Gonadal steroid modulation of LHRH-stimulated LH secretion by pituitary cell cultures

Enzymatically dispersed rat pituitary cells were grown in primary culture, and LHRH-stimulated LH secretion was measured. Testosterone (T) decreased and 17 beta-estradiol (E) increased pituitary responsiveness to LHRH. The effect of E on LH secretion was partly due to an increase in LH content. There was a latent period of 12 h for E and 18 h for T between the onset of steroid treatment and the manifestation of steroid action. Neither steroid was required to be continuously present in order to exert its effects. After steroid withdrawal, the effect of T persisted for 72 h and that of E for more than 96 h. The actions of both steroids were blocked by protein-synthesis inhibitors. These results are consistent with the hypothesis that steroid effects rely on a mechanism involving alterations in protein synthesis; the affected proteins may be involved in the process of LHRH action.     

一氧化氮在L-精氨酸促生长激素分泌中的作用

氨基酸是促进垂体生长激素(GH)分泌的潜在刺激因子.在所有氨基酸中,左旋精氨酸(L-精氨酸)促GH分泌作用最为明显.口服或静脉滴注精氨酸均可刺激垂体GH的分泌.L-精氨酸促GH的分泌可能涉及多种机制,但一氧化氮(NO)依赖的可溶性鸟苷酸环化酶-环鸟苷酸-蛋白激酶G(sGC-cGMP-PKG)信号转导通路在此过程中起着重...     

Antiprogestins RU486 and ZK299 suppress basal and LHRH-stimulated FSH and LH secretion at pituitary level in the rat in an oestrous cycle stage-dependent manner

We have previously shown that administration of antiprogestin (AP) type II RU486 to ovariectomized (OVX) rats on the morning of pro-oestrus decreases the magnitude of preovulatory gonadotrophin surge. This suggests that the effect of RU486 on LHRH-dependent gonadotrophin release may be independent of its ability to block progesterone actions. The aim of the present research was to study the possible site of RU486 action and to determine whether the gonadotrophin suppressive effect of APs RU486 and ZK299 is dependent on the oestrogen background. Intact or OVX rats in the morning of pro-oestrus were injected s.c. with 4 mg of RU486 or ZK299 (AP type I) at 0900 h on pro-oestrus. At 1830 h, serum concentration of FSH and LH and median eminence (ME) content of LHRH were determined. In the second experiment, the effect of RU486 and ZK299 on pituitary responsiveness to LHRH (100 ng, i.p.) and ME content of LHRH at 1830 h pentobarbital-blocked intact or OVX rats was evaluated. In the last study, the anterior pituitary release of FSH and LH from pro-oestrus or metoestrus donors incubated with or without LHRH (1, 10 or 100 nM) in the presence or absence of APs (20 nM) was evaluated. Both APs reduced serum FSH and LH levels at 1830 h on pro-oestrus in intact and OVX rats. The suppressive effect on gonadotrophin release brought about by AP treatment was also evidenced in PB-blocked intact and OVX rats. This suggested that the inhibitory effect of APs occurred, at least in part, at pituitary level. Furthermore, in the absence of the natural ligand, APs significantly reduced basal and LHRH-stimulated FSH and LH release from pro-oestrous but not from metoestrus pituitaries. In conclusion, these experiments have shown, both 'in vivo' and 'in vitro', that APs RU486 and ZK299 have suppressive effects at pituitary level on basal and LHRH-stimulated FSH and LH secretion, regardless of their antiprogestagenic activity, in pro-oestrus but not in metoestrus.     

一氧化氮及其合酶在哮喘发病机制中的作用

探讨一氧化氮及其合酶在哮喘发病机制中的作用。方法 采用哮喘豚鼠模型，将豚鼠分为４组；１．哮喘组，用１０％卵白蛋白腹腔注射１ｍｌ致敏，２周后用１％卵白蛋白超声雾化吸入致其哮喘发作．２；肾上腺皮质激素预防组；诱喘同哮喘组，在每次诱喘前腹腔滴注地塞米松０．５ｍｇ／ｋｇ。３．硝基精氨酸甲酯预防组；诱喘同哮喘组，每次诱喘产腹腔注射ＬＮＮＡ０．４ｍｇ／ｋｇ。４．正常对照组；用生理盐水代替诱喘剂。每组分别测定其     

The role of LH in the autofeedback inhibition of LH and FSH secretion in ovariectomized rats

This study examined the role of exogenous LH in the autofeedback regulation of LH and FSH release in ovariectomized rats. The rats were implanted with third ventricular cannulae three weeks after ovariectomy and fitted with silastic jugular cannulae one week later. Baseline hormone levels were established on the day of experimentation in conscious, unrestrained animals. Thereafter, experimental animals received intraventricularly (IVT) either a 9 ug or 20 ug dose of a purified preparation of human (h)LH that did not crossreact in our rLH RIA. In response to 20 ug, but not 9 ug of LH, plasma levels of both LH and FSH were significantly reduced during the following one hour period compared to values in controls receiving buffer IVT. Administration of ovine (o)LH (6 ug, IVT), a preparation which crossreacts in the rLH RIA, significantly elevated plasma levels of detectable LH during the experimental period indicating that LH reaches the blood stream from the third ventricle and, thus, may effect endogenous hormone release at either the pituitary or hypothalamic levels. However, in animals preinjected with 9 or 20 ug of hLH IVT one hour earlier the surge of both LH and FSH in response to LHRH (25 ng iv) was not different from that in the buffer-injected controls receiving LHRH which indicates that pituitary responsiveness was not suppressed by the effective dose of hLH. The results of this study suggest that the inhibitory shortloop feedback of LH on endogenous LH and FSH secretion in ovariectomized rats occurs at the level of the hypothalamus.     

The role of nitric oxide

When studying the impact of endothelins (ETs) on physiology and pathophysiology, this needs to be done in the context of nitric oxide (NO) synthesis and action, since these two are closely intertwined in their action. Here, we will review the work demonstrating the crosstalk between endothelin-1 (ET-1) and NO, and the recent developments regarding the role of these two mediators in inflammatory processes. Moreover, we will discuss the role of NO in pro-inflammatory diseases and the potential mechanisms of the anti-inflammatory activity of ET receptor antagonism.     

Age-related changes in the mechanisms of LHRH-stimulated LH release from pituitary cells in vitro.

In vitro release of LH in response to LHRH, phorbol myristate acetate (PMA), the ionophore A23187, and nifedipine was evaluated in primary cultures of anterior pituitary cells from intact mature (6 to 7 month) and old (23 to 24 month) male Wistar rats. LH release from pituitary cells is reduced approximately 30% and 60% after 4 and 48 h of 10(-7) M LHRH stimulation in cells of old rats, respectively. This impairment may be secondary to a loss of LHRH receptors. LHRH-stimulated LH release from cells of mature rats was inhibited 70% by the voltage-gated calcium channel blocker, nifedipine (10(-6) M), whereas LHRH-stimulated LH release from cells of old rats was too low to detect the effects of this drug. Age changes can be partially reversed by A23187 and PMA during 4 h, but not 48 hrs of stimulation. It therefore appears that short- and long-term (4 h and 48 h, respectively) stimulation of LH release may proceed through separate mechanisms that are differentially affected by aging.     

Role of endogenous nitric oxide in the control of exocrine and endocrine pancreatic secretion in humans.

BACKGROUND: Nitric oxide (NO) is an unstable vasodilator formed by NO synthetase (NOS) from L-arginine (L-Arg) in various cells but its role in the control of pancreatic secretion in humans has not been examined. AIMS: This study was designed to determine the role of endogenous NO in the control of exocrine and endocrine pancreas using NOS inhibitor, NG-monomethyl-L-Arg (L-NMMA). METHODS: Pancreatic secretion was stimulated by intravenous infusion of secretin (80 pmol/kg/h) plus caerulein (50 pmol/kg/h) and duodenal content was aspirated by gastroduodenal tube. Two series of tests with secretagogue infusion were performed, one, with addition of graded doses of L-NMMA and, another, with addition of a constant dose of L-Arg alone followed by L-NMMA alone and finally by a combination of L-Arg and L-NMMA. RESULTS: Addition of L-NMMA in graded doses (2-8 mumol/kg/h) reduced dose dependently the secretin-caerulein stimulated pancreatic enzyme secretion without alterations in the volume flow and bicarbonate outputs. The addition of L-Arg to L-NMMA reversed the inhibitory action of L-NMMA on protein enzyme response to secretin-caerulein in these subjects. Secretin-caerulein infusion caused significant increase in plasma insulin and pancreatic polypeptide levels but without changes in plasma glucagon or somatostatin levels. L-NMMA alone resulted in a significant fall in plasma insulin and pancreatic polypeptide levels, while L-Arg added to pancreatic secretagogue infusion caused a significant increase of plasma insulin and pancreatic polypeptide levels above those attained with secretagogues alone. After the addition of L-Arg to L-NMMA, both plasma insulin and pancreatic polypeptide levels rose significantly above the levels observed with L-NMMA plus secretin-CCK stimulation. CONCLUSION: This study provides evidence that the suppression of NOS reduces pancreatic enzyme secretion and the plasma insulin and pancreatic polypeptide levels suggesting that endogenous NO affects both exocrine and endocrine pancreatic secretion in humans.     

The effect of triflusal on human platelet aggregation and secretion: the role of nitric oxide

INTRODUCTION AND AIMS: The thrombotic process is a multicellular phenomenon in which not only platelets are involved but also neutrophils are involved. Recent in vitro studies performed in our laboratory have demonstrated that triflusal reduced platelet aggregation by stimulating nitric oxide (NO) production by neutrophils. The aim of the present study was to evaluate whether the in vivo treatment with triflusal could also modify the ability of neutrophils to produce NO. Furthermore, the role of NO released by neutrophils on platelet aggregation and secretion was also tested. METHODS: The study was performed in 12 healthy volunteers of 32 +/- 6 years of age. The volunteers were treated with triflusal (600 mg/day) for 5 days and platelets and neutrophils were isolated before and after treatment. The ability of neutrophils to produce NO and the capacity of inhibiting platelet aggregation and secretion of transforming growth factor-beta (TGF-beta) were assessed. RESULTS: After the treatment with triflusal we obtained the following results: a) an increase in NO production by neutrophils; b) potentiation of the inhibition of platelet aggregation by neutrophils, an effect that was reverted by incubating neutrophils with an L-arginine antagonist, L-NAME, and c) the presence of neutrophils reduced the release of TGF-beta by platelets measured as index of platelet secretion by a NO-independent mechanism. CONCLUSIONS: Triflusal (600 mg/day/5 days) stimulated NO production by neutrophils. After the treatment with triflusal, neutrophils inhibited both platelet aggregation and secretion. The antiaggregating effect of neutrophils was an NO-dependent mechanism while the inhibition of platelet secretion mediated by neutrophils after the treatment with triflusal was an NO-independent mechanism.     

Nitric oxide synthase in the rat anterior pituitary gland and the role of nitric oxide in regulation of luteinizing hormone secretion.

By using immunohistochemistry and in situ hybridization, we have demonstrated that the nitric oxide (NO)-synthesizing enzyme NO synthase is present in gonadotrophs and in folliculo-stellate cells of the anterior pituitary gland of male and female rats. A marked increase in levels of NO synthase protein and mRNA was observed after gonadectomy. In vitro studies on dispersed anterior pituitary cells suggest that NO inhibits gonadotropin-releasing-hormone-stimulated luteinizing hormone release. An inhibitory effect of NO has also been shown on growth-hormone-releasing-hormone-stimulated release of growth hormone [Kato, M. (1992) Endocrinology 131, 2133-2138]. Thus these findings support a dual mechanism for NO in the control of anterior pituitary hormone secretion, an autocrine mediation of luteinizing hormone release on gonadotrophs, and a paracrine effect on growth hormone secretion involving folliculo-stellate cells closely related to somatotrophs. We speculate that NO may participate in producing the pulsatile secretion patterns of these two pituitary hormones.     

The role of nitric oxide in articular cartilage damage.

The production of large amounts of NO in vitro by cytokine-activated chondrocytes has been established. In vitro studies suggest that NO compromises chondrocyte survival. The role of NO in regulating matrix biosynthesis and degradation has received much attention. Most studies indicate that NO is at least partly responsible for IL-1-induced suppression of glycosaminoglycan and collagen synthesis. NO also may be involved as a mediator of IL-1-induced expression of MMP, mRNA, and protein and may contribute as an activator of the latent forms of the enzymes. Although the interaction of NO and prostaglandins is of considerable interest, current data are inconclusive with respect to the role of NO in the regulation of prostaglandin synthesis, although it seems clear that prostaglandin is not involved in NO synthesis. It is important to note that NO does have protective effects in cartilage and other tissues. Under certain conditions, NO may have anabolic and anticatabolic effects in cartilage. In other tissues, notably in skin and muscle, NO has been found to have a stimulatory role in extracellular matrix repair. In antimicrobial defense, in general, and in bacterial arthritis specifically, NO is an important protective molecule. Production of NO in arthritis-affected cartilage and synovium is a consistent feature of human and experimentally induced arthritis. The production of NO is associated with matrix degradation and chondrocyte apoptosis. The administration of NO synthase inhibitors in experimentally induced arthritis has resulted in reduction of synovial inflammation and destruction of cartilage and bone.     

The role of nitric oxide in osteoarthritis

Elevated levels of markers of nitric oxide (NO) production are found in osteoarthritic joints suggesting that NO is involved in the pathogenesis of osteoarthritis (OA). In OA, NO mediates many of the destructive effects of interleukin-1 (IL-1) and tumour necrosis factor-alpha (TNF-alpha) in the cartilage, and inhibitors of NO synthesis have demonstrated retardation of clinical and histological signs and symptoms in experimentally induced OA and other forms of arthritis. As an important factor in cartilage, the regulation of inducible nitric oxide synthase (iNOS) expression and activity, and the effects of NO are reviewed, especially in relation to the pathogenesis of OA.     

Multifunctional role of nitric oxide in inflammation.

In response to infection or tissue damage, an array of soluble and lipid mediators as well as cytokines and growth factors cause both immune and nonimmune cells to produce rather large amounts of nitric oxide. Nitric oxide and its oxidation products are toxic and can cause tissue injury. The endocrine system can protect against nitric-oxide-mediated tissue damage by producing corticosteroids, growth factors, and cytokines that are potent inhibitors of nitric oxide production. This review focuses on our current understanding of the role of nitric oxide in the inflammatory response. An emphasis has been placed on the potential for nitric oxide in tissue damage.     

Distribution of nitric oxide synthase and secretory role of exogenous nitric oxide in the isolated rat pancreas.

BACKGROUND: Pancreatic production and in vivo effects of nitric oxide (NO) have been shown by several studies. In order to examine the direct actions of the NO donor sodium nitroprusside (SNP), this study used in vitro specimens of the rat pancreas where the distribution of neuronal nitric oxide synthase (NOS) and the secretory effects of SNP and the cyclic GMP (cGMP) analog 8-bromo cyclic GMP (8-Br cGMP) were investigated. METHODS: NO containing pancreatic nerves were visualized by NOS immunohistochemistry. Basal and stimulated amylase output from rat pancreatic segments was measured by an on-line fluorimetric method. Stimulation was achieved by either acetylcholine (ACh) or electrical field stimulation (EFS). Intracellular free calcium concentration ([Ca2+]i) was measured in dispersed pancreatic acinar cells. RESULTS: NOS containing nerves were demonstrated in the vicinity of pancreatic acini and blood vessels. SNP and 8-Br cGMP inhibited both basal and EFS evoked amylase output but failed to inhibit ACh induced amylase output. Basal [Ca2+]i was decreased by both SNP and 8-Br cGMP but neither SNP nor 8-Br cGMP influenced the ACh evoked increase in [Ca2+]i. CONCLUSION: NO is well distributed in the rat exocrine pancreas. Exogenous nitric oxide may have a dual action in the isolated rat pancreas: Inhibition of basal amylase secretion in acinar cells and inhibition of ACh release from intrinsic nerve terminals. Both effects seem to be calcium dependent and possibly mediated by cGMP.     

The ubiquitous role of nitric oxide in cardioprotection

In recent years, major advances have been made toward understanding the role of nitric oxide (NO) in the ischemic biology of the heart. It is now clear that NO, either endogenous or exogenous, represents one of the most important defenses against myocardial ischemia-reperfusion injury. The purpose of this review is to provide an update on the cardioprotective actions of NO, with particular emphasis on the function of the inducible isoform of NO synthase (iNOS) and on the role of mitochondria in NO-mediated protection. This essay underscores some of the more prominent areas of ischemic biology that relate to NO, such as ischemic preconditioning, pharmacological cardioprotection, and gene therapy. The hypothesis that the late phase of preconditioning is mediated by increased iNOS activity resulting in enhanced NO bioavailability, first proposed by our group, is now widely accepted and can be regarded as a proven hypothesis. Likewise, the burgeoning field of postconditioning may share such a requirement for NO. Various drugs (e.g. statins, ACE inhibitors, angiotensin-receptor blockers, etc.) also produce salubrious effects in experimental models of myocardial infarction via their enhancement of NO bioavailability. Thus, NO appears to be a common mediator of the protection afforded by a wide array of seemingly unrelated pharmacological and nonpharmacological interventions, underscoring its fundamental role as a ubiquitous defense of the heart against ischemia and reperfusion. This review challenges the conventional wisdom that iNOS is deleterious during myocardial ischemia-reperfusion and instead proposes the concept that iNOS, when expressed in cardiac myocytes, is a profoundly protective protein. We also emphasize the emerging importance of the mitochondrial actions of NO. Although the precise molecular events remain to be defined, we propose that NO interacts with components of the electron transport chain and/or the mitochondrial permeability transition pore to limit post-ischemic myocardial damage, and that this action potentially provides a fundamental molecular explanation for the mechanism of NO-mediated cardioprotection.