Antenatal dexamethasone and the growth hormone–insulin-like growth factor axis

O. Ogueh1, J.P. Miell2, J.C. Jones3, J.S. Jones2, J. Alaghband-Zadeh3 and M.R. Johnson1,4

1 Section of Obstetrics and Gynaecology, Imperial College School of Medicine, Chelsea and Westminster Hospital, 369 Fulham Road, London SW10 9NH, 2 Department of Medicine, King's College School of Medicine and Dentistry and 3 Department of Chemical Pathology, Imperial College School of Medicine, Charing Cross Hospital, London W6 9RF, UK


    Abstract
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 Abstract
 Introduction
 Materials and methods
 Results
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Dexamethasone administration has marked effects on the growth hormone-insulin-like growth factor axis (GH–IGF) in animal and human studies. During pregnancy in the rat, it is associated with fetal growth restriction due to inhibition of IGF bioactivity. In the human only repeated dosages have been associated with fetal growth restriction. The aim of this study is to test the hypothesis that antenatal dexamethasone administration to pregnant women is associated with reduced activity of the GH–IGF axis. To achieve this blood samples were taken from 12 pregnant women pre- and at 24 h and 48 h after dexamethasone administration. In these samples GH, IGF-I, IGF bioactivity and IGF binding protein (IGFBP)-3 protease activity were measured. In view of the interaction between insulin and the GH–IGF axis, glucose and insulin concentrations were also measured. There were no significant differences between the concentrations of GH, IGF-I, IGF bioactivity and IGFBP-3 protease activity before and after dexamethasone. The concentrations of glucose and insulin were significantly higher at 24 h, but not 48 h post-dexamethasone. It is concluded that a single antenatal course of dexamethasone does not alter the GH–IGF-I axis in pregnant women at the time points studied.

Key words: antenatal/dexamethasone/IGF


    Introduction
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
The administration of glucocorticoids prior to preterm delivery reduces the incidence of respiratory distress syndrome in the newborn (Liggins and Howie, 1972Go; Crowley, 1995Go). In addition, the efficacy of neonatal surfactant therapy is enhanced and there is a reduction in the risk of intra-ventricular haemorrhage, neonatal hyperbilirubinaemia and neonatal death (Sinclair, 1994Go). However, concern has been expressed about the adverse effects of glucocorticoid therapy with reports of infection due to impaired immune response, pulmonary oedema, altered blood glucose control and adrenal suppression (Crowley, 1995Go). Moreover, animal data suggest that fetal growth may be impaired and long-term changes in blood pressure regulation and insulin sensitivity induced (Price et al., 1992Go; Nyirenda et al., 1998Go; Dodic et al., 1998Go). The effect on fetal growth is thought to be through a reduction in insulin-like growth factor (IGF) bioactivity (Luo and Murphy, 1989Go; Luo et al., 1990Go; Price et al., 1992Go).

Short-term administration of dexamethasone leads to a reduction of mean IGF bioactivity in the human male, despite an increase in the concentrations of IGF-I (Miell et al., 1993Go). The change in IGF bioactivity is probably secondary to changes in circulating binding protein concentrations as IGF binding protein (IGFBP)-1 and IGFBP-2 were reduced and IGFBP-3 increased (Miell et al., 1993Go). The dexamethasone-induced reduction in IGF bioactivity in the rat is thought to be due to increases in the circulating concentrations of IGFBP-1 (Price et al., 1992Go). It has been reported previously that IGFBP-1 was not altered by the antenatal administration of dexamethasone (Ogueh et al., 1998Go). However, it is possible that IGFBP-3 may be altered by dexamethasone administration as described above (Miell et al., 1993Go). IGFBP-3 inhibits the mitogenic actions of IGF-I in the perfused rat heart, fat cells and chick embryo fibroblasts (Martin and Baxter, 1992Go; Lalou et al., 1996Go). IGFBP-3 is proteolysed in the circulation, by serine proteases, to two major fragments. The larger 22/25-kDa fragment has low affinity for IGF-I and weakly inhibits IGF-I mitogenic effects, whilst the smaller 16-kDa fragment does not bind to IGF-I, but inhibits IGF-I bioactivity to a similar extent as intact IGFBP-3 (Lalou et al., 1996Go, 1997Go). Hence, IGFBP-3 proteolysis may inhibit IGF-I-stimulated mitogenesis by a mechanism independent of IGF concentration.

Antenatal dexamethasone administration in the human has only been associated with fetal growth restriction with repeated treatments (French et al., 1999Go). However, if the fetal growth restriction is mediated through an effect on the growth hormone (GH)–IGF axis, it is likely that an effect would be seen following a single treatment course. Indeed, using a total dose of 16 mg in the human male the effects on IGF-bioactivity were profound and persisted for more than 24 h (Miell et al., 1993Go). Therefore, given the available human data, to test the hypothesis that antenatal dexamethasone administration to pregnant women is associated with reduced activity of the GH–IGF axis, blood samples were obtained pre- and at 24 and 48 h after the administration of 24 mg dexamethasone. In addition, given the relationship between insulin and the GH–IGF axis (Holly et al., 1988Go; Suikkari et al., 1989Go), the concentrations of glucose and insulin were also measured.


    Materials and methods
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 Materials and methods
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A longitudinal study was performed on 12 pregnant women who received dexamethasone therapy for fetal lung maturation in anticipation of premature delivery before 34 completed weeks of gestation. The obstetric problems that threatened premature birth were preterm labour (n = 1), preterm rupture of membranes (n = 3), antepartum haemorrhage due to placenta praevia (n = 4) and antepartum haemorrhage of unknown origin (n = 3), and severe pre-eclampsia (n = 1). These women served as their own controls. A standard regimen of dexamethasone (Merck, Sharp & Dohne Ltd, Hoddesdon, Herts, UK) that comprised two doses of 12 mg i.m. injections at 12 hourly intervals was administered to all women. The number of women (12) was chosen on the basis of an earlier study by Miell and colleagues who reported a mean baseline IGF bioactivity of 0.93 ± 0.08 IU/ml, and demonstrated that it fell by a mean difference of 0.54 IU/ml following short-term dexamethasone administration (Miell et al., 1993Go). This was statistically significant with a P value of <0.0001 (Miell et al., 1993Go). Power calculations showed that a comparable difference could be demonstrated with the number of subjects used in this study with an {alpha} of 0.05 and a ß of 0.2.

All women gave informed consent to the study, which was approved by the local research ethics committee. Blood samples were collected before starting the dexamethasone therapy, and 24 h and 48 h after completing therapy. The subjects were fasting at the time samples were obtained 24 and 48 h after completing therapy. Samples were centrifuged for 15 min at ~250g at 4°C for the separation of plasma which were stored at –20°C until analysed in a single batch. Statistical analysis was performed using the Statistical Package for Social Sciences (SPSS). Statistical significance was assumed where P < 0.05.

IGF-I was measured by an in-house radioimmunoassay (Morrel et al., 1986Go) following an acid ethanol extraction. Interassay coefficient of variation (CV) (concentration) was 19.1% (6.7 nmol/l) and 8.7% (21.7 nmol/l). The normal ranges of IGF-I for individuals of <60 years is 30–60 nmol/l and for those >60 years it is 10–30 nmol/l.

IGF bioactivity was measured using a porcine costal cartilage bioassay as previously described (Miell et al., 1993Go).

The amount of proteolytic activity directed against recombinant IGFBP-3 was assessed (Lamson et al., 1993Go). Plasma samples were diluted 1 in 10 with 0.1 mol/l Tris-HCl pH 7.4. A total of 30 µl of dilute sample was incubated for 5h with 10µl 125I-IGFBP-3 (30 000 cpm) and the reaction quenched with 30 µl sample buffer. The samples were subjected to sodium dodecyl sulphate—polyacrylamide gel electrophoresis (SDS–PAGE) and the resultant gels dried and autoradiographed. Autoradiographs resulting from the above three methods were assessed by densitometry (SW2000; Ultra-Violet Products Ltd, Cambridge, UK). The density of cleavage fragments appearing as a result of proteolytic activity was calculated and expressed as a percentage of the total density of all bands in each lane to give a percentage protease activity.

GH was measured using the Omnia® radioimmunometric assay (IDS Ltd, Tyne and Wear, UK). Interassay CV (concentration) was 6.4% (1.6 mIU/l) and 8.0% (24.2 mIU/l).

Insulin was measured using an enzyme immunoassay on Boehringer ES700® (Boehringer Mannheim Immunodiagnostics, Lewes, Sussex, UK). Interassay CV (concentration) was 6.0% (88.6 mIU/l) and 10.8% (17.9 mIU/l). Blood glucose was measured by an enzymatic colorimetric assay (glucose oxidase) on the BM/Hitachi 747® (Boehringer Mannheim).


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 Materials and methods
 Results
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The subjects had a mean age of 33.1 (SD 5.7) years (range 24–40 years); parity ranged from 0 to 4. The median gestational age at administration of the first dose of dexamethasone was 28 weeks (range 24–33 weeks).

The post-therapy values of IGF bioactivity, IGFBP-3 protease activity, and the plasma concentrations of IGF-I and GH were not different from the pre-therapy concentrations, but the concentrations of glucose and insulin increased 24 h after dexamethasone therapy, and fell towards the pre-therapy value 48 h after therapy (Table IGo).


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Table I. IGF bioactivity, IGFBP-3 protease activity, plasma concentrations of IGF-I, GH, insulin and glucose before and after dexamethasone therapy
 

    Discussion
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 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
This is the first study to investigate the impact of antenatal dexamethasone on the GH–IGF axis. Previous animal and non-pregnant human data showed a marked effect of dexamethasone on GH–IGF axis (Price et al., 1992Go; Miell et al., 1993Go). In contrast, in this study it was found that antenatal dexamethasone administration did not significantly alter IGF bioactivity, circulating concentrations of IGF-I, GH or IGFBP-3 protease activity. Dexamethasone administered to six male volunteers reduced IGF bioactivity by 40% and significantly increased the serum concentrations of IGF-I; both effects lasted for more than 24 h (Miell et al., 1993Go). In the current study, despite using larger doses of dexamethasone (24 versus 16 mg), both IGF bioactivity and circulating IGF-I concentrations were unaltered.

In pregnant animals, dexamethasone administration is consistently associated with impaired fetal growth due to reduced IGF bioactivity (Luo and Murphy, 1989Go; Luo et al., 1990Go; Price et al., 1992Go). In the human, only multiple courses of antenatal corticosteroids have been associated with significant reduction in birth weight (French et al., 1999Go). The data presented here are confined to a single treatment course and samples obtained at 24 and 48 h after dexamethasone administration and thus an effect on the GH–IGF axis of multiple treatments or a subtle effect of less than 24 h duration cannot be excluded. Nevertheless, the non-pregnant human study used a lower total dosage (16 versus 24 mg) and the pregnant animal data are based on a single treatment (Price et al., 1992Go; Miell et al., 1993Go). In both studies, profound, protracted effects were reported on the GH–IGF axis. If the fetal growth restriction induced in the human by multiple steroid treatments does involve the GH–IGF axis it would have been expected that an effect would be apparent in the current study. Moreover, in contrast to Miell et al.'s data, there was a trend for IGF bioactivity actually to increase in the current data. Although this did not reach statistical significance, it supports the idea that fetal growth restriction in the human following dexamethasone administration is not induced through changes in the GH–IGF axis.

An alternative explanation for the fetal growth restriction is altered placental function as it has previously been found that the circulating concentrations of human chorionic gonadotrophin were reduced following dexamethasone administration (Ogueh et al., 1999Go). Indeed, dexamethasone administration has also been reported to cause fetal hypoxia independent of increases in fetal glucose concentrations (Bennett et al., 1999).

Glucocorticoid therapy has been suggested to reduce GH secretion or to alter it in a time dependent mechanism (Hartog et al., 1964Go; Casanueva et al., 1990Go). Casanueva and colleagues found that after administration of 4 mg dexamethasone to eight volunteers, the basal GH concentrations started to rise after 2 h, reached a peak after 3–3.5 h, and declined after 5 h (Casanueva et al., 1990Go). However, in pregnancy, most circulating GH is placental and not pituitary in origin and is secreted in a tonic fashion (Alsat et al., 1998Go). Therefore, the lack of change in the concentrations of GH following dexamethasone therapy in this study may be because of the difference in origin or because the samples were obtained only 24 and 48 h after therapy.

Acute and chronic administration of glucocorticoids increases plasma insulin concentrations (Miell et al., 1993Go). This rise is likely to be secondary to a slight elevation of plasma glucose concentrations (Lambillotte et al., 1997Go). In the current study a transient increase in the circulating concentrations of glucose and a more prolonged elevation in insulin concentrations after dexamethasone administration were found. The fact that the glucose concentrations had fallen to close to baseline by 48 h post-treatment suggests that the insulin concentrations would also fall towards baseline thereafter. However, a further study of longer duration is required to establish this. These data contrast with those of a study of 12 women who were given dexamethasone 1 mg orally four times daily for an average of 7.8 days; the circulating concentrations of insulin and glucose did not change during the treatment period when compared to pre-therapy concentrations (Tuimala et al., 1975Go). Although the average total dexamethasone dosage of 31.2 mg used is higher than the current dosage of 24 mg, the duration of treatment was longer (Tuimala et al., 1975Go). Therefore, the current treatment regimen is likely to have attained a higher concentration of dexamethasone and so induced a more profound, if short lived, effect. Given the overall lack of effect of dexamethasone on the GH–IGF axis, the increase in insulin seems not to be significant.

In conclusion, antenatal dexamethasone did not alter the GH–IGF axis at 24 and 48 h after administration and had a transient effect on glucose and insulin concentrations. These data do not exclude an effect of antenatal dexamethasone administration on the GH–IGF axis, but show that in contrast to non-pregnant human and animal data any effect must be short lived.


    Notes
 
4 To whom correspondence should be addressed. E-mail: mark.johnson{at}ic.ac.uk Back


    References
 Top
 Abstract
 Introduction
 Materials and methods
 Results
 Discussion
 References
 
Alsat, E., Guibourdenche, J., Couturier, A. and Evain-Brion, D. (1998) Physiological role of human placental growth hormone. Mol. Cell. Endocrinol., 140, 121–127.[ISI][Medline]

Bennet, L., Kozuma, S., McGarrigle, H.H.G. and Hanson, M.A. (1999) Temporal changes in fetal and cardiovascular, behavioural, metabolic and endocrine responses to maternally administered dexamethasone in the late gestation sheep. Brit. J. Obst. Gynaecol., 106, 331–339.[ISI]

Casanueva, F.F., Burguera, B., Muruais, C. and Dieguez, C. (1990) Acute administration of corticoids: a new and peculiar stimulus of growth hormone secretion in man. J. Clin. Endocrinol. Metabol., 70, 234–237.[Abstract]

Crowley, P. (1995) Antenatal corticosteroid therapy: a meta-analysis of randomised trials, 1972–94. Am. J. Obstet. Gynecol., 173, 322–335.[ISI][Medline]

Dodic, M., May, C.N., Wintour, E.M. and Coghlan, J.P. (1998) An early prenatal exposure to excess glucocorticoid leads to hypertensive offspring in sheep. Clin. Sci., 94, 149–155.[ISI][Medline]

French, N., Hagan, R., Evans, S. et al. (1999) Repeated antenatal corticosteroids: growth and early childhood outcome. Obstet. Gynecol., 180, 114–121.

Hartog, M., Gaafar, M.A. and Fraser, R. (1964) Effects of corticosteroids on serum growth hormone. Lancet, i, 376–378.

Holly, J.M.P., Biddlecombe, R.A., Dunger, D.B. et al. (1988) Circadian variation of GH-dependent IGF-binding protein in diabetes mellitus and its relationship to insulin. Clin. Endocrinol., 29, 667–675.[ISI][Medline]

Lalou, C., Lassarre, C. and Binoux, M. (1996) A proteolytic fragment of insulin-like growth factor (IGF) binding protein-3 that fails to bind IGFs inhibits the mitogenic effects of IGF-I and insulin. Endocrinology, 137, 3206–3212.[Abstract]

Lalou, C., Sawamura, S., Segovia, B. et al. (1997) Proteolytic fragments of insulin-like growth factor binding protein-3: N-terminal sequences and relationships between structure and biological activity. Canad. Roy. Acad. Sci. III, 320, 621–628.

Lambillotte, C., Gilon, P. and Henquin, J-C. (1997) Direct glucocorticoid inhibition of insulin secretion. An in vitro study of dexamethasone effects in mouse islets. J. Clin. Invest., 99, 414–423.[Abstract/Free Full Text]

Lamson, G., Guidice, L.C., Cohen, P. et al. (1993) Proteolysis of IGFBP-3 may be a common regulatory mechanism of IGF action in vivo. Growth Reg., 3, 91–95.[ISI][Medline]

Liggins, G.C. and Howie, R.N. (1972) A controlled trial of antepartum glucocorticoid treatment for prevention of respiratory distress syndrome in premature infants. Paediatrics, 50, 515–525.[ISI][Medline]

Luo, J.M. and Murphy, L.J. (1989) Dexamethasone inhibits growth hormone induction of insulin-like growth factor-I (IGF-I) messenger ribonucleic acid (mRNA) in hypophysectomized rats and reduces IGF-I mRNA abundance in the intact rat. Endocrinology, 125, 165–171.[Abstract]

Luo, J., Reid, R.E. and Murphy, L.J. (1990) Dexamethasone increases hepatic insulin-like growth factor binding protein-1 (IGFBP-1) mRNA and serum IGFBP-1 concentrations in the rat. Endocrinology, 127, 1456–1462.[Abstract]

Martin, J.L. and Baxter, R.C. (1992) Insulin-like growth factor binding protein-3: biochemistry and physiology. Growth Reg., 2, 88–99.[ISI][Medline]

Miell, J.P., Taylor, A.M., Jones, J. et al. (1993) Effect of dexamethasone on immunoreactive and bioreactive insulin-like growth factors (IGFs) and IGF-binding proteins in normal male volunteers. J. Endocrinol., 136, 525–533.[Abstract]

Morrel, D.J., Ray, K.P., Holder, A.T. et al. (1986) Somatomedin-C/insulin-like growth factor-1; simplified purification procedure and biological activities of the purified growth factor. J. Endocrinol., 110, 151–158.[Abstract]

Nyirenda, M.J., Lindsay, R.S., Kenyon, C.J. et al. (1998) Glucocorticoid exposure in late gestation permanently programs rat hepatic phosphoenolpyruvate carboxykinase and glucocorticoid receptor expression and causes glucose intolerance in adult offspring. J. Clin. Invest., 101, 2174–2181.[Abstract/Free Full Text]

Ogueh, O., Hills, F., Chard, T. and Johnson, M.R. (1998) Antenatal dexamethasone does not affect circulating concentrations of IGFBP-1. Hum. Reprod., 13, 1714–1716.[Abstract]

Ogueh, O., Jones, J., Mitchell, H. et al. (1999) Effect of antenatal dexamethasone therapy on maternal plasma human chorionic gonadotrophin, oestradiol and progesterone. Hum. Reprod., 14, 303–306.[Abstract/Free Full Text]

Price, W.A., Stiles, A.D., Moats-Staats, B.M. and D'Ercole, A.J. (1992) Gene expression of insulin-like growth factors (IGFs), the type 1 IGF receptor, and IGF-binding proteins in dexamethasone-induced fetal growth retardation. Endocrinology, 130, 1424–1432.[Abstract]

Sinclair, J. (1994) Discussion of Crowley's meta-analysis of randomised controlled trials of antenatal corticosteroids for prevention of respiratory distress syndrome. In Report of the Consensus Development Conference on the Effects of Corticosteroids for Fetal Maturation on Perinatal Outcomes. National institute of Health, Bethesda, pp. 95–96.

Suikkari, A., Koivisto, V.A., Koistinen, R. et al. (1989) Dose-response characteristics for suppression of low molecular weight plasma insulin-like growth factor binding protein by insulin. J. Clin. Endocrinol. Metabol., 68, 135–140.[Abstract]

Tuimala, R., Kauppila, A. and Ylikorkala, O. (1975) Effect of dexamethasone on blood glucose, serum insulin, free fatty acid and triglyceride concentrations during the last trimester of pregnancy. Int. J. Gynaecol. Obstet., 13, 81–84.

Submitted on November 11, 1999; accepted on February 29, 2000.