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Circulating growth hormone (GH) concentrations increase in pregnancy and administration of GH during early-mid pregnancy increases fetal growth in well-fed pigs. To determine whether increased maternal GH could promote fetal growth when feed availability is restricted, fifteen cross-bred primiparous sows (gilts) were fed at approximately 30% of ad libitum intake, from mating onwards and were injected daily i.m. with recombinant porcine GH (pGH) at doses of 0, 13.4+/-0.3 and 25.6+/-0.5 microg/kg live weight from day 25 to day 51 of pregnancy (term approximately 115 days). Treatment with pGH increased maternal backfat loss between day 25 and day 51 of pregnancy, and increased maternal plasma IGF-I concentrations measured at day 51 of pregnancy. Fetal body weight, length and skull width at day 51 of pregnancy were increased by maternal treatment with pGH. Fetal plasma glucose concentrations were increased and maternal/fetal plasma glucose concentration gradients were decreased by maternal pGH treatment at 13.4, but not 25.6 microg/kg.day. Fetal plasma concentrations of urea were decreased by both levels of pGH treatment. Overall, fetal weight was negatively correlated with fetal plasma concentrations of urea, positively correlated with maternal plasma alpha-amino nitrogen concentrations and unrelated to glucose concentrations in either maternal or fetal plasma. This suggests that the availability of amino acids, not glucose, limits fetal growth in the first half of pregnancy in underfed gilts, and that maternal GH treatment may improve amino acid delivery to the fetus.

The effect of fasting (17-18 h) versus food restriction (70% for 80 +/- 13 days) on the IGF-IGF binding protein (BP) axis in female guinea pigs was studied and related to body weight, weight gain and food conversion efficiency. Circulating IGF-I was reduced in the fasted (13%) and food-restricted (50%) animals. IGF-II was only decreased (61%) in the food-restricted group. There was no effect of fasting on IGFBP-1 to -4 while IGFBP-1, -3 and -4 were reduced by 56%, 60% and 44% respectively, and IGFBP-2 increased by 72%, in the food-restricted group. Food restriction reduced the relative sizes of fat depots, spleen, liver, thymus and heart, increased those of adrenals, kidneys, pancreas, gastrointestinal tract, M. Biceps, M. Soleus and brain while those of uterus, lungs, thyroids and M. Gastrocnemius were unchanged. IGFBP-1 and -2 were negatively correlated to weight gain and food conversion efficiency in the ad libitum-fed group, while IGF-I, -II, IGFBP-1, -3 and -4 were positively correlated to body weight, weight gain and food conversion efficiency in the food-restricted group. The results show that acute and chronic food restriction have different consequences for the IGF-IGFBP axis. Furthermore, IGF-II as well as IGF-I are implicated in the control of body weight, weight gain and food conversion efficiency under conditions of restricted nutrition. Finally, IGFBP-1 and -2 may have different roles during chronic undernutrition compared with unrestrained nutrition in adult life.

Poor prenatal growth is associated with limited evidence of GH deficiency in adult humans, which may contribute to their increased risk of cardiovascular and metabolic disease. We therefore examined the effects of placental restriction of fetal growth (PR) on size at birth, neonatal fractional growth rate (FGR) and the circulating GH profile in adolescent and young adult sheep of both sexes. Moderate or severe PR decreased birth size and increased neonatal FGR of weight, crown-rump length and abdominal circumference. In adolescent males, mean and baseline GH concentrations correlated negatively and independently with birth weight and FGR of weight, and mean GH concentrations correlated negatively with current weight. In young adult males, mean GH concentrations correlated negatively and independently with birth shoulder height and FGR of shoulder height whilst, in young adult females, these correlations were positive. This suggests that restricted fetal growth and reduced neonatal growth rate in sheep are followed by elevated circulating GH in adolescent and adult males, but GH deficiency or increased GH clearance in adult females.