ADMINISTRATION OF INSULIN-LIKE GROWTH FACTOR-I, BUT NOT GROWTH-HORMONE, INCREASES MATERNAL WEIGHT-GAIN IN LATE PREGNANCY WITHOUT AFFECTING FETAL OR PLACENTAL GROWTH

During late pregnancy in the rat, circulating levels of insulin-like growth factor-I (IGF-I) and some IGF-binding proteins (IGFBP) decline. The aim of the present study was to determine the relationship of GH to circulating IGF and IGFBP in the late-pregnant rat and to examine the effects on maternal, fetal and placental growth of preventing the decline in serum IGF and IGFBP concentrations. During the first 9 days of pregnancy, IGF-I concentrations increased from 340 to 500-mu-g/l. Recombinant human (rh) GH at 2.4 mg/kg per day and rhIGF-I at 1.4 mg/kg per day were infused into pregnant rats via osmotic mini pumps during the second half of pregnancy. After pump implantation on day 11 of pregnancy, only IGF-I infusion significantly increased circulating IGF-I. A maximum IGF-I concentration of 907-mu-g/l was measured on day 14 during treatment with IGF-I, after which the serum concentration decreased to 510-mu-g/l by day 20 of pregnancy. The serum IGFBPs were examined using a Western ligand blot technique. Infusion of neither GH nor IGF-I returned the IGFBPs to non-pregnant levels. Administration of IGF-I slightly increased IGFBP-3 and a smaller 32 kDa IGFBP at days 17 and 20 of pregnancy. Neither fetal nor placental weight was significantly different between treatment groups. However, administration of IGF-I significantly increased maternal weight gain during the 10-day treatment period. Thus, pregnant rats infused with IGF-I gained 99 +/- 4 g (mean +/- S.E.M., n = 10) compared with rats treated with GH or vehicle which gained 72 +/- 4 g (n = 9) and 77 +/- 4 g (n = 10) respectively. The increase in maternal weight after administration of IGF-I was not due to increased litter size, fetal or placental weight. The increased maternal weight gain after IGF administration, without affecting fetal and placental weights, suggests a modification in the mode of maternal nutrient repartitioning during late pregnancy.