Osteocalcin as an Index of Osteoblast Function during and after Ovine Pregnancy*

Abstract

Fetal and neonatal calcium requirements impose heavy demands on maternal bone and mineral homeostasis. The functional response of maternal osteoblasts to this stress is poorly understood. Therefore, plasma osteocalcin (OC) levels were measured by homologous RIA in age-matched nonpregnant, pregnant, and postpartum ewes to evaluate osteoblast function. In pregnant ewes from day 35 of gestation to term, the plasma OC level was suppressed to 8.2 +/- 0.5 micrograms/liter (mean +/- SEM; n = 36) compared with age-matched nonpregnant ewes (18.3 +/- 1.1 micrograms/liter; n = 39; P less than 0.0005). Plasma OC rose to the nonpregnant value by day 20 postpartum and was elevated above this level for the following 40 days (e.g. 44.0 +/- 5.0 micrograms/liter at 48-53 days; P less than 0.0005). The timing of changes in plasma OC levels and weaning did not correlate. The validity of plasma OC measurement as a marker of osteoblast function was assessed by determining the OC plasma production and clearance rates using an [125I]ovine OC infusion method. The OC plasma production rates in matched controls (n = 6), pregnant (n = 9), and 48-53-day postpartum sheep (n = 7) were 1.5 +/- 0.2, 0.5 +/- 0.04 (P less than 0.001 vs. control), and 3.6 +/- 0.6 mg/day (P less than 0.005 vs. pregnant sheep), respectively. In one ewe studied longitudinally, the OC plasma production rate increased by 15 days after parturition and achieved a 10-fold elevation at 49 days postpartum. The OC plasma clearance rate (3.3 +/- 0.3 liters/h) was the same in control, pregnant, and postpartum ewes. It is concluded that 1) changes in plasma OC levels during and after ovine pregnancy reflected changes in OC production, 2) plasma OC measurements are likely to be a useful index of osteoblast function in pregnancy, and 3) osteoblast function appears to be depressed during ovine pregnancy and enhanced markedly in the interval 20-60 days postpartum. The relationship between osteoblast function, as indicated by OC production, and bone formation remains to be clarified.

Osteocalcin, Skeletal Alkaline Phosphatase, and Bone Mineral Content in Very Low Birth Weight Infants: A Longitudinal Assessment

“…The maternal serum Gla concentrations measured in peripheral blood drawn immediately before delivery were consistent with previous reports from both animal and human studies (25,26). The Gla concentrations were low.…”

“…Two of the 20 were below the lower detection limit (0.034 nmol/L) of the RIA, and the mean + SD serum concentration for all 20 women was 0.2 + 0.2 nmol/L. The low maternal Gla serum concentration observed throughout pregnancy has been postulated to reflect both placental clearance (25) and decreased osteoblast production (26). A definitive explanation awaits further study.…”

Impact of parity on bone metabolism throughout the reproductive cycle in sows

“…Therefore, the influence of feed intake is probably minimal. The fluctuations of bone formation and resorption observed in the present study are in accordance with fluctuations around parturition found in cows (Naito et al, 1990;Peterson et al, 2005;Ekelund et al, 2006), sows (Liesegang et al, 2005;Counotte et al, 2009;Lauridsen et al, 2010;Cools et al, 2014), and goats and sheep (Farrugia et al, 1989;Liesegang et al, 2006 and.…”

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

“…In the bovine (Van Mosel and Corlett, 1990) as in the ovine (Farrugia et al, 1989;Pastoureau et al, 1991) and human species (Delmas et al, 1986) (Braithwaite, 1976 Blum et al, 1972) and healthy cows .…”