The effects of maternal undernutrition on maternal and fetal serum insulin-like growth factors, thyroid hormones and cortisol in the guinea pig.

The insulin-like growth factors (IGF-I and -II) are potential mediators of the effects of maternal undernutrition on fetal growth and muscle development. The effects of a 40% reduction in maternal feed intake on serum levels of the IGFs, the thyroid hormones and cortisol, were investigated for the last two trimesters (day 25 to birth). This level of undernutrition is known to cause a 35% reduction in fetal and placental weights, and a 20-25% reduction in muscle fibre number. Maternal IGF-I level was greater than non-pregnant levels on day 25 gestation, in both control and restricted dams, and declined with gestational age. The increase in IGF-I level in the 40% restricted group was approximately two-thirds that of control animals. Fetal serum IGF-I was also reduced in undernourished fetuses throughout gestation. Maternal IGF-II did not change with gestational age and was unaffected by undernutrition. Fetal IGF-II reached a peak at day 55 of gestation, this peak was greatly diminished by maternal feed restriction. Both IGF-I and IGF-II tended to be related to fetal, placental and muscle weights at day 65 of gestation. Thyroid hormone concentration declined in maternal serum and increased in fetal serum with increasing gestational age. Levels were not significantly affected by undernutrition. Both triiodothyronine (T3) and thyroxine (T4) were correlated with IGF-I in maternal serum (P < 0.05), but not in fetal serum. Cortisol levels were elevated by undernutrition in both maternal and fetal serum, and increased with gestational age. Cortisol was inversely correlated with serum IGF-I in both maternal and fetal serum. Maternal serum IGF-I may mediate the effects of undernutrition on fetal growth by affecting the growth and establishment of the feto-placental unit in mid-gestation. Fetal IGF-I may mediate the effects on muscle growth, whereas IGF-II seems to be related to hepatic glycogen deposition. Cortisol may play a role via its effect on the IGFs, but the thyroid hormones are unlikely to be important until the late gestation/early postnatal period.