Natriuretic peptide receptors on rat thymocytes: Inhibition of proliferation by atrial natriuretic peptide.

Because the thymus expresses the natriuretic peptides (NP) as well
as their respective receptors, an involvement of NP in the
physiology of this organ has been suggested. To evaluate functional
aspects of NP in the thymus, we looked for thymic cells bearing NP
receptors (Npr). Furthermore, the regulation of Npr expression by
activation of cells and the influence of NP on the proliferation of
thymocytes was studied. Expression of receptor messenger RNAs
CmRNAs) was examined by PCR and Northern blot. Existence of
functional Npr was confirmed by measurement of cGMP, the second
messenger of NP. Proliferation of thymocytes upon concanavalin A
(Con A) stimulation was analyzed by incorporation of [“Hlthymidine.
We report here that thymocytes express mRNAs for the three Npr,
namely Npra, Nprb, and Nprc and that activation of Npra and Nprb
increases cGMP levels. Stimulation of thymocytes with Con A (1
pg/ml, 48 h) resulted in an increase of mRNA coding for Npra, the
receptor specific for atria1 natriuretic peptide (ANP) and brain
natriuretic peptide. Nprb and Nprc receptor expression was not
altered under these conditions. In agreement with these data only
ANP, but not the C-type natriuretic peptide, elicited increased
cGMP response in Con A-stimulated cells. ANP inhibited also the
proliferation of Con A stimulated thymocytes, whereas C-type
natriuretic peptide did not show this effect. These results suggest
that ANP affects the complex mechanisms of thymocyte proliferation
and differentiation.