Metabolic aspects of bone resorption in calcium-deficient lactating rats

Abstract

Lactating female rats were fed diets containing 1.0, 0.1, or 0.04% Ca for 21 days. Fat-free dry weight, ash weight, calcium and phosphorus content of the humerus, plasma calcium levels, and bone acid and alkaline phosphatase activities were compared to those of nonlactating rats fed the same diets. Bone, plasma, and urinary cAMP levels were also studied. Dietary calcium deficiency and/or lactation caused significant loss of bone mass from experimental animals. Urinary cAMP levels reflecting increased parathyroid activity were elevated by the stresses of lactation and calcium deficiency over those of control animals. Plasma and bone levels of cAMP were not different. Bone alkaline and acid phosphatase activities were affected only by the most extreme stress. The results demonstrated that the calcium-deficient lactating rat is an excellent model for bone resorption studies.

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

“…That resorption of bone during lactation is needed to support milk production has been confirmed by finding that a low-calcium diet initiated at delivery causes greater skeletal losses that can exceed 43% of trabecular bone mineral content in rats and mice (37, 271,320,350,355,708,991). Furthermore, nursing larger numbers of pups, which means increased milk production, causes greater resorption of bone in rats (320,708).…”

“…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).…”

The impact of mammalian reproduction on cancellous bone architecture

“…The animals above were fed ad libitum a balanced preparatory diet recommended for caged rats, with a calcium content of 0n88 % and they should not have been calcium-deficient according to established animal husbandry practice. In a study by Wong et al (1980) using a calcium-deficient diet in which the calcium content of the feed was reduced to 0n04 % the rats lost a significant amount of bone during the experimental period (see also Bawden & McIver, 1964). Similarly Ellinger et al (1952), who studied the effect of 3 successive pregnancy and lactation cycles in rats on calcium-deficient diets, observed that the animals had a moderate loss of bone during the first pregnancy followed by a severe loss during the lactation period that was apparently independent of dietary calcium (Blanusa et al 1971 ;Rasmussen, 1977 ;Brommage & DeLuca, 1985).…”

1α-Hydroxyvitamin D₃ Prevents the Decrease of Bone Mineral Density in Lactating Beagles

“…Lactating rats were found to have lost bone mineral, as determined by a variety of methods [7,10,18,27]. The bone loss could be increased by consumption of a low calcium diet starting at delivery [7,19,24]. Rats, which are short-lived animals, have large litter sizes and the bone change during lactation would be substantial.…”