Biomedical subjects

R Collu

Publications and source records attributed to R Collu.

At least 19 recordsLinked to original sources

PubMed1995

Familial adrenocorticotropin unresponsiveness associated with alacrima and achalasia: biochemical and molecular studies in two siblings with clinical heterogeneity.

UNLABELLED: The syndrome of familial adrenocorticotropin (ACTH) unresponsiveness is a rare form of primary adrenal insufficiency, usually without mineralocorticoid deficiency. It is characterized by elevated plasma ACTH concentrations and undetectable plasma cortisol levels not responding to exogenous ACTH. Alacrima and achalasia have also been occasionally associated with adrenal insufficiency (triple A syndrome). Pathogenetic mutations have been identified in the ACTH receptor gene in families with isolated familial ACTH unresponsiveness. Whether the ACTH receptor represents the locus of the defect for the triple A syndrome is not known. Here we report two siblings with familial ACTH unresponsiveness who were discrepant for skin pigmentation and mineralocorticoid function. In addition, achalasia and alacrima were documented only in the older sibling. The boy, studied at the age of 2 years, was hyperpigmented, in contrast to his normally pigmented sister, studied at the age of 9 years; basal plasma alpha-melanocyte stimulating hormone immunureactivity levels were 79 and 38 pg/ml, respectively (normal < 40 pg/ml). Furosemide-induced diuresis resulted in normal rises of plasma renin activity in both patients; however, plasma aldosterone levels increased only in the boy and not in his sister. Screening for abnormalities of the ACTH receptor gene by single strand conformation polymorphism analysis revealed no abnormality. Direct sequencing of the entire coding area of the ACTH receptor gene was also normal. CONCLUSION: The syndrome of familial ACTH unresponsiveness can vary clinically and biologically within the same family.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Gland Diseases↗

PubMed1995

Mammosomatotroph adenoma causing gigantism in an 8-year old boy: a possible pathogenetic mechanism.

The pathophysiology of mammosomatotroph adenomas remains unclear. We studied a mammosomatotroph adenoma removed from an 8-year old boy with a 5-year history of growth acceleration and acromegalic gigantism at presentation. Elevated basal GH (mean 28 micrograms/l) and PRL (mean 120 micrograms/l) plasma levels were observed, as well as paradoxical responses of GH to L-dopa, TRH and oral glucose administration; PRL was reduced by L-dopa and slightly increased by TRH; GHRH stimulated release of both GH and PRL. Two operations were required to remove the very large tumour and the patient was treated with bromocriptine before the second. Hormonal secretion by tumour explants in culture was evaluated under basal conditions and after stimulation or inhibition. High levels of GH and PRL were secreted for up to 24 days. Furthermore, GHRH and TRH caused a dose-related stimulation of both hormones, while somatostatin and dopamine were effective in suppressing either basal or stimulated hormone release only at very high (microM) concentrations. Intracellular events were studied by determination of the guanosine triphosphate binding (G) protein levels and adenylate cyclase (AC) activity in the tumour tissue. Before bromocriptine treatment, AC activity was very high in the tumour and could be further stimulated by various agents; very high levels of the AC-stimulatory G protein alpha subunit Gs alpha and very low amounts of the AC-inhibiting G protein alpha subunit Gi3 alpha and of the phospholipase C-stimulating G protein alpha subunit Gq alpha were found in the tumour. After bromocriptine, baseline AC activity was normalized and could no longer be stimulated; Gs alpha and Gi3 alpha levels were unchanged while those of Gq alpha were normalized. Screening of tumour DNA after amplification by polymerase chain reaction followed by single-strand conformational polymorphism analysis did not reveal any mutations in the hot spots of G protein alpha subunits (alpha s, alpha i2, alpha o2 and alpha 11) genes or in the H-ras and p53 genes. Gs alpha and GH transcription factor-1 (pit-1) expression were evaluated by amplification of cDNA. While the mRNA expression of pit-1 decreased after bromocriptine treatment, that of Gs alpha increased. These data suggest the possibility of an oncogenic process involving overexpression of Gs alpha, resulting in chronic activation of adenylate cyclase. Furthermore, our results suggest that the anti-secretory and anti-proliferative effects of bromocriptine may be mediated through a decrease in Pit-1 secondary to the inhibition of adenylate cyclase activity.

Adenoma↗

PubMed1995

Identification of human growth hormone-releasing hormone receptor splicing variants.

The expression pattern of the receptor for human GHRH (hGHRHr) was investigated in normal human tissues and in pituitary and ovarian tumors by reverse transcription-polymerase chain reaction. Three transcriptional variant forms of the hGHRHr were found to be expressed in the normal pituitary and in GH-secreting pituitary tumors. Form a is identical to the previously reported hGHRHr, whereas forms b and c are not described in the literature. Form b and c are predicted to be transcribed into two truncated proteins. We amplified genomic DNA using primers designed from the complementary DNA of hGHRHr. A 2-kilobase genomic DNA fragment was cloned that contains part of the hGHRHr gene consisting of two exons, e864 and e934, separated by three introns, i863, i933, and i1025. Alternative splicing of i1025 was responsible for three variant forms of hGHRHr. Nonsecreting pituitary tumors showed an abnormal expression of the hGHRHr, probably due to alternative usage of exons at the 5'-end of the gene, although they also expressed the three variant forms. No hGHRHr expression was identified in a human mammosomatotroph cell line insensitive to GHRH, in normal human liver or ovary, or in various human ovarian tumors.

Alternative Splicing↗

PubMed1993

Hypothalamic dysfunction in a child: a distinct syndrome? Report of a case and review of the literature.

We report the case of a 9-year-old girl with multiple problems due to hypothalamic dysfunction of obscure origin: apnoeic spells, behavioural problems, developmental delay, hypodipsia with bouts of hypernatraemia, episodes of spontaneous hypothermia, obesity, petit-mal seizures, non-progressive precocious puberty, absence of respiratory response to CO2 and probably insensitivity of hyposensitivity to pain. She also had hyperprolactinaemia and decreased human growth hormone secretion. Hypothyroidism of central origin and hyposecretion of cortisol were also present. Multiple brain CT-scans failed to reveal any tumour or other anatomical abnormality. Her clinical course was improved initially by treatment with clomipramine, but she died suddenly, and the autopsy failed to disclose any anatomical lesion. We compare this case with three similar previously reported cases.

Child↗

PubMed1993

MMQ cells: a model for evaluating the role of G proteins in the modulation of prolactin release.

It is well known that dopamine (DA) inhibits while vasoactive intestinal peptide (VIP) and angiotensin II (ANG II) stimulate prolactin (PRL) release from normal anterior pituitary lactotrophs; however, elucidation of the intracellular mechanisms involved in these effects has been hindered by the cellular heterogeneity of the anterior pituitary. MMQ cells, isolated from the PRL-secreting rat pituitary tumor 7315a is an interesting model since they only secrete PRL. In order to determine whether and which GTP-binding (G) proteins are involved in the modulation of cyclic 3',5'-adenosine monophosphate (cAMP) accumulation and phospholipids turnover and eventually PRL release, we have performed studies with MMQ cells. For this purpose, the levels of various G proteins (alpha o, alpha s, alpha i, alpha q and beta) and their mRNAs, measured by Western and Northern blots respectively, were correlated with intracellular cAMP accumulation in response to DA, VIP or DA plus VIP, and with inositol phosphates (IPx) formation in response to ANG II, DA or DA plus ANG II. This study shows that, when compared to normal pituitary tissue, the levels of alpha o, alpha o2 and alpha i3 were significantly decreased in MMQ cells; those of alpha o1, alpha i (alpha i1 + alpha i2), alpha s42 and alpha q were very low or undetectable while those of alpha s47 and beta were normal. DA was unable to inhibit basal PRL release and cAMP accumulation. VIP increased both cAMP accumulation and PRL release, while cAMP accumulation elicited by VIP could be suppressed by DA. BAY K 8644-induced PRL release also could be suppressed by DA.(ABSTRACT TRUNCATED AT 250 WORDS)

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

PubMed1992

Identification of G protein alpha subunit mutations in human growth hormone (GH)- and GH/prolactin-secreting pituitary tumors by single-strand conformation polymorphism (SSCP) analysis.

We have applied the polymerase chain reaction (PCR) and single-strand conformation polymorphism analysis (SSCP) to detect activating mutations in the Gs alpha subunit gene, amplifying genomic DNA extracted from growth hormone (GH)- and GH/prolactin (PRL)-secreting human pituitary tumors. Of 15 tumors tested six contained mutations in the analyzed regions of the Gs alpha. SSCP analysis revealed band shift in exon 8 in four GH- and in one GH/PRL-secreting tumors, and in exon 9 in one GH/PRL-secreting tumor. Direct sequencing of PCR reaction products identified the mutations as R201-H, R201-S and R201-C in exon 8 and Q227-L in exon 9. These results show the efficacy of PCR/SSCP analysis in the detection of G protein mutations and extend the generalization that these sites are hot spots in tumor-inducing mutations.

Adenoma↗

PubMed1991

G protein modulation by estrogens.

Levels of various G protein subunits were assayed by immunoblot and densitometry, using specific antibodies, in anterior pituitaries and striata of female rats exposed to physiological or pharmacological modifications of ovarian hormone levels and, for comparison, in the same tissues of coeval male rats. Treatment of ovariectomized rats with 17 beta-estradiol 10 micrograms/rat/day for 5, 10 or 20 days induced a time-dependent rise in plasma prolactin (PRL) levels. While no change in G protein levels was observed in the striatum, estrogen treatment induced a significant reduction of all pituitary G protein levels except those of alpha i1, which remained unchanged, and of alpha s42, which increased in a time-dependent manner. A highly significant correlation was observed between pituitary alpha s42 values and plasma PRL levels. During the estrous cycle, pituitary values of alpha o, alpha i3 and alpha s47 were generally lower than those of ovariectomized rats, suggesting the existence of tonic inhibitory influence of circulating ovarian hormones. Pituitary levels of alpha o, alpha i1 and alpha s42 also showed a significant modulation during the various phases of the estrous cycle, and those of alpha o, alpha i3, alpha s47 and beta were significantly lower in female than in male rats. No significant effects of estrous cycle hormone variations or sex differences were observed in the values of striatum G proteins. In conclusion, these data clearly indicate that ovarian hormones, and particularly estrogens, have a significant and specific effect on pituitary G protein levels which may modulate the secretion of pituitary hormones such as PRL.

Animals↗

PubMed1991

G proteins in normal rat pituitaries and in prolactin-secreting rat pituitary tumors.

It is still undetermined which GTP-binding (G) protein is involved in the regulation of prolactin (PRL) release and through which effector. This study shows that, when compared to normal pituitary tissue, the levels of alpha o protein were very low in dopamine (DA)-resistant, PRL-secreting pituitary tumors 7315a and MtTW15, while alpha o mRNA was present in the two tumors. In the MtTW15 tumor alpha i1, alpha i2 and alpha i3 levels were decreased while those of alpha s42 and alpha s47 were increased, and in the 7315a tumor alpha i2, alpha i3 and beta levels were decreased and those of alpha s47 increased. In an estrone-induced, DA-sensitive prolactinoma the levels of alpha i3 were greatly reduced. DA was unable to inhibit basal PRL release by 7315a and MtTW15 and basal cAMP accumulation by adenomatous and MtTW15 cells. Vasoactive intestinal peptide (VIP) increased both cAMP accumulation and PRL release by all cell preparations which could be suppressed by DA with adenomatous and 7315a but not with MtTW15 cells. These and previously published results provide circumstantial evidence that alpha o, alpha i1 and alpha i3 are all involved in the transduction of the DA inhibitory message while alpha s47 transduces cAMP activating messages and alpha s42 is responsible for the constitutive activation of L-type Ca2+ channels, adenylate cyclase and baseline PRL release.

Adenoma↗

PubMed1990

Structural differences between dopamine D2 receptors present in a rat pituitary adenoma and in transplantable rat pituitary tumors 7315a and MtTW15.

We have investigated the structure of dopamine (DA) D2 receptors present in an estrone-induced, prolactin (PRL)-secreting, DA-sensitive adenoma and in two PRL-secreting and DA-insensitive transplantable tumors 7315a and MtTW15, in order to identify better the anomalies present in DA-resistant lactotrophs. D2 receptors were found in both a high- and a low-affinity state in adenomatous lactotrophs as shown by displacement studies with the agonist N-propylnorapomorphine (NPA), but only in the low-affinity state in the two DA-resistant tumors. Treatment with the alkylating agent N-ethylmaleimide induced a disappearance of the high-affinity state of the D2 receptor in the adenoma and a reduction in receptor concentration, but did not have any effect on the affinity of receptors present in DA-resistant tumors. Moreover, target size analysis and radiation inactivation studies of D2 receptors, using membranes preincubated with NPA and [3H]spiperone as ligand or using [3H]NPA as ligand on membranes preparations, have shown the presence of distinct structural differences between adenomatous and tumoral D2 receptors and between the two tumoral receptors themselves; these results suggest that the normal functional unit of the D2 receptor is a dimer associated with a guanine nucleotide-binding protein (G protein) subunit and that tumoral D2 receptors may exist in various polymeric forms unassociated with G proteins. The anomalies found to be present in tumoral D2 receptor complexes may be responsible for the insensitivity of these tumors to dopaminergic agonists' inhibitory activity on PRL release and tumor growth.

Adenoma↗

PubMed1989

Reduced pituitary volume in children with short stature: clinical and radiological correlates.

A retrospective evaluation of 80 cases of growth retardation evaluated at the Hôpital Sainte-Justine of Montreal has revealed that 20 of them (25%; 15 boys and 5 girls) had a reduction of pituitary volume as revealed by high-resolution CT scanning of the pituitary gland. Of these patients, 8 had complete growth hormone (GH) deficiency, as evaluated by arginine infusion and L-Dopa-propranolol testing and nocturnal blood sampling, and 3 had GH neurosecretory dysfunction. Five patients had combined or multiple hormonal deficiencies. A statistically significant correlation was found between nocturnal plasma GH values and pituitary volumes. From this study it can be concluded that reduced pituitary volume is a frequent finding in growth-retarded children with hypopituitarism.

Adolescent↗

PubMed1988

Cyclooxygenase products formed by primary cultures of cells from human chorion laeve: influence of steroids.

Cells were isolated from human chorion laeve obtained at term (38-40 weeks gestation) by elective caesarean section and were maintained in primary culture for 1 week in defined media supplemented with 10% fetal calf serum. The production of various cyclooxygenase products by the cultures was examined. Little or no prostaglandin (PG) F2 alpha, 6-keto-PGF1 alpha, thromboxane B2, or 13,14-dihydro-15-keto-PGF2 alpha was found. In contrast, the cells produced PGE2 which was low on day 0, increased during culture to a maximum on day 1 or 2, then declined to low levels. When cells were grown in the presence of media containing cortisol, dexamethasone, progesterone, and estradiol (at 10(-7) or 10(-9) M), the glucocorticoids (at 10(-7) and 10(-9) M), but not estrogen or progesterone, markedly inhibited the increase in PGE2 output. There was no difference in the protein content and thymidine incorporation of cells grown in the presence of glucocorticoids when compared with controls. This inhibitory effect was not sensitive to cycloheximide (1 microgram/mL) indicating protein synthesis may not be involved in the process. These studies indicate that PGE2 is the major prostaglandin formed by primary cultures of chorion laeve and that prostaglandin metabolism in the chorion is sensitive to glucocorticoid inhibition.

Cells, Cultured↗

PubMed1988

Selective deficiency of guanine nucleotide-binding protein Go in two dopamine-resistant pituitary tumors.

G proteins were quantitated by immunoblot in normal rat anterior pituitary, an estrone-induced pituitary adenoma, and in two transplantable pituitary tumors resistant to dopamine, 7315a and MtTW15. Antisera specific for the alpha o and beta subunits or the alpha i subunit of G proteins were tested with all preparations. While the alpha i and beta subunits were found to be present in variable concentrations in all preparations, the alpha o subunit was very low or undetectable in the transplantable tumors. These findings suggest that tumor resistance to the dopamine inhibitory actions on prolactin release and on tumor growth may be due to the deficiency of a Go protein.

Adenoma↗

PubMed1987

Effects of sulpiride and apomorphine on prolactin release in adrenalectomized animals. Role of sodium ions.

The present experiments were performed to demonstrate in vivo the existence of a modulatory role of Na+ in the inhibitory control of prolactin (PRL) secretion. Groups of adult male rats were either adrenalectomized (adrenex) or sham-operated (normals) and implanted in the right atrium with a chronic cannula for the infusion of solutions or the sequential withdrawal of blood samples. Four days later, adrenex rats were infused for 1 h with either saline 0.9% or dextrose 5.6% (310 mOsm/kg H2O) at the rate of 10 ml/kg/h from Time -60 min until Time 0 min. All animals were injected at Time -45 min with sulpiride 0.05 mg/kg. At Time 0 min, some animals received apomorphine 5 mg/kg while others received a 0.05 mg/kg dose of the drug. Blood samples were obtained at -45, -30, -15, 0, 5, 10, 20 and 30 min for PRL assay. Plasma Na+ concentration was measured at -45, 0 and 30 min and plasma osmolarity at 0 min in adrenex rats. In normal controls plasma Na+ values were measured at the end of the experiment. Binding values (KD and Bmax) of pituitary D2-receptors were measured in adrenex and sham-operated rats using [3H]spiroperidol as ligand and D-butaclamol to define non-specific binding. Plasma Na+ values remained constant in saline-infused adrenex rats and similar to those of normal controls, while in dextrose-infused adrenex rats they fell progressively during the experimental period and were always lower than in the two other groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenalectomy↗

PubMed1987

Characterization of D2 dopamine receptors in dopamine-resistant prolactin-secreting rat pituitary tumors 7315a and MtTW15.

We have investigated the structure of D2 receptors present in two prolactin-secreting, dopamine-resistant, transplantable rat pituitary tumors, 7315a and MtTW15. These receptors specifically bind with high affinity the dopamine antagonist [3H]spiroperidol when membrane bound or solubilized by [3-(3-cholamidopropyl)-dimethyl-ammonio]-1-propane sulfonate 10 mM and are pharmacologically characterized as D2 type. Target-size analysis by radiation inactivation indicated a molecular mass of approximately 100,000 and 200,000 daltons for receptors present respectively in 7315a and MtTW15 tumors either membrane bound or solubilized. The minimal size of the D2 binding site was evaluated at 94,000 daltons by photoaffinity labeling with [125I]azido-N-(p-aminophenethyl)-spiperone followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. A guanine nucleotide had no effect on the displacing potency of the agonist N-propylnorapomorphine evaluated with membrane-bound or solubilized receptors obtained from either tumor. These results suggest the absence or inactivation of a guanine nucleotide binding protein in the receptorial complex of these tumors. Thus, our data indicate that a structural anomaly is present in the D2 receptorial complex of these prolactin-secreting rat pituitary tumors, which may be responsible for their resistance to the inhibitory effects of dopamine.

Affinity Labels↗

PubMed1987

Effect of catecholamines on porcine Sertoli and Leydig cells in primary culture.

The accumulation by purified immature porcine Leydig and Sertoli cells of cyclic adenosine 3',5'-monophosphate in the presence of 1-methyl-3-isobuthylxathine was studied and their respective testosterone and 17 beta-estradiol production in response to catecholamines was assessed in vitro. These substances increased both basal and FSH-stimulated cyclic adenosine 3',5'-monophosphate accumulation in Sertoli cells. In contrast, catecholamines slightly enhanced basal cyclic adenosine 3',5'-monophosphate production but inhibited its human chorionic gonadotropin-stimulated accumulation by Leydig cells. Catecholamines had no effect on basal and stimulated testosterone release by these cells, while dopamine inhibited 17 beta-estradiol synthesis by Sertoli cells. Using various alpha- and beta-adrenergic agonists and antagonists, beta-receptors, likely of the beta 1-subtype, were shown to be present in both cell lines. Taken together these data suggest the presence of a cyclic adenosine 3',5'-monophosphate-linked adrenergic receptor in porcine Leydig and Sertoli cells, the role of which remains to be determined.

1-Methyl-3-isobutylxanthine↗

PubMed1986

Persistent effects of a marathon run on the pituitary-testicular axis.

Plasma levels of testosterone (T), LH, FSH, prolactin (PRL), cortisol (F), dehydroepiandrosterone sulfate (DHAS), noradrenaline (NA), NA sulfate (NAS), adrenaline (A) and A sulfate (AS) were measured in 7 adult males before and immediately after a marathon run as well as every morning for 5 days after the run. While plasma T levels fell significantly on the first and the second postmarathon day, those of LH rose significantly during the first 3 postrun days. Plasma PRL and F values increased significantly only at the end of the marathon. Plasma levels of NA and NAS rose significantly at the end of the run and again on days 2 and 5 postmarathon, respectively. A similar pattern was observed for A and AS except for the second peak of free A. These results show that a strenuous physical exercise leads to a persistent relative insensitivity to LH of the testicular T biosynthetic machinery, while the feedback mechanisms operating at the hypothalamic-pituitary level are normal. Furthermore, they suggest that catecholamines may be responsible for the prolonged inhibitory effect of stress on T biosynthesis.

Adult↗

PubMed1986

Effects of repeated stimuli on prolactin release in vitro from normal and adenomatous rat lactotrophs.

It is now well known that dopamine (DA) plays a major role in the inhibitory control of prolactin (PRL); however, the mechanisms that are physiologically involved in the stimulation of PRL release are still under investigation. Indeed, although suppression of DA inhibitory tonus, administration of thyrotropin-releasing hormone (TRH) or vasoactive intestinal peptide (VIP) are all known PRL releasers, it is not clear whether they interact during physiological periods of PRL release such as suckling and estrus. No clear indications exist, furthermore, on whether they all act upon a same pituitary pool that may become depleted following repeated exposure to stimuli. Refractoriness to a single or a repeated stimulus has been reported to occur in prolactinoma-bearing or normal humans, respectively, the mechanism of which is still matter for discussion. Our present studies performed by perifusing normal or adenomatous rat lactotrophs attached to Cytodex I microcarrier beads was undertaken to try and answer some of these questions. The experimental period consisted in perifusing the cells for 1 h with Dulbecco's modified Eagle's medium (DMEM) containing DA 10(-5) M, then for 2 h with either DMEM, DMEM and TRH 10(-8) M, DMEM and VIP 10(-7) M, then again with DA in DMEM for 1 h, and finally with DMEM, DMEM and TRH, or DMEM and VIP. Three experiments of various combinations were performed. Lower PRL levels were observed under DA, while two periods (first and second) of PRL release followed the suppression of DA infusion with or without the addition of either one of the two peptides.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenoma↗

PubMed1986

Inhibition of prolactin release and blockade of adenohypophyseal cell cyclic AMP accumulation are two dissociable effects of dopaminergic and non-dopaminergic drugs.

The secretion of PRL by the anterior pituitary gland is under a tonic inhibitory control exerted by dopamine (DA). However, the mechanism(s) involved in the inhibition of PRL secretion is not clearly defined. Several recently published papers supported the hypothesis that DA inhibits the release of PRL through blockade of the pituitary adenylate cyclase-cyclic AMP system. We have recently demonstrated that sodium ions are essential for dopaminergic inhibitory action on PRL secretion. The present paper reports the effects, in the presence or in the absence of Na+, of either DA, bromocriptine, apomorphine or 2 anticalmodulin drugs, penfluridol and W-7, on cyclic AMP accumulation by rat adenohypophyseal cells in primary culture. Studies with dopaminergic agonists show that in the presence of Na+ inhibition of both PRL and cyclic AMP is obtained at 15 and 30 min, while in the absence of the ion a dissociation exists between the inhibition of PRL release which is completely abolished, and that of cyclic AMP content which is still present. Dose-response studies done in the presence of Na+ show the existence of a good correlation between hormone and nucleotide effects of dopaminergic agonists while, in the absence of Na+, a dissociation is observed between the inhibition of PRL release, which is completely suppressed, and that of cyclic AMP accumulation which is slightly or not at all decreased. The inhibitory effects of penfluridol after 15 and 30 min of incubation were not suppressed by Na+ removal, although its hormonal actions were slightly decreased.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗