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BACKGROUND. Bilirubin is toxic to the brain and enters the brain in unbound form. Serum unconjugated, unbound bilirubin may be a good predictor of bilirubin encephalopathy. Unbound bilirubin levels may depend on the bilirubin-binding capacity of albumin, which has not been described for neonates of OBJECTIVE. The purpose of this work was to determine the ontogeny of bilirubin-binding capacity and the effect of clinical status in very preterm neonates. METHODS. A total of 152 neonates (23–31 weeks’ gestational age; 440–1300 g) were enrolled prospectively. At 5 days of age, total serum bilirubin and unbound bilirubin were measured with the unbound bilirubin-A1 analyzer (Arrows Co, Osaka, Japan) and albumin with the Bromocresol-purple method. Scatchard plots were used to estimate bilirubin-binding affinity and capacity. Clinical status for each infant was rated as high, moderate, or low risk by using a modified Score for Neonatal Acute Physiology model. Low risk was considered clinically stable. RESULTS. Unbound bilirubin has a significant, direct correlation to total bilirubin and is greater in unstable than in stable neonates. For the entire cohort, bilirubin-binding capacity had a direct relationship to gestational age. The bilirubin-binding capacities of infants in the low- and high-risk groups also had a direct relationship to gestational age. Bilirubin-binding capacity was greater in the low-risk group (20.8 ± 4.6 mg/dL; 356 ± 79 μmol/L) than in the moderate- (17.8 ± 3.5 mg/dL; 304 ± 60 μmol/L) or high- (17.3 ± 3.4 mg/dL; 296 ± 58 μmol/L) risk groups. Bilirubin-binding affinity did not differ by clinical risk status or gestational age. CONCLUSIONS. In very preterm, very low birth weight infants, bilirubin-binding capacity is directly proportional to gestational age. Bilirubin-binding capacity is lower and unbound bilirubin higher in unstable than in stable neonates. These data may be useful in guiding the management of hyperbilirubinemia in very low birth weight infants.

OBJECTIVE: Retinopathy of prematurity (ROP) is a complication seen in many very low birth weight infants. Severe ROP has been called a “marker” for severe disability. The purpose of this study was to evaluate the occurrence and severity of ROP among infants ≤1250 g birth weight treated in the Special Care Nursery at Women & Infants’ Hospital over a period of 7 years from 1994 to 2000. STUDY DESIGN: This was a retrospective review of ROP data combined with neonatal follow-up data. Of the 1002 infants born with birth weights

Although it has been customary to treat neonatal jaundice at lower serum bilirubin levels in low-birth weight infants than in term infants, the threshold bilirubin levels and long-term benefits for early treatment of preterm infants have not been validated. This article summarizes and evaluates existing evidence and strategies for early treatment of bilirubin in micropremies and recommends a conservative but flexible approach to early monitoring and phototherapy for jaundice in extremely low-birth weight infants.

The uptake of tyrosine as precursor of dopamine in striatal nerve endings was studied in rat striatal synaptosomes to evaluate the role of different bilirubin concentrations on this mechanism of synaptic neurotransmission. Freshly prepared striatal synaptosomes obtained from adult male Sprague-Dawley rats (200–300 g) were homogenized in about 25 vol of 0.32 M sucrose and 5 nM Hepes at pH 7.4 and centrifugated at 12,000–16,000 rpm for 20 min. 14C tyrosine was evaporated under N2 and resuspended in tyrosine 100 μl/ml. Different concentrations of crystalline bilirubin ranging from 70 to 140 μM at 10-min intervals were prepared. Eighty microliters of synaptosomes were added to 5 μl of the different bilirubin concentrations and 20 μl of 14C tyrosine. The results of this study show a statistically significant correlation between bilirubin levels and tyrosine uptake in rat synaptosomes (p < 0.05) supporting the hypothesis that the effect of bilirubin on neuronal excitability is dose-dependent.

Jaundice is a common clinical finding in the neonate. During the first week after birth, visible jaundice may appear in as many as one third of them.1 For most, clinical jaundice and transient elevation of serum bilirubin concentration are part of the physiologic maturation of bilirubin metabolism and excretion. In some neonates, however, severe or persistent hyperbilirubinemia results from underlying disorders of bilirubin production, conjugation, or excretion.

Recent clinical and research findings on kernicterus and bilirubin toxicity are reviewed. Bilirubin binds to cell membranes and appears to interfere with the metabolism, depolarization, and transmitter functions of neurons. The neurobehavioral and clinical findings associated with bilirubin encephalopathy and low bilirubin kernicterus are presented and evaluated. Cardiorespiratory stabilization, avoidance of displacing drugs, and preventive use of phototherapy appear to have decreased the incidence of low bilirubin kernicterus in high-risk newborns.

1. This complex of symptoms appears to be congenital, familial, and hereditary. It is apparently transmitted by a dominant gene, probably on chromosome 5. 2. Hypertonicity with rigidity of all voluntary muscles usually presents at birth. 3. Feeding problems are due to dysphagia or laryngospasm associated with aspiration and dyspnea. 4. Respiratory problems are characterized by apneic episodes due to muscle spasm. 5. Prolonged episodes of muscular rigidity secondary to sudden stimuli result in frequent falls, characteristically en bloc, like a statue. 6. Continuous electromyographic activity even at rest (with absence of fasciculations) improves after intravenous diazepam.

The review and recommendations by Newman and Maisels1 in this issue of Pediatrics constitute a provocative critique of our current state of knowledge concerning the risks of hyperbilirubinemia in term infants and should begin a dialogue about the recommended standard of care for jaundiced newborns. For several decades, the use of exchange transfusions to prevent kernicterus and phototherapy to prevent exchange transfusions, the puzzling emergence of low-bilirubin kernicterus, the "discovery" of breast milk jaundice, and concern over the possible contribution of bilirubin to neurologic handicap have combined to encourage preemptive intervention for moderate jaundice in asymptomatic newborns. But has this strategy of anticipatory management become hardened into an overly aggressive pattern of testing and treatment? Newman and Maisels conclude that it has.

To survey the attitudes and recommendations of staff members before and after the implementation of sibling visitation in a neonatal intensive care unit.Staff survey conducted before (1992) and after (1993) the implementation of sibling visitation.A perinatal tertiary care center.Staff members including physicians, nurses, respiratory therapists, social workers, and unit clerks (n = 139 in 1992; n = 120 in 1993).A 7-point Likert scale survey (1 = strongly disagree: 7 = strongly agree) was designed for the study. In both 1992 and 1993, the staff most strongly agreed that visitation requires special supervision, should have designated times, increases sibling knowledge, enhances sibling attachment to the baby, and increases family satisfaction. Wilcoxon rank sum tests comparing the staff across the 2 years indicated substantial attitudinal changes in favor of sibling visitation, including less perceived interference with nursing care and nursery routines (P.01) and less concern about the infants' risk of respiratory infection and exposure to chickenpox (P.05). There was greater attitudinal agreement between disciplines in 1993 than in 1992, suggesting better staff consensus about sibling visitation following its implementation. The recommended minimum age for visitation was 4.67 years and 4.05 years in 1992 and 1993, respectively. Brief visits of 10 to 15 minutes' duration were consistently recommended. Staff rated the sibling visitation program as successful (median = 6) on a scale ranging from 1 (very poor) to 7 (very successful).Staff members have concerns about sibling visitation that include increased risk of infection, organization, and supervision. A sibling visitation program that addresses these concerns can be successfully implemented and supported by staff, thereby fostering family-centered care in the neonatal intensive care unit.

The postnatal maturation of the blood-brain barrier (BBB) for unbound bilirubin was studied in 2-day- and 2-week-old piglets. Hyperbilirubinemia was induced by bolus infusion of bilirubin at 25 mg/kg followed by continuous infusion of 20 mg/kg/h for 3 h. During the study period, arterial blood pH and blood gas tensions, serum osmolarity, and mean arterial blood pressures were within the physiologic range. Brain bilirubin content and the brain/blood distribution ratio for bilirubin were higher in the 2-day-old than in the 2-week-old piglets. In both age groups, regional brain bilirubin concentration and brain/blood ratios were higher in subcortical regions (cerebellum and brainstem) than in the cerebral cortex. We conclude that in newborn piglets the blood-brain barrier for unbound bilirubin matures with increasing postnatal age and that irrespective of maturity the relative permeability of the BBB for bilirubin appears higher in subcortical than in cortical regions.

The mechanism for the preferential distribution of bilirubin to basal ganglia (‘kernicterus’) is unknown. We hypothesized that differences in bilirubin clearance rates between brain regions might explain this phenomenon. Bilirubin [30mg/kg over 5 min, with 370-740 kBq (10-20 μCi) tritiated bilirubin] was infused into a peripheral vein in unanesthetized, young Sprague-Dawley rats (n = 36, weight 149 ± 15 g, mean ± SD). After blood sampling, groups of rats were killed at 15, 30, 45, 60, 75, 180, and 360 min with an intravenous injection of pentobarbital. Brain vasculature was flushed in situ and brains dissected into seven regions, which were weighed, dissolved and scintillation counted. Blood was analyzed for bilirubin, albumin, and blood gases. Brain bilirubin concentrations were calculated after determining the specific activity of bilirubin in serum at the time of sacrifice. Bilirubin half-lives in serum and brain regions were (in minutes, mean ± SD): serum 24.6 ± 17.2, whole brain 18.5 ± 21.5, cortex 17.6 ± 19.3, hippocampus 19.0 ± 21.5, striatum 17.1 ± 18.5, midbrain 16.3 ± 18.6, hypothalamus 17.4 ± 21.0, cerebellum 21.6 ± 33.8, medulla 20.0 ± 24.1. There were no significant differences in bilirubin half-lives between regions. The half-life of bilirubin in brain reported here is appreciably shorter than the 1.7 h previously found in rats with opened blood-brain barriers, but appears compatible with data on auditory brainstem response reversibility following exchange transfusion in jaundiced infants. We conclude that bilirubin disappeares rapidly from brains with intact blood-brain barriers. The rates of clearance found in different brain regions in this model cannot explain the kernicterus phenomenon (i.e. preferential staining of basal ganglia and cerebellum).

To investigate the possible role of sepsis with endotoxemia in kernicterus, we studied the effect of endotoxin on accumulation of bilirubin and albumin in rat brain. Male Sprague-Dawley rats were given Escherichia coli endotoxin i.v. After 150 min 10 µCi 125I-bovine serum albumin was given intravenously, followed by a 1-hour bilirubin infusion. Brain bilirubin was significantly higher in the endotoxin group than in the controls (1.34 ± 0.47 vs. 0.83 ± 0.31 µg/g, p < 0.05). However, the difference between the ratios of brain bilirubin to total serum bilirubin at the time of sacrifice were not significant. Total and unbound bilirubin values were significantly higher in the endotoxin-treated group at 165 min. Endotoxemia increased the net accumulation of bilirubin in rat brain, but this increase was probably secondary to an increase in total and unbound bilirubin, rather than an increase in the transfer per se of bilirubin across the blood-brain barrier.

We studied the relationship between changes in auditory brainstem responses (ABR) and serum and cerebrospinal fluid levels of neuron-specific enolase (NSE) in hyperbilirubinemic 2- to 8-d-old piglets. Infusion of a stabilized solution of bilirubin resulted in serum bilirubin levels of 571.1 +/- 48.8 mumol/L (mean +/- SEM) after 6 h. ABR were obtained at baseline and then hourly until the piglets were killed. We measured peak amplitudes and latencies for waves I-V, as well as latency for the post-V trough. Changes in amplitudes and latencies were analyzed as slopes because of heterogeneous variances. Over time, a significant reduction was observed in peak II-V amplitudes of bilirubin-infused piglets, but not in those of corresponding controls. No change was observed in latencies. NSE was analyzed by RIA. Serum NSE remained stable throughout the experiment (means 5.1-6.6 micrograms/L) and did not differ between the groups. Cerebrospinal fluid NSE values also remained stable, and no differences that could be ascribed to hyperbilirubinemia were detected. We conclude that hyperbilirubinemia induced significant changes in piglet ABR amplitudes without concomitant evidence of severe neuronal compromise, as might have been indicated by significant increases in serum and/or cerebrospinal fluid NSE levels. This provides further support to the clinical impression that early ABR changes during hyperbilirubinemia may be reversible.

The purpose of this study was to test the hypotheses that newborn infants with moderate serum bilirubin concentrations have depressed Brazelton scores and increased brain-stem conduction time and that serum bilirubin levels correlate with Brazelton behavior scores and brain-stem auditory evoked response changes. Fifty term infants who were enrolled into either a low serum bilirubin group (less than 8 mg/dl) or a moderate serum bilirubin group (10 to 20 mg/dl) were tested with the Brazelton Neonatal Behavioral Assessment Scale and a brain-stem auditory evoked response test. Partial correlation analysis controlling for phototherapy revealed that increased bilirubin concentration correlated negatively with the Brazelton orientation and with state range clusters and individual Brazelton test items that involve auditory processing. Increased bilirubin concentration correlated with an increased latency of brain-stem auditory evoked response wave 4, 5. An increased interpeak 1-5 (brain-stem conduction time) correlated with the decreased animate visual and auditory item. We conclude that moderate hyperbilirubinemia in term infants affects both infant behavior, as measured by specific components of the Brazelton test, and brain-stem conduction time, as measured by the brain-stem auditory evoked response test.

Twenty-six serial measurements of free bilirubin concentration and apparent association constant of bilirubin for albumin (Ka) at a bilirubin: albumin molar ratio of 0.8 were performed and compared with baseline values in 11 newborn infants with acidosis before treatment and during recovery from acidosis. When arterial pH was corrected from 7.12 +/- 0.02 (Mean +/- S.EM.) to 7.34 +/- 0.02, there was a significant decrease in serum free bilirubin concentration and a significant increase in the Ka at molar ratio 0.8. The data offer in vivo evidence that correction of acidosis in the neonate results in an improvement of the apparent bilirubin binding affinity of albumin.

Since kernicteric lesions are usually found in the subcortical regions of the brain and these areas also receive the highest blood flow during asphyxia and hypercapnia, we hypothesized that increases in brain bilirubin deposition may be related to increases in brain blood flow. Fourteen piglets underwent a 3-h infusion of bilirubin to maintain total serum bilirubin at approximately 8 mg/dl, during which time blood gases, hemodynamic variables, and brain blood flow were determined. After sacrificing the animals, regional brain bilirubin content was determined. Ten piglets underwent the same protocol; in addition, hypercapnia was induced during the last hour of study (PaCO2 approximately 70 mm Hg). The regional brain blood flow and bilirubin deposition were significantly increased over control values (p less than 0.05) following hypercapnia in the subcortical region and significantly so in the midbrain and cerebellum. In separate groups of control (n = 6) and hypercapnia (n = 6) piglets, 125I-labeled albumin was infused and demonstrated that hypercapnia was not associated with increased regional brain albumin content. We conclude that hypercapnia-induced augmentation in regional brain blood flow is associated with increased deposition brain blood flow is associated with increased deposition of unbound bilirubin. Although the causal relationship between these two observations has not been firmly established, the findings deserve future investigation to clarify the role of brain blood flow, brain bilirubin deposition, and the production of kernicterus in high risk infants.

The concentrations of total blood bilirubin, albumin-bound bilirubin, and the reserve and total bilirubin binding capacities of 35 neonatal blood samples (28 patients) were determined by automated front-face fluorometry ((hematofluorometer). These values were compared to results of diazo determinations, Sephadex gel filtration, and peroxidase-oxidation methods. Total blood bilirubin level by fluorometry agreed well with the total plasma bilirubin level by diazotization (r = .96, sigma = 1.7 mg/100 ml). Albumin-bound bilirubin concentrations by fluorometry also correlated well with diazo values (r = .95, sigma = 1.9 mg/100 ml) and were slightly lower than the total blood bilirubin concentrations. Values for total bilirubin binding capacity determined by fluorometry agreed well with results obtained for the same specimens by Sephadex gel filtration (n = 28, r = .97, sigma = 1.8 mg/100 ml) and by peroxidase-catalyzed oxidation (n = 25, r = .97, sigma = 1.7 mg/100 ml). The agreement among the results obtained by the three methods indicates a well-defined in vitro end point at which available primary or "tight" binding sites on albumin are saturated with bilirubin. In this clinical experience the coefficient of variation of results with the hematofluorometer was 8.4% for total blood bilirubin and 6.5% for total binding capacity. A comparison of "sick" with "well" infants revealed that the fraction of bilirubin not bound to albumin was significantly different for these two groups. The assays made with the hematofluorometer are quick (10 to 15 minutes) and require only a small quantity (approximately 150 microliters) of blood.

Sulfisoxazole and furosemide, 0.1-1.0 mM, both decreased reserve albumin concentration for bilirubin binding in pooled cord serum as estimated by rate of dialysis of 14C-monoacetyl-diamino-diphenylsulfone (MADDS) in undiluted serum at 37 degrees C. Peroxidase oxidation at a bilirubin:albumin ratio of 0.5 also showed that both drugs were capable of displacing bilirubin in vitro when added in molar excess of the albumin present. However, when aliquots of the same treated sera which had been used undiluted in the MADDS assay were diluted 40-fold and titrated with bilirubin and peroxidase, no drug-related increase in free bilirubin or decrease in reserve albumin could be shown. In vivo administration of 1 mg/kg furosemide showed no change in total bilirubin or reserve albumin by the MADDS technique in 8 infants. Estimation of the peak plasma level theoretically achievable with 1 mg/kg of furosemide suggests that peak plasma levels achieved with that dose are probably not high enough to produce significant reduction of reserve albumin, in agreement with the in vivo findings. In testing neonatal serum for bilirubin displacement by drugs, the choice of method, drug concentration, and dilution of the sample may influence the interpretation of results.

The effect of hyperosomolality on the blood-brain barrier for bilirubin was studied in rats. Hyperbilirubinemia was induced in the chronically catheterized rat by infusion of bilirubin at a rate of 30 mg/kg/h for three hours. After two hours of bilirubin infusion, three levels of hyperosmolality were induced by bolus of urea at three different doses: 50, 75, and 100 mmol/kg, respectively. The serum osmolality rose from 297 mosm/L in the control group to 345, 383, and 400 mosml/L in the three respective groups. No significant differences were found between the groups in levels of total or free serum bilirubin, serum albumin, blood pH, and blood gases. A significant dose relationship was found in both brain bilirubin and brain albumin content with reference to the serum hyperosmolality. The results indicate that hyperosmolality causes opening of the blood-brain barrier for bilirubin in the rat. It may be speculated that this adverse phenomenon (hyperosmolality) may play a role in the pathogenesis of kernicterus in infants whose serum bilirubin levels are below the range of saturated bilirubin binding capacity.

Reserve albumin concentration (the concentration of albumin available for binding of unconjugated bilirubin) was determined in 95 sera from 76 subjects by dialysis with 14C-monoacetyl diamino diphenyl sulfone (MADDS). An index, I of bilirubin toxicity in the plasma was calculated for each subject, based on the bilirubin and reserve albumin concentrations, the affinity of bilirubin for serum albumin, and the pH-dependent solubility of bilirubin in the plasma. The values of reserve albumin and of I varied significantly with gestational age, clinical condition (whether sick or well), and serum bilirubin level. The value of reserve albumin was decreased and I was increased in association with clinical factors (e. g., hyperbilirubinemia, hypoxia, acidosis, or sepsis) recognized as increasing the risk for bilirubin encephalopathy. The lowest values of reserve albumin and the highest values of I were found in the least mature and sickest infants.

Our observations show that maintenance of pressure in the naso-oro-pharynx when delivered by the nasal prong is dependent on a seal between the palate and the tongue of the baby. If a good seal exists, end expiratory pressure is maintained in the pharynx and, presumably, in the lower airway. Logically, when no seal exists, the further the tongue is from the palate the lower the resistance to airflow and hence the larger the pressure drop. Small movements of the tongue would have significant effect on such airflow, hence the wide scatter in the "mouth open" group. We found no reliable way of predicting which babies would maintain such a seal, either from the history or experimentally. We attempted to assess the "muscle tone" of the oral musculature in babies by measuring the "suck pressure" generated within a nipple, but showed no correlation with maintenance of pharyngeal pressure in six babies studied. During the course of a single study, we observed large variation in the efficiency of the seal over a short period of time in many of the babies. However, babies in whom it was difficult or impossible to record the oropharyngeal pressure due to an active gag reflex more frequently maintained a low AP. Possibly this reflex was involved in the maintenance of the seal in these babies. We have found the monitoring of nasopharyngeal pressure during nasal CPAP a clinically useful method of discovering the probable level of CPAP transmitted to the lower airway. Forcible closure has been used by some to increase the efficiency of nasal CPAP. ~ Our studies indicate that benefit is sporadic and that there is an equal chance of it being detrimental to maintenance of pressure. The lips provided little in the way of seal (a "blow-off" effect was frequently seen). It is reasonable to suppose that any variation in pressure drop was due to variation in the position of the tongue relative to the palate. Moreover, crying always reduced the pharyngeal pressure to atmospheric.

A method is reported for determination of albumin binding capacity for various ligands in 50-μl sample volumes. A small amount of a radioactively labeled test ligand is added to the undiluted sample and the rate of dialysis of the free ligand into an identical sample without added ligand is measured. The reserve albumin-equivalent concentration is defined as the concentration of a standard albumin preparation which in buffered solution gives the same rate of dialysis and hence the same ratio of free/bound concentrations of the added ligand. It is shown that the reserve albumin-equivalent concentration, thus defined, is identical with the sum of concentrations of carrier species, each multiplied by the first stoichiometric binding constant of the test ligand to the carrier and divided by its first stoichiometric binding constant to the standard albumin. Determinations of this parameter are suitable for studies of the chemical potential and transfer affinities of individual ligands and for determination of interaction among several binding substances. Two test ligands have been used, monoacetyldiaminodiphenyl sulfone and diazepam. The former is bound competitively with bilirubin while diazepam engages another, independent binding function. The method can thus be used for separate determinations of the degree of saturation of two distinct binding functions of albumin. Complex mixtures of several carrier proteins with interacting ligands can be studied.

Nutritional support with intravenously administered fat, protein hydrolysate, and glucose was given to 23 premature infants weighing less than 1,500 gm at birth. Growth in the 19 survivors approximated intrauterine growth rates in all dimensions. Complications included sodium imbalance and transient intolerance of the smallest and sickest infants to all components: carbohydrate, protein, fat, and even water. Autopsies in four patients who died did not reveal any untoward findings clearly related to the use of intravenously given lipids. Intravenously given fat has a potentially useful role in the nutritional support of small premature infants.

Lack of Effects of Continuous Positive Airway Pressure on Vagal Control of Breathing in Term and Preterm Newborn Lambs

Two studies were conducted to determine the relationship between variability in acoustic features of the infant cry and medical risk factors. In study 1, 3 groups of preterm infants (healthy, sick and CNS pathology) were compared with term infants at 40 weeks gestational age. The cry was analyzed by computer. The coefficient of variability of cry amplitude and the formant features of the cry differed among the groups of preterm infants. In study 2, 3 groups of term infants at low, moderate and high levels of hyperbilirubinemia were compared on the cry measures. More variability in the formant features of the cry was found in infants with higher levels of bilirubin. The correlation between the coefficient of variation in the cry formants and level of bilirubin was statistically significant. These two studies suggest that variability in the acoustic features of the cry relate to the medical status of the infant and may provide a measure of neurophysiological integrity.

Unbound bilirubin, bilirubin binding capacity, and bilirubin binding affinity were determined by the horseradish peroxidase method at the time of maximum hyperbilirubinemia and/or before exchange transfusions in 13 preterm infants who later died and had autopsies performed. Five of the 13 infants had kernicterus at autopsy. There were no significant differences in weight, gestational age, highest indirect bilirubin level, albumin concentration, severity of acidosis, use of assisted ventilation, sepsis, or other major clinical complications between the five infants with kernicterus and the eight infants without kernicterus. Compared with the eight nonkernicteric infants, the five kernicteric infants had significantly higher unbound bilirubin concentrations (13 ± 10 vs 27 ± 9 nmoles/liter, respectively, P < .05) and significantly lower bilirubin binding capacity and affinity. The data suggest an association between low bilirubin binding capacity and affinity, increased unbound bilirubin, and kernicterus in preterm infants with severe clinical complications.

When pre-established "safe" limits of serum bilirubin are exceeded, or when hyperbilirubinemia is present in association with other conditions such as prematurity with respiratory distress, asphyxia, or neonatal infections, the need to lessen the risk of bilirubin encephalopathy requires specific and effective interventions to lower the unconjugated or indirect-reacting bilirubin level in infants at risk. To this end the authors examine the criteria for intervention, the means of decreasing serum bilirubin levels, phototherapy, exchange transfusion, and the problem of jaundice in breast-fed infants.

Acute hyperosmolality-induced blood brain barrier breakdown has been demonstrated to increase the permeability of sucrose, which is similar in molecular weight to bilirubin, independently of changes in regional brain blood flow. We studied three groups of piglets given continuous bilirubin infusions to maintain serum bilirubin concentrations at approximately 8 mg/dl. Normal serum osmolality was maintained throughout the study in control animals. Two experimental groups were made hyperosmolar (330 and 375 mosmol/liter) with bolus urea infusions during the last hour of the study. Regional brain bilirubin concentrations were elevated in the 375 mosmol/liter hyperosmolal experimental group, but not in the 330 mosmol/liter group. Regional brain albumin concentrations also were increased over the control group in the 375 mosmol/liter animals. There were no differences in regional brain blood flows to account for the increases in brain bilirubin concentrations. Our results show that brain bilirubin deposition occurs following breakdown of the blood brain barrier by acute, severe hyperosmolality (375 mosmol/liter) and that the deposited bilirubin is derived from both bound and unbound fractions. The bilirubin deposition occurs independently of changes in regional brain blood; flow; however, regional differences in the blood brain barrier permeability to albumin also occur.

Effects of bilirubin on transepithelial transport of sodium, water, and urea. Urinary concentrating defects and renal salt wasting have been described in the hyperbilirubinemic Gunn strain of rat. Homozygous animals demonstrate significant reductions in renal medullary urea and sodium ion concentrations. These observations are consistent with possible bilirubin associated disorders in the transepithelial transport of water and solute. To test this hypothesis, measurements of active sodium transport and passive water and urea fluxes were made in hemibladders isolated from the Dominican toad, Bufo marinas. Tissues were exposed to amphibian bicarbonate Ringer's solution containing 0.1 mM bilirubin with 0.05% bovine serum albumin (BSA) or BSA alone Vasopressin-stimulated sodium transport, as reflected by short circuit current (SCC), was inhibited by 18 ± 6% in the presence of bilirubin (N = 10; P < 0.02). Cyclic AMP (p-Cl-phenylthio cAMP 10 -5 M) stimulated SCC was inhibited to a similar degree in the presence of bilirubin. The inhibition was noted only when bilirubin was in the serosal bath, and it could be abolished with BSA 0.5%. Bilirubin had no effect on the increase in SCC induced by higher concentrations of cyclic AMP (10-4 M), aldosterone, or amphotericin B. Furthermore, bilirubin had no effect on the hydro-osmotic response to vasopressin and vasopressin-induced changes in urea permeability. These findings show that short-term exposure to bilirubin exerts a tissue-specific effect on the vasopressin-stimulated active transport of sodium but has no effect on the vasopressin-induced fluxes of water and urea.Effets de la bilirubine sur le transport transépithélial de sodium, d'eau, et d'urée. Des défauts de concentration urinaire et une fuite rénale de sodium ont été observés dans la souche de rats hyperbilirubinémiques Gunn. Les animaux homozygotes présentent une réduction significative des concentrations en urée et en ion sodium dans la médullaire rénale. Ces observations sont compatibles avec des désordres peut-être liés à la bilirubine du transport transépithélial d'eau et de solutés. Afin de tester cette hypothèse, des mesures du transport actif du sodium et des flux passifs d'eau et d'urée ont été effectuées dans des hémi-vessies isolées à partir du Crapaud Dominicain Bufo marinus. Les tissus étaient exposés à une solution de Ringer bicarbonate pour amphibiens contenant 0,1 mM de bilirubine avec 0,05% de sérum albumine de boeuf (BSA) ou de la BSA seule. Le transport de sodium stimulé par la vasopressine reflété par le courant de court circuit (SCC) était inhibé de 18 ± 6% en présence de bilirubine (N = 10; P < 0,02). Le SCC stimulé par l'AMP cyclique (p-Cl-phénylthio cAMP 10 -5 M) était inhibé de façon semblable en présence de bilirubine. L'inhibition était notée uniquement quand la bilirubine était dans le bain séreux, et ne pouvait être abolie avec 0,5% de BSA. La bilirubine n'avait pas d'effet sur l'augmentation de SCC induite par des concentrations plus élevées de cAMP (10-4 M), par l'aldostérone ou par l'amphotéricine B. De plus, la bilirubine était sans effet sur la réponse hydro-osmotique à la vasopressine, ni sur les modifications de la perméabilité à l'urée induite par la vasopressine. Ces résultats montrent qu'une courte exposition à la bilirubine exerce un effet spécifique de tissu sur le transport actif du sodium stimulé par la vasopressine, mais est sans action sur les flux induits par la vasopressine d'eau et d'urée.

Phototherapy has been shown to cause hemolysis of fetal red cells and a shift to the right in the neonatal oxygen dissociation curve (ΔP50) in vitro. To determine if these parameters act similarly in vivo, we have studied 16 icteric infants before and after phototherapy and compared them with eight control infants studied at birth and at 3 days of age, measuring the change in P50, 2,3-diphosphoglycerate (2,3-DPG), serum bilirubin, the percent of bilirubin/albumin saturation, and the hemoglobin concentration in the two groups. Following phototherapy, in the icteric infants there was a shift to the right in the O2 dissociation curve of + 1.7 mm Hg, a rise in 2,3-DPG of 2.26 µmol/gm Hb, a fall in serum bilirubin of 4.3 mg/100 ml, a decrease in percent bilirubin/albumin saturation of 12.4%, and a drop in hemoglobin of 1.1 gm/100 ml. The control group showed a ΔP50 of + 2.0 mm Hg, a rise in 2,3-DPG of 3.67 µmol/gm Hb, an increase in serum bilirubin of 3.2 mg/100 ml, an increase in percent bilirubin/albumin saturation of 9.3%, and a fall in hemoglobin of 0.3 gm/100 ml. Significant differences between the groups were seen only in the changes in bilirubin concentration and percent bilirubin/albunmin saturation. The magnitude of changes in P50, 2,3-DPG, and hemoglobin concentration was similar in the phototherapy and control groups and was related to the expected changes with reference to postnatal age. These results suggest that phototherapy in vivo neither affects fetal erythrocytic affinity for oxygen nor causes hemolysis.