Ontogenesis of tissue catecholamines in fetal and neonatal rabbits

The ontogenesis of tissue catecholamine concentrations in heart, lung, brown adipose tissue, adrenal and para-aortic chromaffin tissue was assessed in fetal and newborn rabbits using a radioenzymatic assay adapted to perchloric extracts of tissue. Measurements were conducted at 20, 24, 27 and 31 days gestation and at 3 and 7 days of age. Myocardial norepinephrine was detectable at 20 days gestation, the earliest age studied. Lung norepinephrine was not detectable until 24 days gestation. Norepinephrine concentrations in brown adipose were similar to myocardial levels. Adrenal and para-aortic tissue catecholamine content increased significantly between 24 days gestation and 7 days of postnatal age. Epinephrine became the predominant adrenal catecholamine by 24 days gestation. Para-aortic body norepinephrine concentrations always were substantially less than adrenal norepinephrine or epinephrine contents. Epinephrine was undetectable in para-aortic bodies at 20 and 24 days and at 31 days was only 27% of norepinephrine content. Adrenal maturation as reflected by epinephrine content or epinephrine/norepinephrine ratio correlated positively with body weight in the 31 day gestation fetuses. Thus, significant changes in tissue norepinephrine concentrations occur during the developmental time period studied. Parallel maturational changes occur in adrenal and para-aortic chromaffin tissue.