Opioid peptides decrease noradrenaline release and blood pressure in the rabbit at peripheral receptors

Cardioprotective properties of opioid receptor agonists in rats with stress-induced cardiac injury

The objectives of this study were to investigate the role of endogenous opioids in the mediation of stress-induced cardiomyopathy (SIC), and to evaluate which opioid receptors regulate heart resistance to immobilization stress. Wistar rats were subjected to 24 h immobilization stress. Stress-induced heart injury was assessed by 99mTc-pyrophosphate accumulation in the heart. The opioid receptor (OR) antagonists (naltrexone, NxMB - naltrexone methyl bromide, MR 2266, ICI 174.864) and agonists (DALDA, DAMGO, DSLET, U-50,488) were administered intraperitoneally prior to immobilization and 12 h after the start of stress. In addition, the selective micro OR agonists PL017 and DAMGO were administered intracerebroventricularly prior to stress. Finally pretreatment with guanethidine was used. Naltrexone did not alter the cardiac 99mTc-PP accumulation in stressed rats. NxMB aggravated stress-induced cardiomyopathy (P=0.005) (SIC). The selective micro OR agonist DALDA, which does not cross the blood-brain barrier, completely prevented (P=0.006) SIC. The micro OR agonist DAMGO exhibited weaker effect than DALDA. The selective delta ligand (DSLET) and kappa OR ligand (U-50,488) did not alter stress-induced 99mTc-pyrophosphate accumulation in the heart. Intracerebroventricular administration of the micro OR agonists aggravated SIC. Pretreatment with guanethidine abolished this effect (P=0.01). Guanethidine alone exhibited cardioprotective properties. A stimulation of central micro OR promotes an appearance of SIC. In contrast, stimulation of peripheral micro OR contributes to an increase in cardiac tolerance to stress.

Detailed Characterization of Sympathetic Chain Ganglia (SChG) Neurons Supplying the Skin of the Porcine Hindlimb

It is generally known that in the skin sympathetic fibers innervate various dermal structures, including sweat glands, blood vessels, arrectores pilorum muscles and hair follicles. However, there is a lack of data about the distribution and chemical phenotyping of the sympathetic chain ganglia (SChG) neurons projecting to the skin of the pig, a model that is physiologically and anatomically very representative for humans. Thus, the present study was designed to establish the origin of the sympathetic fibers supplying the porcine skin of the hind leg, and the pattern(s) of putative co-incidence of dopamine-β-hydroxylase (DβH) with pituitary adenylate cyclase-activating polypeptide (PACAP), somatostatin (SOM), neuronal nitric oxide synthase, substance P, vasoactive intestinal peptide, neuropeptide Y (NPY), leu5-enkephalin and galanin (GAL) using combined retrograde tracing and double-labeling immunohistochemistry. The Fast Blue-positive neurons were found in the L₂-S₂ ganglia. Most of them were small-sized and contained DβH with PACAP, SOM, NPY or GAL. The findings of the present study provide a detailed description of the distribution and chemical coding of the SChG neurons projecting to the skin of the porcine hind leg. Such data may be the basis for further studies concerning the plasticity of these ganglia under experimental or pathological conditions.

Prospects for Creation of Cardioprotective and Antiarrhythmic Drugs Based on Opioid Receptor Agonists

It has now been demonstrated that the μ, δ1 , δ2 , and κ1 opioid receptor (OR) agonists represent the most promising group of opioids for the creation of drugs enhancing cardiac tolerance to the detrimental effects of ischemia/reperfusion (I/R). Opioids are able to prevent necrosis and apoptosis of cardiomyocytes during I/R and improve cardiac contractility in the reperfusion period. The OR agonists exert an infarct-reducing effect with prophylactic administration and prevent reperfusion-induced cardiomyocyte death when ischemic injury of heart has already occurred; that is, opioids can mimic preconditioning and postconditioning phenomena. Furthermore, opioids are also effective in preventing ischemia-induced arrhythmias.

The cardiovascular effects of a chimeric opioid peptide based on morphiceptin and PFRTic-NH2

MCRT (YPFPFRTic-NH(2)) is a chimeric opioid peptide based on morphiceptin and PFRTic-NH(2). In order to assess the cardiovascular effect of MCRT, it was administered by intravenous (i.v.) injection targeting at the peripheral nervous system and by intracerebroventricular (i.c.v.) injection targeting at the central nervous system. Naloxone and L-NAME were injected before MCRT to investigate possible interactions with MCRT. Results show that administration of MCRT by i.v. or i.c.v. injection could induce bradycardia and decrease in mean arterial pressure (MAP) at a greater degree than that with morphiceptin and PFRTic-NH(2). When MCRT and NPFF were coinjected, we observed a dose-dependent weakening of these cardiovascular effects by MCRT. Because naloxone completely abolished the cardiovascular effects of MCRT, we conclude that opioid receptors are involved in regulating the MAP of MCRT regardless of modes of injection. The effect of MCRT on heart rate is completely dependent on opioid receptors when MCRT was administered by i.c.v. instead of i.v. The central nitric oxide (NO) pathway is involved in regulating blood pressure by MCRT under both modes of injection, but the peripheral NO pathway had no effect on lowering blood pressure mediated by MCRT when it was administered by i.c.v. Based on the results from different modes of injection, the regulation of heart rate by MCRT mainly involves in the central NO pathway. Lastly, we observed that the cardiovascular effects of MCRT such as bradycardia and decrease of blood pressure, were stronger than that of its parent peptides. Opioid receptors and the NO pathway are involved in the cardiovascular regulation by MCRT, and their degree of involvement differs between intravenous and intracerebroventricular injection.

Effect of transcutaneous electrical nerve stimulation on primary dysmenorrhea

Objectives. Dysmenorrhea is a disturbing problem among women of childbearing age. The purpose of this study is to investigate the effect of high-frequency transcutaneous electrical nerve stimulation (TENS) on primary dysmenorrhea and to compare the placebo effect by sham TENS in a randomized controlled study. Materials and Methods. Twenty-two women participated in the two-month experiment by using TENS or sham TENS in a random order for their dysmenorrhea. Outcome measures included self-reported pain intensity, symptom and function questionnaire related to dysmenorrhea, quality of life, satisfaction after TENS application, and other pain management agents adapted by the participants. Two-way repeated measures analysis of variance (two-way ANOVA) was conducted to compare pain intensity between pre-post values and groups (TENS vs. placebo). One-way repeated measures analysis of variance (one-way ANOVA) was conducted to compare scores from questionnaire of symptoms and quality of life at baseline, and after placebo or TENS stimulation. Results. Pain intensity in TENS is significantly decreased than in the placebo group (p= 0.018). The decrease of pain intensity after TENS and placebo TENS were both significant, with p < 0.00005 and p < 0.00005 respectively. Furthermore, TENS significantly changed the degree of autonomic symptoms (p= 0.048); but not after placebo TENS. Conclusion. This result supports that women in our country who suffer from primary dysmenorrhea could benefit by using TENS, which is consistent with the previous studies. In addition to pain-relieving effects, relief of the autonomic symptoms associated with dysmenorrhea also indicated that the mechanism of TENS might be different from the placebo effect of the sham TENS stimulation. These findings indicate the immediate effects of TENS in women with primary dysmenorrheal.

Activation of peripheral delta2 opioid receptors increases cardiac tolerance to ischemia/reperfusion injury Involvement of protein kinase C, NO-synthase, KATP channels and the autonomic nervous system

AIMS

This study aims to investigate the role of peripheral delta(2) opioid receptors in cardiac tolerance to ischemia/reperfusion injury and to examine the contribution of PKC, TK, K(ATP) channels and the autonomic nervous system in delta(2) cardioprotection.

MAIN METHODS

Deltorphin II and various inhibitors were administered in vivo prior to coronary artery occlusion and reperfusion in a rat model. The animals were monitored for the development of arrhythmias, infarct development and the effects of selected inhibitors.

KEY FINDINGS

Pretreatment with peripheral and delta(2) specific opioid receptor (OR) antagonists completely abolished the cardioprotective effects of deltorphin II. In contrast, the selective delta(1) OR antagonist 7-benzylidenenaltrexone (BNTX) had no effect. The protein kinase C (PKC) inhibitor chelerythrine and the NO-synthase inhibitor L-NAME (N-nitro-L-arginine methyl ester) also reversed both deltorphin II effects. The nonselective ATP-sensitive K+ (K(ATP)) channel inhibitor glibenclamide and the selective mitochondrial K(ATP) channel inhibitor 5-hydroxydecanoic acid only abolished the infarct-sparing effect of deltorphin II. Inhibition of tyrosine kinase (TK) with genistein, the ganglion blocker hexamethonium and the depletion of endogenous catecholamine storage with guanethidine reversed the antiarrhythmic action of deltorphin II but did not change its infarct-sparing action.

SIGNIFICANCE

The cardioprotective mechanism of deltorphin II is mediated via stimulation of peripheral delta(2) opioid receptors. PKC and NOS are involved in both its infarct-sparing and antiarrhythmic effects. Infarct-sparing is dependent upon mitochondrial K(ATP) channel activation while the antiarrhythmic effect is dependent upon TK activation. Endogenous catecholamine depletion reduced antiarrhythmic effects but did not alter the infarct-sparing effect of deltorphin II.

Peripheral modulation of learning and memory: enkephalins as a model system

Extensive research on the effects of enkephalins on conditioning is reviewed and used as the basis for a model of peripheral modulation of learning and memory. An overall theme emphasized throughout our discussion is that these peptides can influence the strength with which a memory is acquired and stored by acting outside the blood-brain barrier. This assertion is supported by research on the behavioral effects of systemically administered enkephalins and opioid antagonists, the rapid hydrolysis of circulating enkephalins in vivo, and the limited ability of these peptides to penetrate the blood-brain barrier. A consideration of the extensive distribution of enkephalins throughout peripheral autonomic systems leads to the proposal that enkephalins may act to modulate learning and memory by altering peripheral autonomic function; autonomic afferents may then communicate with the memory trace in the CNS through a central modulatory pathway outlined herein. Evidence that some stressful experiences may lead to increases in circulating enkephalins also is discussed. The sites of action of these circulating enkephalins may involve peripheral autonomic sites, or additionally may involve the circumventricular organs. As a further regulatory mechanism, circulating enkephalin levels may be controlled by experience-dependent alterations of the activity of enzyme systems that participate in their breakdown. Finally, it is emphasized that the mechanisms of enkephalin action postulated herein may be applicable to the actions of other peripheral hormones, peptides, and neurotransmitters that participate in the modulation of learning and memory storage processes.

Modulation of ocular hydrodynamics and iris function by bremazocine, a kappa opioid receptor agonist

This study was designed to determine the activity of bremazocine (BRE), a relatively selective kappa opioid receptor agonist, on intraocular pressure (IOP), aqueous humor formation and pupil diameter (PD) in conscious, normal, dark-adapted New Zealand white (NZW) rabbits. IOP was measured in normal and unilaterally sympathectomized rabbits using a calibrated pneumatonometer and the aqueous flow rate was determined by the use of a Fluorotron Master. A masked-design study was conducted in which the rabbits' eyes were treated with BRE topically and unilaterally; the fellow eyes received vehicle. IOP and PD measurements were taken at 0.5 hr and 0 time before BRE and 0.5, 1, 2, 3, 4 and 5 hr post-treatment. Fluorophotometry recordings were taken at 1 hr before and 0.5, 1.5, 2.5 and 3.5 hr after topical application of the drug or vehicle. The effect of the relatively selective kappa opioid receptor antagonist, nor-binaltorphimine (nor-BNI), on bremazocine-induced changes in IOP, PD and aqueous flow was also determined. BRE (10 and 100 micrograms 25 microliters-1 vehicle) produced dose-related, bilateral reductions in IOP, PD and aqueous humor flow. A large increase in IOP (14 mmHg) was observed when BRE (100 micrograms) was applied to sympathectomized eyes. This ocular hypertensive effect was antagonized when the sympathectomized eyes were pretreated with naloxone (200 micrograms), a non-selective opioid receptor antagonist. BRE (10 and 100 micrograms) decreased the aqueous humor flow rate bilaterally by approximately 48 and 60%, respectively, at 0.5 hr after administration to the ipsilateral eye. Nor-BNI (100 micrograms) antagonized the effect of BRE (10 micrograms) on IOP and aqueous flow rates more effectively than on PD. These data indicate that bremazocine causes reductions in IOP by suppressing aqueous flow, but the ocular hypotensive effects are dependent on the presence of intact sympathetic nerves. Antagonism of BRE's effects on aqueous humor dynamics by nor-BNI suggests that the mechanism of IOP and aqueous flow reduction may involve, in part, an action on kappa receptors. Further experiments are necessary to fully define the opioid receptor populations in the ciliary body.

The cardiovascular and central nervous system effects in the human of U-62066E. A selective opioid receptor agonist

The cardiovascular and central nervous system effects of the kappa opioid receptor agonist U-62066E were investigated in ten normal male subjects who received U-62066E or placebo with low or high dose naloxone in a randomized, double blind study. Blood pressure and heart rate in the supine and standing position, plasma adrenaline and noradrenaline, regional Doppler blood velocity indices and psychometric assessments were recorded for 1.25 h before and 6 h following injection. U-62066E caused sedation and dysphoria but no euphoria. Plasma noradrenaline was increased by U62066E when compared with basal levels. This action of U62066E was prevented by high but not low dose naloxone. U-62066E had no significant effect on blood pressure, heart rate or regional blood flow indices in the vessels studied and no effect on plasma adrenaline levels. Since U62066E at a dose known to have marked kappa effects was not found to influence cardiovascular indices our results do not support a major role for kappa opioids in the control of the circulation. However, U62066E may influence noradrenaline release or clearance and cause sedation and psychotomimetic effects.

A comparative study of the effect of high-intensity transcutaneous nerve stimulation and oral naproxen on intrauterine pressure and menstrual pain in patients with primary dysmenorrhea

OBJECTIVE

Our purpose was to compare the effects of high-intensity transcutaneous electrical nerve stimulation and oral naproxen (500 mg) on intrauterine pressure and menstrual pain.

STUDY DESIGN

An open, randomized crossover study was performed on 12 women with primary dysmenorrhea. Intrauterine pressure was recorded with a microtransducer catheter, and the pain score was assessed by a visual analog scale.

RESULTS

Before treatment all patients displayed signs of uterine hyperactivity as judged by a high resting pressure (7.5 +/- 0.4 kPa), high active pressure (24.0 +/- 0.8 kPa), and a high frequency of pressure cycles (13.3 +/- 0.5 contractions per 0.5 hour). Oral administration of naproxen suppressed (p < 0.01) all uterine activity parameters. Treatment with transcutaneous electrical nerve stimulation induced a prompt onset of pain relief in a strictly segmental manner, but there were no significant changes in uterine activity. The pain score was significantly reduced (p < 0.001) from 30 to 60 minutes after treatment with transcutaneous electrical nerve stimulation and from 19 to 120 minutes after naproxen administration.

CONCLUSIONS

Treatment with transcutaneous electrical nerve stimulation induced a prompt onset of pain relief without any significant changes in uterine activity. Possible mechanisms for the pain relief, decreased uterine ischemia or decreased activity in the pain transmission system at spinal or supraspinal levels, are discussed.

Comparative effects on blood pressure and heart rate of dynorphin A(1-13) in anterior hypothalamic area, posterior hypothalamic area, nucleus tractus solitarius, and lateral cerebral ventricle in the rat

The objective of this study was to explore the effects of the endogenous opioid peptide dynorphin A(1-13) on the CNS regulation of blood pressure and heart rate. Wistar rats, anesthetized with pentobarbital and halothane, received dynorphin A(1-13) microinjected into the anterior hypothalamus area (AHA), the posterior hypothalamic area (PHA), the nucleus tractus solitarius (NTS), or the lateral cerebral ventricle (ICV). Dynorphin A(1-13), 20 (12 nmol) or 30 micrograms ICV, produced significant (p < 0.05) reductions in blood pressure and heart rate. Naloxone, 50 micrograms/kg ICV, completely prevented the blood pressure response and significantly (p < 0.05) blunted the heart rate response to the highest dynorphin concentration, 30 micrograms ICV (18 nmol). Dynorphin A(1-13), 5 micrograms, in the NTS significantly (p < 0.05) decreased systolic and diastolic blood pressure and heart rate with the response being evident 10 min and persisting for 30 min after injection. In contrast, the same dose of dynorphin A(1-13) in the AHA produced an immediate, marked, and significant (p < 0.05) decrease in systolic and diastolic blood pressure and heart rate that attained its maximum 1-3 min and returned rapidly towards baseline levels. Dynorphin A(1-13), 5 or 10 micrograms in the posterior hypothalamic area, was not associated with any change in blood pressure or heart rate. Injection of the diluent at any site was not associated with any changes in blood pressure or heart rate. The maximum change in blood pressure with dynorphin was greater in the AHA than NTS, and the maximum change in heart rate was greater in the NTS than AHA.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynorphin A (1-13) in the brain suppresses epinephrine-induced ventricular premature complexes and ventricular tachyarrhythmias

The objectives of this study were to test the hypothesis that dynorphin in the central nervous system modulates epinephrine-induced cardiac arrhythmias and that central cholinergic mechanisms are operative in this action of dynorphin. Cardiac arrhythmias were produced by continuous intravenous infusion of epinephrine, in Wistar rats, previously instrumented with catheters in the lateral cerebral ventricle, femoral vein and femoral artery. Epinephrine produced ventricular premature complexes and later the development of fatal ventricular fibrillation. Dynorphin A (1-13), 5 or 20 micrograms (3 or 12 nM) administered into the lateral cerebral ventricle (ICV), significantly (P less than 0.05) increased the threshold for development of cardiac arrhythmias. Dynorphin A (1-13), 20 micrograms, increased the epinephrine dose at the occurrence of ventricular premature beats to 171 +/- 8 (mean +/- 1 S.E.M.) compared to 120 +/- 5 micrograms epinephrine/kg in the control group and increased the dose at the onset of fatal arrhythmias to 186 +/- 8 compared to 141 +/- 10 micrograms epinephrine/kg in the control group. The action of dynorphin was significantly (P less than 0.05) antagonized by the kappa opioid antagonist MR2266. Atropine sulfate, administered ICV or intravenously, produced a dose dependent antagonism of this action of dynorphin A (1-13). This was not due to the peripheral effects of atropine, as atropine methylnitrate, which does not cross the blood brain barrier, did not oppose the effects of dynorphin A (1-13). These data indicate (i) dynorphin A (1-13) increases the threshold for or suppresses the manifestations of epinephrine-induced ventricular arrhythmias, (ii) dynorphin's action on cardiac arrhythmias is mediated through central cholinergic rather than peripheral parasympathetic mechanisms (iii) dynorphin may play a role as an endogenous opioid within the brain that modulates cardiac arrhythmias in circumstances of elevated circulating epinephrine concentration.

Effect of dynorphin A(1?13) on cardiomyocytes in culture: modulation of the response to increased extracellular calcium, but no effect on intrinsic cardiac contractile frequency or the response to isoproterenol or increased extracellular potassium

The purpose of this study was to determine whether the endogenous opioid peptide dynorphin A(1-13) has a direct effect on the heart or acts to modulate the cardiac chronotropic response to calcium, potassium, or beta-adrenergic receptor stimulation. Spontaneously contracting myocardial cell aggregates were prepared from 7-day-old chick embryos and were maintained in culture for 72 h before study. Dynorphin A(1-13), 10(-8) to 10(-6)M, did not alter spontaneous contractile frequency. Increases in [Ca2+]o spontaneously suppressed cardiac contractile frequency, and dynorphin A(1-13) significantly (p less than 0.05) enhanced this response. Nifedipine, 10(-8) M, antagonized the effect of increased [Ca2+]o on cardiac contractile frequency, but did not block the action of dynorphin A(1-13) to accentuate the effect of increasing [Ca2+]o. Dynorphin A(1-13) did not alter the significant (p less than 0.05) increase in contractile frequency produced by beta-adrenergic receptor stimulation by isoproterenol, or the suppression in contractile frequency produced by increases in extracellular potassium ([K+]o). These data indicate that dynorphin A(1-13) does not act directly on the cardiac myocyte to alter cardiac contractile frequency or alter the response to increases in [K+]o or to isoproterenol, but that dynorphin A(1-13) does modulate the response to increases in extracellular calcium.

Influence of chronic opioid delta receptor antagonism on blood pressure development and tissue contents of catecholamines and endogenous opioids in spontaneously hypertensive rats

Opioid delta receptors seem to be involved in blood pressure regulation of spontaneously hypertensive rats (SHR), possibly by an interaction with the sympathetic nervous system. In the present study the effect of four weeks' chronic delta receptor antagonism with ICI 154 129 on development of blood pressure was evaluated in young SHR. Contents of adrenaline and noradrenaline and the opioid peptides beta-endorphin and leucine-enkephalin were measured in brain stem, mid brain, hypothalamus, and adrenal glands. After four weeks' treatment, systolic blood pressure was lower when compared with control SHR. During chronic delta antagonism, concentrations of adrenaline were higher in hypothalamus, mid brain and adrenal glands, contents of noradrenaline were higher in hypothalamus and adrenal glands than in control rats, contents of opioid peptides were not altered with the exception of an increase of beta-endorphin concentration in the hypothalamus. The changes in concentrations of catecholamines following chronic delta antagonism may reflect an alteration of sympathetic activity and could contribute to the retardation of blood pressure development.

Effects of opioid peptides on neural control of renal function in spontaneously hypertensive rats

The aims of the present study were to examine the effects of opioid receptor agonists and antagonists on the renal vascular (renal blood flow) and tubular (urinary sodium excretion) responses to renal nerve stimulation and norepinephrine in anesthetized spontaneously hypertensive rats (SHR). Graded frequency renal nerve stimulation (0.5-4.0 Hz) and doses of norepinephrine (10-80 ng/kg) produced frequency and dose-dependent decreases in renal blood flow. The renal vasoconstrictor responses were not altered by intravenous infusion of the opioid receptor agonists methionine enkephalin (mu and delta, 75 micrograms/kg/min) or U-50488H (kappa, 20 micrograms/kg/min) or administration of the opioid receptor antagonist naloxone (1 mg/kg i.v.). The antinatriuretic response to low frequency (less than 1.0 Hz) electrical renal nerve stimulation was prevented by naloxone but not affected by methionine enkephalin administration without changes in glomerular filtration rate or effective renal plasma flow. These studies suggest that endogenous opioid receptor mechanisms are involved in the increased renal tubular sodium reabsorption response to low frequency renal nerve stimulation but not in the renal vasoconstrictor response to either renal nerve stimulation or norepinephrine. This might occur by facilitation of the renal nerve terminal release, the direct renal tubular action, or both, of norepinephrine to influence renal tubular sodium reabsorption.

Use dependence of sodium current inhibition by tetrodotoxin in rat cardiac muscle: influence of channel state

Tetrodoxin (TTX) is known to cause a voltage- and frequency-dependent inhibition of the rapid inward sodium current (INa) of cardiac muscle. This effect was studied by means of the loose-patch-clamp method on intact rat papillary muscle. The availability curve of the fast sodium system, determined by variation of the holding potential, is shifted in the presence of TTX (5.5 mumol x 1(-1] by 17 mV to more negative potentials. With clamp pulses of 5 ms duration to 0 mV, a frequency-dependent reduction of INa by TTX is found above 0.1 Hz that saturates at about 10 Hz. This frequency-dependent block was further analysed using trains of pulses (10 Hz) of various durations (minimum 50 microseconds), which allow TTX to equilibrate with channel states reached early during activation. The results show that more than 90% of the frequency-dependent block is attained with pulses of 1 ms duration. An analysis according to the guarded receptor hypothesis reveals that these results are well described by TTX binding to inactivated, activated and probably preactivated channel states.

Alterations of heart dynorphin-A in the development of spontaneously hypertensive rats

In order to investigate the pathophysiological role of heart dynorphin-A (Dyn-A) in genetic hypertension, immunoreactive (ir)-Dyn-A was measured in heart extracts of spontaneously hypertensive rats (SHR) and compared with that of age matched Wistar (WR) and Wistar Kyoto (WKY) rats. Heart ir-Dyn-A contents in 8 week-old WK (84 fmol/g tissue) were not significantly different from those of age matched WKY (109 fmol/g tissue). In control WKY, the levels of ir-Dyn-A did not significantly vary with the age (from 109 to 117 fmol/g) except in 16 week-old animals which displayed a significant increase (238 fmol/g tissue) compared to younger animals. In SHR, the heart content of ir-Dyn-A displayed a 6.5 fold increase at 8 weeks compared to age matched WKY. Older SHR showed a return of their heart ir-Dyn-A content to control (12 week-old) or below control values (16 week-old; 121 compared with 238 fmol/g tissue in WKY). Heart ir-Dyn-A in WKY and SHR eluted as a single peak on mu-Bondapak HPLC, corresponding with the retention time of synthetic Dyn-A. A local function for cardiac ir-Dyn-A is suggested by the presence in heart membrane preparations of a high affinity binding site for the kappa selective opioid ligand, [3H]U-69593, with KD of 6.4 (WKY) and 8.5 (SHR) nM and Bmax of 3.7 (WKY) and 3.6 (SHR) pmol/g protein. The alterations in the levels of cardiac ir-Dyn-A during the development of hypertension in SHR were analyzed in regard with the reported effects of Dyn-related peptides on heart natriuretic and sympathetic functions.

The isolation, identification and structure of a new hydroxylated metabolite of benzbromarone in man

1. The metabolic fate of the uricosuric drug, benzbromarone, in man was reinvestigated. Plasma and urine samples obtained from healthy subjects after administration of a single oral dose of 100 mg were analysed by h.p.l.c. and g.l.c.-mass spectrometry; bromobenzarone and benzarone, previously assumed to be the debrominated metabolites of benzbromarone, were not detectable. 2. Instead, two metabolites (M1 and M2) were present in plasma samples, which had plasma elimination rates lower than those of the parent drug. 3. One of the metabolites (M1) was identified as 1'-hydroxy-benzbromarone using g.l.c.-mass spectrometric analysis of trimethylsilylated and methylated extracts. Chromatographic and spectroscopic data for this metabolite were identical to those of the synthetic compound.

Inhibition of sympathetic neurotransmission by the opioid delta-receptor agonist DAMA in the pithed rat

1. The effects of [D-Ala2,Met5]enkephalinamide (DAMA), an analogue of [Met5]-enkephalin that acts selectively on opioid receptors of the delta-subtype, were studied on pressor responses elicited by sympathetic stimulation in pithed rats. 2. Intravenous injections of bolus doses of 0.1 mg/kg and 0.3 mg/kg of DAMA did not affect either the basal blood pressure or pressor responses to noradrenaline. 3. Pressor responses elicited either by electrical stimulation of the spinal sympathetic outflow or by stimulation of sympathetic ganglion cells with the muscarinic agonist McN-A-343 were reduced by DAMA. 4. Naloxone (1 mg/kg + 0.5 mg/kg per h) had no significant effect on the basal blood pressure or on pressor responses to spinal sympathetic stimulation, but antagonised the inhibitory effect of DAMA. 5. These results indicate that activation of opioid delta-receptors on sympathetic vasomotor nerve terminals can inhibit noradrenergic neurotransmission.

Plasma leucine enkephalin is increased in liver disease

Plasma methionine enkephalin is increased in liver disease and may contribute to some of the clinical manifestations of hepatic failure. To determine if another 'small' opioid peptide is increased in the plasma of patients with liver disease, leucine enkephalin was measured by radioimmunoassay. Its plasma concentration was raised approximately five-fold in patients with acute liver disease (median 1490 pmol/l, range 830-2420) and three-fold in patients with cirrhosis with ascites (960 pmol/l, 470-2900), compared with disease controls (325 pmol/l, 180-740) and healthy controls (305 pmol/l, 180-560). The increase in plasma leucine enkephalin was proportional to the degree of liver damage, as judged in the patients with acute liver disease by its correlation with the prothrombin time (r = 0.691, p less than 0.01) and alanine aminotransferase (r = 0.502, p less than 0.05), and in the patients with cirrhosis by its negative correlation with the plasma albumin (r = -0.743, p less than 0.001). It is unclear whether the raised plasma leucine enkephalin in liver disease is a consequence of diminished hepatic inactivation, increased secretion from sympathetic nerves and adrenal glands, or both.

Modelling frequency- and voltage-dependent effects of a class I antiarrhythmic drug (nicainoprol) on Vmax of the cardiac action potential from guinea-pig papillary muscle

Frequency- and voltage-dependent effects of a class I antiarrhythmic agent (nicainoprol) on the maximal upstroke velocity (Vmax) of the action potential of guinea-pig papillary muscle are compared with the effects predicted by a kinetic model of frequency- and voltage-dependent block of fast sodium channels. The model is based on the guarded-receptor hypothesis, which assumes a constant affinity binding site with the drug access to and egress from the binding site being controlled by the channel conformational state. At normal resting membrane potential (RMP approximately -86 mV) nicainoprol (3.3 x 10(-6) mol/l and 10(-5) mol/l) causes no Vmax-reduction after a resting period (i.e. no resting block) but a frequency-dependent decrease of Vmax (frequency-dependent block), which saturates at above 2.0 Hz. Both, resting and frequency-dependent block strongly depend on the RMP in a way that the frequency-dependent block decreases with depolarizing RMP while the resting block increases. Development of and recovery from frequency-dependent block is faster at depolarized RMP. These results can be interpreted in terms of the guarded-receptor hypothesis with nicainoprol preferentially binding to inactivated sodium channels. All its effects on Vmax can be fully described by only three model parameters: a binding rate coefficient (kB = 8.49 x 10(3) mol-1.1.s-1), an unbinding rate coefficient (k-B = 6.24 x 10(-2).S-1), and a parameter with the meaning of an electrical location of the binding site (about 35% on the way through the membrane field from the extracellular surface).

Is ascites caused by impaired hepatic inactivation of blood borne endogenous opioid peptides?

Methionine enkephalin and catecholamines were measured in carefully collected plasma samples from 25 patients with cirrhosis and ascites, and 25 with cirrhosis without ascites, 15 disease and 15 healthy controls. Methionine enkephalin was invariably raised in the ascites group, the median value being 4.6-6.9 times that of the other three groups. Similarly, in the ascites group, median noradrenaline was increased 2.5-4.2 and median adrenaline 1.8-2.5 times that of the other groups. Plasma methionine enkephalin is considerably raised in patients with cirrhotic ascites and has actions which could enable it to be an initiating factor of ascites formation.

Evaluation of opioid-induced antinociceptive effects in anaesthetized and conscious animals

1. The activity profiles of opioid agonists and non-steroidal analgesic agents have been compared against different nociceptive stimuli in the mouse and rat. 2. Opioid agonists, but not non-steroidal analgesic agents, inhibited reflex depressor responses evoked by visceral distension in anaesthetized rats. The ranked order of potency of opioids in the visceral distension reflex was identical to that observed in the mouse writhing assay. 3. Opioid-induced inhibition of reflex depressor responses and writhing was observed with ligands acting on mu- and kappa-, but not delta-receptors. Antinociceptive activity of opioids in the rat cold water tail-flick assay was restricted to mu-receptor agonists. 4. Morphine- and ethylketocyclazocine (EKC)-induced inhibition of the visceral distension reflex was blocked by naloxone, but not by the quaternary opioid antagonist N-methylnalorphine. 5. Direct cardiovascular effects were observed with ligands for the mu- and kappa-receptor. Blood pressure changes induced by morphine and Tyr.D-Ala.Gly.MePhe.Gly-ol (DAGOL), but not EKC, were blocked by N-methylnalorphine. Pretreatment with 16-methylcyprenorphine (M8008) antagonized morphine-, DAGOL- and EKC-induced cardiovascular effects, but not those of dynorphin-(1-13) or U50488. 6. It is concluded that reflex circulatory responses evoked by visceral distension in anaesthetized rats are a valid index for the evaluation of opioid-induced antinociception. A simultaneous assessment of cardiovascular effects of opioids was achieved.

Peripheral sympatho-inhibitory cardiovascular effects of opioid peptides in anaesthetized rabbits

1. Opioid agonists influence isolated cardiovascular tissues from rabbits, as well as the cardiovascular system of pithed rabbits, through presynaptic receptors on postganglionic sympathetic nerve fibres. The present experiments were carried out in order to study effects which result from activation of these receptors in anaesthetized rabbits. 2. In pithed rabbits with electrically stimulated sympathetic outflow, infusion of [D-Ala2-D-Leu5]-enkephalin (DADLE) 10 micrograms kg-1 min-1 and dynorphin-(1-13) (dynorphin) 1 microgram kg-1 min-1 decreased the plasma noradrenaline concentration, mean arterial pressure (MAP) and heart rate. The effects of dynorphin and, less completely, those of DADLE were antagonized by the peripherally selective opioid antagonists N-methyl naloxone bromide (NMN) 1.3 mg kg-1 and N-methyl levallorphan methanesulphonate (NML) 1-3 mg kg-1. 3. In pentobarbitone-anaesthetized rabbits, DADLE 3-30 micrograms kg-1 min-1 and dynorphin 0.3-3 micrograms kg-1 min-1 decreased the plasma noradrenaline concentration and MAP. The highest dose of dynorphin also decreased heart rate, whereas DADLE 10 micrograms kg-1 min-1 caused slight cardioacceleration. The effects of DADLE but not those of dynorphin decreased upon repeated administration. 4. The effects of dynorphin 10 micrograms kg-1 min-1 were abolished or greatly attenuated by NMN 1.3 mg kg-1 and NML 3 mg kg-1. In contrast, the antagonists reduced only slightly the blood pressure-lowering effect of DADLE 10 micrograms kg-1 min-1 and did not reduce significantly the effects of DADLE on the plasma noradrenaline level and heart rate. 5. It was concluded that systemically administered dynorphin produces sympatho-inhibition and an ensuing fall in blood pressure by an action at peripheral receptors, in all probability presynaptic Kappa-receptors on postganglionic sympathetic nerve fibres. The effects of DADLE are more complex and may involve both central and peripheral components.

Modulation of peripheral sympathetic nerve transmission

The past 15 years have been witness to a remarkable growth in knowledge regarding the modulation of "sympathetic traffic" to neuroeffector organs, including vascular tissue. The release of norepinephrine from peripheral sympathetic neurons is now known to be under both negative and positive feedback control. Norepinephrine, when released from peripheral neurons, acts on presynaptic alpha 2-receptors to inhibit further neurotransmission. Vascular postsynaptic alpha 2-receptors, sensitive to circulating catecholamines, subserve vasoconstriction. The antihypertensive agents clonidine, guanabenz and guanfacin likely reduce blood pressure by acting centrally on alpha 2 postsynaptic neurons to limit sympathetic transmission to blood vessels. Clonidine can produce venoconstriction and thereby improve orthostatic hypotension by activating venous alpha 2-receptors. Additional presynaptic dopaminergic receptors (DA2), muscarinic receptors (acetylcholine), opioid receptors, prostaglandin receptors, adenosine receptors (A1) and histamine (H2) receptors are present on sympathetic nerve membranes and, when engaged with the appropriate ligand, can limit the exocytotic process. Gamma-aminobutyric acid and serotonin demonstrate similar roles in reducing sympathetic nerve activity. In contrast to these inhibitory presynaptic mechanisms, facilitation of norepinephrine release appears to occur by way of neuronal angiotensin II receptor activation and perhaps through stimulation of sympathetic nerve membrane beta 2-receptors. An appreciation of these inhibitory and facilitator mechanisms is useful in the treatment of a variety of clinical conditions, including hypertension, heart failure, orthostatic hypotension, septic shock and a number of common withdrawal syndromes.

Peripheral opiate receptors are not involved in the naloxone-sensitive cardiovascular effects of clonidine in rats

The cardiovascular effects of clonidine and their inhibition by naloxone or naloxone methylbromide were tested in urethane-anesthetized, normotensive Sprague-Dawley rats. Clonidine administered intravenously (5 micrograms/kg) or directly into the nucleus tractus solitarii (NTS, 5 nmol) caused hypotension and bradycardia. The effects of intra-NTS clonidine were dose-dependently inhibited by intra-NTS administration of either antagonist, naloxone being 10 times more potent than naloxone methylbromide. The effects of i.v. clonidine were significantly inhibited by 2 mg/kg of i.v. naloxone, but were unaffected by 20 mg/kg of i.v. naloxone methylbromide. Naloxone alone had no effect on blood pressure or heart rate when given either centrally or systemically, whereas naloxone methylbromide given i.v., but not intra-NTS, caused transient hypotension and tachycardia. It is concluded that central but not peripheral opiate receptors are involved in the cardiovascular effects of clonidine.

Effects of bestatin and phosphoramidon on the hypertensive response to physostigmine in the rat

Intracarotid (IC) injection of bestatin produced a dose-dependent biphasic change in blood pressure (BP) of the rat, consisting of an initial short-lasting fall followed by a long-lasting increase. This effect was regularly depressed or abolished by IV injection of naloxone. IC injection of Leu-enkephalin also produced a biphasic BP response, with the same characteristics as that produced by IC injection of bestatin. This effect was also easily blocked by IV injection of naloxone. IC injection of bestatin significantly potentiated the BP response to IC injection of Leu-enkephalin. This potentiated response was blocked by naloxone. IC injection of both bestatin and phosphoramidon, whether separately or in combination, significantly depressed the hypertensive response to physostigmine. This depressive action of bestatin and phosphoramidon on physostigmine hypertension can be significantly antagonized or even reversed by IV injection of naloxone. IC injection of both bestatin and phosphoramidon did not affect the BP response to either acetylcholine or catecholamines. It is concluded that bestatin and phosphoramidon, injected into the carotid artery, inhibit the activity of aminopeptidase and "enkephalinase", thus producing an accumulation of enkephalins in the central nervous system. These enkephalins activate opioidergic receptors in the brain, but concomitantly produce a depression of the cholinergic-adrenergic interaction in the central nervous system, which is known to be a prerequisite for the hypertensive response to physostigmine in the rat.

Presynaptic opioid receptors in the portal vein of the rabbit

The effects of opioids on sympathetic neuroeffector transmission were studied in superfused strips of the portal vein of the rabbit. In the first series of experiments, the tissue was stimulated electrically every 10 min with 10 pulses at 8 Hz and a current strength of 200 mA. The contractions evoked were concentration dependently inhibited by the slightly kappa-selective agonist ethylketocyclazocine and by the delta-selective agonists [D-Ala2,D-Leu5]enkephalin (DADLE) and [D-Pen2,D-Pen5]enkephalin (DPDPLE). The mu-selective agonist [D-Ala2,NMePhe4,Gly-ol5]enkephalin (DAGO) had no effect. The estimated EC50 values for ethylketocyclazocine and DADLE were 5.5 X 10(-8) and 2.9 X 10(-8) mol/l, respectively. Naloxone shifted the concentration-response curves of ethylketocyclazocine and DADLE to the right; the estimated Kb values were (1.7 +/- 0.4) X 10(-8) mol/l and (2.9 +/- 0.8) X 10(-8) mol/l, respectively. The delta-selective antagonist ICI 174864 antagonized only the inhibitory effect of DADLE but not that of ethylketocyclazocine. In the second series of experiments, the tissue was preincubated with [3H]noradrenaline then superfused and stimulated electrically three times for 3 min at 1 Hz and a current strength of 100 mA. Ethylketocyclazocine and DADLE inhibited the evoked overflow of tritium. The inhibition produced by ethylketocyclazocine was antagonized by naloxone. Our results show for the first time that opioid agonists inhibit noradrenaline release and hence, neurogenic vasoconstriction in a vein. As in other cardiovascular tissues of the rabbit, the presynaptic opioid receptors are of the kappa- and delta- but not the mu-type.

The contributions of mu-, delta- and kappa-opioid receptors to the actions of endogenous opioids on spinal reflexes in the rabbit

Spinal reflexes in the rabbit are suppressed tonically by endogenous opioids. The contributions made to this suppression by mu-, delta- and kappa-opioid receptors have been investigated by studying the actions of a range of opioid antagonists and agonists on reflexes evoked by sural nerve stimulation in the ankle extensor gastrocnemius medialis (g.m.), and in the knee flexor semitendinosus (s.t.). When given at a total dose of 88.5 micrograms kg-1 i.v., either of the universal opioid receptor antagonists (-)-naloxone and (-)-quadazocine enhanced the g.m. response to more than 7 times the pre-drug control values, and the s.t. reflex to 1.5 times controls. The effects of quadazocine were stereospecific. The selective delta antagonist ICI 174864 (3.5 mg kg-1 i.v. total) also augmented the g.m. reflex but only to twice pre-drug controls. The mu-agonists fentanyl (100 micrograms kg-1) and morphine (50 mg kg-1) suppressed both g.m. and s.t. reflex responses to less than half control levels by a naloxone-reversible mechanism. The kappa-agonists bremazocine (50 micrograms kg-1 total), tifluadom (100 micrograms kg-1), ethylketocyclazocine (200 micrograms kg-1) and U50488H (1 mg kg-1) potentiated the g.m. reflex and had variable effects on the s.t. response. Naloxone usually added to the facilitatory actions of these drugs. kappa-Opioid receptor agonists also caused a profound, naloxone-reversible depression of arterial blood pressure. It may be concluded that the endogenous opioid-mediated suppression of spinal reflexes in the rabbit is mediated mainly, if not exclusively, through mu-receptors. There are no known endogenous ligands which are specific for the mu-receptor, so in the present case it seems that selectivity is determined by the receptor population rather than by the ligand.

The opioid peptides. A role in hypertension?

This review is an attempt to highlight evidence that may implicate the endogenous opioid system in the pathogenesis of hypertension in humans. The evidence raised includes biochemical, physiological, pharmacological, and behavioral studies conducted in in vitro and in vivo systems, experimental models of hypertension, and humans with essential hypertension. While the compelling biochemical and pharmacological evidence in experimental animals clearly shows the presence of opioid peptides and their receptors in strategic sites of cardiovascular control and potent cardiovascular response to opioid peptides, opioid antagonists show no consistent blockade or reversal of hypertension in experimental animals or humans. One possible explanation for this phenomenon could be the vast redundancy in systems regulating blood pressure (i.e., the blockade of one system still leaves many other systems fully able to rapidly offset the eliminated system). Regarding the opioid system, the situation is much more complex, since some opioid receptors (mu-type) mediate pressor responses, while other receptors (kappa-type) mediate depressor responses. Therefore, nonselective opioid receptor antagonists (e.g., naloxone), which block both types of receptors, can be devoid of any cardiovascular activity, while a selective mu-receptor antagonist or a selective and potent kappa-receptor agonist may produce the desired antihypertensive effect. A combination of both actions (i.e., a drug that is both a mu-antagonist and a kappa-agonist) might be even more advantageous. Until such compounds are developed, this hypothesis will be hard to prove.

Photoelectric measurement of neurogenic vasoconstriction in jejunal branches of the rabbit mesenteric artery reveals the presence of presynaptic opioid delta-receptors

The perivascular nerves of rabbit mesenteric arteries were stimulated with 15 pulses at 2 Hz, and decreases in external diameter were measured by means of a photoelectric device. Both extra- and intraluminally added [Met5]enkephalin 1 mumol/l depressed vasoconstriction, although with the second mode of application a larger inhibition occurred. Therefore, in the subsequent experiments all opioids were added into the lumen. [Met5]enkephalin 0.1 mumol/l had no effect. [D-Pen2, L-Pen5]enkephalin 3 mumol/l was less potent than [Met5]enkephalin 1 mumol/l. ICI 174864 1 mumol/l was also without effect when given alone, but antagonized the action of [Met5]enkephalin 1 mumol/l. Ethylketocyclazocine, dynorphin A(1-13), normorphine and DAGO, all 1 mumol/l, were ineffective. [Met5]enkephalin 1 mumol/l did not change the vasoconstriction evoked by the application of noradrenaline (0.1-3 mumol/l). It is concluded that in the mesenteric artery action potential-induced transmitter release, and in consequence vasoconstriction can be inhibited by the activation of presynaptic opioid delta-receptors.

On the presence of opioid receptors in guinea-pig ventricular tissue

The cardiac response to sympathetic nerve stimulation, induced by trains of field pulses, was studied in isolated guinea-pig ventricular strips. Dynorphin-(1-13) and [D-Ala2, D-Leu5]enkephalinamide, but not morphine, reduced, in a dose-dependent manner, the cardiac sympathetic response. The effect of the two opioid peptides was antagonized by naloxone. The opioid agonists did not affect the response to exogenous noradrenaline. Neither naloxone nor a mixture of peptidase inhibitors modified the cardiac response to sympathetic nerve stimulation.