Production of parathyroid hormone-related protein by the mammary gland of the goat

Abstract

Parathyroid hormone-related protein (PTHRP) has been quantified by sensitive specific immunoassays in mammary venous blood and milk from 7 days before to 7 days after parturition in the goat. A significant venous-arterial concentration gradient in plasma PTHRP 1-86 concentrations was demonstrated across the mammary gland, indicating that PTHRP enters the maternal circulation and may have a role in calcium homoeostasis during lactation. Significant and sustained increases in mammary venous and milk PTHRP 1-86 concentrations were found from 1 day before parturition to 7 days afterwards, with peak concentrations of 1.57 +/- 0.58 pmol/l (plasma) and 8.69 +/- 2.95 nmol/l (milk) (mean +/- S.E.M.) occurring on day -1 and the day of parturition respectively. Estimates of the mammary output of PTHRP into plasma in four goats averaged 9% (range 1-25%) of that secreted into milk. Suppression of maternal prolactin concentrations by bromocriptine significantly reduced milk yield and the mammary venous PTHRP concentration, without affecting the concentration of PTHRP in milk. In conclusion, parturition in the goat is associated with a sustained increase in secretion of PTHRP into both plasma and milk; the former may be involved in maternal calcium homoeostasis, whereas the latter may have a role in the neonate.

Plasma osteocalcin concentrations in cows around parturition. The influence of a regular versus a very short dry period

“…Parathyroid hormone-related peptide (PTHrP) is a newly characterized calciotropic factor which was originally isolated from tumors associated with the paraneoplastic syndrome of humoral hypercalcemia of malignancy (Broadus et al, 1988;Martin and Suva, 1989). PTHrP might be the putative calciotropic factor functioning during lactation: it has biological effects very similar to PTH (Horiuchi et al, 1987;Orloff et al, 1989); it is synthetized in lactating mammary tissue (Thiede and Rodan, 1988;Ratcliffe et al, 1992) and increases calcium and phosphorus secretion into milk (Barlet et al, 1992); in rats, serum levels of PTHrP are increased during lactation and this coincides with stimulation of bone resorption (Miller et al, 1991 (Horiuchi et al, 1987). However, PTHrP can increase plasma 1,25-dihydroxyvitamin D 3 concentrations (Horiuchi et al, 1987;Barlet et al, 1990 (Yamamoto et al, 1991) and goats (Ratcliffe et …”

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

“…Although PTHrP is expressed by day 14 of pregnancy in rat mammary glands (738), the level remains quite low compared with the expression achieved in the immediate postpartum (738,1004) and with suckling (907,911). Studies in sheep have determined that clearance of PTHrP increased in pregnant goats beginning a day or two before expected delivery and even further during parturition (744,771) compared with nonpregnant animals. Most of the measurements were with assays designed to detect human PTHrP (364,744,956) rather than species-specific assays, and such assays will not detect the potentially more abundant (and biologically active) PTHrP (this issue is discussed in more detail in the next section).…”

Increased mammary blood flow in the lactating goat induced by parathyroid hormone‐related protein

“…The lowest dose of PTHrP infused in the present study gave a 17 % response, which is only just discernible above a background variation of 10 % in natural flow. This dose was equivalent to a calculated concentration of 40 pmol/l in blood supplying the mammlary gland, whereas concentrations of endogenous PTHrP in mammuary venous plasmiia of goats 7 days after parturition average only 1.2 pmol/l (Ratcliffe et al 1992). If one accepts that the lattel is repr-esentative of the concentrations to which the mammilary vasculature is exposed, then the doses of PTHrP infused during the present study must represent pharmacological levels.…”