Galanin enhances corticosterone secretion from dispersed rat adrenocortical cells through the activation of GAL-R1 and GAL-R2 receptors coupled to the adenylate cyclase-dependent signaling cascade.

Galanin is a regulatory peptide, which acts via three subtypes of receptors, named GAL-R1, GAL-R2 and GAL-R3. Reverse transcription-polymerase chain reaction demonstrated the expression of GAL-R1 and GAL-R2, but not GAL-R3 mRNAs in dispersed rat adrenal zona fasciculata-reticularis (inner) cells. The immuno-blockade of GAL-R1 and GAL-R2, but not GAL-R3, decreased the binding of [3H]galanin to dispersed cells, a complete inhibition being obtained only by the simultaneous blockade of both receptor subtypes. Galanin stimulated corticosterone and cyclic-AMP release from dispersed inner rat adrenocortical cells, while inositol triphosphate production was not affected. Again these responses to galanin were reversed by both the GAL-R1 and GAL-R2, but not the GAL-R3 immuno-blockade. The adenylate cyclase inhibitor SQ-22536 and the protein kinase (PK) A inhibitor H-89 abolished the corticosterone response of dispersed cells to galanin, while the phospholipase C inhibitor U-73122 and the PKC inhibitor calphostin-C were ineffective. We conclude that rat inner adrenocortical cells express GAL-R1 and GAL-R2 as mRNA and protein, and galanin stimulates corticosterone secretion acting via these receptor subtypes which are both coupled to the adenylate cyclase/PKA-dependent signaling pathway.