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The Pituitary-Adrenal Responses to Exogenous Human Corticotropin-Releasing Hormone in Preterm, Very Low Birth Weight Infants

Departments of Pediatrics and Chemical Pathology, Prince of Wales Hospital, The Chinese University of Hong Kong (C.W.K.L., D.C.F.C.); and the Department of Mathematics, The Hong Kong University of Science and Technology (M.Y.W.), Shatin, New Territories, Hong Kong

Address all correspondence and requests for reprints to: Dr. P. C. Ng, Department of Pediatrics, Level 6, Clinical Sciences Building, Prince of Wales Hospital, Shatin, New Territories, Hong Kong.

	Abstract

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To evaluate the pituitary-adrenal reserve and to standardize the methodology of performing the human CRH (hCRH) stimulation test, we performed the hCRH test on 14 preterm (<32 gestational weeks), very low birth weight infants, who did not receive antenatal or postnatal corticosteroid treatment, on days 7 and 14 of life. Blood samples were obtained 0 (baseline), 15, 30, and 60 min after an iv dose of hCRH (1 µg/kg). The plasma ACTH concentration rose from a basal value of 5.7 ± 0.6 pmol/L (mean ± SEM) to 11.9 ± 2.1 pmol/L (P < 0.005), 9.2 ± 1.2 pmol/L (P < 0.005), and 7.7 ± 0.8 pmol/L (P < 0.005) at 15, 30, and 60 min, respectively. The corresponding rises in serum cortisol from a basal concentration of 396 ± 67 nmol/L were 509 ± 71 nmol/L (P < 0.0001), 647 ± 62 nmol/L (P < 0.0001), and 578 ± 60 nmol/L (P < 0.0001). The plasma ACTH concentration consistently peaked early at 15 min, whereas the maximum cortisol response occurred 30 min post-hCRH stimulation. No significant differences were detected between the hCRH tests performed on days 7 and 14 (P > 0.15). Mechanical ventilation, infant gender, and mode of delivery did not significantly influence the hormonal responses (P > 0.25).

We have defined in this study the pattern, the magnitude of the pituitary-adrenal response, and the timing of the peak concentrations of plasma ACTH and serum cortisol in relation to a standard iv dose of hCRH. The hCRH test in very low birth weight infants appears to be safe and reproducible, and produces a pituitary-adrenal response comparable to that seen in older children and adults, indicating that pituitary-adrenal function is mature at these early stages of gestation.

	Introduction

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MUCH ATTENTION has been focused on the development and activity of the fetal and newborn adrenal gland in recent years, yet little is known about the function of the hypothalamic-pituitary higher centers in preterm, very low birth weight (VLBW) infants during the neonatal period. As high dose antenatal and postnatal dexamethasone are of proven value and now frequently prescribed for lessening the severity of respiratory distress syndrome (1) and for the treatment of bronchopulmonary dysplasia in preterm VLBW infants (2), it is important to evaluate their effect on hypothalamic-pituitary responsiveness to stressful stimuli and the degree of corticosteroid-induced suppression on the hormonal axis. A reliable and reproducible endocrine test to assess this function is required in VLBW infants. Two studies using ovine CRH (oCRH) have examined the pituitary reserve in preterm infants (3, 4), but were limited by few serially timed measurements, the infants were of variable postnatal ages, and a proportion of the mothers had received high dose antenatal corticosteroids for induction of fetal lung maturation (3, 4). To our knowledge, no evaluation of pituitary-adrenal function has been performed with human CRH (hCRH) in this group of infants. This study aims to prospectively examine in detail a cohort of preterm VLBW infants who have not received antenatal or postnatal corticosteroid treatment and to perform the hCRH stimulation test in a standardized fashion at defined time intervals after birth. The findings will enable us to delineate the pituitary-adrenal response more comprehensively and to standardize the methodology of performing the hCRH stimulation test in this group of very immature infants.

	Subjects and Methods

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Study population

Fourteen preterm infants were prospectively enrolled between August 1994 and July 1996. Inclusion criteria were 1) gestation less than 32 weeks and birth weight below 1500 g, 2) possession of an indwelling arterial cannulas on day 7 (a second hCRH test would also be performed if the arterial cannulas was still in situ on day 14), and 3) no antenatal or postnatal corticosteroid treatment. Antenatal dexamethasone was not given to mothers of these infants because in most cases delivery was imminent, and in two cases, steroid treatment was contraindicated because of maternal chorioamnionitis and acute intestinal obstruction. Gestational age was assessed by the mother’s last menstrual period, early ultrasound dating, and new Ballard score examination (5). Infants were excluded if they had concurrent hypoglycemia, systemic infection, necrotizing enterocolitis, or major surgery in the preceding week.

hCRH stimulation test

We chose to perform the hCRH stimulation test following a standard schedule on days 7 and 14 as we did not wish to disturb these sick immature infants during their first few days of intensive care treatment and also to allow time for elimination of placental hormones from their circulations. The test was performed between 0800–1000 h. Each vial (100 µg) of synthetic hCRH (Ferring, Arzneimittel, Wittland, Germany) was reconstituted and further diluted with sterile water to obtain a concentration of 2 µg/mL. Blood samples (0.5 mL) were taken from the indwelling arterial line for measurement of the baseline (0 min) plasma ACTH and serum cortisol concentrations before hCRH (1 µg/kg) was administered by bolus iv injection. This dose of hCRH was based on the experience of older children and adult studies that demonstrated an effective stimulation of the pituitary and adrenal glands in the absence of any measurable adverse effects (6, 7). Three further sets of blood samples were obtained 15, 30, and 60 min post-hCRH administration. Blood samples for plasma ACTH and serum cortisol assays were collected in chilled ethylenediamine tetraacetic acid bottles and plain containers, respectively. The blood samples were immediately immersed in ice and transported to the laboratory for processing. All samples were centrifuged at 3500 rpm for 15 min at 4 C, and the resulting plasma/serum was stored at -70 C until analysis. Vital signs of the patients, including temperature, heart rate, respiratory rate, blood pressure, and, for mechanically ventilated infants, serial arterial blood gases, were monitored during and up to 2 h after the test.

ACTH and cortisol assays

The plasma ACTH concentration was measured by double antibody RIA (Nichols Institute Diagnostics, San Juan Capistrano, CA), and serum cortisol was determined by solid phase RIA (Diagnostic Products Corp., Los Angeles, CA). The interassay coefficients of variation of the ACTH assay were 4.4% and 3.7% at 10.1 and 79.3 pmol/L, respectively; those of the cortisol assay were 9.1%, 4.2%, and 4.0% at 159, 461, and 1260 nmol/L, respectively, with an accuracy better than the ±0.5 allowable limits recommended by the monthly Royal College of Pathologists of Australia quality assurance program. Plasma ACTH concentration in picomoles per L can be converted to picograms per mL by multiplying by a factor of 4.5; likewise, the conversion of serum cortisol concentration from nanomoles per L to micrograms per dL can be achieved by dividing by 27.6.

Ethical approval

Ethical approval of the study was obtained from the research ethics committee of the Chinese University of Hong Kong. Informed parental consent was obtained for each case before commencement of the test.

Statistical analysis

The descriptive statistics on the demographic data were expressed as the mean and SEM; for comparison of hormone levels, multivariate repeated ANOVA was used.

	Results

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The clinical characteristics of the study population are summarized in Table 1. One of 14 infants was excluded from the analysis after she was diagnosed to have methicillin-resistant Staphylococcus aeurus septicemia and acute bacterial endocarditis on the same day of the hCRH test. Three other infants did not receive the second hCRH test on day 14. One was diagnosed to have coagulase negative staphylococcus septicemia, another developed necrotizing enterocolitis on day 12 and required surgery on the following morning, and one extremely premature infant died on day 10 because of fulminant pulmonary interstitial emphysema and respiratory failure.

View larger version (21K): [in this window] [in a new window]   Figure 1. The effect of exogenous hCRH stimulation on plasma ACTH and serum cortisol concentrations in preterm VLBW infants (n = 13). Results are the mean ± SEM. Poststimulation hormone concentrations were significantly elevated after hCRH administration (* and **, P < 0.005 and P < 0.0001, respectively).

	Discussion

Top Abstract Introduction Subjects and Methods Results Discussion References

 
Different methods have been employed for assessing pituitary-adrenal function in older children and adults (6, 8, 9). The insulin stress test, which induces hypoglycemia and stimulates the release of other hormones, including vasopressin, catecholamines, and oxytocin (10, 11), is considered unsuitable and possibly dangerous because of its potential adverse effects on the developing brain. oCRH has a relatively long plasma half-life compared to hCRH and causes prolonged stimulation of its target organs (3). In contrast, hCRH causes shorter episodes of ACTH and cortisol secretion, which simulates more closely the physiological episodic secretion of endogenous CRH (12). To our knowledge, the hCRH stimulation test has not been assessed or standardized in preterm VLBW infants.

Our results suggest that the hCRH test is safe, reproducible, and capable of producing a consistent pituitary-adrenal response in preterm VLBW infants, similar to that in older children and adults (6, 7). Despite the potential risk that exogenous hCRH may rapidly bind to the circulating CRH-binding protein in vivo, the configuration of the response curves, the magnitude of the responses, and the timing of the peak concentrations for both plasma ACTH and serum cortisol in response to exogenous hCRH stimulation are all comparable to the results demonstrated in normal human adults (7). Furthermore, as there are no significant differences in the pituitary and adrenal responses to hCRH stimulation between days 7 and 14 of postnatal age and as our observations are in full accordance with previously published data for extremely low birth weight infants using oCRH for stimulation (3), it is probable that both the pituitary and adrenal glands are functionally mature even at these very early periods of gestation. The stage of maturation of these endocrine glands also appears to be similar in male and female infants.

No significant differences in the ACTH and cortisol responses in relation to mode of delivery or mechanical ventilation were observed. This may be the result of the relatively small sample size. Alternatively, the responsiveness of the pituitary-adrenal glands might have been influenced by other confounding stressful events occurring during their intensive care treatment period. Moreover, the hCRH tests performed on days 7 and 14 might not be the optimal times for assessing stress on different modes of delivery because of the prolonged time lapse from the initial childbirth process. Nonetheless, the patient who died from acute bacterial endocarditis had extremely high basal and peak concentrations of plasma ACTH (19.7 and 41.2 pmol/L at 0 and 15 min, respectively) and serum cortisol (963 and 1438 nmol/L at 0 and 30 min, respectively). This would suggest that the hypothalamic-pituitary-adrenal axis of preterm infants was capable of responding to stressful stimulus and that bacterial septicemia was probably a more potent stimulant of the endocrine axis than mechanical ventilation.

No measurable adverse effects were detected during and 2 h after the hCRH test. In addition, the identification of the exact timing of the peak plasma ACTH and serum cortisol concentrations in relation to hCRH stimulation may in the future allow less frequent blood sampling during the test. This should be of particular benefit to extremely premature and low birth weight infants. As a single measurement of plasma cortisol does not permit a reliable assessment of pituitary-adrenal function due to episodic secretion of the hormones that has been demonstrated in both newborns and adult subjects (13, 14), a reproducible and standardized stimulation test is, therefore, essential for assessing those infants who are most at risk of hypothalamic-pituitary-adrenal axis suppression. As with other new modalities of treatment, the use of antenatal and postnatal corticosteriods for treatment of respiratory distress syndrome and bronchopulmonary dysplasia in preterm VLBW infants will become more frequent and liberal. Identifying critically suppressed infants who are likely to require replacement therapy during stress could be life saving.

Received July 25, 1996.

Revised October 10, 1996.

Revised November 22, 1996.

Accepted November 26, 1996.

	References

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1. Crowley P. 1989 Promoting pulmonary maturity. In: Chalmers I, Enkin M, Keirse MJNC, eds. Effective care in pregnancy and childbirth. Oxford: Oxford University Press; 746–764.
2. Ng PC. 1993 The effectiveness and side effects of dexamethasone in preterm infants with bronchopulmonary dysplasia. Arch Dis Child. 68:330–336.[Medline]
3. Hanna CE, Keith D, Colasurdo MA, et al. 1993 Hypothalamic pituitary adrenal function in the extremely low birth weight infant. J Clin Endocrinol Metab. 76:384–387.[Abstract]
4. Rizvi ZB, Aniol HS, Myers TF, Zeller WP, Fisher SG, Anderson CL. 1992 Effects of dexamethasone on the hypothalamic-pituitary-adrenal axis in preterm infants. J Pediatr. 120:961–965.[CrossRef][Medline]
5. Ballard JL, Khoury JC, Wedig K, Wang L, Eilers-Walsman BL, Lipp R. 1991 New Ballard score, expanded to include extremely premature infants. J Pediatr. 119:417–423.[CrossRef][Medline]
6. Goji K. 1989 The corticotropin-releasing hormone test in normal short children: comparison of plasma adrenocorticotropin and cortisol responses to human corticotropin-releasing hormone and insulin-induced hypoglyaemia. Acta Endocrinol (Copenh). 120:390–394.[Abstract/Free Full Text]
7. Schlaghecke R, Kornely E, Santen RT, Ridderskamp P. 1992 The effect of long-term glucocorticoid therapy on pituitary-adrenal responses to exogenous corticotropin-releasing hormone. N Engl J Med. 326:226–230.[Abstract]
8. Riddick L, Chrousos GP, Jeffries S, Pang S. 1994 Comparison of adrenocorticotropin and adrenal steroid responses to corticotropin-releasing hormone versus metyrapone testing in patients with hypopituitarism. Pediatr Res. 36:215–220.[Medline]
9. Trainer PJ, Faria M, Newell-Price J, et al. 1995 A comparison of the effects of human and ovine corticotropin-releasing hormone on the pituitary-adrenal axis. J Clin Endocrinol Metab. 80:412–417.[Abstract]
10. Vale W, Vaughan J, Smith M, Yamamoto G, Rivier J, Rivier C. 1993 Effects of synthetic ovine corticotropin releasing factor, glucocorticoids, catecholamines, neurohypophysial peptides, and other substances on cultured corticotropic cells. Endocrinology. 113:1121–1131.[Abstract]
11. Gillies GE, Linton EA, Lowry PJ. 1982 Corticotropin releasing activity of the new CRF is potentiated several times by vasopressin. Nature. 299:355–357.[CrossRef][Medline]
12. Schürmeyer TH, Avgerinos PC, Gold PW. 1984 Human corticotropin-releasing factor in man: pharmacokinetic properties and dose-response of plasma adrenocorticotropin and cortisol secretion. J Clin Endocrinol Metab. 59:1103–1108.[Abstract]
13. Metzger DL, Wright NM, Veldhuis JD, Rogol AD, Kerrigan JR. 1993 Characterization of pulsatile secretion and clearance of plasma cortisol in premature and term neonates using deconvolution analysis. J Clin Endocrinol Metab. 77:458–463.[Abstract]
14. Wand GS, Ney RL. 1985 Disorders of the hypothalamic-pituitary-adrenal axis. Clin Endocrinol Metab. 14:33–53.[Medline]

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