Localization of G protein alpha-subunits in the human fetal adrenal gland

The aim of the present study was to investigate the presence and localizati on of the main G protein alpha -subunits in the human fetal adrenal gland d uring the second trimester of gestation. Immunofluorescence studies conduct ed on sections from frozen glands obtained immediately after therapeutic ab ortion indicated that the alphas subunit of the heterotrimeric G(s) protein was detected in all adrenal cell types, except for endothelial cells. The other alpha -subunits had a more specific pattern of distribution. Indeed, the alpha il-2 protein was restricted to the definitive zone, whereas alpha i3 labeling was mainly expressed in the fetal zone. The alphaq protein sub unit was localized in vascular endothelial cells at the periphery of the ad renal gland and in fetal cells at the center. Finally, chromaffin cells exp ressed alphas, alphaq, and alpha o1, but not alpha o2 nor alphai. Altogethe r, these results indicate that the human fetal adrenal gland is not only un ique in its particular morphology and expression of steroidogenic enzymes, but also by the differential expression of G protein alpha -subunits. Such cell. specific distribution in glands from midgestational fetuses may accou nt for the absence or the different responses to stimuli, when compared wit h the adult adrenal gland.