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.