Penile erection induced by EP 80661 and other hexarelin peptide analogues: involvement of paraventricular nitric oxide

The effect of GAB-D-Trp(2-Me)-D-Trp(2-Me)-LysNH(2) (EP 80661), GAB-D-Trp(2-Me)-D-Trp(2-Me)-D-Trp(2-Me)-LysNH(2) (EP 60761), GAB-D-Trp(2-Me)-LysNH(2) (EP 91071) and GAB-D-Trp(2-Me)-D-beta Nal-Phe-LysNH(2) (EP 50885), four hexarelin peptide analogues that induce penile erection when injected into the paraventricular nucleus of the hypothalamus of male rats, on the concentration of NO(2)(-) and NO(3)(-) in the paraventricular dialysate was studied in male rats. EP peptides (1 microg) induced penile erection and increased the concentration of NO(2)(-) and NO(3)(-) in the paraventricular dialysate. In contrast, hexarelin (1 microg) was ineffective on either penile erection or paraventricular NO(2)(-) and NO(3)(-). EP peptide-induced penile erection was prevented by the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methylester given into the paraventricular nucleus (20 microg), which also reduced the concomitant increase of NO(2)(-) and NO(3)(-) concentration in the paraventricular dialysate. In contrast, the oxytocin receptor antagonist [d(CH(2))(5)Tyr(Me)(2)-Orn(8)]vasotocin (1 microg) given into the paraventricular nucleus, was ineffective on penile erection and on the NO(2)(-) and NO(3)(-) increase induced by EP peptides, despite its ability to prevent the sexual response induced by the above peptides when given into the lateral ventricles. The present results show that EP peptides induce penile erection by activating nitric oxide synthase in the paraventricular nucleus of the hypothalamus, possibly in the cell bodies of oxytocinergic neurons that control penile erection.     

Some properties of brain specific benzodiazepine receptors: new evidence for multiple receptors.

Several new lines of evidence suggest the existence of two or more distinct types of benzodiazepine receptors, in contrast to earlier results suggesting the presence of only one class of receptors. Appropriate thermoinactivation experiments indicate two receptors with different thermostabilities. Several triazolopyridazines, with some of the pharmacological properties of anxiolytics have recently been shown to displace 3H-diazepam and 3H-flunitrazepam with Ki values in the 6 to 100 nanomolar range. These new substances are active in conflict tests in rats and monkeys and prevent metrazol induced seizures in vivo, but strikingly lack the ataxia and sedative properties of the benzodiazepines. Hill analyses of dose-response curves for some of these substances yields Hill coefficients in the range of 0.4--0.6, suggesting that these compounds may be able to discriminate between several types of benzodiazepine receptors.     

Activation of GABAA and opioid receptors reduce penile erection induced by hexarelin peptides

The effect of muscimol, a GABA(A) receptor agonist, and of morphine, an opioid receptor agonist, on penile erection induced by the hexarelin analogue peptide EP 80661 (GAB-D-Trp(2-Me)-D-Trp(2-Me)-LysNH(2)) and on the increase in the concentration of NO(2)(-) and NO(3)(-) that occurs concomitantly in the dialysate obtained from the paraventricular nucleus (PVN) of the hypothalamus by intracerebral microdialysis, was studied in male rats. Muscimol (50, 100 and 200 ng) and morphine (0.1, 0.5, 1 and 5 microg) given into the PVN dose-dependently reduced penile erection induced by EP 80661 (1 microg) injected into the PVN. The reduction of penile erection was parallel to a decrease of the concomitant NO(2)(-) and NO(3)(-) increase that occurs in the paraventricular dialysate in these experimental conditions. Muscimol and morphine effects on EP 80661-induced penile erection and NO(2)(-) increase were prevented by the prior administration into the PVN of bicuculline (250 ng) and naloxone (5 microg), respectively. The present results show that the activation of GABA(A) receptors and of opioid receptors in the PVN reduces penile erection induced by hexarelin analogue peptides by reducing the increase in NO activity that occurs in this hypothalamic nucleus in these experimental conditions.     

Functional evidence for the existence of adenosine receptors in the human heart

Adenosine added to isolated electrically driven preparations of human ventricular heart muscle antagonized the positive inotropic effect of isoprenaline (mean EC50 19 mumol 1(-1), n = 9). Similar effects were observed with the adenosine receptor agonist (-)-N6-phenylisopropyladenosine (mean EC50 0.5 mumol 1(-1), n = 7). These data provide functional evidence for the existence of adenosine receptors in the human myocardium which may modulate the force of contraction during beta-adrenergic stimulation and thus could be involved in the autoregulation of myocardial contractility.     

Pharmacological evidence for the existence of two distinct serotonin receptors in rat brain

The effect of a series of indoleamines on the potassium-evoked release of previously accumulated [³H]serotonin from slices of rat raphe nuclei has been studied. Indoleamine agonists produced a dose-related inhibition of potassium-evoked tritium release which was reversed by methiothepin, metergoline minaserin and methysergide but not cyproheptadine or cinanserin. The relative order of antagonist potency for this effect was different from that obtained for the antagonism of indoleamine-induced inhibition of potassium-evoked tritium release from rat striatal slices previously loaded with [³H]-dopamine. The results show that the serotonin-autoreceptor located on cell bodies and dendrites in the raphe nucleus is different from the postsynaptic serotonin receptor located on dopamine nerve terminals in the striatum.     

Role of prostanoid IP and EP receptors in mediating vasorelaxant responses to PGI2 analogues in rat tail artery: Evidence for Gi/o modulation via EP3 receptors

Prostanoid IP receptors coupled to Gs are thought to be the primary target for prostacyclin (PGI₂) analogues. However, these agents also activate prostanoid EP_1–4 receptor subtypes to varying degrees, which are positively (EP_2/4) or negatively (EP₃) coupled to adenylate cyclase through Gs or Gi, respectively. We investigated the role of these receptors in modulating relaxation to PGI₂ analogues cicaprost, iloprost and treprostinil in pre-contracted segments of rat tail artery. Prostanoid IP (RO1138452), EP₄ (GW627368X), EP₃ (L-798106), EP_1–3 (AH6809), and EP₁ (SC-51322) receptor antagonists were used to determine each receptor contribution. The role of G_i/o was investigated using pertussis toxin (PTX), while dependence on cAMP was determined using adenylate cyclase (2′5′dideoxyadenosine, DDA) and protein kinase A (2′-O-monobutyryladenosine- 3′,5′-cyclic monophosphorothioate, Rp- isomer, Rp-2′-O-MB-cAMPS) inhibitors, and by measurement of tissue cAMP. All analogues caused relaxation which was significantly (P < 0.01) inhibited by RO1138452; with maximum response to cicaprost, iloprost and treprostinil reduced by 51%, 66% and 37%, respectively. GW627368X had no effect when used alone, but in combination with RO1138452, caused a rightward shift of the curves for cicaprost and iloprost but not treprostinil. PTX treatment potentiated relaxation to all 3 analogues (P < 0.01), as did L798106 and AH6809 but not SC-51322. Basal cAMP levels were higher in PTX-treated tissues and DDA- and Rp-2'-O-MB-cAMPs--sensitive responses increased to analogue concentrations < 0.1 μM. In conclusion, prostanoid EP₃ receptors via G_i/o negatively modulate prostanoid IP receptor-mediated relaxation to cicaprost, iloprost and treprostinil. However, other pathways contribute to analogue-induced vasorelaxation, the nature of which remains unclear for treprostinil.     

Oxytocin-induced penile erection and yawning: role of calcium and prostaglandins

The effect of verapamil, flunarizine, nimodipine, nicardipine, and nifedipine, calcium channel inhibitors, and of indomethacin and aspirin, inhibitors of prostaglandin synthesis, on penile erection and yawning induced by oxytocin was studied in male rats. All calcium channel inhibitors given intraperitoneally (IP) 60 min before the intracerebroventricular (ICV) injection of oxytocin (30 ng) prevented in a dose-dependent manner oxytocin effect. Nimodipine and nicardipine were the most effective being active at doses between 5 and 20 mg/kg, while the others were active at doses higher than 15 mg/kg. Prevention of oxytocin effect was also seen after ICV injection of the above compounds. Unlike calcium channel inhibitors, indomethacin given either IP (10 and 50 mg/kg) or ICV (50 micrograms), or aspirin (100 mg/kg IP) were ineffective. Microinjection of calcium, but not of prostaglandin E2 and prostaglandin F2 alpha in the paraventricular nucleus of the hypothalamus, the brain area most sensitive for the induction of the above behavioral responses by oxytocin, induced a symptomatology similar to that induced by oxytocin. The present results suggest that calcium might be the second messenger which mediates the expression of penile erection and yawning induced by oxytocin.     

Piglet saphenous vein contains multiple relaxatory prostanoid receptors: evidence for EP4, EP2, DP and IP receptor subtypes

Prostaglandin E(2) produced endothelium-independent relaxation of phenylephrine- and 5-HT-contracted piglet saphenous vein (PSV; pEC(50)=8.6+/-0.2; n=6).The prostanoid EP(4) receptor antagonist GW627368X (30-300 nM) produced parallel rightward displacement of PGE(2) concentration-effect (E/[A]) curves (pK(b)=9.2+/-0.2; slope=1). Higher concentrations of GW627368X did not produce further rightward shifts, revealing the presence of non-EP(4) prostanoid receptors.In all, 18 other prostanoid receptor agonists relaxed PSV in a concentration-related manner. Relative potencies of agonists most sensitive to 10 muM GW627368X (and therefore predominantly activating EP(4) receptors) correlated well with those at human recombinant EP(4) receptors in human embryonic kidney (HEK-293) cells (r(2)=0.74). In the presence of 10 microM GW627368X, the rank order of agonist relative potency matched that of the human recombinant EP(2) receptor in Chinese hamster ovary cells (r(2)=0.72). Iloprost, cicaprost and PGI(2) relaxed PSV maximally and were antagonised by 10 microM GW627368X, demonstrating that they were full EP(4) receptor agonists. Residual responses to these compounds in the presence of GW627368X suggested the presence of IP receptors.BW245C relaxed PSV maximally (pEC(50)=6.8+/-0.1). In the presence of 10 microM GW627368X, BW245C produced biphasic E/[A] curves (phase one pEC(50)=6.6; alpha=24%; phase two pEC(50)=5.1; alpha=112%). Phase two was antagonised by the DP receptor antagonist BW A868C (1 microM), demonstrating that BW245C is an agonist at DP and EP4 receptors.We conclude that PSV contains EP(4), EP(2), DP and IP receptors; IP receptor agonists are also porcine EP(4) receptor agonists.     

氯胺酮对全身麻醉后阴茎勃起治疗效果的观察

目的 探讨氯胺酮对全身麻醉后阴茎勃起的治疗效果.方法 2011年4月至2013年8月于宁波大学医学院附属医院接受手术治疗的男性患者共741例,其中18例麻醉后发生阴茎勃起为勃起组,余723例为无勃起组.勃起组患者采用静脉注射氯胺酮进行治疗.对勃起组阴茎萎缩变软的时间,注射前后患者的血压、心率、心律及2组麻醉苏醒时间、术后意识障碍、恶心呕吐等情况进行观察.结果 勃起组患者注射氯胺酮后阴茎萎缩变软的时间为（2.9 ±0.4） min;注射前患者的血压为（110±11）/（70 ±9） mmHg（1 mmHg=0.133 kPa）,明显低于注射后的（147±11）/（94±10） mmHg,差异有统计学意义（t=7.51,t=10.26,均P＜0.05）;注射后患者的心率为（89±9）次/min,明显快于注射前（64±8）次/rain,差异有统计学意义（=8.25,P＜0.05）.勃起组患者的麻醉苏醒时间、术后意识障碍率、术后恶心呕吐率与非勃起组患者相比,差异均无统计学意义（t=0.90,x2=0.60,x2=0.52,均P＞0.05）.结论 氯胺酮治疗全身麻醉后阴茎勃起疗效明显,安全迅速.     

Mechanisms of penile erection and basis for pharmacological treatment of erectile dysfunction

Erection is basically a spinal reflex that can be initiated by recruitment of penile afferents, both autonomic and somatic, and supraspinal influences from visual, olfactory, and imaginary stimuli. Several central transmitters are involved in the erectile control. Dopamine, acetylcholine, nitric oxide (NO), and peptides, such as oxytocin and adrenocorticotropin/α-melanocyte-stimulating hormone, have a facilitatory role, whereas serotonin may be either facilitatory or inhibitory, and enkephalins are inhibitory. The balance between contractant and relaxant factors controls the degree of contraction of the smooth muscle of the corpora cavernosa (CC) and determines the functional state of the penis. Noradrenaline contracts both CC and penile vessels via stimulation of α?-adrenoceptors. Neurogenic NO is considered the most important factor for relaxation of penile vessels and CC. The role of other mediators, released from nerves or endothelium, has not been definitely established. Erectile dysfunction (ED), defined as the "inability to achieve or maintain an erection adequate for sexual satisfaction," may have multiple causes and can be classified as psychogenic, vasculogenic or organic, neurologic, and endocrinologic. Many patients with ED respond well to the pharmacological treatments that are currently available, but there are still groups of patients in whom the response is unsatisfactory. The drugs used are able to substitute, partially or completely, the malfunctioning endogenous mechanisms that control penile erection. Most drugs have a direct action on penile tissue facilitating penile smooth muscle relaxation, including oral phosphodiesterase inhibitors and intracavernosal injections of prostaglandin E?. Irrespective of the underlying cause, these drugs are effective in the majority of cases. Drugs with a central site of action have so far not been very successful. There is a need for therapeutic alternatives. This requires identification of new therapeutic targets and design of new approaches. Research in the field is expanding, and several promising new targets for future drugs have been identified.     

酮康唑预防阴茎术后勃起的临床分析

目的探讨酮康唑预防阴茎术后自发性勃起的临床效果。方法61例准备行阴茎手术的患者随机分为治疗组（31例）和对照组（30例）,2组患者分别于术后给予酮康唑和己烯雌酚,观察阴茎术后自发性勃起的状况。结果治疗组总有效率为90.3%,而对照组为70.0%,2组比较差异有统计学意义（P〈0.05）。结论酮康唑可做为一种安全有效的预防阴茎术后自发性勃起的药物,值得临床推广使用。     

Activation of EP4 receptors prevents endotoxin-induced neutrophil infiltration into the airways and enhances microvascular barrier function

Background and Purpose

Pulmonary vascular dysfunction is a key event in acute lung injury. We recently demonstrated that PGE₂, via activation of E-prostanoid (EP)₄ receptors, strongly enhances microvascular barrier function in vitro. The aim of this study was to investigate the beneficial effects of concomitant EP₄ receptor activation in murine models of acute pulmonary inflammation.

Experimental Approach

Pulmonary inflammation in male BALB/c mice was induced by LPS (20 μg per mouse intranasally) or oleic acid (0.15 μL·g^-1, i.v^.). In-vitro, endothelial barrier function was determined by measuring electrical impedance.

Key Results

PGE₂ activation of EP₄ receptors reduced neutrophil infiltration, pulmonary vascular leakage and TNF-α concentration in bronchoalveolar lavage fluid from LPS-induced pulmonary inflammation. Similarly, pulmonary vascular hyperpermeability induced by oleic acid was counteracted by EP₄ receptor activation. In lung function assays, the EP₄ agonist ONO AE1-329 restored the increased resistance and reduced compliance upon methacholine challenge in mice treated with LPS or oleic acid. In agreement with these findings, EP₄ receptor activation increased the in vitro vascular barrier function of human and mouse pulmonary microvascular endothelial cells and diminished the barrier disruption induced by LPS. The EP₂ agonist ONO AE1-259 likewise reversed LPS-induced lung dysfunction without enhancing vascular barrier function.

Conclusion and Implications

Our results show that activation of the EP₄ receptor strengthens the microvascular barrier function and thereby ameliorates the pathology of acute lung inflammation, including neutrophil infiltration, vascular oedema formation and airway dysfunction. This suggests a potential benefit for EP₄ agonists in acute pulmonary inflammation.     

High affinity [3H]ethylketazocine binding: evidence for specific kappa receptors

A study has been made of the inactivation of mu(mu) ([3H]-dihydromorphine), delta (delta) ([3H](D-ala2-D-leu5)enkephalin) and kappa (kappa) ([3H]ethylketazocine) opiate receptor binding sites by N-ethylmaleimide (NEM) and it was observed that in contrast to mu and delta sites, the kappa sites of rat brain membrane preparations were resistant to low concentrations of N-ethylmaleimide. Furthermore, this kappa site was selectively protected, from inactivation with high concentrations of N-ethylmaleimide, by the kappa agonists ethylketazocine and (-)-alpha-(1R,5R,9R)-5,9-dimethyl-2-(L-tetrahydrofurfuryl)-2'-hydroxy-6,7-benzo morphan (MR-2034) but not by morphine or (D-ala2-D-leu5)-enkephalin. These studies suggest that a unique kappa receptor is present in the rat CNS.     

Oxytocin: an extremely potent inducer of penile erection and yawning in male rats

The intracerebroventricular (i.c.v.) injection of oxytocin, in doses ranging from 5 to 90 ng (5–90 pmol) induced penile erection and yawning in male rats. Such response was not induced by doses of the peptide higher than 100 ng, nor by equimolar doses of i.c.v. [Arg⁸]vasopressin, ACTH-(1–24), -MSH, rat corticotropin-releasing factor (rCRF), delta sleep-inducing peptide, neurotensin or substance P. Oxytocin-induced penile erection and yawning were prevented by atropine and morphine, but not by methylatropine or the opiate antagonist naloxone. Haloperidol, a dopamine receptor antagonist, was ineffective at low doses; it partially prevented penile erection but not yawning at high doses. Since oxytocin is present not only in the neurohypophysis but also in other brain areas, our results suggest that oxytocin is implicated in the regulation of penile erection and yawning, and provide further evidence that oxytocin acts as a neuropeptide in the central nervous system.     

Nitric oxide as a mediator of cocaine-induced penile erection in the rat.

1. The effect of local application of cocaine to the corpus cavernosum on intracavernous pressure (ICP), an experimental index for penile erection, was examined in Sprague-Dawley rats anaesthetized with chloral hydrate. The potential involvement of dopamine, noradrenaline or nitric oxide as the chemical mediator in this process, and the pharmacological action of cocaine as a local anaesthetic in the induced increase in ICP, were also investigated. 2. Intracavernous (i.c.) administration of cocaine (40, 80 or 160 micrograms) to the corpus cavernosum resulted in a dose-related increase in both amplitude and duration of ICP. 3. The elevation of ICP induced by cocaine (160 micrograms, i.c.) was not significantly influenced by prior injection into the corpus cavernosum of either the D1 or D2 dopamine receptor antagonist, R-(+)-SCH 22390 (250 pmol) or (-)-sulpiride (250 pmol). 4. Similarly, penile erection promoted by cocaine (160 micrograms, i.c.) was not appreciably affected by i.c. pretreatment with the alpha 1-, alpha 2-, or beta-adrenoceptor antagonist, prazosin (50 pmol), yohimbine (50 pmol) or propranolol (5 nmol). 5. Whereas lignocaine (4 mumol, i.c.) depressed penile erection induced by papaverine (400 micrograms, i.c.), local application of cocaine (160 micrograms) into the corpus cavernosum still elicited significant elevation in ICP in the presence of lignocaine or papaverine. 6. The increase in ICP induced by cocaine (160 micrograms, i.c.) was attenuated dose-dependently by prior cavernosal administration of the NO synthase inhibitor, N omega-nitro-L -arginine methyl ester (L-NAME, 0.5, 1 or 5 pmol) or NG-monomethyl-L-arginine (L-NMMA, 2.5, 5 or 10 pmol). The blunting effect of L-NAME or L-NMMA was reversed by co-administration of the NO precursor, L-arginine (1 nmol, i.c.). 7. Pretreatment by local application into the corpus cavernosum of methylene blue (2.5 mumol), an inhibitor of cytosolic guanylyl cyclase, antagonized cocaine-induced penile erection. 8. Direct i.c. administration of a NO donor, nitroglycerin (10 or 20 nmol), mimicked the local action of cocaine by promoting a significant increase in ICP. 9. It is concluded that cocaine may induce penile erection by increasing ICP via a local action on the corpus cavernosum. This process did not appear to involve either dopamine or noradrenaline as the chemical mediator, nor the pharmacological action of cocaine as a local anaesthetic. On the other hand, it is likely that initiation and maintenance of penile erection elicited by cavernosal application of cocaine engaged an active participation of NO and subsequent activation of guanylyl cyclase in the corpus cavernosum.     

Functional evidence against the existence of β2-adrenoceptors mediating positive inotropic effects in guinea-pig right ventricular myocardium

In guinea-pig isolated papillary muscles we studied the positive inotropic effects of the β-adrenoceptor agonists isoprenaline, fenoterol and noradrenaline in the presence and absence of the β₁-selective antagonist atenolol and the β₂-adrenoceptor antagonist ICI 118.551. In Schild regression analysis pA₂ values for either atenolol (7.14–7.16) and ICI 118.551 (6.79–6.84) were independent of the agonists used. These results support the view that the inotropic response in guinea-pig ventricular myocardium is mediated by β₁-adrenoceptors only. Received: 2 May 1996 / Accepted: 21 August 1996