Synergistic effect of nitric oxide synthase and cyclooxygenase inhibitors on carrageenan-induced paw edema in rats

The present study examined the effects of L-nitroarginine methylester (L-NAME, CAS 50903-99-6), a non-selective nitric oxide synthase (NOS) inhibitor, indometacin (IND, CAS 3305-29-1), a non-selective cyclooxygenase (COX) inhibitor, and a combination of these agents (L-NAME + IND) on carrageenan-induced paw edema for 4 h after the injection of carrageenan in rats. L-NAME at 10 and 30 mg/ kg but not 3 mg/kg (i.p.) decreased paw volume slightly but significantly only at 1 h after the carrageenan injection. IND reduced paw volume slightly at 1 and 3 mg/kg, and markedly at 10 mg/kg (p.o.). A combination of L-NAME and IND at a subthreshold dose (3 mg/kg, i.p. and 1 mg/kg, p.o., respectively) caused a marked reduction of paw edema, which was also confirmed by histopathological examinations. A combination of N-(3-(aminomethyl)benzyl)acetamidine (1400W, CAS 180001-34-7), a selective inhibitor of inducible NOS, and IND at 3 mg/kg, i.p., and 1 mg/kg, p.o., respectively, did not show synergistic anti-inflammatory effects. In conclusion, the combination of non-selective NOS and COX inhibitors had synergistic anti-inflammatory effects on carrageenan-induced paw edema at an early stage, suggesting negative crosstalk between the endogenous NOS-NO and COX-PG pathways in the early stages of acute inflammation.     

Bradykinin receptor antagonists and cyclooxygenase inhibitors in vincristine-and streptozotocin-induced hyperalgesia

Pain that accompanies neuropathy is difficult to treat. Analgesics administered as monotherapies possess low activities in relieving this kind of pain.The effect of the simultaneous administration of indomethacin (a preferential inhibitor of cyclooxygenase-1; COX-1) or celecoxib (a relatively selective inhibitor of cyclooxygenase-2; COX-2), with selective antagonists of bradykinin₂ (B₂) bradykinin1 (B₁) receptors (HOE 140 or des-Arg¹⁰-HOE 140) on the eleviation of diabetic and toxic neuropathic pain was investigated.Pretreatment with indomethacin (0.1 mg/kg, sc) increased the antihyperalgesic activity of low daily doses of HOE 140 or des-Arg¹⁰HOE 140 (70 nmol/kg, ip) in a diabetic (streptozotocin(STZ)-induced) neuropathy/hyperalgesia experimental model. Premedication with celecoxib before HOE 140 or des-Arg¹⁰HOE 140 administration resulted in a gradual reduction of STZ hyperalgesia. Furthermore, on days 23–24, almost complete abolishment of STZ hyperalgesia was observed. After cessation of drug administration, hyperalgesia quickly returned to the baseline threshold.The results of this study suggest that inhibitors of cyclooxygenases can increase the antihyperalgesic activity of selective antagonists of B₂ and B₁ receptors in diabetic and toxic neuropathic pain models. These observations may be clinically relevant.     

Effect of nitric oxide synthase inhibitors on benzodiazepine withdrawal in mice and rats

This study was undertaken to evaluate the effect of nitric oxide (NO) synthase inhibitors on benzodiazepine withdrawal syndrome in mice and rats. Diazepam withdrawal in mice was read out as intensification of the seizures induced by a subthreshold dose of pentetrazole. In rats, the withdrawal syndrome resulting from chronic administration of diazepam, chlordiazepoxide, clonazepam and temazepam was characterized by audiogenic seizures, hypermotility and weight loss. Administration of the non-selective NO synthase inhibitors N(G)-nitro-L-arginine (L-NOARG) and N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) significantly attenuated the withdrawal syndrome (i.e., pentetrazole-induced seizures) in diazepam-dependent mice. L-NOARG significantly suppressed hypermotility in clonazepam-dependent rats and inhibited the decrease in body weight observed after 12 h of withdrawal in chlordiazepoxide- and clonazepam-dependent rats. Moreover, a clear propensity of L-NOARG to protect benzodiazepine-dependent rats against audiogenic seizures was observed. These findings suggest that the cGMP/NO system may participate in causing the signs of benzodiazepine withdrawal.     

Effects of intrathecal administration of nitric oxide synthase inhibitors on carrageenan-induced thermal hyperalgesia.

1. We examined the effects of various nitric oxide synthase (NOS) inhibitors on carrageenan-induced thermal hyperalgesia. 2. First, we determined the time point at which a subcutaneous plantar injection of carrageenan into the rat hindpaw produced maximum thermal hyperalgesia. Subsequently, we demonstrated that intrathecal administration of the non-selective NOS inhibitor L-N(G)-nitro-arginine methyl ester (L-NAME) produces a dose-dependent reduction of carrageenan-induced thermal hyperalgesia. 3. Four relatively selective NOS inhibitors were then tested for their efficacy at reducing carrageenan-induced thermal hyperalgesia. Initially, the effects of prolonged treatment with inhibitors of neuronal [7-nitroindazole (7-NI) and 3-bromo-7-nitroindazole (3-Br)] and inducible [aminoguanidine (AG) and 2-amino-5,6-dihydro-methylthiazine (AMT)] NOS were examined. All agents were injected three times intrathecally during the course of inflammation caused by the plantar injection of carrageenan, and thermal hyperalgesia was measured at 6 h post-carrageenan using a plantar apparatus. 4. All inhibitors, except for 7-NI, were effective at attenuating the carrageenan-induced thermal hyperalgesia when compared with vehicle treatment. 5. Finally, the effects of early versus late administration of neuronal and inducible NOS inhibitors on carrageenan-induced thermal hyperalgesia were examined. We found that neither 3-Br nor AG significantly affected thermal hyperalgesia when administered during the early phase of carrageenan inflammation, while only AG was able to reduce thermal hyperalgesia when administered during the late phase of the injury. 6. Our results suggest that inducible NOS contributes to thermal hyperalgesia in only the late stages of the carrageenan-induced inflammatory response, while neuronal NOS likely plays a role throughout the entire time course of the injury.     

阿魏酸钠对结肠炎大鼠结肠组织一氧化氮合酶和环氧合酶的影响

目的　研究阿魏酸钠 (SF)对大鼠结肠炎的抗炎保护作用及其机制。方法　建立大鼠乙酸性结肠炎模型。SF与5 氨基水杨酸灌肠给药 1wk后评价大鼠结肠黏膜损伤指数(CMDI) ,采用试剂盒及免疫组化方法检测结肠组织NO、MPO、PGE2 含量及结构型一氧化氮合酶 (cNOS) ,诱生型一氧化氮合酶 (iNOS) ,环氧合酶 1(COX 1) ,环氧合酶 2 (COX 2 )和核因子 κBp6 5 (NF κBp6 5 )的表达水平。 结果　SF(2 0 0、4 0 0、80 0mg·kg-1)灌肠用药均降低模型组大鼠升高的CMDI及结肠组织NO、MPO、PGE2 含量 ,下调iNOS、COX 2、NF κBp6 5的过度表达 ,亦抑制cNOS的正常表达水平 ,对COX 1表达影响不明显。SF用药呈现一定量效关系。结论　SF为一氧化氮合酶及部分选择性COX 2抑制剂 ,对大鼠结肠炎具有一定抗炎保护作用。     

Secondary hyperalgesia in the rat first degree burn model is independent of spinal cyclooxygenase and nitric oxide synthase

The present study investigated the mechanisms of vasodilatation of the human pancreatic polypeptide [cPP(1-7), NPY(19-23),Ala(31),Aib(32),Gln(34)]hPP (hPP) in mesenteric small arteries from Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). The arteries were isolated and mounted in microvascular myographs for isometric tension recording. In vasopressin-contracted preparations with endothelium from WKY rats, hPP evoked concentration-dependent relaxations with maximal responses of 50+/-2% (n=5). hPP relaxation was reduced by endothelial cell removal and abolished in the presence of a nitric oxide (NO) synthase inhibitor, N(G)-nitro-L-arginine-methylester (L-NAME). hPP relaxation was blunted in segments with endothelium, and absent in segments without endothelium from SHR. The combined neuropeptide Y(1)- and Y(4)-receptor antagonist, GR23118 (Ile-Glu-Pro-Dpr-Tyr-Arg-Leu-Arg-Tyr-CONH(2)), and the neuropeptide Y(1) receptor antagonist, BIBP3226 ((R) -N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)-methyl]-arginineamide), inhibited hPP-induced vasodilatation. Calcitonin gene-related peptide (CGRP) relaxation was reduced in arteries from SHR compared to WKY. The CGRP receptor antagonist, CGRP (8-37), antagonized vasodilatation induced by CGRP and rightward shifted concentration-response curves for hPP in arteries from WKY rats. There were no differences in nerves immunoreactive for CGRP in arteries from SHR compared to WKY rats. In contrast to neuropeptide Y which evokes contraction by activation of neuropeptide Y(1) and Y(2) receptors, the present results suggest hPP evokes relaxation of mesenteric small arteries by activation of prejunctional neuropeptide Y(1)-like receptors localized in CGRP-containing nerves followed by release of CGRP and of endothelium-derived NO. hPP relaxation is blunted in arteries from SHR probably as a consequence of endothelial cell dysfunction leading to reduced efficacy of CGRP.     

Modulatory role of nitric oxide and cyclooxygenase enzyme pathway in LPS-mediated hyperalgesia

Nitric oxide (NO) is a free radical, is known to play an important role in many physiological and pathological processes. Evidence suggests that NO participates in the pathogenesis of inflammatory reactions. It has been reported that exposure of tissues to endotoxin (LPS) leads to induction of both inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). In the present study we have investigated the role of iNOS in LPS-mediated hyperalgesia in mice and the regulatory role between prostanoids in vivo using L-NAME, a non-specific nitric oxide synthase inhibitor, and spirulina purified protein (SPP) containing C-phycocyanin, NS-398 and rofecoxib, COX-2 selective inhibitor in various nociceptive assays. Acute administration of LPS (50 g/mouse, i.p. or 10 g/paw, i.pl.) significantly demonstrated hyperalgesia in chemical, thermal and mechanical nociception in mice, respectively. Treatments of mice with L-NAME (5-20 mg/kg, i.p. or 10-40 g/paw, i.pl.) significantly reversed the LPS-mediated hyperalgesia in peripheral or central nociception in mice. Treatment with SPP (50 and 100 mg/kg, p.o.), NS398 (10 mg/kg, p.o.) and rofecoxib (10 mg/kg, p.o.), significantly exhibited antihyperalgesic effect in chemical hyperalgesia. These COX-2 inhibitors significantly potentiated the L-NAME reversal of LPS-mediated hyperalgesia. It is concluded that iNOS plays a significant role in LPS-mediated hyperalgesia and simultaneous inhibition of COX-2 enzyme leads to modulatory effect between NO and prostanoids.     

Effect of inhibition of nitric oxide synthase on renal cyclooxygenase in the diabetic rat

Renal cyclooxygenase (COX)-2 expression and arachidonic acid-stimulated prostaglandin release are increased in streptozotocin-diabetic rats and are reduced by tempol treatment, indicating a role for superoxide. Generation of nitric oxide (NO) and its product with superoxide, peroxynitrite, is also increased in diabetes and can induce COX-2. To investigate a role of NO, rats were treated with L-nitroarginine methyl ester (L-NAME; 100 mg/kg/day) to inhibit NO synthase (NOS) for 14-18 days. In isolated perfused kidneys from diabetic rats, prostaglandin release and vasoconstrictor responses to arachidonic acid were increased and renal cortical expression of COX-2 was 2-fold that of control rats. Treatment of diabetic rats with L-NAME reduced arachidonic acid-stimulated release of prostaglandins and the expression of COX-2. L-NAME increased vasoconstrictor responses to AA in diabetic and non-diabetic rats but abolished the differences between the two. These results, coupled with those using tempol, suggest that NO or its product with superoxide may contribute to the induction of renal COX-2 in the diabetic rat.     

Effects of nitric oxide synthase inhibitors on timing and short-term memory in rats

Nitric oxide synthase (NOS) inhibitors have been shown to affect the development of long-term potentiation and the acquisition of new learning. In the present study, we investigated the effects of NOS inhibitors in two animal models in which aspects of cognition are measured in well-learned operant tasks - a delayed non-match-to-position (DNMTP) task and a multiple signalled-unsignalled differential reinforcement of low rates (DRL) 15 s schedule - models of short-term memory and behavioral inhibition/timing, respectively. Since an overlap in the behavioral effects of NOS inhibitors and phencyclidine (PCP)-like N-methyl-D-aspartate (NMDA) antagonists has been observed previously, we compared our results with NOS inhibitors to those obtained with PCP. Whereas PCP produced a delay-independent decrease in the DNMTP task and increased burst responding (consecutive responses with inter-response intervals of < 3 s) in both the signalled and unsignalled components of the DRL procedure, 7-nitroindazole did not affect accuracy in the DNMTP task nor did it alter the pattern of responding in either component of the DRL schedule. Similarly, NG-nitro-L-arginine (L-NOARG) and NG-nitro-L-arginine-methyl-ester (L-NAME) did not affect accuracy in the DNMTP task. These results suggest that NOS inhibitors do not produce PCP-like disruption of behavioral inhibition or timing, nor do they decrease accuracy in a conditional discrimination task, as has been observed with PCP. The present results lend further support to the hypothesis that nitric oxide modulation does not affect retention of well-learned tasks, although it may affect acquisition of novel behavior.     

Interaction between inhibitors of inducible nitric oxide synthase and cyclooxygenase in adjuvant-induced arthritis in female albino rats: an isobolographic study

We studied the interaction of S-methylisothiourea (a selective inducible nitric oxide synthase inhibitor) with rofecoxib (a selective cyclooxygenase-2 inhibitor) and mefenamic acid (a non-selective cyclooxygenase inhibitor) in adjuvant-induced arthritis in female albino Wistar rats, applying the isobolographic analysis. Each drug was effective in reducing the progressive increase in paw volume less than 50% except rofecoxib, when used alone. Log dose-response curve was obtained for each drug along with the corresponding ED(25). Following isobolographic analysis, combination of S-methylisothiourea with rofecoxib and mefenamic acid revealed supra-additive or synergistic interaction. Experimental ED(25) of the combinations was significantly lower than the theoretical ED(25) of the corresponding drug combination which substantiated the synergistic type of interaction between inducible nitric oxide synthase and cyclooxygenase in adjuvant-induced arthritis in female albino rats. Results suggest that NO regulates the cyclooxygenase enzyme activity as the activity of cyclooxygenase enzymes in the LPS-stimulated leukocyte lysates was significantly low or hardly detectable in the presence of varying concentrations of S-methylisothiourea. Simultaneous inhibition of inducible nitric oxide synthase and cyclooxygenase appears to offer an alternative approach for ameliorating the progression of arthritis.     

Effect of nitric oxide donors and nitric oxide synthase inhibitors in neonatal rat endotoxic shock.

Previous studies have shown an increased mortality in response to endotoxin in 24-hr-old neonatal rats compared with older neonates and adults. This increased susceptibility may be related to increased nitric oxide (NO) and thromboxane (TxB2) production. Twenty-four-hour-old neonatal rat pups were given either N(G)-nitro-L-arginine methyl ester (L-NAME; a nonspecific NO synthase inhibitor), S-methylthioisourea (SMT; a specific NO synthase inhibitor), or molsidomine (a NO donor) subcutaneously prior to or after an LD50 of intracardiac endotoxin. Mortality was followed for 72 hr. There was no statistically significant difference in mortality between control animals and those pretreated with L-NAME, SMT, or molsidomine. A trend toward increased mortality with nonspecific NO synthase inhibition and decreased mortality with the NO donor was noted. Splenic cells were obtained for in vitro cytokine stimulation studies. In vitro adherent splenic cell stimulation studies confirmed an increase in NO production with NO donor pretreatment and decreased production of NO with NO synthase inhibition pretreatment. There was no difference in TxB2 production with either the NO synthase inhibitor or the NO donor. In conclusion, at the several doses employed, neither nonselective or selective NO synthase inhibitors nor NO donors prevented endotoxin-induced mortality in rat neonatal shock. Although these findings do not preclude possible involvement of NO in neonatal pathophysiology, increased NO production thus does not appear to be the primary determinant of the increased susceptibility of the neonatal rat to endotoxic shock.     

一氧化氮合酶抑制剂的研究进展

一氧化氮（ｎｉｔｒｉｃｏｘｉｄｅ,ＮＯ）是一种能调节细胞多种功能的信息分子,它参与心血管、外周和中枢神经以及免疫等系统生理过程和生物信号的调节。体内组织中的ＮＯ由ＮＯ合酶（Ｎｉｔｒｉｃｏｘｉｄｅｓｙｎｔｈａｓｅ,ＮＯＳ）催化左旋精氨酸而合成,合成后的ＮＯ迅速跨膜扩散释放。各种调节ＮＯ释放的因素均作用于ＮＯＳ催化的化学反应过程,而体内影响该反应的ＮＯＳ在各组织的表达不同。特异性ＮＯＳ抑制剂通过调控ＮＯ的合成,对ＮＯＳ表达相关的各种疾病的预防和治疗具有重要的临床意义。本文对近年来ＮＯＳ抑制剂的研究进展作一概述。     

Effects of nitric oxide synthase inhibitors on gastric alkaline secretion in rats.

The effects of NG-nitro-L-arginine methyl ester (L-NAME), the nitric oxide (NO) synthase inhibitor, on gastric HCO3- secretion were examined in anesthetized rats. Intravenous administration of L-NAME (1, 2.5, 5 mg/kg) increased HCO3- secretion in a dose-related manner. This effect of L-NAME was mimicked by NG-mono-methyl-L-arginine (50 mg/kg, i.v.) and was antagonized significantly by concurrent administration of L-arginine but not D-arginine (200 mg/kg, i.v.). These results indicate that gastric HCO3- secretion is stimulated by inhibition of NO biosynthesis.     

Effects of nitric oxide synthase inhibitors in attenuating nicotine withdrawal in rats

This study evaluates the effects of three nitric oxide synthase (NOS) inhibitors (L-NNA, L-NAME, L-NMMA) in attenuating the precipitated nicotine withdrawal syndrome in rats. Male albino Wistar rats were made dependent on nicotine by subcutaneous infusion of nicotine (9.0 mg/kg/day) via a 7 day osmotic pump, whereas control rats received saline via osmotic pumps. Test doses of each NOS inhibitor were administered 30 min prior to mecamylamine (1 mg/kg) challenge in control and test rats on the 7th day. Somatic signs of withdrawal were scored for 15 min by using the global Gellert-Holtzman rating scale followed by a measurement of motor activity. A comparison of NOS inhibitors treated rats with the mecamylamine-precipitated nicotine rats showed that at highest dose L-NNA appears to produce a more complete attenuation of all aspects of withdrawal syndrome. On the other hand, L-NAME appears to do so both at moderate and highest doses. This could be due to an incomplete reversal of some signs of withdrawals by L-NMMA. However, motor activity increased in nicotine dependent rats with the administration of NOS inhibitors. This study demonstrates that NO plays an important role in the expression of behavioral signs of nicotine withdrawal syndrome and suggests a potential use of NOS inhibitors as an aid in tobacco smoking cessation.     

Selective neuronal nitric oxide synthase inhibitors

This review includes the non-patent literature up to October 2004 that deals with selective neuronal nitric oxide synthase inhibitors (highest potency is for the neuronal isozyme). Some non-selective inhibitors or selective inducible nitric oxide synthase inhibitors are mentioned if they are related to compounds that are discussed; structures of these compounds generally are not given. In vitro inhibition constants are given either as IC(50) values or as K(i)values. An IC(50) value, the inhibitor concentration that produces 50% inhibition in the presence of a constant concentration of substrate, is obtained by extrapolation of several rate data points to 50% inhibition. K(i) values are derived from several types of plots that relate the concentration of inhibitor with enzyme velocity in the presence of a variety of substrate concentrations [1]. The K(i) value can be estimated from the IC(50) value [2]. Although the two inhibition constants are related, they are not the same; generally, the reported K(i) values tend to be lower than the IC(50) values. If specifics are desired about how the data were collected, then the reader will have to look in the literature cited. No attempt was made to be exhaustive in citing all references related to specific inhibitors; rather, examples of literature references are given for each inhibitor described.     

Catalepsy induced by intra-striatal administration of nitric oxide synthase inhibitors in rats

Systemic administration of nitric oxide synthase (NOS) inhibitors induces catalepsy in a dose-dependent manner in male Albino-Swiss mice. The objective of the present work was to investigate if similar effects occur in rats and if these effects are centrally mediated. The results showed that systemic administration of N(G)-nitro-L-arginine (L-NOARG, 40-160 mg/kg, i.p.), a non-selective NOS inhibitor, induced catalepsy in rats. Similar effects were found after intracerebroventricular (i.c.v.) injection of L-NOARG (50-200 nmol) or N(G)-nitro-L-arginine methylester (L-NAME, 100-200 nmol). The dose-response curve of the former compound, however, had an inverted U shape. The effect of L-NOARG (100 nmol, i.c.v.) was completely prevented by pre-treatment with L-arginine (300 nmol, i.c.v.) but not by D-arginine (300 nmol, i.c.v.). Intra-striatal injection of N(G)-monomethyl-L-arginine (L-NMMA, 100 nmol), 7-nitroindazole (7-NIO, 100 nmol), L-NOARG (25-100 nmol) or L-NAME (50-200 nmol) also induced catalepsy. Similar to i.c.v. administration, the latter two compounds produced bell-shaped dose-response curves. The cataleptic effect of intra-striatal administration of L-NAME (100 nmol) was reversed by local treatment with L-arginine (100 nmol). These results suggest that interference with the striatal formation of nitric oxide may induce significant motor effects in rats.     

Kynurenamines as neural nitric oxide synthase inhibitors

To find new compounds with potential neuroprotective activity, we have designed, synthesized, and characterized a series of neural nitric oxide synthase (nNOS) inhibitors with a kynurenamine structure. Among them, N-[3-(2-amino-5-methoxyphenyl)-3-oxopropyl]acetamide is the main melatonin metabolite in the brain and shows the highest activity in the series, with an inhibition percentage of 65% at a 1 mM concentration. The structure-activity relationship of the new series partially reflects that of the previously reported 2-acylamido-4-(2-amino-5-methoxyphenyl)-4-oxobutyric acids, endowed with a kynurenine-like structure. Structural comparisons between these new kinurenamine derivatives, kynurenines, and 1-acyl-3-(2-amino-5-methoxyphenyl)-4,5-dihydro-1H-pyrazole derivatives also reported confirm our previous model for the nNOS inhibition.     

Catalepsy induced by nitric oxide synthase inhibitors

• 1.1. Previous study showed that N^G-nitro-l-arginine (l-NOARG), an inhibitor of nitric oxide synthase, induces catalepsy in a dose-dependent manner in male albino-Swiss mice.
• 2.2. The objective of the present work was to further investigate this effect, extending it to other NOS inhibitors.
• 3.3. Results showed that l-NOARG (40–80 mg/kg IP), N^G-nitro-l-arginine methylester (l-NAME, 40–160 mg/kg IP) or N^G-monomethyl-l-arginine (l-NMMA, 80 mg/kg IP) were able to induce catalepsy in mice. The effect of l-NOARG (40 mg/kg) was antagonized by pretreatment with l-arginine (300 mg/kg), but not by d-arginine (300 mg/kg). The catalepsy-inducing effect of l-NOARG suffered rapid tolerance, showing a significant decrease after two days of chronic treatment (40 mg/kg IP, twice a day).
• 4.4. The results suggest that interference with the formation of nitric oxide induces significant motor effects in mice.

     

一氧化氮合酶、环氧合酶与女性压力性尿失禁的关系

摘要： 女性压力性尿失禁（FSUI）严重影响中老年女性身心健康, 已成为女性泌尿外科常见的疾病, 其分子学机制尚不清楚。一氧化氮合酶（NOS）和环氧合酶（COX）及其各自的催化产物一氧化氮（NO）和前列腺素（PG）与 FSUI 有密切联系。本文就 NOS 和 COX 在女性下尿路的分布及其在 FSUI 中的研究进展进行综述。     

Effects of nitric oxide synthase inhibitors on the discriminative stimulus effects of cocaine in rats

RATIONALE: Nitric oxide synthase (NOS) inhibitors may modulate the discriminative stimulus effects of cocaine because they alter dopamine (DA) release. OBJECTIVES: The effects of the NOS inhibitors NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitro-indazole (7-NI) were examined in experiments designed to better understand the mechanisms that may underlie the interactions between NOS inhibitors and cocaine. METHODS: Rats were trained to discriminate 10 mg/kg cocaine from saline, and then substitution and pretreatment tests with L-NAME and 7-NI were conducted. To determine if the combined effects of NOS inhibitors and cocaine might be related to DA mechanisms and/or to N-methyl-D-aspartate (NMDA) receptor mechanisms, substitution tests with other indirect DA agonists and NMDA antagonists were carried out in the presence and absence of L-NAME. In addition, the roles of the D1 and D2 families of DA receptors in mediating the cocaine-altering effects of L-NAME and 7-NI were examined in antagonism tests using SCH 23390 and haloperidol, respectively. RESULTS: The results demonstrated that neither NOS inhibitor alone substituted for the 10 mg/kg cocaine training dose, but when given as a pretreatment, 100 mg/kg L-NAME as well as 10 mg/kg 7-NI enhanced the discriminative stimulus and rate-decreasing effects of cocaine. L-NAME pretreatment also enhanced the potency of (+)-amphetamine and GBR 12909, but not MK-801, phencyclidine, or NPC 17742, for producing discriminative stimulus and rate-decreasing effects in substitution tests. Further testing showed that the cocaine-enhancing effects of L-NAME and 7-NI were attenuated by doses of haloperidol and SCH 23390 that minimally altered the effects of cocaine alone. CONCLUSIONS: These findings suggest that L-NAME and 7-NI may increase the potency of cocaine and other indirect DA agonists through a central mechanism whereby DA neurotransmission is directly enhanced by NOS inhibition.