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Five chronically instrumented pregnant ewes and their fetuses were studied to assess the effect of acute maternal hemorrhage. The hemorrhage was produced in two stages; during the first stage 15% of the total maternal blood volume was removed, and then in a second stage an additional 15% was removed. Biophysical and biochemical variables were monitored. Plasma dopamine, norepinephrine, and epinephrine were determined by a sensitive radioenzymatic assay. A significant rise in maternal and fetal catecholamines was observed following an estimated maternal blood volume depletion of 30%. During a 15-minute recovery period, the maternal catecholamine concentrations returned to normal, while the fetal concentrations remained elevated. These changes were accompanied by significant changes in maternal and fetal homeostasis. The significance of these findings is discussed.

To assess the possible mechanism for the increased incidence and severity of the respiratory distress syndrome (RDS) in male versus female infants, we studied neurosympathetic development in. the lung and adrenal glands in male and female 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 females as compared with males at each gestational age and throughout the neonatal period (p<0.005). Adrenal gland content of E, NE, and DA increased exponentially with advancing developmental age (each p<0.005). Adrenal E was significantly (p<0.01) elevated in female as compared with male fetuses, as was the proportion of E. Adrenal NE and DA were similar in male and female fetuses. Sex differences were not significant in the newborn animals. The significant relative delay in adrenal medullary and lung β-receptor maturation may relate to the male susceptibility to neonatal morbidity and neonatal RDS.

Radioligands with high specific activity and high affinity have recently become available to study the β-adrenergic receptor (BAR). BAR may be important in the placenta for mediating a variety of metabolic and hemodynamic effects of catecholamines including placental hormone synthesis and secretion, placental glycogenolysis, and placental blood flow. Little is known regarding the development of the BAR. We have used the tritiated radioligand dihydroalprenolol to study the ontogenesis of BAR in the fetal and maternal portions of the ovine placenta. The receptor number decreased from 415 fmoles · mg−1of protein at 120 days' gestation to 226 fmoles · mg−1at 145 days; this trend was highly significant (r = −0.822, p < 0.01). Similar changes were noted in the dissociation constant. Downward regulation as a result of fetal neurosympathetic maturation is proposed as an explanation for this observation.