Nitric oxide donors modify free intracellular calcium levels in rat anterior pituitary cells

Argentinean Society of Experimental Pharmacology: Brief history and main scientific contributions to the discipline

Argentina Biomedical Science has been historically strong. The development of Human and Veterinary Pharmacology in our country as a pivotal discipline has been acknowledged worldwide because of the quality of its contributions. Argentinean Society of Experimental Pharmacology (SAFE) is a non- profit association whose research fields include Experimental and Clinical Pharmacology. SAFE main goals are described as follow (a) To meet active researchers for studying concerns regarding Experimental and Clinical Pharmacology (b) To launch an initiative for development of the discipline in mainly our country and other collaborative countries worldwide (c) To spread the pharmacological know-how obtained from different research teams (d) To strengthen relations between pharmacologists (e) To facilitate the presentation and discussion of scientific papers. This current article shows the SAFE's more important scientific contribution to pharmacology through its former research scientists to the present.

Relationship between nitric oxide- and calcium-dependent signal transduction pathways in growth hormone release from dispersed goldfish pituitary cells

Nitric oxide (NO) and Ca(2+) are two of the many intracellular signal transduction pathways mediating the control of growth hormone (GH) secretion from somatotropes by neuroendocrine factors. We have previously shown that the NO donor sodium nitroprusside (SNP) elicits Ca(2+) signals in identified goldfish somatotropes. In this study, we examined the relationships between NO- and Ca(2+)-dependent signal transduction mechanisms in GH secretion from primary cultures of dispersed goldfish pituitary cells. Morphologically identified goldfish somatotropes stained positively for an NO-sensitive dye indicating they may be a source of NO production. In 2h static incubation experiments, GH release responses to the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) were attenuated by CoCl2, nifedipine, verapamil, TMB-8, BHQ, and KN62. In column perifusion experiments, the ability of SNP to induce GH release was impaired in the presence of TMB-8, BHQ, caffeine, and thapsigargin, but not ryanodine. Caffeine-elicited GH secretion was not affected by the NO scavenger PTIO. These results suggest that NO-stimulated GH release is dependent on extracellular Ca(2+) availability and voltage-sensitive Ca(2+) channels, as well as intracellular Ca(2+) store(s) that possess BHQ- and/or thapsigargin-inhibited sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPases, as well as TMB-8- and/or caffeine-sensitive, but not ryanodine-sensitive, Ca(2+)-release channels. Calmodulin kinase-II also likely participates in NO-elicited GH secretion but caffeine-induced GH release is not upstream of NO production. These findings provide insights into how NO actions many integrate with Ca(2+)-dependent signalling mechanisms in goldfish somatotropes and how such interactions may participate in the GH-releasing actions of regulators that utilize both NO- and Ca(2+)-dependent transduction pathways.

Dependence of the excitability of pituitary cells on cyclic nucleotides

Cyclic 3',5'-adenosine monophosphate and cyclic 3',5'-guanosine monophosphate are intracellular (second) messengers that are produced from the nucleotide triphosphates by a family of enzymes consisting of adenylyl and guanylyl cyclases. These enzymes are involved in a broad array of signal transduction pathways mediated by the cyclic nucleotide monophosphates and their kinases, which control multiple aspects of cell function through the phosphorylation of protein substrates. We review the findings and working hypotheses on the role of the cyclic nucleotides and their kinases in the control of electrical activity of the endocrine pituitary cells and the plasma membrane channels involved in this process.

Reactive oxygen species are key mediators of the nitric oxide apoptotic pathway in anterior pituitary cells

We previously showed that long-term exposure of anterior pituitary cells to nitric oxide (NO) induces apoptosis. The intracellular signals underlying this effect remained unclear. In this study, we searched for possible mechanisms involved in the early stages of the NO apoptotic cascade. Caspase 3 was activated by NO with no apparent disruption of mitochondrial membrane potential. NO caused a rapid increase of reactive oxygen species (ROS), and this increase seems to be dependent of mitochondrial electron transport chain. The antioxidant N-acetyl-cysteine avoided ROS increase, prevented the NO-induced caspase 3 activation, and reduced the NO apoptotic effect. Catalase was inactivated by NO, while glutathione peroxidase (GPx) activity and reduced glutathione (GSH) were not modified at first, but increased at later times of NO exposure. The increase of GSH level is important for the scavenging of the NO-induced ROS overproduction. Our results indicate that ROS have an essential role as a trigger of the NO apoptotic cascade in anterior pituitary cells. The permanent inhibition of catalase may strengthen the oxidative damage induced by NO. GPx activity and GSH level augment in response to the oxidative damage, though this increase seems not to be enough to rescue the cells from the NO effect.

Nitric Oxide Induces Apoptosis in Bovine Luteal Cells

We previously showed in in vivo and in vitro studies that nitric oxide (NO) is engaged in luteolysis in cattle. Nitric oxide produced locally in the bovine corpus luteum (CL) inhibits progesterone (P4) synthesis and is suggested to be a component of the luteolytic cascade induced by uterine prostaglandin (PG) F2alpha. In the present study, the molecular mechanisms of NO action during structural luteolysis were studied in cultured bovine luteal cells (Days 15-17 of the estrous cycle). The effects of the NO donor (NONOate; 10(-4)M) on DNA fragmentation, cell viability, P4 production and caspase-3 activity were compared with those of PGF2alpha (10(-6)M). Moreover, mobilization of intracellular calcium [Ca2+]i and gene expressions of Fas-L, Fas, bcl-2, bax, and caspase-3 in the cells were determined by semi-quantitative RT-PCR after NONOate treatment. Caspase-3 activity was examined calorimetrically. Contrary to PGF2alpha NONOate decreased cell viability. DNA fragmentation after NONOate treatment increased by more than with PGF22alpha. NONOate increased mobilization of [Ca2+]i in the cells. Although the NO donor did not affect Fas-L and bcl-2 gene expression, it stimulated Fas and bax mRNA and caspase-3 expression. The ratio of bcl-2 to bax mRNA level decreased in the cells treated with NONOate. Moreover, NONOate stimulated caspase-3 activity more effectively than PGF2alpha. The overall results suggest that NO is a luteolytic factor that plays a crucial role in regulation of the estrous cycle in structural luteolysis by inducing apoptosis of luteal cells in cattle.

Nitric oxide protects anterior pituitary cells from cadmium-induced apoptosis

Cadmium (Cd2+) is a potent toxic metal for both plants and animals. Chronic exposure to low doses of Cd2+ results in damage to several organs. We have previously reported that Cd2+ induces apoptosis in anterior pituitary cells by a caspase- and oxidative stress-dependent mechanism. Nitric oxide (NO) synthesis is affected by Cd2+ in several systems. NO has been shown to be either cytoprotective or cytotoxic in many systems. The aim of this study was to evaluate the possible participation of NO in the cytotoxic effect of Cd2+ on rat anterior pituitary cells. Cell viability was evaluated by mitochondrial dehydrogenase activity assay and confirmed by microscopy, studying nuclear morphology. Here we show that DETA NONOate ((Z)-1-[2 (2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate), a long-term NO donor, at concentrations below 0.5 mM, reduces nuclear condensation and fragmentation and reverses the decrease in cellular activity induced by Cd2+. Cd2+, by itself, induced NO synthesis, and inhibition of this synthesis enhanced Cd2+ cytotoxicity. NO also prevented caspase-3 activation and lipidic peroxidation induced by Cd2+. The NO/cGMP pathway does not seem to be involved in the cytoprotective effect of NO. These results indicate that NO has a cytoprotective role in Cd2+ -induced apoptosis, suggesting that endogenous NO could have a physiological role in protecting anterior pituitary cells.

Nitric oxide inhibits prolactin secretion in pituitary cells downstream of voltage-gated calcium influx

The coupling between nitric oxide (NO)-cGMP signaling pathway and prolactin (PRL) release in pituitary lactotrophs has been established previously. However, the messenger that mediates the action of this signaling pathway on hormone secretion and the secretory mechanism affected, calcium dependent or independent, have not been identified. In cultured pituitary cells, basal PRL release was controlled by spontaneous voltage-gated calcium influx and was further enhanced by depolarization of cells and stimulation with TRH. Inhibition of constitutively expressed neuronal NO synthase decreased NO and cGMP levels and increased basal PRL release. The addition of a slowly releasable NO donor increased cGMP levels and inhibited basal PRL release in a time-dependent manner. Expression of inducible NO synthase also increased NO and cGMP levels and inhibited basal, depolarization-induced, and TRH-induced PRL release, whereas inhibition of this enzyme decreased NO and cGMP production and recovered PRL release. None of these treatments affected spontaneous and stimulated voltage-gated calcium influx. At basal NO levels, the addition of permeable cGMP analogs did not inhibit PRL secretion. At elevated NO levels, inhibition of cGMP production and facilitation of its degradation did not reverse inhibited PRL secretion. These experiments indicate that NO inhibits calcium-dependent PRL secretion in a cGMP-independent manner and downstream of voltage-gated calcium influx.

Involvement of nitric oxide on prolactin release induced by immobilization stress in rats

The nitric oxide (NO) has important participation in the control of hypothalamic-pituitary axis. The authors investigated the effect of NO donor, isosorbide dinitrate (ISDN), on prolactin (PRL) release induced by immobilization stress (IS) in male rats. Pretreatment with the NO donor, ISDN (2.5; 5 and 10 mg/kg), inhibited about 60-85% of the PRL response to IS. It is concluded that NO does participate in the regulation of PRL response to IS.

Desensitization of angiotensin II: effect on [Ca2+]i, inositol triphosphate, and prolactin in pituitary cells

Activation of pituitary angiotensin (ANG II) type 1 receptors (AT1) mobilizes intracellular Ca2+, resulting in increased prolactin secretion. We first assessed desensitization of AT1 receptors by testing ANG II-induced intracellular Ca2+ concentration ([Ca2+](i)) response in rat anterior pituitary cells. A period as short as 1 min with 10(-7) M ANG II was effective in producing desensitization (remaining response was 66.8 +/- 2.1% of nondesensitized cells). Desensitization was a concentration-related event (EC(50): 1.1 nM). Although partial recovery was obtained 15 min after removal of ANG II, full response could not be achieved even after 4 h (77.6 +/- 2.4%). Experiments with 5 x 10(-7) M ionomycin indicated that intracellular Ca2+ stores of desensitized cells had already recovered when desensitization was still significant. The thyrotropin-releasing hormone (TRH)-induced intracellular Ca2+ peak was attenuated in the ANG II-pretreated group. ANG II pretreatment also desensitized ANG II- and TRH-induced inositol phosphate generation (72.8 +/- 3.5 and 69.6 +/- 6.1%, respectively, for inositol triphosphate) and prolactin secretion (53.4 +/- 2.3 and 65.1 +/- 7.2%), effects independent of PKC activation. We conclude that, in pituitary cells, inositol triphosphate formation, [Ca2+](i) mobilization, and prolactin release in response to ANG II undergo rapid, long-lasting, homologous and heterologous desensitization.

Role of nitric oxide in the metabolism of arachidonic acid in the rat anterior pituitary gland

Nitric oxide (NO) affects cyclooxygenase (COX) and lipooxygenase (LOX) activities in several tissues. The aim of this study was to investigate the effect of NO on the AA metabolism in the anterior pituitary. LOX and COX products from anterior pituitaries of Wistar male rats were determined by [14C]-AA radioconversion method. Sodium nitroprusside (NP, 0.5 mM) and DETA NONOate (1 mM), NO donors, decreased 5-hydroxy-5,8,11,14-eicosatetraenoic acid (5-HETE) synthesis (P<0.05), effects that were reversed by hemoglobin. L-arginine also inhibited LOX activity. To the contrary, the inhibition of NO synthase by L-NAME (0.5 mM) or aminoguanidine (0.5 mM) increased 5-HETE production (P<0.05). COX activity was slightly stimulated by NP and L-arginine. However, DETA NONOate induced a stimulation of the synthesis of all prostanoids (P<0.05), this effect being reversed by hemoglobin. Neither NOS inhibitors nor hemoglobin modified basal prostanoids synthesis. These results indicate that NO inhibits LOX activity and stimulates COX activity in the anterior pituitary gland. The inhibition of LOX by NO may be another mechanism involved in the effects of NO on hormone release in the anterior pituitary.

Influence of nitric oxide and noradrenaline on prostaglandin F(2)(alpha)-induced oxytocin secretion and intracellular calcium mobilization in cultured bovine luteal cells

Although prostaglandin (PG) F(2alpha) released from the uterus has been shown to cause regression of the bovine corpus luteum (CL), the neuroendocrine, paracrine, and autocrine mechanisms regulating luteolysis and PGF(2alpha) action in the CL are not fully understood. A number of substances produced locally in the CL may be involved in maintaining the equilibrium between luteal development and its regression. The present study was carried out to determine whether noradrenaline (NA) and nitric oxide (NO) regulate the sensitivity of the bovine CL to PGF(2alpha) in vitro and modulate a positive feedback cascade between PGF(2alpha) and luteal oxytocin (OT) in cows. Bovine luteal cells (Days 8-12 of the estrous cycle) cultured in glass tubes were pre-exposed to NA (10(-5) M) or an NO donor (S-nitroso-N:-acetylpenicillamine [S-NAP]; 10(-4) M) before stimulation with PGF(2alpha) (10(-6) M). Noradrenaline significantly stimulated the release of progesterone (P(4)), OT, PGF(2alpha), and PGE(2) (P: < 0.01); however, S-NAP inhibited P(4) and OT secretion (P: < 0.05). Oxytocin secretion and the intracellular level of free Ca(2+) ([Ca(2+)](i)) were measured as indicators of CL sensitivity to PGF(2alpha). Prostaglandin F(2alpha) increased both the amount of OT secretion and [Ca(2+)](i) by approximately two times the amount before (both P: < 0.05). The S-NAP amplified the effect of PGF(2alpha) on [Ca(2+)](i) and OT secretion (both P: < 0.001), whereas NA diminished the stimulatory effects of PGF(2alpha) on [Ca(2+)](i) (P: < 0.05). Moreover, PGF(2alpha) did not exert any additionally effects on OT secretion in NA-pretreated cells. The overall results suggest that adrenergic and nitrergic agents play opposite roles in the regulation of bovine CL function. While NA stimulates P(4) and OT secretion, NO may inhibit it in bovine CL. Both NA and NO are likely to stimulate the synthesis of luteal PGs and to modulate the action of PGF(2alpha). Noradrenaline may be the factor that is responsible for the limited action of PGF(2alpha) on CL and may be involved in the protection of the CL against premature luteolysis. In contrast, NO augments PGF(2alpha) action on CL and it may be involved in the course of luteolysis.

Calcium influx and intracellular stores in angiotensin II stimulation of normal and hyperplastic pituitary cells

In rat pituitary cells from estrogen-induced hyperplasia, angiotensin II (ANG II) does not evoke a clear spike elevation of intracellular Ca2+ concentration ([Ca2+]i) but induces a plateau increase. The present work was undertaken to establish whether this difference was related to a differential participation of intracellular and/or plasma membrane Ca2+ channels. We first tested the effect of 10 nM ANG II on [Ca2+]i in the absence of extracellular Ca2+ in cells depolarized with 25 mM K+ or in the presence of blockers of L-type voltage-sensitive Ca2+ channels (VSCC). These treatments did not alter spike elevation in [Ca2+]i in controls but reduced plateau levels in hyperplastic cells. Intracellular Ca2+ stores were similar in both groups, as assessed by thapsigargin treatment, but this drug abolished spike increase in controls and scarcely modified plateau levels in hyperplastic cells. Finally, inositol trisphosphate (InsP3) production in response to ANG II was significantly higher in control cells. We conclude that the observed plateau rise in hyperplastic cells results mainly from Ca2+ influx through VSCC. In contrast, in control cells, the ANG II-induced spike increase in [Ca2+]i results from mobilization of Ca2+ from thapsigargin-sensitive internal channels, activated by higher inositol 1,4,5-trisphosphate generation.