Immunoextracted calcitonin from human seminal plasma constitutes different forms.

Area of Science:

• Reproductive biology
• Endocrinology
• Biochemistry

Background:

• Calcitonin (CT) is a hormone primarily known for its role in calcium homeostasis.
• Its presence and function in human seminal plasma are not well-established.
• Proteolytic enzymes in semen can degrade peptides, potentially interfering with immunoassays.

Purpose of the Study:

• To quantify immunoreactive calcitonin (iCT) levels in human seminal plasma.
• To investigate the impact of semen liquefaction and proteolysis on iCT measurements.
• To characterize the molecular forms of iCT in seminal plasma.

Main Methods:

• Immunoextraction of seminal plasma using immobilized antibodies to remove interfering enzymes.
• Radioimmunoassay (RIA) for quantifying iCT levels.
• Comparison of iCT levels in liquefied versus immediately diluted semen samples.
• Gel chromatography to determine the molecular weight and heterogeneity of iCT forms.

Main Results:

• Seminal plasma iCT levels are approximately ten times higher than in blood plasma.
• Immediate dilution of semen samples to suppress proteolysis yielded higher iCT levels (120 ± 42 pg-eq/mL) compared to liquefied samples (81 ± 43 pg-eq/mL).
• Gel chromatography revealed that iCT in undiluted semen exists mainly as forms larger than monomeric CT (approx. MW 10,000), with some samples showing higher MW forms (approx. 40,000).
• Diluted samples exhibited greater iCT heterogeneity, ranging from high MW forms to fragments smaller than monomeric CT.

Conclusions:

• Human seminal plasma contains significantly higher levels of immunoreactive calcitonin compared to blood plasma.
• Proteolysis during semen liquefaction impacts iCT quantification, necessitating sample dilution for accurate assessment.
• iCT in seminal plasma exists in various molecular forms, suggesting post-translational modifications or complexation, and these forms appear similar in vasectomized individuals.