Administration of growth hormone or IGF-I to pregnant rats on a reduced diet throughout pregnancy does not prevent fetal intrauterine growth retardation and elevated blood pressure in adult offspring.

Increasing evidence from human epidemiological studies suggests that poor growth before birth is associated with postnatal growth retardation and the development of cardiovascular disease in adulthood. We have shown previously that nutritional deprivation in the pregnant rat leads to intrauterine growth retardation (IUGR), postnatal growth failure, changes in the endocrine parameters of the somatotrophic axis, and to increased blood pressure in later life. In the present study, we investigated whether administration of insulin-like growth factor-I (IGF-I) or bovine growth hormone (GH) during pregnancy could prevent IUGR and/or alter long-term outcome. Dams from day 1 of pregnancy throughout gestation received a diet of ad libitum available food or a restricted dietary intake of 30% of ad libitum fed dams. From day 10 of gestation, dams were treated for 10 days with three times daily subcutaneous injections of saline (100 microl), IGF-I (2 micrograms/g body weight) or GH (2 micrograms/g body weight). Maternal weight gain was significantly increased (P<0.001) in ad libitum fed dams treated with GH, (98.9+/-4.73 g) compared with the IGF-I (80.5+/-2.17 g) and saline-treated (70.7+/-2.65 g) groups. There was a small increase in maternal weight gain (P<0.06) in 30% ad libitum fed dams following GH (16.3+/-2.47 g) and IGF-I (15.8+/-1.97 g) treatment compared with saline (9.2+/-1.96 g). Whole spleen, kidney and carcass weights were significantly (P<0.05) increased in ad libitum fed and 30% ad libitum fed dams with GH treatment. Circulating IGF-I was significantly increased (P<0.001) in ad libitum fed dams with both IGF-I (369.6+/-32.33 ng/ml) and GH (457.9+/-33.32 ng/ml) compared with saline treatment (211.7+/-14.02 ng/ml), and with GH (223.4+/-23.72 ng/ml) compared with saline treatment (112.0+/-7.33 ng/ml) in 30% ad libitum fed dams. Circulating GH binding protein (GHBP) levels were significantly reduced (P<0.05) in GH-treated (299.1+/-51.54 ng/ml) compared with saline-treated (503.9+/-62.43 ng/ml) ad libitum fed dams, but were not altered in 30% ad libitum fed dams. There was no significant effect of either IGF-I or GH treatment on fetal weight, placental weight, fetal organ weights or circulating IGF-I levels in both ad libitum fed and 30% ad libitum fed fetuses. Offspring of 30% ad libitum fed dams remained significantly growth retarded postnatally and showed elevated blood pressure in later life. The increased maternal weight gain following IGF-I or GH administration, without an effect on fetal and placental weights, suggests a modification in the mode of maternal nutrient repartitioning during mid to late pregnancy at the expense of the fetus.

The transition from fetus to neonate--an endocrine perspective.

The transition from fetus to neonate involves three phases: late gestation, parturition and the processes needed to establish independent homoeostatic regulation after separation from the placenta. These phases are regulated by a series of fetal and placental endocrine events. Glucocorticoids have an important role in the preparation for birth, including involvement in lung and cardiac development, and the maturation of enzymes in a variety of pathways. Fetal cortisol production is, in turn, also under hormonal control. Parturition is a complex process, which is still poorly understood in humans. The final steps are largely dependent on the effect of prostaglandin F2 alpha on the myometrium associated with increased oxytocin activity. The transition to birth is accompanied by changes in respiration, circulation, glucose homoeostasis, and the onset of independent oral feeding and thermoregulation. Several examples of endocrine components of the transition from fetal to neonatal life are reviewed here: the role of prostanoids, the onset of thermogenesis, and changes in the thyroid hormone and growth hormone axes. The effects of hormone levels on prematurity and growth retardation are also discussed.

The maternal, fetal and postnatal somatotrophic axes in intrauterine growth retardation.

Both the maternal and fetal somatotrophic axes are closely linked to fetal substrate supply. Nutritional insults at critical stages of fetal development may lead to permanent reprogramming of the relationships between these factors. The consequences of reprogramming during fetal life may be harmful to metabolic, endocrine and cardiovascular homoeostatic mechanisms in postnatal life. The exact mechanisms that lead to reprogramming during fetal life need thorough investigation before effective strategies to deal with this problem can be devised.

Effects of maternal captopril treatment on growth, blood glucose and plasma insulin in the fetal spontaneously hypertensive rat.

In the spontaneously hypertensive rat (SHR) fetal growth and metabolism are abnormal. It has been speculated that maternal hypertension may be the cause of these abnormalities. Captopril treatment, which reduces maternal blood pressure, during pregnancy and lactation, is reported to have a beneficial effect postnatally, normalizing the blood pressure of offspring in the SHR. In the present study, the effects of maternal captopril treatment on fetal growth and plasma metabolites were investigated in the fetuses of two rat strains (SHR and Wistar-Kyoto (WKY)), in order to determine whether normalizing maternal blood pressure also normalized abnormalities in fetal growth and metabolism. On fetal Day 20, SHR fetuses were lighter and placentae were heavier than for the corresponding WKY. Captopril had no effect on fetal weight in the SHR, but decreased it in the WKY. There was no effect of captopril on placental weight. Fetal plasma insulin levels were higher in the SHR than in the WKY and were decreased by captopril treatment in both strains. Fetal blood glucose was elevated and fetal blood lactate was decreased in captopril-treated litters from both strains. Captopril had no effect on fetal plasma IGF-1 but fetal plasma IGF-2 levels were lower in the captopril-treated SHR than in the captopril-treated WKY. These findings suggest that maternal captopril treatment decreases insulin secretion in the fetal rat. High levels of fetal plasma insulin suggest that the SHR fetus is insulin resistant. Fetal insulin levels may contribute to the adverse consequences of gestational captopril treatment observed in many species. The differences in the effect of captopril on the two strains suggest that there are underlying endocrine differences in the SHR.

Consequences of maternal undernutrition for fetal and postnatal hepatic insulin-like growth factor-I, growth hormone receptor and growth hormone binding protein gene regulation in the rat.

The mechanisms that contribute to postnatal growth failure following intrauterine growth retardation (IUGR) are poorly understood. We demonstrated previously that nutritional deprivation in the pregnant rat leads to IUGR in offspring, postnatal growth failure and to changes in endocrine parameters of the somatotrophic axis. The present study examines the effects of maternal undernutrition (30% of the ad libitum available diet; IUGR group) throughout pregnancy on hepatic insulin-like growth factor-I (IGF-I), growth hormone receptor (GHR) and GH-binding protein (GHBP) gene expression using solution hybridisation/RNase protection assays (RPAs). Animals were killed at fetal (E22, term=23 days) and postnatal (birth, days 5, 9, 15, 21) ages, livers were collected and RNA extracted for RPAs. Results demonstrate the presence of all IGF-I mRNAs resulting from transcription start sites (ss) in exon 1 (ss1/2, ss3, ss2 spliced), exon 2, the two IGF-I E-domain variants (Ea and Eb) as well as GHR and GHBP mRNAs in hepatic tissue at E22 in both the ad libitum fed and IUGR offspring. In the postnatal liver, IGF-I ss1/2, ss3, ss2 spliced, Ea and Eb IGF-I variants as well as GHR and GHBP mRNA transcripts increased in abundance from birth to day 21. IGF-I exon 2 transcripts were relatively constant from E22 until postnatal day 15, then increased at postnatal day 21 in both the ad libitum fed and IUGR offspring. The expressions of all hepatic IGF-I leader exon ss and Ea domain variants were significantly reduced in IUGR offspring (P<0.05) from E22 to postnatal day 9. In contrast, relative abundance of hepatic IGF-I Eb variants, GHR and GHBP mRNAs were unaltered in IUGR offspring compared with the ad libitum fed animals. Whether these postnatal effects of undernutrition are a direct consequence of IUGR or whether they are related, in part, to differences in postnatal food intake remains to be investigated. In summary, we have demonstrated that hepatic IGF-I ss within exon 1 and exon 2 are coordinately regulated. Use of exon 1 ss increased during normal development and decreased with IUGR without changes in GHR or GHBP gene expression. Eb transcripts, thought to represent GH-dependent endocrine regulation of IGF-I, were unchanged in IUGR. These results suggest a possible postreceptor defect in GH action as a consequence of IUGR.

Fetal growth and placental function.

Fetal growth is largely determined by the availability of nutrients to the fetus. The fetus is at the end of a supply line that ensures delivery of nutrients from the maternal/uterine circulation to the fetus via the placenta. However, this supply line can not be regarded as a linear relationship. Maternal undernutrition will not only reduce global nutrient availability but will also influence the maternal and fetal somatotrophic axis. Both endocrine systems react in a very similar way to limited substrate supply. The hormones of the fetal somatotrophic axis, and in particular insulin-like growth factor (IGF)-1, are important regulators of fetal growth. Placental function is pivotal to materno-fetal nutrient and metabolite transfer. Placental function in turn, is heavily influenced by the maternal and fetal growth hormone (GH)-IGF-1 system. The placenta itself is also an active endocrine organ and it produces a large number of hormones including GH and IGF-1 as well their corresponding receptors. Thus the placenta can no longer be considered merely a passive conduit for fetal nutrition. Rather, it is actively involved in the integration of nutritional and endocrine signals from the maternal and fetal somatotrophic axes.

Fetal and placental glucose and amino acid uptake in the spontaneously hypertensive rat.

Until late in gestation, fetal spontaneously hypertensive rat (SHR) is growth retarded. Fetal growth rate increases after placental hypertrophy occurs between fetal days 18 and 20. The increase in placental mass may result in improved transfer of macro nutrients to the fetus and thus stimulate growth. In this study, fetal and placental uptake of the glucose analog 3-O-methyl glucose (3MG) and the amino acid analog amino-isobutyric acid (AIB) from the maternal circulation were compared in the SHR and Wistar-Kyoto (WKY) on days 16, 20 and 22 of gestation. Placental 3MG uptake (d/min/g tissue wet weight) was decreased in the SHR on days 20 and 22 but no differences were observed in fetal 3MG uptake. Increased placental mass in the SHR meant that total placental 3MG uptake was greater in the SHR. Placental uptake of AIB (d/min/g tissue wet weight) was much lower in the SHR (on days 16, 20 and 22) and the decrease was not compensated for by increased placental mass. Fetal uptake of AIB was decreased on days 20 and 22 (P<0.05). AIB uptake (d/min/g tissue wet weight) by the carcass and the internal organs (brain, heart, kidney, liver and lung) was also lower in the SHR. These findings indicate that although fetal growth in the SHR increases rapidly in late gestation following placental hypertrophy, it does so despite a pronounced deficit in amino acid uptake.

Glucocorticoid activity in the fetal spontaneously hypertensive rat.

Fetal exposure to high concentrations of corticosteroids in the rat is associated with elevated blood pressure in postnatal life. In this study we have investigated indicators of corticosteroid activity in fetal spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY) in order to determine whether fetal corticosteroid exposure is increased in the SHR. Placental 11beta-hydroxysteroid dehydrogenase (11beta-HSD) activity, which prevents maternal steroids from crossing the placenta, was not impaired in the SHR. Concentrations of amniotic fluid corticosterone were significantly decreased in the SHR compared with the WKY at fetal Day 20, but were not significantly different on fetal Days 16 or 22. This suggests that rather than increased exposure to corticosteroids in the SHR fetus corticosteroid exposure may be reduced. Expression of lung surfactant protein A (Sp-A), a gene induced in late gestation by corticosteroids, was decreased in the SHR. In addition, differences in amniotic fluid electrolyte concentrations were observed which may reflect delayed renal maturation in the fetal SHR. These data suggest that the SHR fetus is exposed to low concentrations of corticosteroids and that the late gestation rise in fetal corticosteroid may be delayed in the SHR.

The effects of ovine placental lactogen and bovine growth hormone on hepatic and mammary gene expression in lactating sheep.

The ability of ovine placental lactogen (oPL) to bind to the growth hormone receptor (GHR) raises the possibility that oPL may exert a growth hormone (GH)-like action on galactopoiesis. We have compared the effects of treating lactating ewes for 5 days with an equimolar dose (0.1 mg/kg/day, administered as two equal doses 12 hourly) of either bovine growth hormone (bGH) (n = 10), oPL (n = 10) or saline (n = 9) on hepatic and mammary GHR, insulin-like growth factor-I (IGF-I) and IGF-binding protein-3 (IGFBP-3) gene expression and hepatic GHR number. Hepatic GHR and IGFBP-3 mRNA were unaltered by bGH or oPL treatment. Hepatic IGF-I mRNAs increased following bGH (P < 0.05) but not oPL treatment. GHR gene expression was greater in liver compared to mammary gland extracts. There was no effect of either bGH or oPL treatment on mammary GHR, IGF-I or IGFBP-3 mRNA or hepatic GHR number. These studies confirm the galactopoietic effects of bGH in lactating ruminants and suggest that the mechanism of this action is not via increased hepatic GHR number or gene expression. In addition, the increase in hepatic but not mammary IGF-I mRNA with bGH treatment suggests an endocrine action of IGF-I on milk synthesis. These studies also demonstrate that an equimolar dose of oPL is not galactopoietic or somatogenic in the lactating ewe.

Perinatal growth disturbance in the spontaneously hypertensive rat.

Disproportionate fetal and placental growth are associated with the development of hypertension in the rat and human. Here we report differences in fetal, neonatal, and placental growth, and in metabolism and endocrinology, between the spontaneously hypertensive rat (SHR), a genetic model for human essential hypertension, and the control Wistar-Kyoto (WKY) strain. Gestation in SHR (23 d) was longer than in WKY by 20 h. Body weights were lower in the SHR from fetal d 16 to 20 and on postnatal d 15. However, on fetal d 22 and postnatal d 1, there was no significant difference in body weight between SHR and WKY. SHR placentas were larger than those of WKY at d 20, and by term there was a difference of 30% (p < 0.01). Other indices of disproportionate growth were hypertrophy of the fetal heart and kidney and decreased ponderal index in the SHR neonate. Blood glucose in SHR fetuses was lower than in WKY fetuses (p < 0.05), whereas blood lactate was higher (p < 0.05) and fetal hematocrit was reduced (p < 0.001). These findings suggest undernutrition and placental insufficiency may occur in SHR fetuses. Plasma IGF-II was increased on the last day of gestation in both strains, whereas IGF-I was unaltered. Fetal liver IGFBP-2 mRNA and plasma IGFBP-2 levels were reduced in SHR on fetal d 20 and 22 (p < 0.01). Differences in growth and endocrine and metabolic parameters suggest abnormal perinatal physiology in the SHR, which may influence the later development of hypertension.

Ovine glucose transporter-1 and -3: cDNA partial sequences and developmental gene expression in the placenta.

Transplacental glucose transfer utilizes specific glucose transporter (GLUT) proteins. cDNAs encoding ovine placental GLUT1 and GLUT3 genes were isolated, cloned and sequenced and then used to investigate their developmental regulation in ovine placenta. A cDNA of approximately 2.2 kb was isolated from a Clontech lambda gt10 ovine adult liver cDNA library using a 436-bp rat GLUT1 cDNA probe. Sequence data obtained from this clone (1600 bp) demonstrated 97 per cent homology to nucleotides 477-2079 of bovine GLUT1. The deduced amino acid sequence of the ovine cDNA presented 99 per cent identity to amino acid 103-493 of bovine GLUT1, and 97-98 per cent identity to corresponding regions in human and rat GLUT1 deduced amino acid sequences. Reverse transcription-PCR (RT-PCR) was used to isolate an ovine cDNA fragment from placental total RNA. Forward and reverse primers (16 mer) were designed to amplify a predicted 483-bp fragment between the second transmembrane-spanning domain (M2) and intracellular loop of GLUT3. The deduced 161 amino acid sequence of the ovine cDNA demonstrated 84 and 88 per cent identity with murine and human GLUT3. These cDNAs were used to investigate the ontogeny of placental oGLUT1 and oGLUT3 gene expression by Northern analysis. Total RNA was extracted from ovine placenta at gestational days 45, 60, 90, 120 and 138 (n=6 per time point). Ovine GLUT1 gene expression increased significantly from days 45 to 60 (P<0.05), peaked at around day 120 of gestation, then decreased to about two-thirds of maximal levels by day 138 of gestation (term 147 +/- 2). Ovine GLUT3 gene expression increased throughout gestation with significant increases from days 45 to 60, 60 to 120 and 120 to 138 (P<0.05). This study confirms the presence of both GLUT1 and GLUT3 genes in the ovine placenta and demonstrates ontogenic regulation of gene expression. The difference in temporal gene expression between oGLUT1 and oGLUT3 suggests distinct roles for each transporter during development. The nucleotide sequences reported in this paper have been submitted to the GenBank/EMBL Data Bank under accession numbers U89029 (oGLUT1) and U89030 (oGLUT3).

The spatial and temporal distribution of insulin-like growth factor-1 following experimental myocardial infarction in the rat.

Insulin-like growth factor-1 (IGF-1) is believed to be involved in the repair and adaptation that follow ischemic injury to the myocardium. The aim of this study was to elucidate the role of IGF-1 by defining the changes that occur in its distribution following regional myocardial infarction. The left anterior descending coronary artery was ligated in adult male Wistar rats, and hearts were examined microscopically from 6 hours to 20 days later. IGF-1 was identified histochemically using the avitin-biotin-peroxidase method with a polyclonal antibody to IGF-1 and was quantified by optical density measurements of standard fields in sections of hearts prepared in a single batch. Immunoreactivity was located in the cytoplasm of viable myocytes, vascular smooth-muscle cells, mast cells, leukocytes, endothelial cells, and fibroblasts. The zone of viable myocardium immediately adjacent to infarcts reacted significantly more intensely for IGF-1 than all other regions at all stages, with a maximum optical density (617% higher than sham-operated control myocardium, p < .001) 24 hours after coronary artery ligation. Immunoreactivity in myocardium tissue distant from the infarcts also increased during the first day (382% at 24 hours), but this increase was not statistically significant thereafter. These temporal and spatial changes in the distribution and amount of IGF-1 indicate that this finding is predominantly associated with a localized response to injury by the viable myocytes adjacent to infarcts.

Differential effects of maternal ovine placental lactogen and growth hormone (GH) administration on GH receptor, insulin-like growth factor (IGF)-1 and IGF binding protein-3 gene expression in the pregnant and fetal sheep.

The role of placental lactogen (PL) in the regulation of maternal metabolism and fetal growth is not understood. Both PL and growth hormone (GH) have been suggested as possible regulators of mammogenesis. Our aim was to compare the effects of recombinant ovine placental lactogen (oPL) and bovine growth hormone (bGH) on maternal mammary gland development and fetal growth. Pregnant ewes were treated from day 101 to 107 of gestation with twice daily subcutaneous injections of recombinant oPL (n = 7), bGH (n = 8) (0.15 mg/kg live weight/day) or saline (n = 8). On day 108 of gestation, fetal and maternal tissues were collected. The relative abundance of growth hormone receptor (GHR), insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) mRNA was assessed in mammary gland, maternal liver and heart, and in fetal and placental tissues. There was no detectable change in mammary tissue GHR, IGF-1 or IGFBP-3 gene expression with either bGH or oPL treatment. Maternal administration of bGH, but not oPL, during pregnancy caused an increase in maternal hepatic IGF-1 gene expression (P < 0.005). Treatment with oPL, but not bGH, resulted in a significant increase (P < 0.025) in the relative abundance of fetal hepatic IGFBP-3 mRNA. Maternal hepatic GHR gene expression was not affected by treatment. This study suggests that while bGH treatment of pregnant ewes induces characteristic somatogenic responses, oPL treatment does not have comparable effects. However, oPL may indirectly influence the fetal somatotropic axis by altering fetal hepatic IGFBP-3 production.

Insulin-like growth factor II is induced during wound repair following hypoxic-ischemic injury in the developing rat brain.

Recent evidence suggests that insulin-like growth factor-I (IGF-I) acts as a neurotrophic factor in the injured CNS. The role of the related peptide IGF-II is unclear. Therefore, we compared the induction of IGF-II in the developing rat brain following mild or severe hypoxic-ischemic (HI) injuries. Ligation of the right carotid artery of 21 day old rats followed by either 15 or 60 min exposure to 8% oxygen led to mild or severe unilateral damage respectively. Brains were collected at 1 day, 3, 5, 7 and 10 days, post-hypoxia. In situ hybridization showed that the 15 min injury (which produced selective neuronal loss) produced no change in basal IGF-II gene expression. However, the 60 min injury, which resulted in cortical infarction and severe neuronal loss in other regions, led to the induction of IGF-II mRNA mainly in the infarcted cortex, from 5-7 days post-hypoxia. Immunohistochemical analysis of brains collected 10 days after the 60 min injury showed that IGF-II immunoreactivity (IR) was also increased, predominantly in damaged regions, but also in the contralateral hippocampus. IGF-II IR was associated with non-neuronal cells that appeared to be microglial-like cells and astrocytes. Together these data suggest that IGF-II may modulate the response of glial cells during recovery from cerebral infarction.

Changes in the abundance of mRNA for type-I 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4 isomerase in the human placenta and fetal membranes during pregnancy and labor.

A local decrease in progesterone synthesis in the placenta and fetal membranes has long been proposed as a possible mechanism in the control of human labor. We have examined whether changes occur in the abundance of mRNA for 3 beta-hydroxysteroid dehydrogenase/delta 5-->delta 4 isomerase (3 beta-HSD), the enzyme which catalyzes the conversion of pregnenolone to progesterone in human placenta and fetal membranes, by Northern blot analysis using a cDNA probe to human placental type-I 3 beta-HSD, the predominant isoenzyme in the placenta. The abundance of 3 beta-HSD mRNA (1.7-kb transcript) was about 10-fold greater in term placenta than in chorio-decidua, but undetectable in total RNA from amnion. There was no change in the abundance of 3 beta-HSD mRNA in either placenta or chorio-decidua obtained after elective cesarean section at term, after preterm labor, or after term or postterm vaginal delivery. We conclude that the abundance of 3 beta-HSD mRNA does not change in the placenta or fetal membranes with labor, consistent with the view that changes in 3 beta-HSD gene expression and decreased progesterone production are unlikely to effect intrauterine paracrine/autocrine regulatory mechanisms leading to term or preterm labor in women.

Localization of the growth hormone receptor, identified by immunocytochemistry, in second trimester human fetal tissues and in placenta throughout gestation.

Pituitary GH secretion appears largely unnecessary for the attainment of normal birth size in many species, including man. This is believed to be due to an immaturity and/or an absence of GH receptors in many fetal tissues. However, in vitro studies using late first trimester human fetal tissues have demonstrated mitogenic actions of GH on liver and stimulation of insulin biosynthesis in pancreas. To resolve this discrepancy, we have employed immunocytochemistry to identify the presence and distribution of GH receptors in various human fetal tissues. Fetuses of 14-16 weeks gestation were obtained after therapeutic abortion, tissues were fixed, and immunocytochemistry was performed using monoclonal antibodies against purified rat or rabbit GH receptor. The specificity of staining was confirmed by preabsorption of the antibodies with 1) adult rat liver membranes or 2) human fetal liver membranes, both of which possess specific GH-binding sites, or 3) human fetal skeletal muscle membranes, which do not specifically bind GH. Positive staining was seen in a subpopulation of liver parenchymal cells, in the ductal and endocrine tissue of pancreas, in the germinal layer of the epidermis and the deeper dermal layers of skin, and in the tubular epithelium of kidney. No immunopositive staining was seen in skeletal or cardiac muscle, epiphyseal growth plate, lung, intestine, or adrenal. Positive staining was present in the neuronal cell bodies of the cerebral cortex. GH receptor was also detectable as early as 8 weeks gestation in syncytial layers of the placenta and was maintained until term. Results demonstrate the presence of immunoreactive GH receptor/binding protein in some human fetal tissues early in development. In particular, these results would support a role for GH in the growth and function of liver and pancreas.

Plasma clearance of radiolabelled IGF-1 in the late gestation ovine fetus.

We investigated the distribution of radiolabelled IGF-1 in the late gestation ovine fetus by exclusion gel chromatography following intravenous injection of 125I rh (recombinant human) met-IGF-1 into the chronically instrumented fetal lamb (120-130 days, n = 7). One minute after injection of 125I rh met-IGF-1 into the fetal femoral vein, 20.9 +/- 3.1% of the counts circulated in the 150K binding protein region, 55.0 +/- 3.7% in the 50K binding protein region and 18.7 +/- 0.6% in the free or 7K region. The chromatographic profiles obtained in the fetus were in general similar to those previously seen in the adult sheep. After an initial equilibration phase the half life of IGF-1 associated with the 150K binding fractions were 412.1 +/- 103.6 min. Two phases of clearance were observed for IGF-1 in association with the 50K binding fractions, an initial phase with a half life of 30.6 +/- 4.5 min followed by a second phase with a half life of 202.3 +/- 10.3 min. The 7K or 'free' form of IGF-1 had an initial half life of 12.6 +/- 5.1 min. Chromatography of samples of fetal tracheal fluid, fetal urine, amniotic fluid, maternal uterine venous plasma and maternal systemic plasma showed no movement of intact IGF-1 out of the fetal circulation into the fetal fluids or into the maternal circulation. However, when simultaneous samples were obtained from the fetal femoral artery and umbilical vein, higher radioactivity was consistently observed in the fetal femoral artery raising the possibility of placental uptake of IGF-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Disappearance of labelled IGF-2 from plasma of the ovine fetus in late gestation.

The role of IGF-2 in the fetus and its possible influence on fetal growth remains speculative. We investigated the size distribution of unsaturated binding sites for labelled oIGF-2 in ovine fetal plasma. In addition, the disappearance of each form of protein bound IGF-2 in the late gestation ovine fetus (125-135 days, n = 5) was estimated. One minute after injection into the fetal femoral vein, 125IoIGF- circulated in the fetal femoral artery bound primarily to a 50 kDa binding protein. Only a small amount of binding to a 150 kDa binding protein was seen with little to no free IGF-2 present. IGF-2 also circulated in association with a large molecular weight complex (ca. 250 kDa) presumed to be circulating receptor bound IGF-2. The half life of the 250 kDa form of IGF-2 was 385.9 +/- 65.4 min, for the 150 kDa form 308.0 +/- 65.0 min, for the 50 kDa form was 35.5 + 2.6 min and for the free form of IGF-2 was 1.6 +/- 0.6 min. There was no apparent movement of intact IGF-2 out of the fetal circulation into any of the fetal fluids or into the maternal circulation. Similarly there was no consistent placental uptake of IGF-2 from the fetal circulation.

The effect of maternal starvation on plasma insulin-like growth factor I concentrations in the late gestation ovine fetus.

In view of the suggested relationship between substrate availability, fetal growth and circulating fetal IGF-I concentrations, we investigated the effect of maternal starvation on plasma IGF-I levels in the late gestation ovine fetus. Ten fetuses aged 125-130 d gestation were sampled daily from indwelling arterial catheters. Ewes were starved for 72 h. Starvation was terminated with an intravenous infusion of 10% glucose to the ewe. Food was then replaced 4 h later. Fetal IGF-I concentrations fell from 176.1 +/- 15.2 ng/mL before starvation to 124.5 +/- 10.3 ng/mL after 72 h starvation (p less than 0.05, n = 10). The fall in IGF-I concentrations was reversed by 4 h of maternal glucose infusion. In five fetuses, where samples were obtained 24 h after terminating the starvation, fetal IGF-I concentrations were comparable to those seen before starvation (180.0 +/- 37.7 ng/mL). This study demonstrates that acute maternal starvation causes a reversible decrease in fetal plasma IGF-I levels. These studies suggest that nutrient and in particular glucose availability is a significant determinant of fetal IGF-I secretion and support the hypothesis that IGF-I may play a role in the regulation of fetal growth.

Presence of a diurnal rhythm in fetal prolactin secretion and influence of maternal nutrition.

The possible effect of altered maternal nutrition on fetal prolactin (PRL) secretion and the possible presence of a diurnal rhythm in fetal PRL secretion has been investigated in 11 fetuses aged between 132 and 140 days of gestation. Fetal PRL levels in 4 of 5 ewes fed once a day were high (greater than 40 ng/ml) and exhibited a distinct diurnal rhythm in PRL secretion. Fetal PRL levels in those fetuses where ewes fed 4-hourly (n = 6) were all low (less than 10 ng/ml) and did not exhibit a diurnal rhythm. This study suggests that frequent maternal feeding results in low fetal PRL concentrations and that maternal undernutrition results in high fetal PRL levels that exhibit a distinct diurnal rhythm.