摘要:

To determine potential mechanisms by which androgens alter gonadotropin secretion and elimination in the pubertal male, we administered the potent nonsteroidal androgen receptor blocking agent, flutamide, to eight males with Tanner IV or V genital development. Venous blood samples were obtained every 10 min for 24 h and assayed for LH by a sensitive and high-precision fluorimmunoassay. Subjects were studied before and after the administration of flutamide. Deconvolution analysis was used to assess specific pulsatile LH secretory characteristics and estimate LH production and metabolic clearance rates quantitatively. After antagonism of endogenous androgen action, mean 24-h serum LH concentrations increased significantly. An increased mean 24-h LH production rate, without evident changes in serum LH half-life, accounted for the increase in average serum LH levels. The increased daily secretion rate of LH was in turn due to both an augmented mass of LH released per secretory episode and increased frequency of secretory events. There was no demonstrable change in the maximal rate of LH secretion attained within each secretory event. Serum concentrations of total testosterone, free-testosterone, and 17β-estradiol all increased during blockade of androgen action. Administration of the antiandrogen had no measurable effect on the pituitary response to a single maximally effective dose of exogenous gonadotropin releasing hormone (GnRH). These results indicate that, in the late pubertal male, endogenous androgen exerts negative feedback control of gonadotropin secretion primarily at a hypothalamic site reflected by regulation of the frequency of pulsatile LH secretion. Antiandrogen had no discernible effects on exogenous GnRH-stimulated pituitary LH release or on the elimination rate of LH, but amplified the mass of LH secreted in response to endogenous GnRH. Assuming that pituitary response to exogenous GnRH reflects responsivity to endogenous releasing factor, we can infer an augmentation of the endogenous GnRH stimulus when androgen negative feedback is withdrawn. Accordingly, we suggest that endogenous androgen acting via androgen receptors negatively regulates both the amount and frequency of hypothalamic GnRH release in late pubertal boys.

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Experimental diabetes was induced in rats with streptozocin before mating, and the influence of diabetes on epidermal growth factor (EGF) in milk and on other milk components was studied. Throughout the lactation period, a significant decrease was found both in the production of milk and in the concentration of EGF in milk from untreated diabetic rats compared with an insulin-treated diabetic group and a control group. Thus, the total output of EGF in milk from diabetic rats was considerably decreased. The concentrations of total protein and haptocorrin, a cobalamin (vitamin B12)-binding protein, and the content of fat, however, were unaltered by diabetes. Therefore, the decrease in milk EGF seemed to be selective compared with total protein in milk. The pups of diabetic dams had reduced body weights within 1 wk of lactation and reduced body lengths on d 16 of lactation compared with control pups. Furthermore, the time of eyelid opening was delayed, but no difference in the time of tooth eruption was observed. Insulin-treatment of diabetic rats restored the milk volume and the EGF concentration to values comparable to those of the controls. Pups of the insulin-treated diabetic dams were comparable to the pups of the controls. These results indicate that insulin deficiency in lactating rats causes a decrease in the lactational performance and in the EGF content of milk.

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Nucleotide supplementation of adapted-milk formulas may be of interest for infant nutrition because nucleotides are involved in the synthesis of proteins and other macromolecules such as phospholipids, and thereby facilitate lipoprotein synthesis. To determine whether dietary nucleotides influence plasma lipoproteins in newborns, we have studied the plasma-lipoprotein concentrations and the composition of the major lipoprotein fractions during the first week of life in two groups of preterm infants fed formulas differing only in their nucleotide content. For comparison, two groups of term infants were studied under the same conditions. Lipoproteins were isolated by density ultracentrifugation, and the lipid and protein content were determined by standard methods; apolipoprotein A-I was determined immunologically. Nucleotide supplementation of formula in preterm infants increased all plasma lipoprotein concentrations. In addition, an increase in the plasma esterification rate was observed. However, total cholesterol concentrations were unchanged. The changes in lipoproteins concentrations were due mainly to an increase in apolipoprotein content. Nucleotides added to formulas affected term-infants' lipoproteins significantly less than to perterm infants. These findings suggest that dietary nucleotides may enhance the synthesis of lipoproteins during the early neonatal period, especially in preterm infants.

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Lactoferrin (Lf) is a major iron (Fe)-binding protein in human milk and has been proposed to facilitate Fe absorption. The potential effect of Lf on Fe absorption was investigated by measuring Fe absorption in infants fed breast milk (with its native content of Lf) and the same milk from which Lf had been removed (>97%) by treatment with heparin-Sepharose. Eight breast-fed infants (2–10 mo; mean age 5 mo) were fed 700 to 1000 g of each milk in a randomized, cross-over design with each child acting as his/her own control. The milk was labeled with 8.6 Mmol (0.5 mg) of58Fe and Fe absorption was measured by quantifying the incorporation of the isotope into red blood cells 14 d after intake using thermal ionization mass spectrometry. Fractional Fe absorption was significantly lower (p< 0.05) from breast milk than from Lf-free breast milk. The geometric mean (range) was 11.8% (3.4–37.4%) for breast milk and 19.8% (8.4–72.8%) for Lf-free breast milk. These results do not support a direct role for Lf in the enhancement of Fe absorption from human milk at this age. In addition, Fe absorption (11.8%) from human milk fed over several feeds was lower than that previously reported for single feed studies.

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

Preterm infants are more prone to bone mineral deficiency the lower their birth weight. To achieve the intrauterine bone mineral accretion rate postnatally, 74 low-birth-weight infants (median birth weight, 980 g; range 430–1.580 g) were each supplemented enterally and/or parenterally with calcium and/or phosphorus in gradually increased amounts. The aim was to yield a simultaneous urinary excretion of Ca and inorganic phosphorus (Pi) at low concentrations (1–2 mmol/L) in spot urine specimens taken twice weekly. The hypothesis was that the intrauterine mineralization rate (4.5 mg cm−1/100 g weight gain) would be achieved postnatally in very low-birth-weight infants, if they were supplemented with enough Ca and/or Pi to effect at least a low (1–2 mmol/L) simultaneous urinary excretion of both ions, as compared with infants who do not excrete both ions and would accrete the bone minerals at a lower rate. The change in bone mineral content was measured by single photonabsorption densitometry and related to weight gain during periods of 2 to 6 wk. Infants who simultaneously excreted Ca (>1.2 mmol/L) + Pi (>0.4 mmol/L) in more than half of the urine samples retrospectively showed the highest bone mineral accretion, 5.1 mg cm−1/100 g weight gain, which was equivalent to the fetal mineralization rate (4.5). In this group the bone mineral status significantly contributed to the variance of the bone mineral accretion rate; severely demineralized infants showed a catch-up mineralization. A significantly lower rate (2.4) was observed in infants who excreted Ca + Pi in less than half of the urinary samples. Supplementation with Ca and Pi up to the point where both ions are simultaneously excreted with the urine at concentrations >1.2 and >0.4 mmol/L, respectively, offers a simple and safe way of achieving the fetal bone mineral accretion rate in preterm infants, taking into account their individual needs, the varying mineral content of breast milk, and the different compositions of special-care formulas. A further prospective study is needed to test the hypothesis.

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

IL-1 receptor antagonist (IL-1ra) is a cytokine that blocks the effects of IL-1 by binding to IL-1 receptors without inducing signal transduction. Amniotic fluid contains high concentrations of IL-1ra. The purpose of this study was 1) to analyze whether factors related to the mother or the fetus influence amniotic fluid IL-1ra concentration, and 2) to study whether the fetus is a source of IL-1ra. Two hundred two specimens of amniotic fluid, as well as 21 urine samples from newborn infants, were analyzed. Women carrying a female fetus had a higher concentration of amniotic fluid IL-1ra than those carrying a male fetus (female 136.4 ± 6.1 μg/L,n= 83; male 74.7 ± 3.7 μg/L,n= 119;p< 0.0001, unpaired two-sidedttest). Length of gestation, presence or absence of labor signs, or elevated IL-1β in amniotic fluid did not affect the concentration of IL-1ra in amniotic fluid. Urine of infants taken during the first 48 h of life contained a high concentration of IL-1ra (91.1 ± 17.5 μg/L). The urinary IL-1ra concentration was higher in female newborns than in male newborns (females 124.0 ± 25.2 μg/L,n= 11; males 54.9 ± 19.1 μg/L,n= 10;p= 0.04). We conclude that1) the concentration of IL-1ra in amniotic fluid and newborn urine is dependent on the gender of the fetus and of the newborn and 2) fetal urine is a major source of amniotic fluid IL-1ra. The higher IL-1ra in female-bearing gestations may contribute to the better resistance of female fetuses against preterm birth and perinatal infections.

ISSN:0031-3998    

出版商:OVID    

年代:1994

数据来源: OVID