- Email: [email protected]
Inositol supplementation in respiratory distress syndrome: Relationship between serum concentration, renal excretion, and lung effluent phospholipids
Inositol supplementation in respiratory distress syndrome' Relationship between serum concentration, renal excretion, and lung effluent phospholipids Inositol or p l a c e b o was given to 48 small preterm infants with respiratory distress syndrome (mean birth w e i g h t 1365 g, gestational a g e 30,1 weeks) between 48 hours and 10 days of age. The dose of inositol, 40 m g / k g every 6 hours, was at least as high as amounts received in full preterm human milk feedings. Serum inositol concentration increased between days 2 and 3 from a mean of 566 ~mol/L to 823 ~mol/L in the infants given supplement and fell from 451 ~mol/L to 292 ~mol/L in the controls~ On d a y 16, serum inositol values remained higher in the infants given supplement than in those given p l a c e b o (mean 334 #moi/L vs 146 ~mol/L, P = 0.014). The infants who d e v e l o p e d bronchopulmonary dysplasia had significantly higher renal inositol clearance, lower inositol intake, and Iowerserum inositol concentrations. Inositol supplementation increased the saturated phosphatidylcholine/sphingomyelin ratio in tracheal aspirates. According to these results, supplementation with inositol in preterm infants leads to a rise in serum inosifol concentration and improvement in the surfactant phospholipids. Inositol deserves further study as a dietary supplement for immature preterm infants who do not receive full human milk feeds. (J PEDIAIR 1987;110:604-10)
Mikko Hallman, M.D., Pirkko Arjomaa, M.A., and Kalle Hoppu, M.D. From the Children's Hospital, University of Helsinki, Finland
myo-Inositol
(henceforth called inositol) is at least as abtmdant in the human body as glucose. In healthy adults, the serum concentration of inositol remains within a narrow, low range, 1-3 one to three orders of magnitude lower than in the liver, lung, kidney, or brain. 4 In newborn infants and fetuses, however, serum concentrations of inositol are 2 to 100 times higher than in adults. 5-9 In the fetus, it has been proposed that there is active synthesis,
Supported by Grants from the Finnish Academy, the Sigrid Juselius Foundation, and the Paulo Foundation (M.H.) Presented in part at a meeting of the Society for Pediatric Research, Washington D.C., 1986. Submitted for publication June 18, 1986; accepted Nov. 7, 1986. Reprint requests: Mikko Hallman, M.D., Children's Hospital, University of Helsinki, Stenb~ckinkatu 11, 00290 Helsinkl, Finland.
604
release into the extracellular space, m, ~ and deficient renal catabolism t2 and excretion 7 of inositol. In the newborn infant, inositol-rich human milk may contribute to the high serum inositol concentration. 13,14 Inositol and inositol-containing phospholipids play important roles in membrane function and in receptor-
BPD L/S RDS
Bronchopulmonary dysplasia Lecithin/sphingomyelin ratio Respiratory distress syndrome
mediated events such as secretion and nerve conduction. ~5 Howevei', inositol is actively synthesized by various tissues and so may not be an essential nutrient (but see Burton and Wells t6 and Chu and Hegsted~7). Exogenous inositol stimulates the growth of human cells in vitro] 8 promotes the differentiation of the surfactant-producing system in
Volume 110 Number 4
Inositol supplementation in R D S
PLACEBO
T a b l e I. Clinical data
Birth weight (g) Mean Range SD Gestational age Mean Range SD Sex (M/F) Hours > 30% oxygen Median Range Bronchopulmonary dysplasia
605
Placebo (n = 2t)
Inositol (n = 27)
1412 930-1890 315
1329 730-1840 294 0.35
30.4 27.0-33.0 1.6 10/11 140 18-1440 5
29.9 27.0-33.0 1.8 15/12
AGE 1 day
AGE 9 days
P
I-Z zm ~
o-,,, ~,~,,,
FI,
,F
0 2 4 6 8 10 12141618
661o12141618 2 o
0 2
I N O S I T O L SUPPLEMENTATION
10" 9"
0.68
65 0.05 12-3080 1 0.05
r LU m
8-
~
6-
Z
54-
AGE 1 day
AGE 9 days
7-
321O-
i
i
i
i
i
, m
i
,
m i
i
m
2 4 6 8 101214161820
rodents, 19 maintains the integrity of insulin secretion in vitro, z~ and improves nerve conduction velocity in experimental diabetes. 2~The possibility that inositol is an important nutrient in human disease has not been ruled out.22,
23
The aim of our study was to evaluate whether diet or renal excretion influences serum inositol levels in preterm infants with respiratory distress syndrome, and whether inositol in excess promotes the "normalization" of surfactant indices. METHODS Fifty-four infants examined at the Children's Hospital, University of Helsinki, participated in a randomized double-blind study involving inositol supplementation?3 Informed consent was obtained from the parents. All the infants weighed <2000 g, and required mechanical ventilation for -->24 hours because of RDS. The diagnosis of RDS was based on symptoms of respiratory failure, requirement of supplementary oxygen, typical chest radiograph, and tracheal aspirate demonstrating a low L / S ratio and undetectable phosphatidylglycerol. Bronchopulmonary dysplasia was diagnosed on the basis of two criteria: respiratory distress and ~equirement of supplemental oxygen for >28 days, and persistent strands of densities in both lungs alternating with areas of normal or increased lucency. The infants were assigned randomly and blindly to receive either inositol or placebo (glucose). Because extremely high serum inositol levels, if associated with uremia, may contribute to uremic neuropathy,24 infants with low urine output or elevated blood urea values (>50 mg/dL) were excluded from the study. The supplementation (inositol or glucose) was started at age 48 hours. The dosage, 40 mg/kg (220 #mol/kg) every 6 hours, was as
m
m
I
m
m
HF] I
I
I
m
m
!
!
m
!
0 2 4 6 8 1012141618202224
INOSITOL CLEARANCE ( 1 0 x ml x kg -1 x min -1) Figure. Renal inositol clearance in infants with respiratory distress syndrome. Stippling, Subgroup of infants whose respiratory course was complicated by bronchopulmonary dysplasia.
high as the amount of inositol in full feeds of infants receiving preterm human milk? 4 The isotonic sugars were given intragastrically shortly before gavage feeds. In six infants (one receiving inositol and five placebo) the gastric feeds were discontinued because of unstable clinical condition. These six infants are excluded from the analysis. Specimens. Serum specimens were withdrawn either from the abdominal aorta or by heel stick at ages 24 to 48 hours and 3, 9, and 16 days. Another study has shown that serum inositol levels are closely similar regardless of the source of the specimen.9 Blood samples were withdrawn 1 hour before and 1 hour after inositol or placebo supplementation. The 12- or 24-hour urine collections were performed twice: starting at the age of one day and ending before the initiation of sugar supplementation, and starting on day 8 and ending before the termination of inositol supplementation. The urine was collected with an external collecting device. Every 6 hours the urine was refrigerated, and at the end of the collection period was stored at - 2 0 ~ C. During storage there was no detectable degradation of inositol. Gastric feeds consisted exclusively of human milk. If the mother's milk was not available, the infants received pooled human milk. Specimens of the milk were collected once a day and frozen until analyzed for inositol content. Neither intravenous fluids, vitamins, nor parenteral nutrients contained inositol. Tracheal aspirates were collected from these patients
606
Hallman, Arjomaa, and Hoppu
The Journal of Pediatrics April 1987
T a b l e II. Effect of inositol supplementation on the phospholipids in tracheal aspirate Placebo Days from birth Days from onset of supplementation n
Phosphatidylcholine Sphingomyelin Phosphatidylinositol Phosphatidylglycerol Phosphatidylethanol amine
Inositol
Placebo
Inosltol
Placebo
Inositol
0.4 -1.5
0.4 -1.5
2 0
2 0
5 3.0
5 3.0
16
17
15
17
15
17
66.2 11.1 5.8 0.0 11.0
_+ 8.6 _+ 5.0 _+ 2.0 _+ 0.0 _+ 6.1
66.6 11.9 6.6 0.1 9.5
_+ 6.9 _+ 4.2 _+ 3.4 _+ 0.0 + 3.2
76.0 8.7 7.0 0.0 5.4
+ 4.8 + 4.2 _+ 2.2 + 0.0 + 2.5
72.8 9.0 6.4 0.1 8.0
__+6.4 + 3.9 + 3.2 _+ 0.1 _+ 3.8
77.5 5.2 9.5 0.2 5.0
_+ 3.3 _+ 2.3 + 2.3 + 0.3 ___ 1.6
79.9 3.4 11.2 0.1 3.5
+ 2.3 + 1.8 + 1.8 + 0.1 _+ 1.8
0.036 0.035 0.035 NS NS
bis-(Monoacylglycerol)
0.2 _+ 0.2
0.1 _+ 0.1
0.2 + 0.3
0.1 + 0.1
0.3 _+ 0.2
0.2 + 0.2
NS
phosphate Phosphatidylserine Lysophosphatidylcholine Saturated phosphatidylcholine/sphingomyelin
5.0 _+ 2.4 0.7 + 0.6 2.2 _+ 1.7
4.8 + 2.6 0.4 _+ 0.5 1.8 ___0.8
2.0_+ 1.1 0.7 + 0.3 4.2 + 2.3
3.0 ___2.3 0.6 + 0.6 2.9 _+ 1.5
1.5 + 0.8 0.8 + 0.7 7.7 + 3.5
0.7 + 0.6 1.0 -+ 0.7 12.7 _+ 6.7
0.031 NS 0.015
Values represent percent. There were no detectable differences in phospholipidsbefore day 5. NS, not significant.
with endotracheal tubes during routine suctioning of the airways, 9 shortly after intubation, and at ages 2, 5, and 9 days. Analytical methods. Concentrations of inositol in serum and milk were analyzed as the trimethylsilyl derivatives on a 50 m capillary column (cross-linked methyl silicone) in a Model 5890 gas-liquid c h r o m a t o g r a p h ( H e w l e t t - P a c k a r d Co., W a l t h a m , Mass.). 9 The peak area was determined with an integrator a n d corrected for recovery of c~-methyl mannoside, which served as an internal standard. U r i n e inositol was m e a s u r e d essentially according to the enzymatic m e t h o d described by Garcia-Bunuel. 25 The specimens were first purified on columns of A G - X 8 (Bi0-Rad Laboratories, Richmond, Calif.) as described by Clements and Starnes. 26 The recovery of inositol was 91%. T h e tracheal aspirate was analyzed for phospholipids as described previously? T h e individual phospholipids were separated by two-dimensional thin-layer c h r o m a t o g r a p h y . S a t u r a t e d phosphatidylcholine was isolated by the osmium adduction method. 9 T h e statistical analyses were performed using B M D P Statistical Software programs 1D, 2D, 3D, 6D, 8D and 1R. 27 T h e significance of differences between the two groups was evaluated by analysis of variance followed by t test, with and without equality of variances. T h e Wilcoxon r a n k sum test or the Fisher exact test was used as a n o n p a r a m e t r i c method. The equality of variances was evaluated with the Levene test. T h e distribution was considered to be n o r m a l when the skewness coefficient/SE
was <2. T h e correlation between inositol intake or inositol excretion and serum inositol concentration was analyzed by linear, logarithmic, exponential, a n d power regression. T h e best fit is reported. Multiple regression analysis (1R) was used for analysis of the factors influencing serum inositol levels. T h e results are expressed as m e a n _+ S D or as median (range). RESULTS Forty-eight infants (27 inositol, 21 placebo) were eligible for the study. Their m e a n birth weight was 1365 g, and m e a n gestational age 30.1 weeks by m a t e r n a l m e n s t r u a l dates. In all infants the L / S ratio was low a n d phosphatidylglycerol was undetectable at birth. T h e two groups were comparable in terms of weight, gestational age, sex distribution, and severity of R D S shortly a f t e r birth. T h e infants who received inositol required supplemental oxygen for a shorter time and had a :lower incidence of BPD (Table I). T r a c h e a l aspirates were collected from all infants in whom endotracheal tubes were placed at birth. The two groups did not differ significantly with regard to the recovery of phospholipids on days 1 a n d 2. O n day 5 the inositol group h a d a significantly higher s a t u r a t e d phosphatidylcholine/sphingomyelin ratio, higher percentages of phosphatidylcholine a n d phosphatidylinositol, and lower percentages of sphingomyelin a n d phosphatidylserine t h a n the control values (Table II). O n day 9 there was no difference in the tracheal aspirate phospholipids (data not shown). However, 22 of the inositol group a n d only 10 of
Volume 110 Number 4
lnositol supplementation in R D S
607
T a b l e III. Intake, serum concentration, and urinary excretion of inositol Inositol
Placebo M e a n • SD
Age 24-48 hours Intake (#mol/kg/24 h) Serum concentration (t~mol/L) Urinary excretion (#mol/kg/24 h) Urinary inositol/creatinine (#mol/#mol) Age 3 days Intake 0zmol/kg/24 h) Serum concentration (#mol/L) 1 hour before sugar 1 hour after sugar Age 8-9 days Intake (/zmol/kg/24 h) Serum concentration (~tmol/L) 1 hour before sugar 1 hour after sugar Urinary excretion 0zmol/kg/24 h) Urinary inositol/creatinine (#mol/#mol) Age 16 days Intake (~mol/kg/24 h) Serum concentration (~mol/L)
n
M e a n • SD
27 27 23 23
0.73 0.18 0.330 0.284
32 566 301 8.3
140 • 98
21
992 • 53
27
<0.0001
292 • 228 310 • 213
19 18
823 • 357 944 • 394
26 25
<0.0001 <0.0001
349 • 137
21
1136 • 136
27
<0.0001
292 310 335 7.2
228 213 183 4.2
19 16 15 15
823 944 607 12.7
357 394 315 6.7
26 24 21 21
<0.0001 <0.0001 0.002 0.004
430 • 127 146 • 82
14 14
398 _+ 106 333 + 197
9 9
0.523 0.014
• • • •
• • • •
the placebo group were extubated before day 9, and therefore a significantly lower percentage of the inositol group could be evaluated for surfactant. The percentage of phosphatidylglycerol in tracheal aspirates was always low, regardless of inositol supplementation. Urine was collected from 41 infants between 24 and 48 hours of age before sugar supplementation began, and from 40 infants at 9 days of age before administration was discontinued. Serum specimens were collected from 48 to 33 infants between days 1 and 16. Inositol intake was calculated as the sum of the free inositol present in the sugar solution and in the milk. The mother's milk tended to have a higher inositol content than the pooled donor milk (see Bromberger and Hallman14). In infants who did not receive extra inositol, urinary excretion often exceeded oral intake (Table III). During inositol supplementation, the serum levels increased between days 1 and 3 (P = 0.0002), but not between days 3 and 9 (P -- 0.182). In the placebo group, serum inositol concentration fell between days 1 and 3 (P = 0.003); there was no significant change between days 3 and 9. Serum specimens were taken 1 hour before and 1 hour after administration of sugar. Only in the inositol group at 3 days of age was the prefeeding value significantly different (i.e., lower) from the postfeeding value (P = 0.035). Inositol supplementation increased urinary inositol
37 220 146 2.8
• • • •
28 337 208 5.3
P
21 21 18 18
29 451 244 6.8
• • • •
n
excretion (Table II1). There was a linear correlation between inositol intake and serum inositol concentration (P <0.01), and a linear correlation between urinary inositol excretion and serum inositol (P <0.05). To better understand the extent to which renal excretion regulates serum inositol concentration, the inositol clearance was calculated. A significant negative linear correlation was found between inositol clearance and serum inositol, when infants in the placebo (P <0.05) or inositol (P <0.01) groups were analyzed separately. The frequency distribution of inositol clearance was skewed to the right, and ranged between 0.09 and 3.61 m l / k g / m i n (Figure). In 20 patients, glucose concentrations in blood and urine, and creatinine clearance were studied. These measurements had no detectable correlation with inositol clearance (data not shown). In the placebo group, inositol clearance increased significantly between days 1 and 9, whereas among the inositol group there was no detectable increase in inositol clearance. The six infants with BPD had higher inositol clearance during day 1 and day 9 than did those without BPD (Table IV). In addition, the infants with BPD had lower serum inositol levels d~ring day 1 (271 # m o l / L , range 135 to 401 # m o l / L , vs,475 # m o l / L , range 107 to 1385/zmol/L, P -- 0.02) and day 9 (262/zmol/L, range 92 to 490/~mol/L, vs 515 # m o l / L , range 73 to 3544 # m o l / L ,
608
Hallman, Arjomaa, and Hoppu
The Journal of Pediatrics April 1987
T a b l e IV. Renal inositol clearance (ml/kg/min) in infants with respiratory distress syndrome: Effect of postnatal age and inositol supplementation Age I day
Placebo Inositol No BPD BPD Pt
Median
Range
0.34 0.31 0.30 0.75
0.09-1.20 0.10-1.92 0.09-1.92 0.39-1.62
Age 9 days
(n = 15) (n = 21) (n = 30) (n = 6)
<0.05
Median
Range
0.62 0.41 0.52 1.50
0.25-3.61 0.15-2.78 0.15-2.32 0.42-3.61
P" n= n= (n = (n =
15 21 30) 6)
0.02 NS NS NS
<0.01
*Age 1 day vs age 9 days, NS, not significant. tNo BPD vs BPD.
Table V. Factors affecting serum inositol concentration: Multiple regression analysis
Age I day Gestational age lnositol intake Inositol clearance Age 9 days Gestational age Inositol intake Inositol clearance
Numerical variable
Regression coefficient
SE
Weeks at birth umol/kg/24 h 10 • ml/kg/min
-56.8 1.7 -260.1
26.6 1.3 129.3
0.04 0.20 0.05
-99.2 0.55 -175.7
49.7 0.22 102.9
0.05 0.019 0.09
P
Constant term and multiple linear regression coefficients were: day I, 2512 ~mol/L and 0.58, respectively; day 9, 3727 #mol/L and 0.67.
P <0.01) than infants with RDS who did not have BPD. Table V shows multiple regression analysis of factors possibly affecting serum inositol concentration. Of these, gestational age, inositol intake, and inositol clearance proved to be significant variables; sex and small size for gestational age were not. There was no detectable correlation either between gestational age and inositol intake or between gestational age and inositol clearance. DISCUSSION Our results demonstrate that in small preterm infants with RDS, high inositol intake accelerated the increase in surfactant phospholipids. These data confirm and extend the experimental data demonstrating that the glucocorticoid-dependent differentiation of surfactant synthesis and secretion was promoted by inositol.19 In another clinical trial, exogenous glueocorticoid in infants with RDS did not have an effect on the severity of the respiratory failure, apparently because the endogenous glucoeorticoid levels were high38 According to these and previous7 data, the homeostasis of serum inositol in small preterm infnats is strikingly different from the process in adults. In infants receiving a ,low" inositol diet (0 to 20 mg/kg/d), excretion exceeds intake (Table III). Even so, in our series serum inositol concentration decreased only gradually, and during the 16
days studied the levels remained two to 10 times higher than in adults. On the other hand, during "high" inositol intake (160 to 220 mg/kg/d), serum inositol increased within 1 day, and 6 days after discontinuation of supplementation, serum inositol concentration was at least twice as high as in the placebo group. A second variable that negatively influenced serum inositol was renal inositol clearance. Finally, there was a negative correlation between the length of gestation and serum inositol values. In contrast, in healthy adults the serum inositol concentration is maintained within a narrow, low range (15 to 40 #tool/L), despite a wide range of dietary inositoI intake. Adult kidneys synthesize approximately 2 g inositol, dispose of 1 g, and thus account for approximately 1 g net production of inositol per day in the absence of inositol intake. 2 This is similar to the mean inositol intake with a normal diet. When transplanted into hosts with hyperinositolemia, on the other hand, the kidneys increased inositol disposal to approximately 7 g/d. However, urinary excretion accounted for only 6% of the total renal disposal. 2 According to another study, a doily intake of 7 g inositol (100 mg/kg/d, or an extra 6 g, in addition to the normal diet) in adults transiently increased serum inositol concentrations, but urinary inositol remained less than 2% of the inositol intake. 22 Although inositol enters the glomerular
Volume I 10 Number 4
filtrate freely, tubular reabsorption in normal adults is almost complete. However, inositol is additionally metabolized by way of the glucuronate-xylulose pathway in the kidney,2. 29 which appears to be responsible for the Uniformly low serum inositol concentration in healthy adultS. There is little information on synthesis and disposal of inositol in fetal tissue. In the rabbit, the activity of inositol oxidase, the enzyme limiting the rate of inositol catabolism in the kidney, is very low in immature fetuses, and increases parallel to a decrease in serum inositoU 2 This supports the concept that inactive inositol catabolism contributes to the tendency toward high serum inositol and that the decrease in inositoi is in part the result of an increase in inositol oxidase activity. According to another study, perfused livers from fetal lambs release about 30% of the inositol that accumulates in the serum of exteriorized fetuses. H'3~ H u m a n fetal liver, lung, and placenta contain low activities of glucose-6-phosphate/inositol-1phosphate cyclase, 8 the enzyme limiting the rate of inositol synthesis, whereas in rodents the high inositol levels in fetal serum may be related to high inositol synthesis in the liver? ~ It is also possible that the high serum inositol concentration is maintained in part through urinary inositol accumulating in the amniotic sac, the m e m b r a n e of which is impermeable to inositol, fetal swallowing of amniotic fluid, and subsequent absorption in the alimentary tract. The observed decline of serum inositol values after birth is in accord with this alternative. Among the preterm infants with RDS, the range of inositol clearance was wide, with skewness to the right. It is unclear whether this was caused by differences in the timetable of "maturation" of renal carbohydrate disposal or by other differences in the ability of the kidneys of conserve inositol. There was no detectable correlation between inositol clearance and gestational age, but clearance tended to increase during the first 9 neonatal days. In the infants who developed BPD, inositol clearance was significantly higher, and serum inositol significantly lower, than in those infants with uncomplicated R D S . These differences were already present on days 1 and 9. The cause of the high inositol clearance is unclear. According to present understanding, the tubular reabsorption of inositol Competes with D-glucose for the membrane potential and for the inositol carrier2 TM Elevated blood glucose concentrations in diabetes or after phlorizin administration result in brisk inositoluria. 3 There was no evidence of abnormally high blood or urinary glucose or high creatinine clearance among the infants who had high inositol clearance. However, inositol is additionally excreted into the urine by a mechanism involving neither glomerular filtration nor proximal tubular reabsorption. 32 We propose that in some immature preterm infants, low serum inositol concentration is a result of negative inositol
Inositol supplementation in R D S
609
balance resulting from lack of inositol-rich feeds or renal "wastage" of inositol. Low inosit01 values were associated with a slow recovery from R D S and a high incidence of BPD, whereas inositol supplementation increased the surfactant indices and tended to decrease the severity of R D S ? 3 This evidence supports the concept that inositol is an important micronutrient for immature infants and should be added to the diet when normal quantities of the mother's milk cannot be given. This possibility remains to be further evaluated. REFERENCES
1. Daughaday WH, Larner J. The renal excretion of inositol in normal and diabetic human beings. J Clin Invest 1954;33:326. 2. Clements RS Jr, Diethelm AG. The metabolism of myoinositol by the human kidney. J Lab Clin Med 1979;93:210. 3. Clements RS Jr, Reynertson R. Myoinositol metabolism in diabetes mellitus: effect of insulin treatment. Diabetes 1975;26:215. 4. Dawson RMC, Freinkel N. The distribution of free mesoinositot in mammalian tissues, including some observations on the lactating rat. Biochem J 1961;78:606. 5. Offergeld H. Uber das Vorkommen yon Kohlehydraten im Fruchtwasser bei Diabetes der Mutter: Z Geburtshilfe Gynak 1906;58:189. 6. Campling JD, Nixon DA. The inositol content of foetal fluids. J Physiol 1954;126:71. 7. Lewin LM, Melmed S, Passwell JH, et al. Myoinositol in human neonates: serum concentrations and renal handling. Pediatr Res 1978;12:3. 8. Quirk JG, Bleasdale JE: myo-Inositol homeostasis in the human fetus. Obstet Gynecol 1983;62:41. 9. Haltman M, Saugstad OD, Porreco RP, Epstein BL, Gluck L. Role of myoinositol in regulation of surfactant phospholipids in the newboi~n. Early Hum Dev 1985;10:245. 10. Burton LE, Wells WW. Studies on the developmental pattern of the enzymes converting glucose 6-phosphate to myoinositol in the rat. Dev Biol 1974;37:35. 11. Nixon DA. The concentration of free meso-inositol in the plasma of perfused sheep fetuses. Biol Neonate 1968; 12:113. 12. Hallman M. Development of pulmonary surfactant. In: Raivio K, Hallman N, Kouvalainen K, et al., eds. Respiratory distress syndrome. Orlando, Fla.: Academic Press, 1984:3350. 13. Ogasa K, Kuboyama M, Kiyosawa I, Suzuki K, Itoh M. The content of free and bound inositol in human and cow's milk. J Nutr Sci Vitaminol (Tokyo) 1975;21 : 129. 14. Bromberger P, Hailman M. Myoinositol in small preterm infants: relationship between intake and serum concentration. J Pediati" Gastroenter Nutr 1986;5:455. 15. Michell RH. Inositol phospholipids and cell surface receptor function. Biochim Biophys Acta 1975;415:81. 16. Burton LE, Wells WW: myo-Inositol metabolism during lactation and development in the rat: the prevention of lactation-induced fatty liver by dietary myo-inositol. J Nutr 1976;106:1617. 17. Chu S-HW, Hegsted DM: myo-Inositol deficiency in gerbils: changes in phospholipid composition of intestinal microsomes. J Nutr 1980;110;1217.
6 10
Hallman, Arjomaa, and Hoppu
18. Eagle H, Oyama V1, Levy M, Freeman AE: myo-Inositol as an essential growth factor for normal and malignant human cells in tissue culture. J Bioi Chem 1957;226:191. 19. Hallman M. Effect of extracellular myo-inositol on surfactant phospholipid synthesis in the fetal rabbit lung. Biochim Biophys Acta 1984;797:67. 20. Pace CS, Clements RS: rnyo-lnositol and the maintenance of /3-cell function in cultured rat pancreatic islets. Diabetes 1981;30:621. 21. Greene DA, DeJesus PV Jr, Winegrad AI. Effects of insulin and dietary myo-inositol on impaired peripheral nerve conduction velocity in acute streptozotocin diabetes. J Clin Invest 1975;55;1326: 22. Gregersen G, Bertelsen B, Harbo H, et al. Oral supplementation of my0inositol: effects on peripheral nerve function in human diabetics and on the concentration in plasmas erythrocytes, urine arid muscle tissue in human diabetics and normals. Acta Neurol Scand 1983;67:164. 23. Hallman M, J~irvenp/i/i A-L, Pohjavuori M. Inositol suppiementation to preterm infants: a double blind study demonstrating reduction in severity of RDS. Arch Dis Child 1986;61:1076. 24. De Jesus PV Jr, Clements RS, Winegrad AI. Hypermyoinositolemic polyneuropathy in rats: a possible mechanism for uremic polyneuropathy. J Neurol Sci 1974;21:237.
The Journal of Pediatrics April 1987 25. Garcia-Bunuel L, Garcia- Bunuel VM. Enzymatic determination of f?ee myoinositol in human cerebrospinal fluid and plasma. J Lab Clin Med 1964;64:468. 26. Ctements RS Jr, Starnes WR. A n improved method for the ~leterminatiori of urinary myo-inositol by gas-liquid chromatography. Biochem Med 1975;12:200. 27. Dixon WL BMDP statistical software. Berkeley, Calif.: University of California Press; 1985. 28. Baden M, Bauer CB, Colle E, Klein G, Taeusch HW Jr, Stern L. A controlled trial of hydrocortisone therapy in infants With respiratory distress syndrome. Pediatrics 1972;50i526. 29. Reddy CC, Pierzchala PA, Hamilton GA. myo-Inositol oxygenase from hog kidney. J Biol Chem 1981;256:8519. 30. Andrews WHH, Britton HG, Hugget A St G, Nixon DA. Fructose metabolism in the isolated perfused liver of the t'oetal and newborn sheep. J. Physiol Lond 1960;153:199. 31. Hammerman MR, Sacktor B, Daughaday WH. myO-tnositol transport in renal brush border vesicles and its inhibition by o-glucose. Am J Physiol 1980;239:F113. 32. Molitoris BA, Hruska KA, Fishman N, Daughaday WH. Effects of glucose and parathyroid hormone on the renal handling of myoinosito! by isolated perfused dog kidneys. J Clin Invest 1979;63:1110.
Mikko Hallman, M.D., Pirkko Arjomaa, M.A., and Kalle Hoppu, M.D. From the Children's Hospital, University of Helsinki, Finland
myo-Inositol
(henceforth called inositol) is at least as abtmdant in the human body as glucose. In healthy adults, the serum concentration of inositol remains within a narrow, low range, 1-3 one to three orders of magnitude lower than in the liver, lung, kidney, or brain. 4 In newborn infants and fetuses, however, serum concentrations of inositol are 2 to 100 times higher than in adults. 5-9 In the fetus, it has been proposed that there is active synthesis,
Supported by Grants from the Finnish Academy, the Sigrid Juselius Foundation, and the Paulo Foundation (M.H.) Presented in part at a meeting of the Society for Pediatric Research, Washington D.C., 1986. Submitted for publication June 18, 1986; accepted Nov. 7, 1986. Reprint requests: Mikko Hallman, M.D., Children's Hospital, University of Helsinki, Stenb~ckinkatu 11, 00290 Helsinkl, Finland.
604
release into the extracellular space, m, ~ and deficient renal catabolism t2 and excretion 7 of inositol. In the newborn infant, inositol-rich human milk may contribute to the high serum inositol concentration. 13,14 Inositol and inositol-containing phospholipids play important roles in membrane function and in receptor-
BPD L/S RDS
Bronchopulmonary dysplasia Lecithin/sphingomyelin ratio Respiratory distress syndrome
mediated events such as secretion and nerve conduction. ~5 Howevei', inositol is actively synthesized by various tissues and so may not be an essential nutrient (but see Burton and Wells t6 and Chu and Hegsted~7). Exogenous inositol stimulates the growth of human cells in vitro] 8 promotes the differentiation of the surfactant-producing system in
Volume 110 Number 4
Inositol supplementation in R D S
PLACEBO
T a b l e I. Clinical data
Birth weight (g) Mean Range SD Gestational age Mean Range SD Sex (M/F) Hours > 30% oxygen Median Range Bronchopulmonary dysplasia
605
Placebo (n = 2t)
Inositol (n = 27)
1412 930-1890 315
1329 730-1840 294 0.35
30.4 27.0-33.0 1.6 10/11 140 18-1440 5
29.9 27.0-33.0 1.8 15/12
AGE 1 day
AGE 9 days
P
I-Z zm ~
o-,,, ~,~,,,
FI,
,F
0 2 4 6 8 10 12141618
661o12141618 2 o
0 2
I N O S I T O L SUPPLEMENTATION
10" 9"
0.68
65 0.05 12-3080 1 0.05
r LU m
8-
~
6-
Z
54-
AGE 1 day
AGE 9 days
7-
321O-
i
i
i
i
i
, m
i
,
m i
i
m
2 4 6 8 101214161820
rodents, 19 maintains the integrity of insulin secretion in vitro, z~ and improves nerve conduction velocity in experimental diabetes. 2~The possibility that inositol is an important nutrient in human disease has not been ruled out.22,
23
The aim of our study was to evaluate whether diet or renal excretion influences serum inositol levels in preterm infants with respiratory distress syndrome, and whether inositol in excess promotes the "normalization" of surfactant indices. METHODS Fifty-four infants examined at the Children's Hospital, University of Helsinki, participated in a randomized double-blind study involving inositol supplementation?3 Informed consent was obtained from the parents. All the infants weighed <2000 g, and required mechanical ventilation for -->24 hours because of RDS. The diagnosis of RDS was based on symptoms of respiratory failure, requirement of supplementary oxygen, typical chest radiograph, and tracheal aspirate demonstrating a low L / S ratio and undetectable phosphatidylglycerol. Bronchopulmonary dysplasia was diagnosed on the basis of two criteria: respiratory distress and ~equirement of supplemental oxygen for >28 days, and persistent strands of densities in both lungs alternating with areas of normal or increased lucency. The infants were assigned randomly and blindly to receive either inositol or placebo (glucose). Because extremely high serum inositol levels, if associated with uremia, may contribute to uremic neuropathy,24 infants with low urine output or elevated blood urea values (>50 mg/dL) were excluded from the study. The supplementation (inositol or glucose) was started at age 48 hours. The dosage, 40 mg/kg (220 #mol/kg) every 6 hours, was as
m
m
I
m
m
HF] I
I
I
m
m
!
!
m
!
0 2 4 6 8 1012141618202224
INOSITOL CLEARANCE ( 1 0 x ml x kg -1 x min -1) Figure. Renal inositol clearance in infants with respiratory distress syndrome. Stippling, Subgroup of infants whose respiratory course was complicated by bronchopulmonary dysplasia.
high as the amount of inositol in full feeds of infants receiving preterm human milk? 4 The isotonic sugars were given intragastrically shortly before gavage feeds. In six infants (one receiving inositol and five placebo) the gastric feeds were discontinued because of unstable clinical condition. These six infants are excluded from the analysis. Specimens. Serum specimens were withdrawn either from the abdominal aorta or by heel stick at ages 24 to 48 hours and 3, 9, and 16 days. Another study has shown that serum inositol levels are closely similar regardless of the source of the specimen.9 Blood samples were withdrawn 1 hour before and 1 hour after inositol or placebo supplementation. The 12- or 24-hour urine collections were performed twice: starting at the age of one day and ending before the initiation of sugar supplementation, and starting on day 8 and ending before the termination of inositol supplementation. The urine was collected with an external collecting device. Every 6 hours the urine was refrigerated, and at the end of the collection period was stored at - 2 0 ~ C. During storage there was no detectable degradation of inositol. Gastric feeds consisted exclusively of human milk. If the mother's milk was not available, the infants received pooled human milk. Specimens of the milk were collected once a day and frozen until analyzed for inositol content. Neither intravenous fluids, vitamins, nor parenteral nutrients contained inositol. Tracheal aspirates were collected from these patients
606
Hallman, Arjomaa, and Hoppu
The Journal of Pediatrics April 1987
T a b l e II. Effect of inositol supplementation on the phospholipids in tracheal aspirate Placebo Days from birth Days from onset of supplementation n
Phosphatidylcholine Sphingomyelin Phosphatidylinositol Phosphatidylglycerol Phosphatidylethanol amine
Inositol
Placebo
Inosltol
Placebo
Inositol
0.4 -1.5
0.4 -1.5
2 0
2 0
5 3.0
5 3.0
16
17
15
17
15
17
66.2 11.1 5.8 0.0 11.0
_+ 8.6 _+ 5.0 _+ 2.0 _+ 0.0 _+ 6.1
66.6 11.9 6.6 0.1 9.5
_+ 6.9 _+ 4.2 _+ 3.4 _+ 0.0 + 3.2
76.0 8.7 7.0 0.0 5.4
+ 4.8 + 4.2 _+ 2.2 + 0.0 + 2.5
72.8 9.0 6.4 0.1 8.0
__+6.4 + 3.9 + 3.2 _+ 0.1 _+ 3.8
77.5 5.2 9.5 0.2 5.0
_+ 3.3 _+ 2.3 + 2.3 + 0.3 ___ 1.6
79.9 3.4 11.2 0.1 3.5
+ 2.3 + 1.8 + 1.8 + 0.1 _+ 1.8
0.036 0.035 0.035 NS NS
bis-(Monoacylglycerol)
0.2 _+ 0.2
0.1 _+ 0.1
0.2 + 0.3
0.1 + 0.1
0.3 _+ 0.2
0.2 + 0.2
NS
phosphate Phosphatidylserine Lysophosphatidylcholine Saturated phosphatidylcholine/sphingomyelin
5.0 _+ 2.4 0.7 + 0.6 2.2 _+ 1.7
4.8 + 2.6 0.4 _+ 0.5 1.8 ___0.8
2.0_+ 1.1 0.7 + 0.3 4.2 + 2.3
3.0 ___2.3 0.6 + 0.6 2.9 _+ 1.5
1.5 + 0.8 0.8 + 0.7 7.7 + 3.5
0.7 + 0.6 1.0 -+ 0.7 12.7 _+ 6.7
0.031 NS 0.015
Values represent percent. There were no detectable differences in phospholipidsbefore day 5. NS, not significant.
with endotracheal tubes during routine suctioning of the airways, 9 shortly after intubation, and at ages 2, 5, and 9 days. Analytical methods. Concentrations of inositol in serum and milk were analyzed as the trimethylsilyl derivatives on a 50 m capillary column (cross-linked methyl silicone) in a Model 5890 gas-liquid c h r o m a t o g r a p h ( H e w l e t t - P a c k a r d Co., W a l t h a m , Mass.). 9 The peak area was determined with an integrator a n d corrected for recovery of c~-methyl mannoside, which served as an internal standard. U r i n e inositol was m e a s u r e d essentially according to the enzymatic m e t h o d described by Garcia-Bunuel. 25 The specimens were first purified on columns of A G - X 8 (Bi0-Rad Laboratories, Richmond, Calif.) as described by Clements and Starnes. 26 The recovery of inositol was 91%. T h e tracheal aspirate was analyzed for phospholipids as described previously? T h e individual phospholipids were separated by two-dimensional thin-layer c h r o m a t o g r a p h y . S a t u r a t e d phosphatidylcholine was isolated by the osmium adduction method. 9 T h e statistical analyses were performed using B M D P Statistical Software programs 1D, 2D, 3D, 6D, 8D and 1R. 27 T h e significance of differences between the two groups was evaluated by analysis of variance followed by t test, with and without equality of variances. T h e Wilcoxon r a n k sum test or the Fisher exact test was used as a n o n p a r a m e t r i c method. The equality of variances was evaluated with the Levene test. T h e distribution was considered to be n o r m a l when the skewness coefficient/SE
was <2. T h e correlation between inositol intake or inositol excretion and serum inositol concentration was analyzed by linear, logarithmic, exponential, a n d power regression. T h e best fit is reported. Multiple regression analysis (1R) was used for analysis of the factors influencing serum inositol levels. T h e results are expressed as m e a n _+ S D or as median (range). RESULTS Forty-eight infants (27 inositol, 21 placebo) were eligible for the study. Their m e a n birth weight was 1365 g, and m e a n gestational age 30.1 weeks by m a t e r n a l m e n s t r u a l dates. In all infants the L / S ratio was low a n d phosphatidylglycerol was undetectable at birth. T h e two groups were comparable in terms of weight, gestational age, sex distribution, and severity of R D S shortly a f t e r birth. T h e infants who received inositol required supplemental oxygen for a shorter time and had a :lower incidence of BPD (Table I). T r a c h e a l aspirates were collected from all infants in whom endotracheal tubes were placed at birth. The two groups did not differ significantly with regard to the recovery of phospholipids on days 1 a n d 2. O n day 5 the inositol group h a d a significantly higher s a t u r a t e d phosphatidylcholine/sphingomyelin ratio, higher percentages of phosphatidylcholine a n d phosphatidylinositol, and lower percentages of sphingomyelin a n d phosphatidylserine t h a n the control values (Table II). O n day 9 there was no difference in the tracheal aspirate phospholipids (data not shown). However, 22 of the inositol group a n d only 10 of
Volume 110 Number 4
lnositol supplementation in R D S
607
T a b l e III. Intake, serum concentration, and urinary excretion of inositol Inositol
Placebo M e a n • SD
Age 24-48 hours Intake (#mol/kg/24 h) Serum concentration (t~mol/L) Urinary excretion (#mol/kg/24 h) Urinary inositol/creatinine (#mol/#mol) Age 3 days Intake 0zmol/kg/24 h) Serum concentration (#mol/L) 1 hour before sugar 1 hour after sugar Age 8-9 days Intake (/zmol/kg/24 h) Serum concentration (~tmol/L) 1 hour before sugar 1 hour after sugar Urinary excretion 0zmol/kg/24 h) Urinary inositol/creatinine (#mol/#mol) Age 16 days Intake (~mol/kg/24 h) Serum concentration (~mol/L)
n
M e a n • SD
27 27 23 23
0.73 0.18 0.330 0.284
32 566 301 8.3
140 • 98
21
992 • 53
27
<0.0001
292 • 228 310 • 213
19 18
823 • 357 944 • 394
26 25
<0.0001 <0.0001
349 • 137
21
1136 • 136
27
<0.0001
292 310 335 7.2
228 213 183 4.2
19 16 15 15
823 944 607 12.7
357 394 315 6.7
26 24 21 21
<0.0001 <0.0001 0.002 0.004
430 • 127 146 • 82
14 14
398 _+ 106 333 + 197
9 9
0.523 0.014
• • • •
• • • •
the placebo group were extubated before day 9, and therefore a significantly lower percentage of the inositol group could be evaluated for surfactant. The percentage of phosphatidylglycerol in tracheal aspirates was always low, regardless of inositol supplementation. Urine was collected from 41 infants between 24 and 48 hours of age before sugar supplementation began, and from 40 infants at 9 days of age before administration was discontinued. Serum specimens were collected from 48 to 33 infants between days 1 and 16. Inositol intake was calculated as the sum of the free inositol present in the sugar solution and in the milk. The mother's milk tended to have a higher inositol content than the pooled donor milk (see Bromberger and Hallman14). In infants who did not receive extra inositol, urinary excretion often exceeded oral intake (Table III). During inositol supplementation, the serum levels increased between days 1 and 3 (P = 0.0002), but not between days 3 and 9 (P -- 0.182). In the placebo group, serum inositol concentration fell between days 1 and 3 (P = 0.003); there was no significant change between days 3 and 9. Serum specimens were taken 1 hour before and 1 hour after administration of sugar. Only in the inositol group at 3 days of age was the prefeeding value significantly different (i.e., lower) from the postfeeding value (P = 0.035). Inositol supplementation increased urinary inositol
37 220 146 2.8
• • • •
28 337 208 5.3
P
21 21 18 18
29 451 244 6.8
• • • •
n
excretion (Table II1). There was a linear correlation between inositol intake and serum inositol concentration (P <0.01), and a linear correlation between urinary inositol excretion and serum inositol (P <0.05). To better understand the extent to which renal excretion regulates serum inositol concentration, the inositol clearance was calculated. A significant negative linear correlation was found between inositol clearance and serum inositol, when infants in the placebo (P <0.05) or inositol (P <0.01) groups were analyzed separately. The frequency distribution of inositol clearance was skewed to the right, and ranged between 0.09 and 3.61 m l / k g / m i n (Figure). In 20 patients, glucose concentrations in blood and urine, and creatinine clearance were studied. These measurements had no detectable correlation with inositol clearance (data not shown). In the placebo group, inositol clearance increased significantly between days 1 and 9, whereas among the inositol group there was no detectable increase in inositol clearance. The six infants with BPD had higher inositol clearance during day 1 and day 9 than did those without BPD (Table IV). In addition, the infants with BPD had lower serum inositol levels d~ring day 1 (271 # m o l / L , range 135 to 401 # m o l / L , vs,475 # m o l / L , range 107 to 1385/zmol/L, P -- 0.02) and day 9 (262/zmol/L, range 92 to 490/~mol/L, vs 515 # m o l / L , range 73 to 3544 # m o l / L ,
608
Hallman, Arjomaa, and Hoppu
The Journal of Pediatrics April 1987
T a b l e IV. Renal inositol clearance (ml/kg/min) in infants with respiratory distress syndrome: Effect of postnatal age and inositol supplementation Age I day
Placebo Inositol No BPD BPD Pt
Median
Range
0.34 0.31 0.30 0.75
0.09-1.20 0.10-1.92 0.09-1.92 0.39-1.62
Age 9 days
(n = 15) (n = 21) (n = 30) (n = 6)
<0.05
Median
Range
0.62 0.41 0.52 1.50
0.25-3.61 0.15-2.78 0.15-2.32 0.42-3.61
P" n= n= (n = (n =
15 21 30) 6)
0.02 NS NS NS
<0.01
*Age 1 day vs age 9 days, NS, not significant. tNo BPD vs BPD.
Table V. Factors affecting serum inositol concentration: Multiple regression analysis
Age I day Gestational age lnositol intake Inositol clearance Age 9 days Gestational age Inositol intake Inositol clearance
Numerical variable
Regression coefficient
SE
Weeks at birth umol/kg/24 h 10 • ml/kg/min
-56.8 1.7 -260.1
26.6 1.3 129.3
0.04 0.20 0.05
-99.2 0.55 -175.7
49.7 0.22 102.9
0.05 0.019 0.09
P
Constant term and multiple linear regression coefficients were: day I, 2512 ~mol/L and 0.58, respectively; day 9, 3727 #mol/L and 0.67.
P <0.01) than infants with RDS who did not have BPD. Table V shows multiple regression analysis of factors possibly affecting serum inositol concentration. Of these, gestational age, inositol intake, and inositol clearance proved to be significant variables; sex and small size for gestational age were not. There was no detectable correlation either between gestational age and inositol intake or between gestational age and inositol clearance. DISCUSSION Our results demonstrate that in small preterm infants with RDS, high inositol intake accelerated the increase in surfactant phospholipids. These data confirm and extend the experimental data demonstrating that the glucocorticoid-dependent differentiation of surfactant synthesis and secretion was promoted by inositol.19 In another clinical trial, exogenous glueocorticoid in infants with RDS did not have an effect on the severity of the respiratory failure, apparently because the endogenous glucoeorticoid levels were high38 According to these and previous7 data, the homeostasis of serum inositol in small preterm infnats is strikingly different from the process in adults. In infants receiving a ,low" inositol diet (0 to 20 mg/kg/d), excretion exceeds intake (Table III). Even so, in our series serum inositol concentration decreased only gradually, and during the 16
days studied the levels remained two to 10 times higher than in adults. On the other hand, during "high" inositol intake (160 to 220 mg/kg/d), serum inositol increased within 1 day, and 6 days after discontinuation of supplementation, serum inositol concentration was at least twice as high as in the placebo group. A second variable that negatively influenced serum inositol was renal inositol clearance. Finally, there was a negative correlation between the length of gestation and serum inositol values. In contrast, in healthy adults the serum inositol concentration is maintained within a narrow, low range (15 to 40 #tool/L), despite a wide range of dietary inositoI intake. Adult kidneys synthesize approximately 2 g inositol, dispose of 1 g, and thus account for approximately 1 g net production of inositol per day in the absence of inositol intake. 2 This is similar to the mean inositol intake with a normal diet. When transplanted into hosts with hyperinositolemia, on the other hand, the kidneys increased inositol disposal to approximately 7 g/d. However, urinary excretion accounted for only 6% of the total renal disposal. 2 According to another study, a doily intake of 7 g inositol (100 mg/kg/d, or an extra 6 g, in addition to the normal diet) in adults transiently increased serum inositol concentrations, but urinary inositol remained less than 2% of the inositol intake. 22 Although inositol enters the glomerular
Volume I 10 Number 4
filtrate freely, tubular reabsorption in normal adults is almost complete. However, inositol is additionally metabolized by way of the glucuronate-xylulose pathway in the kidney,2. 29 which appears to be responsible for the Uniformly low serum inositol concentration in healthy adultS. There is little information on synthesis and disposal of inositol in fetal tissue. In the rabbit, the activity of inositol oxidase, the enzyme limiting the rate of inositol catabolism in the kidney, is very low in immature fetuses, and increases parallel to a decrease in serum inositoU 2 This supports the concept that inactive inositol catabolism contributes to the tendency toward high serum inositol and that the decrease in inositoi is in part the result of an increase in inositol oxidase activity. According to another study, perfused livers from fetal lambs release about 30% of the inositol that accumulates in the serum of exteriorized fetuses. H'3~ H u m a n fetal liver, lung, and placenta contain low activities of glucose-6-phosphate/inositol-1phosphate cyclase, 8 the enzyme limiting the rate of inositol synthesis, whereas in rodents the high inositol levels in fetal serum may be related to high inositol synthesis in the liver? ~ It is also possible that the high serum inositol concentration is maintained in part through urinary inositol accumulating in the amniotic sac, the m e m b r a n e of which is impermeable to inositol, fetal swallowing of amniotic fluid, and subsequent absorption in the alimentary tract. The observed decline of serum inositol values after birth is in accord with this alternative. Among the preterm infants with RDS, the range of inositol clearance was wide, with skewness to the right. It is unclear whether this was caused by differences in the timetable of "maturation" of renal carbohydrate disposal or by other differences in the ability of the kidneys of conserve inositol. There was no detectable correlation between inositol clearance and gestational age, but clearance tended to increase during the first 9 neonatal days. In the infants who developed BPD, inositol clearance was significantly higher, and serum inositol significantly lower, than in those infants with uncomplicated R D S . These differences were already present on days 1 and 9. The cause of the high inositol clearance is unclear. According to present understanding, the tubular reabsorption of inositol Competes with D-glucose for the membrane potential and for the inositol carrier2 TM Elevated blood glucose concentrations in diabetes or after phlorizin administration result in brisk inositoluria. 3 There was no evidence of abnormally high blood or urinary glucose or high creatinine clearance among the infants who had high inositol clearance. However, inositol is additionally excreted into the urine by a mechanism involving neither glomerular filtration nor proximal tubular reabsorption. 32 We propose that in some immature preterm infants, low serum inositol concentration is a result of negative inositol
Inositol supplementation in R D S
609
balance resulting from lack of inositol-rich feeds or renal "wastage" of inositol. Low inosit01 values were associated with a slow recovery from R D S and a high incidence of BPD, whereas inositol supplementation increased the surfactant indices and tended to decrease the severity of R D S ? 3 This evidence supports the concept that inositol is an important micronutrient for immature infants and should be added to the diet when normal quantities of the mother's milk cannot be given. This possibility remains to be further evaluated. REFERENCES
1. Daughaday WH, Larner J. The renal excretion of inositol in normal and diabetic human beings. J Clin Invest 1954;33:326. 2. Clements RS Jr, Diethelm AG. The metabolism of myoinositol by the human kidney. J Lab Clin Med 1979;93:210. 3. Clements RS Jr, Reynertson R. Myoinositol metabolism in diabetes mellitus: effect of insulin treatment. Diabetes 1975;26:215. 4. Dawson RMC, Freinkel N. The distribution of free mesoinositot in mammalian tissues, including some observations on the lactating rat. Biochem J 1961;78:606. 5. Offergeld H. Uber das Vorkommen yon Kohlehydraten im Fruchtwasser bei Diabetes der Mutter: Z Geburtshilfe Gynak 1906;58:189. 6. Campling JD, Nixon DA. The inositol content of foetal fluids. J Physiol 1954;126:71. 7. Lewin LM, Melmed S, Passwell JH, et al. Myoinositol in human neonates: serum concentrations and renal handling. Pediatr Res 1978;12:3. 8. Quirk JG, Bleasdale JE: myo-Inositol homeostasis in the human fetus. Obstet Gynecol 1983;62:41. 9. Haltman M, Saugstad OD, Porreco RP, Epstein BL, Gluck L. Role of myoinositol in regulation of surfactant phospholipids in the newboi~n. Early Hum Dev 1985;10:245. 10. Burton LE, Wells WW. Studies on the developmental pattern of the enzymes converting glucose 6-phosphate to myoinositol in the rat. Dev Biol 1974;37:35. 11. Nixon DA. The concentration of free meso-inositol in the plasma of perfused sheep fetuses. Biol Neonate 1968; 12:113. 12. Hallman M. Development of pulmonary surfactant. In: Raivio K, Hallman N, Kouvalainen K, et al., eds. Respiratory distress syndrome. Orlando, Fla.: Academic Press, 1984:3350. 13. Ogasa K, Kuboyama M, Kiyosawa I, Suzuki K, Itoh M. The content of free and bound inositol in human and cow's milk. J Nutr Sci Vitaminol (Tokyo) 1975;21 : 129. 14. Bromberger P, Hailman M. Myoinositol in small preterm infants: relationship between intake and serum concentration. J Pediati" Gastroenter Nutr 1986;5:455. 15. Michell RH. Inositol phospholipids and cell surface receptor function. Biochim Biophys Acta 1975;415:81. 16. Burton LE, Wells WW: myo-Inositol metabolism during lactation and development in the rat: the prevention of lactation-induced fatty liver by dietary myo-inositol. J Nutr 1976;106:1617. 17. Chu S-HW, Hegsted DM: myo-Inositol deficiency in gerbils: changes in phospholipid composition of intestinal microsomes. J Nutr 1980;110;1217.
6 10
Hallman, Arjomaa, and Hoppu
18. Eagle H, Oyama V1, Levy M, Freeman AE: myo-Inositol as an essential growth factor for normal and malignant human cells in tissue culture. J Bioi Chem 1957;226:191. 19. Hallman M. Effect of extracellular myo-inositol on surfactant phospholipid synthesis in the fetal rabbit lung. Biochim Biophys Acta 1984;797:67. 20. Pace CS, Clements RS: rnyo-lnositol and the maintenance of /3-cell function in cultured rat pancreatic islets. Diabetes 1981;30:621. 21. Greene DA, DeJesus PV Jr, Winegrad AI. Effects of insulin and dietary myo-inositol on impaired peripheral nerve conduction velocity in acute streptozotocin diabetes. J Clin Invest 1975;55;1326: 22. Gregersen G, Bertelsen B, Harbo H, et al. Oral supplementation of my0inositol: effects on peripheral nerve function in human diabetics and on the concentration in plasmas erythrocytes, urine arid muscle tissue in human diabetics and normals. Acta Neurol Scand 1983;67:164. 23. Hallman M, J~irvenp/i/i A-L, Pohjavuori M. Inositol suppiementation to preterm infants: a double blind study demonstrating reduction in severity of RDS. Arch Dis Child 1986;61:1076. 24. De Jesus PV Jr, Clements RS, Winegrad AI. Hypermyoinositolemic polyneuropathy in rats: a possible mechanism for uremic polyneuropathy. J Neurol Sci 1974;21:237.
The Journal of Pediatrics April 1987 25. Garcia-Bunuel L, Garcia- Bunuel VM. Enzymatic determination of f?ee myoinositol in human cerebrospinal fluid and plasma. J Lab Clin Med 1964;64:468. 26. Ctements RS Jr, Starnes WR. A n improved method for the ~leterminatiori of urinary myo-inositol by gas-liquid chromatography. Biochem Med 1975;12:200. 27. Dixon WL BMDP statistical software. Berkeley, Calif.: University of California Press; 1985. 28. Baden M, Bauer CB, Colle E, Klein G, Taeusch HW Jr, Stern L. A controlled trial of hydrocortisone therapy in infants With respiratory distress syndrome. Pediatrics 1972;50i526. 29. Reddy CC, Pierzchala PA, Hamilton GA. myo-Inositol oxygenase from hog kidney. J Biol Chem 1981;256:8519. 30. Andrews WHH, Britton HG, Hugget A St G, Nixon DA. Fructose metabolism in the isolated perfused liver of the t'oetal and newborn sheep. J. Physiol Lond 1960;153:199. 31. Hammerman MR, Sacktor B, Daughaday WH. myO-tnositol transport in renal brush border vesicles and its inhibition by o-glucose. Am J Physiol 1980;239:F113. 32. Molitoris BA, Hruska KA, Fishman N, Daughaday WH. Effects of glucose and parathyroid hormone on the renal handling of myoinosito! by isolated perfused dog kidneys. J Clin Invest 1979;63:1110.