Processing-independent analysis for pro-C-type natriuretic peptide.

C-type natriuretic peptide (CNP) is expressed in several human tissues. We designed a specific processing-independent assay for proCNP-derived products and quantitated the concentrations in human seminal plasma from normal and vasectomized men. Antibodies were raised against the N-terminus of human proCNP 11-27. Samples were incubated with trypsin prior to immunoassay, which allows for the measurement of "total" proCNP irrespective of the degree of post-translational processing. Seminal plasma from normal young men and vasectomized men were collected and quantitated; the molecular heterogeneity was evaluated by gel chromatography. The antiserum displayed high binding affinity. Preanalytical trypsin treatment fully exposed the proCNP 11-27 epitope detected by the antiserum. Seminal plasma from healthy men (n=120) contained ~8-fold higher proCNP concentrations compared to blood plasma (range 104-933 pmol/L, age 18-25 years); gel chromatography suggested the presence of several molecular forms. Parameters associated to male fertility, proCNP concentrations in blood plasma and time of abstinence did not correlate to the seminal proCNP concentrations. Measurement in vasectomized men disclosed seminal proCNP concentrations similar to non-vasectomized men (range 107-705 pmol/L, age 34-44 years). Taken together, our new proCNP assay shows that proCNP is abundantly present in human seminal plasma and that seminal proCNP is secreted from the prostate gland and/or the seminal vesicles.