0021-972X/92/7404-0906$03.00/0 Journal of Clinical Endocrinology Copyright 0 1992 by The Endocrine
and Metabolism Society
Renal Handling Velocity during Short Children SOROKU SHINICHI
NISHIYAMA, TOMOEDA,
Department
of
Pediatrics,
Vol. 74, No. 4 Printed in U.S.A.
of Phosphate Can Predict Growth Hormone Therapy MASAYUKI ICHIRO
AND
Kumamoto
University
IKUTA, TOSHIRO MATSUDA Medical
NAKAMURA,
School, Kumamoto
ABSTRACT. Renal tubular reabsorption of phosphate in response to GH administration was studied in 28 short Japanese children, aged 5-11 yr (height SD score, C-2.0 SD). Three groups included a classical GH deficiency (group 1; n = 12), a partial GH deficiency (group 2; n = 7), and children with non-GH deficiency (group 3; n = 9), depending on the peak response of serum GH in four provocative tests. Serum phosphorus, alkaline phosphatase, insulin-like growth factor-I (IGF-I), osteocalcin, and ratio of the maximum tubular reabsorption rate for phosphorus to the glomerular filtration rate (Tmp/GFR) were all significantly lower in group 1 compared with findings in groups 2 and 3 (P < 0.05, P < 0.01, and P < 0.001). After the administration of GH (0.1 U/kg. day) for 4 consecutive days, increments in serum phosphorus and Tmp/GFR were significantly higher in group 1 than in group 2 (P < 0.01 and P < 0.01) or group 3
Height for
860, Japan
(P < 0.01 and P c O.Ol), whereas the increment in IGF-I was similar in all 3 groups, and the levels of serum alkaline phosphatase and osteocalcin remained unchanged in all 3 groups. The calculated ratio of the increment in Tmp/GFR to the increment in IGF-I (A Tmp/GFR/A IGF-I) was highest in group 1, intermediate in group 2, and lowest in group 3 (P < 0.001). One year after the GH treatment (0.5 U/kg.week), height velocity was 7.9 + 2.2 cm/yr in group 1 and 5.9 f 1.2 cm/yr in group 2; no child in group 3 was treated. When the above calculated parameters, A Tmp/GFR/A IGF-I and increment in height velocity (difference between pre- and posttherapy values), were taken into account, there was a significant positive correlation (n = 19; r = 0.78; P < 0.001). This parameter can be used for purposes of predicting the outcome after 1 yr of GH therapy. (J Clin Endocrinol Metub 74: 906-909, 1992)
T
HE RENAL tubular reabsorption of phosphate is enhanced during GH treatment in humans (l-3) and is decreased by the administration of an antagonist to GH-releasing factors in immature animals (4). The changes seemed to depend on additional factors (1, 5) or a compound such as insulin-like growth factor-I (IGF-I) (6), rather than on a direct effect of GH on the target tissue. Serum levels of osteocalcin and alkaline phosphatase, indicators of bone metabolism, are elevated during GH administration, but several months pass before there is evidence of any significant increase (7,8). Several effects of GH on body function are mediated by IGF-I (9), yet the serum level of IGF-I does not always reflect the physiological activity on the target tissue (10). We examined renal handling of phosphate in response to changes in serum IGF-I during GH treatment of short children. The calculated parameter at the initiation of the treatment, an increment in the maximum reabsorption rate of phosphate at a given increment in IGF-I,
correlated treatment.
well with
height
Materials
velocity
(HV)
1 yr after
and Methods
Twenty-eight Japanese children of short stature (c-2.0 SD) were studied. All patients remained prepubertal (Tanner breast/genitalia) throughout the study period. Informed consent for the study was obtained from the parents. No child had gonadal dysgenesis, malnutrition, or any identified underlying systemic disease. All patients were euthyroid at the time of the study. Four provocative tests for GH secretion, iv administration of arginine (0.5 g/kg), iv administration of insulin (0.1 U/ kg), oral administration of levodopa (10 mg/kg), and oral administration of clonidine (0.1 mg/m’), were used to evaluate GH secretion. An adequate GH response was defined when a peak serum GH level of more than 7.0 pg/L was obtained in response to these tests. Based on the peak levels, the children were classified into three groups. At least 12 months of pretreatment growth records for each child were available. Twelve children (nine males and three females) had a peak GH level less than 7.0 pg/L in all four tests (group 1). The chronological age (CA), bone age (BA), and pretreatment HV of the last year (pre-HV) were 7.9 + 3.0 yr (mean f SD), 5.4 f 3.2 yr (mean + SD), and 3.7 f 0.8 cm/yr (mean f SD), respectively. These subjects were diagnosed as having classical isolated GH deli-
Received June 6, 1991. * Address correspondence and reprint requests to: S. Nishiyama, M.D., Department of Pediatrics, Kumamoto University Medical School, l-l-l Homjo, Kumamoto 860, Japan. 906
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RENAL
PHOSPHATE
ciency (n = 8) or idiopathic hypopituitarism (n = 4). The latter patients had a mean Tq level of 80 pg/m2.day, and serum T4 concentrations were maintained in the normal range; 5-8 mg/ day cortisol replacement was required by individual conditions. Seven children (five boys and two girls) had a peak GH level below 7 pg/L in any two of these tests (group 2). The CA, BA, and pre-HV were 8.6 & 3.1 yr, 6.7 + 2.7 yr, and 3.9 + 0.9 cm/ yr, respectively. A partial GH deficiency was evident. Other hormonal levels were within normal limits. Nine children (five boys and four girls) had a peak GH level of 10 pg/L or more in all four tests (group 3). The CA, BA, and pre-HV were 8.9 + 2.4 yr, 7.3 + 1.8 yr, and 4.1 + 1.2 cm/yr, respectively. Here, the diagnosis was short children without GH deficiency. Renal phosphate for 4 days
reabsorption
rate during
GH administration
The mealsprovided contained approximately 1600 Cal/day, 2 g/kg-day protein, 400 mg/day calcium, and 600 mg/day phosphorus3 days before and every day of the tests. Before the examination, the children consumedapproximately 1800 Cal/ day, 2.5 g/kg.day protein, 550 mg/day calcium, and 900 mg/ day phosphorus.Maximum tubular reabsorption rate for phosphorus/glomerular filtration rate ratio (Tmp/GFR) in the children was evaluated while they were receiving the phosphatedeficient diets. Human biosynthetic somatropin (human GH, 0.1 U/kg) was given im at 1300 h for 4 days. Fasting blood sampleswere collected before and 5 days after treatment, and serum concentrations of calcium, phosphorus, creatinine, alkaline phosphatase,IGF-I, immunoreactive PTH (iPTH), and osteocalcinwere examined. Two-hour urine sampleswere also obtained simultaneouslyto measurethe concentrations of calcium, phosphorus,and creatinine. The Tmp/GFR was calculated by the method of Walton and Bijvoet (11). GH therapy
The children in groups 1 and 2 were injected SCwith human biosynthetic somatropin (0.5 U/kg/week) five to seventimes a week for over 1 yr. The mean number of times that children weregiven GH per week did not differ in the two groups.Height wasmeasuredevery 2 months at each visit using an anthropometer (Yamakoshi Co., Tokyo, Japan), and HV (centimeters per yr) was comparedto findings during the last 1 yr of the pretreatment. Calcium, phosphorus,creatinine, and alkaline phosphatase levels were measuredusing an autoanalyzer (Technicon Co., Tarrytown, NY). Serum IGF-I levels were measuredusing RIA kits (Nichols Institute, San Juan Capistrano, CA). The intraand interassay coefficients of variation were 5.7% and 9.2%, respectively. Serum GH was measuredby RIA with antihuman GH antiserum, obtained by immunization of a rabbit with synthetic human GH (Eiken ICL, Tokyo, Japan). Antirabbit y-globulin goat serum, the samesynthetic GH, and synthetic [‘251]GH were used as a secondantibody, a standard, and a tracer, respectively. This assaydetected aslittle as 1 pg/L GH, and the intra- and interassay coefficients of variation were 6.2%and 8.5%, respectively. SerumiPTH levelswere measured using iPTH kits capable of detecting a midportion of the
HANDLING
AND
HV
907
peptide (Yamasa Shoyu Co., Tokyo, Japan), carried out as describedpreviously (12). Serum osteocalcinlevels were measured using RIA kits (Immunonuclear Co., Stillwater, MN), carried out as describedpreviously (13). Student’s paired and nonpaired t tests, linear regressionline analysis, and one-way analysis of variance were usedfor statistical assessmentof the data.
Results The levels of serum phosphorus and Tmp/GFR in group 1 were significantly lower than those in group 2 (P < 0.01 and P < 0.01, respectively) and group 3 (P < 0.01 and P < 0.001, respectively). IGF-1 levels were lowest in group 1, intermediate in group 2, and highest in group 3 (P < 0.001). Four days after GH loading, the levels of serum phosphorus were significantly increased from 1.50 +- 0.14 (mean f SD) to 1.68 + 0.13 mmol/L in group 1 (P < O.Ol), and Tmp/GFR increased from 4.17 & 0.72 (mean f SD) to 6.10 + 0.82 in group 1 (P C O.OOl), but not in other groups. IGF-I levels were significantly elevated in all three groups (P < 0.001, P < 0.001, and P < 0.001, respectively). Increments in serum phosphorus (A Pi) and Tmp/GFR (A Tmp/GFR) in group 1 were significantly higher than those in group 2 (P < 0.01 and P < 0.01) or group 3 (P < 0.01 and P < O.Ol), but the increment in IGF-I (A IGF-I) did not differ in all three groups (Table 1). The ratio of the increment in Tmp/ GFR to the increment in IGF-I (A Tmp/GFR/A IGF-I) in individuals is shown in Fig. 1. The parameter was highest in group 1, intermediate in group 2, and lowest in group 3 (P < 0.001). In group 1, the response of the ratio of A Tmp/GFR to A IGF-I was 2.76 + 2.12 in the patients with idiopathic hypopituitarism and 2.66 + 1.02 in those with isolated GH deficiency (not significant). Other factors, including A IGF-I and A Tmp/GFR, did not differ between the two groups. Four days after GH loading, the amount of urinary calcium increased from 0.22 f 0.08 (mean + SD) to 0.68 + 0.14 mol/mol creatinine (cr) in group 1, from 0.31 + 0.08 to 0.37 + 0.08 mol/ mol cr in group 2, and from 0.25 + 0.05 to 0.28 + 0.11 mol/mol cr in group 3; the difference was significant only in group 1 (P < 0.05). Serum iPTH levels did not differ among the three groups or in any group before and after GH loading (data not shown). The levels of serum alkaline phosphatase and osteocalcin were 2.98 + 0.75 (mean + SD) pkat/L and 9.5 f 2.3 pg/L (mean f SD) in group 1, 4.08 f 0.96 pkat/L and 14.5 -+ 4.5 pg/L in group 2, and 4.40 +- 0.70 pkat/L and 15.1 + 5.2 pg/L in group 3, respectively. The levels of these two parameters in group 1 were significantly lower than those in group 2 (P < 0.05 and P < 0.05) or group 3 (P < 0.05 and P < 0.05). After GH loading, the levels of serum alkaline phosphatase and osteocalcin did not differ in any group (data not shown). One year after the therapy, HV was 7.9 + 2.2
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908 TABLE
NISHIYAMA 1. Basal
concentrations
and increments Pi (mmol/L)
Group Group Group
1 (n = 12) 2 (n = 7) 3 (n = 9)
(A) of serum A Pi (mmol/L)
1.50 * 0.14 1.65 + 0.13b 1.68 + 0.15b
0.18 + 0.10 0.07 + 0.05b 0.07 + 0.05b
Values are the mean + SD. By one-way analysis of variance, a P < 0.001, basal concentrations us. values after GH loading b P < 0.01 us. group 1. cP < 0.001 vs. group 1.
7-
6-
z u
5
2 g .
4-
F Q
3-
2-
1 -
. .I. . I
Group
I
phosphorous IGF-1
and IGF-I, b.4J
and Tmp/GFR A IGF-I
59 + 37 118 f 56* 242 + 134’
after
GH-loading
(fig/L)
158 + 154” 213 k 154” 270 3~ 101”
group 1 < group 2 < group 3 for IGF-I (pretreatment plus increment values).
test in three
groups
Tmp/GFR
A Tmp/GFR
4.17 f 0.72 4.89 z!z 0.51* 5.31 f 0.50”
1.94 + 0.86 0.43 + 0.11* 0.40 + 0.38’
(P < 0.001).
Q
1
2
3
A
Tmp/
4
5
6
7
8
GFR/A IGF-1
,i,
1
2
3
FIG. 1. Individual values of A Tmp/GFR/A IGF-I after 4 days of GH loading in three groups. By one-way analysis of variance (group 1 > group 2 > group 3), the difference was statistically significant (P < 0.001). A horizontal and a vertical line represent the mean -C SD. The increment in IGF-I (A IGF-I) was expressed as units per mL. 1 U/mL = 220 pg/L IGF-I.
cm/yr in group 1 and 5.9 + 1.2 cm/yr in group 2, while it was 4.0 f 1.3 cm/yr in group 3 during the same period. Levels of A Tmp/GFR/A IGF-I in the 4 days of GH loading obtained before consistent GH therapy and increments in HV after the therapy (difference between pre- and posttherapy values) in group 1 and 2 children are shown in Fig. 2. There was a significant positive correlation between these two parameters (P < 0.001; r = 0.78; n = 19), whereas this significant relationship appeared to be present only in the children with classical GH deficiency. There was no apparant relationship among other parameters, including basal IGF-I, A IGFI, and increment in HV after the therapy, in either group. Discussion Serum phatase, lower in than in
JCE & M .1992 Vol74.No4
ET AL.
concentrations of phosphorus, alkaline phosIGF-I, and osteocalcin and Tmp/GFR were children with classical GH deficiency (group 1) those with partial GH deficiency (group 2) or
FIG. 2. Relationship between GH loading and increment treatment for 1 yr (y = 0.83x increment in IGF-I (A IGF-I) = 220 rg/L IGF-I. 0, Group (partial GH deficiency).
A Tmp/GFR/A IGF-I after short term in HV (centimeters per yr) after GH + 1.50; r = 0.78; n = 19; P < 0.001). The was expressed as units per mL. 1 U/mL 1 (classical GH deficiency); 0, group 2
those without GH deficiency (group 3). A pattern of group 1 < 2 < 3 was observed for the IGF-I level, a condition which sustained the serum IGF-I level and clearly depended on the status of GH secretion. These observations are comparable to previous findings (14, 15). Four days after GH administration, serum IGF-I concentrations were elevated in children in all three groups. Serum concentrations of phosphorus, Tmp/GFR, and urinary calcium excretion were significantly increased only in group 1. Elevations in serum phosphorus, renal reabsorption of phosphate (l-3), and urinary calcium excretion (16) in response to GH administration were observed by other workers. There are data that IGF-I can stimulate renal phosphate transport both in uiuo and in vitro (17). Receptors for IGF-I have been isolated from the proximal tubular cell plasma membrane (18); thus, IGF-I alone or in concert with GH seems to be involved in phosphate reabsorption by the kidney. Data from Gray’s group (19, 20) suggest that IGF-I is required for elevation of serum 1,25dihydroxyvitamin DB [1,25-(OH)2D3] levels in response to phosphate dep-
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RENAL
PHOSPHATE
rivation. Our observation that GH administration increased Tmp/GFR and urinary calcium excretion in group 1 might partly relate to the increased 1,25-(OH)2D3 under conditions of phosphate deprivation; however, the serum concentration of 1,25-(OH)zD3 was not measured in our study. The unique observation in our study is that the increment in Tmp/GFR at a given increment in IGF-I concentration (A Tmp/GFR/A IGF-I) differed among the groups. The pattern of group 1 > 2 > 3 for this parameter indicates that the tubular response of phosphate reabsorption is most sensitive in children with classical GH deficiency, intermediate in children with partial GH deficiency, and rather blunt in children without GH deficiency. The condition was potentially related to the basal level of IGF-I, which was lowest in group 1, intermediate in group 2, and highest in group 3, as discussed above. The iPTH level seems to be intact, since no changes were observed during our study. Increased renal phosphate reabsorption in neonates and phosphate-deprived adults was also found to be independent of PTH (21, 22). Another new observation is that the calculated parameter, A Tmp/GFR/A IGF-I, obtained at the initiation of GH therapy positively correlated with the increment in HV 1 yr after the therapy. Thus, phosphorus plays an important role in body growth, and a parameter showing sensitivity of renal handling of phosphate can serve to predict the outcome of GH treatment to improve HV, albeit limited to the classical type of GH deficiency and after 1 yr of GH therapy. Acknowledgment We are indebted to M. Ohara for critical comments. References 1. Corvilain J, Abramow M. Growth and renal control of plasma phosphate. J Clin Endocrinol Metab. 1972;34:452-9. 2. Gertner JM, Horst RL, Broadus AE, Rasmussen H, Gene1 M. Parathyroid function and vitamin D metabolism during human growth hormone replacement. J Clin Endocrinol Metab. 1979;49:185-8. 3. Brautbar N, Lee DNB, Coburn JW, Kleeman CR. Soft tissue and bone mineral changes in experimental phosphate depletion: the role of growth and growth hormone. Mineral Electrolyte Metab. 1981;5:304-10.
HANDLING
AND HV
909
4. Mulroney SE, Lumpkin MD, Haramati A. Antagonist to GHreleasing factor inhibits growth and Pi reabsorption in immature rats. Am J Physiol. 1989;257:F29-34. 5. Westby GR, Goldfarb S, Goldberg M, Agus ZS. Acute effects of bovine growth hormone on renal calcium and phosphate excretion. Metabolism. 1977;26:525-30. 6. Caverzasio J, Bonjour J-P. Influence of IGF-I (somatomedin C) on sodium-dependent phosphate transport in cultured renal epithelium. Proe Clin Biol Res. 1988:88:385-6. 7. Nishiyama S, Tomoeda S, Ikuta M, Matsuda I. Bone metabolism during treatment with growth hormone in patients with growth hormone deficiency and delayed adolesence. Acta Paediatr Stand. 1989;356(Suppl):141. 8. Kruse K, Kracht U. Evaluation of serum osteocalcin as an index of altered bone metabolism. Eur J Pediatr. 1986;145:27-33. 9. Guler H-P, Zapf J, Froesch ER. Short-term metabolic effects of recombinant human insulin-like growth factor 1 in healthy adults. N Engl J Med. 1987;317:137-40. 10. Bala RM, Lopataka J, Leung A, McCoy E, Mcarthur RG. Serum immunoreactive somatomedin levels in normal adults, pregnant women at term, children at various ages, and children with constitutional delayed growth. J Clin Endocrinol Metab. 1981;52:508-12. 11. Walton RJ, Bijvoet OLM. Nomogram for derivation of renal threshold phosphated concentration. Lancet. 1975;2:309-10. 12. Nishiyama S, Tomoeda S, Inoue F, Matsuda I. Self-limited neonatal familial hyperparathyroidism associated with hypercalciuria and renal tubular acidosis in three siblings. Pediatrics. 1990;86:421-7. 13. Nishiyama S, Tomoeda S, Ohta T, Higuchi A, Matsuda I. Differences in basal and postexercise osteocalcin levels in athletic and nonathletic humans. Calcif Tissue Int. 1988,43:150-4. 14. Lin T-H, Kirkland RT, Sherman BM, Kirkland JL. Growth hormone testing in short children and their response to growth hormone therapy. J Pediatr. 1989;115:57-63. 15. Schwarz ID, Hu C-S, Shulman DI, Root AW, Bercu BB. Linear growth response to exogenous growth hormone in children with short stature. AJDC. 1990;144:1092-7. 16. Gertner JM, Tamborlane WV, Hinz RL, Horst RL, Gene1 M. The effects of mineral metabolism of overnight growth hormone infusion in growth hormone deficiency. J Clin Endocrinol Metab. 1981;53:818-22. 17. Caverzasio J, Bonjour J-P. Stimulatory effects of recombinant IGFI (somatomedin C) on renal phosphate (Pi) transport in uiuo and in epithelial cell culture [Abstract]. Proc of the 10th Int Congr of Nephrology. 1987;418. 18. Hammerman M, Rogers S. Distribution of IGF receptors in the plasma membrane of proximal tubular cells. Am J Physiol. 1987;253:F841-7. 19. Gray RW, Garthwaite TL. Activation of renal 1,25dihydroxyvitamin Ds synthesis by phosphate deprivation: evidence for a role for growth hormone. Endocrinology. 1985;116:189-93. 20. Gray RW. Evidence that somatomedins mediate the effect of hypophosphatemia to increase serum 1,25dihydroxyvitamin D1 levels in rats. Endocrinology. 1987;121:504-12. 21. Haramati A, Mulroney SE, Webster SK. Developmental change in the tubular capacity for phosphate reabsorption in the rat. Am J Physiol. 1988;255:F287-91. 22. Webster SK, Haramati A. Developmental changes in the phosphaturic response to parathyroid hormone in the rat. Am J Physiol. 1985;249:F251-5.
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and Metabolism Society
Renal Handling Velocity during Short Children SOROKU SHINICHI
NISHIYAMA, TOMOEDA,
Department
of
Pediatrics,
Vol. 74, No. 4 Printed in U.S.A.
of Phosphate Can Predict Growth Hormone Therapy MASAYUKI ICHIRO
AND
Kumamoto
University
IKUTA, TOSHIRO MATSUDA Medical
NAKAMURA,
School, Kumamoto
ABSTRACT. Renal tubular reabsorption of phosphate in response to GH administration was studied in 28 short Japanese children, aged 5-11 yr (height SD score, C-2.0 SD). Three groups included a classical GH deficiency (group 1; n = 12), a partial GH deficiency (group 2; n = 7), and children with non-GH deficiency (group 3; n = 9), depending on the peak response of serum GH in four provocative tests. Serum phosphorus, alkaline phosphatase, insulin-like growth factor-I (IGF-I), osteocalcin, and ratio of the maximum tubular reabsorption rate for phosphorus to the glomerular filtration rate (Tmp/GFR) were all significantly lower in group 1 compared with findings in groups 2 and 3 (P < 0.05, P < 0.01, and P < 0.001). After the administration of GH (0.1 U/kg. day) for 4 consecutive days, increments in serum phosphorus and Tmp/GFR were significantly higher in group 1 than in group 2 (P < 0.01 and P < 0.01) or group 3
Height for
860, Japan
(P < 0.01 and P c O.Ol), whereas the increment in IGF-I was similar in all 3 groups, and the levels of serum alkaline phosphatase and osteocalcin remained unchanged in all 3 groups. The calculated ratio of the increment in Tmp/GFR to the increment in IGF-I (A Tmp/GFR/A IGF-I) was highest in group 1, intermediate in group 2, and lowest in group 3 (P < 0.001). One year after the GH treatment (0.5 U/kg.week), height velocity was 7.9 + 2.2 cm/yr in group 1 and 5.9 f 1.2 cm/yr in group 2; no child in group 3 was treated. When the above calculated parameters, A Tmp/GFR/A IGF-I and increment in height velocity (difference between pre- and posttherapy values), were taken into account, there was a significant positive correlation (n = 19; r = 0.78; P < 0.001). This parameter can be used for purposes of predicting the outcome after 1 yr of GH therapy. (J Clin Endocrinol Metub 74: 906-909, 1992)
T
HE RENAL tubular reabsorption of phosphate is enhanced during GH treatment in humans (l-3) and is decreased by the administration of an antagonist to GH-releasing factors in immature animals (4). The changes seemed to depend on additional factors (1, 5) or a compound such as insulin-like growth factor-I (IGF-I) (6), rather than on a direct effect of GH on the target tissue. Serum levels of osteocalcin and alkaline phosphatase, indicators of bone metabolism, are elevated during GH administration, but several months pass before there is evidence of any significant increase (7,8). Several effects of GH on body function are mediated by IGF-I (9), yet the serum level of IGF-I does not always reflect the physiological activity on the target tissue (10). We examined renal handling of phosphate in response to changes in serum IGF-I during GH treatment of short children. The calculated parameter at the initiation of the treatment, an increment in the maximum reabsorption rate of phosphate at a given increment in IGF-I,
correlated treatment.
well with
height
Materials
velocity
(HV)
1 yr after
and Methods
Twenty-eight Japanese children of short stature (c-2.0 SD) were studied. All patients remained prepubertal (Tanner breast/genitalia) throughout the study period. Informed consent for the study was obtained from the parents. No child had gonadal dysgenesis, malnutrition, or any identified underlying systemic disease. All patients were euthyroid at the time of the study. Four provocative tests for GH secretion, iv administration of arginine (0.5 g/kg), iv administration of insulin (0.1 U/ kg), oral administration of levodopa (10 mg/kg), and oral administration of clonidine (0.1 mg/m’), were used to evaluate GH secretion. An adequate GH response was defined when a peak serum GH level of more than 7.0 pg/L was obtained in response to these tests. Based on the peak levels, the children were classified into three groups. At least 12 months of pretreatment growth records for each child were available. Twelve children (nine males and three females) had a peak GH level less than 7.0 pg/L in all four tests (group 1). The chronological age (CA), bone age (BA), and pretreatment HV of the last year (pre-HV) were 7.9 + 3.0 yr (mean f SD), 5.4 f 3.2 yr (mean + SD), and 3.7 f 0.8 cm/yr (mean f SD), respectively. These subjects were diagnosed as having classical isolated GH deli-
Received June 6, 1991. * Address correspondence and reprint requests to: S. Nishiyama, M.D., Department of Pediatrics, Kumamoto University Medical School, l-l-l Homjo, Kumamoto 860, Japan. 906
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RENAL
PHOSPHATE
ciency (n = 8) or idiopathic hypopituitarism (n = 4). The latter patients had a mean Tq level of 80 pg/m2.day, and serum T4 concentrations were maintained in the normal range; 5-8 mg/ day cortisol replacement was required by individual conditions. Seven children (five boys and two girls) had a peak GH level below 7 pg/L in any two of these tests (group 2). The CA, BA, and pre-HV were 8.6 & 3.1 yr, 6.7 + 2.7 yr, and 3.9 + 0.9 cm/ yr, respectively. A partial GH deficiency was evident. Other hormonal levels were within normal limits. Nine children (five boys and four girls) had a peak GH level of 10 pg/L or more in all four tests (group 3). The CA, BA, and pre-HV were 8.9 + 2.4 yr, 7.3 + 1.8 yr, and 4.1 + 1.2 cm/yr, respectively. Here, the diagnosis was short children without GH deficiency. Renal phosphate for 4 days
reabsorption
rate during
GH administration
The mealsprovided contained approximately 1600 Cal/day, 2 g/kg-day protein, 400 mg/day calcium, and 600 mg/day phosphorus3 days before and every day of the tests. Before the examination, the children consumedapproximately 1800 Cal/ day, 2.5 g/kg.day protein, 550 mg/day calcium, and 900 mg/ day phosphorus.Maximum tubular reabsorption rate for phosphorus/glomerular filtration rate ratio (Tmp/GFR) in the children was evaluated while they were receiving the phosphatedeficient diets. Human biosynthetic somatropin (human GH, 0.1 U/kg) was given im at 1300 h for 4 days. Fasting blood sampleswere collected before and 5 days after treatment, and serum concentrations of calcium, phosphorus, creatinine, alkaline phosphatase,IGF-I, immunoreactive PTH (iPTH), and osteocalcinwere examined. Two-hour urine sampleswere also obtained simultaneouslyto measurethe concentrations of calcium, phosphorus,and creatinine. The Tmp/GFR was calculated by the method of Walton and Bijvoet (11). GH therapy
The children in groups 1 and 2 were injected SCwith human biosynthetic somatropin (0.5 U/kg/week) five to seventimes a week for over 1 yr. The mean number of times that children weregiven GH per week did not differ in the two groups.Height wasmeasuredevery 2 months at each visit using an anthropometer (Yamakoshi Co., Tokyo, Japan), and HV (centimeters per yr) was comparedto findings during the last 1 yr of the pretreatment. Calcium, phosphorus,creatinine, and alkaline phosphatase levels were measuredusing an autoanalyzer (Technicon Co., Tarrytown, NY). Serum IGF-I levels were measuredusing RIA kits (Nichols Institute, San Juan Capistrano, CA). The intraand interassay coefficients of variation were 5.7% and 9.2%, respectively. Serum GH was measuredby RIA with antihuman GH antiserum, obtained by immunization of a rabbit with synthetic human GH (Eiken ICL, Tokyo, Japan). Antirabbit y-globulin goat serum, the samesynthetic GH, and synthetic [‘251]GH were used as a secondantibody, a standard, and a tracer, respectively. This assaydetected aslittle as 1 pg/L GH, and the intra- and interassay coefficients of variation were 6.2%and 8.5%, respectively. SerumiPTH levelswere measured using iPTH kits capable of detecting a midportion of the
HANDLING
AND
HV
907
peptide (Yamasa Shoyu Co., Tokyo, Japan), carried out as describedpreviously (12). Serum osteocalcinlevels were measured using RIA kits (Immunonuclear Co., Stillwater, MN), carried out as describedpreviously (13). Student’s paired and nonpaired t tests, linear regressionline analysis, and one-way analysis of variance were usedfor statistical assessmentof the data.
Results The levels of serum phosphorus and Tmp/GFR in group 1 were significantly lower than those in group 2 (P < 0.01 and P < 0.01, respectively) and group 3 (P < 0.01 and P < 0.001, respectively). IGF-1 levels were lowest in group 1, intermediate in group 2, and highest in group 3 (P < 0.001). Four days after GH loading, the levels of serum phosphorus were significantly increased from 1.50 +- 0.14 (mean f SD) to 1.68 + 0.13 mmol/L in group 1 (P < O.Ol), and Tmp/GFR increased from 4.17 & 0.72 (mean f SD) to 6.10 + 0.82 in group 1 (P C O.OOl), but not in other groups. IGF-I levels were significantly elevated in all three groups (P < 0.001, P < 0.001, and P < 0.001, respectively). Increments in serum phosphorus (A Pi) and Tmp/GFR (A Tmp/GFR) in group 1 were significantly higher than those in group 2 (P < 0.01 and P < 0.01) or group 3 (P < 0.01 and P < O.Ol), but the increment in IGF-I (A IGF-I) did not differ in all three groups (Table 1). The ratio of the increment in Tmp/ GFR to the increment in IGF-I (A Tmp/GFR/A IGF-I) in individuals is shown in Fig. 1. The parameter was highest in group 1, intermediate in group 2, and lowest in group 3 (P < 0.001). In group 1, the response of the ratio of A Tmp/GFR to A IGF-I was 2.76 + 2.12 in the patients with idiopathic hypopituitarism and 2.66 + 1.02 in those with isolated GH deficiency (not significant). Other factors, including A IGF-I and A Tmp/GFR, did not differ between the two groups. Four days after GH loading, the amount of urinary calcium increased from 0.22 f 0.08 (mean + SD) to 0.68 + 0.14 mol/mol creatinine (cr) in group 1, from 0.31 + 0.08 to 0.37 + 0.08 mol/ mol cr in group 2, and from 0.25 + 0.05 to 0.28 + 0.11 mol/mol cr in group 3; the difference was significant only in group 1 (P < 0.05). Serum iPTH levels did not differ among the three groups or in any group before and after GH loading (data not shown). The levels of serum alkaline phosphatase and osteocalcin were 2.98 + 0.75 (mean + SD) pkat/L and 9.5 f 2.3 pg/L (mean f SD) in group 1, 4.08 f 0.96 pkat/L and 14.5 -+ 4.5 pg/L in group 2, and 4.40 +- 0.70 pkat/L and 15.1 + 5.2 pg/L in group 3, respectively. The levels of these two parameters in group 1 were significantly lower than those in group 2 (P < 0.05 and P < 0.05) or group 3 (P < 0.05 and P < 0.05). After GH loading, the levels of serum alkaline phosphatase and osteocalcin did not differ in any group (data not shown). One year after the therapy, HV was 7.9 + 2.2
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908 TABLE
NISHIYAMA 1. Basal
concentrations
and increments Pi (mmol/L)
Group Group Group
1 (n = 12) 2 (n = 7) 3 (n = 9)
(A) of serum A Pi (mmol/L)
1.50 * 0.14 1.65 + 0.13b 1.68 + 0.15b
0.18 + 0.10 0.07 + 0.05b 0.07 + 0.05b
Values are the mean + SD. By one-way analysis of variance, a P < 0.001, basal concentrations us. values after GH loading b P < 0.01 us. group 1. cP < 0.001 vs. group 1.
7-
6-
z u
5
2 g .
4-
F Q
3-
2-
1 -
. .I. . I
Group
I
phosphorous IGF-1
and IGF-I, b.4J
and Tmp/GFR A IGF-I
59 + 37 118 f 56* 242 + 134’
after
GH-loading
(fig/L)
158 + 154” 213 k 154” 270 3~ 101”
group 1 < group 2 < group 3 for IGF-I (pretreatment plus increment values).
test in three
groups
Tmp/GFR
A Tmp/GFR
4.17 f 0.72 4.89 z!z 0.51* 5.31 f 0.50”
1.94 + 0.86 0.43 + 0.11* 0.40 + 0.38’
(P < 0.001).
Q
1
2
3
A
Tmp/
4
5
6
7
8
GFR/A IGF-1
,i,
1
2
3
FIG. 1. Individual values of A Tmp/GFR/A IGF-I after 4 days of GH loading in three groups. By one-way analysis of variance (group 1 > group 2 > group 3), the difference was statistically significant (P < 0.001). A horizontal and a vertical line represent the mean -C SD. The increment in IGF-I (A IGF-I) was expressed as units per mL. 1 U/mL = 220 pg/L IGF-I.
cm/yr in group 1 and 5.9 + 1.2 cm/yr in group 2, while it was 4.0 f 1.3 cm/yr in group 3 during the same period. Levels of A Tmp/GFR/A IGF-I in the 4 days of GH loading obtained before consistent GH therapy and increments in HV after the therapy (difference between pre- and posttherapy values) in group 1 and 2 children are shown in Fig. 2. There was a significant positive correlation between these two parameters (P < 0.001; r = 0.78; n = 19), whereas this significant relationship appeared to be present only in the children with classical GH deficiency. There was no apparant relationship among other parameters, including basal IGF-I, A IGFI, and increment in HV after the therapy, in either group. Discussion Serum phatase, lower in than in
JCE & M .1992 Vol74.No4
ET AL.
concentrations of phosphorus, alkaline phosIGF-I, and osteocalcin and Tmp/GFR were children with classical GH deficiency (group 1) those with partial GH deficiency (group 2) or
FIG. 2. Relationship between GH loading and increment treatment for 1 yr (y = 0.83x increment in IGF-I (A IGF-I) = 220 rg/L IGF-I. 0, Group (partial GH deficiency).
A Tmp/GFR/A IGF-I after short term in HV (centimeters per yr) after GH + 1.50; r = 0.78; n = 19; P < 0.001). The was expressed as units per mL. 1 U/mL 1 (classical GH deficiency); 0, group 2
those without GH deficiency (group 3). A pattern of group 1 < 2 < 3 was observed for the IGF-I level, a condition which sustained the serum IGF-I level and clearly depended on the status of GH secretion. These observations are comparable to previous findings (14, 15). Four days after GH administration, serum IGF-I concentrations were elevated in children in all three groups. Serum concentrations of phosphorus, Tmp/GFR, and urinary calcium excretion were significantly increased only in group 1. Elevations in serum phosphorus, renal reabsorption of phosphate (l-3), and urinary calcium excretion (16) in response to GH administration were observed by other workers. There are data that IGF-I can stimulate renal phosphate transport both in uiuo and in vitro (17). Receptors for IGF-I have been isolated from the proximal tubular cell plasma membrane (18); thus, IGF-I alone or in concert with GH seems to be involved in phosphate reabsorption by the kidney. Data from Gray’s group (19, 20) suggest that IGF-I is required for elevation of serum 1,25dihydroxyvitamin DB [1,25-(OH)2D3] levels in response to phosphate dep-
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RENAL
PHOSPHATE
rivation. Our observation that GH administration increased Tmp/GFR and urinary calcium excretion in group 1 might partly relate to the increased 1,25-(OH)2D3 under conditions of phosphate deprivation; however, the serum concentration of 1,25-(OH)zD3 was not measured in our study. The unique observation in our study is that the increment in Tmp/GFR at a given increment in IGF-I concentration (A Tmp/GFR/A IGF-I) differed among the groups. The pattern of group 1 > 2 > 3 for this parameter indicates that the tubular response of phosphate reabsorption is most sensitive in children with classical GH deficiency, intermediate in children with partial GH deficiency, and rather blunt in children without GH deficiency. The condition was potentially related to the basal level of IGF-I, which was lowest in group 1, intermediate in group 2, and highest in group 3, as discussed above. The iPTH level seems to be intact, since no changes were observed during our study. Increased renal phosphate reabsorption in neonates and phosphate-deprived adults was also found to be independent of PTH (21, 22). Another new observation is that the calculated parameter, A Tmp/GFR/A IGF-I, obtained at the initiation of GH therapy positively correlated with the increment in HV 1 yr after the therapy. Thus, phosphorus plays an important role in body growth, and a parameter showing sensitivity of renal handling of phosphate can serve to predict the outcome of GH treatment to improve HV, albeit limited to the classical type of GH deficiency and after 1 yr of GH therapy. Acknowledgment We are indebted to M. Ohara for critical comments. References 1. Corvilain J, Abramow M. Growth and renal control of plasma phosphate. J Clin Endocrinol Metab. 1972;34:452-9. 2. Gertner JM, Horst RL, Broadus AE, Rasmussen H, Gene1 M. Parathyroid function and vitamin D metabolism during human growth hormone replacement. J Clin Endocrinol Metab. 1979;49:185-8. 3. Brautbar N, Lee DNB, Coburn JW, Kleeman CR. Soft tissue and bone mineral changes in experimental phosphate depletion: the role of growth and growth hormone. Mineral Electrolyte Metab. 1981;5:304-10.
HANDLING
AND HV
909
4. Mulroney SE, Lumpkin MD, Haramati A. Antagonist to GHreleasing factor inhibits growth and Pi reabsorption in immature rats. Am J Physiol. 1989;257:F29-34. 5. Westby GR, Goldfarb S, Goldberg M, Agus ZS. Acute effects of bovine growth hormone on renal calcium and phosphate excretion. Metabolism. 1977;26:525-30. 6. Caverzasio J, Bonjour J-P. Influence of IGF-I (somatomedin C) on sodium-dependent phosphate transport in cultured renal epithelium. Proe Clin Biol Res. 1988:88:385-6. 7. Nishiyama S, Tomoeda S, Ikuta M, Matsuda I. Bone metabolism during treatment with growth hormone in patients with growth hormone deficiency and delayed adolesence. Acta Paediatr Stand. 1989;356(Suppl):141. 8. Kruse K, Kracht U. Evaluation of serum osteocalcin as an index of altered bone metabolism. Eur J Pediatr. 1986;145:27-33. 9. Guler H-P, Zapf J, Froesch ER. Short-term metabolic effects of recombinant human insulin-like growth factor 1 in healthy adults. N Engl J Med. 1987;317:137-40. 10. Bala RM, Lopataka J, Leung A, McCoy E, Mcarthur RG. Serum immunoreactive somatomedin levels in normal adults, pregnant women at term, children at various ages, and children with constitutional delayed growth. J Clin Endocrinol Metab. 1981;52:508-12. 11. Walton RJ, Bijvoet OLM. Nomogram for derivation of renal threshold phosphated concentration. Lancet. 1975;2:309-10. 12. Nishiyama S, Tomoeda S, Inoue F, Matsuda I. Self-limited neonatal familial hyperparathyroidism associated with hypercalciuria and renal tubular acidosis in three siblings. Pediatrics. 1990;86:421-7. 13. Nishiyama S, Tomoeda S, Ohta T, Higuchi A, Matsuda I. Differences in basal and postexercise osteocalcin levels in athletic and nonathletic humans. Calcif Tissue Int. 1988,43:150-4. 14. Lin T-H, Kirkland RT, Sherman BM, Kirkland JL. Growth hormone testing in short children and their response to growth hormone therapy. J Pediatr. 1989;115:57-63. 15. Schwarz ID, Hu C-S, Shulman DI, Root AW, Bercu BB. Linear growth response to exogenous growth hormone in children with short stature. AJDC. 1990;144:1092-7. 16. Gertner JM, Tamborlane WV, Hinz RL, Horst RL, Gene1 M. The effects of mineral metabolism of overnight growth hormone infusion in growth hormone deficiency. J Clin Endocrinol Metab. 1981;53:818-22. 17. Caverzasio J, Bonjour J-P. Stimulatory effects of recombinant IGFI (somatomedin C) on renal phosphate (Pi) transport in uiuo and in epithelial cell culture [Abstract]. Proc of the 10th Int Congr of Nephrology. 1987;418. 18. Hammerman M, Rogers S. Distribution of IGF receptors in the plasma membrane of proximal tubular cells. Am J Physiol. 1987;253:F841-7. 19. Gray RW, Garthwaite TL. Activation of renal 1,25dihydroxyvitamin Ds synthesis by phosphate deprivation: evidence for a role for growth hormone. Endocrinology. 1985;116:189-93. 20. Gray RW. Evidence that somatomedins mediate the effect of hypophosphatemia to increase serum 1,25dihydroxyvitamin D1 levels in rats. Endocrinology. 1987;121:504-12. 21. Haramati A, Mulroney SE, Webster SK. Developmental change in the tubular capacity for phosphate reabsorption in the rat. Am J Physiol. 1988;255:F287-91. 22. Webster SK, Haramati A. Developmental changes in the phosphaturic response to parathyroid hormone in the rat. Am J Physiol. 1985;249:F251-5.
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