Maitotoxin increases inositol phosphates in rat anterior pituitary cells

1991 ◽  
Vol 6 (1) ◽  
pp. 95-99 ◽  
Author(s):  
M. A. Sortino ◽  
T. M. Delahunty ◽  
T. Yasumoto ◽  
M. J. Cronin
Keyword(s):  
Anterior Pituitary ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Cell Types ◽  
Calcium Stores ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Anterior Pituitary Cells ◽  
Intracellular Ca

ABSTRACT Maitotoxin is a potent marine poison that mobilizes calcium in most vertebrate cell types and accelerates secretion from anterior pituitary cells. It is not known whether voltage-sensitive calcium channels or other mechanisms initiate the effects of maitotoxin on anterior pituitary cells. Changes in intracellular Ca2+ levels may also be achieved by releasing internal calcium stores via inositol trisphosphate (InsP3). Indeed, maitotoxin rapidly increased inositol phosphate accumulation in a concentration-dependent manner. Calcium channel antagonists such as nifedipine and verapamil did not block this response nor did calcium-mobilizing agents (BAYk8644, A23187) mimic this effect. These data suggest that the mechanism by which maitotoxin acts at the pituitary may include the activation of an enzyme that produces the calcium-mobilizing signal InsP3.

Reserpine is a calcium channel antagonist in normal and GH3 rat pituitary cells

1985 ◽  
Vol 248 (1) ◽  
pp. E15-E19
Author(s):  
I. S. Login ◽  
A. M. Judd ◽  
M. J. Cronin ◽  
T. Yasumoto ◽  
R. M. MacLeod
Keyword(s):  
Calcium Channel ◽  
Calcium Channel Antagonist ◽  
Anterior Pituitary ◽  
Calcium Uptake ◽  
Calcium Ionophore ◽  
Gh3 Cells ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Anterior Pituitary Cells

Reserpine exerts direct effects on several tissues, including inhibition of hormone release from rat anterior pituitary cells. To test the hypothesis that reserpine may be acting as a calcium channel antagonist, normal or GH3 rat anterior pituitary cells were preincubated in reserpine or the conventional calcium channel blocker, D-600, followed by exposure to 45Ca2+ together with stimulants of calcium uptake: maitotoxin, a potent calcium channel activator; A23187, a calcium ionophore; or 50 mMK+. After incubation, the cells were harvested by vacuum filtration and cell-associated radioactivity determined. In normal cells, reserpine blocked both basal and K+-stimulated calcium uptake. Reserpine selectively blocked maitotoxin but not A23187-induced calcium uptake. In GH3 cells 9 microM reserpine and 30 microM D-600 were equally effective in blocking maitotoxin-stimulated calcium uptake. Reserpine appears to block voltage-dependent calcium channels in pituitary cells in a concentration-dependent manner but not calcium uptake caused nonspecifically by A23187.

Mastoparan, a wasp venom peptide, stimulates release of prolactin from cultured rat anterior pituitary cells

1994 ◽  
Vol 142 (1) ◽  
pp. 9-18 ◽  
Author(s):  
S E Mau ◽  
M R Witt ◽  
H Vilhardt
Keyword(s):  
Protein Kinase ◽  
Cell Cultures ◽  
Anterior Pituitary ◽  
Inositol Phosphates ◽  
Pituitary Cell ◽  
Secretory Process ◽  
Protein Kinase Activity ◽  
Pituitary Cells ◽  
Anterior Pituitary Cells ◽  
Intracellular Ca

Abstract Studies have shown that mastoparan and other amphiphilic peptides induce exocytosis of hormones from anterior pituitary cells. We have studied the effect of mastoparan on the secretion of prolactin from cultured rat anterior pituitary cells and on the concomitant functional status of signal-transducing pathways in lactotroph-enriched cell cultures. Mastoparan stimulation of prolactin secretion was dose-dependent, time-dependent, reversible and required the presence of calcium. Pretreatment of pituitary cell cultures with cholera and pertussis toxin had no effect on the secretory response, whereas encapsulation of guanosine 5-[β-thio]diphosphate (GDP-β-S) by reversible electropermeabilization inhibited mastoparan-stimulated secretion. Incubation of mastoparan with myo[3H]inositol-labelled lactotroph-enriched anterior pituitary cell cultures resulted in increased formation of inositol phosphates compared with control cells, and encapsulation of GDP-β-S blocked mastoparan-induced inositol lipid hydrolysis. Mastoparan caused translocation of protein kinase C activity from a soluble to a membrane-attached form. Mastoparan was able to increase the intracellular Ca2+ concentration in Fura-2-loaded individual lactotrophs. Omission of Ca2+ from the extracellular medium did not change the Ca2+ response in lactotrophs when stimulated with mastoparan. On the basis of these results it is concluded that mastoparan-induced release of prolactin is preceded by activation of the inositol(1,4,5)trisphosphate/diacylglycerol pathway with resulting translocation of protein kinase activity and increment in intracellular Ca2+. However, other signal-transducing pathways may be involved in the secretory process. Journal of Endocrinology (1994) 142, 9–18

Dopamine does not attenuate phosphoinositide hydrolysis in rat anterior pituitary cells

1986 ◽  
Vol 110 (3) ◽  
pp. 389-393 ◽  
Author(s):  
P. L. Canonico ◽  
W. D. Jarvis ◽  
A. M. Judd ◽  
R. M. MacLeod
Keyword(s):  
Anterior Pituitary ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Pituitary Cells ◽  
Anterior Pituitary Cells ◽  
Marked Diminution ◽  
Inositol Phosphate Production ◽  
Concomitant Reduction ◽  
Potent Agonist ◽  
Hydrolysis Of

ABSTRACT The hydrolysis of membrane phosphatidylinositol to yield [3H]labelled inositol phosphates by anterior pituitary cells was stimulated significantly by angiotensin II, TRH and neurotensin over a broad range of concentrations. These secretagogues also stimulated release of prolactin. Although the coincident incubation of dopamine with these agents resulted in a marked diminution of prolactin release, no concomitant reduction in inositol phosphate production was observed. In addition, bromocriptine, a potent agonist of dopamine, also proved ineffective in blunting stimulated phosphatidylinositol catabolism. Although it slightly inhibited basal rates of inositol tris-, bis- and monophosphate production, these results show that the secretagogue-mediated enhancement of phosphatidylinositol catabolism may be correlated with an increased release of prolactin and that the inhibition of hormone release produced by dopamine is not achieved by reducing basal or secretagogue-mediated inositol phosphate production. J. Endocr. (1986) 110, 389–393

GRF increases release of growth hormone and arachidonate from anterior pituitary cells

1985 ◽  
Vol 248 (4) ◽  
pp. E438-E442
Author(s):  
A. M. Judd ◽  
K. Koike ◽  
R. M. MacLeod
Keyword(s):  
Growth Hormone ◽  
Anterior Pituitary ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Hormone Release ◽  
Growth Hormone Release ◽  
Concentration Dependent Manner ◽  
Anterior Pituitary Cells ◽  
Arachidonate Release

Arachidonate and its metabolites increase growth hormone release in vitro. A study was designed to determine whether arachidonate release from anterior pituitary cells is modified by growth hormone-releasing factor (GRF) or somatostatin (SRIF). Cultured pituitary cells were incubated with [3H]arachidonate to esterify the long-chain fatty acid into cellular lipids. The cells were extensively washed with medium containing no [3H]arachidonate and then incubated with GRF and/or SRIF for 30 min. The incubation medium was then extracted with ethyl acetate, and following thin-layer chromatographic separation, the radioactivity in the [3H]arachidonate band was measured. GRF in a concentration-dependent manner (1-30 nM) stimulated growth hormone and arachidonate release, whereas SRIF (100 nM) blocked the GRF-induced increase of growth hormone and arachidonate release. The effects of GRF on growth hormone and arachidonate were evident at time intervals as brief as 5 min. These findings support the hypothesis that arachidonate may play a role in the GRF-induced growth hormone release.

Specific oxytocin agonist stimulates prolactin release but has no effect on inositol phosphate accumulation in isolated rat anterior pituitary cells

1993 ◽  
Vol 10 (2) ◽  
pp. 107-114 ◽  
Author(s):  
S E Chadio ◽  
F A Antoni
Keyword(s):  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Pituitary Cells ◽  
Uterine Tissue ◽  
Prolactin Release ◽  
Anterior Pituitary Cells ◽  
Oxytocin Receptors ◽  
Stimulation Of

ABSTRACT We have previously characterized specific oxytocin receptors in the rat anterior pituitary gland, using a highly selective oxytocin receptor antagonist as radio-ligand. The aim of the present study was to examine whether occupation of these receptors by oxytocin produces a stimulation of prolactin release and a rise in the accumulation of total inositol phosphates in the rat adenohypophysis. Anterior pituitary cells harvested from randomly cycling and diethylstilboestrol (100 μg s.c.)-treated rats were perifused with Dulbecco's minimal essential medium at a rate of 0·3 ml/min. Oxytocin and the specific oxytocin agonist [Thr4-Gly7]-oxytocin (TG-OT) both stimulated a significant prolactin release at concentrations of 10-6 and 10-7 m. Oestrogen treatment did not affect the response to oxytocin, indicating that there is no straightforward correlation between receptor number and prolactin secretory response in the rat pituitary gland. The involvement of phosphoinositide hydrolysis was investigated in dispersed anterior pituitary cells and uterine tissue from randomly cycling rats. Oxytocin and arginine-vasopressin stimulated a significant (P<0·05) and dose-related increase in total inositol phosphates, vasopressin being more potent. The specific oxytocin agonist TG-OT had no effect on total inositol phosphate production in pituitary cells, but when tested in uterine tissue it significantly (P< 0.05) stimulated the accumulation of total inositol phosphate at all concentrations tested (10-5 to 10-9 m). In conclusion, the data show that oxytocin has prolactin-releasing activity, acting on specific receptors in the anterior pituitary gland. Furthermore, although oxytocin receptors in the rat uterus are coupled to the inositol phospholipid cycle, it would appear that this is not a prerequisite for the stimulation of prolactin secretion when specific oxytocin receptors in the rat adenohypophysis are activated.

Tyrosine kinase inhibitors enhance GHRH-stimulated cAMP accumulation and GH release in rat anterior pituitary cells

1997 ◽  
Vol 152 (2) ◽  
pp. 193-199 ◽  
Author(s):  
T Ogiwara ◽  
C L Chik ◽  
A K Ho
Keyword(s):  
Tyrosine Kinase ◽  
Cholera Toxin ◽  
Tyrosine Kinase Inhibitors ◽  
Anterior Pituitary ◽  
Kinase Inhibitors ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Camp Accumulation ◽  
Anterior Pituitary Cells ◽  
Site Of Action

Abstract In this study, the role of tyrosine phosphorylation in agonist-stimulated cAMP accumulation and GH release in rat anterior pituitary cells was investigated. It was found that genistein, a tyrosine kinase inhibitor, while having no effect on its own, potentiated GHRH-stimulated cAMP accumulation in a concentration-dependent manner. In comparison, daidzein, an inactive analogue of genistein, was ineffective and vanadate, a phosphotyrosine phosphatase inhibitor, reduced GHRH-stimulated cAMP accumulation. Additional structurally unrelated tyrosine kinase inhibitors, erbstatin and tyrphostins, also potentiated GHRH-stimulated cAMP accumulation. To determine the site of action of the tyrosine kinase inhibitors, pituitary adenylate cyclase-activating polypeptide (PACAP), cholera toxin and forskolin were used to increase cAMP accumulation. Genistein enhanced the PACAP-, cholera toxin- or forskolin-stimulated cAMP accumulation, suggesting that the site of action is at the post-receptor level. However, when the phosphodiesterase was inhibited by isobutylmethylxanthine, genistein did not potentiate and vanadate did not inhibit GHRH-stimulated cAMP accumulation, indicating that phosphodiesterase is a probable site of action for the inhibitor. Genistein and erbstatin also enhanced GHRH-stimulated GH release and the effect of vanadate was inhibitory. These results indicate that tyrosine kinase inhibitors enhance cAMP accumulation through their action on phosphodiesterase activity in rat anterior pituitary cells and the tyrosine kinase pathway appears to be involved in the control of GH release. Journal of Endocrinology (1997) 152, 193–199

Substance P stimulation of polyphosphoinositide hydrolysis in rat anterior pituitary membranes involves a GTP-dependent mechanism

1991 ◽  
Vol 130 (1) ◽  
pp. 63-70 ◽  
Author(s):  
S. E. Mau ◽  
T. Saermark
Keyword(s):  
Substance P ◽  
Pertussis Toxin ◽  
Anterior Pituitary ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Sodium Deoxycholate ◽  
Pituitary Cells ◽  
Guanine Nucleotide ◽  
Nk1 Receptor ◽  
Gtp Binding

ABSTRACT Substance P (SP) stimulates polyphosphoinositide breakdown in the rat anterior pituitary through an NK-1 receptor. In the present study we present evidence that the coupling between the SP–NK1 receptor complex and polyphosphoinositide-specific phospholipase C (PI-PLC) in rat anterior pituitary membranes may involve a mechanism consistent with a GTP-binding protein. The formation of inositol phosphates from [3H]myo-inositol-labelled anterior pituitary membranes induced by SP was potentiated by GTP and non-hydrolysable guanine nucleotides. The stimulatory effects of SP alone and SP plus GTP could be blocked by addition of GDP-β-S (guanosine 5-O-(thiodiphosphate)) in excess. Basal and SP plus guanine nucleotide-induced inositol phosphate formation were stimulated by fluoride, whereas the effect of SP alone was inhibited. Pretreatment of anterior pituitary membranes with sodium deoxycholate attenuated the inositol phosphate response elicited by GTP and GTP-γ-S, whereas basal and SP-stimulated inositol phosphate production showed a peak at 1 mg sodium deoxycholate/ml. SP, fluoride and guanine nucleotide stimulatory effects on hydrolysis of polyphosphoinositide (PPI) were unaffected by pretreatment of anterior pituitary cells with cholera or pertussis toxin for 12 h. Treatment of anterior pituitary membranes with cholera and pertussis toxin yielded [32P]ADP-ribosylation of two proteins with molecular masses of 45 and 41 kDa respectively. We conclude that SP coupling to PI-PLC through the NK1 receptor in the rat anterior pituitary involves a GTP-binding mechanism distinct from the G-proteins associated with adenylate cyclase, Gs and Gi. Journal of Endocrinology (1991) 130, 63–70

Control of secretion in anterior pituitary cells--linking ion channels, messengers and exocytosis

1988 ◽  
Vol 139 (1) ◽  
pp. 287-316
Author(s):  
W. T. Mason ◽  
S. R. Rawlings ◽  
P. Cobbett ◽  
S. K. Sikdar ◽  
R. Zorec ◽  
...  
Keyword(s):  
Ion Channels ◽  
Intracellular Calcium ◽  
Anterior Pituitary ◽  
Hormone Secretion ◽  
Cell Types ◽  
Pituitary Cell ◽  
Pituitary Cells ◽  
Calcium Activity ◽  
Anterior Pituitary Cells ◽  
Voltage Dependent

Normal anterior pituitary cells, in their diversity and heterogeneity, provide a rich source of models for secretory function. However, until recently they have largely been neglected in favour of neoplastic, clonal tumour cell lines of pituitary origin, which have enabled a number of studies on supposedly homogeneous cell types. Because many of these lines appear to lack key peptide and neurotransmitter receptors, as well as being degranulated with accompanying abnormal levels of secretion, we have developed a range of normal primary anterior pituitary cell cultures using dispersion and enrichment techniques. By studying lactotrophs, somatotrophs and gonadotrophs we have revealed a number of possible transduction mechanisms by which receptors for hypothalamic peptides and neurotransmitters may control secretion. In particular, the transduction events controlling secretion from pituitary cells may differ fundamentally from those found in other cell types. Patch-clamp recordings in these various pituitary cell preparations have revealed substantial populations of voltage-dependent Na+, Ca2+ and K+ channels which may support action potentials in these cells. Although activation of these channels may gate Ca2+ entry to the cells under some conditions, our evidence taken with that of other laboratories suggests that peptide-receptor interactions leading to hormone secretion occur independently of significant membrane depolarization. Rather, secretion of hormone and rises in intracellular calcium measured with new probes for intracellular calcium activity, can occur in response to hypothalamic peptide activation in the absence of substantial changes in membrane potential. These changes in intracellular calcium activity almost certainly depend on both intracellular and extracellular calcium sources. In addition, strong evidence of a role for multiple intracellular receptors and modulators in the secretory event suggests we should consider the plasma membrane channels important for regulation of hormone secretion to be predominantly agonist-activated, rather than of the more conventional voltage-dependent type. Likewise, evidence from new methods for recording single ion channels suggests the existence of intracellular sites for channel modulation, implying they too may play an important role in secretory regulation. We shall consider new data and new technology which we hope will provide key answers to the many intriguing questions surrounding the control of pituitary hormone secretion. We shall highlight our work with recordings of single ion channels activated by peptides, and recent experiments using imaging of intracellular ionized free calcium.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of forskolin on LH and GH release

1985 ◽  
Vol 249 (4) ◽  
pp. E392-E397
Author(s):  
W. S. Evans ◽  
T. H. Brannagan ◽  
E. R. Limber ◽  
M. J. Cronin ◽  
A. D. Rogol ◽  
...  
Keyword(s):  
Growth Hormone ◽  
Anterior Pituitary ◽  
Gonadotropin Releasing Hormone ◽  
Female Rats ◽  
Second Phase ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Lh Release ◽  
Biphasic Release

The effects of forskolin, an agent which increases intracellular levels of cAMP, on basal luteinizing hormone (LH) and growth hormone (GH) release and on gonadotropin-releasing hormone (GnRH)-stimulated LH release were documented. Continuously perifused dispersed anterior pituitary cells from female rats at random stages of the estrous cycle were used. Secretory rates of both LH and GH increased in a concentration-dependent manner in response to a 1-h challenge with 0.03, 0.1, 0.3, 1, or 3 microM forskolin. In response to 0.3 microM forskolin, maximum GH release was achieved within 15-20 min, after which secretion decreased. In contrast, LH release increased gradually, became maximal at 1.5-2 h, and remained constant until the forskolin was withdrawn. Cells exposed to 10 nM GnRH for 4 h exhibited a biphasic release of LH with the interphase nadir occurring at 30 min. The second phase of LH release was enhanced by simultaneous addition of forskolin with the GnRH. Whereas second phase release did not increase further, exposure of the cells to forskolin for 60 or 120 min before GnRH resulted in increased first-phase LH release. We suggest that, whereas our data are consistent with a role for cAMP in mediating the acute release of GH, cAMP may be involved in the process through which nonimmediately releasable LH becomes available for release.

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