Immunoreactive dynorphin in rat tissues and plasma

Early post-natal life stress induces permanent adrenocorticotropin-dependent hypercortisolism in male mice

PURPOSE

It has been hypothesized that specific early-life stress (ES) procedures on CD-1 male mice produce diabetes-like alterations due to the failure of negative feedback of glucocorticoid hormone in the pituitary. The aim of this study is to investigate the possible mechanism that leads to this pathological model, framing it in a more specific clinical condition.

METHODS

Metabolic and hypothalamic-pituitary-adrenal-related hormones of stressed mice (SM) have been analyzed immediately after stress procedures (21 postnatal days, PND) and after 70 days of a peaceful (unstressed) period (90 PND). These data have been compared to parameters from age-matched controls (CTR), and mice treated during ES procedures with oligonucleotide antisense for pro-opiomelanocortin (AS-POMC).

RESULTS

At 21 PND, SM presented an increased secretion of hypothalamic CRH and pituitary POMC-derived peptides, as well as higher plasmatic levels of ACTH and corticosterone vs. CTR. At 90 PND, SM showed hyperglycemia, with suppression of hypothalamic CRH, while pituitary and plasmatic ACTH levels, as well as plasma corticosterone, were constantly higher than in CTR. These values are accompanied by a progressive acceleration in gaining total body weight, which became significant vs. CTR at 90 PND together with a higher pituitary weight. Treatment with AS-POMC prevented all hormonal and metabolic alterations observed in SM, both at 21 and 90 PND.

CONCLUSIONS

These findings show that these specific ES procedures affect the negative glucocorticoid feedback in the pituitary, but not in the hypothalamus, suggesting a novel model of ACTH-dependent hypercortisolism that can be prevented by silencing the POMC gene.

Dynorphins in Development and Disease: Implications for Cardiovascular Disease

It is well-established that cardiovascular disease continues to represent a growing health problem and significant effort has been made to elucidate the underlying mechanisms. In this review, we report on past and recent high impact publications in the field of intracrine network signaling, focusing specifically on opioids and their interrelation with key modulators of the cardiovascular system and the onset of related disease. We present an overview of studies outlining the scope of cardiovascular and cerebrovascular processes that are affected by opioids, including heart function, ischemia, reperfusion, and blood flow. Specific emphasis is placed on the importance of dynorphin molecules in cerebrovascular and cardiovascular regulation. Evidence suggests that excessive or insufficient dynorphin could make an important contribution to cardiovascular physiology, yet numerous paradoxical observations frequently impede a clear understanding of the role of dynorphin. Thus, we argue that dynorphin-mediated signaling events for which an immediate regulatory effect is disputed should not be dismissed as unimportant, as they may play a role in cross-talk with other signaling networks. Finally, we consider the most recent evidence on the role of dynorphin during cardiovascular-related inflammation and on the potential value of endogenous and exogenous inhibitors of kappa-opioid receptor, a major dynorphin A receptor, to limit or prevent cardiovascular disease and its related sequelae.

Current research on opioid receptor function

The use of opioid analgesics has a long history in clinical settings, although the comprehensive action of opioid receptors is still less understood. Nonetheless, recent studies have generated fresh insights into opioid receptor-mediated functions and their underlying mechanisms. Three major opioid receptors (μ-opioid receptor, MOR; δ-opioid receptor, DOR; and κ-opioid receptor, KOR) have been cloned in many species. Each opioid receptor is functionally sub-classified into several pharmacological subtypes, although, specific gene corresponding each of these receptor subtypes is still unidentified as only a single gene has been isolated for each opioid receptor. In addition to pain modulation and addiction, opioid receptors are widely involved in various physiological and pathophysiological activities, including the regulation of membrane ionic homeostasis, cell proliferation, emotional response, epileptic seizures, immune function, feeding, obesity, respiratory and cardiovascular control as well as some neurodegenerative disorders. In some species, they play an essential role in hibernation. One of the most exciting findings of the past decade is the opioid-receptor, especially DOR, mediated neuroprotection and cardioprotection. The upregulation of DOR expression and DOR activation increase the neuronal tolerance to hypoxic/ischemic stress. The DOR signal triggers (depending on stress duration and severity) different mechanisms at multiple levels to preserve neuronal survival, including the stabilization of homeostasis and increased pro-survival signaling (e.g., PKC-ERK-Bcl 2) and antioxidative capacity. In the heart, PKC and KATP channels are involved in the opioid receptor-mediated cardioprotection. The DOR-mediated neuroprotection and cardioprotection have the potential to significantly alter the clinical pharmacology in terms of prevention and treatment of life-threatening conditions like stroke and myocardial infarction. The main purpose of this article is to review the recent work done on opioids and their receptor functions. It shall provide an informative reference for better understanding the opioid system and further elucidation of the opioid receptor function from a physiological and pharmacological point of view.

Effects of kappa opioid agonists alone and in combination with cocaine on heart rate and blood pressure in conscious squirrel monkeys

As kappa agonists have been proposed as treatments for cocaine abuse, the cardiovascular effects of the kappa opioid receptor agonists ethylketocyclazocine (EKC) and enadoline were investigated in conscious squirrel monkeys. Both EKC and enadoline increased heart rate with little effect on blood pressure. This effect appeared to be specific for kappa receptors as the mu opioid agonist morphine did not mimic the effects of the kappa agonists. The opioid antagonist naltrexone, at a dose of 1.0 mg/kg, blocked the effect of EKC. An action at both central and peripheral receptors may be responsible for the heart rate increase following kappa agonist treatment. The ganglionic blocker chlorisondamine partially antagonized the effect of EKC on heart rate, suggesting central involvement, while the peripherally-acting agonist ICI 204,448 ((+/-)-1-[2,3- (Dihydro-7-methyl-1H-inden-4-yl)oxy]-3-[(1-methylethyl)amino]-2-butanol hydrochloride) also increased heart rate, supporting a peripheral site of action. When given in combination with cocaine, EKC produced effects that were sub-additive, suggesting that the kappa agonists may be used safely as cocaine abuse treatments.

Administration of antisense oligonucleotide against pro-opiomelanocortin prevents enduring hormonal alterations induced by neonatal handling in male mice

Early life events have been implicated in the programming of adult chronic diseases. Several investigations suggest that the role of early environment in influencing development mainly involves the hypothalamic-pituitary-adrenal axis. Therefore, we examined whether 1) daily neonatal handling, applied from birth to weaning induces HPA hormones alterations in mice lasting up to the adult age; and 2) if the administration of an antisense oligodeoxynucleotide versus pro-opiomelanocortin (As-POMC) prevents hormonal alterations observed in previously handled mice (Handled). In the adult phase (90 days), Handled are overweight and have higher basal plasma immuno-reactive (ir)-corticosterone and adrenocorticotropin (ir-ACTH), and higher pituitary ir-ACTH; while they have lower hypothalamic ir-ACTH and corticotropin-releasing hormone (ir-CRH) in comparison with the non-handled mice. As-POMC (0.05-0.1 nmol/g body weight per day) administered during the same period dose-dependently prevents the increase in body weight, in plasma ir-corticosterone, ir-ACTH, and pituitary ir-ACTH, also preventing the decrease in hypothalamic ir-CRH and ir-ACTH; while the mismatch oligonucleotide is nearly inactive. This data indicates that pharmacological treatment in neonatal life may have enduring effects, reducing the alterations in hormonal homeostatic programming mechanisms induced by early repeated handling.

Melatonin exerts its analgesic actions not by binding to opioid receptor subtypes but by increasing the release of beta-endorphin an endogenous opioid

The occurrence of systematic diurnal variations in pain thresholds has been demonstrated in human. Salivary melatonin levels change following acute pain when other factors that could explain the change have been removed or controlled. Melatonin-induced analgesia is blocked by naloxone or pinealectomy. By using selective radioligands [3H]-DAMGO, [3H]-DPDPE, [3-U69593, and 3H]-nociceptin, we have shown that the bovine pinealocytes contain delta and mu, but not kappa or ORL1 opioid receptor subtypes. In the present study, by using melatonin receptor agonists (6-chloromelatonin or 2-iodo-N-butanoyl-5-methoxytryptamine) or melatonin receptor antagonist (2-phenylmelatonin), we have shown that these agents do not compete with opioid receptor subtypes. However, we observed a time-dependent release of beta-endorphin an endogenous opioid peptide, by melatonin from mouse pituitary cells in culture. Hence, it is suggested that melatonin exerts its analgesic actions not by binding to opioid receptor subtypes but by binding to its own receptors and increasing the release of beta-endorphin.

The role of ACE2 in cardiovascular physiology

The renin-angiotensin system (RAS) is critically involved in cardiovascular and renal function and in disease conditions, and has been shown to be a far more complex system than initially thought. A recently discovered homologue of angiotensin-converting enzyme (ACE)--ACE2--appears to negatively regulate the RAS. ACE2 cleaves Ang I and Ang II into the inactive Ang 1-9 and Ang 1-7, respectively. ACE2 is highly expressed in kidney and heart and is especially confined to the endothelium. With quantitative trait locus (QTL) mapping, ACE2 was defined as a QTL on the X chromosome in rat models of hypertension. In these animal models, kidney ACE2 messenger RNA and protein expression were markedly reduced, making ACE2 a candidate gene for this QTL. Targeted disruption of ACE2 in mice failed to elicit hypertension, but resulted in severe impairment in myocardial contractility with increased angiotensin II levels. Genetic ablation of ACE in the ACE2 null mice rescued the cardiac phenotype. These genetic data show that ACE2 is an essential regulator of heart function in vivo. Basal renal morphology and function were not altered by the inactivation of ACE2. The novel role of ACE2 in hydrolyzing several other peptides-such as the apelin peptides, opioids, and kinin metabolites-raises the possibility that peptide systems other than angiotensin and its derivatives also may have an important role in regulating cardiovascular and renal function.

Vas deferens response to selective opioid receptor agonists in adult mice is impaired following postnatal repeated mild stress

Mild stress repeatedly applied to neonatal rodents induces alterations of central nervous system functions, persisting up to the adult age. Most alterations may be mediated through hormones and neuromediators active on the autonomic nervous system, therefore we tested the efficacy of selective opioid receptor agonists on the vas deferens of adult mice that, as neonates, had undergone daily mild stress until weaning (brief isolation and solvent injection). We found in the adult mouse (90 days old) decreased sensitivity of vas deferens to selective mu-, delta- and kappa-opioid receptor agonist drugs. The neonatal administration of an antisense oligodeoxynucleotide adrenocorticotropin-synthesis-inhibitor partly prevented these effects.

Modulation of sympathetic actions on the heart by opioid receptor stimulation

The sympathetic nervous system, the most important extrinsic regulatory mechanism of the heart, is inhibited postsynaptically and presynaptically by opioid peptides produced in the heart via their respective receptors. The cardiac actions of beta-adrenergic receptor (beta-AR) stimulation are attenuated by activation of the opioid receptor (OR) with OR agonist at ineffective concentrations, implying cross-talk between the OR and beta-AR. This cross-talk results from inhibition of the Gs protein and adenylyl cyclase of the beta-AR pathway by the pertussis toxin-sensitive G protein of the opioid pathway. Alterations in cross-talk between these two receptors occur in pathological situations to meet bodily needs. In myocardial ischemia, when the sympathetic activity is increased, the inhibition of beta-AR stimulation by kappa-opioid stimulation is also enhanced, thus reducing the workload, oxygen consumption and cardiac injury. Whereas cardiac responsiveness to sympathetic discharges is also reduced after chronic hypoxia, the cross-talk between kappa-OR and beta-AR is reduced to prevent undue suppression of the sympathetic influence on the heart. On the other hand, impairment of the cross-talk may result in abnormality. A lack or a significant reduction in the inhibition of beta-AR stimulation by kappa-OR stimulation may lead to an excessive increase in cardiac activities, which contribute to the maintenance of high arterial blood pressure in spontaneously hypertensive rats. Other than opioid peptides, female sex hormone and adenosine also inhibit the sympathetic actions on the heart. In addition, sympathetic action is also inhibited presynaptically by kappa-opioid peptides via their receptor.

Opioidergic innervation of the tree shrew pineal gland: an immunohistochemical study

The tree shrew (Tupaia glis) has been described as a missing link relating primate to insectivore stock. The pineal gland of the tree shrew consists of a superficial pineal and a deep pineal, which are connected by a long and slender pineal stalk. A monoclonal antibody against leu-enkephalin was used in an immunohistochemical investigation of the tree shrew pineal gland. A moderate innervation of leu-enkephalin immunoreactive nerve fibers has been demonstrated in both superficial and deep pineal gland of the tree shrew. The density of the nerve fibers was slightly higher in the superficial pineal than that of the deep one. The number of immunoreactive nerve fibers were observed in the capsule of the pineal gland from where they entered the pineal parenchyma. Only a few immunoreactive fibers were found in the habenular area and the area rostral to the pineal recess, connecting the habenula and the deep pineal. Furthermore, some positive fibers were located in the pineal stalk. There was no evidence of leu-enkephalin immunoreactive intrapineal cells as seen in the other species of mammal. Therefore, the interspecies variation of opioidergic innervation among the mammals may exist. The lack of intrapineal perikarya is interpreted to indicate that the sources of leu-enkephalin nerve fibers were outside the gland. The anatomical location of the leu-enkephalin immunoreactive nerve fibers in the tree shrew pineal gland supports to both central and peripheral pinealopetal pathways in this species.

Pineal opioid receptors and analgesic action of melatonin

Physicians have noted since antiquity that their patients complained of less pain and required fewer analgesics at night times. In most species, including the humans, the circulating levels of melatonin, a substance with analgesic and hypnotic properties, exhibit a pronounced circadian rhythm with serum levels being high at night and very low during day times. Moreover, melatonin exhibits maximal analgesic effects at night, pinealectomy abolishes the analgesic effects of melatonin, and mu opioid receptor antagonists disrupt the day-night rhythm of nociception. It is believed that melatonin, with its sedative and analgesic effects, is capable of providing a pain free sleep so that the body may recuperate and restore itself to function again at its peak capacity. Moreover, in conditions when pain is associated with extensive tissue injury, melatonin's ability to scavenge free radicals and abort oxidative stress is yet another beneficial effect to be realized. Since melatonin may behave as a mixed opioid receptor agonist-antagonist, it is doubtful that a physician simply could potentiate the analgesic efficacy of narcotics such as morphine by coadministering melatonin. Therefore, future research may synthesize highly efficacious melatonin analogues capable of providing maximum analgesia and hopefully being devoid of addiction liability now associated with currently available narcotics.

Characterization of immunoreactive dynorphin B and beta-endorphin in human plasma

Dynorphins and beta-endorphin in human plasma were characterized and studied quantitatively using radioimmunoassay, high-performance liquid chromatography (HPLC), and mass spectrometry. Most immunoreactive (ir) dynorphin B and beta-endorphin in human plasma coeluted with authentic peptides in analysis. Dynorphin A was not detected. Added to human plasma it was rapidly converted into Leu-enkephalin-Arg6 followed by elimination of the C-terminal arginine after prolonged incubation. The rate of dynorphin A conversion was estimated at 40 pmol/min/microl plasma. This process was inhibited by the thiol protease inhibitor, PHMB and by EDTA. Dynorphin B, alpha-neoendorphin and big dynorphin were virtually not metabolized by plasma proteases under the same conditions. beta-endorphin was processed into beta-endorphin(1-19) and the corresponding C-terminal counterpart beta-endorphin(20-31) at a rate of about 25 pmol/min/microl of plasma. Based on the above data, a reliable strategy was established to measure dynorphin B- and beta-endorphin-ir in human plasma samples. The basal levels in a male control group were 0.99 +/- 0.11 (n = 11) and 16.3 +/- 1.5 (n = 11) fmol/ml plasma, respectively.

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.

Opioid peptide modulation of circulatory and endocrine response to mental stress in humans

Healthy subjects were classified according to their percent increase in systolic blood pressure (SBP) after mental arithmetic test (MAT) as low (delta SBP 9.3-15.1%, n = 15) and high (delta SBP 35.1-45.4%, n = 15) responders. During MAT, low responders showed significantly (p < 0.01) increased plasma levels of beta-endorphin, cortisol, catecholamines, and atrial natriuretic factor (ANF) and decreased levels of endothelin-1, whereas high responders showed increased (p < 0.01) levels of Metenkephalin, dynorphin B, and catecholamines. Pretreatment with naloxone hydrochloride enhanced (p < 0.01) SBP, heart rate, noradrenaline, cortisol, and endothelin-1 levels, and reduced (p < 0.01) ANF in low responders in response to MAT, whereas it decreased (p < 0.01) hemodynamic parameters, noradrenaline, and endothelin-1 in high responders. The individual differences in hemodynamic and endocrine responses to MAT may depend on a different activation of the endogenous opioid system.

The presence of opioidergic pinealocytes in the pineal gland of the European hamster (Cricetus cricetus): an immunocytochemical study

By use of antibodies raised against leu-enkephalin and met-enkephalin immunoreactive, opioidergic bi- and multipolar cells were demonstrated in the pineal gland of the European hamster. Ultrastructural analysis of these opioidergic cells revealed them to be pinealocytes. Processes emerged from the cell bodies and terminated in club-shaped swellings containing many small clear and some larger granular vesicles. Some of the terminals made synapse-like contacts with non-immunoreactive pinealocytes. The presence of the opioidergic pinealocytes strongly indicates that the pineal gland of the European hamster, in addition to its pinealopetal nervous regulation, is regulated by intrapineal peptidergic pinealocytes via a synaptic mechanism. A possible paracrine role of the opioidergic cells must also be considered.

Posttranslational processing of proenkephalins and chromogranins/secretogranins

Posttranslational processing of peptide-precursors is nowadays believed to play an important role in the functioning of neurons and endocrine cells. Both proenkephalins and chromogranins/secretogranins are considered as precursor molecules in these tissues, resulting in posttranslationally formed degradation products with potential biological activities. Among the proteins and peptides of neuronal and endocrine secretory granules, the enkephalins and enkephalin-containing peptides have been most extensively studied. The characterization of the post-translationally formed degradation products of the proenkephalins have enabled the understanding of their processing pathway. Chromogranins/secretogranins represent a group of acidic glycoproteins, contained within hormone storage granules. The biochemistry, biogenesis and molecular properties of these proteins have already been studied for 25 years. The chromogranins/secretogranins have a widespread distribution throughout the neuroendocrine system, the adrenal medullary chromaffin granules being the major source of these storage components. Recent data provide evidence for a precursor role for all members of the chromogranins/secretogranins family although also several other functions have been proposed. In this review, some of the methods applied to study proteolytic processing are described. In addition, the posttranslational processing of chromogranins/secretogranins and proenkephalins, especially the biochemical aspects, will be discussed and compared. Recent exciting developments on the generation and identification of potential physiologically active fragments will be covered.

Prodynorphin mRNA expression in adult cultured rat ventricular cardiac myocytes

Prodynorphin mRNA was synthesized both in rat atrial and ventricular tissue, as well as in adult cultured rat ventricular cardiac myocytes. In the cultured cells, the content of prodynorphin mRNA did not differ from that detected in the original ventricle, indicating that the myocardial cell is an important source for prodynorphin mRNA in the rat ventricular tissue. This study demonstrated the presence of immunoreactive dynorphin B-like material in the cultured cardiomyocytes. Gel permeation chromatography analysis of this material revealed the presence of forms with an apparently higher molecular weight than authentic dynorphin B.

Immunoreactive dynorphin A-like material in extracted human hypothalamic-hypophysial plasma

Immunoreactive dynorphin A-like material (ir-dyn A) in human plasma was measured by a validated radioimmunoassay. In peripheral plasma extracts mean concentrations between 20 and 40 fmol/ml were determined in volunteers and in patients with pituitary adenomas. In this latter group superimposable levels were detected three days before and during transsphenoidal microsurgery. Interestingly, ir-dyn A levels evaluated in extracts of hypothalamic-hypophysial plasma obtained during surgery, just after tumor removal, were 4-5 times higher than in peripheral plasma. Reverse-phase high performance liquid chromatography (rp-HPLC) of extracts of peripheral plasma samples revealed two immunoreactive peaks. The major form had the same retention time of dyn A-(1-32); whereas a second, more lipophilic, peak eluted later and was not further characterized. In contrast, rp-HPLC analysis of extracts of plasma collected from the suprapituitary region displayed only one peak eluting in the position of synthetic dyn A-(1-17). The presence of dyn-related peptides in hypothalamic-hypophysial plasma supports the hypothesis that they may play a part in the regulation of hypothalamic and/or pituitary functions in humans.

Dynorphin B-like immunoreactivity in gastroduodenal biopsy specimens from gallstone patients

Dynorphin B-like immunoreactivity (ir-dyn B) was measured by a validated radio-immunoassay in gastroduodenal biopsy specimens from control and gallstone patients. Levels were significantly lower in acetic acid extracts of specimens of the transverse portion of the duodenum from gallstone patients. Gel permeation chromatography showed that almost all ir-dyn B in duodenal samples corresponded to a molecular form co-eluting with authentic dyn B. Duodenal extracts from gallstone patients had less of this form. Reverse-phase high performance liquid chromatography of the pooled gel chromatography fractions showed up a molecular form with the same retention time as synthetic dyn B which was significantly less in fractions from duodenal extracts of gallstone patients. These results indicate the occurrence of dyn B in the human gastrointestinal tract; however, at this stage of our understanding, no causal relationship can be demonstrated with functional alterations of the biliary tree.

Differential regulation of anterior pituitary prodynorphin and gonadotropin-subunit gene expression by steroid hormones

Prodynorphin is expressed by neurons of the hypothalamus and gonadotrophs of the anterior pituitary gland (AP) and plays a role in the negative feedback regulation of the reproductive neuroendocrine axis. The present study examined whether gonadal steroid hormones are capable of modulating pituitary prodynorphin expression in immature, female rats. Steroids were administered via subcutaneous Silastic implants and rats were killed at 29 days of age. Northern blot analysis was used to measure AP prodynorphin, luteinizing hormone-beta (LH beta), follicle-stimulating hormone-beta (FSH beta), and common alpha-subunit mRNA levels (normalized to 18S ribosomal RNA). Treatment groups (n = 5-6) consisted of control (CNT; empty implants), estradiol (E2; 4 days), E2 + progesterone (E2 + P4; 8 days and 4 days, respectively), and dihydrotestosterone (DHT; 4 days). Pituitary prodynorphin mRNA was significantly suppressed in only the DHT-treated animals (26 +/- 10% of CNT, p < 0.01). LH beta mRNA was suppressed by all steroid treatments (p < 0.01), FSH beta was lower in only the E2 group, and alpha-subunit was reduced in both the E2 + P4 and DHT groups (p < 0.01). Serum LH was suppressed by all steroid treatments but FSH was reduced in only the E2 and E2 + P4 groups (p < 0.01). Treatment of prepubescent rats with continuous high levels of gonadal steroids is known to severely reduce endogenous hypothalamic gonadotropin releasing hormone (GnRH) release and this is supported by our observation of reduced gonadotropin-subunit gene expression.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynorphin A-(1–17) and dynorphin B are released from in vitro superfused rat hypothalami. Effects of depolarizing agents and ovariectomy

We measured the release of immunoreactive (ir) dynorphin (dyn) A-(1-17) and dyn B from the rat hypothalamus by an in vitro superfusion technique. The system was validated on the basis of the recovery and stability of radiolabeled peptides added to the superfused hypothalami. These were detected as authentic peptides by reverse-phase high-performance liquid chromatography (rp-HPLC) only in the presence of a cocktail of peptidase inhibitors added to the superfusion medium. We observed spontaneous release of ir-dyn B, evaluated by a validated radioimmunoassay in the superfusates, that was increased by potassium and veratridine depolarization. It was calcium-dependent and tetrodotoxin-sensitive. We could not evaluate ir-dyn A-(1-17) directly in the superfusates, because the peptidase inhibitors added to the medium significantly altered the tracer-antibody reaction. To obviate this problem, pooled superfusate samples were purified on C18 cartridges and assayed by rp-HPLC. Rp-HPLC analysis of superfusates revealed two molecular forms with the same retention time as authentic dyn A-(1-17) and dyn B which were four times higher in K(+)-stimulated fractions. We could not detect dyn A-(1-32), comprising dyn A-(1-17) and dyn B, even though this peptide is recognized by the antibodies used in this study and is detected in acetic acid extracts of the rat hypothalamus. The spontaneous and K(+)-evoked release of ir-dyn A-(1-17) and ir-dyn B were significantly higher in 2-week ovariectomized rats, in parallel with the increase of their content in the anterior hypothalamus preoptic area.

Kappa and delta opioid receptor stimulation affects cardiac myocyte function and Ca2+ release from an intracellular pool in myocytes and neurons

We investigated the effects of mu, delta, and kappa opioid receptor stimulation on the contractile properties and cytosolic Ca2+ (Cai) of adult rat left ventricular myocytes. Cells were field-stimulated at 1 Hz in 1.5 mM bathing Ca2+ at 23 degrees C. The mu-agonist [D-Ala2,N-Me-Phe4,Gly5-ol]-enkephalin (10(-5) M) had no effect on the twitch. The delta-agonists methionine enkephalin and leucine enkephalin (10(-10) to 10(-6) M) and the kappa-agonist (trans-(dl)-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclo-hexyl]- benzeneacetamide)methanesulfonate hydrate (U-50,488H; 10(-7) to 2 x 10(-5) M) had a concentration-dependent negative inotropic action. The sustained decrease in twitch amplitude due to U-50,488H was preceded by a transient increase in contraction. The effects of delta- and kappa-receptor stimulation were antagonized by naloxone and (-)-N-(3-furyl-methyl)-alpha-normetazocine methanesulfonate, respectively. In myocytes loaded with the Ca2+ probe indo-1, the effects of leucine enkephalin (10(-8) M) and U-50,488H (10(-5) M) on the twitch were associated with similar directional changes in the Cai transient. Myofilament responsiveness to Ca2+ was assessed by the relation between twitch amplitude and systolic indo-1 transient. Leucine enkephalin (10(-8) M) had no effect, whereas U-50,488H (10(-5) M) increased myofilament responsiveness to Ca2+. We subsequently tested the hypothesis that delta and kappa opioid receptor stimulation may cause sarcoplasmic reticulum Ca2+ depletion. The sarcoplasmic reticulum Ca2+ content in myocytes and in a caffeine-sensitive intracellular Ca2+ store in neurons was probed in the absence of electrical stimulation via the rapid addition of a high concentration of caffeine from a patch pipette above the cell. U-50,488H and leucine enkephalin slowly increased Cai or caused Cai oscillations and eventually abolished the caffeine-triggered Cai transient. These effects occurred in both myocytes and neuroblastoma-2a cells. In cardiac myocyte suspensions U-50,488H and leucine enkephalin both caused a rapid and sustained increase in inositol 1,4,5-trisphosphate. Thus, delta and kappa but not mu opioids have a negative inotropic action due to a decreased Cai transient. The decreased twitch amplitude due to kappa-receptor stimulation is preceded by a transient increase in contractility, and it occurs despite an enhanced myofilament responsiveness to Ca2+. The effects of delta and kappa opioids appear coupled to phosphatidylinositol turnover and, at least in part, may be due to sarcoplasmic reticulum Ca2+ depletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Atrial natriuretic polypeptide secretion via selective activation of kappa-opioid receptor: role of dynorphin

The present study was designed to investigate the direct effect of dynorphin on atrial natriuretic polypeptide (ANP) secretion in cultured rat atrial cardiocytes via a kappa-opioid receptor activation as well as the involvement of adenosine 3',5'-cyclic monophosphate (cAMP) system in the secretion of ANP from cardiocytes. Dynorphin stimulated ANP secretion dose and time dependently from 2-day cultured atrial cardiocytes. The dynorphin-induced ANP secretion was partially antagonized by MR2266, a selective kappa-opioid receptor antagonist. U-62066E, a selective kappa-opioid receptor agonist, stimulated ANP secretion. This stimulation was also antagonized by MR2266. However, no stimulation of ANP secretion was seen with [D-Ala2,D-Leu5]enkephalin, methionine (Met)-enkephalin, or [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin. Dynorphin at 10(-6) M significantly decreased the production of cAMP in the cultured cardiocytes. However, 10(-6) M Met-enkephalin had no effect on cAMP at all. The decrease in cAMP production by the addition of dynorphin was partially antagonized with a simultaneous addition of MR2266. The dynorphin-induced ANP secretion, as well as the basal secretion, were significantly decreased by the addition of 3-isobutyl-1-methylxanthine, a phosphodiesterase inhibitor, as compared with the respective controls. Dibutyryl cAMP at 10(-3) M significantly decreased the basal secretion of ANP as compared with the control. Therefore, the present studies show that dynorphin selectively stimulates ANP secretion, at least in part, via the activation of a specific kappa-opioid receptor.

Atypical prodynorphin gene expression in corticosteroid-producing cells of the rat adrenal gland

Prodynorphin (proDyn) gene expression was examined in the rat adrenal gland. In situ hybridization revealed a heterogenous proDyn mRNA distribution limited almost exclusively to the adrenal cortex; the inner cortical layers contained the highest amounts. In the adrenal medulla, only scattered single cells were seen. By Northern (RNA) blot analysis, adrenocortical proDyn mRNA levels were highly abundant but of smaller size than proDyn transcripts found in the brain. Low levels of the brain-size proDyn mRNA transcript were detected but restricted to the medulla. A discrepancy was suggested when comparing the high abundance of proDyn mRNA levels with the low levels of proDyn-derived peptide in the adrenal. A hypothesis of nontranslation of the shorter proDyn mRNA by adrenocortical cells was rejected because polysomal loading analysis suggests that the mRNA is translated. We propose that adrenocortical proDyn-derived peptides are not targeted for storage but are released shortly after synthesis, thus accounting for low peptide levels. We also measured proDyn mRNA levels in response to stimuli known to affect adrenocortical cells and their most important function--steroidogenesis. Adrenals from hypophysectomized rats had less proDyn mRNA by a factor of 5 than adrenals from normal sham-operated rats. Normal levels were restored by adrenocorticotrophic hormone administration, indicating a potential importance of adrenal proDyn in the hypothalamic-adrenal-pituitary axis.

Pharmacology of spinal peptides affecting sensory and motor functions: dynorphins, somatostatins and tachykinins

In recent years, the pharmacological activity of dynorphins and somatostatins on spinal sensory transmission has been intensively investigated with a view to developing new agents for pain control. Similarly, a series of tachykinin-related peptides with apparent receptor antagonist activity on endogenous substance P and neurokinins has been investigated. However, a number of observations suggest that these peptides, injected intrathecally in laboratory animals, not only exert a direct effect on nociceptive transmission but also affect a broader range of spinal somatomotor and autonomic functions and may cause peculiar neurotoxic effects that are not elicited by a large number of peptides affecting spinal neurotransmission. This article makes a critical review of their pharmacological activity on spinal sensory and motor functions and briefly touches on their anatomical and functional organization in the spinal cord.

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.

A novel endocrine cell type in the guinea-pig gastric mucosa: cellular source of pro-enkephalin-derived peptides. A histochemical, immunohistochemical, and electron microscopical characterization

A novel endocrine cell type has been identified in the guinea-pig gastric mucosa which preferentially occurs in the oxyntic area. Cells of this type exhibit immunoreactivities for bovine adrenal medulla dodecapeptide (BAM-12P) and in many cases for Met-enkephalin and are thus presumed to contain a pro-enkephalin-like precursor protein. Systematic immunohistochemical investigations show that these cells do not contain immunoreactivities for various enteric hormones, neuropeptides and biogenic amines (serotonin, histamine). However, they do contain immunoreactivity for chromogranin A, an acidic glycoprotein which is common to the majority of entero-endocrine cells. Using silver impregnation techniques BAM-12P immunoreactive cells prove to be argyrophil, but fail to react argentaffin. On the electron microscopical level, these cells contain a well-developed endoplasmic reticulum and Golgi apparatus and numerous polymorphous secretion granules which measure about 290 nm in diameter. The secretion granules are ovoid or pear-shaped but largely plump compared to those of enterochromaffin cells. Light and electron microscopical findings indicate that BAM-12P immunoreactive cells constitute an endocrine cell population of the gastric epithelium in addition to the "established" endocrine cells hitherto known in this location.

Immunohistochemistry of opioid peptides in the guinea pig endocrine pancreas

Previous immunochemical investigations have demonstrated various opioid peptides in the pancreas. However, controversies exist related to the cellular localization of these peptides in the endocrine pancreas. Therefore, the guinea pig endocrine pancreas was immunohistochemically investigated for the presence of opioid peptides derived from pro-dynorphin, pro-enkephalin or pro-opiomelano-cortin. Immunoreactivities were demonstrated on serial semithin sections by the peroxidase anti-peroxidase technique. In routinely immunostained sections, immunoreactivities for dynorphin A and alpha-neo-endorphin were localized in pancreatic enterochromaffin cells, but not in islet cells. Immunoreactivity for Met-enkephalin was confined exclusively to B-cells and was localized only in some secretory granules. However, pre-treatment of semi-thin sections with trypsin and carboxypeptidase B led to a marked increase of Met-enkephalin immunoreactivity in B-cells. In addition, immunoreactivities for Met-enkephalin-Arg-Gly-Leu and bovine adrenal medulla dodecapeptide could be demonstrated in B- and A-cells, and beta-endorphin immunoreactivity was localized in A-cells. In no case, however, were immunoreactivities detected for bovine adrenal medulla docosapeptide, peptide F, corticotropin, melanotropin or dynorphin 1-32. The immunohistochemical findings indicate that opioids of different peptide families are present in the guinea pig endocrine pancreas. Since several opioid peptides of the corresponding pro-hormones could be demonstrated in the reference organs but not in the pancreas, it is concluded that the biosynthetic pathways of the respective precursors are different from those in the adrenal medulla or in the pituitary.

Beta-endorphin-like and adrenocorticotropin-like materials in heart tissues of the rat, gerbil, hamster and guinea pig

1. Heart tissues of several rodent species including the rat, gerbil (Meriones unguiculatus), hamster (Mesocricetus auratus) and guinea pig (Cavia porcellus) were extracted with an acetone-water-HCl mixture. An acid acetone powder was obtained by adding a copious volume of acetone to the extract. 2. Rat heart acid acetone powder was subjected to ion exchange chromatography on CM-cellulose. Gerbil heart acid acetone powder was subjected to salt fractionation, gel filtration on Sephadex G-10 and then ion exchange chromatography on CM-cellulose. Hamster and guinea pig heart acid acetone powders were subjected to gel filtration on Sephadex G-25. 3. The fractions were assayed for the ability to stimulate corticosterone production in isolated rat adrenal decapsular (zona fasciculata, zona reticularis and medulla) cells, to displace D-ala2-D-leu5-(tyrosyl-3,5-3H) enkephalin from binding to rat brain membranes, and to inhibit 125I-human beta-endorphin from binding to its antibodies. 4. The widespread occurrence of beta-endorphin-like immunoreactivity among the rat heart CM-cellulose fractions may reflect different species of beta-endorphin. The fraction with the highest beta-endorphin-like immunoreactivity and opiate receptor binding activity was strongly adsorbed on CM-cellulose. 5. In hamster and guinea pig hearts, beta-endorphin-like immunoreactivity and opiate receptor binding activity were distributed among high molecular weight and low molecular weight fractions. 6. In gerbil hearts, opiate receptor binding activity was present in fractions unretarded on Sephadex G-10 (i.e. with a molecular weight greater than 700) as well as in the retarded fractions (i.e. with a molecular weight smaller than 700).(ABSTRACT TRUNCATED AT 250 WORDS)

Beta-endorphin-like and adrenocorticotropin-like materials in turtle heart and intestine

1. Turtle heart and intestine acetone powders were extracted with an acetone-water-HCl mixture. An acid acetone powder resulted by adding a copious volume of acetone to the extract. The powder was subjected to gel filtration on Sephadex G-25 and ion exchange chromatography on CM-cellulose. 2. In turtle heart, corticotropin-like bioactivity was distributed among chromatographic fractions (derived from material unretarded on Sephadex G-25) unadsorbed and adsorbed on CM-cellulose. The highest opiate receptor binding activity and beta-endorphin-like immunoreactivity were adsorbed on CM-cellulose. 3. In turtle intestine, corticotropin-like bioactivity was absent. Opiate receptor binding activity was present in fractions unretarded as well as in fractions retarded on Sephadex G-25, indicating a molecular weight of greater and smaller than 5000 respectively. 4. The highest opiate receptor binding activity and beta-endorphin-like immunoreactivity were found in a fraction adsorbed on CM-cellulose.

Opioid receptors in rat cardiac sarcolemma: effect of phenylephrine and isoproterenol

The present study demonstrates the presence of opioid receptors in the rat cardiac sarcolemma isolated by the hypotonic LiBr-shock procedure. Opioid binding was measured by using [3H]U69 593, [3H](2-D-penicillamine,5-D-penicillamine)enkephalin ([3H]DPDPE) or [3H][D-Ala2,MePhe4,Gly-(ol)5]enkephalin ([3H]DAGO) as selective radioligands for K, delta and mu opioid receptors, respectively. Both the K- and delta-selective ligands exhibited highly specific (75-86%) binding, saturable at a concentration of about 20 nM. No specific binding for the selective agonist DAGO was observed. A marked increase in both [3H]U69 593 and [3H]DPDPE binding was observed after incubation of the sarcolemma with the alpha-adrenoceptor agonist phenylephrine or with the beta-adrenoceptor agonist isoproterenol. These stimulatory effects were associated with an increase in the Bmax values, a decrease in the Kd values, and were completely antagonized by the respective antagonists phentolamine and propranolol.

The presence of corticotropin-like and opiate-like activities in tissues of adult sea lamprey, Petromyzon marinus L

Sexually mature landlocked sea lamprey were captured during their upstream migration. Different tissues, including the brain, pituitary, heart, liver, gut, testis, and ovary, were dissected from the animals and an acetone powder was prepared from each tissue. The tissue acetone powders were subjected to heat treatment and were then extracted with an acidic medium in order to inactivate any proteases present. The resulting acid acetone powders were then tested for their ability to stimulate corticosterone production from isolated rat adrenal cells and to displace the binding of D-Ala2-D-Leu5-[tyrosyl-3,5-3H]-enkephalin to rat brain membranes. It was found that the brain and liver contained steroidogenic activity while opiate activity was detected in the heart, liver, gut, brain, and pituitary. No steroidogenic activity was found in the heart, ovary, testis, gut, and pituitary while ovary and testis did not contain assayable opiate activity. None of the tissues contained beta-endorphin-like immunoreactivity.

Measurement and chromatographic characterization of prodynorphin-derived peptides in the guinea-pig ileum

Guinea-pig ileum was dissected and the mucosa, submucosa and external musculature extracted with aqueous acetic acid for measurement of four prodynorphin-derived peptides, namely dynorphin A 1-8, dynorphin A 1-17, dynorphin B, and alpha-neoendorphin. The peptide-like immunoreactive material extracted from the external musculature was characterized by multi-dimensional chromatographic analysis and compared to synthetic porcine standards. The chromatographic methods utilized were: reversed-phase high performance liquid chromatography (RP-HPLC), using two different eluants; cation exchange high performance liquid chromatography (CE-HPLC) and gel filtration chromatography. The dynorphin A 1-8-like immunoreactive material was homogeneous and coeluted with the standard in all chromatographic modes. The dynorphin A 1-17-like and dynorphin B-like immunoreactive material was heterogeneous but showed a peak that coeluted with synthetic standard in all chromatographic modes. The alpha-neoendorphin-like immunoreactive material also appeared to be heterogeneous with the major component on CE-HPLC coeluting with the synthetic peptide standard while the major component on RP-HPLC eluted differently. It was concluded that the guinea-pig ileum contains immunoreactivity for peptides derived from all coding regions of the prodynorphin gene and that these peptides may be present in multiple immunoreactive forms.

Role of the ventromedial hypothalamus in the regulation of adenohypophyseal immunoreactive dynorphin in the rat

In this study, we have examined the role of the dorsomedial (DMH), ventromedial (VMH) and arcuate (ARH) nuclei of the hypothalamus in the control of hypothalamic and pituitary immunoreactive (ir) dynorphin (Dyn) A and ir-Dyn B in the rat, by evaluating the effect of discrete, bilateral radiofrequency lesions in these structures. Lesions limited to the VMH reduced the content of ir-Dyn in the anterior pituitary but not in the neurointermediate lobe or in the hypothalamus. Gel chromatographic analysis of anterior pituitary extracts confirmed that ir-Dyn is mainly associated with high molecular weight forms containing Dyn A and Dyn B in their sequence. Anterior pituitary extracts of VMH-lesioned rats displayed a clearly lower proportion of these forms. Destruction of the DMH affected only the hypothalamic content of ir-Dyn; ablation of the ARH did not cause any significant change. Our results suggest that ablation of the VMH may disrupt critical neuronal connections to the median eminence originating in this nucleus or crossing it and participating in control of the adenohypophyseal pool of ir-Dyn.

Immunohistochemical evidence for the presence of peptides derived from proenkephalin, prodynorphin and proopiomelanocortin in the guinea pig pineal gland

By using a plethora of region-specific antisera, this light microscopic immunohistochemical study revealed that derivatives from the three opioid precursors, i.e. proenkephalin, prodynorphin and proopiomelanocortin are differentially distributed in the pineal gland of guinea pig. Various molecular forms of immunoreactive opioid peptides derived from proenkephalin or prodynorphin were present in a minority of pinealocytes as well as in nerves. In contrast to this dual distribution pattern of opioid-active peptides, the opioid-inactive derivative from proopiomelanocortin, alpha-melanocyte stimulating hormone, was exclusively present in a large proportion of pinealocytes. A multiple and differential origin and function of opioidergic pineal innervation involving sympathetic, parasympathetic and sensory components is suggested. alpha-MSH is proposed as a pineal hormone which may act in concert with melatonin to regulate pineal rhythms or may function like MSH of pituitary origin.

Regional distribution of immunoreactive dynorphin A in the human gastrointestinal tract

Immunoreactive dynorphin A (ir-Dyn A) was detected throughout the human gastrointestinal tract by a validated radioimmunoassay. Moreover, the stability of 125I-Dyn A during extraction procedures was confirmed by high performance liquid chromatography. Levels of ir-Dyn A were higher in the stomach and in the small bowel. In tissue samples separated into the main layers composing the gut wall (muscularis externa, submucosa and mucosa) ir-Dyn A was uniformly distributed. An exception was the colon, where concentrations were higher in the muscular portion. Gel permeation chromatography on samples of mucosa and muscularis externa extracts of ileum and gastric fundus, showed immunoreactive material eluting in several forms of apparently higher molecular weight than Dyn A, while only a minor peak was found to coelute with authentic Dyn A.

Proenkephalin-A derived peptides do not modulate cardiovascular effects of epinephrine on the isolated rat atrial preparations

The catecholamines and the opioid peptides are found to be co-localized in the adrenomedullary chromaffin cells. They are co-secreted from the chromaffin granules in response to various stimuli. The stress-induced released of epinephrine is known to exert its effect on the cardiovascular system resulting in the changes in heart rate and blood pressure. However, the role of the co-released proenkephalin-A derived peptides has not been extensively characterized. Previous work from several investigators suggested that the peptides modulate cardiac functions of the catecholamines. There is considerable conflicting results among these reports. Results from the isolated rat atrial preparation indicated that enkephalins attenuated the increase in atrial rate induced by norepinephrine through restriction of the calcium fluxes. Nonetheless, others reported insensitivity of the enkephalins in similar or different test systems. We further re-examined these discrepancies using the isolated rat atrial preparation to investigate the opioid peptide modulatory effect on the cardiovascular changes induced by exogenous epinephrine. Alterations in rate and force of contraction resulting from epinephrine and the peptides were both studied in parallel. The opioid peptides used in this study were [Met5]-enkephalin (ME), [Leu5]-enkephalin (LE), FMRFamide, [Met5]-enkephalyl-Arg6-Phe7 (MEAP), peptide E, and the non-selective opioid agonist, etorphine. We report here that none of the opioid peptides were effective in alleviating or attenuating the increase in heart rate and developed tension caused by epinephrine. The peptides did not affect the basal beating rate nor the force of contraction. Thus, the present results clearly demonstrate the insensitivity of the enkephalins in modulating the cardiac effects of epinephrine. They further indirectly support the prejunctional synaptic nerve endings as the potential peripheral site of action of the peptides.

Chromatographic characterization of dynorphin and [Leu5]enkephalin immunoreactivity in guinea pig and rat testis

Tissues of the reproductive tract have been shown to contain mRNAs coding for pro-opiomelanocortin (POMC), pro-enkephalin and pro-dynorphin. However, the amounts of immunoreactive opioid peptides in these tissues are low, and in the case of the enkephalins and dynorphin, the molecular species responsible for the immunoreactivities have not been characterized. The chromatographic properties of dynorphin and enkephalin immunoreactivities in extracts of guinea pig and rat testis have therefore been determined. Dynorphin A and dynorphin B immunoreactivity was heterogeneous, with a significant amount attributable to high-molecular-weight forms. About 20% of the dynorphin A immunoreactivity, and about 40% of the dynorphin B immunoreactivity, in guinea pig testis extracts behaved as authentic dynorphin A or B, respectively during fractionation by ion exchange, gel filtration and high-performance liquid chromatography. Both high- and low-molecular-weight forms of [Leu5]enkephalin immunoreactivity were also present, with roughly 50-70% of the immunoreactivity attributable to low-molecular-weight forms. In extracts of guinea pig testis only a small part of this immunoreactivity eluted as authentic [Leu5]enkephalin during high-performance liquid chromatography. In rat testis most of the low-molecular-weight [Leu5]enkephalin immunoreactivity behaved as the authentic peptide. These results confirm that opioid peptides are produced in guinea pig and rat testis, and demonstrate that immunoreactive forms of the peptides similar to those found in brain and pituitary are present in the tissue.

Inhibitory action of opioid peptides on ouabain-sensitive Na+-K+ and Ca2+-dependent ATPase activities in bovine cardiac sarcolemma

The present study demonstrates that morphine (10(-6) and 10(-5) M), methionine-enkephalin or leucine-enkephalin (10(-10), 10(-8), and 10(-6) M) were able to inhibit significantly, in a dose-dependent manner, both the sarcolemmal Ca2+-dependent ATPase and the ouabain-sensitive Na+-K+ ATPase activities. The inhibitory action of these opioids on the two ATPases was not antagonized by preincubation with naloxone (10(-6) M). Naloxone alone (10(-8), 10(-6) and 10(-5) M) did not affect both the sarcolemmal Ca2+-dependent ATPase and the ouabain-sensitive Na+-K+ ATPase activities. Heat-denatured methionine-enkephalin (10(-6) M) or leucine-enkephalin (10(-6) M) also unaffected both the ATPases. The possibility is also discussed that opioid peptides may regulate myocardial contractility by modulating the movement of ions across the heart sarcolemma.

Effects of naloxone on the mechanical activity of isolated rat hearts perfused with morphine or opioid peptides

In isolated rat hearts, the infusion for 10 min of 10(-10), 10(-8) or 10(-6) M (-)naloxone affected the cardiac function by markedly increasing the coronary pressure and by reducing both the heart rate and the developed tension. A lower dose of (-)naloxone (10(-11) M) or a dose of 10(-6) M (+)naloxone, did not modify the cardiac function. Morphine (10(-6) or 10(-5) M) and 10(-10), 10(-8) or 10(-6) M methionine-enkephalin or leucine-enkephalin, both significantly reduced the coronary pressure of the isolated rat hearts, during the first 4-6 min of perfusion, but the coronary pressure progressively increased above the control value in the last 4 min of perfusion. Each opioid also influenced the mechanical activity of the isolated rat heart, by significantly lowering both the heart rate and the developed tension. (-)Naloxone, at all the doses tested, was only able to antagonise the hypotensive effect induced by the opioids on the coronary pressure and was ineffective in counteracting the negative inotropic and chronotropic effects produced by each opioid. The perfusion in the presence of (+)naloxone (even at a dose of 10(-6) M) did not affect the opioid-induced changes on both the coronary pressure and the mechanical performance of the isolated heart.

Lack of effect of dynorphin on consummatory behaviors in obese and normal rats

The possible role of dynorphin, an endogenous opioid peptide, in the regulation of appetite was studied in male genetically-obese (Zucker) rats and their litter mates of normal weight. Eighteen pairs were divided into 3 treatment groups: control, acutely dynorphin-treated (5 mg/rat), and implanted with Alzet mini-osmotic pumps containing 2 mg dynorphin to be delivered at a rate of 10 micrograms/hr. Body weights and food and water consumption were determined daily for 7 days. Body weights were not significantly changed from initial values for any treatment group. Food and water consumption per 24 hours were generally the same for obese rats and their normal littermates, but in terms of consumption per 100 g body weight, the obese rats generally consumed less food and water. Neither acute nor continuous dynorphin administration affected consummatory levels.

Effect of discrete brain lesions on hypothalamic and pituitary immunoreactive dynorphin

Radiofrequency lesions of the anterior hypothalamic area reduced immunoreactive dynorphin (ir-DYN) in the hypothalamus and in the neurointermediate lobe of the pituitary. Ablation of the medial preoptic area was not associated with any significant modification of ir-DYN in the tissue examined. Destruction of the medial basal hypothalamus in parallel lowered ir-DYN in the hypothalamus and in both pituitary lobes. Neonatal administration of monosodium glutamate had no significant effect on ir-DYN. These findings indicate that changes of ir-DYN in the hypothalamus and pituitary are associated with the destruction of anatomically and functionally distinct neural systems.