PTH-related protein is released into the mother's bloodstream during lactation: Evidence for beneficial effects on maternal calcium-phosphate metabolism
Open Access
- 1 October 1996
- journal article
- research article
- Published by Oxford University Press (OUP) in Journal of Bone and Mineral Research
- Vol. 11 (10) , 1394-1399
- https://doi.org/10.1002/jbmr.5650111004
Abstract
Recent studies have indicated that parathyroid hormone-related protein (PTHrP) may have important actions in lactation, affecting the mammary gland, and also calcium metabolism in the newborn and the mother. However, there are as yet no longitudinal studies to support the notion of an endocrine role of this peptide during nursing. We studied a group of 12 nursing mothers, mean age 32 years, after they had been nursing for an average of 7 weeks (B) and also 4 months after stopping nursing (A). It was assumed that changes occurring between A and B correspond to the effect of lactation. Blood was assayed for prolactin (PRL), PTHrP (two-site immunoradio-metric assay with sheep antibody against PTHrP(1-40), and goat antibody against PTHrP(60-72), detection limit 0.3 pmol/1), intact PTH (iPTH), ionized calcium (Ca2+), 25-hydroxyvitamin D3 (25(OH)D3) and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), alkaline phosphatase (alkP), as well as for creatinine (Cr), protein, phosphorus (P), and total calcium (Ca). Fasting 2-h urine samples were analyzed for Ca excretion (CaE) and renal phosphate threshold (TmP/GFR). PRL was significantly higher during lactation than after weaning (39 ± 10 vs. 13 ± 9 μg/l; p = 0.018) and so was PTHrP (2.8 ± 0.35 vs. 0.52 ± 0.04 pmol/l; p = 0.002), values during lactation being above the normal limit (1.3 pmol/l) in all 12 mothers. There was a significant correlation between PRL and PTHrP during lactation (r = 0.8, p = 0.002). Whole blood Ca2+ did not significantly change from A (1.20 ± 0.02 mmol/l) to B (1.22 ± 0.02, mmol/l), whereas total Ca corrected for protein (2.18 ± 0.02 mmol/l) or uncorrected (2.18 ± 0.02 mmol/l) significantly rose during lactation (2.31 ± 0.02 mmol/l, p = 0.003 and 2.37 ± 0.03 mmol/l, p = 0.002, respectively). Conversely, iPTH decreased during lactation (3.47 ± 0.38 vs. 2.11 ± 0.35 pmol/l, A vs. B, p = 0.02). Serum-levels of 25(OH)D3 and 1,25(OH)2D3 did not significantly change from A to B (23 ± 2.3 vs. 24 ± 1.9 ng/ml and 29.5 ± 6.0 vs. 21.9 ± 1.8 pg/ml, respectively). Both TmP/GFR and P were higher during lactation than after weaning (1.15 ± 0.03 vs. 0.86 ± 0.05 mmol/l GF, p = 0.003 and 1.25 ± 0.03 vs. 0.96 ± 0.05 mmol/l, p = 0.002, respectively) as was alkP (74.0 ± 7.1 vs. 52.6 ± 6.9 U/l, p = 0.003). CaE did not differ between A and B (0.015 ± 0.003 vs. 0.017 ± 0.003 mmol/l GF, A vs. B, NS). We conclude that lactation is accompanied by an increase in serum PRL. This is associated with a release of PTHrP into the maternal blood circulation. A rise in total plasma Ca ensues, probably in part by increased bone turnover as suggested by the elevation of alkP. PTH secretion falls, with a subsequent rise of TmP/GFR and plasma P despite high plasma levels of PTHrP.Keywords
This publication has 26 references indexed in Scilit:
- Parathyroid hormone‐related protein: a possible endocrine function in lactationClinical Endocrinology, 1992
- Post‐pregnancy osteoporosis associated with hypercalcaemiaClinical Endocrinology, 1992
- Suckling increases plasma PTH-rp levels in lactating womenBone and Mineral, 1992
- Production of parathyroid hormone-related protein by the mammary gland of the goatJournal of Endocrinology, 1992
- Parathyroid hormone-related peptide might stimulate calcium secretion into the milk of goatsJournal of Endocrinology, 1992
- Parathyroid hormone-related protein in milk and its correlation with bovine milk calciumJournal of Endocrinology, 1991
- Parathyroid hormone-related protein relaxes rat gastric smooth muscle and shows cross-desensitization with parathyroid hormoneJournal of Bone and Mineral Research, 1989
- Expression of a Calcium-Mobilizing Parathyroid Hormone-Like Peptide in Lactating Mammary TissueScience, 1988
- Effects of a synthetic peptide of a parathyroid hormone-related protein on calcium homeostasis, renal tubular calcium reabsorption, and bone metabolism in vivo and in vitro in rodents.Journal of Clinical Investigation, 1988
- NOMOGRAM FOR DERIVATION OF RENAL THRESHOLD PHOSPHATE CONCENTRATIONThe Lancet, 1975