Vasoactive intestinal peptide (VIP) stimulates cortisol secretion from the H295 human adrenocortical tumour cell line via VPAC1 receptors

Vasoactive intestinal peptide (VIP) shows a wide tissue distribution and exerts numerous physiological actions. VIP was shown in a dose-dependent manner to increase cortisol secretion in the NCI-H295R human adrenocortical carcinoma (H295) cell line (threshold dose 3-3x10(-10) M, maximal dose 10(-7) M), coupled with a parallel increase in cAMP accumulation. Receptor-specific agonists were employed to determine which of the two known VIP receptor subtypes was involved in cortisol secretion. Treatment with the VPAC1 receptor agonist, [K-15, R-16, L-27]VIP(1-7)/GRF(8-27), produced a dose-dependent increase in H295 cell cortisol secretion (threshold dose 10(-11) M, maximal dose 10-7 M) similar to that seen with VIP. Meanwhile, the high-affinity VPAC2 receptor agonist, RO-25-1553, failed to stimulate significantly cortisol or cAMP production from H295 cells. Inhibition of VIP-mediated H295 cell cortisol secretion by PG97-269, a competitive VPAC1-specific antagonist, produced parallel shifts of the dose-response curve and a Schild regression slope of 0.99, indicating competitive inhibition at a single receptor subtype. VIP is known also to interact with the PAC1 receptor, albeit with lower affinity (EC50 of similar to200 nM) than the homologous ligand, PACAP (EC50 of similar to 0.5 nM). PACAP stimulated cortisol secretion from H295 cells (EC50 of 0.3 nM), suggesting the presence of functional PAC1 receptors. However, stimulation of cortisol secretion by nanomolar concentrations of VIP (EC50 of 5 nM), coupled with real-time PCR estimation that VPAC1 receptor transcripts appear 1000-fold more abundant than PAC1 transcripts in H295 cells, makes it unlikely that VIP signals via PAC1 receptors. Together, these data suggest that VIP directly stimulates cortisol secretion from H295 ce Is via activation of the VPAC1 receptor subtype.