Abstract
We examined the effect of EGF and angiotensin II (AII) on the formation of
inositol phosphates and aldosterone secretion, and observed the role of tyrosine
phosphorylation in EGF or AII-mediated aldosterone secretion. As cultured
glomerulosa cells were incubated with increasing concentrations of EGF (0.01-100
ng/mL), aldosterone secretion increased and reached a plateau at EGF
concentration of 10-50 ng/mL. Although EGF alone did increase aldosterone
secretion in glomerulosa cells, it did not enhance AII-induced aldosterone
secretion when both EGF and AII were added. EGF-induced tyrosine phosphorylation
peaked at around 1 min after stimulation and at a concentration of 10-50 ng/mL.
AII stimulated tyrosine phosphorylation, but the stimulatory effect was less
than that observed in the presence of EGF. Although the latter induced tyrosine
phosphorylation of various proteins, it failed to stimulate the formation of
inositol phosphates. On the other hand, AII stimulated the production of
inositol phosphates in a dose-dependent manner, with maximal stimulation at
10(-8)M. The addition of 10 ng/mL EGF did not affect the AII-induced formation
of inositol phosphates. In conclusion, EGF-stimulated aldosterone secretion
might be mediated by tyrosine kinase. However, since EGF did not stimulate
inositol phospholipid hydrolysis in cultured porcine adrenal glomerulosa cells,
its effect does not seem to be mediated by phospholipase C.