Natriuretic peptides in the human testis: evidence for a potential role of C-type natriuretic peptide in Leydig cells.

Functional studies indicate that natriuretic peptides have direct effects on Leydig cells of the testis. In this report, we demonstrate local synthesis of one member of the natriuretic peptide family, C-type natriuretic peptide (CNP), in Leydig cells of human testes. Using RT-PCR assays, messenger RNA (mRNA) for the CNP precursor was detected in human testis and found to be prominently expressed in Leydig cells. Immunohistochemical analyses revealed CNP to be almost exclusively associated with Leydig cells. Distinct differences in the staining intensity-including cells without detectable staining-suggest a heterogeneity of CNP expression within the Leydig cells. Moreover, the presence of transcripts for the CNP receptor, a particulate guanylate cyclase, termed GC-B, was demonstrated by RT-PCR in human testis and in isolated Leydig cells. The expression of this receptor in human testis membranes could be confirmed by affinity labeling with 125I-labeled CNP. These findings demonstrate, for the first time, the production of a natriuretic peptide in human Leydig cells. The occurrence of CNP and its receptor in the human testis points to a local role of the peptide, presumably acting in an auto- or paracrine manner to modulate organ-specific functions.