SERUM PARATHYROID HORMONE-RELATED PROTEIN-LEVELS DURING LACTATION

We measured parathyroid hormone-related protein (PTHrP) in the serum o f 15 healthy women within three days of beginning breast-feeding and w ithin one hour of completing nursing. A sensitive immunoradiometric as say that measures N-terminal PTHrP containing at least the first 74 am ino acids was used. We found normal PTHrP values in all patients. Valu es one day before and two days after delivery in a hypoparathyroid wom an who chose not to breast-feed were also normal. Since N-terminal PTH rP fragments of 1-36 amino acids or more are biologically active, we b elieve additional studies using sensitive PTHrP assays that measure sm aller fragments and investigations performed under other conditions of breast-feeding are necessary before concluding that PTHrP does not ha ve a role in calcium homeostasis in nursing mothers. Furthermore, addi tional studies in hypoparathyroid nursing mothers should be performed.