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C Dieguez

Publications and source records attributed to C Dieguez.

212 records · Page 12Linked to original sources
PubMed1984

Rat anterior pituitary cells maintained on artificial capillaries: responses of thyrotrophs and lactotrophs to depolarization, TRH and dopamine.

Rat anterior pituitary cells have been maintained over an 18-day period in a perfusion system designed around artificial capillaries. Using novel methodology the cells have been visualized by light microscopy and appear as aggregates, closely attached to and sometimes stretching around the capillaries. Their morphology is consistent with previous histology at the level of light microscopy. The techniques described are compatible with immunohistochemistry and electron microscopy. The functional integrity of thyrotrophs and lactotrophs maintained in the system has been examined by measuring the dynamics of TSH and PRL secretion in response to depolarization, TRH and dopamine (DA). TSH and PRL were significantly and reproducibly released by TRH over a 7-day period. On each day the release was dose-dependent with a threshold of at least 28 pg. Qualitatively the responses were rapid in onset (within minutes) for both hormones. Similar responses were measured in response to high K+ depolarization. Basal secretion of TSH and PRL was rapidly and significantly inhibited by DA in a dose-dependent manner (ED50 20 +/- 25 nM for TSH and 70 +/- 40 nM for PRL). Inhibition was dependent on the continued presence of DA and could be mimicked by bromocriptine and stereospecifically prevented by the active but not the inactive isomer of the DA receptor antagonist butaclamol. Simultaneous administration of 10(-6) M DA with 10(-8) M TRH prevented the release of TSH and PRL. The effect of DA was transient, subsequent TRH responses being qualitatively and quantitatively normal.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Interactions among epinephrine, thyrotropin (TSH)-releasing hormone, dopamine, and somatostatin in the control of TSH secretion in vitro.

Epinephrine and TRH independently release TSH from rat anterior pituitary cells in primary monolayer culture (ED50, 11 and 5 nM, respectively; maximum responses, 80% and 110%, respectively). The effects of these compounds together are additive, even at concentrations at which each is maximally effective alone. Dopamine inhibited basal and epinephrine-stimulated TSH secretion by 25 +/- 5% (+/-SE; ED50, 50 +/- 9 nM in each case). Somatostatin was effective against epinephrine-stimulated, but not basal, TSH secretion (80 +/- 4% inhibition; ED50, 1 +/- 3 nM). The data show that epinephrine is a potential regulator of TSH secretion by its own action and via its interactions with TRH, dopamine, and somatostatin.

Animals↗
PubMed1984

Hypothyroid pituitary cells in culture: an analysis of thyrotropin and prolactin responses to dopamine (DA) and DA receptor binding.

Monolayer cultures were prepared from the anterior pituitary (AP) lobes of normal male rats and male rats made hypothyroid by treatment with aminotriazole. After 3 days in culture, the cells from hypothyroid animals showed significantly greater TSH and PRL secretory activity and significantly less GH secretory activity than did parallel euthyroid cultures. The responses of euthyroid and hypothyroid cultures to dopaminergic agonists and antagonists were examined. Bromocriptine, apomorphine, and dopamine (DA) inhibited euthyroid TSH secretion by approximately 30%, whereas each drug inhibited hypothyroid TSH secretion by approximately 60% (P less than 0.01 for each drug). In contrast, the three agonists were less effective in inhibiting PRL secretion from hypothyroid cells (P less than 0.05 for each drug). The rank order of potency [bromocriptine greater than (+)butaclamol greater than apomorphine greater than DA greater than (-)butaclamol] shown against secretion was the same for TSH and PRL in both euthyroid and hypothyroid cell cultures and is typical of a DA receptor-mediated process. The binding of [3H]dihydroergocryptine (DHE) to DA receptors on euthyroid and hypothyroid cells was examined under the same conditions in which the secretory responses were determined. One micromolar concentration of (+)butaclamol was used to define nonspecific binding. Specific binding was saturable and stereospecific in each case. The rank order of potency of dopaminergic agonists and antagonists in competing for [3H] DHE binding was the same as that demonstrated against the secretion of TSH and PRL. Each compound displaced significantly more [3H]DHE from hypothyroid cells than from euthyroid cells (P less than 0.05 for each drug). Construction of adsorption isotherms for [3H]DHE binding to DA receptors on euthyroid and hypothyroid cells and subsequent Scatchard analysis revealed a 3- to 4-fold increase in receptor number without a significant change in affinity. Immunohistochemistry on AP lobes before and after dispersion revealed an increase in thyrotrophs and thyroidectomy cells in hypothyroid rats relative to those in control animals. In euthyroid animals thyrotrophs were 10.1% of the total AP cell population, in hypothyroid animals they plus the thyroidectomy cells were 36.3% of the total AP cells. Therefore, the increased number of DA receptors per lobe could be accounted for by increased numbers of thyrotrophs. The mechanism of the altered sensitivity to DA induced by hypothyroidism in lactotrophs and thyrotrophs remains to be clarified.

Animals↗
PubMed1984

Release of an active sodium transport inhibitor (ASTI) from rat hypothalamic cells in culture.

To investigate the hypothesis whether the hypothalamus releases an active (ouabain-sensitive) sodium transport inhibitor, we cultured hypothalamic and cortical cells from day 17 fetal rats. Culture media from hypothalamic cells reduced the total erythrocyte sodium efflux rate constant from 0.487 +/- (SE) 0.014 to 0.408 +/- 0.013 (P less than 0.001), and the ouabain-sensitive rate constant from 0.305 +/- 0.015 to 0.240 +/- 0.016 (P less than 0.01). Hypothalamic media also showed a dose-dependent displacement of [3H]-ouabain-binding to erythrocyte membranes. Neither cortical nor conditioned media (incubated without cells) had any effect. Various well-characterized hormones of hypothalamic origin failed to inhibit sodium efflux rate constant. These studies demonstrate that fetal rat hypothalamic cells contain and release a factor which inhibits sodium transport in human erythrocytes.

Animals↗
PubMed1983

The influence of methimazole on thyroglobulin-induced autoimmune thyroiditis in the rat.

Experimental autoimmune thyroid disease was induced in August rats by immunization with rat thyroglobulin in complete Freund's adjuvant. Disease severity, assessed by thyroid histology and circulating levels of anti-TG antibody measured by an enzyme immunoassay, was maximal between 30 and 60 days after the initial immunization and thereafter waned. Thyroid function through the duration of the disease, assessed by measurement of serum TSH levels by RIA, remained normal. Once the natural history of the disease was established, groups of rats received methimazole (MMI) with or without T4 in their drinking water, either before or after disease induction. The animals were bled at regular intervals and killed on day 49 for histological grading of their thyroids. MMI alone (group 3) or with T4 (group 4) before disease induction significantly reduced the severity of the disease, although the effect on circulating antibody levels was less marked in the animals in group 4. In animals given MMI alone (group 5) or with T4 (group 6) after establishment of the disease, MMI again significantly reduced the severity of the established disease, although this effect was less marked in the T4 supplemented animals. MMI significantly impaired the induction and reduced the severity of experimental autoimmune thyroid disease in August rats. The ability of MMI to influence the autoimmune process may have important implications for the use of this and other agents that act on the immune system in the management of human autoimmune disease.

Animals↗
PubMed1983

Dopamine receptors on intact anterior pituitary cells in culture: functional association with the inhibition of prolactin and thyrotropin.

Dopamine (DA) and the dopaminergic agonists bromocriptine and apomorphine inhibit the secretion of TSH as well as that of PRL by rat anterior pituitary (AP) cells in monolayer culture. The order of potency of the drugs is the same for the inhibition of both hormones: bromocriptine ED50 = 0.006 nM against PRL and 0.017 nM against TSH; apomorphine ED50 = 2.9 and 4.8 nM, respectively, and DA, ED50 = 30 and 370 nM, respectively. The dopaminergic antagonists domperidone (DOM) and metoclopramide prevent the inhibition of TSH and PRL by 10(-6) M DA (IC50 = 0.012 and 0.32 nM for metoclopramide against PRL and TSH, respectively; similarly, IC50 = 0.01 and 0.61 nM for DOM). The action of butaclamol is shown to be stereospecific, in that the (+) isomer is 1000-fold more potent in reversing the inhibition of both TSH and PRL by 10(-6) M DA than the (-) isomer [IC50 = 1.1 and 7200 nM for the (+) and (-) isomers against PRL; similarly, 6.3 and 2600 nM against TSH]. The use of radioligand-binding techniques with tritiated DOM ([3H]DOM) and dihydroergocriptine ([3H]DHE) has demonstrated a high affinity dopaminergic binding site upon rat AP cells under the same conditions as the cell cultures used in the hormone secretion studies. Both ligands have been shown to label a site with high affinity (Kd = 1-2 nM) and low capacity (2-3 fmol/10(5) cells). At this site, dopaminergic agonists and antagonists compete with both radioligands and display a rank order of potency which is the same as that shown against TSH and PRL secretion and which is typically dopaminergic. For [3H]DHE: bromocriptine Ki (0.04 nM) greater than metoclopramide = DOM (0.07 nM) greater than (+)butaclamol (0.7 nM) greater than apomorphine (20 nM) greater than DA (700 nM) greater than (-)butaclamol (2000 nM). Similar data were derived using [3H]DOM. The high affinity site is saturable, has rapid association and dissociation rates, as determined for both radioligands used, and is temperature dependent. In contrast, both radioligands bind to a second binding site on the cells that is of lower affinity (Kd = 244 nM for [3H]DOM and 678 nM for [3H]DHE) and larger capacity (100 fmol/10(5) cells for both ligands). This second site is neither stereospecific nor, using the methodology presented here, does it discriminate between other dopaminergic compounds. It is thus not considered to represent specific DA receptor binding. It is concluded that the dopaminergic stimulus causing the inhibition of TSH and PRL secretion from rat AP cells in culture is mediated via a high affinity DA receptor present upon lactotrophs and thyrotrophs and that this receptor has similar characteristics on the two cell types.

Animals↗
PubMed1983

Alpha 1-adrenoreceptors on intact rat anterior pituitary cells: correlation with adrenergic stimulation of thyrotropin secretion.

An in vitro study of the alpha-adrenergic control of TSH secretion was carried out on rat anterior pituitary cells in monolayer culture. The ability of adrenergic agonists and antagonists to alter TSH release from the cells was determined. With the use of parallel cell cultures under the same conditions, alpha-adrenergic binding sites were measured and characterized with [3H]dihydroergocryptine (DHE) as the radioligand. Epinephrine (E) and norepinephrine (NE) released TSH over a 2-h period in a dose-dependent and stereospecific manner (ED50 = 1 and 700 nM for the (-) and (+/-) stereoisomers of E; 7 and 600 nM for the active and inactive stereoisomers of NE respectively). Maximum release was 3- to 4-fold greater than basal secretion for both isomers of E but less (2- to 3-fold) for the isomers of NE. Phenylephrine, an alpha 1-agonist, elicited a 2- to 3-fold increase in TSH secretion (ED50 = 13 nM). Clonidine, an alpha 2-agonist, produced only slight stimulation at concentrations greater than 10(-6) M, and isoproterenol was ineffective. Prazosin, an alpha 2-antagonist (IC50 = 0.12 nM), was 500-fold more effective than yohimbine, an alpha 2-antagonist (IC50 = 60 nM), in reversing the TSH stimulation induced by 10(-7) M E. With [3H]DHE and prazosin as competing ligands, alpha-adrenergic receptors could be quantified independently of dopamine receptors present upon the same mixed cell preparations. The kinetics of specific radioligand binding to the cells were rapid (k1 = 1.75 X 10(-7) M-1 min-1, k2 = 0.131 min-1), equilibrium being reached within 15 min at 22 C. Adsorption isotherms and Scatchard analysis revealed a single population of binding sites with high affinity (kd = 7.2 nM) and low capacity (3 fmol/10(5) cells). Competition by adrenergic agonists for [3H]DHE binding was stereospecific. The rank order of potency against binding was identical with that determined functionally against TSH secretion (Ki for prazosin, 0.7 nM greater than thymoxamine, 2.7 nM greater than (-) E, 7 nM greater than phentolamine, 8 nM greater than (-) NE, 11.5 nM greater than phenylephrine, 100 nM greater than yohimbine, 300 nM greater than clonidine, 4500 nM greater than (+/-) E, 5000 nM greater than (+/-) NE, 7000 nM greater than isoproterenol, 3 X 10(5) nM), and typical of binding to an alpha 1-adrenoreceptor. It is concluded that TSH can be specifically released from rat anterior pituitary cells in monolayer culture by the direct effects of adrenergic agonists and that the stimulation is mediated via a single high affinity population of alpha 1-adrenergic receptors.

Animals↗
PubMed1983

Exaggerated circadian variation in basal thyrotropin (TSH) and in the dopaminergic inhibition of TSH release in pathological hyperprolactinemia: evidence against a hypothalamic dopaminergic defect.

In order to delineate more accurately the dopaminergic control of anterior pituitary function in normal subjects and in patients with pathological hyperprolactinemia, we investigated the nature of the circadian variation in the dopaminergic inhibition of TSH release in such subjects. Ten euthyroid women with hyperprolactinemia due to presumed PRL-secreting microadenomas (aged 18-60 yr) were compared with 11 normal, euthyroid women (aged 18-32 yr). Each received the dopamine receptor blocking drug domperidone (10 mg, iv) at 1100 and 2300 h (tests randomized and separated by at least 1 week). Blood was sampled 10, 20, 30, 45, and 60 min after drug administration. Normal women had a greater TSH response to domperidone and, hence, greater dopaminergic inhibition of TSH release at 2300 than at 1100 h (sum of TSH increments; mU/liter mean +/- SE, 8.5 +/- 1.3 vs. 4.8 +/- 0.5, P less than 0.01), whereas there was no difference in the dopaminergic inhibition of PRL release at each time of day. Hyperprolactinemic women also had a significantly greater TSH response to domperidone at 2300 than at 1100 h (42.0 +/- 10.2 vs. 19.1 +/- 2.8, P less than 0.001). The hyperprolactinemic women had a greater TSH response to domperidone than normal women at each time of day studied (1100 h, 19.1 +/- 2.8 vs. 4.8 +/- 0.5, P less than 0.001; 2300 h, 42.0 +/- 10.2 vs. 8.5 +/- 1.3, P less than 0.001). The incremental PRL responses to domperidone were significantly less in hyperprolactinemic than in normal women and did not differ at each time of day. In conclusion, the circadian change in the dopaminergic inhibition of TSH secretion is specific for TSH and not PRL. This indicates that the dopaminergic control of TSH and PRL secretion can be dissociated in normal subjects. Second, hyperprolactinemic women with presumed PRL-secreting microadenomas had qualitatively normal but quantitatively exaggerated circadian pattern of dopaminergic inhibition of TSH release. These data argue against a hypothalamic dopaminergic defect in hyperprolactinemia and support the view that the established dopaminergic defect in the inhibition of PRL release is related specifically to PRL control and may well be at the anterior pituitary level.

Adenoma↗
PubMedDate not supplied

The influence of cyclosporin a on experimental autoimmune thyroid disease in the rat.

Female PVG/c rats, thymectomized on weaning and given 4 courses of whole body irradiation to a total dose of 1000 rads, developed experimental autoimmune thyroid disease (EAITD) as assessed by histological evidence of thyroiditis and circulating levels of antithyroglobulin antibodies. Hypothyroidism resulted. Induction of the disease was associated with a highly significant fall in T lymphocyte numbers. Eight weeks after their last dose of irradiation the animals commenced treatment with Cyclosporin A (10 mg/kg rat/day, intragastrically) and were treated for varying time intervals thereafter. The reversal of the T lymphocyte helper: suppressor ratio on Cyclosporin A therapy was associated with a significant improvement in the disease process. The alterations in the T cell subsets and in the disease lasted only as long as the drug was administered and thereafter reverted towards that seen in the control groups of animals receiving no treatment.

Animals↗
PubMedDate not supplied

Influence of cortisol status on leptin secretion.

The discovery of the adipocyte-produced hormone leptin has changed the field of obesity research and our understanding of energy homeostasis. It is now accepted that leptin is the afferent loop informing the hypothalamus about the states of fat stores, with hypothalamic efferents regulating appetite and energy expenditure. I addition, leptin has a role as a metabolic adaptator in overweight and fasting states. New and previously unsuspected neuroendocrine roles have emerged for leptin. Leptin participates in the expression of CRH in the hypothalamus, interacts at the adrenal level with ACTH, and is regulated by glucocorticoids. Since leptin and cortisol show an inverse circadian rhythm, it has suggested that a regulatory feedback is present. However glucocorticoids appears to play a modulatory, but not essential roles in generating leptin diurnal rhythm. Glucocortiocids act directly on the adipose tissue and increase leptin synthesis and secretion in humans. Leptin levels are markedly increased in Cushing's syndrome patients and in other pseudo-Cushing's syndrome states. Glucocorticoids appears to act as a key modulator of body weight and food intake, promoting leptin secretion by adipocytes, limiting central leptin induced effects and favoring those of the NPY. Furthermore the modulatory role of glucocorticoids could be altered in obesity, but the precise mode of action remains to be established. The relevance of this finding merits further studies.

Animals↗
PubMedDate not supplied

Leptin and the pituitary.

Although leptin was originally viewed as an antiobesity hormone, it is now evident that it may have more pleiotropic actions. Experiments in rodents have shown that leptin activates the sympathetic nervous system, is involved in regulation of blood pressure, hematopoiesis, immune function, angiogenesis and brain, bone and pituitary development. Some biological effects expected based on observations in rodents, have so far not been seen in humans. Thus due to species differences in the role of leptin it is difficult to translate the data from rodents to human physiology. Hypothalamus is the primary brain site targeted by circulating leptin, secreted by fat cells. Leptin receptor has homology to members of class I cytokine receptor family, which may imply similarities in molecular events engaged by cytokines and leptin. In view of its cytokine-like properties it is likely that leptin produced and secreted outside of fat tissue i.e. in other tissues (CNS, pituitary, ovary, placenta, etc), is a paracrine regulator. Leptin receptor isoforms, long-signaling and short-nonsignaling, have been recently localized in human pituitaries. This opens the possibility of a direct action of leptin on the pituitary. However this appears to be quite complex and is species dependent. Leptin can be synthesized by normal and tumorous pituitary cells. Leptin protein expression in pituitary adenomas is decreased compared to that in normal pituitaries. Colocalization studies with leptin and anterior pituitary cells showed that 70% of ACTH cells are positive for leptin, 21% of GH cells, 29% of LH cells, 33% of FSH cells, 32% of TSH cells, 64% folliculo-stellate cells whereas very few PRL cells were positive (3%). Leptin is stored in secretory granules and secretory cells retain leptin in granules until stimulated. This follows a different secretory pathway than in adipocytes where upon synthesis leptin is immediately released. Question to be raised is does the pituitary contribute to the body leptin pool or is its action predominantly paracrine/autocrine? Clinically based evidence from studies performed in patients harboring different functional pituitary tumors causing a state of hormonal hypersecretion (acromegaly, prolactinomas, Cushing's disease) or hypopituitarism (due to non-functioning pituitary adenomas), are in favor of a paracrine/autocrine role of the pituitary leptin. Most of the studies have shown that the link between leptin, body composition and hormones of the pituitary is indirect. Thus changes in levels of circulating leptin are most likely due to changes in the metabolic and hormonal milieu during the chronic course of the disease or chronic treatment. Furthermore, circadian rhythm of leptin, its pulsatility and gender difference are preserved in hypopituitarism as well as in patients with functional pituitary adenomas implying that intact hypothalamic-pituitary function is not essential for leptin's circadian rhythm.

Acromegaly↗
PubMedDate not supplied

New diagnostic tests of GH reserve.

Pharmacological tests are essential for the diagnosis of growth hormone (GH) insufficiency. Obesity is a pathological state associated with blunted GH response to all the classical stimuli tested. In the present study, three new pharmacological stimuli for GH reserve were evaluated in three groups of subjects: Normal, GH-insufficient and normal growing obese children. Dexamethasone provokes a clear GH-response in normal children, whereas the response in the other 2 groups of patients is significantly diminished. Galanin-induced GH-secretion is significantly higher in normal than in obese children. GHRP-6 causes a potent GH release in normal children, higher than in GH-insufficiency or obesity. The overlap shown between GH-insufficient patients and normal children reduces the usefulness of the tests. Similar to the classical stimuli, the response to these new tests is also decreased in obesity.

Dexamethasone↗
PubMedDate not supplied

Pituitary enlargement due to primary hypothyroidism: growth hormone response to GHRH, GHRP-6 and GHRH plus GHRP-6.

GH secretion after growth hormone-releasing hormone (GHRH), growth hormone releasing peptide-6 (GHRP-6) and after combined administration of both peptides was studied in a patient with lactotrope and thyrotrope hyperplasia due to primary hypothyroidism. Pituitary pseudotumor disappeared after thyroid hormone replacement; this was evidenced by magnetic resonance imaging (NMR). There was no difference between areas under the curve (AUCzero-120 min) during GHRH test before and after thyroid hormone replacement (136.5 vs 129.0 micrograms/l min). Maximal GH increases over basal values (delta GH) did not change (1.5 and 1.9 micrograms/l). GH secretion induced by GHRP-6 increased after treatment (AUCzero-120 min 197.2 vs 650.4 micrograms/l min). delta GH increments were 4.0 and 18.3 micrograms/l before and after therapy respectively. When the peptides were administered together a synergistic effect on GH secretion was observed but GH release was much more powerful after pituitary pseudotumor disappearance (AUCzero-120 min 1043.2 vs 2046.7 micrograms/l min). This was accompanied by increased delta GH (22.7 vs 35.5 micrograms/l). The synergic action of peptides normalized in euthyroid condition and after the resolution of pituitary pseudotumor mainly due to improved GH response to GHRP-6. Blunted response of GH to GHRP-6 and GHRP-6 plus GHRH were in part due to known effects of hypothyroidism on GH secretion. Hypothalamopituitary disconnection and/or decrease in the synthesis of an unknown factor in the hypothalamus which mediates the effects of GHRP-6 may have participated in the GH responsiveness of this patient. This case adds to in vivo evidence that GHRP-6 operates through a non-GHRH dependent mechanism.

Adolescent↗