pressure is within the predicted normal range. Although administration of 4 micrograms/kg/min dopamine induces further increases in blood pressure and glomerular filtration rate, urine output and sodium excretion remain similar to that on 2 micrograms/kg/min of the drug. These findings demonstrate that the direct tubular effects of dopamine play an important role in the diuretic and natriuretic action of the drug in the one-day old preterm infant. In five preterm neonates, changes in CBF transiently paralleled the dopamine-induced alterations in systemic blood pressure indicating that autoregulation of CBF is impaired but not completely ineffective in the one-day old preterm infant. In eight term neonates, increases in blood pressure had no effect on CBF. Measurements of plasma dopamine and norepinephrine levels in 14 preterm neonates and five children suggest that decreased metabolism of dopamine may contribute to the enhanced pressor responsiveness to dopamine in sick preterm infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine1-receptor blockade inhibits ANP-induced phosphaturia and calciuria in rats

Atrial natriuretic peptide (ANP) is known to enhance the excretion of Pi and Ca, solutes reabsorbed primarily by the proximal tubule. Previous studies have shown that proximal tubule Na transport is inhibited by dopamine (DA), and that the natriuretic action of ANP is blunted by DA-receptor blockade. However, alterations in Na reabsorption cannot localize ANP or DA action to a specific nephron site. Therefore, the possibility that DA mediates the apparent proximal tubule effects of ANP was investigated with the use of Pi and Ca as proximal tubule markers. ANP was infused into normal rats in the presence and absence of specific DA-receptor antagonists, and Na, Pi, and Ca excretion rates were determined. ANP enhanced Na, Pi, and Ca excretion at doses that failed to alter glomerular filtration rate and mean arterial pressure (MAP). DA1-receptor blockade significantly blunted the influence of ANP on urinary Na, Pi, and Ca excretion, whereas DA2-receptor blockade was without effect. MAP and inulin and p-aminohippurate (PAH) clearances remained stable during DA-receptor blockade. Because endogenous ANP levels are elevated in rats with remnant kidneys, and because blockade of endogenous ANP reduces Pi and Ca as well as Na excretion in this model, the effect of DA1-receptor blockade on solute excretion was also examined in rats with 5/6 nephrectomy. DA1-receptor blockade significantly reduced absolute and fractional Na, Pi, and Ca excretion in rats with 5/6 nephrectomy, in the absence of measurable changes in MAP, inulin, or PAH clearance.(ABSTRACT TRUNCATED AT 250 WORDS)

Dopamine and natriuresis. Mechanism of action and developmental aspects

The present paper summarizes our studies on the mechanisms of the dopamine induced changes in renal macro- and microcirculation as well as in proximal and distal tubular sodium handling which contributes to the natriuresis induced by the drug. Some aspects of the physiological role of locally generated dopamine in regulating sodium excretion are also reviewed. Finally, by describing the cardiovascular, renal and hormonal effects of dopamine in the preterm human neonate, some of the developmental aspects of the renal effects of the drug are also discussed.

The significance of L-amino acid decarboxylase and DARPP-32 in the kidney

This study examines the role of endogenous dopamine (DA) for the regulation of renal tubular sodium (Na) transport. The enzyme L-amino acid decarboxylase (L-AADC) that converts L-dopa to DA has been localized to the proximal tubule cells with immunocytochemistry. Locally formed DA will inhibit the activity of Na-K-ATPase, the enzyme that yields energy to active Na transport. The effect is of physiological importance during high salt diet. The phosphoprotein DARPP-32, a DA1 receptor associated third messenger is abundant in the medullary thick ascending limb of Henle (mTAL). DARPP-32 is phosphorylated after activation of DA1 receptors. DARPP-32 is in its phosphorylated form a potent phosphatase inhibitor. Activation of the DA1 receptor in mTAL with the DA1 agonist SKF 82526 causes dose-dependent inhibition of Na-K-ATPase activity. The effect involves activation of cAMP protein kinase. It is likely that this effect is potentiated by DARPP-32.

Influence of Na+ intake on dopamine-induced inhibition of renal cortical Na(+)-K(+)-ATPase

The enzyme L-amino acid decarboxylase (L-AADC), found in abundance in rat proximal tubule cell cytosol, converts L-dopa to dopamine. Dopamine, in turn, suppresses proximal tubule sodium transport by inhibiting Na(+)-K(+)-ATPase activity. We sought to determine whether changes in dietary sodium intake in rats lead to adaptation of dopamine formation and dopamine-induced Na(+)-K(+)-ATPase inhibition. In rats on a high-salt (HS) diet, the maximal velocity (Vmax) of renal cortical L-AADC was 78 +/- 19% higher than that in rats on a low-salt (LS) diet. The Michaelis constant (Km) of the enzyme remained unchanged. In renal cortical tubule cell suspensions the L-dopa-induced inhibition of ouabain-sensitive oxygen consumption (QO2) was significantly greater in rats on HS diet than in rats on LS diet. Furthermore, L-dopa completely inhibited the nystatin-induced rise in QO2 in the HS but not in the LS group. Carbidopa, an inhibitor of L-AADC, abolished the L-dopa-induced inhibition of nystatin-stimulated QO2 in cells from HS rats and was without significant effect in cells from LS rats. L-Dopa-stimulated K+ efflux was greater in cells from HS rats at 28 +/- 1 nmol.min-1.mg protein-1, compared with 7 +/- 6 nmol.min-1.ng protein-1 in cells from LS rats. By contrast, ouabain-stimulated K+ efflux did not differ between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Glomerular adaptation in uninephrectomized young rats

To study the glomerular adaptation during compensatory renal growth starting in infancy, we assessed afferent effective ultrafiltration pressure (PUF), glomerular filtration area and hydraulic conductivity in rats uninephrectomized (Nx) or sham-operated (S) at 5 days of age. Rats were fed a normal protein diet and studied at 20 and 60 days of age. Single nephron glomerular filtration rate was significantly higher in Nx than in S rats both at 20 days of age (mean +/- SEM: 15.0 +/- 1.5 vs 7.4 +/- 0.7 nl/min) and 60 days of age (80.7 +/- 4.6 vs 43.5 +/- 3.2 nl/min). Afferent effective PUF, estimated by the stop-flow method, was significantly higher in Nx than in S rats both at 20 days (22.5 +/- 0.8 vs 18.3 +/- 0.4 mmHg) and 60 days (28.3 +/- 1.0 vs 23.2 +/- 1.1 mmHg). The filtering area per glomerulus, calculated as the area of the glomerular basement membrane facing both the endothelial and the epithelial cells, but not the mesangial cells, was not different in Nx and in S rats at 20 days (3.0 +/- 0.3 vs 2.8 +/- 0.1 10(4) microns 2), but it was significantly greater in Nx than in S rats at 60 days (23.3 +/- 3.7 vs 9.9 +/- 0.9 10(4) microns 2). The hydraulic conductivity determined in isolated glomeruli was similar in Nx and in S rats at 20 days of age (1.40 +/- 0.11 vs 1.69 +/- 0.23 microliters/min.mmHg.cm2) but was significantly decreased in 60-day-old Nx rats, compared with S rats of the same age (1.52 +/- 0.11 vs 2.35 +/- 0.17 microliters/min.mmHg.cm2).(ABSTRACT TRUNCATED AT 250 WORDS)

Locally formed dopamine inhibits Na+-K+-ATPase activity in rat renal cortical tubule cells

Dopamine, generated locally from L-dopa, inhibits Na+-K+-ATPase in permeabilized rat proximal tubules under maximum transport rate conditions for sodium. To determine whether locally formed dopamine inhibits Na+-K+-ATPase activity in intact cortical tubule cells we studied the effect of L-dopa on ouabain-sensitive oxygen consumption rate (QO2) and 86Rb uptake in renal cortical tubule cell suspensions. L-Dopa (10(-4) M) did not affect ouabain-insensitive QO2 or mitochondrial respiration. However, L-dopa inhibited ouabain-sensitive QO2 in a concentration-dependent manner, with half-maximal inhibition (K0.5) of 5 x 10(-7) M and a maximal inhibition of 14.1 +/- 1.5% at 10(-4) M (P less than 0.05). L-Dopa also blunted the nystatin-stimulated QO2 in a concentration-dependent manner, with a K0.5 of 5 x 10(-8) M and a maximal inhibition of 21.8 +/- 1.2% at 10(-5) M (P less than 0.05), indicating that L-dopa directly inhibits Na+-K+-ATPase activity and not sodium entry. Ouabain-sensitive 86Rb uptake was also inhibited by L-dopa (16.0 +/- 2.4%, P less than 0.05). Carbidopa (10(-4) M), an inhibitor of the conversion of L-dopa to dopamine, eliminated the effect of L-dopa on ouabain-sensitive QO2 and 86Rb uptake, indicating that dopamine rather than L-dopa was the active agent. The finding that the L-dopa concentration-response curve was shifted to the left by one order of magnitude in the presence of nystatin suggests that the inhibitory effect is enhanced when the intracellular sodium concentration is increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of low-dose dopamine infusion on urinary prostaglandin E2 excretion in sick, preterm infants

In pharmacological doses dopamine (DA) will interact with several endocrine systems and both inhibit (prolactin, thyrotropin) and enhance (renin, angiotensin) hormonal release. In this study we have examined whether DA given to preterm neonates will influence prostaglandin (PG) production. The question is of importance since vasodilator PGs play a role in postnatal adaptation. We determined the effect of low dose DA infusion on the 24 h urinary PGE2 excretion rate (an index of renal PGE2 synthesis) in preterm infants. Six preterm neonates, with a 24-h requirement of 2 micrograms/kg per min DA treatment for oedema, moderate oliguria, poor peripheral perfusion and/or mild systemic hypotension were studied on days 2 (Day 1), 3 (Day 2, the day of DA infusion), and 4 (Day 3, DA discontinued) of life. Six preterm infants (control group) that did not require DA infusion were also studied to monitor possible spontaneous changes in the renal PGE2 production on days 2, 3 and 4 of life. In the control group urine output (Uv) and PGE2 excretion rate remained unchanged during the study. In the study group DA administration resulted in nearly two-fold increases in both the Uv (194%) and PGE2 excretion (182%). Urinary PGE2 excretion was, however, closely related to urine flow in both the control infants (Day 1-3) and the study group infants (Day 1-2). Since increased diuresis stimulates renal PGE2 production, our data suggest that the increased PGE2 excretion on Day 2 in the study group was not due to a direct effect of DA on PGE2 synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Contribution of dopamine 2 receptors to dopamine-induced increase in glomerular filtration rate

The effects of the interaction of dopamine (DA) and the DA2 receptors on glomerular filtration rate (GFR) has been studied by means of micropuncture technique in adult greater than or equal to 60-day-old and young 24-day-old rats. Most of the studies were performed in rats with intact adrenergic nervous systems to allow for evaluation of the presynaptic DA2 receptors. In adult and young rats, DA and LY-171555 (LY), a selective DA2 receptor agonist, induced prompt and significant increases in the single nephron (SN) GFR. Further studies were performed only in adult rats. The LY-induced increase in SNGFR was completely abolished during DA2 receptor blockade with S-sulpiride (S-SP), while the DA-induced increase in SNGFR was attenuated but still significant during S-SP treatment. Both DA and LY significantly increased the glomerular ultra-filtration pressure (PUFAA). In rats with ganglionic blockade, the LY-induced increase of SNGFR was attenuated but still significant, whereas the DA-induced increase was less affected. The results imply that DA significantly increases GFR by interacting with the DA2 as well as with the DA1 receptors. Interaction between DA and the DA2 receptors increases PUFAA. The results do not rule out the existence of both pre- and postsynaptic renal DA2 receptors.

Role of dopamine2-receptors in mediating renal vascular response to low dose dopamine infusion in the rat

The effects of the interaction of dopamine (DA) and the DA2-receptors on regional blood flows and cardiac output have been studied in the rat. By means of the microsphere technique the blood flow (BF) and vascular resistance (VR) were determined in the kidney, duodenum, spleen, liver, and lung during infusion of DA in the absence and presence of selective DA2-receptor blockade with S-Sulpiride (S-SP), and during infusion of a selective DA2-receptor agonist (LY-171555, LY). In order to evaluate the role of the presynaptic DA2-receptor, the experiments were performed without alpha- and beta-adrenergic blockade. Dopamine was given in such low doses that stimulation of the adrenergic receptors should be negligible. Dopamine, LY and DA + S-SP did not significantly influence BF and VR in the spleen, liver and lung. Dopamine significantly increased BF and decreased VR in the kidney and the duodenum; LY significantly increased BF in the the kidney but not in the duodenum and decreased VR in both the kidney and the duodenum. In the presence of selective DA2-receptor blockade, DA did not significantly influence BF or VR in the kidney but in the duodenum BF increased and VR decreased to the same extent as in the absence of blockade. In conclusion; the kidney and the intestine are more abundantly supplied with vascular DA-receptors than other organs. In the kidney the interaction between DA and the DA2-receptors significantly contributes the the DA-induced vasodilation. The interaction between DA and the DA2-receptors is of less importance for the DA-induced vasodilation in the intestine.