The interactions of nitric oxide and adenosine on penicillin-induced epileptiform activity in rats

In this study, the influence of nitric oxide (NO) and adenosine systems on penicillin-induced epileptiform activity was examined in rats. NO donor, sodium nitroprusside (SNP, 50 micrograms per rat, i.c.v.) reduced the frequency but not the amplitude of epileptiform discharges. Non-selective NOS inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME, 100 micrograms per rat, i.c.v.) practically did not exert any effect on the spike frequency and amplitude. Adenosine (100 micrograms per rat, i.c.) reduced spike frequency but not the amplitude, whereas theophylline (100 micrograms per rat, i.c.v.) increased the mean spike frequency and amplitude of penicillin-induced epileptiform discharges. Co-injection of theophylline and L-NAME did not cause a further increase in the epileptiform activity compared with theophylline. When NO production was blocked with L-NAME, the inhibitory effects of adenosine were lost. The obtained results suggest that NO and adenosine may decrease penicillin-induced epileptiform activity in rats and that NO, at least in part, may mediate the anticonvulsant effect of adenosine.     

Effect of captopril in L-NAME-induced hypertension on the rat myocardium, aorta, brain and kidney

Long-term administration of NG-nitro-L-arginine methyl ester (L-NAME) induces development of hypertension and hypertrophy of the left ventricle in rats. The aim of the present study was to demonstrate the effect of chronic L-NAME treatment on DNA and RNA concentration, and protein synthesis in the rat heart, aorta, brain and kidney and to determine the effect of angiotensin converting enzyme (ACE) inhibitor captopril on these potential alterations. Four groups of rats were investigated: control, L-NAME (40 mg kg-1 day-1), captopril (100 mg kg-1 day-1), and L-NAME (40 mg kg-1 day-1) + captopril (100 mg kg-1 day-1). NO synthase activity in the heart, aorta, brain and kidney was found to be decreased in the L-NAME group. In the group of rats treated with L-NAME + captopril, captopril did not affect NO synthase inhibition. Captopril, however, completely prevented development of hypertension and left ventricular hypertrophy in this group. In the L-NAME group, DNA and RNA concentrations, as well as [14C]leucine incorporation, were significantly increased in all the tissues investigated. In the L-NAME + captopril group, captopril completely prevented the enhancement of DNA and RNA concentrations and [14C]leucine incorporation in all tissues compared to the L-NAME group. Moreover, a significant decrease in RNA concentration and [14C]leucine incorporation below control values was found in the captopril group as well as the L-NAME + captopril group in all the tissues investigated. We conclude that captopril prevented the development of hypertension and increase in nucleic acid concentration and protein synthesis in the heart, aorta, brain and kidney in rats treated with L-NAME + captopril. However, this protective effect of captopril was not associated with increased NO synthase activity in this model of hypertension.     

罗格列酮通过激活PPARγ改善肺动脉高压大鼠肺动脉内皮依赖性舒张功能

 目的：探索过氧化物酶体增殖物激活受体γ（PPARγ）激动剂罗格列酮对肺动脉高压大鼠模型肺动脉血管内皮功能的影响。方法：（1）SD大鼠40只,分为正常对照组、模型组、罗格列酮组和罗格列酮+GW9662（PPARγ拮抗剂）干预组,每组10只,以野百合碱（60 mg/kg）一次性皮下注射复制肺动脉高压大鼠模型,再灌胃给予罗格列酮（2.0 mg·kg-1·d-1）或罗格列酮 + GW 9662（0.3 mg·kg-1·d-1）干预。4周后,取血浆测一氧化氮（NO）及内皮素-1（ET-1）的水平,分离肺动脉二级分支,以微血管张力测定仪测定肺动脉血管功能变化情况。（2）体外培养人肺动脉内皮细胞株（HPAECs）,探讨罗格列酮对HPAECs　NO生成的影响。结果：罗格列酮可显著改善肺动脉高压大鼠血管内皮依赖性舒张功能,但不能显著改善非内皮依赖性舒张功能;罗格列酮干预可降低血浆ET-1水平,升高NO水平;但罗格列酮的以上作用在同时给予PPARγ拮抗剂GW9662时显著被减弱。体外实验证实,罗格列酮可显著增加HPAECsf的NO生成,但该作用同样可被GW9662所阻断。结论：罗格列酮通过激活PPARγ改善肺动脉高压大鼠的血管内皮依赖性舒张功能可能是其治疗肺动脉高压的基础。     

L-精氨酸对缺氧性肺动脉高压大鼠内皮素释放的影响

目的：探讨Ｌ－精氨酸（Ｌ－Ａｒｇ）对缺氧性肺动脉高压（ＨＰＨ）大鼠血浆内皮素－１（ＥＴ－１）释放的影响。方法：将Ｗｉｓｔａｒ大鼠４０只分为：对照组,缺氧组,缺氧＋Ｎ＾ω－硝基－Ｌ－精氨酸甲脂（Ｌ－ＮＡＭＥ）组和缺氧Ｌ－Ａｒｇ组。结果：缺氧组的肺动脉平均压（ｍＰＡＰ）显著高于对照组（Ｐ〈０．０５）,缺氧组＋Ｌ－Ａｒｇ组的ｍＰＡＰ显著低于缺氧组（Ｐ〈０．０５）及缺氧＋Ｌ－ＮＡＭＥ组（Ｐ〈０．０１）,缺     

长期摄取高钠盐饮食引发的高血压

目的:探讨高钠盐引发的高血压发病机制。方法:雄性SD大鼠40只,分为对照(NC)组、高盐(HS)组、高盐+L-精氨酸(HS+Arg)组、高盐+依那普利(HS+En)组和高盐+特拉唑嗪(HS+Ter)组,每组8只。各组饲料相同。NC组饮去离子水;HS组饮1.5%氯化钠溶液;HS+Arg组、HS+En组和HS+Ter组分别饮用1.5%氯化钠溶液配制的L-精氨酸(4g·kg^-1·d^-1)、依那普利(30mg·kg^-1·d^-1)和盐酸特拉唑嗪(4mg·kg^-1·d^-1)。第8周末,大鼠在戊巴比妥钠麻醉下,直接测量颈总动脉血压,开腹抽取下腔静脉血及剖取肾脏、肾上腺。测定前海葱苷原A样物质(PLC)水平,Na^＋-K^＋-ATP酶活性,NO(x)、内皮素(ET)及血管紧张素II(AngII)水平。结果:HS组大鼠血压显著高于NC组,血浆PLC、ET及肾上腺AngII水平皆显著高于NC组;血浆和肾组织NO(x)和AngII水平、肾脏Na^＋-K^＋-ATP酶活性皆明显低于NC组;HS+Arg组、HS+En组和HS+Ter组大鼠血压和血浆PLC水平皆显著低于HS组,血浆和肾组织NO(x)水平及Na^＋-K^＋-ATP酶活性皆明显高于HS组;HS+Arg组、HS+En组和HS+Ter组肾上腺AngII水平及HS+Arg组血浆ET水平明显低于HS组,并与NC组相近。结论:在高钠盐引发的高血压发病机制中,除钠泵抑制因子释放增加致细胞膜Na^＋-K^＋-ATP酶活性减低外,内皮功能损害致NO释放减少也可能起重要作用。     

内皮素在NG-硝基-L-精氨酸甲酯引起的高血压的作用

在口服Ｎ＾Ｇ－硝基－Ｌ－精氨酸甲酯（Ｎ＾Ｇ－ｎｉｔｒｏ－Ｌ－ａｒｇｉｎｉｎｅ－ｍｅｔｈｌｅｓｔｅｒ,Ｌ－ＮＡＭＥ）造成的大鼠高血压模型上,观察血浆内皮素和亚硝酸盐含量,血管内皮素水平和ＮＯ合酶活性和ＥＴ受体的变化,以及应用ＥＴ受体阻断剂ＪＫＣ－３０１对高血压的影响。     

Inhibition of nitric oxide synthase delays the development of tolerance to LPS in rats

The role of nitric oxide (NO) was investigated in endotoxin (lipopolysaccharide, LPS) tolerance in freely moving biotelemetered rats. We monitored changes in febrile response and feeding behavior (food intake, water intake) during the development of tolerance to repeated intraperitoneal injections of LPS (50 microg/kg) along with injections of N(omega)-nitro-L-arginine methyl ester (L-NAME; 50 mg/kg), an inhibitor of NO synthase. Rats were treated with LPS and L-NAME for three consecutive days. On the fourth day, all rats were injected with LPS alone. Control rats were injected with saline along with saline or with L-NAME for four consecutive days. Rats repeatedly injected with LPS became tolerant to pyrogenic and hypophagic/cachexic effects of LPS as early as on the second day of experiment. The treatment with L-NAME prevented the attenuation of febrile response following the second LPS injection. Moreover, the depressive effects of LPS on body weight as well as on water and food intake were prolonged in rats treated with a combination of L-NAME and LPS. Injection of LPS caused a 3.5-fold increase in plasma nitrite within 3 h and nitrite levels remained significantly elevated 6 and 24 h after LPS. Rats injected secondly with LPS did have still 2.5- to 3-fold increase in plasma nitrite levels 3 and 6 h, but not 24 h, after injection. Third injection of LPS did not elevate nitrite level in plasma. Taken together, presented data provide clear evidence that NO formation is involved in mechanisms responsible for development of early-stage tolerance to endotoxin.     

Renal dysfunction after chronic blockade of nitric oxide synthesis

The effects of the chronic inhibition of nitric oxide (NO) on renal hemodynamics and tubular function were studied in rats treated for 8 weeks with the NO synthesis inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME; 40 mg/kg/day). In addition, the effect of L-NAME administration on vasoactive systems (renin-angiotensin system, aldosterone, catecholamines, endothelin, and thromboxane A(2)) was evaluated. Chronic inhibition of NO significantly elevated blood pressure, reduced glomerular filtration rate and renal blood flow, blunted the pressure-diuresis-natriuresis response, and increased protein urine excretion. All these changes were associated with blunted nitrite production in response to acetylcholine in glomeruli. No changes were observed in the plasma levels of either renin activity, aldosterone, or endothelin in L-NAME-treated rats. Similarly, no differences were observed in the urinary excretion of thromboxane B(2) between both group of animals. By contrast, plasma concentrations of both epinephrine and norepinephrine were elevated in rats treated with L-NAME. In summary, the results show that chronic blockade of NO produced not only alterations in renal function, but also renal damage, suggesting an important renoprotective role of NO. An activation of sympathoadrenal system could participate in these renal alterations.     

Central nitric oxide blocks vasopressin, oxytocin and atrial natriuretic peptide release and antidiuretic and natriuretic responses induced by central angiotensin II in conscious rats

The presence of nitric oxide synthase (NOS), the enzyme that catalyses the formation of nitric oxide (NO), in the circumventricular organs and magnocellular neurones suggests an important role of NO in the modulation of vasopressin (AVP) and oxytocin (OT) release. Intracerebroventricular (I.C.V.) injection of angiotensin II (Ang II) stimulates the release of AVP, OT and atrial natriuretic peptide (ANP), with the resultant antidiuretic and natriuretic effects. This study investigated the interaction between nitrergic and angiotensinergic pathways on the release of AVP, OT and ANP and on urinary volume and sodium excretion in water-loaded rats. Unanaesthetized, freely moving, male Wistar rats received two water loads followed by an injection into the lateral ventricle of an inhibitor of NOS (L-NAME), a NO donor [3-morpholinylsydnoneimine chloride (SIN-1) or S-nitroso-N-acetyl penicillamine (SNAP)] or vehicle (isotonic saline) and, 20 min after, they received a second I.C.V. injection of Ang II or vehicle. Injections of L-NAME or Ang II produced an increase in plasma levels of AVP, OT and ANP, a reduction in urinary volume and an increase in sodium excretion. Pretreatment with L-NAME enhanced the Ang II-induced increase in AVP, OT and ANP release, as well as the antidiuresis and natriuresis. Injection of SIN-1 or SNAP did not modify hormonal plasma levels and urinary parameters. In contrast SNAP blocked the AVP, OT and ANP release, as well as antidiuretic and natriuretic responses induced by ANG-II. Thus, the central nitrergic system can act to inhibit AVP, OT and ANP secretion and the antidiuretic and natriuretic effects in response to Ang II.     

The role of nitric oxide in mediating pancreatic endocrine responses to insulin-induced hypoglycaemia in the conscious calf

The role of nitric oxide (NO) in mediating pancreatic endocrine responses to moderate hypoglycaemia has been investigated in conscious unrestrained calves. The synthesis of endogenous NO was inhibited by the administration of N-nitro-L-arginine methyl ester (L-NAME; 100 mg kg-1 I.A.), while sodium nitroprusside was infused continuously (2-4 microg min-1 kg-1 I.V.) to mimic the tonic production of NO. This effectively abolished the rise in plasma pancreatic polypeptide (PP) concentration during moderate hypoglycaemia (0.7 nmol kg-1 insulin I.V.) and significantly reduced the response to more intense hypoglycaemia (2.0 nmol kg-1 insulin I. V.). In contrast, the glucagon response was not significantly affected in either group, although consistently higher plasma glucagon values were obtained in response to the higher dose of insulin following the administration of L-NAME. It is concluded that, in the absence of L-NAME, production of NO contributes to the PP response, but not the glucagon response to hypoglycaemia in this species under physiological conditions.     

Salt-Sensitive Hypertension Resulting From Nitric Oxide Synthase Inhibition is Associated with Loss of Regulation of Angiotensin II in the Rat

In the Dahl salt-sensitive hypertensive rat, a diet containing L-arginine, the natural substrate for nitric oxide synthase, abrogates the hypertension. We postulated that nitric oxide synthase inhibition might induce a salt-sensitive form of hypertension and that this salt sensitivity might be linked to a loss of the regulatory effect of sodium ingestion on angiotensin II (Ang II) and angiotensinogen. Male Wistar-Kyoto rats were randomised to a diet containing 0.008 %, 2.2 % or 4.4 % sodium chloride and to treatment with the NO synthase inhibitor L-NAME (10 mg kg(-1) day(-1)) in the drinking water, or drinking water alone (Controls) for 4 weeks. Blood pressure was measured by tail cuff plethysmography twice weekly. After 4 weeks, the rats were anaesthetised and truncal blood collected for determination of angiotensinogen, renin, angiotensin I (Ang I), Ang II and aldosterone concentrations as well as angiotensin-converting enzyme (ACE) activity. Systolic blood pressure increased with increasing dietary sodium intake in the L-NAME-treated rats (P < 0.05). Plasma renin and aldosterone concentrations decreased with increasing dietary sodium intake in both Control and L-NAME-treated rats. Ang I and ACE activity were unchanged by increasing dietary sodium intake. In contrast, the plasma concentration of Ang II and angiotensinogen increased with increasing dietary sodium (P < 0.05 and P < 0.005, respectively). Treatment with the Ang II receptor blocker, losartan, reversed the blood pressure increase. We conclude that treatment with L-NAME induces an increase in blood pressure that is at least in part salt sensitive. Further, the salt-sensitive component appears to be Ang II-dependent, as it was associated with increasing plasma Ang II levels and could be reversed by treatment with an Ang II receptor antagonist.     

Effects of long-term inhibition of neuronal nitric oxide synthase on blood pressure and renin release

Nitric oxide (NO) produced by neuronal NO-synthase (nNOS) in macula densa cells may be involved in the control of renin release. 7-Nitro indazole (7-NI) inhibits nNOS, and we investigated the effect of short- (4 days) and long-term (4 weeks) 7-NI treatment on blood pressure (BP), plasma renin concentration (PRC) and glomerular filtration rate (GFR) in rats on different salt diets. Rats were divided into three groups and given low-salt (LS), normal (C) and high-salt (HS) diets. Each diet group was subdivided into two groups treated either with 7-NI or vehicle. Long-term 7-NI-treated rats (LS and C) showed increased BP compared with controls (LS: 149 +/- 4 vs. 133 +/- 3; C: 146 +/- 4 vs. 127 +/- 4 mmHg). Blood pressure in HS rats did not differ from that in controls. Plasma renin concentration was stimulated in LS-rats (251 +/- 64 mGU mL(-1)) compared with C and HS rats (42 +/- 8 and 39 +/- 5 mGU mL(-1), respectively) but was not significantly affected by chronic 7-NI treatment (350 +/- 103, 49 +/- 10 and 50 +/- 15 mGU mL(-1) in LS, C and HS, respectively). In rats treated with 7-NI for 4 days, no effect on BP was seen, but PRC was increased in 7-NI treated LS rats compared with vehicle treated LS rats (107 +/- 15 vs. 56 +/- 1 mGU mL(-1)). Stimulation of PRC in LS rats was further enhanced by 7-NI after 4 days of treatment, but not affected in rats treated for 4 weeks. This suggests that inhibition of nNOS stimulates renin release but that this stimulatory effect in the long run might be depressed by the increase in blood pressure.     

内皮素和一氧化氮的失平衡在哮喘发病中的作用

目的:探讨内皮素和一氧化氮的平衡在哮喘发病中的作用。方法:用卵白蛋白作为致敏原制备哮喘大鼠模型,建立大鼠离体气管环的张力测定并用内皮素-1(ET-1)作用观察张力的变化和JKC302及L-亚硝基精氨酸甲酯(L-NAME)对ET-1作用的影响。结果:ET-1对正常大鼠和哮喘大鼠离体气道均有强大的收缩作用,对哮喘组的作用明显高于正常对照组(P＜0.01)。在哮喘大鼠ET-1的收缩气道作用只能被ET_A拮抗剂JKC302部分阻断,比例为13.5%。L-NAME孵育哮喘大鼠气管环后,ET-1的气道收缩反应明显升高(P＜0.05)。结论:哮喘大鼠气道对ET-1的反应性明显提高,一氧化氮可影响ET-1的作用,在大鼠介导ET-1气道收缩作用主要是ET_B受体。气道ET-1和NO平衡失调是引起哮喘发生的机制之一。     

Haemodynamic conditions for renal PGE2 and renin release during alpha- and beta-adrenergic stimulation in dogs

Constriction of the renal artery and infusion of an alpha-adrenergic agonist induce autoregulated vasodilation and increase prostaglandin E2 (PGE2) and renin release. The enhancement of renin release during autoregulated vasodilation might be mediated by prostaglandins. To examine this hypothesis, experiments were performed in three groups of anaesthetized dogs. In six dogs constriction of the renal artery to a perfusion pressure below the range of autoregulation raised renin release from 2 +/- 1 to 27 +/- 6 micrograms AI X min-1 and PGE2 release from 1 +/- 1 to 10 +/- 2 pmol X min-1. After administration of indomethacin (10 mg X kg-1 b.wt), PGE2 release was effectively blocked and constriction of the renal artery raised renin release only from 0.1 +/- 0.1 to 6 +/- 1 micrograms AI X min-1. During subsequent continuous infusion of a beta-adrenergic agonist, isoproterenol (0.2 micrograms X kg-1 X min-1), constriction of the renal artery raised renin release from 0.1 +/- 0.1 to 52 +/- 11 micrograms AI X min-1, although there was no rise in PGE2 release. In six dogs, intrarenal infusion of phenylephrine, an alpha- adrenergic agonist, increased PGE2 and renin release before, but not after, indomethacin administration. In six other dogs, phenylephrine infused during isoproterenol infusion increased renin release equally before and after indomethacin administration. Thus the enhancing effect of constricting the renal artery or infusing an alpha-adrenergic agonist is not dependent upon prostaglandins. We propose that autoregulated dilation enhances renin release whether the stimulatory agent is a prostaglandin or a beta-adrenergic agonist.     

TRPV1 activation prevents high-salt diet-induced nocturnal hypertension in mice

High dietary salt-caused hypertension is associated with increasing reactive oxygen species generation and reduced nitric oxide (NO) bioavailability. Transient receptor potential vanilloid type 1 (TRPV1), a specific receptor for capsaicin, is proposed to be involved in Dahl salt-sensitive hypertension, as determined in acute or short-term experiments. However, it remains unknown whether activation of TRPV1 by dietary capsaicin could prevent the vascular oxidative stress and hypertension induced by a high-salt diet. Here, we report that consumption of a high-salt diet blunted endothelium-dependent relaxation in mesenteric resistance arteries and elevated nocturnal blood pressure in mice. These effects were associated with increased superoxide anion generation and reduced NO levels in mesenteric vessels in mice on a high-salt diet. However, chronic administration of capsaicin reduced the high-salt diet-induced endothelial dysfunction and nocturnal hypertension in part by preventing the generation of superoxide anions and NO reduction of mesenteric arteries through vascular TRPV1 activation. Our findings provide new insights into the role of TRPV1 channels in the long-term regulation of blood pressure in response to high-salt intake. TRPV1 activation through chronic dietary capsaicin may represent a promising lifestyle intervention in populations with salt-sensitive hypertension.     

血浆B型利钠肽预测肺动脉高压的价值

目的:探讨血浆B型利钠肽(BNP)浓度预测肺动脉高压的价值。方法:采用化学发光微粒子免疫分析(CMIA)测定48例肺动脉高压患者和46例健康体检正常者外周血浆BNP浓度。超声心动图根据三尖瓣返流估测肺动脉收缩压(SPAP)。比较正常对照组和肺动脉高压组血浆BNP浓度以及统计分析血浆BNP浓度与肺动脉高压之间相关性。结果:正常对照组血浆BNP浓度与肺动脉高压组有显著性差异(P<0.05),轻、中度肺动脉高压组与重度肺动脉高压组血浆BNP浓度无统计学差异(P>0.05),血浆BNP浓度与肺动脉高压有相关性(r=0.394,P<0.01)。结论:血浆BNP浓度与肺动脉高压存在相关性,但血浆BNP浓度并不代表肺动脉高压严重程度。     

Central galanin stimulates pituitary prolactin secretion in rats: possible involvement of hypothalamic vasoactive intestinal polypeptide

The effect of galanin, a newly identified neuropeptide, on pituitary prolactin (PRL) secretion was examined in the rat. Intracerebroventricular (i.c.v.) injection of all 5 doses of galanin (0.4, 1, 2, 5 and 10 micrograms/rat) raised plasma PRL levels in urethane-anesthetized rats. Galanin injection (2 micrograms/rat, i.c.v.) also increased plasma PRL levels in conscious rats. The intermediate dose of galanin (2 micrograms/rat, i.c.v.) produced a greater response in plasma PRL levels than either smaller or larger doses of galanin. Intravenous injection of galanin did not affect plasma PRL levels. Passive immunization with specific anti-vasoactive intestinal polypeptide (VIP) rabbit serum suppressed plasma PRL response to galanin (2 micrograms/rat, i.c.v.) in anesthetized rats. These findings indicate that central galanin has a stimulatory role in pituitary PRL secretion via the hypothalamus in the rat and that VIP may be involved in rat PRL release induced by galanin.     

Characterization of the cardiovascular actions of endothelin in vivo: comparisons with neuropeptide Y and angiotensin II

The cardiovascular actions of the endothelium-derived peptide endothelin were investigated and characterized in vivo. Intravenous bolus administration of endothelin (4-200 pmol kg-1) in the anaesthetized and chlorisondamine-pre-treated pig caused a dose-dependent increase in mean arterial blood pressure (MABP) with a threshold effect at 20 pmol kg-1 without affecting heart rate. Endothelin induced dose-dependent and long-lasting renal vasoconstriction. A slight effect was observed at 4 pmol kg-1 and the maximal response at 200 pmol kg-1 was a 648 +/- 210% increase in renal vascular resistance. The potency of endothelin in increasing MABP and renal vascular resistance was, on a molar basis, similar to that of angiotensin II and six times higher than that of neuropeptide Y. Administration of the calcium antagonist nifedipine (100 micrograms kg-1 i.v.) markedly inhibited the endothelin-induced increases in MABP and renal vascular resistance. The renal vasoconstrictor responses to angiotensin II and neuropeptide Y were similarily reduced by nifedipine (100 micrograms kg-1). A lower dose of nifedipine (10 micrograms kg-1) slightly attenuated the response to angiotensin II but not that to endothelin or neuropeptide Y. It is concluded that i.v. endothelin induces potent increases in systemic blood pressure and renal vasoconstriction in the pig. Nifedipine reduces the vasoconstrictor response to endothelin but not more than the responses to angiotensin II and neuropeptide Y.     

Inhibition of renin secretion by intrarenal alpha-adrenoceptor blockade

This study was designed to determine whether renal alpha-adrenoceptors can mediate tonic neural stimulation of renin secretion. The effect of alpha-adrenoceptor blockade by phenoxybenzamine (POB) or prazosin on renin secretion rate (RSR) was studied in pentobarbital-anesthetized dogs in which renal perfusion pressure was held constant with an adjustable aortic clamp. POB alone (100 micrograms.kg-1.min-1 iv) did not change arterial plasma renin activity (PRA). However, when beta-adrenoceptors were blocked by intravenous propranolol, intravenous POB infusion (100 micrograms.kg-1.min-1) decreased PRA and RSR to 48 +/- 8 and 21 +/- 9% of previous levels within 30 min. This effect was abolished by acute bilateral renal denervation. Direct intrarenal POB infusion (10 or 3.3 micrograms.kg-1.min-1) decreased RSR, whereas intravenous POB (3.3 micrograms.kg-1.min-1) had no effect on either RSR or PRA in propranolol-pretreated dogs. Prazosin (1 microgram.kg-1.min-1 iv) also significantly decreased PRA. These data indicate that when beta-adrenoceptors are blocked by propranolol, tonic neural stimulation of renin secretion is mediated by renal alpha-adrenoceptors.     

A nitric oxide synthesis inhibitor in the medial preoptic area inhibits copulation and stimulus sensitization in male rats

Dopamine in the medial preoptic area (MPOA) facilitates copulation in male rats, and nitric oxide (NO) regulates basal and female-stimulated MPOA dopamine release. Microinjection of L-nitro-arginine methyl ester (L-NAME, an NO synthesis inhibitor) into the MPOA blocked copulation in naive rats and impaired copulation in sexually experienced males. In other naive rats, L-NAME or saline was microinjected into the MPOA before each of 7 daily exposures to a receptive female placed over their cage. In a drug-free test on Day 8, copulation by L-NAME-treated rats was similar to that of unexposed controls and was impaired relative to saline-treated males. Therefore, NO in the MPOA is important for copulation and stimulus sensitization in male rats.