Neuropeptides and adrenocortical proliferation in vitro

Vasoactive intestinal peptide (VIP) and Neuropeptide Y (NPY) are localised in the capsule and zona glomerulosa region of the adrenal cortex, where they play an important role in regulating steroidogenesis and adrenal blood flow. This study investigates the effect of these neuropeptides on adrenocortical cellular proliferation and steroidogenesis in vitro. Capsular/glomerulosa and innerzone/medulla preparations were either stimulated acutely with NPY or VIP (both 10(-6) M) for up to 2 hours or for 24 hours, four and eight days in vitro in eagles MEM (3.4 mM K+). DNA synthesis was determined using immunocytochemistry through the incorporation of the thymidine analogue 5-bromo-2'-deoxyridine (BrdU, 20 mg/mL). Phosphorylation of mitogen activated protein kinase ERK1/2 was assessed by western blotting. Both VIP (10(-6) M) and NPY (10(-6) M) treatment caused an increase in DNA synthesis after four days in culture. Acute NPY treatment caused an increase in ERK1 and 2 phosphorylation (p < 0.01) in the capsular/zona glomerulosa. Vasoactive intestinal peptide treatment caused a significant increase in ERK 1/2 phosphorylation (p < 0.05) only in innerzones/medulla preparations. Both responses were maximal between 10 and 30 min of incubation and decrease thereafter. These data provide further evidence for the role of the mitogen activated protein kinases ERK1 and 2 in the proliferative events in the adrenal gland and demonstrate stimulation of cell division by the adrenal neuropeptides VIP and NPY in vitro.