摘要:

Maximum flow velocity waveforms were recorded in a longitudinal study from the fetal ascending aorta and fetal pulmonary artery in 46 normal pregnancies and, in addition, from the umbilical artery in 21 cases of intrauterine growth retardation between 19 and 33 wk gestation. In normal pregnancy, the mean peak systolic velocity (PSV) in the ascending aorta increased from 49.4 cm/s at 19 wk of gestation to 79.0 cm/s at 33 wk of gestation. The corresponding increase in PSV in the pulmonary artery was from 39.0 to 63.7 cm/s. The ratio for the PSV between the two arteries remained constant (1.25-1.29). Mean values of PSV in both arteries were linearly related to gestational age. Normal limits according to age were constructed by establishing the 5th and 95th percentiles. In intrauterine growth retardation, the PSV in the pulmonary artery was decreased (<5th percentile) in 95% of cases, PSV in the ascending aorta was reduced (<5th percentile) in only 57%. No relationship was established between PSV in both arteries and the presence or absence of end-diastolic flow velocities in the umbilical artery. The outcome of fetuses with intrauterine growth retardation, as expressed by Apgar score at 1 min and umbilical cord pH, bears no relationship to the PSV in ascending aorta and pulmonary artery.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

We studied the role of the autonomic nervous system in the regulation of heart rate variation (HRV) in 12 chronically instrumented neonatal lambs. HRV was quantified from ECG tracings by computing periodic HRV distributions at frequencies of 0.02-1.00 Hz, using power spectral analysis of heart rate, and also by HRV indices. Heart rate declined more during the 1st than the 2nd mo after birth. Multiple regression analysis showed that the heart rate responses to vagal and to ß-adrenergic blockade had an independent negative association both with age and with the initial mean heart rate, whereas the overall HRV response had a positive association with age. Vagal blockade led to a 70-80% decrease in the beat-to-beat HRV in all lambs (p<0.001). The overall HRV indices decreased by 40-65% in lambs (< 30 d old (p<0.001) and about 30% in those >30 d old (p<0.05). In the power spectrum the greatest decrease was seen in the high-frequency components of HRV. β-Blockade led to a decrease of about 50% in all HRV (p<0.001) in the younger lambs, without frequency selection. In the older lambs, it had no effect on the beat-to-beat HRV, but the overall HRV (coefficient of variance) decreased maximally by 40% (p<0.01), with a significant reduction in the low-frequency components of HRV. These results suggest that in the regulation of HRV after birth dual control via the autonomic nervous system is most important. In the older lambs, developmental changes result in precise regulation of the fast heart rate fluctuations mainly by the vagal division, whereas the slow fluctuations are partially regulated by the vagal and β- adrenergic divisions.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Sodium nitroprusside (SNP), a nonreceptor mediated stimulant of soluble guanylate cyclase, and atrial natriuretic factor, a receptor-dependent stimulator of particulate guanylate cyclase, mediate relaxation responses by increasing intracellular cGMP. Thisin vitrostudy was designed to compare the ontogeny of relaxation responses to SNP and atrial natriuretic factor in the guinea pig thoracic aorta. Aortic rings from fetuses at 55-60 d gestation (term=68 d), 1- to 3-d-old newborn, and 12-wk-old adult Hartley guinea pigs were mounted in an organ bath, bathed in Kreb's solution, and connected to a force-displacement transducer to measure isometric tension. Relaxation responses to SNP and atriopeptin III were studied with the vessels at optimal resting tension and after preconstriction with an EC85concentration of norepinephrine. SNP-mediated relaxation showed a significant increase in sensitivity with development among the three age groups (p<0.05). Methylene blue, an inhibitor of soluble guanylate cyclase, produced no inhibition of relaxation to SNP in fetal aortae, significantly decreased responses along the straight portion of the concentration-response curve in newborn aortae (p<0.05), and significantly shifted the concentration-response curve to the right (p<0.05) in adult aortae; but did not prevent vessels from relaxing almost 100% in any age group. However, atriopeptin III-mediated responses were similar in the three age groups and were unaffected by methylene blue. These results suggest that1) sensitivity to SNP increases with age from fetal through adult life;2) relaxation mediated by atriopeptin III is similar during development;3) methylene blue does not affect SNP mediated relaxation in fetuses but progressively decreases sensitivity to SNP in newborns and adults; and4) methylene blue does not affect atriopeptin III-mediated relaxation in any age group.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

After acute blood volume expansion (BVE) in the rat, diuresis and natriuresis are reported to be minimal in rats 20 to 30 d of age, but increase to mature levels by 40 d of age. To evaluate the role of atrial natriuretic peptide (ANP) and its renal action in BVE, anesthetized Sprague-Dawley rats were studied at 25 to 30 (group I) and 45 to 50 d of age (group II). Hematocrit, mean arterial pressure, glomerular filtration rate, urine flow rate, urine sodium excretion, urine cyclic GMP excretion, and plasma ANP concentration ([ANP]) were measured before and after infusion of donor littermate whole blood, 2.5% body wt (BVE), and in time controls (no BVE) in each group. Baseline hematocrit, mean arterial pressure, and glomerular filtration rate were greater in group II than group I, but urine flow rate, urine sodium excretion, urine cyclic GMP excretion, and [ANP] did not differ. BVE caused a prompt increase in urine flow rate, urine sodium excretion, and [ANP], but not urine cyclic GMP excretion, in both groups, but there was no difference in the response between groups. Additional groups of rats of the same ages as groups I and II studied using a protocol similar to that of a previous report also showed the “mature” diuretic and natriuretic response even in the younger animals. We conclude that there is no further maturation of the renal response to acute BVE in the euvolemic rat after 25 d of age. The increase in [ANP] after acute BVE in the immature weanling rat is consistent with a role for ANP in mediation of the renal response.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

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<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.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

We have evaluated the effects of the combined administration of Galanin (Gal) plus growth hormone- releasing hormone (GHRH) and of pyridostigmine (PD), a cholinergic agonist, plus Gal on GH secretion in 15 children (12 males and three females, age 7.7-14.5 y) with short stature. Children were subdivided into two groups. In group 1 (n=7) Gal (15 µg/kg h i.v.) plus GHRH (1 µg/kg i-v.) administration induced a higher GH rise (peak=73.1 ± 10.2 ng/mL, mean ± SD; area under the curve (AUC)=531.9 ± 78.7 ng. min. mL-1) than did GHRH alone (peak=38.9 ± 26.5 ng/mL,p<0.05; AUC=256.9 ± 165.6 ng/mL/min-1,p<0.005). Gal had a synergistic effect on the GHRH-induced GH response because the GHRH plus Gal AUC response was significantly higher (p<0.01) than the sum of the areas of response to GHRH and Gal alone. In group 2 (n=8) PD administration (60 mg/kg p.o.) had no significant effects on the Gal-induced GH secretion (peak=14.9 ± 8.8 and 16.0 ± 9.8 ng/mL after Gal and PD + Gal, respectively; AUC=91.2 ± 52.1 and 125.2 ± 83.6 ng. mL. min-1after Gal and PD + Gal, respectively). Our results confirm the ability of Gal to stimulate GH secretion in children, and strengthen the view that its mechanism of action involves modulation of endogenous somatostatin release.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

N-acetylglutamate (NAG) content was measured in homogenates of liver and small intestine obtained from normal and 24-h starved syngeneic mice. Subsequently, NAG was determined in normal, and in carbamyl phosphate synthetase I and ornithine transcarbamylase enzyme-deficient human liver tissue homogenates. The method used in this study, which is direct and highly specific, used anion exchange extraction, gas chromatographic separation, and mass spectrometric detection and quantitation. Hepatic NAG content in the fed animals was 94.8 ± 19.8 nmol/g tissue or 602.5 ± 168.4 nmol/g protein (mean ± SD,n=5), whereas it was much lower in the fasted mice (49.4 ± 13.0 nmol/g tissue or 330.1 ± 113.9 nmol/g protein, mean ± SD,n=5). The magnitude of the difference was much smaller for intestinal NAG content, 19.8 ± 5.4 nmol/g tissue or 205.3 ± 70.3 nmol/g protein (mean ± SD,n=5) in the fed mice and 14.2 ± 4.3 nmol/ g tissue or 168.1 ± 80.8 nmol/g protein (mean ± SD,n=5) in the fasted mice. The concentrations of hepatic NAG in normal human livers (controls) ranged from 19.3 to 67.1 nmol/g tissue (41.6 ± 19.3, mean ± SD,n=5) or from 193 to 764.3 nmol/g of protein (437.5 ± 233.4, mean ± SD,n=5). In three patients with apparently complete carbamyl phosphate synthetase I or ornithine transcarbamylase deficiency, hepatic NAG levels were lower than controls (2.2-12.8 nmol/g tissue 42.3-140.7 nmol/g protein), two patients with ornithine transcarbamylase deficiency had levels similar to the controls and one patient with carbamyl phosphate synthetase I deficiency had elevated levels (98.4 nmol/g tissue, 1185.5 nmol/g protein). The livers of two patients with cirrhosis and hyperammonemia contained amounts of NAG within the range of normal livers. The marked variability in tissue NAG concentrations in various nutritional and metabolic conditions favors the hypothesis that NAG plays a role in the regulation of urea synthesis. Hepatic NAG levels are markedly reduced in some but not all patients with defects in urea cycle enzymes.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Odd-chain fatty acids are recognized precursors of propionate in man, but their clinical significance in disorders of propionate metabolism has not been well studied. Urinary excretion of methylmalonate, methylcitrate, propionylglycine, and 3-hydroxypropionate was measured in five children with methylmalonic acidemia and three with propionic acidemia during frequent or continuous feeding and after 10-18 h of fasting. There was a significant (p<0.01) increase in the mean total measured metabolite excretion during fasting (fed 38.1 µmol/kg/h, fasting 54.6 in methylmalonic acidemia, fed 1.45, fasting 2.98 in propionic acidemia). Percentage rises in each subject were similar for all measured metabolites. These increases in metabolite excretion are most easily explained by mobilization and oxidation of odd-chain fatty acids in the fasting state. Prolonged fasting should be avoided in children with disorders of propionate metabolism.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID

摘要:

Hyperuricemic nephropathy can progress to the permanent renal damage even in infancy in partial hypoxanthine-guanine phosphoribosyltransferase (HPRT) deficiency. We have encountered two unrelated patients with partial HPRT deficiency, and found that early detection of the disease and long-term management for hyperuricemia were necessary to prevent renal impairment. The HPRT gene is situated in the q26-27 region of the long arm of the X-chromosome, and females with mutant HPRT alleles are heterozygous for the disease, and they develop gout after menopause. We undertook the investigation of carriers in the two patients' families, using BamHI restriction fragment length polymorphisms and oligonucleotide probes that recognized the specific mutations within the HPRT gene. We also demonstrated that the allele frequencies of BamHI restriction fragment length polymorphisms in 62 Japanese females were 0.36 for the 22-kb/25-kb allele, 0.41 for the 12-kb/25-kb allele, and 0.23 for the 22- kb/18-kb allele, resulting in a heterozygous state in 66% of females.

ISSN:0031-3998    

出版商:OVID    

年代:1990

数据来源: OVID