Search Results

You are looking at 1 - 10 of 17 items for

  • Author: J R E Davis x
Clear All Modify Search
Restricted access

J. R. E. Davis

Production of prolactin is very tissue-specific – the gene is present in all cells, but in the rat it is expressed only in the anterior pituitary gland, while in man it is also expressed at low levels in the decidualized endometrium. Much of the work on rat prolactin gene expression has been greatly facilitated by the availability of the rat pituitary tumour-derived GH cell line (including the GH1, GH3 and GH4 cell subclones) which produces both prolactin and growth hormone. In contrast, much less is so far known about the regulation of the human prolactin gene, due in part to the lack of readily available human pituitary tissue for in-vitro studies.

An increasing amount is known about hormonal and intracellular regulation of prolactin mRNA production, which has been reviewed elsewhere (Davis, Belayew & Sheppard, 1989). However, some of the most impressive and important recent advances have been

Restricted access

J. R. E. Davis and N. Hoggard

Pituitary adenomas are a common form of endocrine neoplasia in man, and cause clinical problems resulting from syndromes of hormone hypersecretion, hypofunction of the residual normal pituitary gland, or from mass effects from the tumour bulk itself. They can now be treated by surgery, by irradiation or by endocrine therapies such as dopamine or somatostatin agonists, but none of these options has proved entirely satisfactory. After intense scrutiny of pituitary physiology and biochemistry, only now are some of the causes of pituitary tumour formation becoming understood, and this short review will discuss some recent advances in the field.

Pituitary tumours generally arise from a single differentiated cell type expressing its appropriate mature pituitary hormone product (such as prolactin, growth hormone (GH), adrenocorticotrophin (ACTH) or thyroid-stimulating hormone (TSH), and the hormone hypersecretion often leads to a clinically recognized syndrome. About 25% of adenomas are clinically 'non-functioning', but most of these in

Restricted access

J. R. E. Davis and M. C. Sheppard

ABSTRACT

Amplification of desensitization of TSH response to thyrotrophin-releasing hormone (TRH) may be important mechanisms in the regulation of its secretion. We have investigated this possibility in vitro, using monolayer culture of rat anterior pituitary cells. Cells (1–1·5 × 105/250 μl per well) were cultured for 72 h, exposed to TRH or dibutyryl cyclic AMP (dbcAMP) for 6 or 8 h, washed, and then treated for 4 h with various doses of TRH, or with K+ (55 mmol/l) as a non-specific secretagogue. Pretreatment with TRH (20 nmol/l) for 8 h reduced subsequent TSH release: basal release fell to 64% of the control value (1·01±0·10 μg/l pretreated, 1·58 ± 0·16 control) and release in response to TRH (100 nmol/l) to 69% of the control (2·7 ± 0·19 μg/l vs 3·98 ± 0·22); K+ response was reduced to 86% of the control (3·77 ± 0·21 μg/l vs 4·39 ± 0·20), significantly less than the other reductions. The extent of the parallel downward shift of the TRH dose–response curve was proportional to dose and duration of prior TRH exposure. There was no significant change in the dose of TRH required to cause half-maximal TSH release (ED50: pretreated 4·8, control 2·8 nmol TRH/l) suggesting depletion of an intracellular pool of TSH rather than 'desensitization'. After 6-h pretreatment with dbcAMP, subsequent TSH responses were augmented: basal release was 130% of the control, response to TRH (100 nmol/l) was 137% and to K+ it was 132% of the control, with a parallel upward shift of the TRH dose–response curve but no change in cellular TSH content. We suggest that an intracellular pool of TSH exists which can be depleted by prior TRH exposure without a desensitization effect. The size of this pool may be increased by dbcAMP, indicating that cyclic nucleotides may modulate the availability of TSH to an acutely releasable intracellular pool.

J. Endocr. (1986) 108, 211–217

Restricted access

J. R. E. Davis and M. C. Sheppard

ABSTRACT

We have studied the effects of cyclic AMP (cAMP) on TSH secretion by cultured rat pituitary cells, using forskolin and dibutyryl cAMP (dbcAMP) to raise the cellular cAMP content by different mechanisms. Forskolin (10 μmol/l), a stimulator of adenylate cyclase, raised the cAMP content within 10 min, but had a more delayed effect on TSH release, with no significant stimulation for at least 6 h, but a clear dose-dependent effect at 24 h. Incubation with dbcAMP likewise increased TSH release after 6–24 h. By contrast, high cellular cAMP levels induced by either forskolin or dbcAMP augmented the TSH response to TRH at an early stage, before any detectable change in unstimulated TSH release. Pretreatment of cells with forskolin led to a parallel upward shift in the subsequent TRH dose-response curve, without a significant change in median effective dose or any change in cellular TSH content.

These findings suggest that cAMP acts to increase the availability of TSH for acute release by TRH by modulation of an intracellular releasable hormone pool, and indicate synergistic interactions between the adenylate cyclase system and the phospholipid-calcium stimulus-release coupling mechanism of TRH.

J. Endocr. (1986) 109, 365–369

Free access

J R E Davis and A J L Clark

Free access

A J L Clark and J R E Davis

Free access

A D Adamson, D Jackson and J R E Davis

The study of gene expression is a major focus in biological research and is recognised to be critical for our understanding of physiological and pathophysiological processes. Methods to study gene expression range from in vitro biochemical assays through cultured cells and tissue biopsies to whole organisms. In the early stages of project development, considerations about which model system to use should be addressed and may influence future experimental procedures. The aim of this review is to briefly describe advantages and disadvantages of the existing techniques available to study eukaryote gene expression in vitro, including the mechanism of transgene integration (transient or stable), the different transgenesis systems available, including plasmids, viruses and targeted integration and knockin approaches, and paying particular attention to expression systems such as bacterial artificial chromosomes and episomal vectors that offer a number of advantages and are increasing in popularity. We also discuss novel approaches that combine some of the above techniques, generating increasingly complex but physiologically accurate expression systems.

Restricted access

P. J. DAVIS, R. I. GREGERMAN and W. E. POOLE

Species differences have been described in the thyroxine-serum protein complexes of various mammals (Blumberg & Robbins, 1960; Farer, Robbins, Blumberg & Rail, 1962; Rösler, 1967a, b). The thyroid hormone-binding serum proteins of the pouched mammals have not been studied. Because this order (Marsupialia) has had a long separate evolutionary history, its protein patterns are of interest and have been used to study speciation (Kirsch & Poole, 1967). We report here electrophoretic studies of the binding of thyroid hormones by serum proteins of the grey kangaroo.

Sera were obtained from Eastern (Macropus giganteus) and Western (Macropus fuliginosus) grey kangaroos and from a hybrid (Eastern x Western) maintained by the Division of Wildlife Research, C.S.I.R.O. Except for one Western specimen, all sera were from adult females. Sera were labelled with 0·9–2·4 μg. [131I]thyroxine (T4)/100 ml. or 0·9–1·4 μg. [125I]tri-iodothyronine (T3)/100 ml. obtained from Abbott Laboratories (North Chicago,

Free access

Julian R E Davis and Adrian J L Clark

Free access

Julian R E Davis and Adrian J L Clark