A dynorphin peptide induces hypotension by stimulating the release of atrial natriuretic peptide from rat atrium

Melatonin and morphine: potential beneficial effects of co-use

Morphine is a potent analgesic agent used to control acute or chronic pain. Chronic administration of morphine results in analgesic tolerance, hyperalgesia, and other side effects including dependence, addiction, respiratory depression, and constipation, which limit its clinical usage. Therefore, identifying the new analgesics with fewer side effects which could increase the effect of morphine and reduce its side effects is crucial. Melatonin, a multifunctional molecule produced in the body, is known to play an important role in pain regulation. The strong anti-inflammatory effect of melatonin is suggested to be involved in the attenuation of the pain associated with inflammation. Melatonin also increases the anti-nociceptive actions of opioids, such as morphine, and reverses their tolerance through regulating several cellular signaling pathways. In this review, published articles evaluating the effect of the co-consumption of melatonin and morphine in different conditions were investigated. Our results show that melatonin has pain-killing properties when administered alone or in combination with other anti-nociceptive drugs. Melatonin decreases morphine consumption in different pathologies. Furthermore, attenuation of morphine intake can be accompanied by reduction of morphine-associated side-effects, including physical dependence, morphine tolerance, and morphine-related hyperalgesia. Therefore, it is reasonable to believe that the combination of melatonin with morphine could reduce morphine-induced tolerance and hyperalgesia, which may result from anti-inflammatory and antioxidant properties of melatonin. Overall, we underscore that, to further ameliorate patients' life quality and control their pain in various pathological conditions, melatonin deserves to be used with morphine by anesthesiologists in clinical practice.

Neuroendocrine control of body fluid metabolism

Mammals control the volume and osmolality of their body fluids from stimuli that arise from both the intracellular and extracellular fluid compartments. These stimuli are sensed by two kinds of receptors: osmoreceptor-Na+ receptors and volume or pressure receptors. This information is conveyed to specific areas of the central nervous system responsible for an integrated response, which depends on the integrity of the anteroventral region of the third ventricle, e.g., organum vasculosum of the lamina terminalis, median preoptic nucleus, and subfornical organ. The hypothalamo-neurohypophysial system plays a fundamental role in the maintenance of body fluid homeostasis by secreting vasopressin and oxytocin in response to osmotic and nonosmotic stimuli. Since the discovery of the atrial natriuretic peptide (ANP), a large number of publications have demonstrated that this peptide provides a potent defense mechanism against volume overload in mammals, including humans. ANP is mostly localized in the heart, but ANP and its receptor are also found in hypothalamic and brain stem areas involved in body fluid volume and blood pressure regulation. Blood volume expansion acts not only directly on the heart, by stretch of atrial myocytes to increase the release of ANP, but also on the brain ANPergic neurons through afferent inputs from baroreceptors. Angiotensin II also plays an important role in the regulation of body fluids, being a potent inducer of thirst and, in general, antagonizes the actions of ANP. This review emphasizes the role played by brain ANP and its interaction with neurohypophysial hormones in the control of body fluid homeostasis.

Elevation of atrial natriuretic peptide levels in aqueous humor of the rabbit by kappa opioid receptor agonists

Following the topical administration of three kappa agonists (bremazocine, spiradoline and ICI 204448) to rabbit eyes, aqueous humor samples were analyzed for levels of atrial natriuretic peptide (ANP). Bremazocine (BRE) and spiradoline (SPR) elevated aqueous ANP levels in a dose-dependent manner. In contrast, ICI had no significant effect on ANP levels in aqueous humor. Nor-binaltorphimine (nor-BNI), a selective kappa opioid receptor antagonist, was used to assess kappa opioid receptor involvement and glibenclamide, an ATP-sensitive K+ channel blocker, was used to test for the role of ATP-sensitive potassium channels in ANP release. Pretreatment with nor-BNI antagonized the increases in ANP levels observed with both BRE and SPR. Likewise, glibenclamide suppressed the stimulation of ANP secretion by bremazocine. In summary, BRE and SPR increased ANP levels in aqueous humor of rabbits, in part, via activation of K+(ATP) channels that are assumed to be associated with kappa opioid receptors.

Pressor effects of endogenous opioid system during acute episodes of blood pressure increases in hypertensive patients

To investigate the involvement of endogenous opioids in acute increases in blood pressure and their functional relationship with atrial natriuretic factor and endothelin-1, we assessed plasma levels of beta-endorphin, met-enkephalin, dynorphin B, catecholamines, atrial natriuretic factor, and endothelin-1 before and after administration of the opioid antagonist naloxone hydrochloride (8 mg i.v.) in 28 hypertensive patients with a stress-induced acute increase in blood pressure. Ten patients with established mild or moderate essential hypertension and 10 normotensive subjects served as control groups. Opioids, atrial natriuretic factor, and endothelin-I were radioimmunoassayed after chromatographic preextraction; catecholamines were determined by high-performance liquid chromatography with electrochemical detection. Patients with an acute increase in blood pressure (systolic, 203.2 +/- 2.2 mm Hg; diastolic, 108.4 +/- 1.3) had plasma opioid, catecholamine, and atrial natriuretic factor levels significantly (P < .01) higher than hypertensive control patients (systolic pressure, 176.4 +/- 1.0 mm Hg; diastolic, 100.0 +/- 1.4), who had a hormonal pattern similar to that of normotensive subjects (systolic pressure, 123.2 +/- 1.5 mm Hg; diastolic, 75.0 +/- 2.0). Endothelin-1 did not differ in any group. In patients with an acute increase in blood pressure, naloxone significantly (P < .01) reduced blood pressure, heart rate, opioids, catecholamines, and atrial natriuretic factor 10 minutes after administration. Naloxone effects on blood pressure, heart rate, opioids, and catecholamines wore off within 20 minutes. In control groups, naloxone failed to modify any of the considered parameters. Our findings suggest that pressor effects of opioid peptides mediated by the autonomic nervous system during stress-induced acute episodes of blood pressure increase in hypertensive patients.

Renal effects of TAPP, a highly selective mu-opioid agonist

1. The effect of i.v. administration of TAPP, a highly selective and exclusively peripherally-acting mu-opioid receptor agonist, on urine output, urinary sodium, potassium and cyclic GMP, and on plasma immunoreactive atrial natriuretic factor (IR-ANF) levels was studied in conscious normally hydrated female rats (200-250 g). 2. TAPP treatment produced a significant dose-dependent increase of urine output and urinary sodium, potassium and cyclic GMP excretion during the first hour. The highest TAPP dose used (2.5 mg kg-1. body weight) elicited a 10 fold elevation of urine output from 0.23 +/- 0.06 ml h-1 to 2.5 +/- 0.3 ml h-1 (n = 18) accompanied by augmented sodium [from 17.0 +/- 4.7 mu Eq h-1 to 79 +/- 12.7 mu Eq h-1, n = 18 (P < 0.001)], potassium [from 9.5 +/- 2.5 mu Eq h-1 to 39.4 +/- 6.6 mu Eq h-1, n = 18 (P < 0.005)], and cyclic GMP excretion [from 191 +/- 21 pmol h-1 to 1340 +/- 322 pmol h-1, n = 18 (P < 0.001)]. Plasma IR-ANF rose from 22 +/- 4 pg ml-1 to 508 +/- 22 pg ml-1 (n = 18) (P < 0.001) 5 min after administration of TAPP (2500 micrograms kg-1). 3. TAPP lowered systemic blood pressure, also in a dose-related manner, 1-5 min after injection. This decrease in blood pressure was transient and did not last more than 10 min. 4. Pretreatment with the opioid antagonist naloxone (0.8 mg per rat) abolished the diuretic, natriuretic and kaliuretic effect of TAPP (250 micrograms kg-1); urine output dropped from 1.16 +/- 0.15 ml h-1, n = 12, to the control value of 0.15 +/- 0.06 ml h-1, n = 12 (P < 0.001), sodium excretion fell from 57.5 +/- 11 mu Eq h-1, to 21.3 +/- 8.5 mu Eq h-1, n = 12 (P < 0.001), and potassium excretion decreased from 45.4 +/- 9.7 mu Eq h-1, n = 12, to 16.1 +/- 7.0 mu Eq h-1, (P < 0.001). 5. Pretreatment with anti-ANF serum (0.4 ml) abolished the diuretic effect of TAPP: urine output diminished significantly from 1.93 +/- 0.28 to 0.88 +/- 0.29 ml h-1 (P < 0.01) (n = 6). The TAPP-induced diuretic action, increased sodium/potassium excretion and elevated urinary cyclic GMP levels were also reversed by anti-ANF antibodies. 6. Since TAPP is totally unable to cross the blood-brain barrier, the ensemble of these observations led to the conclusion that the diuretic, natriuretic, kaliuretic and hypotensive effects produced by this mu-opioid agonist through interaction with peripheral mu-opioid receptors occur via ANF release.

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.

Possible regulatory role of dynorphin A in the urinary bladder

Muscle strips from rat and human detrusor were studied using indirect immunofluorescence and electrical nerve stimulation in an organ bath. Immunoreactivity towards dynorphin was observed in varicose nerve fibres in the detrusor muscle and around immunonegative nerve cell bodies in the prevesical ganglia of the rat. In vitro, dynorphin A (1-13) (10(-13)-10(-6) M) strongly facilitated detrusor contraction induced by electrical field stimulation (EFS). This facilitation was counteracted by morphine (10(-10) and 10(-8) M) and naloxone (10(-10) and 10(-8) M) in a competitive manner. The facilitation could also be counteracted by the addition of the kappa-receptor antagonist M(r) 2266 (10(-7) M). Muscarinic blockade, achieved with atropine (10(-6) M), did not alter the effect of dynorphin A (1-13). Addition of phentolamine mesylate (10(-6) M), and propranolol (10(-6) M) per se facilitated the EFS-induced contractions. Both adrenergic blockade as well as the addition of the substance P blocker spantide, counteracted the facilitating effect of dynorphin A (1-13).

IN CONCLUSION

Dynorphin A immunoreactive material was found to be present in nerves in the rat detrusor and in prevesical ganglia. Dynorphin A (1-13) facilitated the detrusor contraction, possibly via actions on kappa-opioid receptors and interaction with non-cholinergic nerves.

[Atrial natriuretic factor in men]

The atrial natriuretic peptide (ANP) is rapidly secreted in case of acute changes in atrial volume and heart rate. Its effects are mainly natriuretic and vasodilator. This hormone is of interest to the anaesthetist because induction of anaesthesia, epidural anaesthesia and administration of morphine all result in changes in ANP plasma concentration.

Heterogeneity of immunoreactive dynorphin B-like material in human, rat, rabbit and guinea-pig heart

Immunoreactive dynorphin B-like material (ir-dyn B) was detected in acetic acid extracts of human atrial specimens and of rat, rabbit and guinea-pig atria and ventricles by a validated radioimmunoassay. Levels were high in rabbit atrium (66.76 +/- 7.04 pmol/g) but lower and superimposable in human and rat atria (28.18 +/- 3.20 and 30.22 +/- 2.45 pmol/g, respectively). Gel permeation chromatography revealed ir-dyn B eluting close to column exclusion and in forms with an apparently higher molecular weight than authentic dyn B in human and rat samples. In contrast, almost all the immunoreactivity from rabbit and guinea-pig acetic extracts eluted as a single peak in the region of standard dyn B. Reverse-phase high performance liquid chromatography of the pooled gel chromatography fractions of this peak showed up a molecular form with the same retention time as authentic dyn B and a second minor peak of unknown immunoreactive material eluting three fractions earlier. Digestion with carboxypeptidase B excluded the hypothesis that this latter could be dyn B-Arg14. Therefore, it might be a metabolite of endogenous dyn B recognized by the antibody used in this study.

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.

Influence of endogenous opioids on atrial natriuretic factor release during exercise in man

To evaluate to what extent opioid secretion in exercise induces the release of atrial natriuretic factor (ANF), six healthy male volunteers who were trained subjects, were submitted to two maximal exercise tests with and without (control) opioid receptor blockade by Naltrexone. Blood samples were drawn before (rest) and after exercise (post-exercise) in order to measure human ANF (alpha h ANF), beta-endorphin, plasma aldosterone concentration (PAC) plasma renin activity (PRA) and adreno-cortico trophic hormone (ATCH) by radio-immunological methods. Expired gas was collected during exercise to measure oxygen consumption. On average, the same maximal oxygen consumption (VO2max) during exercise was reached by all subjects with and without treatment. Plasma ANF level at rest slightly decreased after administration of Naltrexone; the response to physical exercise was significantly reduced by Naltrexone. There was no statistical difference between plasma levels of beta-endorphin, PRA and ACTH at rest nor in the post-exercise situation under the influence of Naltrexone. The PAC increased significantly at rest after Naltrexone administration but there was no statistical difference between both values after exercise. These data demonstrate that: (1) ANF secretion during exercise is influenced by the level of beta-endorphin in the plasma; (2) the possible inhibitory role of ANF on aldosterone secretion during exercise is probably over-ruled by the increase in plasma ACTH and PRA.

Kappa-opioid-induced changes in renal water and electrolyte management and endocrine secretion

1. Subcutaneous injection of the kappa-opioid agonist U50,488 into conscious, saline-loaded rats was associated with a diuresis, antinatriuresis and antikaliuresis which lasted for up to 3 h. Plasma renin activity and corticosterone levels were elevated but plasma vasopressin (AVP) and aldosterone levels were unaltered in similarly treated rats. 2. U50,488 administration to adrenal demeddulated rats was not associated with a diuresis but produced an antinatriuresis, though sodium excretion rates were higher in demedullated than in sham-operated animals. Plasma AVP and corticosterone levels were not affected by demeddulation or subsequent U50,488 treatment. Sham-operated, U50-488-treated rats showed the expected increase in plasma corticosterone levels. 3. U50,488 administration resulted in an antidiuresis and an antinatriuresis in AVP-deficient Brattleboro DI rats. 4. When coupled with fasting stress U50,488 administration resulted in similar but attenuated renal responses compared with those observed in unfasted rats. Basal plasma corticosterone levels were elevated in fasted animals and were further increased by U50,488. 5. Both water and electrolyte handling by the kidney are altered by U50,488. The diuretic effects of U50,488 were reversed by adrenal demedullation and in the absence of endogenous AVP, but the antinatriuretic actions were not altered, suggesting that the effects upon renal water and electrolyte excretion may be mediated by separate mechanisms.

Effects of morphine and opioid peptides on plasma levels of atrial natriuretic peptide

The effect of opiate ligand administration on plasma levels of atrial natriuretic peptide (ANP) was studied in awake, freely moving Sprague-Dawley rats. Prior to and following the intracerebroventricular (icv) or central venous (iv) injection of morphine (MS), leu-enkephalin (Leu-enk), dynorphin (Dyn) or beta-endorphin (B-endor), plasma samples were obtained for measurement of ANP concentrations by radioimmunoassay. MS was 10 times more potent when given icv than when given iv to increase plasma ANP levels. Icv injection of Leu-enk decreased plasma ANP concentrations. Dyn and B-endor administration (iv or icv) did not alter the plasma concentration of ANP. These effects of MS and Leu-enk on plasma concentrations of ANP appear to be mediated through actions on the central nervous system. MS, Leu-enk, B-endor, and Dyn given icv, produced elevations of plasma norepinephrine (NE) and epinephrine (Epi) concentrations. When MS was given icv, mean Epi and NE plasma levels increased 10-50 times the increases noted with B-endor, Leu-enk and Dyn. A role of catecholamines in mediating MS-stimulated ANP release is supported by the observation that ganglionic blockade with chlorisondamine significantly attenuated the increase of plasma ANP levels. MS, but not B-endor, Leu-enk and Dyn, acts within the brain to increase plasma levels of ANP. MS-induced elevations of plasma ANP levels may be dependent on an intact autonomic nervous system.