Co-release of enkephalins and precursors with catecholamines from the perfused cat adrenal gland in situ

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.

Nitric oxide reduces basal efflux of catecholamines from perfused dog adrenal glands

Norepinephrine, epinephrine, dopamine, and both the free and extended forms of [met]enkephalin spontaneously efflux from adrenal glands under basal conditions. The present study was done to determine whether nitric oxide has a regulatory role in these effluxes. Isolated adrenal glands (n = 63) from mongrel dogs were perfused retrogradely with Krebs-Ringer solution. In some experiments NG-monomethyl-L-arginine (3 x 10(-4) M), an inhibitor of nitric oxide synthesis, was added to the perfusate. In other experiments one of the nitric oxide donors, 3-morpholinosydnonimine (10(-7) M or 10(-5) M) or sodium nitroprusside (10(-6) M or 10(-4) M) was added. Norepinephrine, epinephrine, dopamine and their metabolites 3,4-dihydroxyphenylglycol and 3,4-dihydroxyphenylacetic acid in perfusates were quantitated by high performance liquid chromatography with electrochemical detection and in some experiments the [met]enkephalins were determined by radioimmunoassay. In the presence of NG-monomethyl-L-arginine, the basal effluxes of norepinephrine, epinephrine, and dopamine were significantly increased from control, but the effluxes of the free and extended forms of the [met]enkephalins were not changed. The effects of NG-monomethyl-L-arginine on catecholamine efflux were reversed in the presence of L-arginine (10(-3) M). Sodium nitroprusside (10(-6) M) inhibited effluxes of norepinephrine and epinephrine and 3-morpholinosydnonimine had no effect on these effluxes. Dopamine efflux appeared to be under different controls from those of norepinephrine and epinephrine since dopamine efflux was unaffected by sodium nitroprusside and was decreased over time by 3-morpholinosydnonimine (10(-7) M). It is concluded that endogenously produced nitric oxide inhibits the basal efflux of norepinephrine, epinephrine, and dopamine from isolated dog adrenal glands; this inhibition appears to be near maximal for norepinephrine and epinephrine but not for dopamine.

Cat proenkephalin-A does not contain the opioid octapeptide

The sequence of a large cDNA fragment of proenkephalin-A from the cat adrenal medulla was obtained using reverse transcription followed by polymerase chain reaction, and cloning. This cDNA encompasses the region normally containing all the opioid peptides, except the C-terminal heptapeptide. As with other species, cat proenkephalin-A contains four conserved copies of (Met5)-enkephalin, and one of (Leu5)-enkephalin, flanked by processing sites of paired basic amino acids. However, significant differences were found in the nucleotide and deduced amino acid sequences in the region of the octapeptide. In particular, the essential tyrosyl residue is substituted by a histidyl residue, making it unlikely that the cat equivalent would have opioid activity. Furthermore, the peptide is not flanked by paired basic residues, suggesting it is not processed.

Metabolic profile of opioid peptides differs in the hippocampus and striatum of seizure-susceptible E1 mice

We previously suggested that a deficit of anticonvulsant endogenous methionine enkephalin, in the cerebral cortex, septal area, hippocampus, and striatum of seizure-susceptible El mice plays a role in the pathogenesis of seizures. To determine whether a hypofunction of enkephalinergic neuron may be due to metabolic abnormalities of opioid peptides in the El mouse brain, we measured methionine enkephalin-like immunoreactivity (ME-LI) of 50 fractions eluted by high performance liquid chromatography obtained from those four regions of the brain of El and seizure-nonsusceptible ddY mice (the mother strain of El mice). We observed the same ME-LI patterns of 50 fractions in the cerebral cortex and septal area in El and ddY mice, whereas exhibited differing ME-LI patterns in the hippocampus and striatum in the two stains. Different ME-LI patterns may imply the difference in the metabolic profile of opioid peptides. Thus, an abnormal metabolism of opioid peptides in the hippocampus and striatum of the El mouse may be involved in the pathogenesis of seizures.

Prohormone convertases PC2 and PC3 in rat neutrophils and macrophages. Parallel changes with proenkephalin-derived peptides induced by LPS in vivo

Prohormone- or proneuropeptide-converting enzymes PC2 and PC3 have been observed exclusively in nervous and endocrine tissues. In this work the presence of these enzymes in cells of the immune system was demonstrated. PC2 was detected in peripheral and liver-infiltrating polymorphonuclear leukocytes (PMN) but not in alveolar macrophages (AM) or spleen mononuclear cells (SMC). PC2 proteins corresponded to 75, 71 and 56 kDa forms. PC3 appeared in AM and SMC but not in PMN, and a 66 kDa protein was the only PC3 form detected. Proenkephalin-derived peptides (PENKp) were observed in PMN and AM, showing peptides of 35, 28, 21, 18 and 14 kDa in the former cells and a doublet of 35 and 32 kDa in the latter. PC2 proteins and PENKp decreased in liver PMN and peripheral PMN 90 min after intravenous (i.v.) infusion of LPS, suggesting an increased release. However, in vitro assays showed that the chemotactic peptide FMLP but not LPS increased the basal secretion of PC2 proteins and PENKp in PMN. These results indicate that PC2 proteins are released from PMN, together with PENKp, and suggest that LPS in vivo may act through an indirect mechanism. Low levels of PC3 and PENK were detected in the AM of rats treated for 90 min with SAL or LPS. However, a significant increase of PC3 and PENKp appeared 30 h after LPS infusion. These results show for the first time that PC2 and PC3 are differentially expressed in PMN and AM, respectively, which were paralleled by the presence of different post-translational products of PENK. In addition, the in vivo effect of LPS on PC2, PC3 and PENKp levels in PMN and AM resembles the effect of LPS on prohormone levels in endocrine tissues, suggesting that similar mechanisms may control the turnover of PENK in endocrine and in these immune cells.

The functional role of opioid receptors in acetylcholine release in the rat adrenal medulla

The functional role of opioid receptors in acetylcholine release from splanchnic nerve terminals in the adrenal medulla was investigated in halothane-anesthetized rats. The extracellular acetylcholine level was measured by a newly developed in vivo adrenal microdialysis method. The potassium (K+)-evoked acetylcholine release from the splanchnic nerve terminals was inhibited by morphine (10 microM), a mu-opioid receptor agonist, and [D-Pen2,D-Pen5]enkephalin (DPDPE, 1 and 10 microM), a delta-opioid receptor agonist. These inhibitory effects of morphine and DPDPE were significantly abolished by naltrexone (9 mg/kg i.p.), a mu-opioid receptor antagonist, and naltrindole (9 mg/kg i.p.), a delta-opioid receptor antagonist, respectively. 5 alpha,7 alpha-beta-(-)- N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro(4,5)dec-8-yl]benzene acetamide (U69593, 10 microM), a kappa-opioid receptor agonist, had no influence on the K(+)-evoked acetylcholine release. The findings suggest that both mu- and delta-opioid receptors might have a functional role in acetylcholine release from splanchnic nerve terminals in the adrenal medulla of the rat. The present study indicates that adrenal microdialysis is a useful method for studying the control mechanism of adrenomedullary function in the rat in vivo.

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.

Elevated plasma Met-enkephalin levels in the human newborn are a poor indicator of perinatal stress

OBJECTIVE

This study was designed to investigate whether plasma Met-enkephalin peptides could serve as markers of physiologic stress in the neonate.

STUDY DESIGN

Infants (n = 115) between 1.2 and 4.7 kg and 28 and 42 weeks of gestation were studied at birth. Seventy-four infants were delivered by the vaginal route, 31 by cesarean section after labor, and 10 by cesarean section before labor. Correlations were sought between plasma enkephalin peptides and epinephrine, norepinephrine, and arterial blood gases with linear regression analysis. Various clinical data were also analyzed.

RESULTS

Plasma Met-enkephalin levels were significantly greater in infants exposed to labor (440 +/- 36 vs 260 +/- 30 pg/ml, p less than 0.05). The large-molecular-weight forms of enkephalin peptides were also greater in these infants (approximately 50 +/- 4 vs 23 +/- 2 ng/ml). There was no correlation between plasma enkephalin peptides and catecholamines, arterial pH, or Apgar scores. There was a significant but weak correlation between plasma Met-enkephalin levels and birth weight (r = 0.34, p = 0.03) and PaO2 (r = -0.28, p less than 0.05).

CONCLUSION

The lack of correlation between Met-enkephalin plasma levels and umbilical plasma catecholamine concentrations, acid-base status, or Apgar scores suggests that circulating Met-enkephalin is a poor indicator of stress in the newborn.

Adrenal medullary secretion with splanchnic stimulation in spinal cats

This project was undertaken to determine whether previously observed adrenal medullary hyperactivity that developed following high spinal cord transection in the cat could be explained by increased sensitivity of the synapse between the splanchnic nerve and chromaffin cell. The splanchnic nerve was stimulated in acute (2-3 h; n = 7) or chronic (61-64 days; n = 7), spinally transected (T3) cats that were decerebrate and unanesthetized. Mean arterial blood pressure and adrenolumbar venous blood flow were significantly greater in the chronic animals. Stimulation (30 V; 1 ms pulses) was applied at 3 Hz and 30 Hz to deliver the same number of pulses within 3 min. Adrenal medullary secretion (ng/min) of epinephrine (EPI), norepinephrine (NE), dopamine, neuropeptide Y (NPY), [Met]enkephalin (ENK), and encrypted [Met]enkephalin was determined at baseline and in relation to both patterns of stimulation. With near threshold (3 Hz) stimulation, the following differences were observed between groups: (1) secretion of EPI, NPY, and ENK was significantly greater in the chronic than in the acute animals; and (2) preferential secretion of NE was elicited in the acute animals. These observations suggest that there may be some facilitation of the splanchnic nerve--chromaffin cell synapse that occurs over time following high thoracic spinal cord transection. However, it is likely that central, spinal mechanisms also contribute to adrenal medullary hyperactivity.

Sexually dimorphic, androgen sensitive, enkephalinergic afferents to a lumbar motor nucleus of rats

In male rats, methionine-enkephalin immunoreactivity (enkephalin-ir) has been observed in the dorsal lateral nucleus (DLN), a longitudinal pool of motoneurons in the lumbar spinal cord. Within the DLN a mediodorsal crescent of intense enkephalin-ir staining surrounds the motoneurons innervating the ischiocavernosus muscle of the penis, which suggests a function of the enkephalinergic afferents in male copulatory activities. The present study attempted to determine the roles of gender and adult exposure to androgen in shaping the striking subnuclear distribution of enkephalin-ir. Transverse sections through L5-6 were obtained from mature male and female rats that were gonadally intact, gonadectomized, or gonadectomized and treated with testosterone, as well as from male rats genetically deficient in androgen receptors (Tfm). The sections were incubated with primary antiserum raised against methionine enkephalin and bound antibodies were visualized using the avidin-biotin-peroxidase technique. A microphotometer was used to compare the staining density in laminae I-II of the dorsal horn, ventral grey matter, and the DLN. In all groups the DLN stained more darkly than the ventral grey, demonstrating the presence of enkephalin-ir in the DLN regardless of gender or exposure to androgen. However, the mediodorsal crescent of dense staining in the DLN was obvious only in gonadally intact males, while the entire DLN stained darkly in both sexes of gonadectomized rats treated with androgen. Therefore, the preferential distribution of enkephalin-ir in the mediodorsal crescent of the DLN is sexually dimorphic though the overall content of enkephalin-ir within the DLN responds to androgen.

Differential secretion of enkephalin-like peptides from bovine adrenal chromaffin cells

Stimulation of chromaffin cells in culture with 1,1-dimethyl-4-phenylpiperazinium (DMPP) or depolarizing concentrations of K+ resulted in a significant secretion of high and low molecular weight enkephalin-like peptides (ELPs) into the culture medium. BioGel P-10 column chromatography was used to characterize the ELPs in chromaffin cell extracts and in culture media before and after stimulation with either DMPP or K+. DMPP (50 microM) stimulation produced a significant secretion of primarily low molecular weight (less than 3 kDa) ELPs whereas 56 mM K+ caused a secretion of both high and low molecular weights ELPs. The expected decrease in cellular content of low molecular weight peptides was not observed regardless of stimulation type. Our results support the hypothesis that the precursor/product ratio of secreted ELPs is dependent upon the nature of the chromaffin cell stimulus. Moreover the cellular content of low molecular weight ELPs is not depleted with either type of stimulation.

Maturational changes in expression of enkephalin peptides in adrenal and extra-adrenal tissue of fetal and adult rabbits

Met-enkephalin immunoreactivity (MET-ENKi), total enkephalin immunoreactivity (TOTAL MET-ENKi) and catecholamines were measured in adrenal and extra-adrenal tissue of fetal, newborn and adult rabbits. Met-enkephalin peptides were detected in adrenal and extra-adrenal tissue by 29 days of gestation. There were progressive increases in TOTAL MET-ENKi in both the adrenal and extra-adrenal tissue during development. In 29-day-old fetuses, MET-ENKi represented 43 and 50% of the peptide content in adrenal and extra-adrenal tissues respectively. By 3 days after birth, MET-ENKi represented only 15 and 7% of the peptide content in the same tissues. In the adult adrenals, 10% of enkephalin peptides were found as MET-ENKi. There were progressive increases in adrenal and extra-adrenal catecholamine content in the fetal and newborn rabbits throughout development. The changes in the ratio of MET-ENKi to TOTAL MET-ENKi peptides suggest differences in posttranslational processing of proenkephalin peptide during maturation. We speculate that enkephalin peptides derived from proenkephalin A are important during fetal and early newborn life and that extra-adrenal tissue may be an important source of these peptides during development.

Opioid inhibition of nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells

The ability of a number of opioid agonists and antagonists to affect nicotine-induced 45Ca2(+)-uptake into cultured bovine adrenal medullary cells has been investigated. High (10 microM) concentrations of the opioid agonist bremazocine produced a significant inhibition of nicotine-induced 45Ca2(+)-uptake throughout the 15 min time course examined. The opioid subtype-selectivity of this inhibition was investigated; mu and delta selective agonists produced only minor effects whereas the kappa selective agonist U50-488H and the endogenous opioid peptides dynorphin(1-13) and metorphamide almost abolished nicotine-induced 45Ca2(+)-uptake. The U50-488H inhibition was significant at 10 nM concentrations with an IC50 of approximately 1 microM. U50-488H inhibition could not be reversed or reduced by the opioid antagonists naxolone, diprenophine or Mr2266. Furthermore, Mr2266 and its optical isomer Mr2267 also produced marked inhibition of 45Ca2(+)-uptake. The inhibition was specific to nicotine-induced 45Ca2(+)-uptake in that a similar level of uptake evoked by potassium depolarization was unaffected by high concentrations of U50-488H. These data indicate that opioid inhibition of nicotine-induced 45Ca2(+)-uptake does not involve classical, stereospecific opioid receptors and suggests the involvement of a pharmacologically distinct opioid recognition site. It is speculated that this may be associated with the nicotine receptor-ionophore complex.

Release in vivo of Met-enkephalin and encrypted forms of Met-enkephalin from brain and spinal cord of the anesthetized cat

Processing of the proenkephalin molecule will result in peptide fragments in which the pentapeptide YGGFM is included. We have employed a molecular sieve (2 kDa) separation, enzyme hydrolysis radioimmunoassay (RIA) treatment sequence which permits concurrent measurement of Met-enkephalin (Enk) and several enkephalin-encrypting (X-Enk) peptides in a single sample. Using this protocol, the release of Enk and X-Enk (total Enk-Enk) greater and less than 2 kDa from spinal cord and the mesencephalic aqueductal grey was assessed under resting conditions and during stimulation of the sciatic nerve in the chloralose-urethane anesthetized cat. Under resting conditions measurable levels of Enk (10.5 +/- 4.7; 9.1 +/- 2.1 pg/min) and X-Enk (47.8 +/- 19.7; 45.7 +/- 12.3 pg/min) are found in aqueductal and spinal superfusates, respectively. The X-Enk measured under resting and evoked conditions in aqueductal and spinal perfusates is associated almost exclusively (greater than 90-95%) with fragments greater than 2 kDa in size. There results, showing the relative absence of detectable levels of X-Enk forms greater than 2 kDa, were confirmed by reverse phase chromatography. During sciatic nerve stimulation, the levels of both Enk and X-Enk were mildly elevated in spinal and ventricular perfusates. With the addition of thiorphan (10(-5) M), though there was no effect on the resting release of either Enk or X-Enk, the levels of Enk measured under evoked conditions were significantly augmented in both ventricular and spinal perfusates.

Alpha-chloralose anesthesia inhibits the somato-sympathetic reflex response in cats more effectively than halothane

The effect of halothane anesthesia (H; 0.8 Vol%) or alpha-chloralose anesthesia (AC; 60 mg/kg i.v.) on the somato-sympatho-adrenal reflex response evoked by supramaximal bilateral sciatic nerve stimulation, were examined in two groups of cats (H: n = 6; AC: n = 4). Blood samples were collected simultaneously from the adrenal vein and femoral artery at baseline (S1) and during bilateral sciatic nerve stimulation (S2) for the measurement of norepinephrine, epinephrine, neuropeptide Y, and Metenkephalin, while mean arterial blood pressure (MABP) and heart rate (HR) were recorded. There were no differences between groups at baseline. In halothane anesthetized cats, sciatic nerve stimulation caused significant increases in MABP (S1: 113 +/- 8 mm Hg, S2: 178 +/- 10 mm Hg; mean +/- SE), HR (S1: 223 +/- 15 bpm, S2: 278 +/- 22 bpm), and adrenal vein plasma levels of norepinephrine (S1: 3.1 +/- 0.98 ng/ml, S2: 19.53 +/- 11.5 ng/ml), epinephrine (S1: 15.5 +/- 4.76 ng/ml, S2: 67.31 +/- 14.9 ng/ml), neuropeptide Y (S1: 1.3 +/- 0.12 ng/ml, S2: 2.16 +/- 0.42 ng/ml), and Met-enkephalin (S1: 107 +/- 35.7 pg/ml, S2: 200 +/- 76.5 pg/ml). In contrast, sciatic nerve stimulation in alpha-chloralose anesthetized cats, caused a significant increase only in MABP during sciatic nerve stimulation (S1: 115 +/- 10 mm Hg, S2: 171 +/- 7 mm Hg), while HR and adrenal vein plasma levels of catecholamines, neuropeptide Y and Met-enkephalin remained unchanged from baseline. Adrenal vein epinephrine levels measured during stimulation in the alpha-chloralose group (S2: 6.17 +/- 0.86 ng/ml), were significantly lower as compared to values observed during halothane anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Cryptic Met-enkephalin in adrenal and portal vein during splanchnic artery occlusion shock in cats

Adrenal vein (AD), portal vein (PV), and femoral artery (FA) plasma levels of immunoreactive (IR) Met-enkephalin pentapeptide (ME) and extended ME-IR forms, obtained after sequential incubation of plasma with trypsin and carboxypeptidase B, were examined in 4 cats during splanchnic artery occlusion shock at baseline (S1), during early shock (S2), late shock (S3), and after naloxone (1 mg/kg, i.v.) administration (S4). Early shock (S2) led to a significant increase in levels of extended and fully processed Met-enkephalin IR at all 3 collection sites (AD, PV, FA) without a change in proportional levels of extended Met-enkephalin IR to the pentapeptide IR (ME). Naloxone administration during late shock (S4), however, resulted in a disproportionate increase (150-fold from baseline) in adrenal vein plasma levels of extended Met-enkephalin IR forms, as compared to ME IR (23-fold). In contrast, no changes in plasma levels occurred in PV and FA.

Source of Stress-Induced Increase in Plasma Met-Enkephalin in Rats: Contribution of Adrenal Medulla and/or Sympathetic Nerves*

Abstract The contribution of the adrenal medulla and/or the sympathetic nerves to the plasma levels of Met-enkephalin was investigated. Rats were divided into four groups: sham-operated/saline, sham-operated/guanethidine, adrenal-demedullated/saline, demedulla-ted/guanethidine. After 4 weeks of injection with either saline or guanethidine (25 mg/kg/day), animals were cannulated in the left carotid artery for blood sampling. Three days later, blood samples were taken before and at 2 and 30 min of restraint stress. Adrenal demedullation lowered basal plasma epinephrine levels markedly and prevented entirely the increase induced by restraint stress. Chronic guanethidine treatment lowered basal plasma norepinephrine levels and decreased the response to stress. Guanethidine treatment increased the basal plasma epinephrine level without affecting the response to stress. The combination of guanethidine plus adrenal demedullation lowered basal plasma concentrations of all three catecholamines and further attenuated the norepinephrine response. Restraint stress increased plasma native and peptidase-derivable Met-enkephalin. Adrenal demedullation, resulting in greater than 95% depletion of adrenal catecholamines and significant depletion of adrenal Met-enkephalin, did not inhibit the stress-induced increase in plasma Met-enkephalin, and in fact, was associated with a potentiated response to stress. Guanethidine treatment with or without demedullation increased baseline plasma native Met-enkephalin and abolished the stress-induced increase in plasma native and peptidase-derivable Met-enkephalin. Thus, the stress-induced increase in plasma Metenkephalin results from release from sympathetic nerves, rather than adrenal medulla. However, the sympathetic nerves and adrenal medulla together do not appear to account entirely for basal concentrations of circulating Met-enkephalin. Hepatic portal vein plasma concentration of native Met-enkephalin was greater than that in the carotid artery, suggesting contribution from the gastrointestinal tract; however, evisceration did not decrease plasma native Met-enkephalin. Some compensatory mechanism results in elevation of basal plasma native Met-enkephalin in sympathectomized rats. Also, in the absence of the adrenal medulla there is a compensatory increase in the amount of Met-enkephalin released into the circulation in response to stress.

Adrenal responses to splanchnic nerve stimulation in conscious calves given naloxone

1. The effects of stimulating the peripheral end of the right splanchnic nerve in the presence of naloxone (2 mg kg-1) have been investigated in conscious 3 to 6-week-old calves. 2. Mean aortic blood pressure rose to significantly higher levels during splanchnic stimulation in bursts at 40 Hz for 1 s at 10 s intervals than it did during stimulation at the corresponding continuous frequency (4 Hz). Furthermore, naloxone significantly reduced the fall in mean vascular resistance in response to both patterns of stimulation. 3. The output of catecholamines from the adrenal gland, together with the proportion of noradrenaline released, was significantly enhanced by stimulating the splanchnic nerves in bursts in animals pre-treated with naloxone and the proportion of noradrenaline released also increased. In both cases the output of adrenaline and noradrenaline was within the same range as that reported previously in normal control animals. 4. Naloxone significantly increased the amounts of enkephalin-like immunoreactivity and corticotrophin-releasing factor (CRF)-like immunoreactivity released from the adrenal gland in response to splanchnic nerve stimulation and raised the proportion of total to free met5-enkephalin that was secreted. 5. Naloxone also inhibited the rise in plasma adrenocorticotrophic hormone (ACTH) concentration during continuous stimulation at 4 Hz, but not during stimulation at 40 Hz in bursts. Under these latter conditions the output of cortisol apparently directly from the adrenal gland was inhibited. The finding that splanchnic nerve stimulation can potentiate the output of cortisol in response to ACTH was confirmed. 6. These results provide evidence that release of enkephalins and of CRF from the adrenal is inhibited by activating opioid receptors within the gland itself.

Characterization of alpha-MSH-related peptides released from rat hypothalamic neurons in vitro

Reverse-phase high-performance liquid chromatography analysis, coupled with a sensitive radioimmunoassay for alpha-melanocyte-stimulating hormone (alpha-MSH), was used to characterize the alpha-MSH-related peptides stored in the rat hypothalamus or released from perifused hypothalamic slices. Four peaks of alpha-MSH-like immunoreactivity (alpha-MSH-LI) co-eluting with synthetic des-N alpha-acetyl alpha-MSH, alpha-MSH and their respective sulfoxide derivatives were resolved and quantified. In hypothalamic extract, deacetyl alpha-MSH which was the predominant peptide represented 94.4% of total alpha-MSH-LI content, while the relative amount of alpha-MSH was only 5.6%. Analysis of alpha-MSH-related peptides contained in effluent perifusates showed that deacetyl alpha-MSH and its oxidized form were the major peptides released from neurons in basal conditions or under KCl-induced depolarization (50 mM KCl for 75 min). However, the proportion of acetylated peptide was 3-4 times higher in the perifusion medium than in hypothalamic extracts. Our data indicate that acetylation of des-N alpha-acetyl alpha-MSH may occur during the process of exocytosis. Since acetylation of alpha-MSH markedly increases the behavioural potency of the peptide, these results suggest that regulation of the acetyltransferase activity could be a key mechanism to modulate the bioactivity of alpha-MSH-related peptides in the brain.

Adrenal vein catecholamines and neuropeptides during splanchnic nerve stimulation in cats

Splanchnic nerve stimulation in bursts at low (5 Hz) and high (50 Hz) frequency (30 V, 1 msec; train duration 1 sec; train rate 0.5/second) was employed in 10 cats under halothane anesthesia, during 10-minute periods, while blood samples were concurrently collected from the adrenal vein and femoral artery for the measurement of norepinephrine (NE), epinephrine (EPI), dopamine (DA), Met-enkephalin (ME), neuropeptide Y (NPY), peptide YY (PYY) and neurotensin (NT). In Group I (n = 5), splanchnic nerve stimulation was initially applied at 5 Hz followed after 20 min by a 50 Hz stimulus, while in Group II (n = 5) the stimulation sequence was reversed. Adrenal vein and femoral artery plasma levels of catecholamines and neuropeptides were not significantly affected by the stimulation sequence, while a significant decrease in blood pressure response was observed in Group II during the 5 Hz stimulation as compared to Group I, indicating desensitization. Splanchnic nerve stimulation at 5 Hz caused a preferential increase in adrenal vein NE (9-fold) versus EPI (7-fold) levels as compared to baseline, while 50 Hz stimulation led to further comparable increases in NE (5-fold) and EPI (6-fold) levels. Significant increases in adrenal vein DA and neuropeptide levels were only observed during 50 Hz stimulation, with DA showing a 5-fold, ME a 2.6-fold and NPY a 3-fold increase as compared to 5 Hz stimulation, and NT a 3.6-fold increase as compared to baseline. Present findings indicate different dynamics in the movement of catecholamines and neuropeptides from the adrenal.

Influences of the sympatho-adrenal system on gastric motility and acid secretion and on gastroduodenal bicarbonate secretion in the cat

Experiments were performed on acutely vagotomized cats during chloralose anaesthesia. Gastric H+ and HCO3- secretions were calculated from the pH and PCO2 in a luminal perfusate. Gastric motility was reflected by changes in hydrostatic pressure within the luminal perfusion system ('intragastric pressure'). Duodenal HCO3- secretion was monitored by pH titration in situ. Animals with an intact sympatho-adrenal system (group 1) were compared with others subjected to splanchnicotomy (group 2), adrenal gland ligation (group 3), and splanchnicotomy plus adrenal gland ligation (group 4). Basal gastric H+ secretion, as well as vagally induced H+ secretory responses, did not differ significantly between groups. Basal gastric HCO3- secretion was lower in all groups with a manipulated sympatho-adrenal system compared to the intact controls. Vagally induced increases in gastric HCO3- secretion were enhanced in the splanchnicotomized groups (groups 2 and 4). Basal as well as vagally induced increases in intragastric pressure and duodenal HCO3- secretion were enhanced in animals subjected to splanchnicotomy, with or without simultaneous adrenal gland ligation (groups 2 and 4). Adrenal gland ligation per se had no such effects. The results suggest that the adrenal glands exert a stimulatory action on basal gastric HCO3- secretion. Basal intragastric pressure and basal duodenal HCO3- secretion are inhibited by post-ganglionic sympathetic neurons, not involving the adrenal glands. Also, vagal excitatory effects on gastric motility, as well as on gastric and duodenal HCO3- secretions, are inhibited by such a direct neural mechanism.

The distribution of opioid binding subtypes in the bovine adrenal medulla

Autoradiography has been used to examine the distribution of opioid binding subtypes in the bovine adrenal gland. Specific opioid binding sites were restricted to the adrenal medulla. Kappa sites, labelled with [3H]bremazocine (in the presence of excess unlabelled mu and delta ligands), were highly concentrated over nerve tracts. These nerve tract associated binding sites were sensitive to competition by the endogenous opioid, dynorphin (1-13). Specific [3H]bremazocine binding sites were also found over the adrenal medullary chromaffin tissue. These binding sites were concentrated over the peripheral, adrenaline-containing region of the medulla and were sensitive to competition by diprenorphine but not dynorphin (1-13). Delta opioid sites, labelled with [3H][D-Ala2,D-Leu5] enkephalin (in the presence of excess unlabelled mu ligand) were selectively localized to the central, noradrenaline-containing region of the adrenal medulla. Mu opioid sites, labelled with [3H][D-Ala2, NMePhe4,Gly-ol5]enkephalin, were low in number and distributed throughout the adrenal medulla. These studies demonstrate that mu, delta and two distinct kappa opioid binding sites are differently distributed within the bovine adrenal medulla and suggest possible new sites of action for the adrenal medullary opioid peptides.

Immunohistochemical and biochemical evidence for the presence of serotonin in amphibian adrenal chromaffin cells

The presence of serotonin (5-HT) in chromaffin cells of the frog adrenal (inter-renal) gland has been demonstrated both by immunocytochemical and biochemical techniques. Using antisera against 5-HT and tyrosine hydroxylase (TH) on consecutive sections, we found by means of the indirect immunofluorescence technique that a majority of chromaffin cells were also immunopositive for 5-HT. When antibodies to 5-HT and phenylethanolamine-N-methyltransferase (PNMT) were applied on consecutive sections, 5-HT-like immunoreactivity was observed in almost all epinephrine-producing cells which represented about 90% of the total chromaffin cells. No 5-HT-containing fibres could be detected. At the ultrastructural level, using a pre-embedding procedure associated with gold-silver intensification of the immunoperoxidase reaction, 5-HT-immunoreactivity was visualized in secretory vesicles essentially located in the periphery of epinephrine cells. Combination of high performance liquid chromatography and electrochemical detection showed the presence of both 5-HT and its metabolite 5-hydroxyindolacetic acid (5-HIAA) in frog adrenal extracts. Transection of the splanchnic nerve enhanced 5-HT immunoreactivity and augmented the amount of 5-HT in adrenal extracts. Taken together, these results indicate that epinephrine-producing cells of the frog adrenal contain significant amounts of serotonin. The observation of the storage of 5-HT in secretory vesicles of epinephrine cells suggests that serotonin may be released with catecholamines under stress conditions.

Neuronal and paracrine regulation of adrenal steroidogenesis: interactions between acetylcholine, serotonin and vasoactive intestinal peptide (VIP) on corticosteroid production by frog interrenal tissue

The adrenocortical cells of frog interrenal (adrenal) tissue are controlled by multiple factors. Recently, we have shown that corticosteroidogenesis is stimulated by acetylcholine released from splanchnic nerve terminals as well as by serotonin and vasoactive intestinal peptide (VIP) which are both contained in chromaffin cells. Since these 3 putative neuroregulators are known to interact with each other on various target organs, we have investigated possible coordinate actions of acetylcholine, serotonin and VIP on adrenal steroid production, using a perifusion system technique for frog interrenal tissue. Simultaneous infusion of submaximal doses of VIP (10(-5) M) and acetylcholine (5 X 10(-5) M) induced stimulations of corticosteroids (corticosterone and aldosterone) which were strictly additive. When VIP (10(-5) M) and serotonin (5 X 10(-6) M) were infused together, a potentiation of the individual responses was observed. In contrast, concomitant infusion of acetylcholine (5 X 10(-5) M) and serotonin (5 X 10(-6) M) caused a total blockage of the stimulatory effect of serotonin. Muscarine (10(-5) M) caused a similar blockade of the response of adrenocortical cells to serotonin while nicotine (5 X 10(-5) M) did not alter the stimulatory effect of serotonin. The inhibitory effect of acetylcholine on serotonin-induced steroidogenesis was antagonized by atropine (10(-5) M). Thus, acetylcholine appears to block the corticotropic action of serotonin by interacting with typical muscarinic receptors. Taken together our results indicate that 3 of the neuroregulators which participate in the control of adrenal steroidogenesis, namely acetylcholine, serotonin and VIP, may interact on their target cell to modulate the activity of their congeners.(ABSTRACT TRUNCATED AT 250 WORDS)

Roles of the pituitary-adrenocortical axis in control of the native and cryptic enkephalin levels and proenkephalin mRNA in the sympathoadrenal system of the rat

The effects of hypophysectomy (HPX) and dexamethasone (DEX) on the levels of Met5-enkephalin (ME), ME precursors, and the abundance of proenkephalin (pEK) mRNA, were examined in the adrenal medulla (AM) and superior cervical ganglia (SCG). To assess possible changes in enkephalin processing, both cryptic (after trypsin and carboxypeptidase B digestions) and native (without enzyme digestions) ME-like immunoreactivity (ME-LI) was measured. Three weeks after HPX the proportion of pEK mRNA to the total RNA content in the AM was not significantly changed when compared to sham-operated (SO) animals. Total (native + cryptic) ME-LI was decreased by 45% in the AM of HPX rats. This decrease was paralleled by a 58% depletion of AM proteins. Cryptic ME-LI was also reduced by 43%. In contrast, native ME-LI was not altered after HPX, indicating enhanced processing of ME precursors. Treatment with DEX (5 daily injections--1 mg/kg, i.p.) increased the relative abundance of pEK mRNA (+27%) and total ME-LI in the AM of HPX group, but not in SO group. Native ME-LI, cryptic ME-LI, and their ratio were not significantly affected by DEX in the AM of HPX or SO rats. In SCG, the relative abundance of pEK mRNA decreased by 25% after hypophysectomy. Total and cryptic ME-LI in the SCG of HPX rats were not changed when compared to SO rats. In contrast, HPX reduced native ME-LI suggesting decreased processing of ME precursors. Similarly, as in AM, DEX produced increase in the SCG pEK mRNA only in HPX (+68%) and not in the SO rats. In SCG, DEX produced decreases in total ME-LI which could be attributed to an increased enkephalin release. An overall reduction of cryptic ME-LI was also observed after DEX, whereas native ME-LI remained unchanged suggesting increased processing of enkephalins. Our findings indicate that the pituitary adrenocortical axis controls the relative proportions of ME to its precursors, and that this control involves both glucocorticoid-dependent (SCG) and glucocorticoid-independent (AM) mechanisms. In contrast, our studies do not suggest specific control of pEK synthesis by the pituitary adrenocortical axis. The pituitary adrenocortical axis may also influence the relative contents of ME and catecholamines in the AM and SCG. The ratio of ME/catecholamines increased after HPX (AM and SCG) and after DEX (SCG). Such regulation may contribute to the control of co-transmitter output in the sympathoadrenal system.

Effects of hemorrhage and opiate antagonists on adrenal release of neuropeptides in cats

Concurrent levels of methionine-enkephalin (ME), neuropeptide Y (NPY), peptide YY (PYY), neurotensin (NT), vasoactive intestinal polypeptide (VIP), cholecystokinin (CCK) and bombesin (BMB) were measured in adrenal vein (AD), femoral vein (FV) and femoral artery (FA) under baseline conditions and during hypotensive hemorrhage (HTH) in halothane anesthetized cats (Group II, n = 6) and compared to a non-bled control group (Group I, n = 6). Five cats (Group III) received an IV bolus of naltrexone (1 mg/kg) followed by a continuous infusion prior to induction of HTH. A blood volume loss of approximately 40% evoked a selective increase in AD levels of ME, NPY, PYY and NT. No differences in regard to hemodynamics and pattern of neuropeptide levels were observed between Group II and Group III. Administration of naloxone (1 mg/kg, IV) in Group I and Group II at the end of the experiment led to a significant increase in MABP in both groups but did not evoke changes in neuropeptide levels. We conclude that adrenal neuropeptide release during hypotensive hemorrhage is not modulated by actions on opiate receptors in the halothane anesthetized cat.

Enkephalins and learning and memory: a review of evidence for a site of action outside the blood-brain barrier

A series of studies indicate that enkephalins exert dramatic influences on learning and memory in rats and mice, when studied with conditioning tasks that are both negatively and positively motivated. Pharmacological analysis of these enkephalin actions on conditioning suggests that the [leu]enkephalin acts through a delta opioid receptor which is located outside the blood-brain barrier. Control studies indicate that enkephalins do not simply affect the performance of a conditioned response through actions on shock sensitivity or locomotor activity. Characterization of the peripheral enkephalin mechanism that affects behavior suggests an action through an enzymatic system that controls the concentrations of enkephalin present at its receptors in the periphery. This enzymatic mechanism is sensitive to experience, since its activity changes following conditioning, which suggests that it may be a regulatory mechanism for behavior.

Differential release of enkephalin and enkephalin-containing peptides from perfused cat adrenal glands

We have compared the enkephalin-like material derived from proenkephalin released from perfused cat adrenal glands stimulated with pilocarpine (5 X 10(-4)M) and nicotine (5 X 10(-6) M). In addition, two doses of acetylcholine (10(-5) and 10(-4) M) and 50 mM K+ were tested. Free Met-enkephalin immunoreactivity and total Met-enkephalin immunoreactivity, as determined by enzymatic digestion of large enkephalin-containing fragments, were coreleased with catecholamines. Free Met-enkephalin immunoreactivity represented 13% of total immunoreactivity for nicotinic stimulation, 46% for pilocarpine, 33% for 10(-5) M acetylcholine, 22% for 10(-4) M acetylcholine, and 16% for 50 mM K+. Analysis of the perfusate by gel filtration showed that 80% of the total Met-enkephalin immunoreactivity whose release was induced by pilocarpine was eluted in fractions corresponding to fragments of low molecular weight, whereas these fractions accounted only for 10% of the total Met-enkephalin immunoreactivity whose release was induced by nicotine. HPLC analysis of low-molecular-weight peptide fractions revealed that Met-enkephalin, Met-enkephalin-Arg-Gly-Leu, and Met-enkephalin-Arg-Phe represented 69% of total Met-enkephalin immunoreactivity whose release was induced by pilocarpine. These results indicate that selective activation of muscarinic receptors is followed by release of low-molecular-weight material, whereas nicotine application also yielded high-molecular-weight peptides. Furthermore, increasing the acetylcholine concentration from 10(-5) to 10(-4) M and using 50 mM K+ increased proportionally the high-molecular-weight peptide secretion. Results are discussed in relation to the existence of a heterogeneous population of granules either in the same cell or in different cells, containing proenkephalin-derived peptides. (ABSTRACT TRUNCATED AT 250 WORDS)

Effects of opioid compounds on basal and muscarinic induced accumulation of inositol phosphates in cultured bovine chromaffin cells

The mammalian adrenal medulla expresses a variety of both opioid peptides and opioid receptors. The function of this adrenal opioid system is, however, largely unknown. We have examined the ability of a number of opioid compounds to influence basal and muscarinic stimulated accumulation of inositol phosphates in cultured bovine chromaffin cells. Muscarine produced a dose-dependent 1.5-fold increase in total inositol phosphates. This response was sensitive to atropine inhibition. The ten opioid compounds examined were chosen because between them they possess selectivity for all of the identified opioid receptor subtypes. However, none of these opioids in the concentration range 10nM-10 microM had any significant effect on either basal or muscarinic induced total inositol phosphate accumulation. We conclude that it is unlikely that opioid peptides released from either the chromaffin cells themselves or the splanchnic nerve can modulate the inositol phosphate second messenger system within the adrenal chromaffin cells.

Characterization of 1,1-dimethyl-4-phenylpiperazinium induced increased proenkephalin processing in bovine chromaffin cells

Acute stimulation of bovine adrenal chromaffin cells in culture with 1,1-dimethyl-4-phenylpiperazinium (DMPP) gives rise to a significant increase in secretion of [Met5]-enkephalin immunoreactive material (ME-IRM) into the culture medium (1). Following this secretion the cellular ME-IRM levels do not decrease, suggesting the replenishment of the peptides. The repletion of the cellular ME-IRM appears to result from an increase in processing of large molecular weight peptides containing [Met5]-enkephalin and [Leu5]-enkephalin. Gel filtration chromatography on Bio-Gel P-10 was used to fractionate the enkephalin-like peptides (ELPs) present in the culture media and chromaffin cell extracts. Fractionation was done for samples before and after nicotinic receptor stimulation by DMPP to demonstrate the secretion and repletion of the ELPs. Gel chromatographic profiles of ELPs present in the culture media after DMPP stimulation revealed the presence of 4 peaks, representing different molecular forms of these peptides (Peaks 1-4), with a selective increase in secretion of Peaks 3 and 4. The chromatograms of ELPs extracted from cultured chromaffin cells showed similar patterns to those obtained from ELPs present in the culture medium after stimulation. Analyses of individual peaks after fractionation of cell culture extracts showed an increase in the amount of immunoreactive material found in Peak 4 with a concomitant decrease in the immunoreactivity found in the higher molecular weight peaks (Peaks 1-3). Further purification of Peak 4 from cell extracts on reversed-phase HPLC (RP-HPLC) showed a significant amount of ELPs existed as the sulfoxide derivative of [Met5]-enkephalin. The content of [Met5]-enkephalin sulfoxide (ME-O-enk) did not decrease following DMPP stimulation. We conclude that acute stimulation of nicotinic receptors in the chromaffin cells enhances the processing of proenkephalin precursors to keep pace with the secretion of low molecular weight peptides.

Effects of hemorrhage and naloxone on adrenal release of methionine-enkephalin and catecholamines in halothane anesthetized dogs

Concurrent levels of methionine-enkephalin and catecholamines in adrenal vein, femoral vein and femoral artery were measured under baseline conditions and during graded hemorrhage in halothane anesthetized dogs and compared to a non-bled control group. Naloxone was administered in both groups at the end of the experiment. Normotensive hypovolemia with a remaining blood volume of 76% led to a moderate decrease in mean arterial blood pressure from baseline and a 15- to 20-fold increase in norepinephrine, epinephrine and dopamine, and a 5-fold increase in enkephalin in the adrenal vein. Subsequent induction of hypotensive hypovolemia with a remaining blood volume of 51% resulted in a profound drop in blood pressure and evoked a further increase in the level of catecholamines (40- to 50-fold from baseline) and enkephalin (8-fold from baseline) in the adrenal vein. In the control group only a 3- to 4-fold increase from baseline in adrenal vein hormone levels was observed over time. Naloxone administration at the end of the experiment, led to a 2- to 6-fold further increase in hormones at the 3 collection sites in both groups of dogs. Joint calculation of the partial correlation coefficients for the influence of preceding blood volume and blood pressure, and concurrent blood volume and blood pressure on hormone secretion in the adrenal vein revealed that these variables explained the variation in hormone levels between 56 and 92% during normotensive hypovolemia and 62-83% during hypotensive hypovolemia. In one dog with bilateral adrenalectomy, hemorrhage was poorly tolerated, and naloxone administration did not lead to increased systemic plasma levels of catecholamines and enkephalin or improved hemodynamics. In the hemorrhage group, molar ratios of norepinephrine/epinephrine in the adrenal vein showed a significant increasing trend during the experiment. Findings in these experiments support the idea of differential monoaminergic and enkephalinergic regulation in adrenal medullary cells.

Opioid receptor systems and the endorphins: a review of their spinal organization

A review of the spinal organization of opioid receptor systems and endorphins is presented. The review is a consideration of the physiological mechanisms underlying the effect of spinal opioids, the pharmacology of the opioid receptors that moderate a variety of spinal processing systems, and the endorphin systems that act upon the spinal receptors.

Beta-endorphin-sensitive opioid receptors in the rat tail artery

Isolated tail arteries of rats were perfused and field-stimulated every 2 min with 2 pulses at 1 Hz. Different opioid peptides depressed the contractile responses to stimulation; their concentration-response curves showed a maximum at about 40% inhibition. The rank order of potency of the peptides was beta-endorphin (IC50 = 97 nmol/l) approximately equal to BAM-22P greater than FK-33824 greater than DAGO greater than [D-Ala2,D-Leu5]-enkephalin greater than or equal to metorphamide greater than dynorphin A-(1-13) approximately equal to [Met5]enkephalin. All these substances have in common a certain activity at opioid mu-receptors, although the enkephalins are preferential delta-, and the dynorphins preferential kappa-agonists. However, the selective delta-agonist [D-Pen2,L-Pen5]enkephalin was ineffective at up to 10 mumol/l, and the kappa-agonists ethylketocyclazocine and U-50488 acted only at concentrations higher than 3 mumol/l. Whereas the effects of beta-endorphin, DAGO and [D-Ala2,D-Leu5]enkephalin could be reduced by the mu-preferential antagonist naloxone, the effects of ethylketocyclazocine and U-50488 were not changed. The delta-selective antagonist ICI 174864 did not influence the action of [D-Ala2,D-Leu5]enkephalin. Naloxone in a concentration (1 mumol/l) which nearly abolished the effect of DAGO 3 mumol/l, slightly enhanced responses to stimulation. Neither beta-endorphin nor DAGO influenced vasoconstriction evoked by the application of noradrenaline or adenosine triphosphate; U-50488 reduced it. In arteries preincubated with [3H]noradrenaline DAGO depressed, whereas naloxone enhanced the tritium overflow and vasoconstriction evoked by field stimulation (0.4 Hz, 24 pulses every 14 min). In addition, naloxone antagonized the effect of DAGO.(ABSTRACT TRUNCATED AT 250 WORDS)

Non-cholinergic component of rat splanchnic nerves predominates at low neuronal activity and is eliminated by naloxone

1. Effects of nicotinic (mecamylamine) and muscarinic (atropine) receptor antagonists were investigated on the secretion of catecholamines evoked by stimulation of splanchnic nerve terminals and acetylcholine in the isolated perfused adrenal gland of the rat to determine whether non-cholinergic substances released from nerve terminals participate in the secretion of catecholamines. 2. Increasing the frequency of stimulation from 0.5 to 10 Hz (300 pulses) caused enhanced secretion of catecholamines (26-110 ng/collection period). After blockade of nicotinic and muscarinic receptors with mecamylamine and atropine, the secretion was reduced by 40, 65 and 80% at 0.5, 1 and 10 Hz, respectively. Acetylcholine-evoked secretion of catecholamines, which was roughly equivalent to that produced by stimulation at 10 Hz, was blocked by over 90% by the cholinergic antagonists. 3. Naloxone (3-300 microM) caused a concentration-dependent inhibition of catecholamine secretion evoked by stimulation of splanchnic nerves (1 Hz); acetylcholine-evoked secretion was much less affected by naloxone. 4. The secretion of catecholamines that remained after blockade of cholinergic receptors at different frequencies of stimulation (see 2 above) was almost completely inhibited by inclusion of 30 microM-naloxone in the medium. The inhibitory effect of naloxone was concentration dependent (3-30 microM) and reversible. 5. Splanchnic nerve-evoked secretion of catecholamines was facilitated by 400% in the presence of tetraethylammonium or tetraethylammonium plus mecamylamine and atropine. The facilitatory effect of tetraethylammonium was inversely related to the frequency of stimulation. 6. The residual secretion of catecholamines obtained after blockade of cholinergic receptors was facilitated by increasing concentrations of tetraethylammonium (1-5 mM). 30 microM-naloxone antagonized the facilitatory effects of tetraethylammonium at 1 and 3 mM by 60% and 25%, respectively, but failed at 5 mM-tetraethylammonium; higher concentrations of naloxone (100 microM) were also ineffective. 7. It is concluded that neurally evoked secretion of catecholamines is mediated by acetylcholine and a non-cholinergic substance(s); the contribution of non-cholinergic substance(s) predominates at low neuronal activity, whereas that of acetylcholine is maximum at high neuronal activity. Blockade of the non-cholinergic component by naloxone suggests that an opioid peptide may be involved in the secretion of catecholamines in the rat adrenal medulla.

Evaluation of parameters for central neuronal activity in cerebrospinal fluid of rabbits following yohimbine

Rabbits were treated intravenously with yohimbine at a dose of 5 mg/kg. The concomitant increase in noradrenergic activity was followed in function of time by measuring dopamine-beta-hydroxylase activity and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) and 3-methoxy-4-hydroxymandelic acid (VMA) levels in cerebrospinal fluid. In addition, the effect of yohimbine on the dopaminergic, serotonergic and enkephalinergic neurotransmission was also determined. For this purpose, the dopamine metabolite, 3-methoxy-4-hydroxyphenylacetic acid (HVA), the serotonin metabolite, 5-hydroxy-indole acetic acid (5-HIAA) and methionine-enkephalin (Met-Enk) were quantified. The D beta H activity in control experiments, in which physiological saline was administered, increased up to 200% whereas in the yohimbine experiments a rise to 500-600% was observed. VMA and MHPG levels increased to 290%, and 209% respectively. HVA levels reached a value of 233% versus the concentration before drug injection, whereas 5-HIAA concentrations initially slightly increased and thereafter decreased. In the corresponding control experiments metabolite concentrations were virtually stable. Following yohimbine injection, methionine-enkephalin concentrations did not show significant variations compared with the control experiments. We conclude that noradrenergic and dopaminergic neurotransmission are increased following administration of the alpha 2-antagonist yohimbine whereas serotonergic neurotransmission is slightly decreased and enkephalinergic neurotransmission is unaltered. The value of the different parameters for measuring neuronal activity in cerebrospinal fluid is discussed.

Effects of opioid peptides and morphine on histamine-induced catecholamine secretion from cultured, bovine adrenal chromaffin cells

The effect of opioid peptides and morphine on histamine-induced catecholamine secretion has been studied in monolayer cultures of dispersed, bovine adrenal chromaffin cells. Histamine-induced a dose-dependent secretion of both adrenaline and noradrenaline with a threshold dose of approximately 5 nM, an EC50 of 150 nM and maximal secretion at 10 microM. Catecholamine secretion induced by 1 microM histamine was completely dependent on extracellular calcium, was inhibited in a dose-dependent manner by mepyramine (1 nM-1 microM), and was unaffected by cimetidine (10 microM) and hexamethonium (0.1 mM). Dynorphin-1-13 (1 nM-20 microM), metorphamide (0.1 nM-10 microM), morphine (1 nM-0.1 mM) and diprenorphine (1 nM-0.1 mM) each had no effect on adrenaline or noradrenaline secretion induced by 1 microM histamine. The characteristics of histamine-induced catecholamine secretion from bovine adrenal chromaffin cells were similar to those reported previously for cat and rat adrenal medulla being calcium-dependent and mediated by H1 histamine-receptors. The results with opioid peptides and morphine suggest that endogenous adrenal opioid peptides do not act on the opioid binding sites found on adrenal medullary chromaffin cells to modify their secretory response to histamine.

Effects of synthetic adrenocorticotrophin on adrenal medullary responses to splanchnic nerve stimulation in conscious calves

Right medullary and various cardiovascular responses to stimulation of the peripheral end of the splanchnic nerve have been investigated in the presence and absence of exogenous adrenocorticotrophin, ACTH1-24, (5 ng min-1 kg-1). The adrenal-clamp technique was employed in conscious calves, after the pituitary stalk had been cauterized and they had recovered from anaesthesia. The intravenous infusion of ACTH1-24 increased the plasma ACTH concentration by about 1100 pg ml-1 and right adrenal venous output of cortisol by about 400 ng min-1 kg body weight-1. Stimulation of the splanchnic nerve at 4 Hz for 10 min had no effect on either arterial plasma ACTH concentration or the adrenal output of cortisol. Closely similar amounts of both adrenaline and noradrenaline were released in response to nerve stimulation in the presence and absence of exogenous ACTH. In contrast, the fall in adrenal vascular resistance of about 40%, which normally occurred in response to splanchnic nerve stimulation, was completely abolished by ACTH. The adrenal produced relatively large quantities of met-enkephalin-containing peptides. During splanchnic nerve stimulation the output of these increased 2-100-fold, at which time free met5-enkephalin accounted for only 10-20% of total. During ACTH infusion the output of free met5-enkephalin was reduced at rest and during nerve stimulation, but that of total met-enkephalin-containing peptides was unaffected. These results indicate that ACTH or an adrenal steroid may alter the processing of proenkephalin in the adrenal medulla acutely but not total opiate secretion. Alternatively, the presence of ACTH could act by influencing the population of chromaffin cells activated by splanchnic nerve stimulation.

The prohormone processing activity is enriched in a low-density subpopulation of chromaffin granules

Bovine adrenomedullary chromaffin granules can be separated into two subpopulations by differential centrifugation. The subpopulation which sediments at the interface of two sucrose layers, 1.6 and 1.8 M respectively, is found to be enriched about 10-times in prohormone processing activity, as measured by in vitro degradation of synthetic peptide substrates. The enhanced proteolytic activity is not due to lysosomal contaminations which are very low and only slightly increased in the more active fraction. The low density of the enriched subpopulation suggests that we are dealing with immature granules. The physiological implications of this finding are discussed. Furthermore, the enriched fraction can be used as the starting material for the isolation of proenkephalin processing enzymes.

Metorphamide, a novel endogenous adrenal opioid peptide, inhibits nicotine-induced secretion from bovine adrenal chromaffin cells

Opioid peptides are found in high concentrations in the adrenal medulla. Recently, a novel opioid octapeptide, metorphamide, possessing an amidated C-terminal, was characterized and also found to be present in adrenal tissue. We have studied the ability of this novel peptide to modify nicotine-induced secretion from isolated bovine adrenal chromaffin cells. Exocytosis was monitored by measuring adenosine triphosphate (ATP) release on-line by the luciferin-luciferase bioluminescence method, or by measuring endogenous catecholamine release by high-performance liquid chromatography (HPLC) with electrochemical detection. Metorphamide inhibited 5 microM nicotine-induced ATP release from fresh chromaffin cells by almost 50% at 5 microM. Metorphamide at concentrations less than 1 microM had no effect on 5 microM nicotine-induced adrenaline and noradrenaline release from cultured cells, but at higher concentrations inhibited their release equally, with an IC50 of approximately 10 microM. By contrast, Met5-enkephalin inhibited the release of both catecholamines equally with an IC50 of greater than 1 mM, making metorphamide greater than 100-fold more potent than Met5-enkephalin in this system. Naloxone (10 microM) and diprenorphine (1 microM) failed to antagonise the inhibitory action of metorphamide on nicotine-induced catecholamine release. Metorphamide inhibited the nicotinic response in a non-competitive manner, and failed to affect either adrenaline or noradrenaline release induced by elevated potassium ion concentrations. The results suggest metorphamide acts on naloxone- and diprenorphine-resistant receptors to inhibit chromaffin cell nicotinic secretion and that the novel amidated C-terminal of the peptide is important for this action.

Effects of opioid peptides containing the sequence of Met5-enkephalin or Leu5-enkephalin on nicotine-induced secretion from bovine adrenal chromaffin cells

Eighteen endogenous opioid peptides, all containing the sequence of either Met5- or Leu5-enkephalin, were tested for their ability to modify nicotine-induced secretion from bovine adrenal chromaffin cells. ATP released from suspensions of freshly isolated cells was measured with the luciferin-luciferase bioluminescence method as an index of secretion. None of the peptides affected 5 microM nicotine-induced ATP release at 10 nM. Three peptides inhibited secretion at 5 microM: dynorphin1-13, dynorphin1-9, and rimorphin inhibited by 65%, 37%, and 29% respectively. Use of peptidase inhibitors (bestatin, thiorphan, bacitracin, or 1,10-phenanthroline) did not result in any of the other peptides showing potent actions on the nicotinic response, although bestatin and thiorphan did enhance the inhibitory actions of dynorphin1-13 and dynorphin1-9 by 20-30%. Nicotine-induced secretion of endogenous catecholamines from bovine chromaffin cells cultured for 3 days was also studied to assess any selective actions of the peptides on adrenaline or noradrenaline cell types. Dynorphin1-13 was 1,000-fold more potent than Leu5-enkephalin at inhibiting endogenous catecholamine secretion. Dynorphin1-13 was slightly more potent at inhibiting noradrenaline release than adrenaline release whereas Leu5-enkephalin showed the opposite selectivity. The structure-activity relationships of opioid peptide actions on the chromaffin cell nicotinic response are discussed in relation to the properties of the adrenal opioid binding sites.

Potentiation of hemorrhage-evoked catecholamine release by prior blood loss in cats

The effect of prior blood loss on the plasma catecholamine response to acute hemorrhage (H) was assessed in alpha-chloralose-urethane anesthetized cats. Animals sustained an initial H period of 0 (samples only), 10, or 20% H total blood volume. Ninety minutes after reinfusion of the shed blood, all animals sustained a rapid 20% H. The catecholamine and arterial pressure responses to this second 20% H were assessed every 2 min for 20-min duration. Plasma norepinephrine increased modestly in the 0/20% group (+0.63 +/- 0.13 ng/ml) and 10/20% group (+0.66 +/- 0.07 ng/ml), whereas the 20/20% group showed a much larger (P less than 0.01) mean increase of 3.58 +/- 1.16 ng/ml. Plasma epinephrine did not increase after 0/20% (+0.05 +/- 0.02 ng/ml), increased slightly after 10/20% H (+0.10 +/- 0.05 ng/ml), and demonstrated a large significant increase after 20/20% H (+0.48 +/- 0.18 ng/ml). The differential effect of 20% H on catecholamine release, depending on the magnitude of prior blood loss, was not the result of altered mean arterial or pulse pressure responses to H. Correlation analyses revealed that the mean increases in epinephrine and norepinephrine during the post-H sampling period were well correlated in each animal (r = 0.864, P less than 0.001). The data indicate that the priming effect of prior blood loss on H evoked catecholamine release: requires an initial blood loss of 20% of total blood volume; occurs rapidly, as it is seen by 90 min after the initial H period; and affects epinephrine and norepinephrine similarly. We conclude that the immediate past secretory history of the sympathoadrenal system affects its responsiveness to subsequent blood loss.

(Met)enkephalin and carboxypeptidase processing enzyme are co-released from chromaffin cells by cholinergic stimulation

A carboxypeptidase B-like enzyme is involved in processing of proenkephalin in adrenal medulla. Nicotine stimulated the co-release of this enzyme with (Met)enkephalin pentapeptide from bovine chromaffin cells in primary culture. The ratio of enzyme activity/immunoreactivity was determined for the released carboxypeptidase to provide an index of the level of enzyme activity per unit number of enzyme molecules. The ratio for the Co++-stimulated carboxypeptidase secreted into the cell culture medium upon nicotinic stimulation was 10.1 +/- 1.02 (pmol Met-enkephalin formed per ng carboxypeptidase immunoreactivity), while the Co++-stimulated carboxypeptidase in the soluble and membrane components of purified chromaffin granules had lower ratios of 5.46 +/- 0.70 and 1.07 +/- 0.13, respectively. Hexamethonium, a nicotinic receptor antagonist, blocked the nicotine-induced release of the carboxypeptidase processing enzyme and (Met)enkephalin. These data suggest that a pool of carboxypeptidase enzyme molecules at a high state of activation are present in functionally mature granules whose contents are released by nicotinic receptor stimulation.