Increases in lung expansion alter pulmonary hemodynamics in fetal sheep.

Prolonged increases in fetal lung expansion stimulate fetal lung growth and development, but the effects on pulmonary hemodynamics are unknown. Our aim was to determine the effect of increased fetal lung expansion, induced by tracheal obstruction (TO), on pulmonary blood flow (PBF) and vascular resistance (PVR). Chronically catheterized fetal sheep (n = 6) underwent TO from 120 to 127 days of gestational age (term approximately 147 days); tracheas were not obstructed in control fetuses (n = 6). PBF, PVR, and changes to the PBF waveform were determined. TO significantly increased lung wet weight compared with control (166.3 +/- 20.2 vs. 102.0 +/- 18.8 g; P < 0.05). Despite the increase in intraluminal pressure caused by TO (5.0 +/- 0.9 vs. 2.4 +/- 1.0 mmHg; P < 0.001), PBF and PVR were similar between groups after 7 days (TO 28.1 +/- 3.2 vs. control 34.1 +/- 10.0 ml.min(-1).100 g lung wt(-1)). However, TO markedly altered pulmonary hemodynamics associated with accentuated fetal breathing movements, causing a reduction rather than an increase in PBF at 7 days of TO. To account for the increase in intraluminal pressure, the pressure was equalized by draining the lungs of liquid on day 7 of TO. Pressure equalization increased PBF from 36.8 +/- 5.2 to 112.4 +/- 22.8 ml/min (P = 0.01) and markedly altered the PBF waveform. These studies provide further evidence to indicate that intraluminal pressure is an important determinant of PBF and PVR in the fetus. We suggest that the increase in PBF associated with pressure equalization following TO reflects an increase in growth of the pulmonary vascular bed, leading to an increase in its cross-sectional area.     

The development of beta-adrenergic mediated inhibition of growth hormone secretion in the ovine fetus

The ontogeny of the suppressive effect of the beta-adrenergic agonist, isoprenaline, on fetal growth hormone (GH) release was examined in 14 chronically-catheterized ovine fetuses. Isoprenaline was administered as an intravenous infusion over 1 h (200 micrograms/kg). In seven fetuses between 72 and 99 days of gestation, isoprenaline had no effect on fetal plasma GH concentrations. In seven older fetuses between 114 and 140 days of gestation, isoprenaline infusion suppressed (P less than 0.02) fetal GH release. No effect was observed in five saline-treated control fetuses (119-131 days). Propranolol (250 micrograms/kg i.v.) administered 5 min prior to the isoprenaline infusion to four fetuses (117-136 days) delayed (P less than 0.05) the onset of the suppressive effect of isoprenaline demonstrating that the action of isoprenaline was mediated by the beta-adrenergic receptor. Propranolol alone (n = 6) had no effect. These observations demonstrate that the potential for beta-adrenergic inhibition of fetal GH release differentiates after 100 days of gestation. Comparison with previous studies of the ontogenesis of the control of GH secretion suggests that the hypothalamic beta-adrenergic control of GH release differentiates with an intermediate time course compared to other potential neuroendocrine controls.     

The effect of prolonged hypobaric hypoxia on growth of fetal sheep

The effect of prolonged hypobaric hypoxia on fetal sheep was studied. Pregnant ewes were subjected to an atmospheric pressure of 429 torr from 30 days to 135 days gestation (long-term study). Average fetal weight for the hypoxaemic group (3.35 +/- 0.53 kg; n = 4; mean +/- SD) was significantly lower than for the controls (4.23 +/- 0.29 kg; n = 7; P less than 0.05). A short-term study was undertaken with fetuses (n = 8) which were catheterized at 110 days gestation and whose dams were subjected to hypobaric hypoxia from 120 to 141 days gestation. The mean carotid PO2 of fetuses in the hypoxic group was 12.7 +/- 0.7 torr compared to 22.7 +/- 0.7 torr for the control group (n = 9; P less than 0.001) throughout the period of treatment. Fetal arterial oxygen content fell from 6.5 +/- 1.7 to 4.9 +/- 0.4 ml/dl (P less than 0.05), but rose to control values after 7 days due to an increase in fetal haemoglobin concentration (9.6 +/- 1.1 to 13.0 +/- 1.9 g/dl, P less than 0.001) and packed cell volume (33 +/- 3 to 45 +/- 4%, P less than 0.001). In the hypoxaemic fetuses, pH fell initially from 7.34 +/- 0.02 to 7.28 +/- 0.03 (P less than 0.05) and then recovered to 7.32 +/- 0.03 within 24 h. Mean fetal weight of the short-term hypoxic group was 3.46 +/- 0.72 kg compared to 4.15 +/- 0.51 for the control group (P less than 0.05). Both long- and short-term hypoxia produced a similar reduction in fetal body weight. The adrenal glands were significantly heavier in the hypoxic fetuses than in controls. Placental weight was not effected by hypoxia, but exposure from 30 days gestation reduced the average size of cotyledons (P less than 0.05). It is concluded that the fetal sheep increases its ability to acquire and transport oxygen in response to chronic hypoxia, but this compensation is not sufficient to prevent growth retardation or changes to the pattern of tissue growth.     

Continuous measurement of biparietal distance in the intact and hypophysectomized fetal sheep using ultrasound

Piezoelectric transducers were implanted into the parietal bones of intact (n = 4) and hypophysectomized (n = 8) fetal sheep of approximately 110-120 days gestational age (term 145-150 days). Intertransducer distance was determined by measuring the time taken for an ultrasonic pulse, generated by one transducer, to elicit a piezoelectric response in an opposing transducer. The limit of sensitivity of the timer was +/- 0.033 microsec. The ultrasonic velocity through fetal sheep brain tissue was 1549.6 +/- 2.2 m.s-1 (SEM; n = 33). This velocity remained constant throughout the entire period studied in both intact and hypophysectomized fetuses. At this velocity, the sensitivity of the measuring device was +/- 0.05mm. The ultrasonic transit time was measured daily between 0900 and 1100h until term in all fetuses. Three hypophysectomized fetuses were allowed to remain in utero until day 163 of gestation. The mean biparietal distance growth rate prior to day 135 for the intact and hypophysectomized fetuses was 0.25 +/- 0.03 and 0.27 +/- 0.025 mm/day respectively. These values were not significantly different (P greater than 0.05). A significant decrease (P less than 0.05) in growth rate was detected in both experimental groups between days 135 and 147 and was more pronounced in the sham (0.05 +/- 0.04 mm/day) than in the hypophysectomized (0.14 +/- 0.03 mm/day) group. However, the growth rate of the sham animals after day 135 was not significantly different from that of the hypophysectomized animals. In the three hypophysectomized fetuses killed at day 163 the biparietal distance growth was maintained at 0.12 +/- 0.005 mm/day. We conclude that fetal biparietal distance growth is pituitary independent from day 110 of gestation and that this technique for measuring distance is a valid and extremely accurate method for the continuous measurement of this parameter of fetal growth and may have further applications in other areas of growth research.     

Increased expansion of the lung stimulates calmodulin 2 expression in fetal sheep

Obstruction of the fetal trachea causes the lungs to expand with accumulated liquid. Although this is a potent stimulus for lung growth, the mechanisms involved are unknown. Our aim was to identify genes that are differentially expressed as a result of increased fetal lung expansion. Using differential display RT-PCR, we isolated a cDNA fragment partially encoding calmodulin 2 (CALM2) and identified the remainder of the coding region by 5'-rapid amplification of cDNA ends. Differential expression of CALM2 was confirmed by Northern blot analysis; CALM2 mRNA levels were increased to 161 +/- 5% of control at 2 days of increased lung expansion, induced by tracheal obstruction (TO), and had returned to control levels at days 4 and 10. Using in situ hybridization analysis, we found that the proportion of CALM2-labeled cells increased from 10.3 +/- 1.0% to 21.4 +/- 6.8% by 2 days of TO. This increase in CALM2 expression was reflected by a tendency for calmodulin protein levels to increase from 122.7 +/- 17.3 to 156.5 +/- 17.7 at 2 days of TO. Thus increases in fetal lung expansion result in time-dependent changes in CALM2 mRNA levels, which closely parallels the changes in lung DNA synthesis rates. As calmodulin is essential for cell proliferation, increased CALM2 mRNA levels may reflect an important role for calmodulin in expansion-induced fetal lung growth.     

Increased lung expansion alters the proportions of type I and type II alveolar epithelial cells in fetal sheep

Type I and type II alveolar epithelial cells (AECs) are derived from the same progenitor cell, but little is known about the factors that regulate their differentiation into separate phenotypes. An alteration in lung expansion alters the proportion type II AECs in the fetal lung, indicating that this may be a regulatory factor. Our aim was to quantify the changes in the proportion of type I and type II AECs caused by increased fetal lung expansion and to provide evidence for transdifferentiation of type II into type I cells. Lung tissue samples were collected from ovine fetuses exposed to increased lung expansion induced by 2, 4, or 10 days of tracheal obstruction (TO). The identities and proportions of AEC types were determined with electron microscopy. The proportion of type II cells was reduced from 28.5 +/- 2.2% in control fetuses to 9.4 +/- 2.3% at 2 days of TO and then to 1.9 +/- 0.8% at 10 days. The proportion of type I AECs was not altered at 2 days of TO (63.1 +/- 2.3%) compared with that of control cells (64.8 +/- 0.5%) but was markedly elevated (to 89.4 +/- 0.9%) at 10 days of TO. The proportion of an intermediate AEC type, which displayed characteristics of both type I and type II cells, increased from 5.7 +/- 1.3% in control fetuses to 23.8 +/- 5.1% by 2 days of TO and was similar to control values at 10 days of TO (7.7 +/- 0.9%). Our data show that increases in fetal lung expansion cause time-dependent changes in the proportion of AEC types, including a transient increase in an intermediate cell type. These data provide the first evidence to support the hypothesis that increases in fetal lung expansion induce differentiation of type II into type I AECs via an intermediate cell type.     

Fetal lung growth after short-term tracheal occlusion is linearly related to intratracheal pressure.

Prenatal tracheal occlusion (TO) has been shown to accelerate fetal lung growth, yet the mechanism is poorly understood. The goal of this study was to determine the relationship between fetal intratracheal pressure (Pitr) and fetal lung growth after TO. Fetal lambs underwent placement of an intratracheal catheter and a reference catheter at 115--120 days gestation (term, 145 days). Fetal Pitr was continuously controlled at three levels (high, 8 mmHg; moderate, 4 mmHg; low, 1 mmHg) by a servo-regulated pump. The animals were killed after 4 days, and the parameters of lung growth were compared. Lung volume (136.0 +/- 16.7, 94.9 +/- 9.7, 55.5 +/- 12.4 ml/kg), lung-to-body weight ratio (6.31 +/- 0.70, 4.89 +/- 0.38, 3.39 +/- 0.22%), whole right lung dry weight (3.01 +/- 0.29, 2.53 +/- 0.15, 2.07 +/- 0.24 g/kg), right lung DNA (130.0 +/- 11.3, 116.7 +/- 8.6, 97.5 +/- 10.9 mg/kg), and protein contents (1,865.5 +/- 92.5, 1,657.6 +/- 106.8, 1,312.0 +/- 142.5 mg/kg) in high, moderate, and low groups, respectively, all increased in the moderate compared with the low group and increased further in the high compared with the moderate group. Morphometry confirmed a stepwise increase in the volume of respiratory region and alveolar surface area. We conclude that lung growth in the first 4 days after TO is closely correlated with fetal Pitr, offering additional evidence that an increase in lung expansion is one of the major factors responsible for TO-induced lung growth.     

Ontogeny of the response to growth hormone-releasing factor

Primary cell cultures were prepared from fetal, neonatal and adult rat pituitaries and evaluated for their ability to secrete growth hormone (GH) in response to growth hormone-releasing factor (GRF). Pituitary cells prepared from fetuses at days 19 and 21 of gestation, neonatal animals at the day of birth (day 0) or the following day (day 1) and peripubertal male rats showed full dose response curves to GRF with maximal GH release when stimulated with 1 X 10(-10) M rat GRF. At this concentration of GRF, the amount of GH released was not different from that elicited by activation of adenylate cyclase with 1 X 10(-5) M forskolin. In contradistinction, a preparation of cells from fetuses at day 18 of gestation did not show the same release of GH when challenged with 1 X 10(-10) M GRF and forskolin (0.057 +/- 0.001, compared to 0.076 +/- 0.003 micrograms/10(5) cells per 4.5 h), although the cells clearly responded to both secretagogues (basal levels of GH, 0.029 +/- 0.002 micrograms/10(5) cells per 4.5 h). While cells prepared from fetuses at day 21 of gestation or from animals after birth released 5-10% of their total cellular GH content, those prepared from 18- and 19-day fetuses released as much as 40% of their total GH suggesting there is a maturation of intracellular GH processing that occurs late in gestation. The results show that, in late pregnancy, the rat fetal pituitary is highly responsive to growth hormone-releasing factor and suggest that this peptide participates in regulating GH levels during the perinatal period.     

Effect of mammalian growth hormone and prolactin on the growth of hypophysectomized chickens

Body weight gain and shank-toe growth during a 26-day treatment period following hypophysectomy were 55 and 46%, respectively, of control values, but the body weight gain was unaffected and bone growth only slightly reduced when the hypophysectomized chickens were fed a low dose of corticosterone (5 ppm). Bovine growth hormone (0.5 mg GH/kg body wt/day for 18 days) enhanced body weight gain and shank-toe length increase (an estimate of bone growth) by 46 and 33%, respectively, compared to the growth of hypophysectomized chickens receiving only corticosterone. These same endpoints were increased approximately 24% after ovine growth hormone treatment in hypophysectomized chickens not receiving corticosterone. Body weight gain during 18 days of treatment with bovine prolactin (0.5 mg PRL/kg/day) was 27% greater than the value for corticosterone-treated hypophysectomized chickens, but bone growth was unaffected. The mammalian GH preparations increased heart weight of the hypophysectomized chickens (25-29%), but pectoralis muscle weight was unaffected. GH treatment enhanced thymal weights by 71% in corticosterone-treated hypophysectomized chickens, and by 93% in hypophysectomized animals not receiving corticosterone. GH had no significant effect on bursal weights, and PRL had no effect on either of these lymphoid organ weights in corticosterone-treated hypophysectomized chickens. GH increased liver and adipose tissue weights considerably more than the large increases that followed treatment of hypophysectomized chickens with corticosterone alone (69 and 126% greater, respectively), but had no effect on these endpoints in hypophysectomized chickens not receiving corticosterone. PRL also greatly increased liver and adipose tissue weights in corticosterone-treated hypophysectomized chickens (79 and 75%, respectively). These results provide evidence that mammalian GH enhances body weight gain, bone growth, and the growth of several organs in the hypophysectomized chicken. Mammalian PRL increased body weight gain, liver weight, and adipose tissue weight in corticosterone-treated hypophysectomized chickens, but did not influence bone growth or the weights of the heart, pectoralis, thymi, or bursa.     

Influence of growth hormone on bone marrow adipogenesis in hypophysectomized rats

The hypophysectomized rat has been used as a model to study the effects of growth hormone deficiency on bone. Here, we have investigated the influence of growth hormone administration to hypophysectomized rats (HX) for 6 wk on accumulation of triglycerides in bone marrow and on the differentiation of primary marrow stromal cells into adipocytes under in vitro conditions. We found that hypophysectomy significantly increased triglyceride concentration in bone marrow, which was attenuated by growth hormone administration. Primary bone marrow stromal cells derived from HX rats also had more adipocytes at confluence compared with growth hormone-treated hypophysectomized (GH) rats. When stimulated with 3-isobutyl-1-methylxanthine plus dexamethasone (IBMX-Dex), preadipocyte colony counts increased more significantly in GH rats. Markers of adipocyte differentiation were higher in HX than in control or GH rats at confluence. However, after stimulation with IBMX-Dex, increased expression of markers was seen in GH compared with HX rats. In conclusion, growth hormone administration to hypophysectomized rats attenuated triglyceride accumulation in bone marrow and inhibited the differentiation of stromal cells into adipocytes in vitro.     

Meclofenamate does not affect lung development in fetal sheep

Prostaglandins may be involved in some aspects of fetal lung development, including surfactant metabolism, tracheal fluid production, and possibly lung growth. In the fetus, during the days before delivery, plasma PGE2 concentration increases and concurrently, tracheal fluid production decreases and surfactant production increases. To determine whether the increase in PGE2, specifically plasma PGE2 concentration, is responsible for these changes, we continuously infused the prostaglandin synthetase inhibitor, meclofenamate (0.7 mg/h per kg), into 8 fetal sheep for 5-13 days before delivery; 5 control fetuses received a continuous infusion of solvent for 5-11 days before delivery. Meclofenamate infusion significantly decreased plasma PGE2 concentrations until the day of delivery. However, meclofenamate did not affect tracheal fluid production or its decrease before delivery, fetal plasma cortisol concentration, surfactant content of tracheal fluid and lung tissue, organ weights, lung weights, or lung DNA and protein content. We conclude that the changes in lung development during the days before delivery are not dependent on the usual high fetal plasma concentration of PGE2 or its increase before delivery.     

Decline in lung liquid volume and secretion rate during oligohydramnios in fetal sheep

Reduced amniotic fluid volume often results in fetal lung hypoplasia. Our aim was to examine the effects of prolonged drainage of amniotic and allantoic fluids on lung liquid volume (Vl), secretion rate (Vs), and tracheal flow rate (Vtr) in fetal sheep. In five experimental animals, amniotic and allantoic fluids were drained from 107 to 135 days of gestation. The volume of fluid drained from the experimental animals was 411.8 +/- 24.4 ml/day (n = 140). In six control animals, amniotic fluid volume was 747.7 +/- 89.7 ml (n = 15). Wet and dry lung weights were 20-25% lower in experimental fetuses than in control fetuses. Fetal hemoglobin, O2 saturation, arterial PO2, pH, and hematocrit were unchanged by drainage. During the drainage period, Vl was up to 65% lower, Vs was up to 35% lower, and Vtr was up to 40% lower in experimental fetuses than in control fetuses. We conclude that prolonged drainage of amniotic and allantoic fluids decreases Vl, Vs, and Vtr in fetal sheep. These findings indicate that fetal lung hypoplasia associated with oligohydramnios may be the result of a prolonged reduction in Vl.     

Fetal breathing and pressures in the trachea and amniotic sac during oligohydramnios in sheep

Oligohydramnios commonly leads to fetal lung hypoplasia, but the mechanisms are not fully understood. Our aim was to determine, in fetal sheep, the effects of prolonged oligohydramnios on the incidence and amplitude of tracheal pressure fluctuations associated with fetal breathing movements (FBM), on tracheal flow rate during periods of FBM (VtrFBM) and periods of apnea (Vtrapnea), on tracheal pressure relative to amniotic sac pressure, and on amniotic sac pressure relative to atmospheric pressure. In five sheep, oligohydramnios was induced by draining amniotic and allantoic fluids from 107 to 135 days of gestation (411.8 +/- 24.4 ml/day), resulting in fetal lung hypoplasia. In five control sheep, amniotic fluid volume was 732.3 +/- 94.4 ml. Oligohydramnios increased the incidence of FBM by 14% at 120 and 125 days and the amplitude of FBM by 30-34% at 120-130 days compared with controls. From 120 days onward, VtrFBM was 35-55% lower in experimental fetuses than in controls. Influx of lung liquid during FBM was 87% lower in experimental fetuses than in controls. Vtrapnea, tracheal pressure, and amniotic sac pressure were not significantly altered by oligohydramnios. Our tracheal flow rate data suggest that transient changes in lung liquid volume during periods of FBM and periods of apnea were diminished by oligohydramnios. We conclude that the primary factor in the etiology of oligohydramnios-induced lung hypoplasia is not an inhibition of FBM (as measured by tracheal pressure fluctuations) or a reduction in amniotic fluid pressure.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of pulsatile growth hormone administration to the growth-restricted fetal sheep on somatotrophic axis gene expression in fetal and placental tissues

We have previously reported (Bauer MK, Breier BH, Bloomfield FH, Jensen EC, Gluckman PD, and Harding JE. J Endocrinol 177: 83-92, 2003) that a chronic pulsatile infusion of growth hormone (GH) to intrauterine growth-restricted (IUGR) ovine fetuses increased fetal circulating IGF-I levels without increasing fetal growth. We hypothesized a cortisol-induced upregulation of fetal hepatic GH receptor (GH-R) mRNA levels, secondary increases in IGF-I mRNA levels, and circulating IGF-I levels, but a downregulation of the type I IGF receptor (IGF-IR) as an explanation. We, therefore, measured mRNA levels of genes of the somatotrophic axis by real-time RT-PCR in fetal and placental tissues of fetuses with IUGR (induced by uteroplacental embolization from 110- to 116-days gestation) that received either a pulsatile infusion of GH (total dose 3.5 mg/day) or vehicle from 117-126 days and in control fetuses (n = 5 per group). Tissues were collected at 127 days (term, 145 days). Fetal cortisol concentrations were significantly increased in IUGR fetuses. However, in liver, GH-R, but not IGF-I or IGF-IR, mRNA levels were decreased in both IUGR groups. In contrast, in placenta, GH-R, IGF-I, and IGF-IR expression were increased in IUGR vehicle-infused fetuses. GH infusion further increased placental GH-R and IGF-IR, but abolished the increase in IGF-I mRNA levels. GH infusion reduced IGF-I expression in muscle and increased GH-R but decreased IGF-IR expression in kidney. IUGR increased hepatic IGF-binding protein (IGFBP)-1 and placental IGFBP-2 and -3 mRNA levels with no further effect of GH infusion. In conclusion, the modest increases in circulating cortisol concentrations in IUGR fetuses did not increase hepatic GH-R mRNA expression and, therefore, do not explain the increased circulating IGF-I levels that we found with GH infusion, which are likely due to reduced clearance rather than increased production. We demonstrate tissue-specific regulation of the somatotrophic axis in IUGR fetuses and a discontinuity between GH-R and IGF-I gene expression in GH-infused fetuses that is not explained by alterations in phosphorylated STAT5b.     

Growth hormone dependence of somatomedin-C/insulin-like growth factor-I and insulin-like growth factor-II messenger ribonucleic acids

The GH dependence of somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) and insulin like growth factor II (IGF-II) mRNAs was investigated by Northern blot hybridizations of polyadenylated RNAs from liver, pancreas, and brain of normal rats, untreated hypophysectomized rats, and hypophysectomized rats 4 h or 8 h after an ip injection of human GH (hGH). Using a 32P-labeled human Sm-C/IGF-I cDNA as probe, four Sm-C/IGF-I mRNAs of 7.5, 4.7, 1.7, and 1.2 kilobases (kb) were detected in rat liver and pancreas but were not detectable in brain. In both liver and pancreas, the abundance of these Sm-C/IGF-I mRNAs was 8- to 10-fold lower in hypophysectomized rats than in normal rats. Within 4 h after injection of hGH into hypophysectomized animals, the abundance of liver and pancreatic Sm-C/IGF-I mRNAs was restored to normal. A human IGF-II cDNA was used as a probe for rat IGF-II mRNAs which were found to be very low in abundance in rat liver and showed no evidence of regulation by GH status. In pancreas, IGF-II mRNA abundance was below the detection limit of the hybridization procedures. The brain contained two IGF-II mRNAs of 4.7 and 3.9 kb that were 5-fold lower in abundance in hypophysectomized rats than in normal rats. These brain IGF-II mRNAs were not, however, restored to normal abundance at 4 or 8 h after ip hGH injection into hypophysectomized animals. To investigate further, the effect of GH status on abundance of Sm-C/IGF-I and IGF-II mRNAs in rat brain, a second experiment was performed that differed from the first in that hypophysectomized rats were given an injection of hGH into the lateral ventricle (intracerebroventricular injection) and a rat Sm-C/IGF-I genomic probe was used to analyze Sm-C/IGF-I mRNAs. In this experiment, a 7.5 kb Sm-C/IGF-I mRNA was detected in brain polyadenylated RNAs. The abundance of the 7.5 kb mRNA was 4-fold lower in hypophysectomized rats than in normal rats and was increased to 80% of normal within 4 h after icv administration of hGH to hypophysectomized animals. As in the first experiment, the abundance of the 4.7 and 3.9 kb brain IGF-II mRNAs was lower than normal in hypophysectomized rats. Brain IGF-II mRNAs were increased to 50% of normal in hypophysectomized rats given an icv injection of hGH but within 8 h after the injection rather than at 4 h as with Sm-C/IGF-I mRNAs.     

Effect of a recombinant human growth hormone preparation on the urinary 15nitrogen balance in growth-hormone-deficient children

In 10 patients with idiopathic growth hormone (GH) deficiency (9 boys and 1 girl, aged 7.5-14.5 years, mean 12.1 +/- 2.2 years), urinary 15N-balance studies were performed before and on recombinant hGH (2 x 3 IU/m2 of body surface area subcutaneously on consecutive days). Before and on the 2nd day of recombinant hGH, 99% 15N-labeled ammonium chloride (0.05 g/kg, divided in 3 doses per day, corresponding to 389 +/- 30 mg/m2 of 15N) was administered and 24 h urine was collected. In urine, total nitrogen and the percentage of 15N were measured. From the ingested and excreted quantity, a urinary 15N balance was calculated. Mean 15N percentage from total N was 3.3 +/- 0.5. In 9 patients, basal 15N balance was +79 +/- 15 mg/m2 or +2.9 +/- 0.4 mg/kg. On recombinant hGH, it was +166 +/- 16 mg/m2 or +6.1 +/- 0.6 mg/kg (p less than 0.001). The recombinant hGH-induced positive 15N balance change was +87 +/- 17 mg/m2 or +3.2 +/- 0.6 mg/kg. 1 patient with a higher basal 15N balance (+196 mg/m2, +7.1 mg/kg) had no positive 15N balance change due to latent hypothalamic hypothyroidism. In previous similar studies with pituitary hGH the change of 15N balance was +80 +/- 27 mg/m2 or +2.8 +/- 1.1 mg/kg. It is concluded that the acute nitrogen-retaining effect of recombinant hGH is at least equal to that of pituitary hGH.     

Increased pulmonary vascular filtration pressure does not alter lung liquid secretion in fetal sheep.

The purpose of this study was to determine whether an increase in pulmonary vascular filtration pressure affects net production of liquid within the lumen of the fetal lung. We studied 14 chronically catheterized fetal lambs [130 +/- 3 (SD) days gestation] before, during, and after a 4-h rapid (500 ml/h) intravenous infusion of isotonic saline. In seven fetuses we measured pulmonary arterial and left atrial pressures, lung lymph flow, and protein osmotic pressures in plasma and lymph. In eight lambs with a chronically implanted tracheal loop cannula, we measured the change in luminal lung liquid volume over time by progressive dilution of tracheally instilled 125I-albumin, which stays within the lung lumen. Saline infusion increased pulmonary vascular pressures by 2-3 mmHg and decreased the plasma-lymph difference in protein osmotic pressure by 1 mmHg. Lung lymph flow increased from 1.9 +/- 0.6 to 3.9 +/- 1.2 (SD) ml/h; net production of luminal lung liquid did not change (12 +/- 5 to 12 +/- 6 ml/h). Thus an increase in net fluid filtration pressure in the pulmonary circulation, which was sufficient to double lung lymph flow, had no significant effect on luminal lung liquid secretion in fetal sheep.     

Demonstration of in vitro actions of growth hormone on isolated rat adipocytes

Previous studies have shown that adipocytes isolated from normal rats possess specific receptors for growth hormone (GH). Thus, we have now investigated the direct effects on such cells of GH added in vitro. The biological actions of GH determined were the stimulation of 14C-glucose oxidation to 14CO2 and conversion to 14C-lipid. As in adipose segments, hGH stimulation of these parameters required a 3-4 hr preincubation period in GH-free medium. The effect of hGH or bGH was dose-dependent with maximal effects at 1-2 micrograms/ml (CO2 55 +/- 13% stimulation above basal n = 9; lipid 33 +/- 4% n = 21, mean +/- SEM). The magnitude of the effect in isolated adipocytes was lower than that seen in adipose segments from similar groups of animals (lipid 67 +/- 26%, n = 4). The induction of responsiveness by preincubation was accompanied by a parallel increase in 125I-hGH binding. These studies have demonstrated that adipocytes from normal rats not only possess specific receptors for GH but also are metabolically responsive to GH added in vitro. These data suggest that the isolated rat adipocyte should be a useful model for further investigation of the relationship between GH receptor and post-receptor events.     

Lipid deposition after hypophysectomy and growth hormone treatment in the sheep fetus

Fifteen sheep fetuses hypophysectomized around 115 days gestation (term 150 days) were treated with growth hormone (GH), adrenocorticotrophin (ACTH) or triiodothyronine (T3) by continuous intravenous infusion. At normal or caesarian delivery, about 149 days gestation, body weights and dissectible internal brown fat and subcutaneous white fat depots were compared with seven control hypophysectomized fetuses and four sham-operated controls, the latter groups receiving no hormone infusions. Hypophysectomy caused the appearance of a large persistent depot of subcutaneous fat which was unaffected by ACTH or T3 infusion. Treatment with ovine pituitary GH resulted in the disappearance of this depot which was also absent from the sham-operated controls. Although the GH source was not subjected to extensive purification, there was very little contamination with prolactin or TSH, suggesting that GH itself has a major role in the control of lipid metabolism in the fetus.