The origins of mammalian adrenocortical zonation and the factors that maint
ain it are poorly understood. We have examined the roles of the tissue reni
n-angiotensin system and other paracrine morphogens and growth factors, and
of specific transcription factors in adrenocortical cellular proliferation
and development. From the data obtained, we propose a hierarchy of potenti
al tissue modeling agents. These include morphogens, such as angiotensin II
derived from an intraadrenal origin, growth factors, for example insulin-l
ike growth factor-I, which can be considered to be the paracrine amplifiers
of the morphogenic signal and finally transcription factors, such as c-fos
and c-jun, that directly stimulate mitosis and other events of differentia
tion. In particular, transcription of representative genes in all three cat
egories is increased in the glomerulosa by a low sodium diet, correlated wi
th its hypertrophy and increased aldosterone synthase. Corticotrophin treat
ment tends to eliminate these indices of zonal differentiation.
The adrenal cortex can also set up electrochemical gradients in response to
stimulation. We postulate that the electrochemical gradient informs adreno
cortical cells of their position within the gland, and may also facilitate
"directed diffusion" of other morphogenic paracrine factors to precise loca
tions of action.