Detection and measurement of hormone secretion from individual pituitary cells

Ontogenic development of corticotrophs in fetal buffalo (Bubalus bubalis) pituitary gland

To evaluate the subpopulation of corticotrophs in developing buffalo (Bubalus bubalis) fetus, pituitary glands were recovered (n=6 per group) from late first, second and third gestational female buffalo dams. The corticotrophs were identified by using specific antibodies against proopiomelanocortin (POMC) and adrenocorticotrophic hormone (ACTH) through immunohistochemistry. There was a significant (P≤0.05) increase of immunoreactive (ir) ir-ACTH cells during late 2^nd trimester while, ir-POMC cells were more (P≤0.05) at late 3^rd trimester of gestation as compared to other age groups. The quantity of co-localized cells for POMC and ACTH was significantly (P≤0.05) greater at the end of 1^st gestation rather than 2^nd and 3^rd gestational fetal adenohypophyseal cells. This study is the first to demonstrate co-localization of POMC+ACTH and the affect of gestational age on the expression of these cells in buffalo fetus adenohypophysis.

[18F]2-fluoro-2-deoxy-D-glucose positron emission tomography demonstration of estrogen negative and positive feedback on luteinizing hormone secretion in women

CONTEXT

Precise regulation of the neuroendocrine components of the female reproductive axis involves both negative and positive feedback of estrogen on gonadotropin secretion.

OBJECTIVE

Our objective was to determine the hypothalamic and/or pituitary sites of estrogen negative and positive feedback using neuroimaging techniques.

DESIGN AND SETTING

A graded estrogen infusion protocol was administered at a General Clinical Research Center in an academic medical center.

SUBJECTS

Healthy postmenopausal women (n = 11) were recruited for study.

INTERVENTIONS

Serum samples were measured every 4 h. A structural magnetic resonance imaging was performed at baseline, and [(18)F]2-fluoro-2-deoxy-d-glucose ((18)FDG) positron emission tomography was performed at baseline and 24 and 72 h. FDG positron emission tomography was co-registered with magnetic resonance imaging scans, and region of interest analysis was performed.

MAIN OUTCOME MEASURES

Serum LH and estradiol were assessed. Normalized values for glucose uptake were extracted from each region of interest for each subject at each time point.

RESULTS

A decrease in normalized (18)FDG uptake was apparent in the hypothalamus at 24 h (P < 0.02) associated with decreased LH (P < 0.0005). The increase in LH at 72 h (P < 0.0005) was associated with increased pituitary (18)FDG uptake (P < 0.02) but no change in hypothalamic uptake.

CONCLUSIONS

Changes in (18)FDG uptake as a measure of metabolic activity can be demonstrated in the hypothalamus and pituitary in association with discrete hormonal events. Results are consistent with mediation of estrogen negative feedback on LH at the hypothalamus, whereas estrogen positive feedback occurs at the pituitary with no evidence of increased hypothalamic activity in women.

A regulator of G protein signaling, RGS3, inhibits gonadotropin-releasing hormone (GnRH)-stimulated luteinizing hormone (LH) secretion

BACKGROUND

Luteinizing hormone secreted by the anterior pituitary gland regulates gonadal function. Luteinizing hormone secretion is regulated both by alterations in gonadotrope responsiveness to hypothalamic gonadotropin releasing hormone and by alterations in gonadotropin releasing hormone secretion. The mechanisms that determine gonadotrope responsiveness are unknown but may involve regulators of G protein signaling (RGSs). These proteins act by antagonizing or abbreviating interaction of Galpha proteins with effectors such as phospholipase Cbeta. Previously, we reported that gonadotropin releasing hormone-stimulated second messenger inositol trisphosphate production was inhibited when RGS3 and gonadotropin releasing hormone receptor cDNAs were co-transfected into the COS cell line. Here, we present evidence for RGS3 inhibition of gonadotropin releasing hormone-induced luteinizing hormone secretion from cultured rat pituitary cells.

RESULTS

A truncated version of RGS3 (RGS3T = RGS3 314-519) inhibited gonadotropin releasing hormone-stimulated inositol trisphosphate production more potently than did RSG3 in gonadotropin releasing hormone receptor-bearing COS cells. An RSG3/glutathione-S-transferase fusion protein bound more 35S-Gqalpha than any other member of the G protein family tested. Adenoviral-mediated RGS3 gene transfer in pituitary gonadotropes inhibited gonadotropin releasing hormone-stimulated luteinizing hormone secretion in a dose-related fashion. Adeno-RGS3 also inhibited gonadotropin releasing hormone stimulated 3H-inositol phosphate accumulation, consistent with a molecular site of action at the Gqalpha protein.

CONCLUSIONS

RGS3 inhibits gonadotropin releasing hormone-stimulated second messenger production (inositol trisphosphate) as well as luteinizing hormone secretion from rat pituitary gonadotropes apparently by binding and suppressing the transduction properties of Gqalpha protein function. A version of RGS3 that is amino-terminally truncated is even more potent than intact RGS3 at inhibiting gonadotropin releasing hormone-stimulated inositol trisphosphate production.

Regulation of chicken embryonic growth hormone secretion by corticosterone and triiodothyronine: evidence for a negative synergistic response

We reported that growth hormone (GH)-secreting cells differentiated by d 16 of chick embryonic development and that these somatotrophs were responsive to GH-releasing hormone and thyrotropin-releasing hormone. The present experiments evaluated effects of corticosterone and triiodothyronine (T3) on embryonic GH secretion. Anterior pituitary cells from embryonic day (e) 16, e18, and e20 were subjected to reverse hemolytic plaque assays (RHPAs) for GH in the absence or presence of corticosterone or T3. Corticosterone increased GH secretion from embryonic somatotrophs, an effect particularly evident on e16 and e18. T3 decreased GH secretion on e16, while no effect of T3 was significant on e18 or e20. Next, pituitary cells were subjected to RHPAs with T3 and corticosterone alone or in combination. Combined treatment with these hormones suppressed GH secretion from e16, e18, and e20 somatotrophs to levels below those found under basal conditions. We conclude that corticosterone can stimulate GH secretion in vitro at all embryonic ages tested. Furthermore, T3 can suppress basal GH secretion on e16, and the combination of T3 and corticosterone can suppress GH secretion at all ages. These findings indicate that GH secretion during the end of chicken embryonic development may be regulated by the interactions of endogenous glucocorticoids and thyroid hormones that increase prior to hatching.

Involvement of phosphoinositide-3-kinase and p70 S6 kinase in regulation of proliferation of rat lactotrophs in culture

Phosphoinositide-3-kinase (PI-3K) and p70 S6 kinase (p70S6k) are suggested as important molecules for mediating mitogenic actions of growth factors and cytokines in a variety of cell types. The purpose of the present study was to investigate whether these kinases were involved in mediation of the mitogenic actions of not only the growth factor insulin but also cyclic adenosine monophosphate (cAMP) and estrogen on rat cultured lactotrophs. Treatment with wortmannin or LY294002, a PI-3K inhibitor, or rapamycin, a p70S6k inhibitor, decreased basal levels of 5-bromo-2-deoxyuridine (BrdU)-labeling indices of lactotrophs in a dose-dependent manner. These inhibitors were effective in blocking an increase in BrdU-labeling indices induced by insulin. LY294002 and rapamycin also suppressed an increase in BrdU-labeling indices induced by forskolin, an adenylate cyclase activator, or dibutyryl cAMP, a membrane-permeable cAMP analog, as well as that induced by estradiol, a physiologic extracellular activator of lactotroph proliferation. However, the dibutyryl cAMP-, but not insulin-induced proliferation, acquired a resistance to LY294002 and rapamycin by pretreatment with bromocriptine, a dopaminergic agonist that is able to suppress lactotroph proliferation. These results suggest that the mitogenic actions of cAMP and estradiol on rat lactotrophs are mediated by PI-3K and p70S6k, and that dopaminergic inhibition modifies the PI-3K and p70S6k dependence of the regulation of lactotroph proliferation.

Functional heterogeneity of corticotrophs in the anterior pituitary of the sheep fetus

1. Parturition in the sheep is dependent on prepartum stimulation of the hypothalamo-pituitary-adrenal axis and an increase in fetal plasma cortisol concentration. We have investigated whether there are changes in the functional characteristics of the corticotrophic cells in the week before delivery or in response to an increase in circulating cortisol. 2. Fetal sheep were infused with cortisol (2-3 mg 24 h-1 i.v.; n = 11), or saline (4.4 ml 24 h-1 i.v.; n = 10) between 109 and 116 days gestation and pituitary glands were collected from these two groups, and from a late gestational group (140-145 days gestation; n = 10) for cell culture. Cells in half the wells from each pituitary were treated with cytotoxin (Cx; a cytotoxic analogue of corticotrophin releasing hormone (CRH)) to eliminate CRH target cells before exposure to ovine (o)CRH (10-8 M), arginine vasopressin (AVP; 10-7 M) or oCRH + AVP. 3. We have demonstrated that around 70 % of adrenocorticotrophic hormone (ACTH) in the fetal anterior pituitary is stored within corticotrophs which are CRH responsive. Cortisol acts to inhibit ACTH synthesis in corticotrophic cells which are CRH responsive, whereas AVP-responsive cells in the fetal pituitary are relatively resistant to cortisol. 4. We propose that the stimulatory influence of the fetal hypothalamus must counteract the negative feedback effect of cortisol in the CRH-responsive cells to stimulate the increase in pituitary ACTH output which occurs before delivery.

Effects of acute administration of growth hormone-releasing hormone (GHRH) and oxytocin on somatotroph cells in sheep: morphometric study and growth hormone (GH) secretion

In this work, the combined use of the morphometric study of somatotroph cells and plasma GH levels provided new data for the interpretation of the role played by OT and GHRH on GH cells. GHRH 1-29 (15 micrograms/kg), oxytocin (2.5 IU animal) or 1 ml saline solution were administered to male lambs. The GH plasma concentration was measured by RIA and for the morphometric study the cellular area, nuclear area and volume density of the somatotroph cells were measured in 1 micron semi-thin sections immunolabeled with avidin-biotin technique (ABC). The area under the GH response curve for 3 hours after injection was similar in both saline and OT-treated animals (24.8 +/- 9.1 and 31.4 +/- 14.7 micrograms/ml, respectively) and much lower than that observed in GHRH-treated animals (445.5 +/- 126.7 micrograms/ml). The cell area of somatotrophs was smaller in the GHRH-treated lambs and larger in the OT-treated lambs than in the control lambs (71.47 +/- 1.56, 91.42 +/- 1.72 and 83.1 +/- 1.74 microns 2, respectively). A similar change was observed in the nuclear area; it decreased in the GHRH-treated lambs (21.61 +/- 0.52 microns 2) and increased in the OT-treated lambs (25.45 +/- 0.68 microns 2) with respect to the control group (23.75 +/- 0.44 microns 2). No significant differences were found in volume density.(ABSTRACT TRUNCATED AT 250 WORDS)

Three-dimensional and quantitative observation of the hypertrophy of rat corticotrophs following adrenalectomy

The three-dimensional form of corticotrophs in the anterior pituitary gland of rats was studied by reconstruction from serial semi-thin sections both in control rats and rats one week after adrenalectomy. The corticotrophs have large depressions and cup-shaped cavities on their surface, and these features became more conspicuous after adrenalectomy. The hypertrophy of corticotrophs in adrenalectomized rats was quantified by measuring the area and perimeter of all serially sectioned profiles. The volume of the whole cell increased from 1129 +/- 114 microns3 to 2902 +/- 201 microns3 (P less than 0.01) after adrenalectomy, while the surface area of the cells increased from 690 +/- 45 microns2 to 1431 +/- 116 microns2 (P less than 0.01). The volume of the nucleus increased from 87 +/- 11 microns3 to 172 +/- 14 microns3 (P less than 0.05). Though the complexity of the form of corticotrophs seems to be increased after adrenalectomy, the ratios (adrenalectomized/control) of cell volume and surface area were 2.57 and 2.07, respectively; this indicates that the increase of the cell volume was greater than that of the surface area.

Human tumour-associated NK cells secrete increased amounts of interferon-gamma and interleukin-4

Numerous interactions between malignant and stromal/inflammatory cells take place within solid human tumours, which are mediated, in part, by the release of signalling proteins called cytokines. In the present study, we have compared the secretion of two important immunomodulatory cytokines, IFN-gamma and IL-4 by individual, immunophenotyped NK cells freshly isolated from either malignant tumour biopsies, or peripheral blood samples from patients with ductal invasive breast cancer. Due to the marked heterogeneity amongst cells isolated from these clinical samples, we have employed a technique called the reverse haemolytic plaque assay to identify and enumerate cytokine-secreting cells at the single cell level. Our data indicate that NK cells isolated directly from the tumour site secrete more IFN-gamma and IL-4 than NK cells from the blood of the same patients. However, a greater proportion of CD16+ cells from both sources in breast cancer patients secreted IFN-gamma than of those from the blood of healthy donors. We also show that factors secreted by the human breast cell lines, MCF-7 and MDA-231 PN9, were able to mimic the stimulatory influence of the tumour microenvironment on secretory activity of NK cells.