Effect of Chronic Parathyroidectomy on Calcium Metabolism in the Lactating Rat

Abstract

This study examined the effect of chronic parathyroidectomy (PTX) in rats on calcium homeostasis in milk and serum and on litter growth rate throughout lactation. Parathyroidectomy was carried out by excision 8 weeks before mating and any animals with evidence of parathyroid regeneration over this time were discarded. Maternal serum and milk samples were collected at days 6, 12 and 20 of lactation and serum samples from the pups were obtained at day 20. Litter growth was measured by weighing the pups daily. Significantly lower concentrations of ionized and total calcium and significantly higher concentrations of phosphate in the serum were found in the PTX animals compared with the sham-operated controls (P< 0·001). The ratio of ionized to total calcium in serum was significantly lower in the PTX group. The mean total calcium concentration in milk was significantly higher at day 6 in the PTX group (P< 0·05) but was not different from the sham-operated group at days 12 and 20. The ratio of milk calcium to percentage milk solids was the same in both groups of animals at all three sampling periods. Litter growth rate was not significantly different in the two groups up to day 5 or from days 12 to 20. It was lower in the PTX group (P< 0·001) between days 5 and 12. The total concentration of calcium in serum from the young was not significantly different in the two groups. It was concluded that parathyroid hormone (PTH) is required for normal maternal calcium homeostasis in serum during lactation and therefore its absence may affect milk homeostasis indirectly for part of lactation. In contrast the concentration of calcium in milk and litter growth rate can be maintained at normal levels in late lactation suggesting that PTH is not an essential hormone in the regulation of calcium levels in milk.

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

“…Intestinal calcium absorption increased normally during lactation despite simultaneous parathyroidectomy and vitamin D deficiency (93). Milk calcium content was significantly higher at day 6 of lactation and normal during the remainder of lactation in parathyroidectomized rats, despite the serum calcium being 50% of normal (295). This confirms that achieving a normal calcium content in milk does not require PTH.…”

“…In other studies, parathyroidectomy in rats during lactation caused a 50% fall in serum or ionized calcium and an increase in serum phosphorus when 0.4 and 1% calcium diets were consumed (295,569,718). The magnitude of hyperphosphatemia in parathyroidectomized rats lessened as lactation progressed (295).…”

“…The magnitude of hyperphosphatemia in parathyroidectomized rats lessened as lactation progressed (295). Calcitriol increased in lactating, parathyroidectomized rats to at least double the value of nonlactating, parathyroidectomized rats and nonlactating, sham-operated rats, but remained below the concentration of lactating sham-operated rats (569,718).…”

“…Weight gain of the pups was normal when lactating, parathyroidectomized rats consumed a 2% calcium diet (395), whereas weight gain was modestly reduced as early as 24 h after parathyroidectomy when the mothers consumed 1 or 0.4% calcium diets (295,569). This reduced weight gain was not seen in pups nursed by Pth null mice compared with WT mice; the ash weight and calcium content were no different at the end of 3 wk of lactation (133).…”

Maintenance of Secretion of Calcium and Magnesium During Infusions of Parathyroid Hormone to Lactating Goats

“…In most studies of lactating, parathyroidectomized rats reduced growth rates of the offspring have been reported (Cowie & Folley, 1945;Fairney & Weir, 1970;Fry, Curnow, Gutteridge & Retallack, 1979). Considerable controversy exists in the literature concerning the role of PTH in regulating calcium secretion into the milk, however.…”