Studies of zinc metabolism in pregnant and lactating rats

The metabolism of 65Zn administered intramuscularly (Expt 1) or enterally (Expt 2) at the beginning of pregnancy in rats given a control or marginal-Zn diet was measured. In Expt 2 a comparison was also made between pregnant and non-pregnant rats. The loss of 65Zn (assumed to represent labile body Zn) was markedly reduced in animals fed on a marginal-Zn diet compared with controls, and this effect occurred very rapidly, i.e. within 48 h of introducing the marginal-Zn diet. Pregnancy itself had a much less important effect on 65Zn turnover than diet. Transfer of 65Zn to the litter was significantly greater in the animals fed on a marginal-Zn diet compared with controls but total Zn transfer was reduced. The effect of length of time on a marginal-Zn diet on fetal growth and composition was examined. Compared with controls, fetal weight was significantly greater in litters from mothers fed on a marginal-Zn diet during the last 4, 7 or 14 d of pregnancy, but no different in litters from mothers fed on a marginal-Zn diet throughout pregnancy. There were no differences in the proportions of protein or fat in the fetuses from mothers fed on the control or marginal-Zn diets but the Zn concentration was lower in litters from mothers fed on a marginal-Zn diet during part or all of the pregnancy when compared with controls. The transfer of 65Zn from mothers to litters during birth and the first 3 d of lactation was measured. There were no differences in maternal or litter 65Zn just before or just after birth, but within 72 h maternal 65Zn had significantly decreased and litter 65Zn increased. Increases in litter size were associated with greater total litter 65Zn but reduced individual fetal 65Zn. These experiments demonstrate the importance of an adequate daily supply of Zn during pregnancy. Although there is room for adaptation to a marginal-Zn intake (by reducing Zn excretion) the maintenance of Zn homeostasis is only possible in the absence of other forms of stress, such as pregnancy, to the body. The consequence of insufficient Zn at times of rapid fetal growth on carbohydrate and lipid metabolism warrants further investigation.