Parathyroid hormone: another pregnancy protein present in human seminal plasma and amniotic fluid.

Parathyroid hormone (PTH) has been found in human seminal plasma at concentrations of 302 +/- 65 (222-482) pmol l-1 (n = 16), which is about 5 times the concentration in human blood serum. Concentrations in human amniotic fluid at 16-22 weeks of gestation were 43 +/- 9 (28-65) pmol l-1 (n = 24), which is about 80% of the concentration in blood serum. The Amersham assay uses an antiserum raised against the synthetic middle piece of the PTH molecule from the parathyroid glands. It estimates amino acids 44-68 of the 84 amino acid intact molecule, together with fragments containing this part of the chain. It is considered that a placental type of parathyroid hormone was being measured, some of which escapes into the amniotic fluid. The placenta contains a complete PTH-dihydroxyvitamin D3 system that causes the absorption of more calcium from the gut for foetal needs during pregnancy. It is postulated that the seminal vesicles also contain a PTH-dihydroxyvitamin D3 system that has a paracrine action in passing large amounts of calcium into the ejaculate.