Vollmar, Angelika M.; Schmidt, Karin-Nicole; Schulz, Rüdiger
Natriuretic peptide receptors on rat thymocytes: Inhibition of proliferation by atrial natriuretic peptide.
In: Endocrinology, Vol. 137, No. 5: pp. 1706-1713
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