Stimulation of cortisol release by the N terminus of teleost parathyroid hormone-related protein in interrenal cells in vitro

Abstract

The mode of action of PTHrP in the regulation of sea bream (Sparus auratus) interrenal cortisol production was studied in vitro using a dynamic superfusion system. Piscine (1–34)PTHrP (10−6–10−11 m) stimulated cortisol production in a dose-dependent manner. The ED50 of (1–34)PTHrP was 2.8 times higher than that of (1–39)ACTH, and maximum increase in cortisol production in response to 10−8 m of (1–34)PTHrP was approximately 7-fold lower than for 10−8 m of (1–39)ACTH. In contrast to (1–34)PTHrP, piscine (10–20)PTHrP, (79–93)PTHrP, and (100–125)PTHrP (10−9–10−7 m) did not stimulate cortisol production. The effect of piscine (1–34)PTHrP on cortisol production was abolished by N-terminal peptides in which the first amino acid (Ser) was absent and by simultaneous addition of inhibitors of the adenylyl cyclase-protein kinase A and phospholipase C-protein kinase C intracellular pathways but not by each separately. The PTHrP-induced signal transduction was further investigated by measurements of cAMP production and [H3]myo-inositol incorporation in an interrenal cell suspension. Piscine (1–34)PTHrP increased cAMP and total inositol phosphate accumulation, which is indicative that the mechanism of action of PTHrP in interrenal tissue involves the activation of both the adenylyl cyclase-cAMP and phospholipase C-inositol phosphate signaling pathways. These results, together with the expression of mRNA for PTHrP and for PTH receptor (PTHR) type 1 and PTHR type 3 receptors in sea bream interrenal tissue, suggest a specific paracrine or autocrine steroidogenic action of PTHrP mediated by the PTHRs.