Parathyroid hormone-related protein in milk and its correlation with bovine milk calcium

Abstract

Parathyroid hormone-related protein (PTHrP) has been shown to be present in milk of various mammals. We have assayed PTHrP in milk of various species by radioimmunoassay and estimated the molecular weights by Western blot analysis. PTHrP concentrations in bovine, ovine and human milk were 59.2 +/- 18.5, 74.1 +/- 35.0 and 36.6 +/- 20.7 micrograms/l (mean +/- S.D.) respectively, in pooled samples collected at various stages of lactation. PTHrP in mammalian milk was found to exist in two forms with molecular weights of 17.5 kDa and 21.5 kDa approximating those of PTHrP(1-108) and (1-141) respectively. In comparison, marsupial milk PTHrP appeared as a single low molecular weight form of 14.4 kDa which approximated to that of PTHrP(1-84). We performed a longitudinal study measuring the concentration of PTHrP in milk throughout lactation in cows, and found it to increase with the duration of lactation (r = 0.669, n = 91). We further examined the relationship between the concentration of PTHrP and total calcium in bovine milk, and the differences between these constituents in milk from Friesian and Jersey cows. PTHrP concentrations correlated positively with total milk calcium (r = 0.346, n = 105). The mean milk concentration of PTHrP of the Jerseys was significantly higher than that of the Friesians (52.6 +/- 5.4 micrograms/l compared with 41.0 +/- 4.8 micrograms/l, P less than 0.01), as was the mean milk calcium concentration (30.5 +/- 3.0 mmol/l compared with 26.7 +/- 2.7 mmol/l, P less than 0.01). We therefore postulate that production of PTHrP by the mammary gland may be associated with calcium transport from blood to milk. Also PTHrP may play a role in the development of milk fever in Jerseys which are predisposed to this condition.

Plasma parathyroid hormone-related peptide and bone metabolism in periparturient dairy cows

“…A significant increase in the concentration of PTHrP established in our study in early lactation is in agreement with the study conducted by Lippuner et al (1996) in humans, in which significantly higher PTHrP values were observed in the blood of lactating women than in that of nonlactating ones. The results of our study are probably connected with the role of PTHrP in the mammary gland during lactation, which is assumed to promote calcium transport in milk (Law et al, 1991;Barlet et al, 1992). However, Onda et al (2006) did not establish significant arterial-venous differences in the blood concentration of PTHrP upstream and downstream of the mammary gland as evidence of the release of PTHrP from the mammary gland, possibly as a result of the very low PTHrP concentrations in both arterial and venous blood, which were below the detection limit in their respective tests.…”

“…During lactation, PTHrP is presumed to have a local role in the regulation of calcium transport in milk and a systemic role in the adaptation to lactation (Bromage and DeLuca, 1985). In cows, a positive correlation has been found between PTHrP and calcium levels in milk (Law et al, 1991). Barlet et al (1992) observed an increased calcium concentration in the milk of lactating goats after the administration of human PTHrP (1-34) and (1-86).…”

Maternal Mineral and Bone Metabolism During Pregnancy, Lactation, and Post-Weaning Recovery

“…The intense expression of PTHrP in lactating mammary tissue, and its secretion into milk at high concentrations, have prompted investigations to determine whether PTHrP regulates the calcium content of milk. Early studies showed that the PTHrP concentration in milk was positively correlated with calcium content of milk from cows (539,681) and rats (989), but not in all studies from rats (738,1004). One study found that with time since suckling, PTHrP content of milk decreased while the calcium content increased (1004).…”

Comprehensive Proteomic Analysis of Human Milk-derived Extracellular Vesicles Unveils a Novel Functional Proteome Distinct from Other Milk Components

“…5B). Interestingly, various isoforms of PTHLH have been identified in human milk (26), which were detected with varying intensities between donors.…”