Effect of Natriuretic Peptides on in vitro Stimulated Adrenocorticotropic Hormone Release and Pro-Opiomelanocortin mRNA Expression by the Fetal Rat Pituitary Gland in Late Gestation

Objective and Methods: We investigated the effects of individual natriuretic peptides (atrial natriuretic peptide, ANP; brain natriuretic peptide, BNP, and C-type natriuretic peptide, CNP) on rat corticotropin-releasing factor stimulated adrenocorticotropic hormone (ACTH) secretion by the pituitary gland of 21-day-old rat fetuses in vitro and on pro-opiomelanocortin gene expression using in situ hybridization. Results: Graded concentrations of ANP, BNP, or CNP (10 –10 , 10 –9 , and 10 –8 mol/l) induced a log dose dependent inhibition of ACTH secretion induced by rat corticotropin-releasing factor (10 –10 mol/l). These natriuretic peptides showed equipotent effects on a molar basis. Moreover, ANP, BNP, or CNP at 10 –10 mol/l reduced significantly the pituitary pro-opiomelanocortin mRNA expression. In addition, the immunoreactive ANP, BNP, and CNP cells were localized in the anterior lobe, but not in the intermediate lobe of the fetal pituitary gland. Conclusions: These data suggest that the fetal pituitary gland may be both a source and a target for natriuretic peptides that might control ACTH synthesis and release via an endocrine and/or paracrine mechanism. The natriuretic peptides could participate, as well as glucocorticoids, in the control of the corticotropin-stimulating activity of the fetal rat in late gestation.