Oxytocin enhanced basal corticosterone secretion by dispersed rat adrenal zonae fasciculata and reticularis cells, the maximum effect being observed at a concentration l0_9-10_8 M. Video-imaging analysis revealed the existence of a small population of isolated cells (about 5%), responding to the addition of oxytocin (10_8 M) by a marked rise in the cytosolic free Ca" concentration. An interesting phenomenon was also noted, suggesting the propagation of the oxytocin-evoked signal from activated to non-activated cells.The role of oxytocin in the regulation of adrenocortical function is far from being fully understood (see 4, for review). The presence of oxytocin has been demonstrated in the adrenal glands of many mammalian species, including the rat (1): immunoreactive oxytocin is distributed throughout the entire cortex with the most intense staining in zona glomerulosa, while in the medulla only norepinephrine cells are immunopositive. Such a localization of oxytocin suggests the involvement of this peptide in the regulation of adrenal cortex function. Accordingly, Hinson er a/. (2) demonstrated a direct stimulatory effect of oxytocin on aldosterone secretion. Here we report findings showing that oxytocin exerts a direct glucocorticoid secretagogue effect on dispersed rat adrenal zonae fasciculata and reticularis cells (inner adrenocortical cells), by activating intracytoplasmatic Ca2+ redistribution in a small population of responsive cells. MATERIALS AND METHODSThe adrenal glands removed from adult female Wistar rats were decapsulated, and isolated inner adrenocortical cells were obtained by sequential collagenase digestion and mechanical dispersion (8). The viability of isolated cells was checked by the trypan-blue exclusion test and found to be higher than 92%.Dispersed cells obtained from 6 rats were pooled to obtain a single cell suspension, and 6 cell preparations were employed. Aliquots of each cell suspension (105 cells/ml) were incubated with oxytocin (Gedeon-Richter, Budapest, Hungary). The incubation was carried out for 60 min in a shaking bath at 37°C in an atmosphere of 95% O2 and 5% CO2. Corticosterone was measured in the medium by a specific radioimmunoassay (5). Intraand inter-assay variations were 6% and 8%, respectively.
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