Effect of betamethasone on the expression of dopamine D 1 receptor mRNA in the developing rabbit adrenal gland

Abstract

Background: Antenatal corticotherapy is widely used to enhance pulmonary fetal maturation in cases in which premature birth is likely. The adrenal gland, which has a key role in controlling fetal and neonatal adaptation, appears to be a target organ of glucocorticoids.Objectives: The aim of this study was first to determine the ontogenic profile of dopamine D 1 receptor (DA D 1 -R) messenger RNA (mRNA) in the rabbit. The effects of antenatal exposure to exogenous corticoids on levels of adrenal DA D 1 -R mRNA expression were examined.Methods: Pregnant rabbits free of any treatment or handling before delivery were chosen for the study of DA D 1 -R mRNA ontogenic profile. For the study of the antenatal exposure to exogenous corticoids, pregnant rabbits were given 2 injections of either betamethasone 0.1 mg/kg or saline 0.1 mL/kg. DA D 1 -R mRNA expression was determined using northern blot analysis at 4 developmental ages: fetus (at 27 days of gestation), 1 day of age, 25 days of age, and adulthood. Rabbits were allocated to their respective group (treated or untreated) depending on maternal treatment (betamethasone or saline, respectively).Results: Four pregnant rabbits were used for the ontogenic-profile group, which comprised 11 fetuses, seven 1-day-old rabbits, four 25-day-old rabbits, and 2 adults. Six other pregnant rabbits received betamethasone; 6 saline. The treated group comprised 12 fetuses, twelve 1-day-old rabbits, four 25-day-old rabbits, and 3 adults. The untreated group comprised 12 fetuses, fifteen 1-dayold rabbits, five 25-day-old rabbits, and 3 adults. DA D 1 -R mRNA was expressed in rabbit adrenal glands from the fetal period to adulthood and this expression was not age dependent. Moreover, antenatal corticotherapy induced a significant increase in respective DA D 1 -R mRNA levels of 20%, 15%, and 8% in treated fetuses, 1-day-old rabbits, and 25-day-old rabbits compared with the untreated groups (P Ͻ 0.003, 0.003, and 0.005, respectively). This increase was not observed in adulthood.