scholarly journals Gonadotropin releasing hormone stimulates the formation of inositol phosphates in rat anterior pituitary tissue

1985 ◽  
Vol 226 (2) ◽  
pp. 563-569 ◽  
Author(s):  
M P Schrey
Keyword(s):  
Anterior Pituitary ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Inositol Trisphosphate ◽  
Gonadotropin Releasing Hormone ◽  
Releasing Hormone ◽  
Inositol 1 ◽  
Pituitary Tissue ◽  
Inositol Phosphate Production ◽  
Stimulation Of

The production of inositol phosphates in response to gonadotropin releasing hormone (GnRH) was studied in rat anterior pituitary tissue preincubated with [3H]inositol. Prelabelled paired hemipituitaries from prepubertal female rats were incubated in the presence or absence of GnRH in medium containing 10 mM-Li+ X Li+, which inhibits myo-inositol-1-phosphatase, greatly amplified the stimulation of inositol phosphate production by GnRH (10(-7) M) to 159, 198 and 313% of paired control values for inositol 1-phosphate, inositol bisphosphate and inositol trisphosphate respectively after 20 min. The percentage distribution of [3H]inositol within the phosphoinositides was 91.3, 6.3 and 2.4 for phosphatidylinositol, phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate respectively and was unaffected by GnRH. The stimulation of inositol trisphosphate production by GnRH was evident after 5 min incubation, was dose-dependent with a half-maximal effect around 11 nM, and was not inhibited by removal of extracellular Ca2+. Elevation of cytosolic Ca2+ by membrane depolarization with 50 mM-K+ had no significant effect on inositol phosphate production. These findings are consistent with the hypothesis that GnRH action in the anterior pituitary involves the hydrolysis of phosphatidylinositol 4,5-bisphosphate. The resulting elevation of inositol trisphosphate may in turn lead to intracellular Ca2+ mobilization and subsequent stimulation of gonadotropin secretion.

Oxytocin and vasopressin stimulate inositol phosphate production in human gestational myometrium and decidua cells

1986 ◽  
Vol 6 (7) ◽  
pp. 613-619 ◽  
Author(s):  
Michael P. Schrey ◽  
Alison M. Read ◽  
Philip J. Steer
Keyword(s):  
Arachidonic Acid ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Diacylglycerol Lipase ◽  
Inositol 1 ◽  
Inositol Phosphate Production ◽  
Acid Accumulation ◽  
Free Arachidonic Acid ◽  
Hydrolysis Of ◽  
Related Increase

The involvement of phosphoinositide hydrolysis in the action of oxytocin and vasopressin on the uterus was investigated in gestational myometrium and decidua cells by measuring the production of inositol phosphates. Both peptides stimulated a dose related increase in all three inositol phosphates in myometrium. This may be related to the control of sarcoplasmic Ca++ levels in the myometrium. Oxytocin and vasopressin also stimulated inositol 1-phosphate (IP) production in decidua cells. The hydrolysis of phosphatidylinositol by decidua homogenates exhibited a precursor-product relationship for diacylglycerol and arachidonic acid accumulation. Hence both peptides may mobilise free arachidonic acid, for prostaglandin biosynthesis, from decidua cell phosphoinositides by the sequential action of phospholipase C and diacylglycerol lipase.

Progesterone, testosterone and estradiol-17β inhibit gonadotropin-releasing hormone stimulation of G protein GTPase activity in plasma membranes from rat anterior pituitary lobe

1992 ◽  
Vol 126 (4) ◽  
pp. 345-349 ◽  
Author(s):  
Rudravajhala Ravindra ◽  
Robert S Aronstam
Keyword(s):  
G Protein ◽  
Anterior Pituitary ◽  
Plasma Membranes ◽  
Gonadotropin Releasing Hormone ◽  
Gonadal Steroids ◽  
Gtpase Activity ◽  
Releasing Hormone ◽  
Low K ◽  
Estradiol 17Β ◽  
Stimulation Of

In order to understand the biochemical mechanisms underlying the rapid, non-genomic effects of gonadal steroids on gonadotropin secretion, we examined the effects of progesterone, testosterone and estradiol-17β on the low Km GTPase activity associated with transducer G proteins coupled to gonadotropin-releasing hormone (GnRH) receptors. Homogenates of anterior pituitary lobes from adult male rats were processed by discontinuous sucrose gradient centrifugation to isolate plasma membranes. The low Km GTPase activity (EC 3.6.1.-) was assayed in 5 μg membrane protein using [γ-32P]GTP at 37°C in an ATP-regenerating buffer containing 1 μmol/l unlabeled GTP. One hundred nmol/l each of progesterone, testosterone and estradiol-17β maximally stimulated low Km GTPase activity by 61%, 59% and 45%, respectively (p<0.05). Time course studies revealed that 100 nmol/l progesterone stimulated the enzyme activity by 93% and 62% at 5 and 30 min, respectively; 100 nmol/l testosterone stimulated GTPase activity by 100% and 72% at 5 and 30 min, respectively: 100 nmol/l estradiol-17β stimulated GTPase activity by 80% and 70% at 5 and 30 min, respectively. GnRH stimulated the low Km GTPase activity by about 60% in a concentration-dependent manner. In the presence of the gonadal steroids, the ability of GnRH to stimulate the GTPase activity was inhibited. For example, stimulation ranged from 36% to 60% with 0.1–100 nmol/l GnRH alone, but only from 7% to 20% in the presence of GnRH and 100 nmol/l progesterone (p<0.05). Similarly, in the presence of 100 nmol/l estradiol-17β, GnRH stimulation of the enzymatic activity ranged from 12% to 19%. It appeared that testosterone was less effective in inhibiting GnRH-stimulated GTPase activity; stimulation ranged from 15% to 32% in the presence of GnRH and 100 nmol/l testosterone (p<0.05). These results, while suggesting that the gonadal steroids disrupt GnRH receptor-G protein interactions, are consistent with the notion that steroids have a profound effect at the membrane level prior to their interaction with the cytosolic receptors.

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

scholarly journals Thrombin-induced inositol trisphosphate production by rabbit platelets is inhibited by ethanol

1988 ◽  
Vol 251 (1) ◽  
pp. 279-284 ◽  
Author(s):  
M L Rand ◽  
J D Vickers ◽  
R L Kinlough-Rathbone ◽  
M A Packham ◽  
J F Mustard
Keyword(s):  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Inositol Trisphosphate ◽  
Thromboxane A2 ◽  
Second Messenger ◽  
Inhibitory Effect ◽  
Thromboxane B2 ◽  
Rabbit Platelets ◽  
Platelet Functions ◽  
Stimulation Of

Ethanol has an inhibitory effect on some platelet functions, but the mechanisms by which it exerts this effect are not known. Using suspensions of washed platelets, we observed that ethanol (1-9 mg/ml) did not affect the aggregation of rabbit platelets stimulated with ADP (0.5-10 microM). When platelets were prelabelled with 5-hydroxy[14C]tryptamine, aggregation and secretion of granule contents in response to thrombin (0.01-0.10 unit/ml) were not inhibited by ethanol, but these responses to thrombin at lower concentrations (less than 0.01 unit/ml) were inhibited by ethanol (2-4 mg/ml). Platelets were prelabelled with [3H]inositol so that increases in inositol phosphates upon stimulation could be assessed by measuring the amount of label in these compounds. ADP-induced increases in IP (inositol phosphate) and IP2 (inositol bisphosphate) were not affected by ethanol. IP3 (inositol trisphosphate) was not changed by ADP or ethanol. Although ethanol did not affect the increases in IP, IP2 and IP3 caused by stimulation of platelets with thrombin at concentrations greater than 0.01 unit/ml, ethanol did inhibit the increases observed at 2 and 3 min in these inositol phosphates caused by lower concentrations of thrombin (less than 0.01 unit/ml). Since ADP did not cause formation of IP3 in rabbit platelets, and since no thromboxane B2 was detected in platelets stimulated with the lower concentrations of thrombin, it is unlikely that the inhibitory effect of ethanol in IP3 formation was due to effects on further stimulation of platelets by released ADP or by thromboxane A2. Ethanol may inhibit platelet responses to thrombin by inhibiting the production of the second messenger, IP3.

scholarly journals Muscarinic-receptor stimulation enhances polyphosphoinositide breakdown in guinea-pig ileum smooth muscle

1984 ◽  
Vol 223 (2) ◽  
pp. 527-531 ◽  
Author(s):  
M C Sekar ◽  
B D Roufogalis
Keyword(s):  
Guinea Pig ◽  
Muscarinic Receptor ◽  
Longitudinal Muscle ◽  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Exchange Chromatography ◽  
Guinea Pig Ileum ◽  
Receptor Stimulation ◽  
Inositol 1 ◽  
Stimulation Of

Muscarinic-receptor stimulation by 0.1 mM-carbachol in longitudinal muscle of the guinea-pig ileum increases the incorporation of [3H]inositol into inositol-containing phospholipid. This effect was blocked by 16 microM-atropine. After 60 min incubation, carbachol increased the accumulation of total inositol phosphates 20-fold in the presence of 10 mM-Li+. Less than 20% of the total inositol phosphate corresponded to inositol 1-phosphate by ion-exchange chromatography, whereas of the remainder about two-thirds corresponded to inositol bisphosphate and one third to inositol trisphosphate. It is concluded that stimulation of muscarinic receptors in guinea-pig ileum enhances breakdown of polyphosphoinositides, suggesting that this may be a primary event associated with Ca2+ mobilization in the guinea-pig ileum.

Cholinergic Stimulation of Inositol Phosphate Production in Cultured Anterior Pituitary Cells

1987 ◽  
Vol 46 (4) ◽  
pp. 306-311 ◽  
Author(s):  
P. Luigi Canonico ◽  
David Jarvis ◽  
Maria Angela Sortino ◽  
Umberto Scapagnini ◽  
Robert M. MacLeod
Keyword(s):  
Anterior Pituitary ◽  
Inositol Phosphate ◽  
Pituitary Cells ◽  
Cholinergic Stimulation ◽  
Anterior Pituitary Cells ◽  
Inositol Phosphate Production ◽  
Stimulation Of

scholarly journals Changes in free cytosolic calcium and accumulation of inositol phosphates in isolated hepatocytes by [Leu]enkephalin

1986 ◽  
Vol 238 (2) ◽  
pp. 537-542 ◽  
Author(s):  
R P Leach ◽  
S B Shears ◽  
C J Kirk ◽  
M A Titheradge
Keyword(s):  
Inositol Phosphates ◽  
Inositol Phosphate ◽  
Cytosolic Calcium ◽  
Isolated Hepatocytes ◽  
Opioid Peptide ◽  
Alpha Activity ◽  
Dose Dependency ◽  
Significant Stimulation ◽  
Inositol Phosphate Production ◽  
Stimulation Of

Isolated hepatocytes from fed rats were used to study the effects of the opioid peptide [Leu]enkephalin on intracellular free cytosolic Ca2+ ([Ca2+]i) and inositol phosphate production. By measuring the fluorescence of the intracellular Ca2+-selective indicator quin-2, [Leu]enkephalin was found to increase [Ca2+]i rapidly from a resting value of 0.219 microM to 0.55 microM. The magnitude of this response was comparable with that produced by maximally stimulating concentrations of either vasopressin (100 nM) or phenylephrine (10 microM). The opioid-peptide-mediated increase in [Ca2+]i showed a dose-dependency comparable with the activation of phosphorylase, but it preceded the increase in phosphorylase alpha activity. Addition of [Leu]enkephalin to hepatocytes prelabelled with myo-[2-3H(n)]inositol resulted in a significant stimulation of inositol phosphate production. At 10 min after hormone addition, there were increases in the concentrations of inositol mono-, bis- and tris-phosphate fractions of 12-, 9- and 14-fold respectively. No effect was apparent on the glycerophosphoinositol fraction. The effect of 10 microM-[Leu]enkephalin on inositol phosphate production was significantly greater than that obtained with 10 microM-phenylephrine, but marginally smaller than that induced by 100 nM-vasopressin. However, at these concentrations all three agonists gave a comparable increase in [Ca2+]i and activation of phosphorylase a. These data provide evidence for [Leu]enkephalin acting via a mechanism involving a mobilization of Ca2+ as a result of increased phosphatidylinositol turnover.

Kallidin-induced stimulation of inositol phosphate production and prolactin release in rat anterior pituitary cells

1990 ◽  
Vol 123 (1) ◽  
pp. 37-42 ◽  
Author(s):  
T. Hugh Jones ◽  
Barry L. Brown ◽  
Pauline R. M. Dobson
Keyword(s):  
Anterior Pituitary ◽  
Inositol Phosphate ◽  
Prolactin Secretion ◽  
Male Rat ◽  
Pituitary Cells ◽  
Phosphoinositide Metabolism ◽  
Prolactin Release ◽  
Anterior Pituitary Cells ◽  
Inositol Phosphate Production ◽  
Stimulation Of

Abstract. The effect of the kinin, kallidin (lysyl-brady-kinin) on phosphoinositide metabolism and prolactin secretion was examined in male rat anterior pituitary cells in primary culture. Kallidin was found to stimulate both total inositol phosphate production and prolactin release. The stimulation of inositol phosphate was biphasic in nature, similar to that previously reported for bradykinin, although kallidin was approximately 10-fold more potent. Kallidin also stimulated prolactin secretion provoking a maximal stimulation of 193.0±11.1 (sem)% at 1 μmol/l. These findings suggest that kallidin-induced prolactin secretion may be mediated intracellularly by activation of phosphoinositide metabolism. The B2 receptor antagonists had no significant inhibitory effects on kallidin-stimulated phosphoinositide metabolism or prolactin release. The B1 agonist des-Arg9-bradykinin has previously been shown to have no effect on either parameter. As the effects of kinins on anterior pituitary cells do not appear to be mediated by either of the known kinin receptors, they may, therefore, act via a hitherto unrecognised kinin receptor.

Sign in / Sign up

Export Citation Format

Share Document