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 mediator s of the effects of maternal undernutrition on fetal growth and muscle development. The effects of a 40% reduction in maternal feed intake o n serum levels of the IGFs, the thyroid hormones and cortisol, were in vestigated for the last two trimesters (day 25 to birth). This level o f undernutrition is known to cause a 35% reduction in fetal and placen tal weights, and a 20-25% reduction in muscle fibre number. Maternal I GF-I level was greater than non-pregnant levels on day 25 gestation, i n both control and restricted dams, and declined with gestational age. The increase in IGF-I level in the 40% restricted group was approxima tely two-thirds that of control animals. Fetal serum IGF-I was also re duced in undernourished fetuses throughout gestation. Maternal IGF-II did not change with gestational age and was unaffected by undernutriti on. 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 seru m and increased in fetal serum with increasing gestational age. Levels were not significantly affected by undernutrition. Both triiodothyron ine (T3) and thyroxine (T4) were correlated with IGF-I in maternal ser um (P<0.05), but not in fetal serum. Cortisol levels were elevated by undernutrition in both maternal and fetal serum, and increased with ge stational age. Cortisol was inversely correlated with serum IGF-I in b oth maternal and fetal serum. Maternal serum IGF-I may mediate the eff ects of undernutrition on fetal growth by affecting the growth and est ablishment of the feto-placental unit in mid-gestation. Fetal IGF-I ma y mediate the effects on muscle growth, whereas IGF-II seems to be rel ated to hepatic glycogen deposition. Cortisol may play a role via its effect on the IGFs, but the thyroid hormones are unlikely to be import ant until the late gestation/early postnatal period.