Somatostatin partially reverses desensitization of somatotrophs induced by growth hormone-releasing factor

1987 ◽  
Vol 112 (1) ◽  
pp. 69-76 ◽  
Author(s):  
R. N. Clayton ◽  
L. C. Bailey
Keyword(s):  
Primary Cultures ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Release Mechanism ◽  
Ionophore A23187 ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Response Curves

ABSTRACT The effect of somatostatin on GH-releasing factor (GRF)-induced desensitization of somatotrophs was studied in vitro. Primary cultures of rat anterior pituitary cells pretreated for 4 or 18 h with GRF(1–40) (100 nmol/l) showed a 50% or greater reduction in maximal GH release when rechallenged with 10 nmol GRF/l. Rechallenge GRF dose–response curves were either very flat, making accurate measurement of the dose giving 50% maximum stimulation (ED50) impossible, or the ED50 concentration was increased from 0·3 nmol/l (untreated) to 2 nmol/l (GRF pretreated). Although GRF pretreatment reduced cellular GH content by 40–50%, correction for this did not restore GRF responsiveness measured in terms of maximal GRF-stimulated/unstimulated GH release (maximal/basal ratio), or the GRF ED50 concentration. Maximal/basal GH release per 4 h from GRF-pretreated cells was reduced when cells were rechallenged with forskolin (5 μmol/l) or calcium ionophore (A23187; 10 μmol/l), to the same extent as when rechallenged with 10 nmol GRF/l. Although this might be explained by a reduction in the pool of releasable GH, an alternative explanation is that pretreatment with GRF disrupts the GH release mechanism(s) at a common step(s) beyond cyclic AMP generation and Ca2+ influx. Co-incubation of cells with somatostatin and GRF (100 nmol/l) partially reversed the desensitizing action of GRF during both 4- and 18-h pretreatments in a dose-dependent manner, with 1 μmol somatostatin/l being most effective. Maximal GRF (100 nmol/l)-stimulated/basal GH release was 4·4 ± 1·0 (mean ± s.e.m., n = four experiments), 1·55 ± 0·09 and 2·43 ± 0·1 for control, GRF-pretreated (4 h) and GRF plus somatostatin-pretreated cells respectively. Comparable values for cells pretreated for 18 h were 3·66 ± 0·44 (n = three experiments), 1·78 ± 0·28 and 3·04 ± 0·04 for control, GRF- and GRF plus somatostatin-pretreated cells. Somatostatin reduced the 50% depletion of cellular GH caused by GRF pretreatment to 15–20%, as well as attenuating GH released during the pretreatment period by 40 ± 5% (mean ± s.e.m., n = seven experiments). Somatostatin restored somatotroph sensitivity of GRF-desensitized cells indicating that, in addition to reversing depletion of the releasable pool of GH, the counter-regulatory hormone also prevents disruption of post-receptor cellular biochemical events which remain to be identified. These results add to the list of GRF actions inhibited by somatostatin and suggest a potentially important role for somatostatin in vivo to maintain somatotroph responsiveness to GRF. J. Endocr. (1987) 112, 69–76

scholarly journals Tulathromycin Exerts Proresolving Effects in Bovine Neutrophils by Inhibiting Phospholipases and Altering Leukotriene B4, Prostaglandin E2, and Lipoxin A4Production

2014 ◽  
Vol 58 (8) ◽  
pp. 4298-4307 ◽  
Author(s):  
Carrie D. Fischer ◽  
Stephanie C. Duquette ◽  
Bernard S. Renaux ◽  
Troy D. Feener ◽  
Douglas W. Morck ◽  
...  
Keyword(s):  
Calcium Ionophore ◽  
Leukotriene B4 ◽  
Calcium Ionophore A23187 ◽  
Lipid Signaling ◽  
Prostaglandin E ◽  
Ionophore A23187 ◽  
Proinflammatory Mediators ◽  
Bovine Neutrophils

ABSTRACTThe accumulation of neutrophils and proinflammatory mediators, such as leukotriene B4(LTB4), is a classic marker of inflammatory disease. The clearance of apoptotic neutrophils, inhibition of proinflammatory signaling, and production of proresolving lipids (including lipoxins, such as lipoxin A4[LXA4]) are imperative for resolving inflammation. Tulathromycin (TUL), a macrolide used to treat bovine respiratory disease, confers immunomodulatory benefits via mechanisms that remain unclear. We recently reported the anti-inflammatory properties of TUL in bovine phagocytesin vitroand inMannheimia haemolytica-challenged calves. The findings demonstrated that this system offers a powerful model for investigating novel mechanisms of pharmacological immunomodulation. In the present study, we examined the effects of TUL in a nonbacterial model of pulmonary inflammationin vivoand characterized its effects on lipid signaling. In bronchoalveolar lavage (BAL) fluid samples from calves challenged with zymosan particles (50 mg), treatment with TUL (2.5 mg/kg of body weight) significantly reduced pulmonary levels of LTB4and prostaglandin E2(PGE2). In calcium ionophore (A23187)-stimulated bovine neutrophils, TUL inhibited phospholipase D (PLD), cytosolic phospholipase A2(PLA2) activity, and the release of LTB4. In contrast, TUL promoted the secretion of LXA4in resting and A23187-stimulated neutrophils, while levels of its precursor, 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], were significantly lower. These findings indicate that TUL directly modulates lipid signaling by inhibiting the production of proinflammatory eicosanoids and promoting the production of proresolving lipoxins.

Effects of crude and highly purified bovine inhibin (Mr 32 000 form) on gonadotrophin production by ovine pituitary cells in vitro: inhibin enhances gonadotrophin-releasing hormone-induced release of LH

1990 ◽  
Vol 127 (1) ◽  
pp. 149-159 ◽  
Author(s):  
S. Muttukrishna ◽  
P. G. Knight
Keyword(s):  
Primary Cultures ◽  
Suppressive Effect ◽  
Pituitary Cells ◽  
Dependent Manner ◽  
Α Subunit ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone

ABSTRACT Primary cultures of ovine pituitary cells (from adult ewes) were used to investigate the actions of steroid-free bovine follicular fluid (bFF) and highly-purified Mr 32 000 bovine inhibin on basal and gonadotrophin-releasing hormone (GnRH)-induced release of FSH and LH. Residual cellular contents of each hormone were also determined allowing total gonadotrophin content/well to be calculated. As in rats, both crude and highly purified inhibin preparations promoted a dose (P < 0·001)- and time (P < 0·001)-dependent suppression of basal and GnRH-induced release of FSH as well as an inhibition of FSH synthesis, reflected by a fall in total FSH content/well. However, while neither inhibin preparation affected basal release of LH or total LH content/well, GnRH-induced LH release was significantly (P< 0·001) increased by the presence of either bFF (+ 75%) or highly-purified inhibin (+ 64%) in a dose- and time-dependent manner. This unexpected action of bFF on GnRH-induced LH release was abolished in the presence of 5 μl specific anti-inhibin serum, confirming that the response was indeed mediated by inhibin. Furthermore, neither oestradiol-17β (1 pmol/l–10 nmol/l) nor monomeric α-subunit of bovine inhibin (2·5–40 ng/ml) significantly affected basal or GnRH-induced release of LH. These in-vitro findings for the ewe lend support to a number of recent in-vivo observations and indicate that, in addition to its well-documented suppressive effect on the synthesis and secretion of FSH, inhibin may actually facilitate LH release in this species, in marked contrast to its action in the rat. Journal of Endocrinology (1990) 127, 149–159

Calcium-translocating and cardiotonic properties of oxidation products of linoleic acid

1985 ◽  
Vol 63 (11) ◽  
pp. 1392-1397 ◽  
Author(s):  
Ryungsoon Song Kim ◽  
Ivan Bihler ◽  
Frank S. LaBella
Keyword(s):  
Linoleic Acid ◽  
Calcium Ionophore ◽  
Physiological Role ◽  
Calcium Ionophore A23187 ◽  
Oxidation Products ◽  
Ionophore A23187 ◽  
Guinea Pig Heart ◽  
Adrenergic Antagonist

Calcium-translocating activity of linoleic acid and its lipoxygenase (linoleate: oxygen oxidoreductase; EC 1.13.11.12) metabolites or autoxidation products was determined in vitro by estimation of 45Ca transport from a bulk aqueous to a bulk organic phase. Fresh commercial linoleic acid, tested immediately after removal from a sealed vial, stimulated calcium translocation only at concentrations greater than 1 mM. In contrast, 45Ca translocation by linoleic acid exposed to air was detectable at 10 μM. Oxidation products of linoleic acid obtained either by incubation with lipoxygenase or by autoxidation were much less potent than the calcium ionophore A23187. The products obtained by enzymic oxidation of linoleic acid enhanced contractility in the Langendorff-perfused guinea pig heart up to 45% over control (at 3 × 10−8 M). The inotropic response was transient with rapid onset and not affected by the beta-adrenergic antagonist, propranolol. The autoxidation products of linoleic acid increased cardiac contractility up to 43% at 10−6 M. In contrast, fresh linoleic acid caused only a negative inotropic effect at 10−8 to 3 × 10−7 M, progressing to contracture at 10−6 M. These findings suggest that conflicting reports on the cardiostimulant effect of linoleic acid may be due to varying levels of the autoxidation products. Linoleic acid metabolites in vivo may have a physiological role in myocardial function related to their Ca2+-ionophoric activity.

L-arginine restores endothelium-dependent relaxation in pulmonary circulation of chronically hypoxic rats

1992 ◽  
Vol 263 (2) ◽  
pp. L194-L200 ◽  
Author(s):  
S. Eddahibi ◽  
S. Adnot ◽  
C. Carville ◽  
Y. Blouquit ◽  
B. Raffestin
Keyword(s):  
Vascular Tone ◽  
Pressor Response ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Relaxing Factor ◽  
Isolated Lungs ◽  
Endothelium Dependent Relaxation

We investigated whether loss of endothelial-derived relaxing factor (EDRF) activity in the pulmonary vessels of chronically hypoxic rats could be restored by pretreatment with L-arginine. We measured vasodilation to acetylcholine (ACh), calcium ionophore A23187, or linsidomine (Sin-1) under conditions of increased vascular tone induced by U-46619 (50 pmol/min), as well as vasoconstriction to endothelin-1 (ET) in isolated lungs pretreated with meclofenamate (3 microM). In lungs from normoxic (N) rats, in vitro L- or D-arginine (10(-3) M) did not alter vasodilation to the endothelium-dependent agents ACh (10(-9)-10(-6) M) and A23187 (10(-9)-10(-7) M), but NG-monomethyl-L-arginine (10(-3) M) completely abolished it. In lungs from rats exposed to 3 wk of hypoxia (H), vasodilation to ACh or A23187 was fully restored after in vitro L-arginine (10(-3) M) or N alpha-benzoyl-L-arginine (5 x 10(-5) M) but remained abolished after D-arginine, L-citrulline, L-ornithine, or L-argininosuccinic acid. In vivo pretreatment of H rats with L-arginine (300 mg/kg iv) 30 min before isolating the lung also restored vasodilation to A23187. Vasodilation to the endothelium-independent agent Sin-1 was similar in both groups of lungs and was not altered by in vitro L-arginine. L-arginine attenuated the increased pressor response to ET (300 pmol) of H rat lungs but had no effect in N rats. Our results demonstrate that loss of EDRF activity associated with hypoxic pulmonary hypertension may be reversed by supplying L-arginine.

scholarly journals A neurotransmitter role for red-pigment-concentrating hormone in ovarian maturation in the red swamp crayfish Procambarus clarkii

1995 ◽  
Vol 198 (6) ◽  
pp. 1253-1257 ◽  
Author(s):  
R Sarojini ◽  
R Nagabhushanam ◽  
M Fingerman
Keyword(s):  
Procambarus Clarkii ◽  
Calcium Ionophore ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Ovarian Maturation ◽  
Red Pigment ◽  
In Vitro Techniques ◽  
Red Swamp Crayfish

The influence of red-pigment-concentrating hormone (RPCH) on ovarian maturation in the red swamp crayfish Procambarus clarkii was studied using both in vivo and in vitro techniques. In vivo, RPCH stimulated ovarian maturation. However, RPCH did not affect the ovary in vitro when only RPCH, muscle and ovarian explants were used. But when RPCH, thoracic ganglia, which are known to contain gonad-stimulating hormone-like (GSH-like) activity, and ovarian explants were incubated together, significant ovarian maturation ensued. The calcium ionophore A23187 mimicked RPCH both in vivo and in vitro. These results provide evidence to support the hypothesis that RPCH has a role as a neurotransmitter in Procambarus clarkii to stimulate GSH release, with calcium acting as a second messenger for RPCH.

scholarly journals Prolactin (PRL)-Releasing Peptide Stimulates PRL Secretion from Human Fetal Pituitary Cultures and Growth Hormone Release from Cultured Pituitary Adenomas1

2001 ◽  
Vol 86 (6) ◽  
pp. 2826-2830 ◽  
Author(s):  
Tami Rubinek ◽  
Moshe Hadani ◽  
Gad Barkai ◽  
Shlomo Melmed ◽  
Ilan Shimon
Keyword(s):  
Primary Cultures ◽  
Pituitary Hormones ◽  
Pituitary Cells ◽  
Maximal Effect ◽  
Dependent Manner ◽  
Human Pituitary ◽  
Cell Adenoma ◽  
In Vitro Effects

The hypothalamic peptide PRL-releasing peptide (PrRP) has recently been cloned and identified as a ligand of an orphan pituitary receptor that stimulates in vitro PRL secretion. PrRP also induces PRL release in rats in vivo, especially in normal cycling females. However, no information on the effects of PrRP in the human is available. To elucidate the role of PrRP in regulating human anterior pituitary hormones, we used human PrRP-31 in primary cultures of human pituitary tissues, including fetal (20–27 weeks gestation) and normal adult pituitaries, as well as PRL- and GH-secreting adenomas. PrRP increased PRL secretion from human fetal pituitary cultures in a dose-dependent manner by up to 35% (maximal effect achieved with 10 nm), whereas TRH was slightly more potent for PRL release. Coincubation with estradiol resulted in enhanced fetal PRL response to PrRP, and GH release was only increased in the presence of estradiol. Although PRL secretion from PRL-cell adenomas was not affected by PrRP, PrRP induced PRL release from cultures of a GH-cell adenoma that cosecreted PRL. PrRP enhanced GH release in several GH-secreting adenomas studied by 25–27%, including GH stimulation in a mixed PRL-GH-cell tumor. These results show for the first time direct in vitro effects of PrRP-31 on human pituitary cells. PrRP is less potent than TRH in releasing PRL from human fetal lactotrophs and is unable to release PRL from PRL-cell adenomas in culture, but stimulated GH from several somatotroph adenomas. Thus, PrRP may participate in regulating GH, in addition to PRL, in the human pituitary.

Effects of prostaglandin F2α and other potential secretagogues on oxytocin secretion and second messenger metabolism in the ovine corpus luteum in vitro

1990 ◽  
Vol 126 (1) ◽  
pp. 89-98 ◽  
Author(s):  
T. J. McCann ◽  
A. P. F. Flint
Keyword(s):  
Arachidonic Acid ◽  
Lactate Dehydrogenase ◽  
Calcium Ionophore ◽  
Prostaglandin F2α ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Lactate Dehydrogenase Release ◽  
Intracellular Ca

ABSTRACT Release of oxytocin by sliced or minced sheep luteal tissue in vitro was stimulated up to 1·6- and 2·3-fold by arachidonic acid and the calcium ionophore A23187 respectively. Prostaglandin (PG) F2α and the PGF2α analogue cloprostenol, and other potential agonists known to be active in vivo, including noradrenaline and acetylcholine, were ineffective, as was the phorbol ester tetradecanoylphorbol acetate (TPA). The ineffectiveness of PGF2α was not due to a general unresponsiveness of the tissue in vitro, as PGF2α reduced LH stimulation of tissue concentrations of cyclic AMP and activated inositol lipid hydrolysis. The effect of arachidonic acid was accompanied by release from the tissue of the cytosolic enzyme lactate dehydrogenase (at arachidonic acid concentrations below those required to release oxytocin) and its effect on oxytocin and lactate dehydrogenase release was mimicked by oleic and linolenic acids; arachidonic acid was concluded to act by a non-physiological physicochemical effect without conversion to an eicosanoid. As PGF2α in vitro is known to raise intracellular Ca2+ concentrations in the large luteal cells that secrete oxytocin, and as A23187 stimulates oxytocin release in vitro in the presence and absence of TPA, it is concluded that in-vitro incubation results in an artifactual blockade of the oxytocin-releasing action of PGF2α at an unidentified point distal to the effect on intracellular Ca2+. Journal of Endocrinology (1990) 126, 89–98

Inhibition of Human Platelet Functions by Verapamil

1981 ◽  
Vol 45 (02) ◽  
pp. 158-161 ◽  
Author(s):  
Y Ikeda ◽  
M Kikuchi ◽  
K Toyama ◽  
K Watanabe ◽  
Y Ando
Keyword(s):  
Platelet Aggregation ◽  
Calcium Ionophore ◽  
Serotonin Release ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Dependent Inhibition ◽  
Platelet Functions

SummaryThe effects of verapamil, a coronary vasodilator, on platelet functions were studied.Platelet aggregation induced by ADP, epinephrine or collagen was inhibited by verapamil in vitro. Calcium ionophore A23187-induced platelet aggregation was also inhibited by verapamil in a concentration dependent manner. In washed platelets, verapamil caused a dose-dependent inhibition of serotonin release induced either by thrombin or A23187 in the absence of extracellular calcium. Addition of 1 mM CaCl2 with A23187 or thrombin partially overcame this inhibition. Addition of 1 mM CaCl2 in the absence of verapamil had no effect on thrombin- or A23187-induced secretion. When verapamil was administered to the healthy volunteers at the dosage commonly used, inhibition of platelet aggregation was observed 2 hrs after the drug ingestion. It is of great interest that verapamil potentiated the anti-aggregating activity of prostacyclin in vitro.Our results may suggest a potential role for verapamil in the treatment of thrombotic disorders.

scholarly journals Calcium/Calmodulin Regulates Ubiquitination of the Ubiquitin-specific Protease TRE17/USP6

2005 ◽  
Vol 280 (43) ◽  
pp. 35967-35973 ◽  
Author(s):  
Chuanlu Shen ◽  
Ying Ye ◽  
Sarah E. Robertson ◽  
Alan W. Lau ◽  
Don-On D. Mak ◽  
...  
Keyword(s):  
Point Mutations ◽  
Calcium Ionophore ◽  
Rab Gtpase ◽  
Ionophore A23187 ◽  
Dependent Manner ◽  
C Terminus ◽  
Specific Protease ◽  
Ubiquitin Specific Protease

The TRE17 (USP6/TRE-2) oncogene induces tumorigenesis in both humans and mice. However, little is known regarding its regulation or mechanism of transformation. TRE17 encodes a TBC (Tre-2/Bub2/Cdc16)/Rab GTPase-activating protein homology domain at its N terminus and a ubiquitin-specific protease at its C terminus. In the current study, we identified the ubiquitous calcium (Ca2+)-binding protein calmodulin (CaM) as a novel binding partner for TRE17. CaM bound directly to TRE17 in a Ca2+-dependent manner both in vitro and in vivo. The CaM-binding site was mapped to two hydrophobic motifs near the C terminus of the TBC domain. Point mutations within these motifs significantly reduced the interaction of TRE17 with CaM. We further found that TRE17 is monoubiquitinated and promotes its own deubiquitination in vivo. CaM binding-deficient mutants of TRE17 exhibited significantly reduced monoubiquitination, suggesting that binding of Ca2+/CaM to TRE17 promotes this modification. Consistent with this notion, treatment of cells with the CaM inhibitor W7 reduced levels of TRE17 monoubiquitination. Interestingly, the calcium ionophore A23187 induced accumulation of a polyubiquitinated TRE17 species. The effect of A23187 was attenuated in CaM binding-deficient mutants of TRE17. Taken together, these studies indicate a role for Ca2+/CaM in regulating ubiquitination through direct interaction with TRE17.

205 CAPACITATION OF STALLION SPERMATOZOA EVALUATED BY FERTILIZATION OF BOVINE OOCYTES

2008 ◽  
Vol 20 (1) ◽  
pp. 181
Author(s):  
M. R. Hudson ◽  
G. E. Seidel Jr ◽  
E. L. Squires ◽  
B. E. Spizzirri ◽  
D. J. Walker ◽  
...  
Keyword(s):  
Calcium Ionophore ◽  
Cumulus Cells ◽  
Calcium Ionophore A23187 ◽  
Ionophore A23187 ◽  
Dependent Manner ◽  
Cell Stage ◽  
Vitro Fertilization ◽  
Cell Divisions ◽  
Bovine Oocytes

In vitro fertilization in the horse does not work reliably. Several methods of capacitating sperm in other species fail in the horse. The goal of this experiment was to develop a method to capacitate equine spermatozoa using calcium ionophore A23187 or phosphatidylcholine 12 (PC12). We also studied effects of maturing bovine oocytes for 24 or 28 h on fertilizability by capacitated equine sperm, hypothesizing that longer maturation would yield oocytes more easily fertilized by equine spermatozoa. Two sets of bovine oocytes were aspirated from 3 to 8 mm follicles of abattoir ovaries 4 h apart, but fertilized at the same time. On the day of fertilization, semen from 1 of 3 stallions was collected, evaluated, and centrifuged through 33% Percoll to remove seminal plasma. The resultant pellet was extended to 5 × 107 cells mL–1 in M199 containing 0.6% BSA, 2 mm caffeine, and 5 mm CaCl2. Sperm were treated with A23187 (1 or 3 μm) or PC12 (40 or 70 μm) or both A23187 and PC12 (1 μm/40 μm) in 500- μL aliquots. Sperm were incubated at 39°C for 10 min (for A23187 and combination treatments) or 15 min (for PC12 treatments), and then diluted 1:20 for fertilization. Oocytes from each maturation time were fertilized using the same semen preparation for each treatment. Oocytes and sperm were incubated together for 18 h in FCDM in 5% CO2 at 39°C (De La Torre-Sanchez et al. 2006 Reprod. Fertil. Devel. 18, 585–596). Presumptive zygotes were cultured for 30 h in CDM-1, vortexed to remove cumulus cells, and evaluated for cleavage. Oocytes were also co-incubated with killed sperm to determine the level of parthenogenesis. Cleaved embryos were stained with orcein to ensure that each cell had a nucleus. Number of cell divisions were recorded as 0 for a 1-cell, 1 for a 2-cell, 1.5 for a 3-cell, etc. More oocytes cleaved after 28 h (18%) than 24 h (14%) maturation (P < 0.01). Sperm of Stallion 1 resulted in higher overall cleavage (24%) than Stallions 2 or 3 (11 and 12%; P < 0.01). Highest cleavage was seen with 28 h maturation and 70 μm PC12 and 3 μm A23187 (27 and 24%, respectively). The most cell divisions were seen with 28 h maturation and 70 μm PC12 (0.48); 28 of the 49 cleaved in this treatment reached ≥4-cell stage. In conclusion, both A23187 and PC12 were able to capacitate equine sperm in a dose-dependent manner as determined from cleavage of bovine oocytes matured for 28 h; maturation for the conventional 24 h was an inferior model for this purpose. Table 1. Mean responses of bovine oocytes fertilized by equine sperm

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