Fetal growth, glucose tolerance and plasma insulin concentration in rats given a marginal-zinc diet in the latter stages of pregnancy

Abstract

1.Wistar rats were fed on a control semi-synthetic diet throughout pregnancy, or a control diet in the first 2 weeks and a marginal-zinc diet in the 3rd week of pregnancy. On day 20, after an overnight fast, half the animals in each group were given glucose by gavage and the 0-30 rnin rise in blood glucose measured in tail blood. After 60 rnin blood was taken by cardiac puncture for glucose and insulin assay. Maternal pancreases were removed and the Zn contents measured. Fetuses from each litter were combined for wet/dry weights, protein and DNA determinations.2. Plasma insulin concentration was higher, and glucose concentration and pancreatic Zn content lower, in pregnant v. non-pregnant animals of similar age, fed on the same diet. Pancreatic Zn content was lowest in the marginal-Zn group of pregnant rats. Fetuses from mothers fed on the marginal-Zn diet during the last week of pregnancy were slightly heavier than controls and had a significantly higher protein: DNA ratio. The &30 min rise in blood glucose was significantly greater in the marginal-Zn animals.3. In a second experiment, pregnant rats were given similar diets to those used in the first study, but the marginal-Zn diet was given for a shorter period (days 15-19 of pregnancy). On day 19 the rats were meal-fed and on day 20, after an overnight fast, an oral glucose dose was administered. Tail-blood was taken at timed intervals up to 60 min post-dosing for glucose assay. Both maternal and fetal blood glucose and insulin concentration was measured 70 rnin post-dosing.4. Values for maternal and fetal blood glucose and plasma insulin, measured 70 rnin after the administration of a glucose dose, were similar in the two groups, but the initial rise in blood glucose concentration was again significantly higher in pregnant rats given the marginal-Zn diet towards term.5. It is suggested that the change in growth and composition, observed in fetuses from rats given a marginalZn diet in later pregnancy, is associated with altered maternal carbohydrate metabolism.Rats given a marginal-zinc diet towards the end of pregnancy produce pups which are large for their gestational age. However, rats given a marginal-Zn diet from the start of pregnancy are no different from control-fed animals, and the earlier in pregnancy the marginal-Zn diet is introduced the less is the effect on fetal growth (Fairweather-Tait et al. 1984. This indicates an adaptive response to longer periods of marginal-Zn intake. The reasons for the observed increase in fetal growth are unclear, but the fact that glucose is the major metabolic fuel for the developing fetus (Schwartz, 1968), together with evidence that inadequate dietary Zn results in abnormal carbohydrate metabolism in rats (Reeves & O'Dell, 1983) and man (Baer et al. 1985), suggest that the increased size of pups may be linked to changes in glucose utilization.This possibility was investigated by studying the effect of marginal-Zn intake during the latter stages of pregnancy in the rat on growth, blood glucose and insulin levels ...

Effect of reduced dietary zinc intake on carbohydrate and Zn metabolism in the genetically diabetic mouse (C57BL/KsJ db+/db+)

“…Although there was no evidence from the first experiment of a difference in feeding pattern between dietary groups, investigations to verify the increased blood glucose concentrations observed in the second experiment should be repeated under conditions of strict dietary control. Results from the present study, and those of a previous study showing increased blood glucose concentations after oral dosing in rats fed on a marginal-Zn diet in late pregnancy (Southon et al 1988 a), suggest a relation between carbohydrate utilization and dietary Zn supply, particularly in conditions associated with hyperinsulinaemia and tissue insulin resistance. Since circulating insulin levels in both studies were unaffected by the reduced dietary Zn intake, the possibility of increased insulin resistance or reduced physiological potency of the hormone should be.…”

The effect of dietary zinc depletion and repletion on rats: Zn concentration in various tissues and activity of pancreatic γ-glutamyl hydrolase (EC3.4.22.12) as indices of Zn status

“…Findings from the present study identify pancreas, spleen, tibia, liver, kidney and plasma as tissues where the Zn concentration was responsive to short-term Zn depletion. The pancreas is reported to be highly sensitive to Zn depletion in rats (Williams & Mills, 1970;Kramer, 1984;Southon et al 1988), sheep (Ott et al 1964) and pigs (Crofton et al 1983). In the present study the concentration of Zn in the spleen was also sensitive to depletion.…”