Modulation of serum parathyroid hormone and ionized calcium concentrations during reproduction in rats fed a low calcium diet

Abstract

Moderate dietary restriction of calcium (0.1% Ca) was used to accentuate the changes in serum immunoreactive parathyroid hormone (iPTH) that had been reported earlier in lactating rats fed 0.4% Ca diet. In addition, the effects of this low-Ca diet on serum total and ionized Ca and iPTH during pregnancy, extended lactation, and weaning were examined. The positive correlation between serum total and ionized Ca was highly significant (r = 0.88, p less than 0.001, n = 120). Serum iPTH was significantly higher (36%) in pregnant rats on the day of parturition compared to nonmated controls, and there was a concomitant decrease in both total and ionized serum Ca. Within 1 day after parturition, however, serum Ca had risen to the control level. Serum iPTH remained significantly elevated during the first 2 weeks of lactation, and increased further during the third week of lactation to a level more than twice that of nonlactating controls. Serum Ca fell gradually during the second week of lactation. The high serum iPTH levels were maintained for another 2 weeks when lactation was extended with foster litters. Within 6 hr of removal of the suckling pups on day 16 of lactation, maternal serum ionized and total Ca had risen and serum iPTH had fallen; all three parameters were at levels similar to those of nonmated controls by 24-48 hr after weaning. The data suggest that serum ionized Ca is a major factor contributing to the hyperparathyroid state during lactation in rats fed a low-Ca diet.

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

“…This may be especially true in rats where the hourly fetal demand for calcium almost equals the amount of calcium present in the maternal circulation (196). Consistent with this, increased litter number and weight are associated with a lower serum calcium in the mother (90), while pregnant rats fed a low-calcium (0.1%) diet experienced a marked decline in both serum calcium and ionized calcium during the last several days before delivery (321). A low-calcium diet similarly provoked hypocalcemia in pregnant ewes compared with consumption of a usual and a high-calcium diet (69).…”

“…The serum calcium of lactating rats has been quite variable in published reports, and not clearly explained by the calcium content of the diet: hypercalcemia on 1.5 or 1.2% calcium (86,318); normocalcemia on 1.6% (568), 1% (991), 0.5% (114), 0.4% calcium (91,318,569), and an unspecified diet (337); low blood calcium on 1.2, 0.9, 0.8, and 0.4% calcium (76,90,320,321,568,718,920,927,989); and marked hypocalcemia on 0.1, 0.04, and 0.01% calcium (32,320,321,568,991). The ionized calcium has been low on a 1.6% calcium diet (568), high on a 1.2% calcium diet (318), low on a 0.8% calcium diet (989), normal (318) and low on a 0.4% calcium diet (90,568,569), and low on a 0.1% calcium diet (32, 568).…”

“…In most studies of lactating rats PTH has increased across a wide range of diets containing 0.4 -1.4% calcium (32,90,254,318,320,337,627,807,920); however, PTH remained unchanged in lactating rats on 1.6, 0.4, and 0.1% calcium in one study (568), and on an unspecified diet (337). A low-calcium diet (320,321) and nursing larger litters (320, 708) cause higher PTH concentrations, whereas if only three pups are nursed PTH is normal (320).…”

TRIENNIAL GROWTH SYMPOSIUM— Effects of dietary 25-hydroxycholecalciferol and cholecalciferol on blood vitamin D and mineral status, bone turnover, milk composition, and reproductive performance of sows12

“…According to Meissonier et al (1980) and Lingaas et al (1992), plasma Ca of sows decreased with progressing parity, which was confirmed by Liesegang et al (2005) and which is consistent with the observations in study 1. Likewise in the rat, plasma Ca has been reported to decrease during the last several days of pregnancy (Garner et al, 1988). Kovacs and Kronenberg (1997) suggested that maternal losses of Ca to a litter of rapidly growing fetuses probably exceed the maternal Ca stores (Garel, 1987).…”

Renal Regulation of Calcium-Phosphate Metabolism in Single- and Twin Pregnant Goats

“…As a consequence, hormonal regulation undergoes adaptive changes. This particularly applies to parathormone, calcitriol, and calcitonin (GARNER et al 1988; DE ROUFFIGNAC & QUAMME 1994;DAI et al 2001;HUBERT et al 2007;MUSCHER et al 2008). In pregnant women, blood plasma concentrations of parathormone and calcitonin do not differ significantly from those observed in non-pregnant women (ARDAWI et al 1997;MESTMAN 1998;PRENTICE 2000), whereas the level of calcitriol increases more than twofold.…”