Developmental regulation of the inhibitory effect of dopamine on prolactin release in the preterm neonate

Prolactin response to growth hormone stimulation tests

BACKGROUND

Despite many similarities between the structure, receptors, proliferative and growth promoting actions, the relationship between Prolactin (PRL) and Growth Hormone (GH) in clinical conditions has received little attention.

OBJECTIVE

To determine the PRL response to GH stimulation tests.

SUBJECTS

Prepubertal and early pubertal boys (n = 581) and girls (n = 502) with idiopathic, non-syndromatic short stature.

DESIGN

Data was retrieved from the computerized records of the Endocrine Laboratory, Schneider Children's Medical Center. Peak GH and PRL levels during GH stimulation tests with glucagon (Gluc), Clonidine (Clon) and Clonidine with arginine (Clon+Arg), were compared. Both PRL and GH were determined by radioimmunoassay.

RESULTS

Whereas Gluc stimulated both GH and PRL to similar levels, Clon alone or combined with Arg suppressed the PRL secretion (p < 0.0001). It is also evident that in both boys and girls Clon alone and Clon±Arg are superior to Gluc in GH stimulation. The higher GH levels during Clon+Arg than with Clon alone are attributed to the pubertal stage.

CONCLUSION

This study provides further information on the Prolactin-Growth hormone relationship in children.

Effect of dopamine infusion on thyroid hormone tests and prolactin levels in very low birth weight infants

OBJECTIVE

To evaluate the effect of dopamine on thyroid hormone tests and prolactin (PRL) and to assess requirement for L-thyroxin (LT4).

METHODS

The infants (n = 102) were divided into three groups (Group 1; received no dopamine, Group 2 received ≤25 mg/kg cumulative dose and Group 3; received >25 mg/kg cumulative dose). Blood samples were taken at 6-8 days (timepoint 1), 13-15 days (timepoint 2), and 4-6 weeks of life (timepoint 3).

RESULTS

Respiratory distress syndrome was higher in group 2 and 3. Patnet ductus arteriosus was higher in group 3 than in groups 1 and 2. Duration and cumulative dose in group 3 were higher than group 2. There was no difference between thyroid hormones that were taken after stopping infusion at timepoint 3 among all groups. No therapy with LT4 was needed. PRL levels were higher at timepoint 1 in group 1 than compared to group 2 and 3 (p < 0.05), and no difference between group 2 and 3 (p > 0.05). This difference was disappeared at following timepoints.

CONCLUSIONS

The release of TSH, FT3, FT4 and PRL were not inhibited and prophylactic thyroid hormone treatment was not required in VLBW infants receiving dopamine infusions.

Neonatal blood pressure support: the use of inotropes, lusitropes, and other vasopressor agents

A solid understanding of the mechanisms of action of cardiovascular medications used in clinical practice along with efforts to develop comprehensive hemodynamic monitoring systems to improve the ability to accurately identify the underlying pathophysiology of cardiovascular compromise are essential in the management of neonates with shock. This article reviews the mechanisms of action of the most frequently used cardiovascular medications in neonates. Because of paucity of data from controlled clinical trials, evidence-based recommendations for the clinical use of these medications could not be made. Careful titration of the given medication with close monitoring of the cardiovascular response might improve the effectiveness and decrease the risks associated with administration of these medications.

T1 signal intensity and height of the anterior pituitary in neonates: correlation with postnatal time

BACKGROUND AND PURPOSE

The anterior pituitary of a term neonate is usually hyperintense on T1-weighted MR images, which may represent histologic changes of the gland due to the effect of high estrogen levels during the fetal period; however, MR findings of a preterm neonate have not been fully evaluated. The purpose of this study was to investigate whether intensity and size of the neonatal anterior pituitary on MR images obtained near term of corrected age correlates with the gestational age at birth or postnatal time.

MATERIALS AND METHODS

Data of 88 consecutive neonates (gestational age, 24-41 weeks; mean, 31.5 weeks) were analyzed. All of the neonates underwent MR imaging at a corrected age of 0 months +/- 4 weeks. Relative signal intensity of the anterior pituitary compared with that of the pons on T1-weighted sagittal images was calculated. Height of the pituitary was also measured. Stepwise regression analysis was performed to evaluate the effects of gestational age at birth and postnatal time on the relative signal intensity and on the pituitary height.

RESULTS

The relative signal intensity significantly negatively correlated with postnatal time (P = .001) but not with gestational age at birth (P = .42). Pituitary height significantly negatively correlated with postnatal time (P = .049) but not with gestational age at birth (P = .071).

CONCLUSION

A significant negative correlation exists between postnatal time and signal intensity on T1-weighted MR images of the anterior pituitary obtained near term. A nonhyperintense anterior pituitary is a normal MR finding of preterm neonates when imaged near term.

Dopamine versus dobutamine in very low birthweight infants: endocrine effects

OBJECTIVES

To compare the endocrine effects of dopamine and dobutamine in hypotensive very low birthweight (VLBW) infants.

DESIGN

Non-blinded randomised prospective trial.

SETTING

Level III neonatal intensive care unit.

PATIENTS

35 hypotensive VLBW infants who did not respond to volume loading, assigned to receive dopamine or dobutamine.

MEASUREMENTS

Haemodynamic variables and serum levels of thyroid stimulating hormone (TSH), total thyroxine (T(4)), prolactin (PRL) and growth hormone were assessed during the first 72 h of treatment and the first 72 h after stopping treatment.

RESULTS

Demographic and clinical data did not significantly differ between the two groups. Necessary cumulative and mean drug doses and maximum infusion required to normalise blood pressure were significantly higher in the dobutamine than in the dopamine group (p<0.01). Suppression of TSH, T(4) and PRL was observed in dopamine-treated newborns from 12 h of treatment onwards, whereas levels of growth hormone reduced significantly only at 12 h and 36 h of treatment (p<0.01). TSH, T(4) and PRL rebound was observed from the first day onwards after stopping dopamine. Dobutamine administration did not alter the profile of any of the hormones and no rebound was observed after stopping treatment.

CONCLUSION

Dopamine and dobutamine both increase the systemic blood pressure, though dopamine is more effective. Dopamine reduces serum levels of TSH, T(4) and PRL in VLBW infants but such suppression is quickly reversed after treatment is stopped. Further research is required to assess if short-term iatrogenic pituitary suppression has longer-term consequences.

Dopamine infusion and anterior pituitary gland function in very low birth weight infants

BACKGROUND

Previous studies demonstrated that dopamine infusion reduces plasma concentration of thyroxine (T4), thyroid stimulating hormone (TSH), prolactin (PRL), and growth hormone (GH) in adults, children, and infants.

OBJECTIVES

The purpose of this prospective observational study was to evaluate the relationship between dopamine infusion and the dynamics of T4, TSH, PRL, and GH in preterm newborns weighing less than 1,500 g (very low birth weight infants, VLBW) admitted in a neonatal intensive care unit of a university hospital over a one year period.

METHODS

A total of 97 preterm newborns were enrolled and divided into two groups: group B included hypotensive infants treated with plasma expanders and dopamine infusion; group A was the control group including newborns who were never treated with dopamine. The newborns were studied dynamically through blood samples taken every day till 10 days. Newborns of group B were studied during dopamine infusion and after its withdrawal.

RESULTS

Among the VLBW newborns who were given dopamine, the four pituitary hormones had different dynamics: a reduction of T4, TSH, and PRL levels was noticed since the first day of treatment, and a rebound of their levels was evident since the first day after its interruption. On the contrary, the postprandial GH levels were roughly constant: GH plasma concentrations were in fact a little lower in newborns treated with dopamine, and a slight increase was observed after its withdrawal. However, observed differences were not statistically significant.

CONCLUSIONS

The results suggest that dopamine infusion reduces T4, TSH, and PRL plasma levels in preterm VLBW infants and have no effect on postprandial GH rate. This hormonal suppression reverses rapidly after dopamine withdrawal. This observation suggests that the iatrogenic pituitary suppression probably cannot produce long-term injuries.

Hypothyroxinemia in mechanically ventilated term infants is associated with increased use of rescue therapies

OBJECTIVE

Although common in preterm infants, transient hypothyroxinemia (TH) has not been investigated extensively in ill term infants. The objectives of this study were to investigate serum thyroxine (T4) and thyroid-stimulating hormone (TSH) in sick term infants and to determine whether there is any association between measures of thyroid function and short-term outcome in term infants who receive mechanical ventilation.

METHODS

The investigation consisted of both a prospective observational study and a retrospective cohort study. In the prospective study, T4 and TSH were measured after birth in a group of sick term infants (n = 38) and compared with a group of well term infants (n = 18). Infants in the sick group received mechanical ventilation or continuous positive airway pressure and/or had neonatal seizures. Illness severity was quantified using the Score for Neonatal Acute Physiology. The retrospective cohort study included term infants who required mechanical ventilation and were born over a 5-year period (n = 347). Routine T4 screening was collected on the fifth day of life. TH was diagnosed in infants with a T4 <10%, with a TSH <25 microIU/mL. Clinical outcomes in infants with TH were compared with infants without TH.

RESULTS

In the prospective study, infants in the sick group had lower T4 on the fifth day of life as compared with infants in the well group (11.7 +/- 4.9 vs 18.9 +/- 5.4 microg/dL), and 34% of infants in the sick group had a T4 <10th percentile compared with 6% of infants in the well group. T4 on day of life 5 was inversely correlated with Score for Neonatal Acute Physiology (R = -0.52). In the retrospective study, 21% of mechanically ventilated infants developed TH and were given statistically more inhaled nitric oxide, high-frequency ventilation, vasopressors, and pharmacologic paralysis when compared with infants without TH. Moreover, infants with TH were statistically more likely to die or require transfer to an extracorporeal membrane oxygenation center compared with infants without TH.

CONCLUSION

Our data show that, similar to preterm infants, ill term infants develop TH. Term infants with TH required more intensive rescue interventions, including inhaled nitric oxide and transfer to an extracorporeal membrane oxygenation center. However, whether T4 levels are a marker or a mediator of clinical outcome remains to be determined.

Serum prolactin in breastfeeding: state of the science

Prolactin is one of two major hormones involved in lactation. While the role of infant suckling and oxytocin in the lactation process are well understood, the role of prolactin is less clear. A variety of factors related to prolactin have been investigated, and these are used as an organizing framework for this article. Factors include pregnancy, lactation, nursing frequency, prior lactation experience, milk production, and pharmacologic agents. The literature, while substantial in amount, presents inconsistencies. Implications for practice are discussed.