Effect of thyroid status on plasma silicon levels of rats

The present study was undertaken to investigate the nature of the relationship between thyroid status and plasma silicon concentrations in bone maturation of rats from birth until the time of weaning. Virgin female Sprague-Dawley rats were bred overnight and then assigned to one of three groups: control, hypothyroid or hyperthyroid. Offsprings of dams were made hypothyroid or hyperthyroid relative to euthyroid controls during the neonatal period. Hypothyroid pups were given 0.05% (w/v) propylthiouracil in deionized water as the sole source of drinking fluid of the dams from day 12 of gestation until the young were sacrificed. Hyperthyroid pups received daily subcutaneous injection of L-thyroxine at a dose of 0.15-0.30 ug/g of body weight from postnatal day 2 until the day of sacrifice. All animals were allowed ad libitum access to standard Purina Rat Chow and to deionized water in polyethylene bottles. No attempt was made to control the dietary intake of silicon in these animals. All dams were weighed weekly throughout pregnancy and lactation or until the litter of young was sacrificed. Food consumption was recorded for control and hypothyroid dams during pregnancy. All offsprings of the dams were weighed daily until sacrificed. Six pups from the control group were each killed on postnatal days 3, 6, 9, 12, 15, 20, 25 and 30. Twenty four pups each.from hypo- and hyperthyroid groups were killed on each of days 7, 14, 21, and 28. Blood samples of these pups were later analyzed for plasma silicon by furnace atomic absorption spectrometry and for thyroxine and triiodothyronine by radioimmunoassay. Six pups from the longest surviving litters in each group were x-rayed weekly for serial assessment of bone maturation by the method of Hughes and Tanner. The study found no differences among the three groups of dams in food intake during pregnancy or in total weight gain during pregnancy and lactation. There was a significant effect of treatment on body weight and bone maturation of hypo- and hyperthyroid pups as compared with control. Significantly reduced body weight was apparent in hypo- and hyperthyroid pups by days 2 and 10 respectively. Hypothyroid pups exhibited retarded bone development by day 14, while hyperthyroid pups showed advanced skeletal maturation by day 7. These were accompanied by correspondingly lower and higher levels of thyroid hormones respectively. Thyroid function appeared to influence the pattern of plasma silicon levels during the postnatal period. Plasma silicon of control pups averaged 0.668 ppm on day 6, which rose to a maximum of 0.970 ppm on day 12 and then declined to 0.247 ppm after weaning. Silicon levels in thyroid privia and excess were generally lower and altered in developmental patterns relative to levels found in euthyroid condition. Changes in plasma silicon concentration with age were significant in each group of pups. The highest values for plasma silicon were 0.404 and 0.365 ppm on days 7 and 14 for hypothyroid pups and 0.466 ppm on day 14 for hyperthyroid pups. Periods of maximal plasma values for silicon corresponded to periods of the highest increment in bone maturity scores in each group. However, the data of the present study did not permit statistical analysis of the relationship between plasma silicon, chronological age and bone age of rats during the neonatal period. It is concluded that under the experimental conditions employed in this study, plasma silicon level is not influenced by thyroid status or related to bone development in rats.Land and Food Systems, Faculty ofGraduat