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J M Burrin

Publications and source records attributed to J M Burrin.

At least 91 records · Page 5Linked to original sources
PubMed1989

Regulation of transfected glycoprotein hormone alpha-gene expression in primary pituitary cell cultures.

Studies of gene regulation are greatly facilitated by the ability to transfect DNA into cultured cells. We examined a variety of transfection techniques to optimize transient expression of the human glycoprotein hormone alpha-gene in primary pituitary cells and subsequently investigated the regulation of alpha-promoter transcription. Expression vectors driven by either the rous sarcoma virus-chloramphenicol acetyl transferase (RSVCAT) or the human alpha-gene (alpha CAT) promoters were transfected into cultures of dispersed female rat pituitary cells using calcium phosphate (CaPO4), diethylaminoethyl-dextran, lipofection, and electroporation procedures. CAT activity was optimal using the CaPO4 technique, resulting in 511 +/- 49% and 57 +/- 5% conversion/100 micrograms protein/4 h for RSVCAT and alpha CAT, respectively. Immunohistochemical analyses of alpha CAT expression using anti-CAT monoclonal antibodies demonstrated that the alpha-gene promoter is expressed in pituitary cells, predominantly if not exclusively, in gonadotropes and thyrotropes. Hormonal regulation of alpha-promoter activity was assessed using both the CAT and the luciferase (LUC) reporter systems. alpha-Promoter activity was significantly (P less than 0.001) stimulated by 8-bromo-cAMP (217% increase), GnRH (75% increase), GnRH agonist analog (141% increase), and TRH (75% increase). The expression of control plasmids (RSVLUC, TKLUC, pOLUC) was not affected by treatment with these agents. We conclude that CaPO4-mediated transfection allows analyses of transient gene expression in primary pituitary cells. The alpha-promoter directs expression specifically in pituitary cells, predominantly gonadotropes and thyrotropes. alpha-Gene transcription is stimulated by GnRH, TRH, and 8-bromo-cAMP.

Animals↗
PubMed1989

Cyclic AMP (cAMP) effects on chorionic gonadotropin gene transcription and mRNA stability: labile proteins mediate basal expression whereas stable proteins mediate cAMP stimulation.

Cyclic AMP stimulates a marked accumulation of CG alpha and CG beta mRNAs that reflects, in part, increased rates of gene transcription. We find that a major component of cAMP stimulation of alpha and CG beta mRNAs is independent of new protein synthesis. After treatment of JEG-3 choriocarcinoma cells with cycloheximide, basal levels of alpha and CG beta mRNAs decreased over 12 h to 27% and 13% of control values, respectively. However, cycloheximide treatment did not affect the degree of cAMP-stimulation of alpha and CG beta mRNA levels which increased 20- and 26-fold, respectively. Similarly, cycloheximide did not block cAMP-stimulated transcription of the alpha and CG beta genes. The effect of cAMP treatment on alpha and CG beta mRNA stability was assessed by decay after removal of cAMP, pulse-chase analyses, and decay after inhibition of RNA synthesis by actinomycin D. The half-lives of alpha and CG beta mRNAs determined by decay rates after removal of cAMP were 6.0 h and 7.2 h, respectively. Consistent with these measurements of mRNA stability, alpha and CG beta mRNA half-lives determined by pulse-chase analyses were 8.8 h and 8.6 h, respectively. Cyclic AMP treatment increased the half-lives of alpha and CG beta mRNAs 1.8- and 3.4-fold, respectively. Thus, the effects of cAMP on alpha and CG beta gene expression are predominantly transcriptional, but cAMP also increases mRNA levels via a posttranscriptional mechanism.(ABSTRACT TRUNCATED AT 250 WORDS)

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1989

Continuous subcutaneous octreotide infusion markedly suppresses IGF-I levels whilst only partially suppressing GH secretion in diabetics with retinopathy.

The response to GH releasing hormone (GHRH 1-29) and 24-h serum GH and IGF-I levels were measured in 9 insulin-dependent diabetics with retinopathy and 6 normal volunteers before and after different treatment regimens with octreotide, a long-acting somatostatin analogue. Octreotide, 50 micrograms by sc injection, completely suppressed GHRH-stimulated GH release in both groups. Thrice daily sc injections for up to 20 weeks were associated with variable plasma octreotide levels and failed completely to suppress GH secretion in either the patients or the normal controls. Three days of continuous sc pump infusion (500 micrograms/24-h) resulted in consistently high plasma octreotide levels and completely suppressed 24-h GH in 4 normal subjects, whilst treatment for up to 16 weeks only partially suppressed GH levels in 6 patients (AUC mU.l-1.h-1; 209 +/- 81 vs 121 +/- 82; P = 0.01). Mean +/- SD IGF-I levels (micrograms/l) in the patients (but not controls) were suppressed into the hypopituitary range by median 6 weeks (range 2-16) pump administration (203 +/- 62 vs 60 +/- 25; P = 0.02). Pump treatment achieved total GH suppression in normal subjects; diabetics with retinopathy seem more resistant to the GH suppressing effects of the drug. However, the reduction of serum IGF-I with prolonged treatment may be of clinical value in arresting the progress of diabetic retinopathy.

Adult↗
PubMed1989

The anterior pituitary content of neuromedin U-like immunoreactivity is altered by thyrotrophin-releasing hormone and thyroid hormone status in the rat.

In this study we have examined the effects of TRH, thyroid hormones and dopamine on the rat anterior pituitary content of neuromedin U-like immunoreactivity. Oral administration of TRH (20 mg/100 g per day) to euthyroid animals evoked a fivefold increase in peptide content after 12 days of treatment. This effect was found to be dependent upon circulating levels of thyroid hormone, since administration of TRH to thyroidectomized animals failed to show a similar effect without simultaneous treatment with tri-iodothyronine. The possibility that the TRH-induced increase in anterior lobe neuromedin U content reflected alterations in prolactin secretion or synthetic rate was also examined. Treatment of euthyroid animals with a dopamine agonist and antagonist was, however, without effect. These results demonstrate a unique relationship between TRH and thyroid hormone levels in increasing the anterior lobe content of neuromedin U immunoreactivity.

Animals↗
PubMed1989

Burmese Russell's viper venom causes hormone release from rat pituitary cells in vitro.

Acute and chronic hypopituitarism is associated with severe envenoming by the Burmese Russell's viper. We have demonstrated that in vitro, Burmese Russell's viper venom (0.1-10 micrograms/ml) causes a dose-dependent release of GH, TSH and ACTH from dispersed rat anterior pituitary cells in culture. At 10 micrograms/ml, venom causes a significant increase in the release of GH (344%, P less than 0.001), TSH (168%, P less than 0.005) and ACTH (greater than 700%, P less than 0.001). We have also shown that the component (or components) responsible for this stimulatory effect is stable to heat (60 degrees C, 1 h) and mild trypsinization. Repeated addition of venom (1 microgram/ml) to pituitary cells in a perifusion column system demonstrated attenuation of GH release. This reduced response was not due to depletion of the GH pool since the pituitary cells were subsequently able to respond to both GH-releasing factor (GRF) stimulation and KCl depolarization. Somatostatin in a dose which abolished GRF-stimulated GH release failed to affect venom-stimulated GH release, implying that venom acts in a cyclic AMP-independent manner. We conclude that Burmese Russell's viper venom has direct effects on pituitary hormone release in vitro. Whether these effects contribute to its known actions in vivo on the function of the pituitary remains to be established.

Adrenocorticotropic Hormone↗
PubMed1989

Growth hormone-releasing factor-induced growth hormone secretion from perifused rat anterior pituitary cells: lack of influence of glucose concentration, and normal responses in pituitary cells from diabetic animals.

The mechanism responsible for the suppression of GH secretion in hyperglycaemia and hypoglycaemia in rats has been investigated using perifusion of anterior pituitary cells. When perifused with Krebs-Ringer bicarbonate containing normal (5 mmol/l), high (20 mmol/l) and low (1 mmol/l) concentrations of glucose, the GH responses to GH-releasing factor (GRF) were 85 +/- 5, 85.5 +/- 5.4 and 89 +/- 3.0 (S.E.M.)% respectively compared with the initial response to GRF at 5 mmol/l in each column. The mean GH response to GRF from anterior pituitary cells of normal rats was 6.58 +/- 0.88 micrograms/three pituitaries, which was not statistically different form that of cells from rats with streptozotocin-induced diabetes (5.40 +/- 0.68 micrograms/three pituitaries). It is concluded that GH suppression in diabetic rats and during hypoglycaemia is not mediated by changes in the GH response to GRF.

Animals↗
PubMed1989

High-dose porcine galanin infusion and effect on intravenous glucose tolerance in humans.

The neuropeptide galanin inhibits glucose-stimulated insulin release in dogs and rodents and has been proposed as having a role in the control of insulin release in humans. The effect of infused galanin on intravenous glucose tolerance in humans was investigated by giving an intravenous glucose tolerance test (0.5 g glucose/kg body wt) alone and with infusions of synthetic porcine galanin at high-dose levels (80 and 160 pmol.kg-1.min-1) to seven healthy male volunteers. The results showed no effect of galanin infusion on plasma glucose or serum insulin, although a rise in serum growth hormone even in the face of the intravenous glucose load confirmed the potent growth hormone-stimulating effect of galanin. These results suggest that caution should be exercised in extrapolating a physiological role for galanin in humans from the results of animal studies.

Animals↗
PubMed1989

Double-blind crossover trial of isophane (NPH)- and lente-based insulin regimens.

Isophane (NPH) and lente insulin preparations have been the basis of insulin-injection regimens for many decades but were never formally compared. After a 2-mo run-in period, 82 patients were randomized to NPH (Protaphane) or lente (Monotard) insulin preparations given together with Actrapid as a twice-daily injection regimen in a double-blind study. Patients were seen monthly and crossed over after 5 mo of treatment. Control as assessed by glycosylated hemoglobin (NPH 9.2 +/- 0.1%, lente 9.3 +/- 0.1%, mean +/- SE) and fructosamine (1.55 +/- 0.02 and 1.57 +/- 0.02 mM) concentrations was identical for the two regimens as were home-collected laboratory-measured fasting blood glucose (BG) (NPH 8.8 +/- 0.5 mM, lente 9.0 +/- 0.5 mM) and mean BG (8.2 +/- 0.3 and 7.6 +/- 0.3 mM) concentrations. For both regimens, the major control problem was the BG concentration before and after breakfast. Total insulin dosage was similar (NPH 56.3 +/- 0.6 U/day, lente 57.2 +/- 0.6 U/day) with no tendency for a difference in the evening intermediate-acting dose (NPH 17.0 +/- 0.3 U/day, lente 17.0 +/- 0.3 U/day) to counter fasting hyperglycemia. Serum lipid concentrations and body weight confirmed the equivalence of control. Hypoglycemic events were recorded in personal diaries and graded by predetermined criteria. Self-treated, relative-assisted, and hospital/doctor-treated hypoglycemic events did not differ in frequency. We conclude that lente- and NPH-based twice-daily human insulin regimens give indistinguishable metabolic control.

Adult↗
PubMed1988

The effect of cholinergic blockade on the growth hormone response to galanin in humans.

The effect of cholinergic blockade with pirenzepine or atropine on growth hormone (GH) release after galanin administration was investigated in five normal male subjects. The mean peak GH response to an infusion of galanin (40 pmol/kg/min for 40 minutes) was significantly reduced from 17.2 mU/L to 2.9 mU/L (P less than .001) with prior administration of pirenzepine (30 mg IV). When galanin was infused at a higher dose (80 pmol/kg/min), this suppression of release by pirenzepine was partially overcome, with GH rising to a mean peak response of 8.0 mU/L (P less than .05). Repeated administration of atropine (two bolus doses of 0.6 mg IV) also failed to abolish the GH response to this higher dose of galanin in two subjects. It has been proposed that cholinergic pathways control GH release via somatostatin, and this study suggests that galanin may also act by modulating hypothalamic somatostatinergic tone either directly or by facilitating cholinergic transmission.

Adult↗
PubMed1988

Differential expression of alpha-CGRP and beta-CGRP by primary sensory neurons and enteric autonomic neurons of the rat.

Expression of the calcitonin gene-related peptide, alpha-calcitonin gene-related peptide (CGRP), and the homologous beta-CGRP were compared in sensory and enteric nerves of the rat. Analysis of CGRP-like immunoreactivity by cation exchange chromatography and radioimmunoassay showed that in the dorsal root ganglia, dorsal spinal cord and in those peripheral tissues where CGRP-like immunoreactivity is primarily localized to sensory fibres, alpha-CGRP concentrations were three to six times greater than beta-CGRP concentrations. In the intestine, however, beta-CGRP concentrations were up to seven times greater than alpha-CGRP concentrations. Only beta-CGRP was detected in the intestines of capsaicin-treated rats. Northern blot and in situ hybridization to alpha-CGRP- and beta-CGRP-specific probes showed that while both alpha-CGRP and beta-CGRP messenger ribonucleic acids occurred in the dorsal root ganglia, only beta-CGRP messenger ribonucleic acid occurred in the intestine, where it was localized to enteric neurons. Receptor binding sites on membranes of rat heart and colon had approximately equal affinities for alpha-CGRP and beta-CGRP. The two peptides were equipotent in increasing the rate and force of atrial contractions but alpha-CGRP was slightly (2.6 times) more potent than beta-CGRP in relaxing colonic smooth muscle. Thus, both alpha-CGRP and beta-CGRP occur in the rat nervous system and are both biologically active. Sensory neurons and enteric neurons have been identified as populations which preferentially express alpha-CGRP and beta-CGRP, respectively.

Animals↗
PubMed1988

The distribution of melanin-concentrating hormone-like immunoreactivity in the central nervous system of rat, guinea-pig, pig and man.

The distribution of melanin-concentrating hormone-like immunoreactivity was investigated by radioimmunoassay in the CNS of rat, guinea-pig, pig and man. Highest concentrations of melanin-concentrating hormone-like immunoreactivity were found in the hypothalamus of all the species: rat 204.4 +/- 14.9; guinea-pig 159.5 +/- 23.3; pig 10.9 +/- 4.5 and man 80.1 +/- 19.1 pmol/g. Gel chromatographic analysis of hypothalamic extracts showed five immunoreactive peaks of melanin-concentrating hormone-like immunoreactivity in the rat and pig and six in the guinea-pig and man. High-performance liquid chromatography analysis of hypothalamic extracts showed five immunoreactive peaks in rat, guinea-pig, pig and four in man. However, these peaks appeared at different retention times from that of the single peak of salmon melanin-concentrating hormone. Examination of subcellular fractions of whole rat brain showed that most of the melanin-concentrating hormone-like immunoreactivity is found in the synaptosome fraction. Stimulation of melanin-concentrating hormone-like immunoreactivity release from rat hypothalamic slices revealed that potassium in the presence of calcium stimulated melanin-concentrating hormone-like immunoreactivity release. These findings suggest that mammalian melanin-concentrating hormone-like immunoreactivity has a different amino acid sequence from salmon melanin-concentrating hormone and may exist in multiple molecular forms. It is possible that melanin-concentrating hormone may play a role as a neurotransmitter or modulator in the mammalian CNS.

Adult↗
PubMed1988

Postprandial glycaemic effects of a long-acting somatostatin analogue (octreotide) in non-insulin dependent diabetes mellitus.

Postprandial changes in blood glucose, insulin and glucagon were examined in 7 non-insulin dependent diabetic patients, before and after 3 days' treatment with the somatostatin analogue, octreotide (50 ug injected subcutaneously thricedaily). After octreotide injection, postprandial rises in plasma insulin and glucagon were significantly flattened. The postprandial glycaemic rise was delayed but the area under the glycaemic curve was not increased. Animal studies have suggested that octreotide inhibits growth hormone and glucagon secretion much more powerfully than native somatostatin, while relatively sparing insulin secretion. However, the present findings suggest that this analogue is not sufficiently selective to be therapeutically useful in non-insulin dependent diabetes.

Aged↗
PubMed1988

The prevalence of thyroid autoantibodies in dermatitis herpetiformis.

The prevalence of IgG class thyroglobulin and microsomal antibodies, estimated using a sensitive ELISA, was 48% in 115 patients with dermatitis herpetiformis, which was significantly greater than the prevalence of 16% in 107 unselected controls without dermatitis herpetiformis. IgA class thyroid antibodies were found in 29% of dermatitis herpetiformis patients. Overt thyroid disease had been diagnosed in six (5%) of the dermatitis herpetiformis group and a further six patients had elevated TSH levels. The presence of thyroid antibodies was not associated with particular HLA-DR antigens. These results demonstrate the frequent occurrence of thyroid antibodies in dermatitis herpetiformis, although thyroid failure is less commonly associated with this condition. Immune response genes outside the HLA-DR region may be involved in the immune hyper-responsiveness seen in dermatitis herpetiformis which is reflected in the high prevalence of thyroid autoimmunity.

Adolescent↗
PubMed1988

The role of a highly sensitive amplified enzyme immunoassay for thyrotrophin in the evaluation of thyrotroph function in hypopituitary patients.

Using a highly sensitive amplified enzyme-linked immunoassay (AEIA) for thyrotrophin (TSH), we have assessed the ability of a single basal measurement of TSH to predict the subsequent response of TSH to TRH in a group of 11 patients with known pituitary pathology and some evidence of hypopituitarism. All patients were clinically euthyroid. Basal levels of AEIA-TSH ranged from less than 0.2 mU/l ('undetectable') to 0.9 mU/l; within this range there was no correlation with the subsequent TSH levels at 30 min in the TRH test. The TSH response in the TRH test did not correlate with the direct measurements of prevailing thyroid hormone levels (Total T4 or Free T4). We suggest that in patients with pituitary disease, the formal TRH test yields additional information regarding residual thyrotroph function that cannot reliably be predicted by a single basal TSH value, even when measured by a sensitive method. The current and potential thyroid status in patients with hypopituitarism must continue to rest on the overall picture provided by clinical assessment, direct measurement of thyroid hormones and the TRH test response. A basal TSH alone gives little useful information regarding thyroid status in such patients.

Adult↗