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L Vanhaelst

Publications and source records attributed to L Vanhaelst.

At least 19 recordsLinked to original sources
PubMed1992

Differential dopamine-induced prolactin mRNA levels in various prolactin-secreting cell (sub)populations.

We have examined the effects of dopamine on prolactin gene expression using quantitative in-situ hybridization histochemistry in different pituitary cell (sub)populations separated according to their density on a discontinuous Percoll gradient. Administration of dopamine resulted in a drastic reduction in hybridization of 35S-labelled DNA probe complementary to prolactin mRNA in total pituitary cells and in lactotrophs with low density. In contrast, dopamine significantly stimulated mRNA accumulation in prolactin-secreting cells with high density compared with other cell layers. The combined use of Percoll gradient and quantitative in-situ hybridization is a valuable and sensitive method with which to examine prolactin-secreting cell response to a given stimulation. Prolactin-secreting cells with high and low density clearly show functional heterogeneity in their response to dopamine.

Animals↗
PubMed1991

Pharmacokinetics of intravenous and oral chlordesmethyldiazepam in patients on regular haemodialysis.

The pharmacokinetics of a single 2 mg IV dose of chlordesmethyldiazepam has been studied in 11 patients with renal failure on regular haemodialysis and in 11 age-matched healthy controls. The kinetics was also examined after a single 2 mg oral dose in 6 of the 11 renal failure patients. After intravenous administration the kinetics of total chlordesmethyldiazepam in renal patients and controls were the same. The unbound fraction of the drug in renal patients was higher (5.5%) than in controls (2.9%). Correction for differences in protein binding revealed a reduced apparent volume of distribution (47 vs. 140 l.kg-1) and a reduced clearance (5.0 vs. 10.5 ml.min-1.kg-1) in the patients. The systemic availability of oral chlordesmethyldiazepam was good (82%) despite a relatively slow absorption rate.

Administration, Oral↗
PubMed1991

Protective effects of felodipine and verapamil against imipramine-induced lethal cardiac conduction disturbances in the anaesthetized rat.

The effect of verapamil and felodipine on imipramine-induced cardiac toxicity was assessed in anaesthetized rats. Rats received either infusion of saline (n = 13), or non-hypotensive doses of felodipine (n = 36) or verapamil (n = 36) over 40 minutes. In saline-pretreated rats IV bolus injection of imipramine (10 mg/kg) resulted in severe hypotension, bradycardia, electromechanical dissociation, and death within 3 minutes. Rats pretreated with nonhypotensive doses of felodipine (1, 3, 6, and 10 micrograms/kg/min) or verapamil (10, 30, 100, and 300 micrograms/kg/min) survived throughout the experiment, despite an initial fall in blood pressure within the first 5 minutes after imipramine administration. Blood pressure returned to baseline levels within 15 minutes. Intermittent ECG monitoring showed significant prolongation of QRS duration after imipramine in both saline (by 138%) and verapamil-pretreated rats (by 63%), whereas in the rats pretreated with felodipine no prolongation was observed (+3%). We conclude that, in our experimental model, felodipine, more than verapamil, protects against the cardiac effects of imipramine intoxication.

Animals↗
PubMed1991

Quantitative in situ hybridization in neuro-endocrinology.

In situ hybridization has become one of the most powerful tools for localizing specific gene products in a tissue. Labelled molecular probes are used on tissue sections or on cells for localization of their hybridization sites. In situ hybridization makes it possible to define the spatial and temporal distribution of specific genes. The use of probes dually labelled, or the combined use of a molecular probe and labelled antibodies provides unprecedented opportunities to examine gene expression in individual cells. In addition, the quantification of gene products can shed light on regulation of gene expression at the cellular level.

Animals↗
PubMed1991

Cyclical Cushing's disease. A case report.

A 41-year-old man with clinical Cushing's syndrome and intermittent central ACTH hypersecretion for a period of 9 1/2 years follow-up is described. Episodes of biochemical and clinical remission alternated with periods of florid Cushing's disease, characterized by circadian hyperpulsatile ACTH and cortisol secretion. Responses to metyrapone and inhibition of ACTH and cortisol hypersecretion after high dose dexamethasone during active phases of the disease favored a central origin of ACTH hypersecretion, confirmed by simultaneous bilateral venous sampling of the sinus petrosus inferior. Prolonged clinical remission followed near total anterior hypophysectomy. However, on anatomopathological examination of the pituitary neither corticotroph cell hyperplasia nor a microadenoma could be documented. The possibility of a functional ACTH hypersecretion is discussed.

Adrenal Glands↗
PubMed1991

Interleukin-1, interleukin-6: messengers in the neuroendocrine immune system?

Recent findings indicate that interleukin-1 (IL-1) and interleukin-6 (IL-6), cytokines secreted by immunologically activated monocytes and macrophages modulate neuroendocrine function. The site of production (centrally, peripherally), the site of action and the physiological significance of IL-1 and IL-6 as "classical hormones" are questioned.

Adrenocorticotropic Hormone↗
PubMed1991

Identification of a D1 dopamine receptor, not linked to adenylate cyclase, on lactotroph cells.

1. We studied the lactotroph cells of the rat by both in vivo and in vitro pharmacological techniques for the presence of D1-receptors. Both approaches revealed the presence of D2-receptor, stimulated by quinpirole (resulting in an inhibition of prolactin secretion) and blocked by domperidone. 2. Administration of fenoldopam, the most selective D1-receptor agonist currently available, resulted in a dose-dependent decrease of prolactin secretion in vivo (after pretreatment with alpha-methyl-p-tyrosine) and in vitro (cultured pituitary cells). This increase was dose-dependently blocked by the selective D1-receptor antagonist, SCH 23390, and although the effect of fenoldopam was less than that obtained by D2-receptor stimulation, these data suggest that a D1-receptor also controls prolactin secretion. 3. In order to detect the location of these dopamine receptors, autoradiographic studies were performed by use of [3H]-SCH 23390 and [3H]-spiperone as markers for D1- and D2-receptors, respectively. Specific binding sites for [3H]-SCH 23390 were demonstrated. Fenoldopam dose-dependently reduced [3H]-SCH 23390 binding, but had no effect on [3H]-spiperone binding. Immunocytochemical labelling of prolactin cells after incubation with [3H]-SCH 23390 revealed that the granulae and hence, D1 binding sites were present on the lactotroph cells. 4. Radioligand binding studies performed on membranes from anterior pituitary cells revealed the presence of the D2-receptor (54 fmol mg-1 protein) with a Kd of 0.58 nM for [3H]-spiperone, but failed to detect D1-receptors. 5. Finally, we studied the effect of dopamine and of fenoldopam on the adenosine 3':5'-cyclic monophosphate (cyclic AMP) content of anterior pituitary cells. Although cyclic AMP increased upon prostacyclin administration, indicating an intact adenylate cyclase system, fenoldopam failed to increase the cyclic AMP production. 6. It is tempting to speculate that fenoldopam reduces prolactin secretion through interaction with a non-cyclase-linked D1-receptor on the lactotroph cells.

Adenylyl Cyclases↗
PubMed1991

Analysis of the receptor specificity of tolerance induction in stress versus opioid-related prolactin secretion in rats.

The effects of restraint stress and opiates on prolactin secretion in male rats have been measured. Both induced a short-lived increase in prolactinaemia. Experimental evidence indicates that both opioids and restraint stress bring about their actions by the activation of opioid receptors. When restraint stress was followed by administration of the specific kappa-agonist bremazocine, a second prolactin peak was observed. In contrast, morphine (predominantly a mu-agonist) lost its prolactin-stimulating capacity when given after a period of restraint stress. This indicates cross-tolerance between restraint stress and morphine. Tolerance was overcome when the dose of morphine was doubled, and an increase in prolactin secretion could again be obtained. The cross-tolerance phenomenon argues that a common opioid receptor is involved in morphine- and restraint stress-stimulated prolactin release. In another set of experiments, in which morphine administration replaced restraint stress as a means of inducing tolerance, a second rise in prolactinaemia was seen only with bremazocine and not with a further administration of morphine. This suggests a morphine (mu) receptor-specific development of tolerance. Two consecutive administrations of bremazocine also produced tolerance, in this case for the kappa-receptor. This illustrates the rapid and receptor-specific development of tolerance for the prolactin-releasing capacity of opioid compounds.

Animals↗
PubMed1990

The growth hormone secretory response to fentanyl in rat: an involvement of mu type receptors.

Fentanyl, a selective mu opioid receptor agonist, administered intravenously, influences growth hormone secretion in conscious male rats. A dose-response study demonstrated that the maximum growth hormone release was obtained with 10 micrograms/kg while higher doses were less or not effective. MR-2266 (6 mg/kg i.v.), a mu and kappa opioid receptor antagonist, and bremazocine (0.1 mg/kg i.v.) a mu opioid receptor antagonist with kappa agonistic properties, both potently inhibited the growth hormone response to fentanyl (10 micrograms/kg i.v.). In contrast, the effect of fentanyl on growth hormone release was not blocked in rats treated with either ICI-154129 (30 mg/kg i.v. or 150 micrograms/kg intracerebroventricularly a selective delta opioid receptor antagonist, or U-50488 (10 mg/kg i.v.), a specific kappa opioid receptor agonist. These results suggest that opioid receptors of the mu type are involved in the fentanyl-induced growth hormone release.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗
PubMed1990

Development of monoaminergic neurotransmitters in fetal and postnatal rat brain: analysis by HPLC with electrochemical detection.

The monoamines dopamine, norepinephrine, epinephrine, and serotonin and their major metabolites 3,4-dihydroxyphenylacetic acid, homovanillic acid, 3-methoxy-4-hydroxyphenylethylene glycol, and 5-hydroxyindoleacetic acid were measured in the CNS of the rat during development from fetal day 18 to young adult. The catecholamines, serotonin, and their major metabolites remained low during fetal life. Concentrations measured in total brain started to increase around birth till the end of the fourth week of life after which steady-state levels were measured. Our results suggest that although monoamine systems are already morphologically well developed during late gestational life, they probably become a significant functional system only around birth and early postnatal life.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1989

Localization of interleukin 6 mRNA in human tonsils by in situ hybridization.

We have investigated which areas produce interleukin 6 (IL 6) in human tonsils. This growth factor is required for the terminal differentiation of B lymphocytes into plasmocytes. Using 35S-labeled IL 6 cDNA we demonstrated IL 6 gene expression over various areas of the tonsils, with consistent exception of the follicles, by in situ hybridization. It is, therefore, proposed that B cells are stimulated during their migration out of the follicles.

B-Lymphocytes↗
PubMed1989

Ontogeny of hormone-secreting cells of the rat pituitary gland: an immunocytochemical study on dissociated cells.

An immunocytochemical study was undertaken in foetal, prepubertal and mature rats to determine the time of differentiation of various types of adenohypophyseal cells during development. Freshly dissociated pituitary cells from foetal (18-21 days postconception), neonatal (from birth up to 30 days) and adult rats (more than 8 weeks) were characterized using immunocytochemical methods. All types of hormone-producing cells were present at day 18 postconception, although only 20% of the cells were immunolabelled. Adrenocorticotropin (ACTH)-secreting cells accounted for the highest number of hormone-positive cells. Growth hormone-secreting cells increased remarkably from day 18 postconception onwards. Prolactin-secreting cells were not seen in the foetal adenohypophysis and did not start to increase until 10 days after birth, whereas by that time the number of ACTH, thyrotropin, follicle-stimulating and luteinizing hormone-secreting cells had stopped increasing. By day 30 after birth, 80-95% of the cells were immunoreactive.

Adrenocorticotropic Hormone↗
PubMed1989

Multiple forms of rat prolactin and growth hormone in pituitary cell subpopulations separated using a Percoll gradient system: disulphide-bridged dimers and glycosylated variants.

Prolactin and GH cells from rat pituitary glands were separated into three main fractions on discontinuous Percoll gradient layers. SDS-PAGE and subsequent immunoblotting of these fractions revealed that: (1) multiple rat prolactin (rPRL) molecular variants were present in total culture, Percoll layer 1 and 2; four variants were clear-cut: Mr approximately 23,000, Mr doublet approximately 25,000-26,000, Mr approximately 40,000 and Mr approximately 42,000; (2) cell cytosol from Percoll gradient layer 1 was particularly enriched in prolactin; (3) cells from gradient layer 1 secreted into the culture medium only prolactin in detectable amounts; (4) three distinct molecular forms of rat growth hormone (rGH) were recorded in layer 3: Mr approximately 36,000, 24,000 and 20,000; the 20,000 variant was paramount; and (5) cells from layer 3 secreted both rPRL and rGH into the culture medium. Reduction experiments showed that, on the one hand, 42,000 and 40,000 rPRL variants and, on the other hand, 36,000 rGH variants are disulphide-bridged dimers. An important finding was the presence of glycosylated rPRL and rGH: indeed Concanavalin A-Sepharose 4B affinity chromatography indicated that 26,000 rPRL and 24,000 rGH display a very strong affinity for lectin. Competitive inhibition tests showed that this affinity is specific and not due to hydrophobic binding. When rPRL was submitted to deglycosylation in conditions specific for O-linked glycoproteins, the 26,000 rPRL variant disappeared. The biological role of glycosylated rPRL is as yet unknown.

Animals↗
PubMed1988

Treatment of hyperthyroidism with radioiodine: adjunctive therapy with antithyroid drugs reconsidered.

To assess the value of antithyroid drugs as an adjunct to radioactive iodine for the treatment of hyperthyroidism the incidence of relapse or hypothyroidism after a mean follow-up of 5 1/2 years (range 2-7 years) was reviewed retrospectively for 206 patients, some treated with and others without antithyroid drugs after radioiodine therapy. Allocation to treatment group had been random, and both groups were similar in all respects except for the adjunctive treatment with antithyroid drugs. All doses of 131I had been calculated by one physician. Compared with those who received 131I alone, those starting on antithyroid drugs within 8 days after 131I had a lower incidence of hypothyroidism but a higher incidence of early post-treatment recurrence or persistence of hyperthyroidism, and a considerably lower incidence of remission.

Adult↗