Large forms of immunoreactive calcitonin in human seminal fluid exhibit PDN-21 immunoreactivity

Beta-endorphin and calcitonin in human semen

The levels of beta-endorphin (beta-E) and calcitonin were estimated in 36 samples of seminal plasma from semen of normospermic, oligozoospermic, and azoospermic origins and in pools of isolated sperm. The mean levels in plasma calculated for all samples examined were 192 +/- 224 pg/ml for beta-E and 754 +/- 397 pg/ml for calcitonin. The amounts in sperm were as follows: for beta-E in pools with sperm counts of 0.1-10 x 10(6)/ml, 157.2 +/- 99.7 pg/10(8) and 27.9 +/- 23.6 pg/ml protein; in pools of greater than 10-30 x 10(6)/ml, 71.2 +/- 41.5 pg/10(8) and 6.5 +/- 1.2 pg/mg protein; in pools of greater than 30-200 x 10(6)/ml, 24.9 +/- 9.7 pg/10(8) and 61 +/- 1.9 pg/mg protein. For calcitonin the amounts were: 501.2 +/- 170.8 pg/10(8) and 27.4 +/- 21.5 pg/mg protein, correspondingly. It was suggested that beta-E and calcitonin present in seminal plasma are synthesized mostly in a compartment of the male reproductive system. The high cellular beta-E and calcitonin levels would be involved in the process of motility through their effect on calcium transport.

Evidence for precursors of calcitonin/PDN 21 in human milk

Large amounts of immunoreactive PDN-21 (iPDN -21) were found in human milk in concentrations similar to those of immunoreactive calcitonin (iCT): 187 +/- 73 pM (mean +/- S.D.) vs 210 +/- 83 pM. (n = 17). Calcitonin (CT) was immunoextracted from milk by means of CT antibodies coupled to Sepharose 4B, and the extracts were gel-chromatographed on Sephadex G-75 after treatment with 6 M guanidine HCl. iCT and iPDN-21 in the fractions were determined with radioimmunoassay. The main part of iCT eluted as high molecular weight forms and these fractions also contained iPDN-21. Enzymatic cleavage of immunoextracted milk CT by trypsin demonstrated that iPDN-21 could be split apart from the high molecular weight forms and be recovered at the position of synthetic human PDN-21 on gel chromatography. iCT was eluted in the region of monomeric CT and as larger forms. Since PDN-21 constitutes the carboxyterminal of preprocalcitonin, our results indicate that human milk contains precursors of calcitonin.