1389 SEX DIFFERENCES IN LUNG AND ADRENAL NEUROSYMPATHETIC DEVELOPMENT

Abstract

Adrenergic mechanisms are known to be important in the synthesis and release of pulmonary surfactant and in the prevention of neonatal respiratory distress syndrome (RDS). We studied neuro-sympathetic development in the lung and adrenal glands in male (M) and female (F) fetal and newborn rabbits. Tissue levels of catecholamines, norepinephrine (NE), epinephrine (E), and dopamine (DA) were measured using a sensitive radioenzymatic assay. Beta adrenergic receptor development in the lung was studied using the tritiated radioligand dihydroalprenolol. Neurosympathetic innervation of the lung was assessed by measuring tissue NE levels which increased gradually from 27 day fetuses to 8 day old newborns. Sex differences were not significant. Lung β-receptor number was significantly elevated in F over M at each gestational age and throughout the neonatal time period investigated (p<0.005) Adrenal gland content of E, NE and DA increased exponentially with advancing developmental age (p<.005). Adrenal E was significantly (p<.01) elevated in F as compared to M fetuses as was the proportion of E. Adrenal NE and DA were similar in M and F fetuses. Sex differences were not significant in the newborn animals. Conclusions: 1) Lung β receptor development but not innervation is accelerated in F fetuses; 2) Adrenal maturation is accelerated in F fetuses; 3) Delayed neurosympathetic and neurohumoral development may explain the male susceptibility to RDS.