Biomedical subjects

S L Lightman

Publications and source records attributed to S L Lightman.

At least 163 records · Page 9Linked to original sources

PubMed1994

p53 gene mutations in pituitary adenomas: rare events.

OBJECTIVE: Occult pituitary adenomas are said to occur in up to 20% of random autopsy examinations, yet the only oncogene known to be associated with pituitary adenomas, gsp, is found in only 40% of somatotrophinomas, a subtype that accounts for a minority of pituitary tumours. Mutations of the p53 tumour suppressor gene are thought to be involved in the pathogenesis of as many as 50% of all human cancers, including tumours of the central nervous system. The objective of this study was to determine whether p53 gene mutations are associated with pituitary adenomas. DESIGN AND PATIENTS: Fragments of pituitary adenoma tissue from 29 patients undergoing routine hypophysectomy for pituitary tumour were coated in cryostat embedding medium and frozen at -80 degrees C within 24 hours of resection. They consisted of 9 somatotroph, 4 corticotroph, 1 mammotroph and 15 endocrinologically inactive adenomas, all of the non-invasive clinical phenotype. Sequential frozen sections were subjected to in situ hybridization analysis for anterior pituitary hormone transcripts and examined histologically to ensure that the frozen sections used to generate DNA templates for polymerase chain reaction amplification were not contaminated with non-tumour tissue. MEASUREMENTS: p53 exons 7 and 8, within which 98% of substitution mutations are thought to occur, and exons 4-6 in tumours immunopositive for p53, were amplified by polymerase chain reaction and ligated into the vector pCR2. DNA from small-scale plasmid preparations of pCR2 containing cloned p53 exons from human pituitary adenomas was sequenced using an automated fluorescence-based system (DuPont Genesis 2000) and compared with wild-type sequence. Apparent mutations were confirmed or refuted by sequencing a further 2-4 clones isolated from the same template. RESULTS: Although immunocytochemical staining patterns for wild-type p53 varied markedly between different tumours, no mutations were identified in any of the exonic sequences examined. CONCLUSIONS: p53 mutations, at least within the high mutation domains of p53, occur infrequently in human pituitary adenomas. Increased steady-state levels of p53 protein identified immunocytochemically may be a consequence of binding to other cellular proteins in these tumours.

Adenoma↗

PubMed1994

Chronic administration of glucocorticoids directly upregulates prepro-neuropeptide Y and Y1-receptor mRNA levels in the arcuate nucleus of the rat.

The complete sequence of the cDNA encoding the neuropeptide Y (NPY) Y1-receptor has recently been deduced from a rat brain library, and the presence of messenger ribonucleic acid (mRNA) encoding Y1-receptor protein has been demonstrated within the brain. Using quantitative in situ hybridization histochemistry, the content and distribution of Y1-receptor and preproNPY mRNAs have been investigated in the hypothalamic arcuate nucleus of adrenalectomized rats receiving glucocorticoid replacement therapy for 12 days by means of either high doses of dexamethasone in their drinking water or by subcutaneous corticosterone pellets. Basal metabolic parameters such as weight gain or loss, blood glucose and plasma insulin were monitored: Dexamethasone treatment induced weight loss and a state of hyperinsulinemia with normoglycemia, while corticosterone treated animals displayed metabolic parameters identical to sham ADX animals. Within the arcuate nucleus of glucocorticoid treated animals, levels of Y1-receptor and preproNPY mRNAs were increased. In contrast, adrenalectomy itself had no effect upon Y1-receptor mRNA levels or preproNPY mRNA levels in the arcuate nucleus. These studies demonstrate that glucocorticoids exert a stimulatory action on levels of Y1-receptor mRNA and preproNPY mRNA levels in the hypothalamic arcuate nucleus. This is the first evidence to suggest that the expression of a neuropeptide-receptor gene in the central nervous system may be directly sensitive to peripheral hormonal signals.

Adrenalectomy↗

PubMed1994

Plasma concentrations of prolactin, noradrenaline, vasopressin and oxytocin during and after a prolonged epileptic seizure.

The time course and extent of changes in plasma prolactin, noradrenaline, vasopressin and oxytocin levels is reported following serial observations of a prolonged epileptic seizure arising in the temporal lobe, recorded by video-EEG-telemetry, in which the epileptic activity evolved from a simple partial to complex partial to secondarily generalised attack. The prolactin levels were markedly elevated during the phase of the simple partial seizure, at a time when consciousness was preserved, when motor activity was minimal and when EEG activity was highly localised. The hormonal levels continued to rise during the subsequent seizure evolution, suggesting that the duration (or intensity) of the seizure is an important, perhaps the most important, factor determining the degree of prolactin release during limbic seizures. Indeed, the prolactin elevation in this case (26 times the baseline level) is higher than any previously recorded, reflecting the unusual duration and intensity of this seizure. We did not observe the phenomenon of "exhaustion" of prolactin release and levels peaked after 49 min, and were high for over 2 h after the onset of the seizure, and after the convulsion had ceased. The concentrations of vasopressin, oxytocin and noradrenaline remained low during the aura, but rapidly increased during the phase of generalisation. The oxytocin and noradrenaline levels peaked during the phase of generalised convulsion, but the vasopressin levels peaked well into the post ictal phase, and remained high for several hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1994

Comparison of the expression of interferon gamma, IL2, IL4, and lymphotoxin mRNA in experimental autoimmune uveoretinitis.

The aim of this study was to investigate the T lymphocyte subsets involved in experimental autoimmune uveoretinitis (EAU) by quantifying the numbers of cells expressing mRNA for each of the lymphokines interferon gamma, interleukin 2, interleukin 4, and lymphotoxin throughout the disease process. Lewis rats were immunised with retinal S-antigen to provide a model of inflammatory eye disease. In situ hybridisation using cDNA probes specific for interferon gamma, IL2, IL4, and lymphotoxin mRNA were utilised to localise lymphokine mRNA expression by infiltrating cells and the numbers of positive cells counted. Localisation of mRNA for all four probes was found on increasing cell numbers as the disease process progressed. Similar numbers of cells expressed mRNA for each lymphokine, generally a small percentage of the T lymphocyte total. Activated cells within the eye express mRNA for interferon gamma, IL2, IL4, and lymphotoxin in EAU suggesting a mixed population of T lymphocyte subsets.

Animals↗

PubMed1994

Thyroid hormone-mediated regulation of corticotropin-releasing hormone messenger ribonucleic acid in the rat.

We have used in situ hybridization histochemistry to investigate interactions between the thyroid and adrenal axes in the rat. Propylthiouracil (PTU)-induced hypothyroidism caused a significant reduction in CRH gene transcripts in the paraventricular nucleus of male rats, with a concomitant decrease in both POMC gene expression in the anterior pituitary gland and circulating corticosterone. Conversely, adrenalectomy alone or adrenalectomy with high dose corticosterone pellet replacement had no significant effect on the thyroid hormone axis. The effect of thyroid hormones on the adrenal axis was not secondary to changes in the level of circulating corticosteroids, as the same effect of PTU-induced hypothyroidism was seen in adrenalectomized rats given corticosterone replacement. Neither was the effect of PTU simply the result of a direct toxic effect on the hypothalamus, as concurrent treatment with T3 blocked the response. We conclude that circulating levels of thyroid hormones have a major effect on the central regulation of the hypothalamic-pituitary-adrenal axis.

Adrenalectomy↗

PubMed1994

Neuropeptide-Y potentiates the secretion of vasopressin from the neurointermediate lobe of the rat pituitary gland.

Neuropeptide-Y (NPY) is colocalized with vasopressin and oxytocin in magnocellular neurons of the hypothalamo-neurohypophysial system, and a very high density of NPY-binding sites is present within the neurohypophysis. To investigate the possibility that NPY exerts a modulatory role on the release of neurohypophysial hormones, we have studied the actions of NPY on potassium-evoked release of vasopressin and oxytocin from the rat neurointermediate lobe in vitro. NPY dose-dependently potentiated vasopressin release evoked by high extracellular potassium (56 mM), with a maximal enhancement of 223% (10(-7) M NPY). A similar effect was obtained with the Y2-selective agonist NPY-(13-36). In contrast, no effect on the potassium-evoked release of oxytocin was observed at this concentration. In the absence of Ca2+ in the incubation medium, NPY did not potentiate vasopressin secretion, indicating that the effect of NPY on potassium-evoked secretion of neurohypophysial vasopressin is critically dependent on extracellular calcium ions. The number of neurohypophysial NPY-binding sites is drastically down-regulated in animals subjected to chronic osmotic stimulation. In the present study, it was observed that the potentiating effect of NPY on vasopressin secretion was completely abolished in neurointermediate lobes recovered from animals that had been drinking 2% NaCl for 12 days, reflecting the concomitant down-regulation of neurohypophysial NPY-binding sites observed during this state. Finally, it was confirmed that stimulation by high K+ significantly evoked the release of endogenous NPY from neurointermediate lobes of the pituitary gland. The present results provide evidence that NPY selectively and potently enhances evoked vasopressin secretion. Considering the coexistence of the two neuropeptides in magnocellular hypothalamo-neurohypophysial neurons, this action is likely to be part of an autostimulatory feedforward loop. NPY may be an important component in the mechanisms associated with the control of body fluid homeostasis.

Animals↗

PubMed1994

Pituitary ATP receptors: characterization and functional localization to gonadotropes.

We have used real-time dynamic video imaging of Fura-2 fluorescence to study the acute effects of extracellular ATP on [Ca2+]i in pituitary cells and found that ATP produced a rapid biphasic cytosolic Ca2+ increase in a dose-dependent manner in both rat pituitary gonadotropes and gonadotrope-derived alpha T3-1 cells. Removal of extracellular Ca2+ only attenuated the plateau phase of ATP-induced intracellular Ca2+ response and suramin (100 microM), a P2-purinoceptor antagonist, reduced the ATP effect by 40-60%. Further studies revealed the following rank-order of agonist potency in the Ca2+ response: -ATP = ADP = UTP > 2-methylthioATP >> beta, gamma-methylene ATP/alpha,beta-methylene ATP. Both homologous and heterologous desensitization occurred with ATP and UTP and these did not have additive effects. Together the data suggest that the intracellular Ca2+ responses of gonadotropes and alpha T3-1 cells to these nucleotides are mediated by a single class of receptor pharmacologically characterized as the P2U subtype. This is the first demonstration of functional ATP receptors in pituitary gonadotropes.

Animals↗

PubMed1994

Pharmacokinetics and efficacy of the long-acting somatostatin analogue somatuline in acromegaly.

The aim of this work was to assess the use of a sustained-release formulation of somatuline, a long-acting analogue of somatostatin, in the treatment of acromegaly. Fifteen patients with active acromegaly, as defined by random growth hormone (GH) levels greater than 10 mU/l, which fail to be suppressed to less than 5 mU/l following an oral glucose load, were studied. Somatuline was administered as an intramuscular injection in two regimens: eight patients were given a single injection of the sustained-release formulation and blood samples taken over the next month for the measurement of both basal levels of GH and the GH response to thyrotrophin-releasing hormone; and eight patients were given injections of the sustained-release formulation at 2-week intervals over a 6-month period and basal plasma GH levels and the GH response to both an oral glucose load and to thyrotrophin-releasing hormone was assessed. Following a single intramuscular dose of the sustained-release preparation, random GH levels were reduced to below 10 mU/l in five patients and by greater than 50% of basal levels in the remainder. The insulin-like growth factor I (IGF-I) levels fell to within the normal range in three patients. In the long-term efficacy study. GH levels were reduced to < 10 mU/l in 7/8 patients. The IGF-I levels were normalized in four patients. Five of the eight patients experienced diarrhoea, two of mild and three of moderate severity; none of the patients withdrew from the study.(ABSTRACT TRUNCATED AT 250 WORDS)

Acromegaly↗

PubMed1994

Expression of chorionic gonadotrophin in human pituitary adenomas.

In addition to the classical anterior pituitary hormones, many human pituitary adenomas express hormone genes ectopically. Expression of glycoprotein hormone alpha-subunit and, less commonly, free luteinizing hormone beta (LH-beta) or follicle-stimulating hormone beta is characteristic of endocrinologically inactive adenomas, a subgroup thought to be derived predominantly from the gonadotroph line. Thyrotrophin beta expression in these tumours is unusual, and specific chorionic gonadotrophin beta (CG-beta) expression, identified using oligonucleotide probes that reliably distinguish LH-beta and CG-beta in situ, is not well described. Using in situ hybridization histochemistry with a CG-beta transcript-specific oligonucleotide probe and a non-specific LH/CG-beta oligonucleotide and riboprobe, we have demonstrated specific CG-beta expression in two of 35 random pituitary adenomas; LH-beta expression occurred in a further eight adenomas. Unlike prolactin, growth hormone and proopiomelanocortin, which are transcribed in the vast majority of cells in their respective hormone-positive tumour subtypes, the pattern of LH/CG-beta was typically a scattering of single or small clusters of hormone-positive cells in a predominantly LH/CG-beta-negative tumour. Finally, although bona fide CG-beta expression in human pituitary adenomas does occur, it is only at an incidence similar to that described for carcinomas of other tissues.

Adenoma↗

PubMed1994

Neonatal monosodium glutamate treatment alters both the activity and the sensitivity of the rat hypothalamo-pituitary-adrenocortical axis.

We have investigated the effects of monosodium glutamate (MSG) lesioning of the arcuate nucleus on both central and peripheral components of the hypothalamo-pituitary-adrenocortical (HPA) axis under basal conditions and under acute and chronic stress. Plasma ACTH levels were lower in MSG-lesioned rats (27 +/- 7 pg/ml) compared with controls (71 +/- 18 pg/ml) while corticosterone levels were elevated (523 +/- 84 ng/ml compared with 176 +/- 34 ng/ml). Quantitative in situ hybridization histochemistry revealed that corticotrophin-releasing factor mRNA levels in the medial parvocellular part of the hypothalamic paraventricular nucleus were significantly lower in MSG-treated rats. MSG lesioning resulted in an enhanced response of corticosterone to restraint stress (1309 +/- 92 ng/ml compared with 628 +/- 125 ng/ml in sham-lesioned animals), while ACTH responses to restraint stress in MSG-lesioned and sham-MSG groups were not significantly different (160 +/- 24 pg/ml and 167 +/- 24 pg/ml respectively). These data suggest that MSG-lesioned rats have an increased adrenocortical sensitivity. In rats subjected to the chronic osmotic stimulus of drinking 2% saline for 12 days, plasma ACTH levels were significantly reduced (15 +/- 5 pg/ml) and the ACTH and corticosterone responses to restraint stress were eliminated. ACTH levels were also reduced in MSG-treated animals given 2% saline and the ACTH response to acute stress remained absent in these animals. However, a robust corticosterone response to restraint stress was observed in saline-treated MSG-lesioned rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1994

The regulation of plasma relaxin levels during human pregnancy.

The factors that determine the circulating levels of relaxin during pregnancy have been investigated by comparing the plasma levels of relaxin throughout pregnancy in women who became pregnant spontaneously (singleton, n = 240) or following superovulation (singleton and multifetal pregnancies (two to ten conceptuses), n = 83). Some of the women with multifetal pregnancies underwent selective fetal reduction to twin pregnancies. Relaxin levels were higher at 7-34 weeks of gestation in singleton pregnancies achieved following superovulation when compared with levels in spontaneously conceived singleton pregnancies (p < 0.05-0.001). In samples obtained between 10 and 12 weeks of gestation (before fetal reduction for the multifetal pregnancies), plasma relaxin levels correlated with fetal number (r = 0.526, P = 0.0001). Reduction in fetal number to a twin pregnancy did not alter relaxin levels. These data suggest that the circulating levels of relaxin throughout pregnancy are determined during the cycle of conception by gonadotrophin stimulation, and within the first 10 weeks of pregnancy by the luteotrophic stimulus from the conceptus. Furthermore, once corpus luteum synthesis of relaxin is established, then reduction in the luteotrophic stimulus does not appear to affect it.

Adult↗

PubMed1994

An investigation of the effects of interleukin-1 beta on plasma arginine vasopressin in the rat: role of adrenal steroids.

While the effects of cytokines on the hypothalamo-pituitary-adrenal axis have received a great deal of attention in recent years the effects of cytokines on posterior pituitary hormone release has been less well characterized. In the present study we have investigated the effects of a single i.p. injection of interleukin (IL)-1 beta on circulating levels of vasopressin (AVP) in the rat. We have found that the ability of IL-1 beta to increase plasma AVP is strongly influenced by circulating levels of glucocorticoid steroids. IL-1 beta did not affect plasma AVP in sham-operated control animals over the 4 h period of study. In contrast, following adrenalectomy we were able to stimulate AVP substantially with increases over the 4 h period. This effect was reduced by treatment of adrenalectomized rats with a low dose of dexamethasone and abolished with a high dose. These data suggest an inverse relationship between circulating levels of glucocorticoids and the ability of IL-1 beta to stimulate plasma AVP.

Adrenalectomy↗

PubMed1994

Real time computerized intracellular calcium ion imaging: a rapid method of neuronal receptor evaluation.

Real time computerized intracellular calcium ion analysis using fura-2-based fluorescence imaging has been used to evaluate neurotransmitter receptor function in primary cultures of rat hypothalamic neurons and a rat hypothalamic neuronal cell line (LT6/4). A wide range of neurotransmitters induced an increase in intracellular Ca2+ in cultured hypothalamic neurons. In contrast, undifferentiated LT6/4 cells failed to response to 56mM K+ or to a battery of neurotransmitters with the exception of histamine (100microM). LT6/4 cells, induced to differentiate by prior exposure to dibutyryl cAMP and NGF, responded to K+ but lost their responsiveness to histamine. Computerized imaging allowed the intracellular Ca2+ response of up to 50 cells to be determined simultaneously without resort to complex electrophysiological manipulations or receptor binding studies. The assessment of receptor complement and coupling using this technique allows large amounts of reproducible data to be rapidly collected from small populations of cells.

Animals↗

PubMed1993