ProCNP and CNP are expressed primarily in male genital organs

Lack of knowledge about the cellular origin of C-type natriuretic peptides (CNP) in the body has hampered the understanding of their biology. We examined the tissue specific expression of proCNP and CNP in the pig. The concentration of the CNP precursor, proCNP, was measured in extracts of 32 different tissues using a newly developed RIA. In 22 tissue extracts, we also measured CNP using a commercial RIA. In selected tissues, CNP mRNA was quantified by PCR, and the cellular CNP and proCNP localization was visualized by immunocytochemistry. Extracts from selected tissues were examined by gel chromatography. The highest peptide concentrations were found in extracts from the epididymis, seminal vesicles and prostate. CNP mRNA in the seminal vesicles and epididymis was 125-fold higher than in the other tissues examined. Gel chromatography showed that a CNP-53-like peptide is the dominant CNP tissue-form. Immunocytochemistry confirmed the pattern of peptide expression measured by RIA. In conclusion most proCNP-derived peptides are synthesized in epithelial cells in the epididymis, the prostate gland and in the seminal vesicles. The expression in male genital organs suggests a role of CNP in reproduction.