Biomedical subjects

R de Leeuw

Publications and source records attributed to R de Leeuw.

At least 19 recordsLinked to original sources

PubMed1992

Effects of gonadotropin-releasing hormone variants on plasma and testicular androgen levels in intact and hypophysectomized male frogs, Rana esculenta.

The effects of vertebrate gonadotropin-releasing hormone (GnRH) variants on plasma and testicular androgen level in intact and hypophysectomized (PDX) male frogs, Rana esculenta, have been investigated. In intact animals, mammalian (m)-GnRH, m-GnRH analog (buserelin), salmon (s)-GnRH, chicken (c) I-GnRH, cII-GnRH, D-Arg6-cII-GnRH (cII-GnRHA), and lamprey (l)-GnRH (1.5 micrograms and 6 micrograms, total dose given on alternate days for 5 days) were able to enhance androgen production showing that specificity of pituitary responsiveness to GnRH variants appears to be low. Chicken II-GnRH was more effective than s-GnRH in eliciting testicular and circulatory androgen level increase. Moreover, in animals treated with 6 micrograms of cII-GnRH and s-GnRH in combination, androgens decreased as compared with animal treated with cII-GnRH only, suggesting that GnRH receptors bind preferentially the s-GnRH form. In PDX animals, buserelin (1.5 and 6 micrograms), cII-GnRH, and its analog (6 micrograms) were able to increase plasma androgen levels whereas testis androgen concentrations were increased by cII-GnRH (1.5 and 6 micrograms), D-Arg6-cII-GnRHA, and buserelin (6 micrograms). Since androgen production in PDX animals is influenced especially by peptides sharing cII-GnRH structure, it is suggested that a testicular cII-GnRH-like material play a role as local modulator of the gonadal activity in Rana esculenta.

Amino Acid Sequence↗

PubMed1992

Regulation of aromatase activity in FSH-primed rat granulosa cells in vitro by follicle-stimulating hormone and various amounts of human chorionic gonadotrophin.

The influence of various amounts of human chorionic gonadotrophin (HCG), with or without follicle-stimulating hormone (FSH), on aromatase activity, progesterone- and cAMP-accumulation in rat granulosa cells was investigated. Cells were isolated from immature diethylstilbestrol-treated rats and primed for 2 days in vitro with FSH (50 mIU/ml) to give a maximum response of the cells with respect to the induction of aromatase activity. After FSH priming, small amounts of HCG (1-5 mIU/ml) increased aromatase activity during an additional culture period of 24 h, with a maximum of 4- to 5-fold at 5-8 mIU/ml HCG. At higher concentrations of HCG, aromatase activity declined reaching a plateau (1.5-fold stimulation) at 20 mIU/ml HCG. When HCG was combined with FSH (50 mIU/ml) following the priming period, aromatase activity was stimulated in an additive way, reaching a maximum at 4-5 mIU/ml HCG followed by a decline, similar to that seen in the absence of FSH. HCG induced a dose-dependent increase in cAMP with a maximum at 20 mIU/ml. This increase in cAMP was higher when HCG was combined with FSH. Aromatase activity was inhibited by 3-isobutyl-methyl-xanthine and forskolin, both of which induce elevated cAMP levels in the cell. HCG, and HCG in combination with FSH, increased the production of progesterone in a dose-dependent manner until a plateau was reached. In the presence of FSH, this plateau was reached at lower HCG concentrations. Both R5020 and progesterone showed dose-dependent inhibition of aromatase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Possible involvement of protein kinase C in gonadotropin and growth hormone release from dispersed goldfish pituitary cells.

Static incubation with tumor-promoting 4 beta-phorbol esters, activators of the Ca2(+)- and phospholipid-dependent protein kinase C enzyme (PKC), caused dose-dependent increases in gonadotropin (GTH) and growth hormone (GH) secretion in primary cultures of dispersed goldfish pituitary cells. The estimated half-maximal effective doses (ED50) for stimulating GTH and GH release were 0.35 +/- 0.17 and 0.32 +/- 0.13 nM 12-O-tetradecanoyl phorbol 13 acetate (TPA), 3.71 +/- 1.30 and 1.37 +/- 0.76 nM 4 beta-phorbol 12,13-dibutyrate, 6.90 +/- 4.84 and 1.89 +/- 0.25 nM 4 beta-phorbol 12,13-dibenzoate, and 455 +/- 258 and 311 +/- 136 nM 4 beta-phorbol 12,13-diacetate, respectively. In contrast, treatments with up to 10 microM of the inactive 4 alpha-phorbol 12,13-didecanoate ester did not alter GTH and GH release. Additions of the synthetic diacylglycerol, dioctanoyl glycerol, also enhanced GTH and GH secretion in a dose-dependent manner and with ED50s of 1.73 +/- 0.83 and 1.73 +/- 1.19 microM, respectively. The GTH and GH responses to stimulation by TPA were attenuated by incubation with Ca2(+)-depleted medium containing EGTA or by treatment with the Ca2+ channel blocker verapamil. Coincubation with the PKC inhibitor H7 reduced the GTH and GH responses to TPA. As in previous studies, additions of salmon gonadotropin-releasing hormone (sGnRH) or chicken GnRH-II (cGnRH-II) induced GTH and GH release; these hormone responses to sGnRH and cGnRH-II were also decreased by the addition of H7. These results indicate that activation of PKC may stimulate GTH and GH release in goldfish and suggest that sGnRH and cGnRH-II actions on goldfish pituitary GTH and GH secretion are also mediated, at least partially, by PKC.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1991

Physiological effects of kangaroo care in very small preterm infants.

Kangaroo care for preterm infants has great benefits for the parents and for the parent-infant bonding process. A clinical observational study was conducted in which several physiological variables were collected, including among others transcutaneous oxygen pressure, heart rate, respiratory rate, occurrence of apneic attacks, breathing pattern (studied with power spectrum analysis), behavioral states and rectal temperature, during kangaroo care in small preterm infants. Kangaroo-care did not significantly affect any of these physiological variables comparing the period of 1 h before, 1 h during and 1 h after kangaroo care. We conclude that kangaroo care is a safe method, even for very small nonstabilized preterm infants.

Blood Gas Monitoring, Transcutaneous↗

PubMed1991

Comparative in vitro and in vivo studies on the biological characteristics of recombinant human follicle-stimulating hormone.

The in vitro and in vivo activities of recombinant human FSH (recFSH) produced by a Chinese hamster ovary cell line were studied and compared with those of natural FSH preparations. The specific FSH activities of recFSH established by immunoassay and in vivo bioassay were greater than 10,000 IU/mg protein and considerably higher than the activities of tested urinary FSH references, while the in vivo bio/immuno ratios of these preparations were not significantly different. Compared to a highly purified pituitary standard (IS 83/575), recFSH had a comparable high specific in vivo bioactivity, but the specific immunoreactivity of IS 83/575 was about 2 times lower. In receptor displacement and in vitro bioassay studies recFSH provided dose-response curves parallel to those of pituitary and urinary FSH references. When equal amounts of immunoreactivity FSH were tested, recFSH and urinary and pituitary FSH displayed comparable activities in both assays. The in vitro bioactivity of recFSH could be neutralized effectively by each of three monoclonal antibodies raised against recFSH (alpha-specific), urinary FSH (beta-specific), and pituitary FSH (alpha beta-specific), respectively. Moreover, 50% inhibition of comparable responses induced by recFSH, urinary "pure" FSH, or pituitary FSH was established by the same amount of monoclonal antibody. These results support the structural and functional similarity of recFSH and natural FSH. To test whether recFSH is capable of inducing LH-specific biological responses, the in vitro induction of testosterone production in mouse Leydig cells was assessed. At least 16 IU recFSH/ml incubate were needed to increase testosterone production, indicating that the intrinsic LH bioactivity of recFSH is negligible (less than 0.025 mIU LH/IU FSH). The in vivo efficacy of recFSH was examined by treating immature female hypophysectomized rats during 4 days with recFSH only or with recFSH supplemented with hCG. RecFSH only treatment increased ovarian weight and aromatase activity in a dose-dependent manner. When recFSH dosages providing submaximal responses were supplemented with 1 IU hCG, both ovarian weight and aromatase activity were largely augmented. Neither recFSH nor urinary pure FSH, administered in a high dose was able to increase plasma estradiol levels, while ovarian weight and aromatase activity were increased to the same extent. However, when recFSH was supplemented with only 0.1 IU hCG, a 3-fold increase in median plasma estradiol levels was obtained. These findings support the two-cell two-gonadotropin theory, holding that both FSH and LH are required for estrogen biosynthesis, but also reveal that only very small amounts of LH activity are sufficient to increase estrogen secretion up to measurable plasma levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

[Parental visiting and involvement in the neonatal intensive care unit].

Out of 145 neonatal departments of Dutch hospitals 120 participated in an inquiry concerning parental visiting and involvement. The results point to the conclusion that involvement of the parents is a fact that concerns practically all departments. Parents are allowed much more than some ten years ago. However, talks with parents reveal that many of them are not satisfied by far concerning these matters. Therefore the value of this kind of study is in revealing social desirability rather than actual reality.

Consumer Behavior↗

PubMed1990

Characterization of gonadotropin-releasing hormone (GnRH) binding sites in the pituitary and testis of the frog, Rana esculenta.

Frog, Rana esculenta, pituitary and testis gonadotropin-releasing hormone (GnRH) receptors were characterized by using 125I-chicken IIGnRH (cIIGnRH) as radiolabeled ligand. At 4 C equilibrium binding of 125I-cIIGnRH to pituitary homogenates was achieved after 90 min of incubation; binding of 125I-cIIGnRH to testis membrane fractions reached its maximum at 60 min of incubation. Binding of the radioligand was a function of tissue concentration, with a positive correlation over the range 0.5-2 tissue equivalents per tube. One pituitary and one testis per tube were used as standard experimental condition. Incubation of the pituitary homogenate with increasing concentrations of 125I-cIIGnRH indicated saturable binding at radioligand concentrations of 1 nM and above while for the testis membrane preparation saturation was achieved using 5 nM 125I-cIIGnRH. The binding of 125I-cIIGnRH was found to be reversible after addition of the cold analog and the displacement curves could be resolved into one linear component for both tissues. Scatchard analysis suggested the presence of one class of binding sites for both pituitary and testis (Pituitary: Kd = 1.25 +/- 0.14 nM and Bmax = 8.55 +/- 2.72 fmol/mg protein; testis: Kd = 2.23 +/- 0.89 nM and Bmax = 26.48 +/- 7.39 fmol/mg protein). Buserelin displaced the labeled 125I-cIIGnRH with a lower IC50 as compared with cIIGnRH cold standard, while Arg-vasopressin (AVP) was completely ineffective, confirming the specificity of binding.

Amino Acid Sequence↗

PubMed1990

In vitro goldfish growth hormone responses to gonadotropin-releasing hormone: possible roles of extracellular calcium and arachidonic acid metabolism?

Two hours of incubation of primary static cultures of dispersed goldfish pituitary cells with 0.01 nM to 1 microM [Trp7,Leu8]-gonadotropin-releasing hormone (sGnRH) increased growth hormone (GH) secretion in a dose-dependent manner with an ED50 estimate of 0.13 +/- 0.04 nM. Addition of calcium ionophores, 1 to 100 microM A23187 and 5 to 100 microM ionomycin, significantly elevated GH release with ED50s of 0.84 +/- 0.38 and 4.34 +/- 1.02 microM, respectively. Replacement of normal calcium-containing media with calcium-deficient media (prepared without the addition of calcium salts) significantly depressed basal GH secretion, attenuated the A23187- and ionomycin-stimulated GH release, and completely abolished the GH response to sGnRH. Arachidonic acid (AA) at 1 to 50 microM also enhanced GH secretion with an ED50 of 4.72 +/- 1.52 microM. Coincubation with 1 and 10 microM of a lipoxygenase inhibitor, nordihydroguaiaretic acid (NDGA), 10 microM of the cyclooxygenase inhibitor, indomethacin, and 10 microM of eicosatetraynoic acid, an enzyme blocker with mixed activities on both the lipoxygenase and cyclooxygenase pathways, did not alter basal, AA-, and sGnRH-induced GH release. However, at 100 microM concentration, NDGA increased AA- and sGnRH-stimulated, as well as basal GH, responses. These results confirm the direct stimulatory action of GnRH on goldfish somatotropes and indicate the importance of extracellular calcium in mediating basal and GnRH-induced GH responses. Although AA stimulates GH secretion, its lipoxygenase and cyclooxygenase metabolites probably do not mediate sGnRH action on somatotropes.

Animals↗

PubMed1990

Use of a pituitary cell dispersion method and primary culture system for the studies of gonadotropin-releasing hormone action in the goldfish, Carassius auratus. I. Initial morphological, static, and cell column perifusion studies.

Two cell dispersion methods for excised goldfish pituitary glands were tested, and a cultured dispersed cell system based on trypsin enzymatic tissue digestion was developed and characterized. Controlled trypsin/DNase treatment of goldfish pituitary gland yielded dispersed cells of high viability (trypsin blue exclusion test) that responded to gonadotropin (GTH)-releasing hormone (GnRH) challenges with GTH secretion in a time- and dose-dependent manner following overnight culture. Electron microscopy revealed that cell preparations produced by the trypsin dispersion were free of cell debris and nerve terminals. The dispersed pituitary cells also retained distinct morphological and immunological identities. Under static incubation conditions, 2-hr treatments with 0.1 nM to 1 microM [Trp7,Leu8]-GnRH (sGnRH) and [D-Arg6,Pro9-N-ethylamide]-sGnRH (sGnRHa) stimulated GTH release with similar efficacy, but with ED50S of 1.92 +/- 0.48 and 0.19 +/- 0.08 nM, respectively. [His5,Trp7,Tyr8]-GnRH (cGnRH-II) stimulated GTH release in a nonsigmoidal, but dose-dependent manner, and with a higher efficacy than sGnRH. In contrast, sGnRH, sGnRHa, and cGnRH-II were equipotent in inducing growth hormone (GH) secretion in static culture studies and with ED50S of 0.29 +/- 0.13, 0.18 +/- 0.11, and 0.19 +/- 0.17 nM, respectively. When trypsin/DNase-dispersed cells cultured overnight with cytodex beads were tested in a cell column perifusion system, dose-related increase in GTH secretion, as well as GH release, were also observed with 0.5 to 50 nM sGnRH. These results suggest that trypsin-dispersed goldfish pituitary cells can be used effectively to study the actions of GnRH on teleost pituitary either in short-term static incubation or column perifusion studies. Differences in the GTH and GH responses to the two native GnRH forms, sGnRH and cGnRH-II, are also indicated.

Animals↗

PubMed1990

Use of a pituitary cell dispersion method and primary culture system for the studies of gonadotropin-releasing hormone action in the goldfish, Carassius auratus. II. Extracellular calcium dependence and dopaminergic inhibition of gonadotropin responses.

Primary static cultures of dispersed goldfish pituitary cells obtained by controlled trypsinization released gonadotropin (GTH) in response to 2-hr stimulations of 0.1 nM to 1 microM [Trp7,Leu8]-gonadotropin-releasing hormone (sGnRH), [D-Arg6,Pro9-N-ethylamide]-sGnRH (sGnRHa), and [His5,Trp7,Tyr8]-GnRH (cGnRH-II) in a dose-dependent manner. Coincubation with 10 to 1000 nM of a dopamine agonist, apomorphine, dose dependently reduced the GTH response to increasing concentrations of sGnRH. Apomorphine at 1 microM completely abolished the dose-dependent GTH response to sGnRHa and cGnRH-II, but only partially inhibited the GTH-releasing action of high concentrations of sGnRH. Addition of calcium ionophores, 1 to 100 microM A23187 and 10 to 100 microM ionomycin, significantly increased GTH release. The ED50S of the GTH response to A23187 and ionomycin were 0.88 +/- 0.15 and 13.67 +/- 2.76 microM, respectively. Incubation with Ca2(+)-deficient media (media prepared without the addition of Ca2+ salts) did not significantly affect basal GTH release, but severely decreased the hormone response to increasing concentrations of sGnRH, A23187, and ionomycin. These results confirm the direct inhibitory dopaminergic influence on GTH release in goldfish and further suggest that extracellular Ca2+ plays a role in mediating GnRH action on gonadotropes in fish.

Animals↗

PubMed1989

Participation of arachidonic acid metabolism in gonadotropin-releasing hormone stimulation of goldfish gonadotropin release.

Two intraperitoneal injections of a mammalian gonadotropin-releasing hormone (GnRH) analog, [D-Ala6, Pro9-N-ethylamide]-GnRH (mGnRHa; 0.1 micrograms/g), at 12-hr intervals increased serum gonadotropin (GTH) levels in sexually mature and sexually regressed female goldfish 2 and 6 hr after the second injection. This serum GTH response was decreased by the coinjection of a lipoxygenase enzyme inhibitor, nordihydroguaiaretic acid (NDGA: 0.1 to 10 micrograms/g) at the time of the second mGnRHa application. In static cultures of dispersed goldfish pituitary cells, 1-100 microM arachidonic acid (AA) and 0.1-1000 nM [Trp7, Leu8]-GnRH (salmon GnRH, sGnRH) and [D-Arg6, Pro9-N-ethylamide]-sGnRH (sGnRHa) caused dose-dependent increases in GTH release. Additions of 1-40 microM NDGA reduced the sGnRH-stimulated GTH release in a dose-dependent manner, and completely inhibited the GTH response to increasing concentrations of AA. NDGA 40 microM also decreased the elevated GTH levels induced by sGnRHa treatment. Exposure to 10 microM 5,8,11,14-eicosatetraynoic acid, an inhibitor with mixed action on lipoxygenase and cyclooxygenase enzymes, reduced the dose-dependent GTH response to sGnRH and AA. In contrast, coincubation with another cyclooxygenase blocker, indomethacin, at 10 microM, did not alter AA and sGnRH-induced GTH release. These results provide in vivo and in vitro evidence for the participation of AA metabolism in mediating GnRH-stimulated GTH release in the goldfish. The importance of AA metabolism through the lipoxygenase pathway is also indicated.

5,8,11,14-Eicosatetraynoic Acid↗

PubMed1989

Characterization of gonadotropin-releasing hormone binding sites in the pituitary of the three-spined stickleback, Gasterosteus aculeatus.

Binding sites for gonadotropin-releasing hormone (GnRH) in stickleback pituitary homogenates were characterized using an iodinated, superactive analog of salmon GnRH (sGnRH), D-Arg6-Pro9-sGnRH-NEt (sGnRHa). Binding of 125I-sGnRHa reached equilibrium after 60 min incubation at 4 degrees and was a function of tissue concentration. The specificity of 125I-sGnRHa binding was demonstrated by displacement with sGnRHa, sGnRH, and Buserelin [D-Ser(t-Bu)6-Pro9-GnRH-NEt]. Both Scatchard analyses of saturation data and displacement curves revealed a single class of high-affinity binding sites (Ka = 0.71 +/- 0.03 X 10(9) M-1, Bmax = 1087 +/- 165 fmol/mg protein).

Animals↗

PubMed1989

Clinical outcome of small for gestational age preterm infants.

Data from 55 preterm SGA infants and 55 preterm AGA infants matched for gestational age and sex were reviewed retrospectively. An increased incidence of perinatal hypoxia (30 vs. 18), gastrointestinal problems, minor infections (27 vs. 9), hematological problems and increased mortality (21.8% vs. 7.2%) was observed in the SGA infants. The incidence of HMD was higher in the AGA group (not significant), but the HMD was much more severe in the SGA group. Mortality as a result of HMD was significantly higher in the SGA group. The percentage of handicapped children is 19% in the SGA group and 9% in the AGA group. The percentages of severely handicapped children are 4.8% and 2.3% respectively. The combination of prematurity and severe intrauterine growth retardation in the SGA group caused a higher mortality and morbidity than was seen in their AGA controls. This clinical performance of SGA preterm infants is important especially for those who have to decide at what moment such a child should be delivered by caesarean section.

Birth Weight↗

PubMed1989