Central antagonism of atrial natriuretic peptides on behavioral and hormonal responses to angiotensin 11: mapping with c-fos

Abstract

The expression of the immediate early gene (IEG)c-fos has been used to map the antagonistic effects between atrial natriuretic peptide (ANP) and angiotensin II (Ang II). Intracerebroventricular (i.c.v.) infusions of ANP (100, 250, 1000 or 2000 pmol) did not induce detectable c-fos expression in the forebrain when compared with CSF-treated rats. Neither did C-type natriuretic peptide (CNP, 10, 100, 500 or 1000 pmol), another member of the natriuretic peptide family, which appears to be predominant in the brain. ANP was found to inhibit the water intake and corticosterone release induced by i.c.v. infusions of Ang II. However, ANP could not suppress the c-fos expression in the organum vasculosum of the lamina terminalis (OVLT), medial preoptic nucleus (MNPO), subfornical organ (SFO), supraoptic (SON) and paraventricular (PVN)nuclei of forebrain induced by the same dose of Ang II. The activation of second messenger pathways following i.c.v. infusion of Ang II may result in two different sets of effects: immediate behavioural and physiological responses (presumably through postsynpatic responses in neurons sensitive to Ang II), and the delayed expression of c-fos (and other IEGs proteins) which control the expression of late response genes. Whilst there is considerable, and growing evidence that IEGs mark the pattern of neuronal activity induced by peptides such as Ang II, the precise role played by these gene products is still problematical and awaits clarification by further experiments.