Co-expression of the natriuretic peptides (ANP, BNP, CNP) and their receptors in normal and acutely involuted rat thymus.

The natriuretic peptides (NP) ANP, BNP and CNP constitute circulating hormones as well as neuropeptides. The present investigation reveals that these peptides are also constituents of the immune system. BNP and CNP, in addition to ANP as previously communicated, are synthesized in the rat thymus. The NP seem to be produced by different types of thymic cells. Moreover, expression of NP is differentially affected by acute involution of the organ caused by dexamethasone (DEX). The concentration of BNP and CNP mRNA was not changed in gradually involuted thymi (i.e. at day 2, 3 and 4 after DEX administration). ANP mRNA was increased in parallel with the degree of involution (2-, 5- and 40-fold, respectively). The concentration of immunoreactive CNP (CNP-IR) was not affected by acute involution of the thymus (4th day after DEX); BNP-IR, however, was increased 2-fold and for comparison, ANP-IR as previously shown, was found 10-fold elevated. Our studies also revealed the presence of the specific mRNAs coding for the A-, B-, and C-type NP receptor in the thymus. The thymic NP system may be involved in the communication between the immune and neuroendocrine system.