Determination of serum amyloid P component in seminal plasma and correlations with serum hormone levels in young, healthy men.

Serum amyloid P component (SAP) belongs to the pentraxin family of proteins. SAP is evolutionary conserved, and involved in amyloidosis, innate immunity, inflammation, and apoptosis. We have previously described SAP in the male reproductive tract, where it occurs in seminal fluid, on spermatozoa, and in epididymal, seminal vesicle, and prostate tissue. In the present investigation, our aim was to characterize SAP in male reproduction. In short, we developed and evaluated an immunoassay, analysed the concentration of SAP in seminal plasma and serum in samples from healthy men (N = 203), and studied hormonal regulation. SAP in seminal plasma showed a positively skewed distribution and a median concentration of 1.01 mg/L (inter quartile range [IQR] 0.56-1.65 mg/L). SAP in serum had a Gaussian distribution and a median concentration of 40.5 mg/L (IQR 34.2-49.2 mg/L). Furthermore, SAP concentrations in seminal plasma were not correlated with serum concentrations of SAP, testosterone, sex hormone-binding globulin (SHBG), the testosterone/SHBG ratio, inhibin B, or estradiol. Only a weak negative correlation was found between seminal plasma SAP and serum levels of follicle-stimulating hormone (FSH) (Spearman's rho -0.159; p = 0.023) and luteinizing hormone (LH) (Spearman's rho -0.162; p = 0.021). In conclusion, all men investigated had measurable SAP levels in seminal plasma and in serum. SAP concentrations were 40 times lower in seminal fluid than in serum, and there was no correlation between those two variables. It seems that hormonal regulation is not the major pathway regulating seminal plasma SAP, and seminal plasma SAP and serum SAP are not co-regulated.