GnRH ACTION IN RAT ANTERIOR PITUITARY GLAND: REGULATION OF PROTEIN, GLYCOPROTEIN AND LH SYNTHESIS

1977 ◽  
Vol 86 (3) ◽  
pp. 473-488 ◽  
Author(s):  
K. M. J. Menon ◽  
K. P. Gunaga ◽  
S. Azhar
Keyword(s):  
Cyclic Amp ◽  
Anterior Pituitary ◽  
Amino Acid Mixture ◽  
Acid Mixture ◽  
Dependent Manner ◽  
Dibutyryl Cyclic Amp ◽  
Concomitant Increase ◽  
Cyclic Amp Accumulation ◽  
Dose Dependent

ABSTRACT The effect of synthetic GnRH on the synthesis of proteins and glycoproteins in the anterior pituitary and in vitro release of LH into the medium was studied. A maximal dose (25 ng/ml) of synthetic GnRH caused optimum release of radioimmunoassayable LH into the medium after 2 h of incubation. A concomitant increase in cyclic AMP accumulation in the tissue and LH in the incubation medium was also observed under the influence of GnRH during different periods of incubation time. Incubation of the rat anterior pituitary with GnRH stimulated the incorporation of [3H]proline into acid precipitable proteins in a time- and dose-dependent manner, similar to radioimmunoassayable LH released into the medium. Similar results were obtained when pituitary was incubated with dibutyryl cyclic AMP. LH, in addition, enhanced the incorporation of [3H]glucosamine and [3H]amine acids mixture into acidprecipitable proteins suggesting that proteins including glycoproteins are synthesized by the rat anterior pituitary under the influence of GnRH. Approximately 10 % of the radioactivity associated with proteins comigrated with radioimmunoassayable LH on the gels. GnRH also enhanced the incorporation of [3H]glucosamine and [3H]amino acid mixture into immunoprecipitable LH. The GnRH-induced incorporation of [3H]proline into anterior pituitary proteins was abolished by specific translation inhibitors.

Glutamine promotes triglyceride absorption in a dose-dependent manner

2002 ◽  
Vol 282 (2) ◽  
pp. G317-G323 ◽  
Author(s):  
Jeffrey B. Schwimmer ◽  
Looi Ee ◽  
Shuqin Zheng ◽  
Patrick Tso
Keyword(s):  
Amino Acid ◽  
Amino Acid Mixture ◽  
Lipid Absorption ◽  
Acid Mixture ◽  
Dependent Manner ◽  
Sprague Dawley ◽  
Feeding Tubes ◽  
Mesenteric Lymph ◽  
Sprague Dawley Rats ◽  
Dose Dependent

Dietary proteins may play a role in lipid absorption. Whether amino acids are specifically involved is unknown. We hypothesized that enterally administered l-glutamine (l-Gln) given with a lipid meal increases triglyceride (TG) absorption in rats. Mesenteric lymph fistulae and gastroduodenal feeding tubes were placed in adult male Sprague-Dawley rats. The animals received an enteral bolus of Intralipid (5 ml) followed by enteral infusion of increasing concentrations of l-Gln in saline (0, 85, 170, or 340 mM) or equimolar concentrations of the inactive isomer d-Gln or an essential amino acid mixture without Gln. Lymph was collected continuously for 6 h and analyzed for TG content. Animals infused with 85 mM l-Gln had a 64% increase in total TG output vs. controls ( P < 0.05) despite no difference in lymph flow rate. Total TG output for animals infused with 340 mMl-Gln declined by 43% vs. controls ( P < 0.05). The effect of Gln in promoting lymphatic fat transport is specific to l-Gln and not shared by d-Gln or an equivalent amino acid mixture. l-Gln is capable of either promoting or impairing lymphatic TG transport in a dose-dependent manner.

Biochemical parameters regulating forward motility initiation in vitro in goat immature epididymal spermatozoa

1998 ◽  
Vol 10 (4) ◽  
pp. 299 ◽  
Author(s):  
Bijay S. Jaiswal ◽  
Gopal C. Majumder
Keyword(s):  
Cyclic Amp ◽  
Sperm Motility ◽  
Biochemical Parameters ◽  
Vital Role ◽  
Dependent Manner ◽  
Alkaline Ph ◽  
Heat Stable ◽  
Heat Stable Protein ◽  
Dose Dependent

An investigation was carried out to analyse the biochemical parameters influencing forward motility (FM) initiation in vitro in the goat caput-epididymal immature spermatozoa. Forward motility was induced in approximately 55% of caput-sperm upon incubation in an alkaline (pH 8.0) modified Ringer’s solution containing theophylline (30 mM) (an inhibitor of cyclic AMP phosphodiesterase), dialysed epi-didymal plasma (EP) and bicarbonate. Both EP and bicarbonate induced sperm motility in a dose-dependent manner, and at saturating doses EP (0.6 mg protein mL–1) and bicarbonate (25 mM) induced FM in approx-imately 38% and 44% of the cells, respectively. The motility-promoting efficacy of EP was attributed to a heat-stable protein termed ‘forward motility protein’ (FMP). Bicarbonate served as an initiator as well as a stabilizer of FM and its action was not dependent on FMP. FMP can induce FM in the caput-sperm, but it is not essential for sperm motility initiation. Alteration of the medium pH from 6.60 to 8.00 caused a marked increase in the EP or bicarbonate-dependent sperm FM initiation, as well as intrasperm pH. At the physio-logical pH, bicarbonate served as a much more potent motility activator than FMP, although both the motility promoters showed maximal efficacy at alkaline pH (~7.8). EP as well as bicarbonate elevated the intrasperm cyclic AMP level. Unlike EP, bicarbonate is capable of increasing intrasperm pH. The intrasperm pH increased from 6.54 0.02 to 6.77 0.03 during sperm transit from caput to cauda. The data are con-sistent with the view that FMP activates sperm forward motility by enhancing the intrasperm cyclic AMP level and that extracellular bicarbonate and pH play a vital role in the initiation of sperm FM during the epi-didymal transit.

scholarly journals Cross-talk between glucagon- and adenosine-mediated signalling systems in rat hepatocytes: effects on cyclic AMP-phosphodiesterase activity

1995 ◽  
Vol 312 (3) ◽  
pp. 763-767 ◽  
Author(s):  
M Robles-Flores ◽  
G Allende ◽  
E Piña ◽  
J A García-Sáinz
Keyword(s):  
Cyclic Amp ◽  
Pertussis Toxin ◽  
Plasma Membranes ◽  
Rat Hepatocytes ◽  
Dependent Manner ◽  
Phosphodiesterase Activity ◽  
Cyclic Amp Phosphodiesterase ◽  
Cyclic Amp Accumulation ◽  
A1 Adenosine Receptors ◽  
Dose Dependent

The effect of adenosine analogues on glucagon-stimulated cyclic AMP accumulation in rat hepatocytes was explored. N6-Cyclopentyladenosine (CPA), 5′-N-ethylcarboxamidoadenosine and N6-(R-phenylisopropyl)adenosine inhibited in a dose-dependent manner the cyclic AMP accumulation induced by glucagon. This effect seems to be mediated through A1 adenosine receptors. Pertussis toxin completely abolished the effect of CPA on glucagon-stimulated cyclic AMP accumulation in whole cells which suggested that a pertussis-toxin-sensitive G-protein was involved. On the other hand, this action of adenosine analogues on glucagon-induced cyclic AMP accumulation was reverted by the selective low-Km cyclic AMP-phosphodiesterase inhibitor Ro 20-1724. Analysis of cyclic AMP-phosphodiesterase activity in purified hepatocyte plasma membranes showed that glucagon in the presence of GTP inhibited basal PDE activity by 45% and that CPA reverted this inhibition in dose-dependent manner. In membranes derived from pertussis-toxin-treated rats, we observed no inhibition of cyclic AMP-phosphodiesterase activity by glucagon in the absence or presence of CPA. Our results indicate that in hepatocyte plasma membranes, stimulation of adenylate cyclase activity and inhibition of a low-Km cyclic AMP phosphodiesterase activity are co-ordinately regulated by glucagon, and that A1 adenosine receptors can inhibit glucagon-stimulated cyclic AMP accumulation by blocking glucagon's effect on phosphodiesterase activity.

Characteristics of Action of Prostaglandins on Cyclic AMP Accumulation in Rat Anterior Pituitary Gland

1975 ◽  
Vol 53 (4) ◽  
pp. 455-460 ◽  
Author(s):  
Pierre Borgeat ◽  
Fernand Labrie ◽  
Pierre Garneau
Keyword(s):  
Cyclic Amp ◽  
Pituitary Gland ◽  
Incubation Medium ◽  
Anterior Pituitary ◽  
Complete Removal ◽  
Anterior Pituitary Gland ◽  
Pituitary Hormone ◽  
Maximal Effect ◽  
Cyclic Amp Accumulation

Prostaglandins (PGs) were found to lead to a marked stimulation of cyclic AMP accumulation in rat anterior pituitary gland in vitro in the following decreasing order of potency: [Formula: see text]. The effect of PGs is potentiated by theophylline. The stimulatory effect of PGs on cyclic AMP accumulation is already detected 2 min after the addition of 1 × 10−7 to 1 × 10−6 M PG E2 and its maximal effect is reached after approximately 30 min of incubation, with a progressive decrease toward basal cyclic AMP levels at later time intervals. Increased intracellular cyclic AMP concentrations are accompanied by an increased release of the nucleotide into the incubation medium. Complete removal of Ca2+ from the incubation medium by addition of EGTA was found to increase the stimulatory effect of PG E2 on cyclic AMP accumulation. The action of PGs on hormonal release and cyclic AMP accumulation support the hypothesis of a role of PGs in the mechanism of anterior pituitary hormone (particularly growth hormone) release.

scholarly journals Rainbow trout hypocalcin stimulates bone resorption in embryonic mouse calvaria in vitro in a PTH-like fashion

1989 ◽  
Vol 143 (1) ◽  
pp. 165-175
Author(s):  
F. P. Lafeber ◽  
M. P. Herrmann-Erlee ◽  
G. Flik ◽  
S. E. Wendelaar Bonga
Keyword(s):  
Bone Resorption ◽  
Cyclic Amp ◽  
Tertiary Structure ◽  
Lactate Production ◽  
Dependent Manner ◽  
Embryonic Mouse ◽  
Molar Basis ◽  
Mouse Calvaria ◽  
Dose Dependent

Hypocalcin, the major hormone with hypocalcaemic action in fish, was isolated from trout corpuscles of Stannius (SCs). The bioactivity of hypocalcin was assessed in a parathyroid hormone (PTH) bioassay involving bone resorption in embryonic mouse calvaria. Calcium and phosphate release and lactate production were stimulated in a dose-dependent manner by hypocalcin. On a molar basis about equal amounts of hypocalcin and PTH were required to obtain similar effects in this assay. Hypocalcin did not stimulate cyclic AMP production either in mouse calvaria or in cultured osteoblasts. In this respect hypocalcin resembles shortened or N-terminus-modified PTH molecules that induce bone resorption without increasing cyclic AMP levels. Since hypocalcin and PTH have comparable bioactivity in this mammalian bioassay (as well as in fish bioassays), we tentatively suggest that both hormones are structurally similar and that both hormones may act via the same receptors. The two hormones show no resemblance to one another in primary structure, so we suggest that they have similarities in tertiary structure.

Serotonin enhances oestradiol production by hamster preovulatory follicles in vitro: effects of experimentally induced atresia

1990 ◽  
Vol 125 (3) ◽  
pp. 433-438 ◽  
Author(s):  
P. F. Terranova ◽  
J. Th. J. Uilenbroek ◽  
L. Saville ◽  
D. Horst ◽  
Y. Nakamura
Keyword(s):  
Cyclic Amp ◽  
Dependent Manner ◽  
Glucose Medium ◽  
Preovulatory Follicles ◽  
In Vitro Effects ◽  
Dose Dependent ◽  
Oestradiol Production

ABSTRACT Preovulatory follicles from adult hamsters on the morning of pro-oestrus were used in this study. Serotonin stimulated oestradiol production by preovulatory follicles during a 5-h incubation in 1 ml Krebs–Ringer bicarbonate glucose medium containing isobutylmethylxanthine (0.1 mmol/l; IBMX) and androstenedione (1 μmol/l). The enhanced oestradiol production by serotonin was dependent on the dose of IBMX and androstenedione. Mianserin, a serotonin type-1 and serotonin type-2 receptor antagonists, prevented the serotonin-enhanced oestradiol production in a dose-dependent manner. Ketanserin, a specific serotonin type-2 receptor antagonist, was ineffective in blocking the action of serotonin, indicating that the effect of serotonin was mediated by the serotonin type-1 receptor. In the presence of androstenedione (1 μmol/l), serotonin was unable to enhance oestradiol production in isolated granulosa cells. It was also unable to enhance oestradiol production in early atretic follicles; atresia was induced experimentally by an injection of phenobarbital in order to prevent ovulation. The data indicate that serotonin stimulates oestradiol production by hamster preovulatory follicles in vitro. The mechanism of action of serotonin involves an intact healthy follicle, a serotonin type-1 receptor and possibly cyclic AMP. The increased oestradiol secretion might be related to increased androgen production by the follicle and increased permeability (leakiness) of the follicle to androstenedione which serves as substrate for aromatization to oestradiol by the granulosa cell. Journal of Endocrinology (1990) 125, 433–438

scholarly journals Use of forskolin to study the relationship between cyclic AMP formation and bone resorption in vitro

1986 ◽  
Vol 240 (2) ◽  
pp. 529-539 ◽  
Author(s):  
U H Lerner ◽  
B B Fredholm ◽  
M Ransjö
Keyword(s):  
Bone Resorption ◽  
Cyclic Amp ◽  
Phosphodiesterase Inhibitor ◽  
Inhibitory Effect ◽  
Cyclic Amp Accumulation ◽  
The Relationship ◽  
Dose Dependent ◽  
Old Mice ◽  
45Ca Release

The effect of the adenylate cyclase activator forskolin on bone resorption and cyclic AMP accumulation was studied in an organ-culture system by using calvarial bones from 6-7-day-old mice. Forskolin caused a rapid and fully reversible increase of cyclic AMP, which was maximal after 20-30 min. The phosphodiesterase inhibitor rolipram (30 mumol/l), enhanced the cyclic AMP response to forskolin (50 mumol/l) from a net cyclic AMP response of 1234 +/- 154 pmol/bone to 2854 +/- 193 pmol/bone (mean +/- S.E.M., n = 4). The cyclic AMP level in bones treated with forskolin (30 mumol/l) was significantly increased after 24 h of culture. Forskolin, at and above 0.3 mumol/l, in the absence and the presence of rolipram (30 mumol/l), caused a dose-dependent cyclic AMP accumulation with an calculated EC50 (concentration producing half-maximal stimulation) value at 8.3 mumol/l. In 24 h cultures forskolin inhibited spontaneous and PTH (parathyroid hormone)-stimulated 45Ca release with calculated IC50 (concentration producing half-maximal inhibition) values at 1.6 and 0.6 mumol/l respectively. Forskolin significantly inhibited the release of 3H from [3H]proline-labelled bones stimulated by PTH (10 nmol/l). The inhibitory effect by forskolin on PTH-stimulated 45Ca release was significant already after 3 h of culture. In 24 h cultures forskolin (3 mumol/l) significantly inhibited 45Ca release also from bones stimulated by prostaglandin E2 (1 mumol/l) and 1 alpha-hydroxycholecalciferol (0.1 mumol/l). The inhibitory effect of forskolin on spontaneous and PTH-stimulated 45Ca release was transient. A dose-dependent stimulation of basal 45Ca release was seen in 120 h cultures, at and above 3 nmol of forskolin/l, with a calculated EC50 value at 16 nmol/l. The stimulatory effect of forskolin (1 mumol/l) could be inhibited by calcitonin (0.1 unit/ml), but was insensitive to indomethacin (1 mumol/l). Forskolin increased the release of 3H from [3H]proline-labelled bones cultured for 120 h and decreased the amount of hydroxyproline in bones after culture. Forskolin inhibited PTH-stimulated release of Ca2+, Pi, beta-glucuronidase and beta-N-acetylglucosaminidase in 24 h cultures. In 120 h cultures forskolin stimulated the basal release of minerals and lysosomal enzymes.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Thyrotropin-stimulated recruitment of free monoribosomes on to membrane-bound thyroglobulin-synthesizing polyribosomes

1978 ◽  
Vol 172 (2) ◽  
pp. 227-231 ◽  
Author(s):  
E Davies ◽  
J E Dumont ◽  
G Vassart
Keyword(s):  
Cyclic Amp ◽  
Dibutyryl Cyclic Amp ◽  
Concomitant Increase ◽  
Initial Effect ◽  
Membrane Bound

Treatment of ox and dog thyroid slices in vitro with either thyrotropin or dibutyryl cyclic AMP elicited a variety of changes in polyribosome distribution. The most marked and consistent responses were decreases in both free and membrane-bound monoribosomes with a concomitant increase in the specific peak of thyroglobulin-synthesizing polyribosomes. On some occasions there was a shift towards heavier aggregates in the free polyribosomes. The increase in the amount of thyroglobulin-synthesizing polyribosomes was not accompanied by a shift in its location on the gradients. These changes were apparent within 30 min of thyrotropin addition and within 60 min of the addition of dibutyryl cyclic AMP. It is suggested that the major initial effect on translation of both thyrotropin and dibutyryl cyclic AMP is to stimulate the recruitment of pre-existing free monoribosomes on to pre-existing unloaded or under-loaded thyroglobulin mRNA molecules.

scholarly journals Effects of verapamil on lipolysis due to dibutyryl cyclic AMP

1984 ◽  
Vol 220 (1) ◽  
pp. 321-324 ◽  
Author(s):  
H Goko ◽  
S Takashima ◽  
S Shimizu ◽  
S Kagawa ◽  
A Matsuoka
Keyword(s):  
Cyclic Amp ◽  
Adrenergic Receptors ◽  
Inhibitory Effect ◽  
Dependent Manner ◽  
Dibutyryl Cyclic Amp ◽  
Alpha Adrenergic Receptors ◽  
Biphasic Effect ◽  
Adrenergic Antagonists ◽  
Dose Dependent ◽  
Isolated Rat

The effects of verapamil, a calcium antagonist, on lipolysis in isolated rat adipocytes were studied. Verapamil (100 microM) potentiated lipolysis due to dibutyryl cyclic AMP (Bt2cAMP) at submaximal concentrations, with or without extracellular Ca2+. Lipolysis due to 0.5 mM-Bt2cAMP was potentiated by verapamil in a dose-dependent manner up to 200 microM, whereas at concentrations higher than 100 microM the stimulatory effect of verapamil was progressively diminished with or without extracellular Ca2+. Verapamil showed only an inhibitory effect on lipolysis due to adrenaline (0.1-10 microM) or 3-isobutyl-1-methylxanthine (IBMX; 25-200 microM). The stimulatory effect of verapamil on lipolysis due to Bt2cAMP was not blocked by alpha-adrenergic antagonists. These results suggest (i) that verapamil has a biphasic effect on lipolysis due to Bt2cAMP and only an inhibitory effect on that due to adrenaline or IBMX, and (ii) that extracellular Ca2+ or alpha-adrenergic receptors are not involved in the action of verapamil.

Inhibition of aromatase activity in rat Sertoli cells by thyroid hormone

1994 ◽  
Vol 140 (3) ◽  
pp. 431-436 ◽  
Author(s):  
S Ulisse ◽  
E A Jannini ◽  
E Carosa ◽  
D Piersanti ◽  
F M Graziano ◽  
...  
Keyword(s):  
Thyroid Hormone ◽  
Cyclic Amp ◽  
Sertoli Cells ◽  
Inhibitory Effect ◽  
Aromatase Activity ◽  
Dependent Manner ◽  
Maximal Dose ◽  
Cyclic Amp Accumulation ◽  
Order Of Magnitude ◽  
Dose Dependent

Abstract Basal and FSH-induced aromatase activity in prepubertal rat Sertoli cells was inhibited by l-tri-iodothyronine (T3) in a time- and dose-dependent manner. The effect was evident only after 6 h of preincubation with T3 (10−7 m) and the half-maximal dose was 0·5 ±0·2 nm, which correlated with the Kd of the nuclear T3 receptor of rat Sertoli cells (Kd=1–2 nm). The effect was specific as judged by the lack of effect of the T3 analogue 3-iodo-l-thyrosine. The inhibitory effect of T3 was present over the entire range of FSH concentrations used (0·001–100 ng/ml). In T3-treated Sertoli cells, aromatase activity induced by 8-bromo-cyclic AMP was inhibited by the same order of magnitude as that of FSH, thus suggesting that the inhibitory effect of T3 was downstream from cyclic AMP formation. Furthermore, pretreatment of Sertoli cells cultures with T3 (24 h, 10−7 m) did not affect basal or FSH-induced extracellular cyclic AMP accumulation. This effect of T3 on rat Sertoli cell aromatase activity may be regarded as a part of the integrated mechanism by which thyroid hormone modulates the functions of the seminiferous epithelium. Journal of Endocrinology (1994) 140, 431–436

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