Philip L. Ballard

Scientific basis and therapeutic regimens for use of antenatal glucocorticoids

Abstract The scientific basis for use of prenatal steroid therapy in preparing the human fetus for premature delivery is extensive and convincing. Studies in numerous animal species have documented precocious maturation of lung and other tissues after administration of glucocorticoids to the fetus, and ablation experiments indicate delayed organ maturation with a deficiency of endogenous corticosteroid. The timing of lung differentiation correlates well with the developmental increase in circulating corticosteroid, supporting the concepts that endogenous corticosteroids, interacting with other hormones, are important physiologic modulators of tissue maturation and that prenatal steroid therapy mimics the effect of endogenous glucocorticoids. In fetal lung the response to glucocorticoid involves induction of a limited number of proteins, including all the components of surfactant, as well as key lipogenic enzymes. These effects are mediated by glucocorticoid receptors, occur with physiologic concentrations of hormone, are primarily exerted at the level of gene activation, and are reversible on removal of hormone from cultured tissue. These various observations predict that a relatively brief exposure of the human fetus to glucocorticoid accelerates the normal developmental process in lung and other tissues and reduces disease resulting from developmental immaturity. Prenatal treatment with either betamethasone or dexamethasone at the recommended doses provides similar physiologic stress levels of glucocorticoid activity in fetal plasma sufficient to provide a near-maximal occupancy of receptors and induction of target proteins. Elevated glucocorticoid levels are maintained during the course of treatment and values return to normal by 2 days after the last dose. Treatment causes a transient suppression of maternal and fetal adrenal function; however, treated infants respond to newborn stress with a near-normal cortisol surge. However, there is little information, and reason for concern, regarding the safety of higher or repeated dose of prenatal steroid, and accordingly, routine retreatment of women who are not in active labor is not advised. The recommendation of the consensus panel that corticosteroid therapy is indicated for women at risk of premature delivery with few exceptions is thus well supported by evidence relating to glucocorticoid effects, mechanisms, and pharmacokinetics.

Steroid and Growth Hormone Levels in Premature Infants After Prenatal Betamethasone Therapy to Prevent Respiratory Distress Syndrome

Summary: Prenatal maternal therapy with glucocorticoid reduces the incidence of respiratory distress syndrome (RDS) in premature infants. To investigate the effects of this treatment on the fetal endocrine system, we determined serum concentrations of betamethasone, cortisol, dehydroepiandrosterone sulfate, growth hormone, and prolactin in cord blood of 215 treated infants and 117 untreated infants of 26–36 wk of gestation. Cortisol levels are suppressed within 6 hr of betamethasone treatment, decrease to 45% of the concentration in untreated infants (8.4 μg/dI), and return to normal by 7 days. Dehydroepiandrosterone sulfate is reduced maximally by 65% and returns to normal concentrations (123.5 μg/dI) in 7½ days. The suppression of both steroids was similar after treatment with 12 mg betamethasone (acetate and phosphate) daily 2 times or with 6 mg betamethasone (alcohol) twice daily 4 times. Peak betamethasone levels were higher after the 12 mg dose, but the two-treatment regimens produced a similar total exposure of the fetus to elevated serum glucocorticoid activity for 2½ days and decreased plasma activity for the subsequent 4½ days. Treated infants with low cortisol concentrations at birth increased their cortisol levels severalfold after birth in response to either intrapartum asphyxia or RDS.Betamethasone therapy did not affect cord serum prolactin levels, but the concentration of growth hormone was reduced at all gestational ages. The suppression was greatest (53% decrease) among infants of 28<32 wk, and, among older infants, there was a subsequent increase above control levels between 2 and 4 days after treatment.This study indicates that prenatal betamethasone treatment causes a transient suppression of fetal growth hormone and presumably those pituitary hormones which regulate steroid production by both the definitive and fetal zones of the fetal adrenal. However, the suppression of fetal cortisol does not interfere with the pituitary-adrenocortical response to stress after birth.Speculation: We speculate that the results of betamethasone treatment on the fetal endocrine system described here may represent only some of the effects which exogenous corticosteroids have on the human fetus. Continuing research in this area will further the understanding of the role of glucocorticoids during development, and will help in establishing the safest and most efficacious treatment regimen for prevention of RDS.

Thyroid hormone stimulation of phosphatidylcholine synthesis in cultured fetal rabbit lung.

To investigate the mechanism of thyroid hormone action on pulmonary surfactant synthesis, we characterized the effect of triiodothyronine on phosphatidylcholine synthesis in cultured fetal rabbit lung. Since glucocorticoids stimulate surfactant synthesis and reduce the incidence of Respiratory Distress Syndrome in premature infants, we also examined the interaction of triiodothyronine and dexamethasone. The rate of choline incorporation into phosphatidylcholine was determined in organ cultures of rabbit lung maintained in serum-free Waymouths medium. In 23-d lung cultured for 72 h, the increase in choline incorporation with triiodothyronine alone, dexamethasone alone, and triiodothyronine plus dexamethasone was 50, 62, and 161%, respectively. Both triiodothyronine and dexamethasone also increased incorporation rates with glucose, glycerol, and acetate as precursors, and stimulation with triiodothyronine plus dexamethasone was at least additive. Dexamethasone, but not triiodothyronine, affected distribution of radioactivity from [3H] acetate among phospholipids. Stimulation was first detected 8-12 h after addition of triiodothyronine, and then increased in a linear fashion. With triiodothyronine plus dexamethasone, stimulation was maximal at 48-72 h, and was supra-additive at all times. Exposure of cultured lung to dexamethasone enhanced the subsequent response to triiodothyronine, but not vice versa. When triiodothyronine was removed from cultures, there was no further stimulation and the triiodothyronine effect was partially reversed within 24 h. Half-maximal stimulation of choline incorporation occurred at a triiodothyronine concentration (0.10 nM) very similar to the dissociation constant for triiodothyronine binding to nuclear receptor (0.11 nM). The relative potencies of thyroid hormone analogs for nuclear binding and stimulation of phosphatidylcholine synthesis were also similar: triiodothyroacetic acid greater than triiodothyronine-proprionic acid greater than L-triiodothyronine approximately D-triiodothyronine much greater than thyroxine much greater than 3,5-diethyl-3-isopropyl-DL-thyronine approximately 3,5-dimethyl-3-isopropyl-L-thyronine approximately reverse triiodothyronine. The effect of triiodothyronine was blocked by the presence of either actinomycin D or cycloheximide, inhibitors of ribonucleic acid and protein synthesis, respectively. We conclude that triiodothyronine stimulates phosphatidylcholine synthesis by a process involving nuclear receptors and de novo ribonucleic acid and protein synthesis. These findings support the concept that endogenous triiodothyronine has a physiologic role in lung maturation and suggest that a combined antenatal therapy with thyroid hormone and glucocorticoid may be useful for prevention of Respiratory Distress Syndrome in the premature infant.

Fetal sex and prenatal betamethasone therapy.

We examined the influence of fetal sex on the occurrence of respiratory distress syndrome in premature infants after maternal treatment with betamethasone. Among treated infants of 1,251 to 1,750 gm birth weight, the incidence of RDS was 40.9% in 22 males and 7.1% (P = 0.03) in 14 females. Cord serum levels of betamethasone were similar for infants of both sexes, and there was no sex difference in suppression of serum cortisol, dehydroepiandrosterone sulfate, and growth hormone after treatment. These findings suggest that prenatal corticosteroid therapy is less effective in male infants than in female infants. This effect is not due to a difference in transfer or metabolism of betamethasone, nor is it reflected in the responsiveness of the fetal hypothalamic-pituitary-adrenal axis to synthetic glucocorticoid.

Plasma Thyroid Hormones and Prolactin in Premature Infants and Their Mothers after Prenatal Treatment with Thyrotropin-Releasing Hormone

ABSTRACT: We assayed TSH, triiodothyronine, free thyroxine, and prolactin (PRL) in plasma of women and infants participating in a trial of prenatal thyrotropin-releasing hormone (TRH) treatment for prevention of newborn lung disease. Women in labor at 26–34 wk of gestation received 400 μg of TRH i.v. every 8 h (one to four doses) plus 12 mg betamethasone (one or two doses); controls received saline plus betamethasone. Mean cord concentrations in control infants were TSH 9.7 mU/L, triiodothyronine 0.6 nmol/L (40.2 ng/dL), free thyroxine 14.4 pmol/L (1.13 ng/dL), and PRL 67.6 μg/L. TRH increased maternal plasma TSH by 100% at 2–4 h after treatment and decreased levels by 28–34% at 5–36 h. In cord blood of treated infants delivered at 2–6 h, TSH, triiodothyronine, and PRL were all increased about 2-fold versus control, and free thyroxine was increased 19%; the response was similar after one, two, three, or four doses of TRH. In treated infants delivered at 13–36 h, cord TSH and triiodothyronine levels were decreased 62 and 54%, respectively, and all thyroid hormones were lower after birth at 2 h of age versus control. We conclude that prenatal TRH administration increases thyroid hormones and PRL in preterm fetuses to levels similar to those normally occurring at term. Pituitary-thyroid function is transiently suppressed after treatment to a greater extent in fetus than mother, and infants born during the early phase of suppression do not have the normal postnatal surge in thyroid hormones.

Failure to detect an effect of prolactin on pulmonary surfactant and adrenal steroids in fetal sheep and rabbits.

Recent reports have indicated an association between low cord prolactin (PRL) and the occurrence of respiratory distress syndrome in premature infants, and it is reported that PRL administration increases the lecithin content of fetal rabbit lung. We administered 1 mg ovine PRL to 32 rabbit fetuses on day 24 of gestation and evaluated lung phospholipid synthesis and content on day 26. Compared with diluent-injected littermates, PRL had no effect on the rate of choline incorporation into lecithin, tissue content of phospholipid and disaturated lecithin, or plasma corticoids. However, both choline incorporation and corticoids were increased in all animals undergoing surgery compared with unoperated controls. We also infused PRL (1 mg/day, i.v.) into three fetal sheep continuously over five periods of 5-8 days. Although supraphysiologic concentrations of PRL were achieved in plasma and amniotic fluid, there was no effect of this treatment on the flux of tracheal fluid surfactant or on plasma concentrations of corticoids of dehydroepiandrosterone sulfate. Thus, in this study, we failed to detect either a stimulation of the surfactant system or an adreno-corticotropic effect by PRL as previously postulated. This suggests that the relationship between PRL and respiratory distress sundrome is an indirect association.

Corticosteroid binding by fetal rat and rabbit lung in organ culture

To further characterize glucocorticoid action in fetal lung cells, we investigated corticosteroid metabolism and binding in explants of fetal rat and rabbit lung. Cortisone (E) was concerted to cortisol (F) and bound by receptor with a time course only somewhat slower than for F. Production of F (0.243 pmol/min/mg DNA) was the same in male and female rabbits and was not affected by prior exposure to glucocorticoid in utero or in culture. The t 1/2 for dissociation of nuclear-bound [3H]F was 84 min on changing the culture medium and 21 min on addition of excess non-labeled dexamethasone. Dissociation of [3H]dexamethasone was approx 5-fold slower by both procedures. The KD for nuclear binding of dexamethasone, F, E, and corticosterone in rabbit lung were 0.7, 7.3, 6.8 and 70.6 nM, respectively. In rat lung, the KD for dexamethasone was 6.8 nM. The concentrations of dexamethasone and F required for half-maximal stimulation of phosphatidylcholine synthesis were similar to the KD values. Dexamethasone binding capacity (sites/mg DNA) increased with age in both rat (+103% increase from day 16 to 22) and rabbit (+47% between day 23 and 30). Receptor concentration was the same in both sexes, and there were no developmental changes in non-specific binding, nuclear:cytoplasmic distribution, or KD. In 27-day rabbit fetuses, the rate of choline incorporation was higher in lungs with greater binding capacity. We conclude that (1) E is rapidly converted to F in rabbit lung to become an active glucocorticoid, whereas corticosterone probably has little physiologic activity, (2) there is a species difference in the affinity of dexamethasone binding which is reflected in responsiveness (3) there is no difference between sexes in E conversion, receptor capacity, or phosphatidylcholine synthesis, and (4) the concentration of binding sites per lung cell increases during fetal development. We suggest that developmental increases in both F production and receptor may be important factors in the expression of endogenous glucocorticoid effects.

Glucocorticoid activity in cord serum: Comparison of hydrocortisone and betamethasone regimens

Our patients had surprisingly high concentrations of unbound PHT in their predialysis samples, levels which might ordinarily be associated with clinical evidence of PHT toxicity. None of our patients, however, had overt or subtle evidence of phenytoin toxicity. Atypical neurotoxicity, such as movement disorders and pseudodementia, have been caused by PHT, and is found most often in patients who are neurologically abnormal. TM 12 Very high concentrations ~0f. phenytoin may cause seizures. ~ Because these symptoms also may occur in uremic encepha!opathy, it is important to rule out PHT toxicity caused by high concentrations of unbound PHT in patients who are suspected of having uremic encephal0pathy. Although PHT is relatively nondialyzable, dialysis can reduce the effective PHT concentration. No seizures occurred following dialysi s during our studies. It is possible, however, that when patients unbound PHT concentrations are lowered during dialysis, subtherapeutic concentrations might result and allow seizures to recur. According to our findings, this would be most likely in patients with significant weight loss during dialysis or if albumin is given. In these instances, or if PHT-induced neurotoxicity were suspected, the unbound PHT concentration should be measured and the dosage adjusted accordingly. The therapeutic range of unbound phenytoin is 1.0 to 2.0 ~zg/ml.

Glucocorticoids in Prevention of Respiratory Distress Syndrome

Low doses of the synthetic steroid betamethasone can be effective in preventing neonatal RDS. Administration during the 48 hours immediately before delivery of infants between the 26th and 34th weeks of gestation is optimally effective. The article provides guidelines for this approach, describes its hazards, and discusses possible ways by which glucocorticoids prevent neonatal RDS.