ENDOCRINE CONTROL OF FETAL ADRENAL MEDULLA CATECHOLAMINE

The purpose of the proposed study is to investigate the role of selected
hormones and the adrenal cortex in the regulation of adrenal medullary
catecholamine secretion in the ovine fetus. To study the hormone effects,
fetuses of 100-115 days, 120-135 days, and 135-145 days gestation, newborns
at 1-5 days and 5-10 days, and the adult ewe will be studied. The adrenal
medulla will be dispersed into single cells, plated and cultured in
Krebs-Henseleit medium. The effects of prolactin, angiotensin II, arginine
vasopressin and cortisol on the synthesis and release of the three
catecholamines-dopamine, norepinephrine, and epinephrine-will be determined
at 1, 3, 6, 9, 12 and 24 hours of incubation. A radioenzymatic assay will
be used to measure the concentrations of the three catecholamines.
Dose-response relationships will be established. The responsiveness of the
adrenal medulla to each of the hormones will be compared among animals of
different age groups. To study the role of the adrenal cortex in
regulating medullary catecholamine secretion, the ability of the cortex to
release a catecholamine stimulatory factor will be determined using adrenal
tissues from fetuses of 135 to 140 days gestation. First, cortical cell
incubation medium will be tested for catecholamine stimulatory activity in
adrenal medullary cells. Second, the secretory pattern of this
catecholamine stimulatory factor will be determined by testing the medium
obtained from incubating adrenal cortical cells for periods up to 48
hours. Third, the augmentation of release of this catecholamine
stimulatory factor from the cortical cells by ACTH and by the presence of
adrenal medullary cells will be tested. For the latter study, fetal
adrenal cortical cells will be recombined with medullary cells and
coincubated. The release of the cortical factor will be correlated with
morphologic changes or structural specialization as examined under the
phase-contrast and electron microscope. Fourth, the isolation of this
adrenal cortical catecholamine stimulatory factor will be performed using
biochemical separation procedures. Finally, the presence of this cortical
factor in the adrenal cortex of younger fetuses, newborns and adults will
be investigated. These studies will provide the basic understanding of the
endocrine factors involved in the regulation of adrenal medullary
catecholamine secretion in the fetus during development. They will
evaluate the significance of the role of the adrenal cortex in the control
of adrenal medullary secretory function in the near-term fetus.