Changes in the skeleton during gestation and lactation in the rat

Abstract

The amount present in the liver must be very small, however, and it is evident that the main tendency is for azobenzene to be rapidly eliminated as the water-soluble hydrazo derivative. Azobenzene is not carcinogenic, but in work which is being carried out with the carcinogenic p-dimethylamino-azobenzene evidence has been obtained that similar metabolic changes take place. In this case, however, the hydrazo derivative dbes not appear to be so stable and undergoes the benzidine rearrangement in the body more readily, since a substance giving the colour reaction of one of the 'benzidine change' products of p-dimethylamino-azobenzene can be extracted directly from the neutral or alkaline urine.

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

“…Consistent with this, an increase in femoral ash weight and calcium content has been found in rats and sheep at mid-pregnancy and term (69,629), which correlates with an increasing calcium content of the diet (818), while a progressive 10 -15% increase in total body mineral content during pregnancy has been observed by DXA in normal Black Swiss mice (296,478,827,994). However, not all studies are consistent with this since no change in femoral or tibial ash weight or calcium content was observed in several studies of rats (362,598,628,972), decreases in lumbar spine BMD by DXA and histomorphometry have been observed at mid-pregnancy and term in rats (408), and BMD of the whole body and lumbar spine decreases by DXA in C57BL/6J mice (477,580). Some of these differences are likely due to differing calcium contents of the diet, with dietary calcium restriction consistently causing reduced skeletal mineral content by the end of pregnancy in rats (64,271,740) and goats (55).…”

“…Histomorphometric studies have shown that osteoclast-mediated bone resorption is increased primarily in trabecular compartments during lactation in rats (271,408,629,920,972), beagles (300,626), and mice (34,194,956). Increases in osteoblast number, osteoblast surface, osteoid thickness, osteoclast number, and resorptive surfaces are noted, with the increases being more marked in the resorptive parameters (34,194,626,956).…”

“…In most histomorphometry, microCT, and electron microscopy studies, despite this apparent increase in bone turnover, there was no net change in femoral or tibial bone mass at the end of pregnancy in Cobs, Holtzman, Lister, and Sprague-Dawley rats on a 0.45% calcium diet (362,598,628,972) or in beagles on a 2% calcium diet (300). Exceptions include reduced bone volumes and trabecular thickness in the lumbar spine at the end of pregnancy in SpragueDawley rats consuming 1.2% calcium (920), and the opposite result of increased trabecular number, thickness, and bone volume of the vertebrae, and increased calcein labeling and bone formation rates throughout the vertebrae, in Wistar rats on a 0.88% calcium diet (822).…”

Plasma Calcium Control in the Rat Fetus. I. Influence of Maternal Hormones

“…As for TX pregnant rats, the rela tive content of calcium in TX lactating fe males was unchanged [21]. The epiphysis be ing more sensitive to demineralization occur ring during lactation [18], it would be of interest to check the effect of CT deficiency on this part of bone during gestation in rats.…”

“…The difference in bone response to TX between the two species during gesta tion might be explained by a difference in bone sensitivity to the calcium stress. It is known that there is no loss of ash in femurs during gestation in the rat [17,18]. Using 45Ca kinetic data, a 20% decrease in the total skeletal calcium was calculated in ewes dur ing gestation and early lactation [19].…”